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Copyright of Special Oil & Gas Reservoirs is the property of Special Oil & Gas Reservoirs Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Interpreting reservoir properties through log data and logging responses in complex strata is critical for efficient petroleum exploitation, particularly for metamorphic rocks. However, the unsatisfactory accuracy of such interpretations in complex reservoirs has hindered their widespread application, resulting in severe inconvenience. In this study, we proposed a multi-mineral model based on the least-square method and an optimal principle to interpret the logging responses and petrophysical properties of complex hydrocarbon reservoirs. We began by selecting the main minerals based on a comprehensive analysis of log data, X-ray diffraction, petrographic thin sections and scanning electron microscopy (SEM) for three wells in the Bozhong 19-6 structural zone. In combination of the physical properties of these minerals with logging responses, we constructed the multi-mineral model, which can predict the log curves, petrophysical properties and mineral profile. The predicted and measured log data are evaluated using a weighted average error, which shows that the multi-mineral model has satisfactory prediction performance with errors below 11% in most intervals. Finally, we apply the model to a new well "x" in the Bozhong 19-6 structural zone, and the predicted logging responses match well with measured data with the weighted average error below 11.8% for most intervals. Moreover, the lithology is dominated by plagioclase, K-feldspar, and quartz as shown by the mineral profile, which correlates with the lithology of the Archean metamorphic rocks in this region. It is concluded that the multi-mineral model presented in this study provides reasonable methods for interpreting log data in complex metamorphic hydrocarbon reservoirs and could assist in efficient development in the future. [ABSTRACT FROM AUTHOR]

As a buried-hill oil and gas reservoir in Zhuyi Hollow of Pearl River Mouth Basin, Huizhou 27-1 well area has large thickness of fractured interval, multiple layers, strong heterogeneity, and great difficulty in fracturing reconstruction. Therefore, it is difficult to understand the expansion and extension law of artificial fractures in buried-hill reservoir. In order to solve this problem, the dynamic parameter logging interpretation model was first established, and the static rock mechanics data was co-corrected to establish a one-dimensional rock mechanics profile. Combined with the deep diagenesis theory, a three-dimensional geomechanical model was established to simulate the diagenetic environment of the block. Finally, based on the three-dimensional geomechanical model, the influences of parameters such as displacement, fluid volume, sand ratio, pre-fluid ratio and perforation zone thickness on the longitudinal and plane extension of fractures were studied to optimize the fracture design. The results show that the mean value of Young's modulus is 45. 47 GPa, the mean value of maximum horizontal principal stress is 100. 91 MPa, the mean value of minimum horizontal principal stress is 80. 98 MPa, and the mean value of Poisson's ratio is 0. 30 in Huizhou 27-1 block. The optimal construction parameters are 6 ~7 m³ / min displacement, 600 ~ 700 m³ fluid volume, 10% ~ 15% sand ratio, 50% ~60% pad fluid ratio and 8 ~11 m perforation thickness, which provide guidance for on-site construction. [ABSTRACT FROM AUTHOR]

The Xihu Sag is the main are of oil and gas exploration in the East China Sea continental shelf basin. Gradual development and utilization of traditional oil and gas in the Pinghu Formation. Basement-buried hills are gradually becoming popular fields for oil and gas exploration in the East China Sea. Based on core, logging curve, and reservoir analyses and testing, this study presents the reservoir characteristics and high-quality reservoir development model of a buried basement hill in the Pinghu slope zone. The reservoir of the buried hill is dominated by granite, and the reservoir space is controlled by structural fractures and dissolution pores. The structural fractures are the main reservoir spaces that connect the dissolution pores. The reservoir has a typical binary structure in the vertical direction, which is divided into weathered and inner fracture zones. The reservoir physical properties of the weathered fracture zone were better, and those of the inner fracture zone were more heterogeneous. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum Geology & Recovery Efficiency is the property of Petroleum Geology & Recovery Efficiency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In recent years, with the exploration and development of granite buried-hill oil and gas reservoirs, petrophysics research has played an important role in the study of reservoir characteristics and fluid identification. Through analysis of the relationship between the fluid-bearing petrophysical parameters and the reservoir, the seismic response changes caused by reservoir fluid changes can be determined. Mesozoic granites in the coastal area of Fujian Province in eastern China were investigated as the research object of this project. The mineral composition, density, porosity, P-wave velocity, and S-wave velocity of the granite were measured and analyzed by X-ray diffraction, rock density, rock porosity, and rock acoustics methods. Therefore, the granite's petrophysical properties, fluid response characteristics, and gas sensitivity parameters were analyzed. The result of the study shows that the granite is predominantly monzogranite. According to the type of reservoir space assemblage, the samples can be divided into two types: those containing fracture-dissolution pores and those containing only dissolution pores. All the samples were characterized by medium to high densities and low to extra-low porosity. There was a linear correlation between the P-wave velocity and S-wave velocity under gas and water-saturated conditions. Factors such as P-wave to S-wave velocity ratio, Poisson's ratio, Lame coefficient, and other parameters of the samples were analyzed, and the threshold values that distinguished the water and gas-saturated states of the samples were measured and determined. In addition, there were negative correlations between the P- and S-wave velocities and porosity. The sensitivities of the petrophysical parameters to the gas capacity from high to low are Ip2 − 2.03 Is2, λ − 0.03 μ, λ, λ/μ, E − 2.03 μ, σ, K/μ, K, Ip, Vp/Vs, Vp, E, μ, Vs, and Is. For granite-buried hill reservoirs, the variation ranges of the parameters, such as the density, porosity, and P-wave velocity, of the fracture-dissolution pore granite samples were larger than those of the dissolution pore samples. The bulk parameters (Ip, Vp, K, λ) and combination parameters (Ip2 − 2.03 Is2, K/μ, λ− 0.03 μ, E − 2.03 μ, λ/μ) of the dissolution pore samples were more sensitive to the gas capacity. The results of this study provide a basis for the geophysical identification of granite-buried hill reservoirs. [ABSTRACT FROM AUTHOR]

The Dawangzhuang buried hill zone is a typical representative of Paleozoic oil and gas exploration in the Jiyang Depression, Bohai Bay Basin, and has experienced a complicated accumulation process. Using petrographic observation, microthermometry and abundance of hydrocarbon inclusions, the Paleozoic hydrocarbon charging process in Dawangzhuang buried hill zone was discussed. The study shows that the Paleozoic reservoirs developed hydrocarbon inclusions in the study area. Ordovician hydrocarbon inclusions with pale yellow and blue-green fluorescence distributed along the calcite veins and particle healing joints. Asphalt inclusions and oleaginous are only distributed in Dagu 671 oil reservoir with a small scale. The main peaks of the homogenization temperature are from 80 ℃ to 90 ℃ and from 100 ℃ to 110 ℃; Carboniferous-Permian hydrocarbon inclusions with blue-green fluorescent distributed along the micro-cracks of quartz particles and secondary enlarged edges. The main peak of the homogenization temperature is from 100 ℃ to 110 ℃. Combining with the hydrocarbon generation and expulsion periods of source rocks, it can be concluded that there are two stages of hydrocarbon charging in the Paleozoic in the study area. The first stage of oil and gas charging occurred in the late Dongying period (27~25 Ma), which was a small-scale accumulation of Paleozoic, mainly in the Ordovician; the second stage of oil and gas charging occurred from the end of Guantao period to the end of Minghuazhen period (5~2 Ma), which was a large-scale accumulation of Ordovician and Carboniferous-Permian. The development of asphalt inclusions near the Dagu 671 well area and the fact shown by the Effective Grids containing Oil Inclusions (EGOI) that the ancient oil-water interface is lower than the current one are related to the activity of the Da 1 fault at the end of the Minghuazhen period (2 Ma), resulting in local adjustments and smaller scope of oil and gas reservoir.

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Lower Paleozoic carbonate strata experience multi-stage tectonic activity and post-depositional volcanic activity in the Dongying Depression, Bohai Bay basin. These tectonic and magmatic activities have caused the reservoir to undergo severe diagenesis, resulting in strong reservoir heterogeneity. This study aims to identify the characteristics of dolomite, various reservoir spaces' characteristics, the origin of different types of dolomite, and the porosity evolution. According to crystal size and morphology, dolomites can be divided into three kinds of matrix dolomites and four kinds of dolomite cements. The petrology and geochemistry of the dolomite suggests that matrix dolomite is formed from seawater. The medium-to-coarse-crystalline dolomite cement (D3) has a higher 87Sr/86Sr ratio (0.7119 to 0.7129) and a higher homogenization temperature (>125 °C), suggesting that the fluid for the precipitation of D3 is a mixed fluid formed by hydrothermal fluid eroding the 87Sr-rich feldspar sandstone. The strikingly negative δ18O values (−23.7 to −25.7‰ VPDB) of saddle dolomite (D4) indicate that D4 precipitated from hydrothermal fluids and the Mg2+ source may be due to dissolution of the host dolomite that formed in the evaporation environment. The reservoir spaces of the target strata in the study area mainly include fractures, dissolution vugs, intercrystalline pores, and moldic pores. Dissolution is the basis for forming high-quality dolomite reservoirs. The faults and fractures provided favorable conditions for dissolution. Hydrothermal fluid and organic acid were the main dissolution fluids for the dolomite reservoir, which were beneficial to the development of secondary pores. In the study area, organic acid dissolution was shown to contribute more than hydrothermal dissolution in the study area. [ABSTRACT FROM AUTHOR]

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Lower Paleozoic carbonate strata experience multi-stage tectonic activity and post-depositional volcanic activity in the Dongying Depression, Bohai Bay basin. These tectonic and magmatic activities have caused the reservoir to undergo severe diagenesis, resulting in strong reservoir heterogeneity. This study aims to identify the characteristics of dolomite, various reservoir spaces’ characteristics, the origin of different types of dolomite, and the porosity evolution. According to crystal size and morphology, dolomites can be divided into three kinds of matrix dolomites and four kinds of dolomite cements. The petrology and geochemistry of the dolomite suggests that matrix dolomite is formed from seawater. The medium-to-coarse-crystalline dolomite cement (D3) has a higher 87Sr/86Sr ratio (0.7119 to 0.7129) and a higher homogenization temperature (>125 °C), suggesting that the fluid for the precipitation of D3 is a mixed fluid formed by hydrothermal fluid eroding the 87Sr-rich feldspar sandstone. The strikingly negative δ18O values (−23.7 to −25.7‰ VPDB) of saddle dolomite (D4) indicate that D4 precipitated from hydrothermal fluids and the Mg2+ source may be due to dissolution of the host dolomite that formed in the evaporation environment. The reservoir spaces of the target strata in the study area mainly include fractures, dissolution vugs, intercrystalline pores, and moldic pores. Dissolution is the basis for forming high-quality dolomite reservoirs. The faults and fractures provided favorable conditions for dissolution. Hydrothermal fluid and organic acid were the main dissolution fluids for the dolomite reservoir, which were beneficial to the development of secondary pores. In the study area, organic acid dissolution was shown to contribute more than hydrothermal dissolution in the study area.

The Bozhong (BZ) 19-6 gas field in the Bohai Bay Basin is a fractured metamorphic reservoir with proven reserves of over 1000 × 108 m3. However, the fracture development in the Archaean metamorphic buried hill reservoir in the BZ19-6 area is still not clear. In this study, cores, thin sections, imaging logs and laboratory measurements were used to elucidate the influences of lithology, tectonics and weathering on the formation and development of natural fractures. Both tectonic fractures and dissolution fractures are well developed, and 96.8% of these are interconnected. Lithology exerts the primary control on fracture formation, while stress and weathering influence the development of the fractures. Leucogneiss, cataclasite and gneiss with high contents of brittle minerals are favorable for fracture formation. Buried hill reservoirs near faults commonly exhibit a high linear density of fractures due to greater stress perturbation. Based on the degree of weathering in the study area, a metamorphic buried hill reservoir may be divided vertically into three zones: a weathered fracture zone, an inner fracture zone, and the basement. Fracture linear density and fracture aperture decrease significantly with a decrease in the intensity of weathering, while paleo-topographic highs with more intense weathering have a higher fracture density. A reservoir evolution pattern is proposed that can be used for targeting the favorable reservoirs in the study area. • Investigated fracture development in the metamorphic buried hill reservoirs in Bozhong 19–6. • Disclosed why high-density fractures were well-developed in leptynite, cataclasite, and gneiss. • Explained the relationship between tectonics and the formation of natural fractures. • Found that the weathering finally determined the vertical and regional distributions of fractures. • Concluded a pattern to interpret the formation of metamorphic buried hill reservoirs. [ABSTRACT FROM AUTHOR]

Abstract: In order to realize the effective development of buried hill light oil reservoirs, mid-deep massive heavy oil reservoirs with interbeds, and ultra-deep massive heavy oil reservoirs in the Liaohe Oilfield, three tridimensional development models are established: superposition of horizontal wells in multi-intervals and multi-layers, steam assisted plane displacement (vertical wells) with combination of vertical gravity drainage (horizontal wells), and steam assisted liquor drainage by two superposed horizontal wells and production by vertical wells. The development mechanisms for these three tridimensional development models have been studied by field test, physical simulation and numerical simulation. The tridimensional development mechanisms of buried hill light oil reservoirs are uniform compaction action, vertical gravity action and joint supply action. The tridimensional development mechanisms of mid-deep massive heavy oil reservoir with interbeds are gravity drainage and steam flooding, and the tridimensional development mechanisms of ultra-deep massive heavy oil reservoir are gravity water drainage, reduction of heat losses and enhancement of production injection ratio. The field tests in the light oil reservoir of the Xinggu buried hill, mid-deep massive heavy oil reservoir in Xing VI oil layer of Block Du 84 and ultra-deep massive heavy oil reservoir of Block Wa 59 in the Liaohe Oilfield showed that tridimensional development can significantly improve crude oil production, and realize efficient development of oilfield. [Copyright &y& Elsevier]

Abstract: It is very complicated for the relationship between water injection and injection-production through horizontal well in a naturally fractured buried-hills reservoir. On the basis of simplifying and hypothesizing for the flowing equations of the dual medium, the mathematical model for fluid flowing in a reservoir is obtained, and 7 similarity principles is proposed also. To aim at simulating the practical development effect, with the direction of the similarity principle, the triaxial fluid physical models were formed. With this model, the physical simulations, such as different well deployment patterns for the horizontal wells, various well distance, various difference between injection and production, were all carried out, the oil-sweeping mechanics for the horizontal wells were analyzed. Thus, the optimum well deployment patterns, well distance, differential pressure between injection and production were all Fig. out, so that the research achievement can provide a technical foundation for the production with water-injection within horizontal wells in a naturally fractured buried-hill reservoir. [Copyright &y& Elsevier]

Abstract: The optimum deployment of stereoscopically injecting and producing well pattern is a key to the buried hill reservoir''s development. in the given reservoir, the spacing allocation factor of injecting and producing well type, vertical correspondent relationship, flat orientation relationship, injecting and producing well spacing for the stereoscopically injecting and producing the well pattern between the vertical well-horizontal well, horizontal well-horizontal well is optimized. With numerical simulation and by optimizing the multi injecting and producing schemes, the optimized scheme of stereoscopically injection-production well pattern for the buried hill reservoir is confirmed. [Copyright &y& Elsevier]

Abstract: Metamorphicrock buried hill reservoir is a type of complex fracture reservoirs and hard to characterize. The paper proposes a new method for buried hill modeling, to establish double porosity model, including fracture and matrix. In matrix modeling process, metamorphic lithology theory is used to characterize the complicated distribution of lithology for phase modeling, and matrix model with porosity and permeability under the control of lithology phase condition is completed by random simulation modeling. The data of lithology come from well logging in buried hill reservoir. In fracture modeling, the feature of strong anisotropy of permeability in formation is considered and a new method of fracture modeling is applied to characterize the fracture system. Then the method is used in history matching of real reservoir simulation to test the reliability, and the result shows the model by new method are closer to real reservoir than model by common method. [Copyright &y& Elsevier]

Abstract: With core observation, thin slice identification and imaging logging data, reservoir evaluation and fracture characterization are studied in the Archaean metamorphic buried hill reservoir in the JZ25-1S field in the Bohai Bay Basin. The reservoir is divided into three zones vertically: weathered crust, semi-weathered crust and base rock, belonging to three reservoir types of fracture-pore pattern, pore-fracture pattern and micro fracture-compact pattern. The fracture effectiveness is estimated using crude oil inclusions testing technology, the direction of regional geostress, and full wave train acoustic logging data. It is concluded that the reservoir in the semi-weathered crust is most developed and the reservoir of pore-fracture pattern is the main oil producing layer. The main trend of fractures is nearly parallel to the main fault trend in the buried hill. The inclined fractures of late opening-mode parallel to the current direction of maximum geostress are the most effective fractures. At last, in combination of imaging logging interpretation with actual production, the qualitative and semiquantitative reservoir classification criteria are proposed and the buried hill reservoir is divided into three levels of I, II and III. [Copyright &y& Elsevier]

Abstract: The buried hill reservoirs of Hexiwu structural belt in Langgu Sag, Bohaiwan Basin are comprehensively studied by core and outcrop observation. The reservoir lithology is dominantly carbonate rock, and the reservoir spaces include dissolved pores, dissolved cavities, cracks and bedrock micropores, forming pore-cavity type, crack type, crack-cavity type and combination pore-cavity-crack type reservoirs. Multiple-phase fossil karstification is an important factor during reservoir formation. The fossil karsts are developed in the weathering and leaching belt, submerged current belt, fracture belt and bedding direction along buried hill unconformities. The cracks formed by tectonic movement increase porosity, improve connection of pores and cavities and permeability. The reservoirs developed in different lithologies and tectonic positions have different physical properties: dolomite reservoir is better than carbonate reservoir, and reservoir not overlapped by Permo-Carboniferous stratum is better than that overlapped by Permo-Carboniferous stratum, and reservoir in the fault-developed area is better than that in the non-fault-developed area. The reservoirs are favorable areas for oil and gas exploration. [Copyright &y& Elsevier]

Abstract: In recent years, various breakthroughs have been made in buried hill reservoir exploration in Liaohe Depression. Exploration targets have shifted from the Shallow-medium buried hill reservoirs with clearer reservoir-forming conditions to the low and inner buried hill reservoirs with deeper, hidden, and more complex features. Reservoir-forming conditions of low and inner buried hills were studied in aspects of basement tectonic activity, type of buried hills, lithology and reservoir characteristics, hydrocarbon generating system, and hydrocarbon conducting system. A practical classification method of inner buried hill reservoirs has been reestablished in accordance with the relationship between buried hills and hydrocarbon accumulations by studying reservoir characteristics of inner buried hill reservoirs with consideration of exploration practices. Such a classification method has widened the hydrocarbon searching scope in buried hills and built up a reservoir-forming pattern for the exploration targets inside buried hills with low amplitude, multiphase fractures, and multisource charging. Based on the theoretical studies and exploration practices of low and inner buried hill reservoirs, the 3P reserves reported for low and inner buried hill reservoirs reached 2.54 × 108 t and 1.76 × 108 t, respectively, from 2001 to 2006. The buried hill reservoirs have made significant contribution to increasing reserves and stabilizing production in Liaohe Oilfield. [Copyright &y& Elsevier]