Search

This paper discusses the Mr. Wang Lansheng's arguments about the origin of petroleum. It is well known that metal elements and their isotopes can be combined with organic compounds to form coordinating ions or complex compounds, which can be applied to petroleum tracing and isotopic dating. The Fischer-Tropsch reaction can synthesize different kinds of hydrocarbons (including crude oils), under different catalysts, higher temperatures and pressures. Daqing's exploration shows that abiogenic gas not only is existent, but also can form big gas reservoirs, such as the Xincheng Gas Pool. In the Tarim Basin, the Silurian bitumen whose reserves are 917.8×108t was generated by inorganic reaction rather than by organic matter. Abiogenic oil and gas were also found in meteorites and in continental scientific drillings. Some other topics related to the origin of petroleum are also discussed. According to the inorganic origin theory of petroleum, some exploration targets are presented in this paper. Key words: inorganic origin, metal isotope, Fischer-Tropsch reaction, exploration target

This paper summarizes the important progress in the field of oil and gas production engineering during the “Thirteenth Five-Year Plan” period of China, analyzes the challenges faced by the current oil and gas production engineering in terms of technological adaptability, digital construction, energy-saving and emission reduction, and points out the future development direction. During the “Thirteenth Five-Year Plan” period, series of important progresses have been made in five major technologies, including separated-layer injection, artificial lift, reservoir stimulation, gas well de-watering, and workover, which provide key technical support for continuous potential tapping of mature oilfields and profitable production of new oilfields. Under the current complex international political and economic situation, oil and gas production engineering is facing severe challenges in three aspects: technical difficulty increases in oil and gas production, insignificant improvements in digital transformation, and lack of core technical support for energy-saving and emission reduction. This paper establishes three major strategic directions and implementation paths, including oil stabilization and gas enhancement, digital transformation, and green and low-carbon development. Five key research areas are listed including fine separated-layer injection technology, high efficiency artificial lift technology, fine reservoir stimulation technology, long term gas well de-watering technology and intelligent workover technology, so as to provide engineering technical support for the transformation, upgrading and high-quality development of China’s oil and gas industry.

Based on the analysis of the fluid inclusion homogenization temperature and apatite fission track on the northern slope zone of the Bongor Basin in Chad, this paper studied the time and stages of hydrocarbon accumulation in the study area. The results show that: (1) The brine inclusions of the samples from the Kubla and Prosopis formations in the Lower Cretaceous coexisting with the hydrocarbon generally present two sets of peak ranges of homogenization temperature, with the peak ranges of low temperature and high temperature being 75–105 °C and 115–135 °C, respectively; (2) The samples from the Kubla and Prosopis formations have experienced five tectonic evolution stages, i.e., rapid subsidence in the Early Cretaceous, tectonic inversion in the Late Cretaceous, small subsidence in the Paleogene, uplift at the turn of the Paleogene and Neogene, and subsidence since the Miocene, in which the denudation thickness of the Late Cretaceous and after the turn of the Paleogene and Neogene are ~1.8 km and ~0.5 km, respectively. The cumulative denudation thickness of the two periods is about 2.3 km; (3) Using the brine inclusion homogenization temperature coexisting with the hydrocarbon as the capture temperature of the hydrocarbon, and combining with the apatite fission track thermal history modeling, the result shows that the Kubla and Prosopis formations in the Lower Cretaceous on the northern slope of the Bongor Basin have the same hydrocarbon accumulation time and stages, both of which have undergone two stages of hydrocarbon charging at 80–95 Ma and 65–80 Ma. The first stage of charging corresponds to the initial migration of hydrocarbon at the end of the Early Cretaceous rapid sedimentation, while the second stage of charging is in the stage of intense tectonic inversion in the Late Cretaceous.

Based on imbibition replacement of shut-in well in tight oil reservoirs, this paper expounds the principle of saturation rebalancing during the shut-in process after fracturing, establishes an optimization method for shut-in time after horizontal well volume fracturing with the goal of shortening oil breakthrough time and achieving rapid oil breakthrough, and analyzes the influences of permeability, porosity, fracture half-length and fracturing fluid volume on the shut-in time. The oil and water imbibition displacement in the matrix and fractures occurs during the shut-in process of wells after fracturing. If the shut-in time is too short, the oil-water displacement is not sufficient, and the oil breakthrough time is long after the well is put into production. If the shut-in time is too long, the oil and water displacement is sufficient, but the energy dissipation in the formation near the bottom of the well is severe, and the flowing period is short and the production is low after the well is put into production. A rational shut-in time can help shorten the oil breakthrough time, extend the flowing period and increase the production of the well. The rational shut-in time is influenced by factors such as permeability, porosity, fracture half-length and fracturing fluid volume. The shortest and longest shut-in times are negatively correlated with porosity, permeability, and fracture half-length, and positively correlated with fracturing fluid volume. The pilot test in tight oil horizontal wells in the Songliao Basin, NE China, has confirmed that the proposed optimization method can effectively improve the development effect of horizontal well volume fracturing.

The existing approaches for identifying events in horizontal well fracturing are difficult, time-consuming, inaccurate, and incapable of real-time warning. Through improvement of data analysis and deep learning algorithm, together with the analysis on data and information of horizontal well fracturing in shale gas reservoirs, this paper presents a method for intelligent identification and real-time warning of diverse complex events in horizontal well fracturing. An identification model for “point” events in fracturing is established based on the Att-BiLSTM neural network, along with the broad learning system (BLS) and the BP neural network, and it realizes the intelligent identification of the start/end of fracturing, formation breakdown, instantaneous shut-in, and other events, with an accuracy of over 97%. An identification model for “phase” events in fracturing is established based on enhanced Unet++ network, and it realizes the intelligent identification of pump ball, pre-acid treatment, temporary plugging fracturing, sand plugging, and other events, with an error of less than 0.002. Moreover, a real-time prediction model for fracturing pressure is built based on the Att-BiLSTM neural network, and it realizes the real-time warning of diverse events in fracturing. The proposed method can provide an intelligent, efficient and accurate identification of events in fracturing to support the decision-making.

Different configurational orders of sand bodies and interlayers in lacustrine nearshore sand bar reservoirs frequently interact, causing complicated genesis and distribution of argillaceous sediments, as well as other issues. This paper investigates the spatial configuration of sand and mud in the sand bar reservoir, and analyzes its internal structure. Modern sand bar deposits in the Xiashan Lake, Shandong Province, China, were analyzed and compared with the sand bar reservoirs of the Member 2 of the Paleogene Shahejie Formation in the Banqiao Sag, China. The configurational mode of sand bar deposits was explored from the perspective of the spatial distribution and composition relationships between sand and mud. Based on the alternate deposition characteristics of sand and mud in the longitudinal direction, lacustrine nearshore sand bars can be divided into three sedimentary combination patterns: thin-sand and thin-mud interbed pattern, thick-mud thick-sand pattern, and thin-mud thick-sand pattern. Their mud components manifest as the deposition of fine-grained lithofacies of multiple genetic types. These include (semi-)deep lacustrine mud, sand and mud interbedded beach, argillaceous sediments in the water retention area behind the bar, and fall-silt seams that resulted from flood discharge. By summarizing the specific developmental locations and sequential relationships of each fine-grained argillaceous facies in modern sand bar deposits, a depositional process-based argillaceous sediment composition model is proposed. Based on this, this paper discusses the spatial configuration of sand bodies and argillaceous sediments in sand bar reservoirs, and introduces the typical stratigraphic structures of sand bars in two environments, i.e., vertical superposition and lateral migration. In lacustrine nearshore sand bar reservoirs, the deposition and preservation degrees of mud mainly depend on three factors: accommodation space change, frequency of base-level cycles, and exposure-erosion time. These in turn influence the continuity and relative contents of sand and mud in reservoirs. The distribution of argillaceous sediments forms different orders of interlayers, which affects the heterogeneity and fluid percolation of sand bar reservoirs. Clarifying the space-matching relationship of sand and mud in sand bar deposits provides geological models and information parameters for the refined characterization and modeling of the internal configuration of sand bar reservoirs. Furthermore, this work offers guidance for the optimal adjustment of reservoir development strategies or the optimization of reservoir development plans. Key words: lacustrine, nearshore sand bar, internal structure, modern deposit, space configuration, Xiashan Lake, Banqiao sag

Through analysis of four aspects, including the distribution and production of global oil and gas fields, the distribution and changes of remaining recoverable reserves, the differences in oil and gas production between regions/countries, and the development potential of oil and gas fields with production capacity not built and to be built, this paper presents the situation and trends of global oil and gas development in 2022. It is found that, in 2022, oil and gas fields are widely distributed worldwide, and upstream production activities continue to recover; the oil and gas reserves decrease slightly year on year, and the oil and gas reserves in sea areas increase significantly; the oil and gas production increases continuously, and the key resource countries make a significant contribution in oil and gas production growth; the oil and gas fields with production capacity not built and to be built hold abundant reserves, and their development potential will be gradually released with the economic benefits increase. Further analysis is conducted from the perspectives of global oil and gas resources continuity, geopolitical risks, potential of international cooperation, and upgrade of unconventional oil and gas technology. Finally, in view of core business domains and strategies under the new situation, the Chinese oil companies are recommended to: (1) keep a foothold in onshore conventional oil and gas development by virtue of their comparative advantages and learning from other's experience in cooperation; (2) carry out pilot tests on development adjustment, and deepen the international cooperation in enhanced oil/gas recovery; (3) improve the oil and gas operation capabilities in sea areas to transform from follower as minority shareholder to joint venture and then to independent operations; and (4) seek appropriate ways for shale oil/gas development to reduce the dependence on foreign oil and gas.

This paper establishes a 3D multi-well pad fracturing numerical model coupled with fracture propagation and proppant migration based on the displacement discontinuity method and Eulerian-Eulerian frameworks, and the fracture propagation and proppant distribution during multi-well fracturing are investigated by taking the actual multi-well pad parameters as an example. Fracture initiation and propagation during multi-well pad fracturing are jointly affected by a variety of stress interference mechanisms such as inter-cluster, inter-stage, and inter-well, and the fracture extension is unbalanced among clusters, asymmetric on both wings, and dipping at heels. Due to the significant influence of fracture morphology and width on the migration capacity of proppant in the fracture, proppant is mainly placed in the area near the wellbore with large fracture width, while a high-concentration sandwash may easily occur in the area with narrow fracture width as a result of quick bridging. On the whole, the proppant placement range is limited. Increasing the well-spacing can reduce the stress interference of adjacent wells and promote the uniform distribution of fractures and proppant on both wings. The maximum stimulated reservoir volume or multi-fracture uniform propagation can be achieved by optimizing the well spacing. Although reducing the perforation-cluster spacing also can improve the stimulated reservoir area, a too low cluster spacing is not conducive to effectively increasing the propped fracture area. Since increasing the stage time lag is beneficial to reduce inter-stage stress interference, zipper fracturing produces more uniform fracture propagation and proppant distribution.

This paper systematically reviews the trend of carbon dioxide capture, utilization and storage (CCUS) industry in the world and China, presents the CCUS projects, clusters, technologies and strategies/policies, and analyzes the CCUS challenges and countermeasures in China based on the comparison of CCUS industrial development at home and abroad. The global CCUS development has experienced three stages: exploration stage, policy driven stage, and dual-drive stage. Currently, the active large-scale CCUS projects around the world focus on enhanced oil recovery (EOR) and are expanding into storage in saline aquifers. The CCUS industry of China has evolved in three stages: exploration, pilot test, and industrialization. In the current critical period of transition from field test to industrialization, China's CCUS projects are EOR-dominated. By comparing the industrial development of CCUS in China and abroad, it is found that the scale-up and industrialization of CCUS in China face challenges in technology, facilities and policies. Finally, future solutions to CCUS development in China are proposed as follows: strengthening the top-level design and planning of CCUS; developing high-efficiency and low-cost CCUS technologies throughout the whole industrial chain; deploying CCUS oil and gas + new energy clusters; improving the policy support system of CCUS; and strengthening discipline construction and personnel training, etc.

China's continental oil and gas geological theory occupies an important academic position in the world's academic circle of petroleum geology. China's oil and gas resources are dominated by continental resources. Chinese geologists have successfully explored and developed complex continental oil and gas, and developed a continental oil and gas geological theory system. This paper summarizes the development history and theoretical achievements of continental oil and gas geological theory since the 1940s and proposes that the development of this theory should be divided into three stages (i.e., proposal, formation and development). The China's continental oil and gas geological theory has formed a basically perfect theoretical system consisting of five parts, i.e., continental basin structure theory, continental basin sediments and reservoirs theory, continental oil generation theory, continental oil and gas accumulation theory, and continental sandstone oil and gas field development geology. As an advanced geological theory, it has a universal significance globally. This paper focuses on the major discoveries of oil and gas exploration and development and the production growth in the basins of the Central and Western China in the past 30 years as well as the major advances in the continental oil and gas geological theory, including the continental basin tectonics of Central and Western China under the compression background, special reservoir geology such as various types of lake basin sedimentary systems and deep conglomerate, new fields of continental hydrocarbon generation such as coal-generated hydrocarbons, continental oil and gas enrichment regularity such as foreland thrust belts and lithologic-stratigraphic reservoirs, continental unconventional oil and gas geology and continental low-permeability oil and gas development geology. These major advances have greatly developed and enriched the continental oil and gas geological theory and become an important part of it. Key words: continental petroleum geology, Central and Western China basins, foreland basin thrust belt, theoretical development stage

To achieve the goals of carbon peaking and carbon neutrality under the backgrounds of poor resource endowments, weak theoretical basis and other factors, the development of the coalbed methane industry of China faces many bottlenecks and challenges. This paper systematically analyzes the coalbed methane resources, key technologies and progress, exploration effect and production performance in China and abroad. The main problems are summarized as low exploration degree, low technical adaptability, low return on investment and small development scale. This study suggests that the coalbed methane industry in China should follow the “two-step” (short-term and long-term) development strategy. The short-term action before 2030, can be divided into two stages: (1) From the present to 2025, to achieve new breakthroughs in theory and technology, and accomplish the target of annual production of 10 billion cubic meters; (2) From 2025 to 2030, to form the technologies suitable for most geological conditions, further expand the industry scale, and achieve an annual output of 30 billion cubic meters, improving the proportion of coalbed methane in the total natural gas production. The long-term action after 2030 is to gradually realize an annual production of 100 billion cubic meters. The strategic countermeasure to achieve the above goals is to adhere to “technology+management dual wheel drive”, realize the synchronous progress of technology and management, and promote the high-quality development of the coalbed methane industry. Technically, the efforts will focus on fine and effective development of coalbed methane in the medium to shallow layers of mature fields, effective development of coalbed methane in new fields, extensive and beneficial development of deep coalbed methane, three-dimensional comingled development of coalbed methane, applying new technologies such as coalbed methane displacement by carbon dioxide, microwave heating and stimulation technology, ultrasonic stimulation, high-temperature heat injection stimulation, rock breaking by high-energy laser. In terms of management, the efforts will focus on coordinative innovation of resource, technology, talent, policy and investment, with technological innovation as the core, to realize an all-round and integrated management and promote the development of coalbed methane industry at a high level.

Based on paleogeomorphology, drilling and seismic data, this paper systematically studies the structural and sedimentary evolution, source rock characteristics, reservoir characteristics and formation mechanism, hydrocarbon accumulation model and enrichment law in the Linhe Depression of the Hetao Basin, NW China. The Hetao Basin mainly experienced three stages of evolution, namely, weak extensional fault depression, strong extensional fault depression and strike-slip transformation, giving rise to four positive structural belts (Jilantai, Shabu, Nalinhu and Xinglong), which are favorable areas for oil and gas accumulation. The two main saline lacustrine source rocks, Lower Cretaceous Guyang Formation and Oligocene Linhe Formation, are characterized by high sulfur content, rich algae, early maturity, early expulsion, and wide oil generation window. The large structural transition belt in the intermountain area around the Hetao Basin controls the formation of large-scale braided river delta deposits, which are characterized by high quartz content (50%–76%), long-term shallow burial and weak compaction, low cement content, and good reservoir properties in delta front sandbody. The burial depth of the effective Paleogene reservoirs is predicted to reach 8000 m. Three hydrocarbon accumulation models, nose-uplift near sag, buried hill surrounding sag, fault nose near source rock, are constructed. The law of hydrocarbon accumulation in the Linhe Depression is finally clarified as follows: near-source around the depression is the foundation, high-quality thick reservoir is the premise, good tectonic setting and trap conditions are the key.

This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny (Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55–94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170–196 m and 11 298 kmbrespectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle–Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma4 Member–pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.

This paper reviews the multiple rounds of upgrades of the hydraulic fracturing technology used in the Gulong shale oil reservoirs and gives suggestions about stimulation technology development in relation to the production performance of Gulong shale oil wells. Under the control of high-density bedding fractures, fracturing in the Gulong shale results in a complex fracture morphology, yet with highly suppressed fracture height and length. Hydraulic fracturing fails to generate artificial fractures with sufficient lengths and heights, which is a main restraint on the effective stimulation in the Gulong shale oil reservoirs. In this regard, the fracturing design shall follow the strategy of “controlling near-wellbore complex fractures and maximizing the extension of main fractures”. Increasing the proportions of guar gum fracturing fluids, reducing perforation clusters within one fracturing stage, raising pump rates and appropriately exploiting stress interference are conducive to fracture propagation and lead to a considerably expanded stimulated reservoir volume (SRV). The upgraded main hydraulic fracturing technology is much more applicable to the Gulong shale oil reservoirs. It accelerates the oil production with a low flowback rate and lifts oil cut during the initial production of well groups, which both help to improve well production. It is suggested to optimize the hydraulic fracturing technology in six aspects, namely, suppressing propagation of near-wellbore microfractures, improving the pumping scheme of CO2, managing the perforating density, enhancing multi-proppant combination, reviewing well pattern/spacing, and discreetly applying fiber-assisted injection, so as to improve the SRV, the distal fracture complexity and the long-term fracture conductivity.

This paper proposes a methodology for an alternative history matching process enhanced by the incorporation of a simplified binary interpretation of reservoir saturation logs (RST) as objective function. Incorporating fluids saturation logs during the history matching phase unlocks the possibility to adjust or select models that better represent the near wellbore waterfront movement, which is particularly important for uncertainty mitigation during future well interference assessments in water driven reservoirs. For the purposes of this study, a semi-synthetic open-source reservoir model was used as base case to evaluate the proposed methodology. The reservoir model represents a water driven, highly heterogenous sandstone reservoir from Namorado field in Brazil. To effectively compare the proposed methodology against the conventional methods, a commercial reservoir simulator was used in combination with a state-of-the-art benchmarking workflow based on the Big Loop™ approach. A well-known group of binary metrics were evaluated to be used as the objective function, and the Matthew correlation coefficient (MCC) has been proved to offer the best results when using binary data from water saturation logs. History matching results obtained with the proposed methodology allowed the selection of a more reliable group of reservoir models, especially for cases with high heterogeneity. The methodology also offers additional information and understanding of sweep behaviour behind the well casing at specific production zones, thus revealing full model potential to define new wells and reservoir development opportunities.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal).This article has been retracted at the request of the Editor.The authors have plagiarized part of a paper that had already appeared in [Journal of China University of Mining & Technology, 45 (2016) 754–764. http://zgkd.cbpt.cnki.net/WKD/WebPublication/paperDigest.aspx?paperID=b8b04bba-3a40-4290-919c-a16475261903]. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

This paper gives a contrastive analysis of the main progress made in petroliferous basins sedimentary geology domestically and internationally, and discusses the main problems and their solutions in the development of petroliferous basins sedimentology in China, New developments include coarse-grained depositional sysytem, shallow-water deltic depositional system, beach bar depositional system, deep-water gravity flows, fine-grained depositional system, carbonate reefs, mixosedimentite, microbialite, seismic sedimentology and sedimentary physical simulation. It also reveals the developing gap of Chinese sedimentology in the areas of microbialite and sedimentary simulation, etc. and analyzes the sedimentary features and paleogeography pattern of prototype basins, multi-scale paleogeographic recovery during major tectonic movements, the different explanation of new sedimentology theories in the deep-buried sandbodies development. The paper details the difficulties when it comes to the typical depositional systems combination and the setup of sedimentary models in China. Therefore, the developing tendency is described of sedimentology theories like source to sink, sedimentary dynamics as well as regional sedimentology in China, seismic sedimentology, and studying methods and technologies in sedimentary simulation. Key words: development, shallow-water delta, gravity flow, beach-bar, mixosedimentite, microbialite, seismic sedimentology, sedimentology, China

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been retracted at the request of the Editor.The authors have plagiarized part of a paper that had already appeared in [Journal of China University of Mining & Technology, 45 (2016) 754 – 764. http://zgkd.cbpt.cnki.net/WKD/WebPublication/paperDigest.aspx?paperID=b8b04bba-3a40-4290-919c-a16475261903]. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

The major enrichment type of shale oil in the Chang 73 shale of Upper Triassic Yanchang Formation in the Ordos Basin is unknown. This paper analyzes the organic matter transformation ratio, hydrocarbon expulsion efficiency and roof/floor sealing conditions of the Chang 73 shale, and evaluates the major enrichment type of shale oil in this interval. The average organic matter transformation ratio of the Chang 73 shale is about 45%; in other words, more than 50% of the organic matters have not transformed to hydrocarbons, and the lower the maturity, the greater the proportion of untransformed organic matters. The cumulative hydrocarbon expulsion efficiency of the transformed hydrocarbon is 27.5% on average, and the total proportion of untransformed organic matters plus retained hydrocarbons is greater than 70%. The relative hydrocarbon expulsion efficiency of the Chang 73 shale is 60% on average, that is, about 40% of hydrocarbons retain in the shale. The Chang 73 shale corresponds to Chang 71+2 and Chang 8 sandstones as the roof and floor, respectively, and is further overlaid by Chang 6 shale, where extensive low porosity and low permeability–tight oil reservoirs have formed in the parts with relatively good porosity and permeability. Moreover, the Chang 73 shale is tested to be in a negative pressure system (the pressure coefficient of 0.80–0.85). Therefore, the roof/floor sealing conditions of the Chang 73 shale are poor. The retained hydrocarbons appear mostly in absorbed status, with low mobility. It is concluded that the medium–high mature shale oil is not the major enrichment type of shale oil in the Chang 73 shale, but there may be enrichment opportunity for shale oil with good mobility in the areas where the sealing conditions are good without faults and fractures and oil reservoirs are formed off Chang 71+2, Chang 6 and Chang 8. Furthermore, low–medium mature shale oil is believed to have great potential and is the major enrichment type of shale oil in the Chang 73 shale. It is recommended to prepare relevant in-situ conversion technologies by pilot test and figure out the resource availability and distribution.

Based on well horizon calibration, the typical seismic profiles in southwestern Tarim Basin were interpreted systematically, regional geological sections were established, and the regional denudation thickness of each tectonic period was restored. On this basis, the plane morphology maps of ancient structures of the Cambrian pre-salt dolomites in different periods were compiled, and the spatial distribution, development, evolution and migration of paleo-uplift in the late Early Paleozoic were analyzed. In the late Early Paleozoic, there existed a unified regional paleo-uplift widely distributed in southwestern Tarim Basin, which is called the southwestern Tarim plaeo-uplift. The “Tarim SW paleo-uplift” and “Hetian paleo-uplift” proposed in previous literatures are not independent, but the result of the spatio-temporal migration and evolution of the southwestern Tarim paleo-uplift identified in this paper. The southwestern Tarim paleo-uplift emerged at the end of Middle Ordovician, and took its initial shape with increased amplitude in the Late Ordovician. During the Silurian, the southwestern Tarim paleo-uplift rose steadily and expanded rapidly to the east, incorporating Pishan—Hetian and other areas, with the structural high locating in the Pishan—Hetian area. During the Devonian, the southwestern Tarim paleo-uplift began to shrink gradually, to a limited range in the Pishan—Hetian area in the southern part of the basin. During the Carboniferous, the southwestern Tarim paleo-uplift became an underwater uplift, that is, the paleo-uplift gradually died out. The southwestern Tarim paleo-uplift belongs to the forebulge of the southwestern Tarim foreland basin in the late Early Paleozoic, and its formation and evolution are related to the early Paleozoic orogeny of the West Kunlun orogenic belt in the south of the Tarim Basin. The migration of the southwestern Tarim paleo-uplift from the northwestern part of the southwestern Tarim Basin to the Pishan—Hetian area indicates the early Paleozoic orogenic process of the West Kunlun orogenic belt, which started in the western section at the end of Middle Ordovician and extended from west to east in a “scissor” style. The migration and evolution of the southwestern Tarim paleo-uplift controlled the development of unconformities at the end of Middle Ordovician, the end of Late Ordovician, and the end of Middle Devonian, and the spatial distribution of dissolved fracture-cave reservoirs in weathered crust below the unconformities in the southwest of Tarim Basin. The migration of the structural high of the southwestern Tarim paleo-uplift also played an important role in controlling the development of dissolved fracture-cave reservoirs in weathered crust.

In this paper, a viscoelasticity-plastic damage constitutive equation for naturally fractured shale is deduced, coupling nonlinear tensile-shear mixed fracture mode. Dynamic perforation-erosion on fluid re-distribution among multi-clusters are considered as well. DFN-FEM (discrete fracture network combined with finite element method) was developed to simulate the multi-cluster complex fractures propagation within temporary plugging fracturing (TPF). Numerical results are matched with field injection and micro-seismic monitoring data. Based on geomechanical characteristics of Weiyuan deep shale gas reservoir in Sichuan Basin, SW China, a multi-cluster complex fractures propagation model is built for TPF. To study complex fractures propagation and the permeability-enhanced region evolution, intersecting and competition mechanisms between the fractures before and after TPF treatment are revealed. Simulation results show that: fracture from middle cluster is restricted by the fractures from side-clusters, and side-clusters plugging is benefit for multi fractures propagation in uniformity; optimized TPF timing should be delayed within a higher density or strike of natural fractures; Within a reservoir-featured natural fractures distribution, optimized TPF timing for most clustered method is 2/3 of total fluid injection time as the optimal plugging time under different clustering modes.

This paper systematically presents the established technologies and field applications with respect to research and engineering practice of CO2 capture, enhanced oil recovery (EOR), and storage technology in Jilin Oilfield, NE China, and depicts the available series of supporting technologies across the industry chain. Through simulation calculation + pilot test + field application, the adaptability of the technology for capturing CO2 with different concentrations in oilfields was confirmed. The low energy-consumption, activated N-methyl diethanolamine (MDEA) decarburization technology based on a new activator was developed, and the operation mode of CO2 gas-phase transportation through trunk pipeline network, supercritical injection at wellhead, and produced gas-liquid separated transportation was established. According to different gas source conditions, liquid, supercritical phase, high-pressure dense phase pressurization technologies and facilities were applied to form the downhole injection processes (e.g. gas-tight tubing and coiled tubing) and supporting anti-corrosion and anti-blocking techniques. In the practice of oil displacement, the oil recovery technologies (e.g. conical water-alternating-gas injection, CO2 foam flooding, and high gas-oil ratio CO2 flooding) and produced fluid processing technologies were developed. Through numerical simulation and field tests, three kinds of CO2 cyclic injection technologies (i.e. direct injection, injection after separation and purification, and hybrid injection) were formed, and a 10×104 m3/d cyclic injection station was constructed to achieve “zero emission” of associated gas. The CO2 storage safety monitoring technology of carbon flux, fluid composition and carbon isotopic composition was formed. The whole-process anti-corrosion technology with anticorrosive agents supplemented by anticorrosive materials was established. An integrated demonstration area of CO2 capture, flooding and storage with high efficiency and low energy-consumption has been built, with a cumulative oil increment of 32×104 t and a CO2 storage volume of 250×104 t.

This paper mainly discusses the industrialization progress, “sweet spot” evaluation criterion, E&P technologies, success experiences, challenges and prospects of China's shale gas. Based on the geologic and engineering parameters of the Fuling, Changning and Weiyuan shale gas fields in the Sichuan Basin, this paper points out that China's shale gas has its particularity. The discoveries of super-giant marine shale gas fields with high evolution degree (Ro=2.0%−3.5%) and ultrahigh pressure (pressure coefficient=1.3−2.1) in southern China is of important scientific significance and practical value to ancient marine shale gas exploration and development to China and even the world. It's proposed that shale gas “sweet spots” must be characterized by high gas content, excellent frackability and good economy etc. The key indicators to determine the shale gas enrichment interval and trajectory of horizontal wells include “four highs”, that is high TOC (>3.0%), high porosity (>3.0%), high gas content (>3.0 m3/t) and high formation pressure (pressure coefficient>1.3), and “two well-developed” (well-developed beddings and well-developed micro-fractures). It's suggested that horizontal well laneway be designed in the middle of high pressure compartment between the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation. The mode of forming “artificial shale gas reservoir” by “fracturing micro-reservoir group” is proposed and the mechanisms of “closing-in after fracturing, limiting production through pressure control” are revealed. Several key technologies (such as three-dimensional seismic survey and micro-seismic monitoring of fracturing, horizontal wells, “factory-like” or industrialized production mode, etc.) were formed. Some successful experiences (such as “sweet spot” selection, horizontal well laneway control, horizontal length optimization and “factory-like” production mode, etc.) were obtained. The four main challenges to realize large-scale production of shale gas in China include uncertainty of shale gas resources, breakthroughs in key technologies and equipment of shale gas exploration and development below 3 500 m, lower cost of production, as well as water resources and environment protection. It is predicted that the recoverable resources of the Lower Paleozoic marine shale gas in southern China are approximately 8.8×1012 m3, among which the recoverable resources in the Sichuan Basin are 4.5×1012 m3 in the favorable area of 4.0×104 km2. The productivity of (200−300)×108 m3/a is predicted to be realized by 2020 when the integrated revolution of “theory, technology, production and cost” is realized in Chinese shale gas exploration and development. It is expected in the future to be built “Southwest Daqing Oilfield (Gas Daqing)” in Sichuan Basin with conventional and unconventional natural gas production. Key words: shale gas field, economic sweet spot, micro gas reservoir, horizontal well, factory-like production, volume fracturing, development cost, resource potential, favorable target

By analyzing the distribution of global oil and gas fields and the reasons why some oil and gas fields are not in production, the distribution characteristics of oil and gas remaining recoverable reserves and their year-on-year changes, the distribution characteristics of oil and gas production and their year-on-year changes, and the development potential of oil and gas to be tapped in 2021, this paper sorts out systematically the current status and characteristics of global oil and gas development, summaries the major trends of global oil and gas development, puts forward enlightenment for international oil and gas cooperation. In 2021, oil and gas fields were widely distributed, the number of non-producing oil and gas fields was large; the whole oil and gas remaining recoverable reserves declined slightly, unconventional oil and gas remaining recoverable reserves dropped significantly; the overall oil and gas production continuously increased, the outputs of key resource-host countries kept year-on-year growth; undeveloped oilfields had abundant reserves and great development potential. Combined with global oil and gas geopolitics, oil and gas industry development trends, oil and gas investment intensity, and the tracking and judgment of hotspot fields, the major trends of global oil and gas development in 2021 are summarized. On this basis, the four aspects of enlightenment and suggestions for international oil and gas cooperation and development strategies are put forward: attach great importance to the obligation of marine abandonment to ensure high-quality and long-term benefit development of offshore oil and gas; adhere to the principle of not going to dangerous and chaotic places, strengthen the concentration of oil and gas assets, and establish multi stable supply bases; based on the multi-scenario demand of natural gas, realize the transformation from integrated collaboration to full oil and gas industry chain development; increase the acquisition of high-quality large-scale assets, and pay attention to the continuous optimization of the shareholding ratio of projects at different stages.

This paper analyzes the differences in geological and development characteristics between continental shale oil in China and marine shale oil in North America, reviews the evaluation methods and technological progress of the continental shale oil development in China, and points out the existing problems and development directions of the continental shale oil development. The research progress of development evaluation technologies such as favorable lithofacies identification, reservoir characterization, mobility evaluation, fracability evaluation, productivity evaluation and geological-mathematical modeling integration are introduced. The efficient exploration and development of continental shale oil in China are faced with many problems, such as weak basic theoretical research, imperfect exploration and development technology system, big gap in engineering technology between China and other countries, and high development cost. Three key research issues must be studied in the future: (1) forming differentiated development technologies of continental shale oil through geological and engineering integrated research; (2) strengthening the application of big data and artificial intelligence to improve the accuracy of development evaluation; (3) tackling enhanced shale oil recovery technology and research effective development method, so as to improve the development effect and benefit.

This paper investigates the deposition of asphaltenes in the porous medium of the studied field in Russia and predicts production profiles based on uncertainty evaluation. This problem can be solved by dynamic modeling, during which production profiles are estimated in two scenarios: with and without the activation of the asphaltene option. Calculations are carried out for two development scenarios: field operation under natural depletion and water injection into the aquifer as a reservoir pressure maintenance system. A full-scale compositional reservoir simulation model of the Russian oilfield was created. Within a dynamic simulation, the asphaltene option was activated and the asphaltene behavior in oil and porous medium was tuned according to our own special laboratory experiments. The model was also matched to production historical data, and a pattern model was prepared using the full-scale simulation model. Technological and the asphaltene option parameters were used in sensitivity and an uncertainty evaluation. Furthermore, probable production profiles within a forecast period were estimated. The sensitivity analysis of the pattern model to input parameters of the asphaltene option allowed determining the following heavy-hitters on the objective function: the molar weight of dissolved asphaltenes as a function of pressure, the asphaltene dissociation rate, the asphaltene adsorption coefficient and the critical velocity of oil movement in the reservoir. Under the natural depletion scenario, our simulations show a significant decrease in reservoir pressure and the formation of drawdown cones leading to asphaltene deposition in the bottom-hole area of production wells, decreasing their productivity. Water injection generally allows us to significantly reduce the volume of asphaltene phase transitions and has a positive effect on cumulative oil production. Injecting water into aquifer can keep the formation pressure long above the pressure for asphaltene precipitation, preventing the asphaltene deposition resulted from interaction of oil and water, so this way has higher oil production.

The mechanisms causing quality variations and key control factors of submarine-fan reservoirs in the gas field X of the Rovuma Basin, East Africa are analyzed based on core and well-log data in this paper. Depositional fabric, lithofacies difference and characteristics of genetic units are the fundamental reasons of reservoir quality variations. In the case of weak cementation, porosity and permeability of submarine-fan reservoirs are controlled by grain sorting and clay content, respectively. Reservoir quality variations for 5 main lithofacies are related to variable depositional fabrics and calcite cementation. Among them, massive medium-coarse sandstones with weak cementation have the highest porosity and permeability, and coarser or finer sandstones have poorer reservoir quality. The existence of bottom current can develop laminated sandstones, improving the pore structure and physical properties greatly. Lithofacies vary among different types, locations and stages of genetic units, and they control the distribution patterns of submarine-fan reservoir quality: the physical properties of channel shaft or lobe main body are better than those of the channel or lobe edge. The sandstone sorting and physical properties are gradually improved from near-source to far-source. When multi-stage sand bodies are superimposed, the sand-mud ratio in the later stage is higher than that in the earlier stage, making the physical properties get better in the later stage.

The existing acoustic logging methods for evaluating the hydraulic fracturing effectiveness usually use the fracture density to evaluate the fracture volume, and the results often cannot accurately reflect the actual productivity. This paper studies the dynamic fluid flow through hydraulic fractures and its effect on borehole acoustic waves. Firstly, based on the fractal characteristics of fractures observed in hydraulic fracturing experiments, a permeability model of complex fracture network is established. Combining the dynamic fluid flow response of the model with the Biot-Rosenbaum theory that describes the acoustic wave propagation in permeable formations, the influence of hydraulic fractures on the velocity dispersion of borehole Stoneley-wave is then calculated and analyzed, whereby a novel hydraulic fracture fluid transport property evaluation method is proposed. The results show that the Stoneley-wave velocity dispersion characteristics caused by complex fractures can be equivalent to those of the plane fracture model, provided that the average permeability of the complex fracture model is equal to the permeability of the plane fracture. In addition, for fractures under high-permeability (fracture width 10~100 μm, permeability ~100 μm2) and reduced permeability (1~10 μm, ~10 μm2 as in fracture closure) conditions, the Stoneley-wave velocity dispersion characteristics are significantly different. The field application shows that this fluid transport property evaluation method is practical to assess the permeability and the connectivity of hydraulic fractures.

A dynamic transient flow analysis method considering complex factors such as the cyclic injection and production history in a gas field storage facility was established in view of the limitations of the existing methods for transient flow analysis and the characteristics of the injection-production operation of strongly heterogeneous gas reservoirs, and the corresponding theoretical charts were drawn. In addition, an injection-production dynamic transient flow analysis model named “three points and two stages” suitable for an underground gas storage (UGS) well with alternate working conditions was proposed. The “three points” refer to three time points during cyclic injection and production, namely, the starting point of gas injection for UGS construction, the beginning and ending points of the injection-production analysis stage; and the “two stages” refer to historical flow stage and injection-production analysis stage. The study shows that the dimensionless pseudo-pressure and dimensionless pseudo-pressure integral curves of UGS well flex downward in the early stage of the injection and production process, and the dimensionless pseudo-pressure integral derivative curve is convex during the gas production period and concave during the gas injection period, and the curves under different flow histories have atypical features. The new method present in this paper can analyze transient flow of UGS accurately. The application of this method to typical wells in Hutubi gas storage shows that the new method can fit the pressure history accurately, and obtain reliable parameters and results.

Aiming at the scientific problem that only part of dolomite acts as dolomite reservoir, this paper takes the multiple dolomite-bearing formations in the Tarim and Ordos basins, NW China and Sichuan Basin, SW China as the study object, by means of mineral petrological analysis and geochemical methods including carbonate clumped isotope, U-Pb isotopic dating, etc., to rebuild the dolomitization pathway and evaluate its effects on reservoir formation. On the basis of detailed rock thin section observation, five dolomitic structural components are identified, including original fabric-retained dolomite (microbial and/or micrite structure), buried metasomatic dolomite I (subhedral–euhedral fine, medium and coarse crystalline structure), buried metasomatic dolomite II (allotriomorphic–subhedral fine, medium and coarse crystalline structure), buried precipitation dolomite and coarse crystalline saddle dolomite. Among them, the first three exist in the form of rocks, the latter two occur as dolomite minerals filling in pores and fractures. The corresponding petrological and geochemical identification templates for them are established. Based on the identification of the five dolomitic structural components, six dolomitization pathways for three types of reservoirs (preserved dolomite, reworked dolomite and limestone buried dolomitization) are distinguished. The initial porosity of the original rock before dolomitization and the dolomitization pathway are the main factors controlling the development of dolomite reservoirs. The preserved dolomite and reworked dolomite types have the most favorable dolomitization pathway for reservoir formation, and are large scale and controlled by sedimentary facies in development and distribution, making them the first choices for oil and gas exploration in deep carbonate formations.

Focusing on the extending length restriction of the completion screen pipe resistance running into ultra-short radius horizontal well, this paper proposed technology of hydraulic drive completion tubular string running into ultra-short radius horizontal well. Innovative hydraulic drive tools and string structure are designed, which are composed of guide tubing, hydraulic drive tubing and non-metallic completion screen pipe from inside to outside. A novel mechanical-hydraulic coupling model is established. Based on the wellbore structure of an ultra-short radius horizontal well for deep coalbed methane, the numerical calculations of force and hydraulic load on tubular strings were accomplished by the mechanical-hydraulic coupling model. The results show that the extending length of completion tubular string with the hydraulic drive is 17 times that of conventional completion technology under the same conditions. The multi-factor orthogonal design is adopted to analyze the numerical calculations, and the results show that the extending length of the completion tubular string is mainly affected by the completion tubular string structure and the friction coefficient between the non-metallic composite continuous screen pipe and the wellbore. Two series of hydraulic drive completion tubular string structures suitable for ultra-short radius horizontal wells under different conditions are optimized, with the extending limits of 381 m and 655 m, respectively. These researches will provide theoretical guidance for design and control of hydraulic drive non-metallic composite continuous completion screen pipe running into ultra-short radius horizontal wells.

Carbon dioxide capture, EOR-utilization and storage (CCUS-EOR) are the most practical and feasible large-scale carbon reduction technologies, and also the key technologies to greatly improve the recovery of low-permeability oil fields. This paper sorts out the main course of CCUS-EOR technological development abroad and its industrialization progress. The progress of CCUS-EOR technological research and field tests in China are summarized, the development status, problems and challenges of the entire industry chain of CO2 capture, transportation, oil displacement, and storage are analyzed. The results show a huge potential of the large-scale application of CCUS-EOR in China in terms of carbon emission reduction and oil production increase. At present, CCUS-EOR in China is in a critical stage of development, from field pilot tests to industrialization. Aiming at the feature of continental sedimentary oil and gas reservoirs in China, and giving full play to the advantages of the abundant reserves for CO2 flooding, huge underground storage space, surface infrastructure, and wide distribution of wellbore injection channels, by cooperating with carbon emission enterprises, critical technological research and demonstration project construction should be accelerated, including the capture of low-concentration CO2 at low-cost and on large-scale, supercritical CO2 long-distance transportation, greatly enhancing oil recovery and storage rate, and CO2 large-scale and safe storage. CCUS-EOR theoretical and technical standard system should be constructed for the whole industrial chain to support and promote the industrial scale application, leading the rapid and profitable development of CCUS-EOR emerging industrial chain with innovation.

Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack, a mechanical performance design method of cement sheath is established to meet the wellbore sealing requirements during fracturing. This method takes the failure types of the cement sheath, such as tensile failure, plastic yield, interface crack propagation along interface and zigzag propagation into account. Meanwhile, the elasticity modulus and Poisson's ratio quantitative design charts of cement sheath are constructed based on this method, and the safety and risk areas of wellbores are defined, which quantify the yield strength and tensile strength indexes of cement sheath. The results show that decreasing elasticity modulus, increasing yield strength and Poisson's ratio of cement sheath can avoid plastic deformation of cement sheath; increasing the tensile strength of cement sheath can prevent its tensile failure; increasing elasticity modulus and Poisson's ratio of cement sheath is good for shortening the length of the interface crack, but will increase the risk of interface cracks zigzagging into cement sheath. The model calculation and case verification has proved that the method in this paper can give accurate calculation results and is convenient for field application.

Under the requirement of well pattern estimation for low-permeability reservoirs, horizontal wells and fracturing wells, this paper presents a new method for 5-spot well pattern productivity estimation by introducing shape factor of the drainage area, equivalence radius of fracture/horizontal well and threshold pressure gradient. By applying mirror image and principle of pressure superposition, steady-state flow for an infinite well net can be transformed into pseudo steady-state flow for a producer or an injector in a closed drainage area. This new productivity estimation method for 5-spot well pattern can be unified with a general formula considering the type of well pattern, type of injection-production, type of well completion and type of reservoir. Application in the Yushulin Oilfield showed that the new method presented in this paper is easy to derive, to calculate and to extend. It can be used to estimate the productivity rapidly in oilfields. 摘要: ： 针对低渗透油藏、压裂井、水平井等对井网评价的要求，从直井五点注采井网产能分析入手，采用镜像反演法、压力叠加法，并引入形状因子、裂缝和水平井当量井径、启动压力梯度等参数，将无穷井排的稳定渗流问题转化成为封闭体中一口注水井或者采油井的拟稳态渗流问题，通过求取封闭边界中油井、注水井的拟稳态压力方程得到注采压差和产量的关系式，建立不同注采井网、不同注采井型、不同投产方式、不同油藏类型的产能计算通式，形成了一套井网产能评价新方法。该方法在大庆榆树林油田井网调整优选中的应用表明，其具有公式简单、计算方便、扩展性好的优点，适用于油田现场井网产能快速评价。图3表2参28 Key words: 5-spot well pattern, productivity estimation, equivalence radius, horizontal-vertical combined well pattern

Based on the summary of theories and methods of well logging interpretation for igneous rock at home and abroad, a complete interpretation process of well logging is formed, which includes lithology identification, quantitative matrix porosity calculation, quantitative saturation calculation, and fluid nature identification. This paper presents a theory and an application model of porosity and saturation calculation for heterogeneous and complex reservoirs, and establishes a framework for interpreting complex volcanic rock reservoirs; proposes a new method combining ECS with FMI logging for 3-D lithology identification of igneous rocks. Based on the study of the micro-fracture simulation well, this paper puts forward a practical quantitative calculation method for calculating the fracture porosity of heterogeneous reservoirs. By experimenting with core of whole diameter under high temperature and high pressure, the authors studied the influence of fracture on saturation calculation through numerical simulation, and proposed a new method of quantitative saturation calculation. The results of the Xujiaweizi area in the Daqing Oilfield and the Ludong-Wucaiwan area in the Xinjiang Oilfield show that the theory and the method are correct and effective. Key words: igneous rock, well-log interpretation, interpretation model, fracture porosity, saturation

Based on distribution of oil and gas in the world, the connotation and characteristics of “continuous” petroleum reservoirs are elaborated in this paper. “Continuous” petroleum reservoirs refer to unconventional trap reservoirs existing in a large-scale unconventional reservoir system, and the distribution of oil and gas is continuous. The main geological characteristics of “continuous” petroleum reservoirs are as follows: located in the center and slope of a basin, large-scale distribution and rich locally; mainly of large-scale unconventional reservoirs; traps have no clear boundaries; mainly of self-generating and self-preserving; mainly of primary migration; accumulated by diffusion and buoyancy is limited; non-Darcy flow; poor oil-water differentiation and different saturation; oil, water and gas coexist and have no common interface and pressure system; resources abundance is low and reserves are calculated by well-control region; the mining technologies are special and tailored techniques are required. In this paper are discussed the cause of deep-water “sandy debris flow” and a few examples on “continuous” reservoirs, the shallow-water delta low or ultra-low porosity and permeability reservoirs, coal-bed methane and shale-cracked reservoirs and so on. Key words: “continuous” petroleum reservoirs, unconventional trap reservoir, sandy debris flow, FORSPAN resources assessment model

Based on the mechanisms of gravity displacement, miscibility, viscosity reduction, and imbibition in natural gas flooding, an integrated reservoir construction technology of oil displacement and underground gas storage (UGS) is proposed. This paper systemically describes the technical connotation, site selection principle and optimization process of operation parameters of the gas storage, and advantages of this technology. By making full use of the gravity displacement, miscibility, viscosity reduction, and imbibition features of natural gas flooding, the natural gas can be injected into oil reservoir to enhance oil recovery and build strategic gas storage at the same time, realizing the win-win situation of oil production and natural gas peak shaving. Compared with the gas reservoir storage, the integrated construction technology of gas storage has two profit models: increasing crude oil production and gas storage transfer fee, so it has better economic benefit. At the same time, in this kind of gas storage, gas is injected at high pressure in the initial stage of its construction, gas is injected and produced in small volume in the initial operation stage, and then in large volume in the middle and late operation stage. In this way, the gas storage wouldn't have drastic changes in stress periodically, overcoming the shortcomings of large stress variations of gas reservoir storage during injection-production cycle due to large gas injection and production volume. The keys of this technology are site selection and evaluation of oil reservoir, and optimization of gravity displacement, displacement pressure, and gas storage operation parameters, etc. The pilot test shows that the technology has achieved initial success, which is a new idea for the rapid development of UGS construction in China.

In view of high water cut and low oil recovery caused by the unidirectional flow in linear pattern of horizontal wells for the carbonate reservoirs in the Middle East, this paper provides a novel approach to improve oil recovery by converting linear water injection to cyclic alternating water injection patterns including cyclic alternating water injection with apparent inverted seven-spot pattern or apparent five-spot pattern and cyclic differential alternating water injection. The main advantage of using this strategy is that the swept efficiency is improved by changing injection-production streamlines and displacement directions, which means displacement from two different direction for the same region during a complete cycle. This technology is effective in increasing the swept efficiency and tapping the remaining oil, thus resulting in higher oil recovery. Field application with three new patterns in a carbonate reservoir in the Middle East is successful. By optimizing injection and production parameters based on the cyclic alternating well pattern, the test well group had a maximum increase of daily oil production per well of 23.84 m3 and maximum water cut drop of 18%. By further optimizing the distance (keep a long distance) between the heels of injection and production wells, the waterflooding performance could be better with water cut decreasing and oil production increasing.

Based on the new seismic and drilling data and the recent related research results, this paper systematically analyzes the diversity and complexity of evolution process of crustal lithosphere structure and basin structure in the Pearl River Mouth Basin on the northern margin of the South China Sea. Three types of detachment faults of different structural levels exist: crust-mantle detachment, inter-crust detachment and upper crust detachment. It is considered that different types of extensional detachment control different subbasin structures. Many fault depressions controlled by upper crust detachment faults have been found in the Zhu I Depression located in the proximal zone. These detachment faults are usually reformed by magma emplacement or controlled by preexisting faults. Baiyun-Liwan Sag located in the hyperextension area shows different characteristics of internal structure. The Baiyun main sag with relative weak magmatism transformation is a wide-deep fault depression, which is controlled by crust-mantle detachment system. Extensive magmatism occurred in the eastern and southwest fault steps of the Baiyun Sag after Middle Eocene, and the crust ductile extensional deformation resulted in wide-shallow fault depression controlled by the upper crust detachment fault. Based on the classical lithosphere extensional breaking and basin tectonic evolution in the Atlantic margin, it is believed that the magmatic activities and pre-existing structures in the Mesozoic subduction continental margin background are important controlling factors for the diversified continental margin faulted structures in the northern South China Sea.

Because of the strong tectonic movement during the formation of limestone buried hills, lots of fractures came into being. The early formed structural fractures have undergone denudation, demorphism, leaching, dissolution from atmosphere precipitation, and surface runoff, which make some of the initial structural fractures enlarged and some half-filled or fully filled with calcite. The fractures formed in the later tectonic movement are not often filled and become the main channel connecting dissolution pores with cavities. This paper calculates the strain magnitude of buried hill formation resulting from every stage tectonic movement using the strain analysis methods such as inversion and forward modeling of structural evolution history of formations. The paper also predicts the 3D fracture network formed during every tectonic movement from the geological genesis standpoint, and therefore, distinguishes the early filled fractures formed during the period of buried hill formation from the unfilled fractures formed later, achieving the goal of predicting fracture reservoirs in the limestone buried hills. Key words: limestone, buried hill, multi-period fracture, effective fracture

To improve the efficiency and accuracy of carbonate reservoir research, a unified reservoir knowledge base linking geological knowledge management with reservoir research is proposed. The reservoir knowledge base serves high-quality analysis, evaluation, description and geological modeling of reservoirs. The knowledge framework is divided into three categories: technical service standard, technical research method and professional knowledge and cases related to geological objects. In order to build a knowledge base, first of all, it is necessary to form a knowledge classification system and knowledge description standards; secondly, to sort out theoretical understandings and various technical methods for different geologic objects and work out a technical service standard package according to the technical standard; thirdly, to collect typical outcrop and reservoir cases, constantly expand the content of the knowledge base through systematic extraction, sorting and saving, and construct professional knowledge about geological objects. Through the use of encyclopedia based collaborative editing architecture, knowledge construction and sharing can be realized. Geological objects and related attribute parameters can be automatically extracted by using natural language processing (NLP) technology, and outcrop data can be collected by using modern fine measurement technology, to enhance the efficiency of knowledge acquisition, extraction and sorting. In this paper, the geological modeling of fracture-cavity reservoir in the Tarim Basin is taken as an example to illustrate the construction of knowledge base of carbonate reservoir and its application in geological modeling of fracture-cavity carbonate reservoir.

“Generalized mobility” is used to realize the unification of tube flow and seepage in form and the unification of commonly used linear and nonlinear flow laws in form, which makes it possible to use the same form of motion equations to construct unified governing equations for reservoirs of different scales in different regions. Firstly, by defining the generalized mobility under different flow conditions, the basic equation governing fluid flow in reservoir coupling generalized tube flow and seepage is established. Secondly, two typical well test analysis models for coupling tube flow and seepage flow are given, namely, pipe-shaped composite reservoir model and partially open cylindrical reservoir model. The log-log pressure draw-down type-curve of composite pipe-shaped reservoir model can show characteristics of two sets of linear flow. The log-log pressure drawdown plot of partially opened cylindrical reservoir model can show the characteristics of spherical flow and linear flow, as well as spherical flow and radial flow. The pressure build-up derivative curves of the two models basically coincide with their respective pressure drawdown derivative curves in the early stage, pulling down features in the late stage, and the shorter the production time is, the earlier the pulling down feature appears. Finally, the practicability and reliability of the models presented in this paper are verified by three application examples.

Because of the differences of hydrocarbon accumulation between in-source and out-of-source oil pools, the demand for source kitchen is different. Based on the establishment of source-to-reservoir correlation in the known conventional accumulations, and the characteristics of shale oil source kitchens as well, this paper discusses the differences of source kitchens for the formation of both conventional and shale oils. The formation of conventional oil pools is a process of hydrocarbons enriching from disperse state under the action of buoyancy, which enables most of the oil pools to be formed outside the source kitchens. The source rock does not necessarily have high abundance of organic matter, but has to have high efficiency and enough amount of hydrocarbon expulsion. The TOC threshold of source rocks for conventional oil accumulations is 0.5%, with the best TOC window ranging from 1% to 3%. The oil pools formed inside the source kitchens, mainly shale oil, are the retention of oil and gas in the source rock and there is no large-scale hydrocarbon migration and enrichment process happened, which requires better quality and bigger scale of source rocks. The threshold of TOC for medium to high maturity of shale oil is 2%, with the best range falling in 3%–5%. Medium to low mature shale oil resource has a TOC threshold of 6%, and the higher the better in particular. The most favorable kerogen for both high and low-mature shale oils is oil-prone type of I–II1. Carrying out source rock quality and classification evaluation and looking for large-scale and high-quality source rock enrichment areas are a scientific issue that must be paid attention to when exploration activity changes from out-of-source regions to in-source kitchen areas. The purpose is to provide theoretical guidance for the upcoming shale oil enrichment area selection, economic discovery and objective evaluation of resource potential.

Taking the Gaoshangpu-Liuzan geothermal field in the Nanpu sag of the Bohai Bay Basin as the research object, this paper discusses the geological conditions and potential of the geothermal resources of the Guantao Formation in the study area, and introduces the development practice of geothermal energy heating in Caofeidian. The average buried depth of the Guantao Formation is 1500–2500 m, the lithology is dominated by sandy conglomerate, and the average thickness of thermal reservoir is 120–300 m. The average porosity of thermal reservoir is 28%–35%, the permeability is (600–2000)×10−3 μm2, and the temperature of thermal reservoir is 70–110 °C. The formation has total geothermal resources of 13.79×1018 J, equivalent to 4.70×108 t of standard coal. Based on a large amount of seismic and drilling data from oil and gas exploration, this study carried out high quality target area selection, simulation of sandstone thermal reservoir, and production and injection in the same layer. The geothermal heating project with distributed production and injection well pattern covering an area of 230×104 m2 was completed in the new district of Caofeidian in 2018. The project has been running steadily for two heating seasons, with an average annual saving of 6.06×104 t of standard coal and a reduction of 15.87×104 t of carbon dioxide, achieving good economic and social benefits. This project has proved that the Neogene sandstone geothermal reservoir in eastern China can achieve sustainable large-scale development by using the technology of “balanced production and injection in the same layer”. It provides effective reference for the exploration and development of geothermal resource in oil and gas-bearing basins in eastern China.

Aiming at the actual demands of petroleum exploration and development, this paper describes the research progress and application of artificial intelligence (AI) in petroleum exploration and development, and discusses the applications and development directions of AI in the future. Machine learning has been preliminarily applied in lithology identification, logging curve reconstruction, reservoir parameter estimation, and other logging processing and interpretation, exhibiting great potential. Computer vision is effective in picking of seismic first breaks, fault identification, and other seismic processing and interpretation. Deep learning and optimization technology have been applied to reservoir engineering, and realized the real-time optimization of waterflooding development and prediction of oil and gas production. The application of data mining in drilling, completion, and surface facility engineering etc. has resulted in intelligent equipment and integrated software. The potential development directions of artificial intelligence in petroleum exploration and development are intelligent production equipment, automatic processing and interpretation, and professional software platform. The highlights of development will be digital basins, fast intelligent imaging logging tools, intelligent seismic nodal acquisition systems, intelligent rotary-steering drilling, intelligent fracturing technology and equipment, real-time monitoring and control of zonal injection and production.

This paper systematically discusses the multiple source characteristics and formation mechanisms of carbonate-rich fine-grained sedimentary rocks through the analysis of material source and rock formation. The hydrocarbon accumulation characteristics of carbonate-rich fine-grained sedimentary rocks are also summarized. The results show that the main reason for the enrichment of fine-grained carbonate materials in rift lake basins was the supply of multiple material sources, including terrestrial material input, formation of intrabasinal authigenic carbonate, volcanic-hydrothermal material feeding and mixed source. The development of carbonate bedrock in the provenance area controlled the filling scale of carbonate materials in rift lake basins. The volcanic-hydrothermal activity might provide an alkaline fluid to the lake basins to strengthen the material supply for the formation of carbonate crystals. Authigenic carbonate crystals induced by biological processes were the main source of long-term accumulation of fine-grained carbonate materials in the lake basins. Carbonate-rich fine-grained sedimentary rocks with multiple features were formed through the interaction of physical, biochemical and chemical processes during the deposition and post-deposition stages. The source and sedimentary origin of the fine-grained carbonate rock controlled the hydrocarbon accumulation in it. In the multi-source system, the types of “sweet spots” of continental shale oil and gas include endogenous type, terrigenous type, volcanic-hydrothermal type and mixed source type.

By analyzing the structural background, petroleum geological conditions, and typical regional (paleo) oil and gas reservoirs in marine ultra-deep oil and gas regions in China, this paper reveals the evolution processes of the marine ultra-deep oil and gas reservoirs and the key controlling factors of accumulation. The marine ultra-deep oil and gas resources in China are buried at depth of greater than 6000 m, and are mainly distributed in the Precambrian and Lower Paleozoic strata in the Sichuan, Tarim and Ordos cratonic basins. The development of marine ultra-deep source rocks in China is controlled by cratonic rifts and cratonic depressions with the background of global supercontinent breakup-convergence cycles. The source rocks in Sichuan Basin have the most developed strata, followed by Tarim Basin, and the development strata and scale of Ordos Basin needs to be further confirmed. The marine ultra-deep reservoir in China is dominated by carbonate rocks, and the reservoir performance is controlled by high-energy sedimentary environment in the early stage, superimposed corrosion and fracture in the later stage. The regional caprocks are dominated by gypsum salt rocks, shale, and tight carbonate rock. The ultra-deep oil and gas fields in China have generally experienced two stages of oil-reservoir forming, cracking (or partial cracking) of paleo-oil reservoirs, and late finalization of cracked gas (or highly mature to over mature oil and gas). The oil and gas accumulation is controlled by static and dynamic geological elements jointly. Major hydrocarbon generation center, high quality and large-scale reservoir resulted from karstification of high energy facies belt, thick gypsum rock or shale caprock, and stable trapping and preservation conditions are the key factors for accumulation of ultra-deep oil and gas. We propose three favorable exploration directions, i.e. the areas around intracratonic rift and intracratonic depression, and craton margin.

To understand the evolution of the Miocene gravity flow deposits in the Lower Cong—Congo Fan Basin, this paper documents the Miocene sequence stratigraphic framework, the depositional characteristics and the controlling factors of the gravity flow system. Based on the establishment of high-resolution sequence stratigraphic framework, lithofacies characteristics and sedimentary units of the gravity flow deposits in the region are identified by using seismic, well logging and core data comprehensively, and the sedimentary evolution process is revealed and the controlling factors are discussed. The Miocene can be divided into four 3rd-order sequences (SQ1—SQ4). The gravity flow deposits mainly include siliciclastic rock and pelite. The main sedimentary units include slumping deposits, mass transport deposits (MTD), channel fills, levee-overbank deposits, and frontal lobes. In the Early Miocene (SQ1), mainly gull-wing, weakly restricted to unrestricted depositional channel-overbank complexes and lobes were formed. In the early Middle Miocene (SQ2), W-shaped and weakly restricted erosional-depositional channels (multi-phase superposition) were subsequently developed. In the late Middle Miocene (SQ3), primarily U-shaped and restricted erosional channels were developed. In the Late Miocene (SQ4), largely V-shaped and deeply erosional isolated channels were formed in the study area. Climate cooling and continuous fall of the sea level made the study area change from toe of slope-submarine plain to lower continental slope, middle continental slope and finally to upper continental slope, which in turn affected the strength of the gravity flow. The three times of tectonic uplifting and climate cooling in the West African coast provided abundant sediment supply for the development of gravity flow deposits. Multistage activities of salt structures played important roles in redirecting, restricting, blocking and destroying the gravity flow deposits. Clarifying the characteristics, evolution and controlling factors of the Miocene gravity flow deposits in the Lower Congo—Congo Fan Basin can provide reference for deep-water petroleum exploration in this basin.

This paper targets the shale oil reservoirs of middle to high maturity in four major basins of China, including the Permian Lucaogou Formation of the Jimsar Sag in the Junggar Basin, the Chang 73 Member of the Triassic Yanchang Formation in the Longdong area of the Ordos Basin, the Kong 2 Member of the Paleogene Kongdian Formation in Cangdong Sag of the Bohai Bay Basin, and the Qing 1 Member of the Cretaceous Qingshankou Formation in Changling Sag of the Songliao Basin. The key parameters of the shale oil reservoirs in the four basins, such as reservoirs effectiveness, oil content, crude oil movability, and fracability, have been revealed under identical experimental conditions using the same evaluation technical system, on the basis of technique development and integrated application of multi-scale spatial distribution depiction, effective connectivity calculation, movable oil assessment based on the charging effect, and simulation of fracture propagation during reservoir stimulation. This research overcomes insufficient resolutions of conventional analysis approaches and difficulties in quantitative evaluation, develops the evaluation method for resource recoverability of different types of shale oil, and gains insights into different types of shale oil via comparison. The results of experiments and comparative analysis show that there are significant differences in the endowment of continental shale oil resources in the four major basins in China. Among them, the Lucaogou Formation in the Junggar Basin has more effective shale reservoirs, the Chang 73 sub-member of the Ordos Basin has a comparatively good proportion of movable oil and the Kong 2 Member of the Bohai Bay Basin has the best fracability. These results can provide references and basis for choosing development plans and engineering techniques.

Carboniferous carbonate reservoirs at the eastern edge of the Pre-Caspian Basin have undergone complex sedimentation, diagenesis and tectonism processes, and developed various reservoir space types of pores, cavities and fractures with complicated combination patterns which create intricate pore-throats structure. The complex pore-throat structure leads to the complex porosity-permeability relationship, bringing great challenges for classification and evaluation of reservoirs and efficient development. Based on the comprehensive analysis on cores, thin sections, SEM, mercury intrusion, routine core analysis and various tests, this paper systematically investigated the features and main controlling factors of pore-throats structure and its impact on the porosity-permeability relationship of the four reservoir types which were pore-cavity-fracture, pore-cavity, pore-fracture and pore, and three progresses are made. (1) A set of classification and descriptive approach for pore-throat structure of Carboniferous carbonate reservoirs applied to the eastern edge of the Pre-Caspian Basin was established. Four types of pore-throat structures were developed which were wide multimodal mode, wide bimodal mode, centralized unimodal mode and asymmetry bimodal mode, respectively. The discriminant index of pore-throat structure was proposed, realizing the quantitative characterization of pore-throat structure types. (2) The microscopic heterogeneity of pore reservoir was the strongest and four types of pore-throat structures were all developed. The pore-fracture and pore-cavity-fracture reservoirs took the second place, and the microscopic heterogeneity of pore-cavity reservoir was the weakest. It was revealed that the main controlling factor of pore-throat structure was the combination patterns of reservoir space types formed by sedimentation, diagenesis and tectonism. (3) It was revealed that the development of various pore-throat structure types was the important factor affecting poroperm relationship of reservoirs. The calculation accuracy of permeability of reservoirs can be improved remarkably by subdividing the pore-throat structure types. This study deepens the understanding of pore-throat structure of complicated carbonate reservoirs, and is conducive to classification and evaluation, establishment of precise porosity-permeability relationship and highly efficient development of carbonate reservoirs.