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Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency 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.)

With the successive discovery of large-scale Proterozoic gas reservoirs worldwide, ultra-deep Proterozoic strata have gradually become a new field of interest with great potential for gas reservoir exploration. The Ordos Basin in China has rich Proterozoic stratigraphic deposits and high gas reservoir exploration potential, but it has not been sufficiently explored. The lack of geological data has become a key shortcoming limiting its in-depth study. This study aimed to clarify the division and evidence of Meso-Neoproterozoic strata in the southern part the Ordos Basin, and clarify the stratum distribution and tectonic evolution process, which need to be prioritized before exploration. To this end, the multi-data joint research method of lithology-drilling-field outcrop-seismic data was used. The results showed that Sinian tillite, Jixianian dolomite, and Changchengian quartz sandstone developed in the Meso-Neoproterozoic strata from top to bottom. Seismic reflections from the bottoms of the Sinian and Jixianian showed weak-amplitude and medium-strong amplitude, respectively. The Changchengian strata can be divided into depression and rift layers. The rift layer presents a high-angle medium-strong amplitude reflection, and the depression layer presents a continuous medium-weak amplitude reflection. In the study area, during the early basin rift of the Changchengian, the NE-trending fault trough was filled with deposits, and the late rifting activities stopped, forming widespread depression deposits, with an angular unconformity contact between them. During the Jixian Period, the southwest continued to be depressed, and during the Sinian, the main body of the basin was uplifted, and the southwest margin was partially depressed. The strata were widely absent in the study area, and showed an "L"-shaped distribution only in the southwest margin of the study area. The depositional range is the largest in the Changchengian, followed by the Jixian, and the smallest in the Sinian. The thickness of the strata gradually thinned to the northeast. The Proterozoic strata in the Qyang paleo-uplift are covered by multiple sets of high-quality Paleozoic source rocks, and the generated oil and gas accumulate along the strata to the paleo-uplift, corresponding to an accumulation model of "multiple sources converge, and paleo-uplifts form reservoirs". This study compensates for the lack of basic research on the Meso-Neoproterozoic strata division in the Ordos Basin, and more accurately determines the distribution pattern of the strata in the basin, which are highly relevant for the Ordos Basin and other Meso-Neoproterozoic gas reservoirs. The exploration has important reference significance. [ABSTRACT FROM AUTHOR]

Hyperpycnal flow deposits, one of the most important deep‐water gravity‐flow deposits in lacustrine basins, have become the research focus in recent years. However, the sedimentary characteristics and depositional model of hyperpycnal flow deposits in lacustrine basins remain unclear due to the differences of depositional settings between lacustrine and marine environments. Hyperpycnal flow deposits observed in the middle of the third member of the Shahejie Formation (Es3z) in the Bonan Sag, Bohai Bay Basin, Eastern China, provide a rare case study to reveal the characteristics and depositional model in lacustrine basins. For the first time, detailed core analysis, high‐resolution 3D seismic data, petrology and grain size analysis were used to unravel the characteristics and depositional model of hyperpycnal flow deposits in this study. Twelve lithofacies, six bed types and four bedsets (corresponding to feeder channel, distributary channel, levee and lobe) were recognized from detailed facies analysis. Plant fragment, an important identification mark for hyperpycnal flow deposits, can be classified into three types: completely broken plant fragments, partially broken plant fragments and complete leaves. The proximal part of the deposit develops a small amount of scattered and completely broken plant fragments in massive or spaced stratified pebbly sandstone and massive sandstone due to strong erosion of sustained high‐density turbidity current. The medial part of the deposit is dominated by laminated partially broken plant fragments in planar laminated or rippled sandstone due to suspended settling of sustained high‐density turbidity current and quasi‐steady low‐density turbidity current. Layered partially broken plant fragments with some complete leaves are common in the upper part mud rich division of hybrid event bed and laminated siltstone in the distal part of the deposit. The distribution pattern of hyperpycnites is controlled comprehensively by palaeogeomorphy and sediment supply. Palaeogullies determine the provenance direction of hyperpycnal flow. The formation of synsedimentary faults and troughs control the transport routing patterns. Local micro‐palaeogeomorphy and depression areas further restrict the distribution of sand bodies. During the early stage of deposition with insufficient sediment supply, sediments are transported to the deep basin along confined faulted troughs forming elongated sandy bodies. During the late stage of deposition with sufficient sediment supply, sediments are transported to the deep basin without confinement accumulating fan‐shaped sandy bodies. This study offers insight for enhancing the recognition criteria of hyperpycnites, as well as their depositional model in lacustrine basins. [ABSTRACT FROM AUTHOR]

Mahu oilfield is the largest tight glutenite oilfield discovered in China, with a reserve of 1 billion tons, and has a good development prospect. However, the tight glutenite reservoir is characterized by strong heterogeneity, low porosity and low permeability, and is difficult to develop. Calcareous conglomerate was encountered during drilling in many reservoirs of Baikouquan Formation in the fault block of the Xia 72 well in the Ma 13 well block of the Mabei Oilfield, resulting in the deterioration of the physical properties of the reservoir and the decrease of gas logging or oil content, which not only reduced the formation drilling encounter rate, but also affected the later deployment of horizontal wells. The genesis, identification and distribution of the calcareous glutenite of the Baikouquan Formation in Mahu Depression were studied based on core data, thin section identification data, logging data and seismic data. The results show that the study area has a good combination of upper and lower strata which supplied both material and environmental conditions for the formation of calcareous glutenite. The calcareous cements of the calcareous glutenite were formed in the late stage of diagenesis, and their distribution are mainly controlled by sedimentary facies and early faults. The calcareous glutenites have bright-point reflection characteristics in seismic, and their distribution characteristics can be accurately reflected by the maximum amplitude attribute. [ABSTRACT FROM AUTHOR]

The Wudaoliang–Changshagongma fault is one of the NW-trending faults located within the southern Bayan Har Block of the Tibetan Plateau in China. In this paper, we used high-resolution imagery and digital elevation model data to study the geomorphological and geological characteristics of the fault. Furthermore, the result also determined the fault trace and estimated the average horizontal slip rate of the fault since the late Quaternary to have been 2.6 ± 0.6 mm/a. This slip rate is approximately equivalent to that of the Awancang, Madoi–Garde, and Dari faults, which are also located within the block. Furthermore, the slip rates of these faults obtained by remote sensing and geological methods are consistent with GPS observations. It indicates that tectonic deformation within the block is continuous and diffuse. Using trenching study results and sedimentary radiocarbon dating, we identified four paleoearthquake events that occurred at 42,378–32,975, 33,935–20,663, 5052–4862, and after 673–628 cal BP, respectively. The recurrence intervals of large earthquakes on the faults within the block are much longer than those of the boundary faults, and the slip rates are also smaller, indicating that faults within the block play a regulatory role in the tectonic deformation of the Bayan Har Block. [ABSTRACT FROM AUTHOR]

In China, complex fault blocks occupied an important position in the development of oilfields. Compared with monolithic sandstone reservoirs, complex fault blocks have the characteristics of complex and diverse structures and relatively developed low-level fault blocks. Such special oil reservoirs often have an impact on the development of the injection-production well pattern. Therefore, it is necessary to study its influence and optimize related deployment. According to the parameters of the selected example blocks, an ideal reservoir model is established and four well pattern distribution forms are designed. According to the simulation results, we will choose the best oil displacement pattern. Under the same physical and well pattern distribution conditions, the injected water or CO2 was simulated and the simulation results were compared. Finally, the influence of the fault length on the oil displacement effect on the two-dimensional plane of the entire reservoir was studied. The results show that under the condition of high injection-production pressure difference, well pattern 1 has the best water drive development effect. Comparing the oil saturation distribution cloud map of water flooding and gas flooding and the oil production rate curve of producing wells, CO2 is significantly better than water flooding in terms of oil displacement speed and production. After changing the length of the fault, it was found that due to the influence of the openness of the fault, as the length of the fault increases, the overall oil saturation distribution of the reservoir is greatly different. The initial oil production increases rapidly, but cumulative oil production changes. It is not obvious. Research reveals that the transfer of fault length affects the formation pressure and then changes the injection-production pressure difference and ultimately affects the initial oil production. [ABSTRACT FROM AUTHOR]

The distribution of lower-order faults affects the development of oil and gas and the distribution of remaining oil, which is also the key to the development of fault block reservoirs in eastern China. The lower-order faults are characterized by short extension, small fault displacement, and difficult identification by traditional seismic interpretation methods. Therefore, it is necessary to predict the development law of faults in combination with the paleostress field during the fault formation period to improve the accuracy of fault seismic interpretation. In this paper, on the basis of reservoir structural analysis and rock mechanics experiments, the geological and mechanical model of the Sanduo period is established to predict the simulation of the paleostress field during the development of lower-order faults. The development of lower-order faults in rift basins is mainly controlled by the minimum principal stress and stress difference, and the shear stress in the profile controls the tendency of faults. Controlled by the paleostress field, the occurrence of lower-order faults in the Weizhuang area, Gaoyou Sag, and Subei Basin is very complex, and the strike of the fault is distributed as a tension shear broom on the plane. The prediction results can provide a reference for the excavation of remaining oil and the development of oil and gas. [ABSTRACT FROM AUTHOR]

The discovery of an oil reservoir in Pishan Caldera of the Tarim Basin, northwest China, highlights the hydrocarbon exploration potential of large calderas. We used 3 D seismic interpretations, waveform clustering analysis, and seismic profiles to investigate the origin and evolution of Pishan Caldera, along with the mechanisms of hydrocarbon accumulation, and its significance for future oil and gas exploration. Pishan Caldera is located at depths of >7000 m, has an elliptical shape, extends over an area of 25 × 20 km, and is surrounded by ring faults. Pishan Caldera were the result of magma withdrawal and later magma intrusion. Volcanic eruptions, caldera collapse, and reactivation of Pishan Caldera resulted in Cretaceous oil migration and accumulation in Cretaceous breccia reservoirs. Ring faults, dense fracture networks, and lava tubes associated with the caldera acted as conduits for upward hydrocarbon migration. We propose a generalized model for hydrocarbon reservoirs related to the caldera, which includes five major reservoir types: drape anticline, fault block, volcanic-trapped, laterally sealed and lava tube type. Further efforts should be made to identify deep caldera structures that may be targets for hydrocarbon exploration. [ABSTRACT FROM AUTHOR]

In order to study the main control factors of volcanic reservoirs with complex oil–water relationships, the Carboniferous in the Chepaizi Uplift of the Junggar Basin was taken as an example and the lithofacies characteristics, main control factors, and hydrocarbon accumulation model of volcanic reservoirs were investigated by combining the petroleum geology with field testing (data of core analysis, well logging, formation testing, and production testing). The results show that the Carboniferous in the Chepaizi Uplift experienced three stages of volcanic activities and developed seven volcanic lithofacies bodies, distributed in a bead-string connected planar form along the Hongche fault. There is no unified oil–water interface across the whole study area and there are multiple oil–water systems within one fault block. The Carboniferous volcanic reservoir experienced two stages of hydrocarbon accumulation from two different source rocks. The distribution of faults penetrating hydrocarbon kitchens and source rocks controls the macro-scale distribution of reservoirs. The physical properties of reservoirs affect the pattern of oil and water differentiation in volcanic rock bodies, while the lithofacies body-controlled hydrocarbon accumulation mode highlighting "one rock body for one reservoir" determines the distribution of reservoirs. The matching between the paleo-structure and hydrocarbon accumulation stage controls the accumulation and adjustment of hydrocarbon distribution. The Permian source rocks in the Shawan Sag serve as the lateral hydrocarbon supply and hydrocarbons accumulate in the Carboniferous structural-lithologic traps, which are summarized as the two stages of hydrocarbon accumulation of newly generated hydrocarbons into older reservoir rocks. This study of the hydrocarbon accumulation pattern in volcanic rocks aims at guiding the development of Carboniferous reservoirs with complex oil and water relationships in this area. [ABSTRACT FROM AUTHOR]

Continental faulted basins are widely distributed in eastern China. Many of these basins, in which the faults block oil and gas reservoirs, have been explored. The heterogeneity of the reservoirs in fault block is very strong, shich restricts the further efficient development of these kinds of oil and gas fields. In this study, porosity and permeability tests, the use of thin sections of rock, mercury injection experiment and CT scan were used to investigate reservoir quality characteristics and control factors. The results showed that the content of quartz, feldspar, and debris in rock had a significant control function on the quality of the reservoir. Reservoir performance improved with increase of quartz and feldspar content, and worsened with increase of debris content. Taking the Ek1 reservoir in the Wang Guantun area as the specific research object, we developed the following understanding. On the one hand, the main compaction in the study area was mechanical compaction. When the compaction rate was greater than 60%, the porosity and permeability were inversely proportional to the compaction rate. On the other hand, dissolution pores were relatively developed in the study area, and the main types of dissolution were intragranular and intergranular dissolution pores. When the surface porosity of the dissolution pore was over 9.2%, porosity increased significantly the increase of dissolution surface porosity. This showed that dissolution surface porosity had greatly improved the reservoir porosity in this range. [ABSTRACT FROM AUTHOR]

In order to study the law and mechanism of fault activation induced by deep continuous mining, this paper takes the fault activation caused by underground mining of Shizishan Copper Mine as the research object. On the basis of field investigation and theoretical analysis of fault activation, the law and mechanism of fault group activation induced by deep continuous mining in the Shizishan mining area are analyzed in detail based on the three-dimensional discrete element method software 3DEC. The results show that the fault effect of rock movement in the footwall of the main orebody in the mine area is obvious. The en echelon steep dipping fault group in the footwall of the goaf will move each fault block in the direction of the goaf and slip along the fault plane when the balance between mining and gravity is disrupted. The fault activation has a domino effect in time and space, and the mechanism of this effect is revealed. The research results have great significance for the deep mining area development, mining alignment arrangement, and disaster prevention and control caused by fault activation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Detailed Rayleigh velocity and azimuthal anisotropy has been obtained in SW China. • The Red River fault strongly controls the low-velocity weak materials distribution. • Results from temporary seismic arrays in different observation periods are reliable. Located on the southeastern margin of the Tibetan plateau (TP), SW China, the southern Sichuan-Yunnan block (SYB) is intersected by boundary faults as the NW-trending Red River fault (RRF) and the nearly NS-trending Xiaojiang fault (XJF). It is a crucial zone for exploring severe crustal deformation and complicated tectonic movement. Using ambient noise data from multiple temporary seismic arrays and regional permanent seismic stations within the southern SYB, we can obtain the high-resolution S-wave velocity and azimuthal anisotropy by the direct inversion method. However, the Rayleigh phase velocity can reveal the structural characteristics of specific range of thickness at various periods. To evaluate the reliability of the direct inversion method in forward calculation, this study further calculates the Rayleigh phase velocity and azimuthal anisotropy at periods of 5–40 s. Compared with the S-wave velocity and azimuthal anisotropy, the forward Rayleigh phase velocity and azimuthal anisotropy illustrate similar patterns. Compared with the traditionally obtained Rayleigh phase velocity and azimuthal anisotropy, the forward results show good consistency, providing more details of the low-velocity anomalies and the azimuthal anisotropy owing to the dense seismic stations. A notable difference from previous results is that the low-velocity anomaly beneath the XJF does not cross over the southern segment of the RRF, resulting in the mechanically weak crustal materials distributed along the faults showing the fast axis of local complex pattern. This may indicate that the RRF strongly controls the deep structures. [ABSTRACT FROM AUTHOR]

This research investigates small-scale tectonic activity in the Jiujing region in Beishan, northwest China through the application of persistent scatterer (PS) Interferometric synthetic aperture radar (InSAR). PS InSAR is an effective monitoring tool in this unpopulated, arid, and unvegetated rural area, whose surface geology is dominated by a single large granitic intrusion, and which represents a candidate site for a geological disposal facility (GDF) for high-level radioactive waste (HLW) in China. This research demonstrates that faults F16-2, F17, F18, and F20-2 are still active, producing dip-slip motions along the fault planes. The lithological variations in weathering and erosion can be discounted as the cause for these small-scale displacement variations. The work has also identified 11 previously unknown faults, characterising them from vertical (DU) and eastward horizontal (DE) displacements along and across the faults. These newly discovered structures demonstrate how PS InSAR can be used to monitor and measure micro-scale movements on regional-scale faults, which, in many cases, were previously considered to be inactive. Thus, this also improves our understanding of local stress regimes in this area. The Jiujing region is part of a convergent fault zone dominated by NE-SW compression, leading to NE-SW crustal shortening and NW-SE elongation. Through determination of the sense of ground movement measured at irregularly distributed PS points, some faults are reverse and trending NW-SE, while others are normal and trending NE-SW, highlighting how InSAR can be used to resolve fault type and relative movements to monitor tectonic fault blocks at a regional scale. [ABSTRACT FROM AUTHOR]

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu 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.)

Recent breakthroughs in petroleum exploration suggest that the Linhe depression in the Hetao Basin in central and western Inner Mongolia has undergone multi-stage Meso-Cenozoic tectonic events and possesses considerable exploration potential. However, structural deformation sequences and the genesis of oil-bearing structures in the basin are still poorly understood. Analyzing the deformation sequences of structural styles can improve the understanding of the basin history and regional tectonic evolution, and is essential for targeting potential traps. In this study, we interpreted 2D seismic profiles, drilling, and well-logging data, and outcrops to elucidate structural styles, tectonic evolution, and temporal distribution characteristics of styles with the assessment of potential petroleum traps in the Linhe Depression, Hetao Basin. We identified four structural styles and sequences with fault associations in the Linhe Depression, namely, NE-striking normal faults (D1), inversion fault-folds (D2), NE-NNE-striking dextral strike-slip faults and normal faults (D3), and near-E-W-striking sinistral strike-slip faults (D4). Analysis of syn-sedimentary normal faults and the cross-cutting relationship of faults and sedimentary strata indicate that D1, D2, D3, and D4 occurred during the Early Cretaceous, Late Cretaceous to Early Eocene, Middle Eocene to Neogene, and Quaternary, respectively. The temporal development of structural styles promoted the formation, re-construction, and finalization of structural traps, while fault geometry and fluid potential influenced the dominant petroleum migration directions. It is shown that the hydrocarbon generally migrated from the northwestern sag to the southeastern slope during the peak hydrocarbon expulsion period in the Neogene. Traps of inversion anticlines and numerous fault blocks developed in the Cretaceous and Paleogene strata are identified as the most favorable trap types. The traps on the slope were produced by numerous NNE-NE-striking faults, and the dominant migration direction implies that hydrocarbons were available to fill the traps. [ABSTRACT FROM AUTHOR]

A variety of unconformity types are commonly developed during the rifting of a continental basin. Identifying their origin and evolution is a prerequisite to understanding the complex tectono-sedimentary evolution of the basin and to evaluate the basin's oil and gas resources. Based on the 2D/3D seismic, geophysical logging, and subsurface lithological data, the unconformities within the rift layer of the Lishu Depression in the Songliao Basin are identified as disconformities, nonconformities, and four "types" of angular unconformities. Their evolution and origin are analyzed by associating the unconformities with the basin's tectonic evolution. The results show that the rifting of the Lishu Depression was not a continuous process. Instead, several regional tectonic episodes influenced the basin's evolution. Episodic compressional events and a phase of extension along the main faults determined the basin configuration and sedimentary fill characteristics of different sub-rifting stages. The tectonic history and related paleogeomorphology changes are the dominant factors in the formation of these different unconformity types. During the rifting process, the type and distribution of unconformity varied. In the initial rifting stage, the basin developed a nonconformity and four types of angular unconformities as the result of both regional uplift and fault block tilt. Rotation and tilting of the fault blocks during the intensive rifting resulted in two types of angular unconformities. Finally, in the recession rifting stage, a different form of angular unconformity and disconformity developed, mainly as a result of the regional uplift and subsequent subsidence. [ABSTRACT FROM AUTHOR]

The identification of the oil-source correlation plays a significant role in petroleum exploration and development. In this study, we identify the oil-source correlation by a hierarchical cluster analysis method combined with traditional methods. The results shed light on the oil-source correlation in Minfeng area and revealed the oil migration and accumulation process. The crude oil in different structural belts and different horizons has different geochemical characteristics. According to the four types of crude oil and their planner distribution, it was considered that the crude oil mainly migrates along with favorable sand bodies and unconformity surfaces in the lateral direction and then charged and accumulated in the glutenite of Sha3 and Sha4 members since the area from sag to Yan Jia Oil and the gas field was lacking of oil source faults. Further analysis shows that the traps of fault blocks in Yong'anzhen are formed in the same phase, while the crude oil generated in the early stage is charged and accumulated in the fault block of the near source. Along with increasing of the buried depth of source rocks, the overlying source rocks gradually entered into the hydrocarbon generation phase, when crude oil started to charge in the fault blocks farther away. [ABSTRACT FROM AUTHOR]

Most of the heavy-oil reservoirs in China belong to little fault blocks. These reservoirs are characterized by high heavy-oil viscosity, severe reservoir heterogeneity, and poor water-flooding development effect, resulting in low oil recovery and exploitation difficulties. Methods to enhance oil recovery are widely investigated both in China and abroad. They also provide an important approach to guarantee the energy supply in China. Modern physical experiments and simulation methods, such as laser confocal experiments and micro-displacement analysis, are used to study the micro-displacement mechanism of polymer flooding and the distributional characteristics of the remaining oil in heavy-oil reservoirs. The results show that polymer flooding can synergistically affect the reservoir and form a plug with the high viscosity heavy oil. High viscosity heavy oil has a better profile control effect and an expanding swept volume effect of displacement than that of thin oil. In the process of heavy oil polymer flooding, most of the remaining oil occurs in a surface-bound state in the pores of the formation, forming a laminar film type on the surface. In-depth research on improving the physical properties of heavy oil and core wettability after the polymer flooding operations is important for further enhancing the recovery in the heavy-oil reservoirs. [ABSTRACT FROM AUTHOR]

Qinghai-Tibet Plateau is one of the regions with the strongest crustal tectonic movement in the world due to its special continental tectonic location. There are many large active faults in the block and its surrounding areas, which are prone to strong earthquakes. The area is also a natural test site for studying the mechanism of plate tectonic movement in the continent. Global Positioning System(GPS)is widely used in the study of crustal deformation monitoring due to its high temporal and spatial resolution, wide coverage, and high observation accuracy. The high-resolution GPS crustal movement velocity field obtainedby China crustal movement observation network(CMONOC-Ⅰ)and China continental tectonic environment monitoring network(CMONOC-Ⅱ), has clearly revealed the crustal tectonic movement and deformation of Qinghai-Tibet Plateau in the past 20 years. The research progress of current crustal movement and deformation characteristics of Qinghai-Tibet Plateau was systematically summarized based on GPS monitoring data, and the GPS data sources, and high-precision data processing methods and strategies for monitoring the crustal movement of Qinghai-Tibet Plateau were reviewed. The influence of different reference data on the processing results of GPS velocity field was discussed, and the current analysis models for crustal movement and deformation of Qinghai-Tibet Plateau were comprehensively explained from kinematics and dynamics. The current tectonic movement and deformation characteristics were deeply analyzed from both the shallow and deep of Qinghai-Tibet Plateau based on the calculations of integrated model. From the perspective of tectonic dynamic mechanism of plate movement, the current regional dynamics background of Qinghai-Tibet Plateau and the uplift mechanism of the mount Qomolangma region under its influence were interpreted in detail. Finally, the results of crustal movement and deformation of Qinghai-Tibet Plateau using GPS technology were summarized, and the important development trend of crustal deformation monitoring of Qinghai-Tibet Plateau in the future was also prospected. [ABSTRACT FROM AUTHOR]

The Fenwei Graben System is an important extensional fault-depression zone, which is the tectonic boundary between the Ordos Block and the South China Block and the North China Block. The graben system presents an "S" shape, with a total length of 1200 km and a width of 30–60 km and an overall strike of NNE. Due to complex tectonic background and active faults, nearly 612 ground fissures develop in these basins, and more than 90% of these ground fissures are tectonic fissures, which are closely associated with fault activities. To reveal the plane symbiotic phenomena, profile symbiotic modes and symbiotic mechanism between tectonic fissures and faults in the Fenwei Graben System, the developmental characteristics were investigated in detail by surveying, mapping, trenching and drilling in the study area. The main conclusions are as follows. (1) The tectonic fissures of the Fenwei Graben System are mainly distributed along the margin faults of basins, the boundary faults between blocks and the hidden faults within blocks, causing serious damages to farmlands, houses and roads. The symbiosis between these fissures and faults is obvious on the surface. (2) The profile symbiotic morphology includes vertical extension type, syncline and anticline "y" type, and stepped type. (3) The symbiotic mechanisms include vertical growth, lateral rupture and clustery derivation. (4) The activities of underlying faults give impetus to the formation and expansion of tectonic fissures. The exposure of the fissures makes underlying faults continue to develop in the form of surface fractures. [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 eastern China, oil and gas reservoirs mainly have fault block traps. Low-order, small-scale faults are well developed, with small fault displacements and short extension lengths, but are difficult to identify by traditional seismic methods. Based on paleotectonic interpretations, rock mechanics experimental results and stratigraphic data, combined with seismic interpretation, structural evolution and fault activity analysis, a geomechanical model of the Majiazui area in the Dongtai Depression in the Subei Basin is established to construct a three-dimensional model of the paleostress field. Finally, the control of the principal stress, shear stress, and strain energy on the occurrence and development of low-order faults is quantitatively analyzed. This research shows that fault activity was weak during the Funing period (65-53 Ma), became strong during the Dainan period (53-46 Ma) and was strongest during the Sanduo period (46-37 Ma). The Sanduo period was the main period during which the low-order faults in the Majiazui area were formed. The minimum principal stress and strain energy controlled the development of low-order faults in the Majiazui area. The low-order faults are most developed in areas that experience high minimum principal stress and strain energy. In the Sanduo period, the minimum principal stress in the Majiazui area was tensile in the north–south direction, and the maximum principal stress was vertical. In an extensional stress environment, lateral shear stress controls the strike of faults, while vertical shear stress controls the inclination of faults. The faults in the northern Majiazui area are inclined mainly to the south, and the faults in the southern Majiazui area are inclined mainly to the north. These results are of practical importance for evaluating the oil–water relationship in oil-bearing fault blocks, solving the conflict between injection and production wells and improving oil recovery. • Quantitative prediction of low-grade faults based on the finite element method. • The regions of low-grade faults development are predicted by the principal stress and the strain energy density. • The shear stresses are used to predict the dip direction of the low-grade faults. [ABSTRACT FROM AUTHOR]

The in-situ stress state of the eastern margin of the Sichuan Basin, where there is a complicated fault zone, is poorly understood. This study offers vital insights into the in-situ stress state based on information from 17 wellbores in the Wufeng-Longmaxi Shale near the eastern boundary fault (i.e., the Qiyueshan Fault) of the Sichuan Basin, China. Drilling-induced tensile fractures and borehole breakouts revealed a decrease in the angle between the S Hmax (maximum horizontal stress) orientation and fault strike when the wellbores are close to the damage zone of the Qiyueshan Fault. This stress rotation may be caused by the lateral contrast in the Poisson's ratio between the country rock and damage zone of the Qiyueshan Fault. A high angle between the S Hmax orientation and fault strike also appeared in the individual fault blocks of the Qiyueshan Fault as a result of local stress concentration. The higher magnitudes of horizontal stresses indicate stronger lateral compression in the Qiyueshan Fault Zone. Owing to the lateral compression of a "sandwich" consisting of a high-E (Young's modulus) roof and low-E shale intervals, natural fractures mainly appeared in the low-E shale intervals when the wellbore was close to the fault damage zone. The low fracture intensity in the low-E shale intervals of the wellbores located at the boundaries of the stress concentration blocks may be associated with an extensional stepover process. • Spatial variations in stress orientation and magnitude around the fault zone. • Lateral mechanical contrast decreases the angle between S Hmax and fault strike. • Stress concentration complicates S Hmax orientations in certain fault blocks. • Vertical mechanical contrast affects the natural fracture intensity of shale. [ABSTRACT FROM AUTHOR]

We investigate the formation and deformation of transfer zones and their impact on sedimentation during multiphase rifting using a three-dimensional seismic dataset in the Baxian Sag, the onshore part of the Bohai Bay Basin, northern China. The fault system in the study area is dominated by two arcuate, opposing boundary faults, that is, the Niudong and Maxi faults, which form an S-type fault system which does not link together. The fault system and structural-stratigraphic features between the Eocene and Oligocene syn-rift sequences were distinctly different during the Palaeogene rifting. These differences allow us to identify the two-phase transfer zones: (1) a NW–SE-trending Eocene transfer zone linking the NW-tilted Baxian Block and the SE-tilted Raoyang Block , and (2) the N–S-trending Oligocene transfer zone forming along the central part of the S-type fault system between the two inward kinks, and linking S-tilted and N-tilted fault blocks. The two-phase transfer zones comprise transverse boundary fault segments and fault styles which are related to strike-slip motion. The strike-slip faults occurred in the sequence where the transfer zone formed. The transfer zones significantly influenced the syn-rift sediments, drainage catchments and reservoir properties during the periods when they formed, and the two-phase transfer zones represent favourable positions for hydrocarbon accumulation in the Eocene and Oligocene sequences, respectively. [ABSTRACT FROM AUTHOR]

Methane microseepage is the result of natural gas migration from subsurface hydrocarbon accumulations to the Earth's surface, and it is quite common in hydrocarbon-prone basins. In this study, by analyzing gas concentrations and isotope composition of soil gas, the potentials of CH4 gas transferred to the surface were studied at three measurement transects in Dawanqi oilfield, Tarim Basin, China. It was found that CH4 from deep-buried reservoirs could migrate upwards to the surface through faults, fissures, and permeable rocks, during which some CH4 was oxidized and the unoxidized methane remained in the soil or was emitted into the atmosphere. Soil gas samples had mean concentrations of 907.1, 62.3, 21.7, 11.0, and 5.8 ppmv for CH4, C2H6, C3H8, C4H10, and C5H12, respectively. The C1/C2+ (13.3 for soil gas and 3.75 for absorbed gas) and gas wetness ratio (12% for soil gas and 26% for absorbed gas) suggested that the hydrocarbons were derived from a thermogenic process. According to isotope composition analysis, the δ13CCO2, δ13CCH4, and δDCH4 values for the soil gas from Dawanqi oilfield varied from -15.5 to -17.2‰, -11‰ to -17‰, and -150 to -189‰, respectively. The extreme 13C enrichment in CH4 is possibly because of the fractionation effects of diffusional migration and methanotrophic oxidation. Soil gas and absorbed gas showed high CH4 concentrations at the edge of the fault block, which indicated that fault was conductive to gas migration. Also, gas migrated from the surface to the atmosphere in the center region of the fault block because of the high permeability and shallow depth of the reservoir in Dawanqi oilfield. [ABSTRACT FROM AUTHOR]

Offshore faulted block oilfields with considerable technical development risks are frequently encountered in offshore oilfield exploitation. This paper proposes a two-level fuzzy hierarchy technique for an integrated evaluation of the technical development risk of offshore faulted block oilfields. The proposed technique can classify the technical recoverable volume quality according to the characteristics of offshore faulted block oilfields. It includes a two-level evaluation index and a two-level fuzzy hierarchy evaluation method. We conducted a thorough evaluation of the proposed technique, using actual offshore faulted block oilfields in Australia and China. The results verified the reliability and applicability of the proposed technique. •. Developed a technique for the quality evaluation of offshore block faulted gas field. •. Established the two-level evaluation index system of the technique. •. Established the two-level fuzzy hierarchy evaluation method of the technique. •. Two different offshore block faulted gas fields were evaluated by using the technique. [ABSTRACT FROM AUTHOR]

Relatively to petroleum exploration on an anticline or in fault block areas in continental basins, the identification of hydrocarbon traps on a synclinalic structure is a challenging task. In order to locate prospects in synclinal areas of Lishu Depression, this study analyzes the structural development of the Qikeshu syncline, describes the sedimentary facies, the sandbody distribution patterns and localizes potential Lishu Depression traps in the syncline based on seismic and well data. Furthermore, the paper summarizes the hydrocarbon trap spatial distribution and discusses the key points points in identifying hydrocarbon traps in faulted-syncline structures of a continental basin. The obtained results show that the tectonic movements at the end of the Barremian and Maastrichtian Ages bounded each limb of the Qikeshu syncline and reoriented paleo-delta lobes deposited in the syncline area. The modifications of the delta lobe affected the distribution of favorable sandbodies and potential hydrocarbon traps. The development of lithologic traps is correlated with the sandbody vertical stacking patterns in a sedimentary sequence. In faulted and folded structures of this continental basin, the post-depositional tectonic modification of paleo-sedimentary bodies strongly influences hydrocarbon play conditions. The petroleum exploration should thus focus on structural history and sedimentary factors, in order to analyze the lithologic and fault-controlled combination traps. [ABSTRACT FROM AUTHOR]

The Weihe Graben is not only an important Cenozoic fault basin in China but also a significant active seismic zone. The Huashan piedmont fault is an important active fault on the southeast side of the Weihe Graben and has been highly active since the Cenozoic. The well-known Great Huaxian County Earthquake of 1556 occurred on the Huashan piedmont fault. This earthquake, which claimed the lives of approximately 830000 people, is one of the few large earthquakes known to have occurred on a high-angle normal fault. The Huashan piedmont fault is a typical active normal fault that can be used to study tectonic activity and the associated hazards. In this study, the types and characteristics of late Quaternary deformation along this fault are discussed from geological investigations, historical research and comprehensive analysis. On the basis of its characteristics and activity, the fault can be divided into three sections, namely eastern, central and western. The eastern and western sections display normal slip. Intense deformation has occurred along the two sections during the Quaternary; however, no deformation has occurred during the Holocene. The central section has experienced significant high-angle normal fault activity during the Quaternary, including the Holocene. Holocene alluvial fans and loess cut by the fault have been identified at the mouths of many stream valleys of the Huashan Mountains along the central section of the Huashan piedmont fault zone. Of the three sections of the Huashan piedmont fault, the central section is the most active and was very active during the late Quaternary. The rate of normal dip-slip was 1.67-2.71±0.11 mm/a in the Holocene and 0.61±0.15 mm/a during the Mid-Late Pleistocene. As is typical of normal faults, the late Quaternary activity of the Huashan piedmont fault has produced a set of disasters, which include frequent earthquakes, collapses, landslides, mudslides and ground fissures. Ground fissures mainly occur on the hanging-wall of the Huashan piedmont fault, with landslides, collapses and mudslides occurring on the footwall. [ABSTRACT FROM AUTHOR]

Several hydrocarbon signatures were discovered in the Nangong Sag during early drilling, indicating the significant exploration potential of this region. However, the structural geometry and kinematics, tectonic evolution, genesis of structural traps, and hydrocarbon distributions in the sag are still poorly understood. Here, we studied the two-dimensional seismic sections, drilling data, logging data, cores, and field outcrops of the Nangong Sag to elucidate its geological architecture, structural style, spatiotemporal differences in structural deformation, and tectonic evolution and predicted traps that are prone to hydrocarbon accumulation. We identified two regional angular unconformities at the base of the Palaeogene and the Neogene. Three tectonostratigraphic units were delineated: the basement unit, the Palaeogene unit characterised by a considerable change in bed thickness and a larger number of faults, and the Neogene-Quaternary unit characterised by a slight change in bed thickness and few faults. There are three tectonic deformation sequences, namely extensional, strike-slip, and inversion deformation sequences, and 10 structural styles were classified. The intensity of deformation varied spatiotemporally. Overall, the extension at the centre of the Nangong Sag was the strongest, followed by that in the north, while the extension in the south was the weakest in the Palaeogene. The northern extension was the strongest in the depositional period of the Kongdian Formation and Member 4 of the Shahejie Formation, the central extension was the strongest in the depositional periods of Members 3, 2, and 1 of the Shahejie Formation, and the overall extension was weak during the Neogene to Quaternary. The strike-slip activity was relatively strong in the depositional periods of Members 3 and 2 of the Shahejie Formation. Strike-slip structures and extensional structures are often symbiotic and jointly controlled and affected the development of the sag. The Cenozoic tectonic evolution was divided into three stages: the syn-rift stage during the Palaeocene to early Oligocene, inversion stage in the late Oligocene, and post-rift stage during the Neogene to Quaternary. The syn-rift stage can be subdivided into the initial, middle, and late syn-rift stages. The formation of structural styles promotes the formation of structural traps, which are transformed and preserved by tectonic evolution. The results suggest that fault block traps, rollover anticline traps, and inversion fold traps, developed in Member 3 of the Shahejie Formation, mainly in the centre of the Nangong Sag, are the potential structural traps in the area. • Extensional, strike-slip and inversion deformation sequences are investigated in the Nangong Sag. • Three tectonostratigraphic units are delineated: basement, Paleogene and Neogene-Quaternary. • Fault-blocks, rollover traps and fold traps can potentially accumulate hydrocarbons. [ABSTRACT FROM AUTHOR]

The NNE-trending Yinchuan Graben is one of several intracontinental grabens that have developed in the extensional environment around the Ordos Block, northern-central China, and is bounded by active normal faults at both its eastern and western margins. In this study, we present new evidence for the Holocene activity and paleoseismicity of the active normal faults developed in the Yinchuan Graben. Interpretations of high-resolution WorldView and Google images, field investigations, trench excavations, seismic data, and radiocarbon dating results reveal the following: (i) two main active fault zones, the Helanshan Piedmont Fault Zone (HPFZ) along the western margin of the graben and the Huanghe Fault (HHF) along the eastern margin, are characterised by conspicuous fault scarps developed on both Holocene alluvial fans and terrace risers; (ii) the active faults are dominated by normal faulting; (iii) the Holocene normal slip rate is estimated to be ∼2–3 mm/yr, and the recurrence interval of morphogenic earthquakes is estimated to be ∼1500–2000 yr for both the HPFZ and HHF; and (iv) the HHF is the most likely seismogenic fault for the triggering of the 1739 M ∼8.0 Pingluo earthquake. Our results show that the HPFZ has the potential to produce a destructive earthquake in the near future, because no large earthquake has occurred on this fault during the past ∼1500 years. This contrasts with previous findings that the fault scarps of the HPFZ were caused by the 1739 Pingluo earthquake and that therefore the likelihood of a large and destructive earthquake on that fault in the near future is relatively small because of the <300 years elapsed since the earthquake. Therefore, it is necessary to reconstruct the model of faulting, tectonic activity, and paleoseismicity of the intracontinental graben and to reassess the seismic hazard of the active normal faults for the densely populated Yinchuan region. [ABSTRACT FROM AUTHOR]

Field investigations and analyses of tectonic topography related to late Pleistocene–Holocene activity of faults and fault-related flexural folds in the northern–western Weihe Graben, central China, reveal that: (1) four main active faults are present in the study area, the Beishan Piedmont Fault (BPF), the Kouzhen-Guanshan Fault (KGF), the Qishan-Mazhao Fault (QMF), and the Weihe Fault (WF), of which the BPF, KGF, and WF are normal faults whereas the QMF is a left-lateral strike-slip fault; (2) active flexural folds trending ENE–WSW are widely developed on the late Pleistocene–Holocene loess tablelands and alluvial fans, as well as on terrace risers; (3) vertical slip rates on the BPF, KGF, and WF are ∼0.5–1.1 mm/yr, and the left-lateral slip rate on the QMF is ∼1.5 mm/yr; and (4) a recent seismic faulting event with a magnitude ( M ) > 7 occurred in the past ∼3000 yr. Our results show that active faults and fault-related flexural folds are developing in the Weihe Graben under an ongoing extensional regime, with listric faulting occurring along pre-existing faults associated with the spreading of continental crust in intracontinental graben systems around the Ordos Block. [ABSTRACT FROM AUTHOR]

Field investigations and trench excavations can provide direct and indirect geological evidence for the occurrence of paleo-earthquakes. In this study, we present geological and topographical evidence for the occurrence of great paleo-earthquakes produced by active normal faults in the southeastern Weihe Graben, central China. Field and trench observations, in combination with radiocarbon ages, reveal that: (i) four surface-faulting events occurred in the past 4000 years with an average recurrence interval of ∼1000 years, which is in contrast with the previously estimated interval of ∼2000–2900 years; (ii) the most recent fault event is correlated to the 1556 M ∼ 8.5 Huaxian earthquake; (iii) an alluvial terrace riser that formed at ∼5300 yr B.P. has been vertically offset by 9–11 m, indicating an average vertical slip rate of 1.7–2.1 mm/yr in the late Holocene. Our results confirm that normal faults in the southeastern Weihe Graben have been active in the late Holocene as source seismogenic faults, and that these faults have the potential to trigger large earthquakes of M > 7 in the future. Therefore, it is important to urgently reevaluate the seismic potential and seismic hazard in the densely populated Weihe Graben region. [ABSTRACT FROM AUTHOR]

Two active faults, including the Huashan piedmont fault (HPF) along the northern margin of Huashan Mountain and the north margin fault of the Weinan loess tableland (NMF-WLT), were developed in the southeastern Weihe Graben, in central China. HPF, which is the most active fault in the Weihe Graben, is known throughout the world for the M8 1 / 4 great Guanzhong earthquake in 1556 AD. Through field investigation, AMS 14 C, and OSL dating in this paper, in combination with previous studies, the following results are obtained: (i) Tectonic landforms, such as triangular fault facets, waterfalls and fault scraps of proluvial fans, were developed in the HPF, but these features were not developed in the NMF-WLT. (ii) HPF experienced three intensive seismic activities in 5920–7670 Cal yr BP, 2215 ± 95–3105 ± 105 Cal yr BP and 1556 AD during the Holocene, but there has only been one seismic event noted for the NMF-WLT since the Holocene (6865 ± 80 Cal yr BP). (iii) The dip-slip rate of the HPF was approximately 0.64 mm/yr since the mid-Pleistocene and approximately 1.67–2.71 mm/yr in the Holocene. In contrast, the dip-slip rate of NMF-WLT was approximately 0.32–0.42 mm/yr since the early Pleistocene and was approximately 0.39–0.58 mm/yr from the late Pleistocene to the Holocene. (iv) The seismic activity at the HPF has been more intense than at the NMF-WLT; the HPF was the triggering seismic fault of the M8 1 / 4 great Guanzhong earthquake in 1556 AD, whereas the NMF-WLT was not the seismogenic fault of this event. These results provide new information for the study of active tectonics of the Weihe Graben. [ABSTRACT FROM AUTHOR]

A 1-million m3 breccia near Laiyuan (Hebei Province, E China) occurs as a block-like lithological unit between dolo-stones of the 1.55-1.45 Ga (Early Mesoproterozoic) Wumishan Formation. It has previously been interpreted as a seismite, but it appears not to fulfil any of the commonly accepted criteria that jointly are considered diagnostic for seis-mites. Its presence in a graben-like structure with almost vertical bounding fault planes rather indicates an origin as a (submarine) valley fill. As the valley originated by tectonic activity in the form of faulting, the breccia can be considered as a secondary effect of seismic activity, but it does not represent a seismite. [ABSTRACT FROM AUTHOR]

Water needs to be depleted to develop coalbed methane (CBM), the classification of desorption system is beneficial to enhance the overall development effect of CBM fields. Based on the production status of the CBM field with complex fault blocks, geological conditions of different gas reservoir and development effect caused by production technology in China, the desorption system was defined as one or several sets of coal seams vertically which can be mutual interference during development and one or multiple small fault blocks or small traps horizontally where reservoirs are connected through faults, collapse-columns, stress relief of goafs and mining areas, hydraulic fracturing and horizontal wells drilling. According to the production behavior analysis of typical desorption systems, several benefits of taking desorption system as the development units are recognized which include dividing development strata and units reasonably, controlling the depletion rate of production wells effectively to realize the fact of mainly gas production in wells in the structural high and water production in wells in the structural low, conducting dynamic analysis, adjusting development programs, optimizing well deployment, and enhancing CBM recovery and development effect. [ABSTRACT FROM AUTHOR]

Systematical reanalysis of previously published data indicates that neotectonics of the Pearl River Delta is characterized by fault activity and differentiated movement of fault-blocks, which has played one of the most important roles in the deltaic development. Basement faults that were developed or had reactivated during Quaternary cut the delta area into fault-blocks. These fault-blocks move in different directions with different rates, but vertically they are dominated by subsidence, which has created accommodation for Quaternary sediments. Distinct differences in distribution of fluvial gravels formed before and after the first transgression in the late Late Pleistocene suggests that the paleo-drainage pattern took a dramatic change, and this change was greatly attributed to fault activities. Since the Holocene, neotectonic influence on channel development turned to be less important as neotectonics became weaker. [ABSTRACT FROM AUTHOR]

The results of magnetotelluric sounding are analyzed along the Korfovo-Astashikha-Novosergeevka profile 200 km long in the south of the Amur-Zeya sedimentary basin. The Korfovo-Astashikha and Korfovo-Novosergeevka profiles were sounded in the AMT and AMT + MTS regimes with a step between the observation points of 1 and 5 km, respectively. The shape of the MTS curves, their variations along the profiles, the shape of the polar plots of the main and additional impedance, and the parameters of the heterogeneity (N) and asymmetry (skew) are characterized. The dimensions of the geological medium is estimated and methods of the interpretation of the magnetotelluric data are chosen. The geoelectric sections are constructed for the depths of 3 and 150 km. The structure and electric properties of the sedimentary cover, the Earth's crust, and the upper mantle are characterized. The thickness of the sedimentary cover in the grabens of the basin attains 1.5-1.7 km. Blocks with various resistivities were identified in the basement. Based on the contrasting changing of the electric resistances, the thickness of the Earth's crust was determined as 38-40 km, which agrees with that established by the seismic data. The geoelectric structure of the upper mantle of the basin is relatively simple. A layer of elevated resistivity from the first hundreds up to a thousand Ohm · m was identified in the background of the low electric resistivity (20-30 Ohm · m) of the mantle in the depth range of 50-80 km. This layer is discrete and divided on the blocks by the zones of the decreased resistivity penetrating to the middle part of the Earth's crust and coinciding with faults of various origins. The petroleum prospectives are estimated for the individual grabens of the basin. [ABSTRACT FROM AUTHOR]

Apatite fission-track signatures of upper Cretaceous Formations in the Yuan'an Graben are made to constraint on the timing of the Yuan'an and Tongchenghe synsedimentary fault activity. The apatite fission-track ages range from 102.0 ± 14.6 to 84.1 ± 3.7 Ma with P(χ 2 ) >0.05; the mean confined track lengths of 14.18 ± 0.09 and 14.16 ± 0.08 μm with mean D par values of 2.25 ± 0.02 and 2.26 ± 0.03 μm, respectively. These data are interpreted as dating their source-area exhumation, recording the exhumation and cooling of the footwall during major normal faulting. The results indicate that the timing of the Yuan'an and Tongchenghe synsedimentary fault activity occurred at 117–82 Ma and the intensive movement at 100–82 Ma; the onset time of extension in Jianghan Basin is ca. 117 Ma, which is related to the lithospheric extension associated with the subduction of the Pacific Plate beneath the Asian Plate. [ABSTRACT FROM AUTHOR]

Abstract: Pre-existing faults or early formed faults may be reactivated or locked in subsequent evolution in a rift basin. The reactivation or sealing of a fault affects sedimentation in the related fault block, and in turn controls the accumulation of oil and gas. Based on fault mechanics of reactivation, this paper established equations denoting the angle range of the reactivated faults or frictional sliding faults by using Mohr stress circles. The results were applied to explain the sealing property of pre-existing faults or early formed faults in Dongpu sag. In the Dongpu sag, reactivation or sealing of the faults in fault blocks is supposed due to the rotation of the fault block which was caused by the activity of high order faults. For quantitative calculation of dip range for activated faults, the sum of the maximum and minimum principal stresses were determined by acoustic emission experiment based on the Kaiser effect of rocks, and the cohesion and inner frictional angle of rocks were measured by rock physical experiment. The calculations show, when the dips of early formed faults are from 87° to 45°, the faults will remain activation in the subsequent deformation. Otherwise, the faults will be locked as sealing faults. The results of petroleum exploration show that the peak dips of sealing faults are from 36° to 40°, and the most of sealing faults are those with dip angles less than 46–50°. These results indicate that a shallower fault is of better sealing property in oil and gas reservoirs than a steeper fault in Dongpu sag. [Copyright &y& Elsevier]

Abstract: The fact that several half-grabens and normal faults developed in the Lower–Middle Cambrian of Tazhong (central Tarim Basin) and Bachu areas in Tarim Basin, northwest China, indicates that Tarim Basin was under extensional tectonic setting at this time. The half-grabens occur within a linear zone and the normal faults are arranged in en echelon patterns with gradually increasing displacement eastward. Extensional tectonics resulted in the formation of a passive continental margin in the southwest and a cratonic margin depression in the east, and most importantly, influenced the development of a three-pronged rift in the northeast margin of the Tarim Basin. The fault system controlled the development of platform – slope – bathyal facies sedimentation of mainly limestone-dolomite-gypsum rock-saline rock-red beds in the half-grabens. The NW-SE trending half-grabens reflect the distribution of buried basement faults. [Copyright &y& Elsevier]

Abstract: The Cenozoic Bohai Bay Basin is located at the center of the Eastern Block of the North China Craton. The structural architecture of this basin provides important clues on the deep-seated lithosphere thinning of the North China Craton. The Cenozoic regional stress field is characterized by NW-oriented extension. However, the various Cenozoic structural patterns of normal faulting and related transverse folding in the Bohai Bay Basin are controlled not only by Cenozoic stress field, but also by strain field and Mesozoic basement fault assemblages in this area. Regionally, the Cenozoic tectonic features and the dynamic evolution of the eastern North China Craton are dominated by two lithosphere-penetrating fault systems including the sinistral Tan–Lu Fault System and the dextral Lan–Liao Fault System. To the west of the Lan–Liao Fault System, Cenozoic extensional tectonics includes NNE-trending listric normal faults that controlled half grabens. However, between these two fault systems are WNW-trending half grabens which show basement-involved faulting in the north and overlapping relations between sedimentary cover and basement in the south. To the east of the Tan–Lu fault, the North Yellow Sea Basin is a WNW-trending fault depression with faulting in the south and overlapping relations in the north. These structural features are inherited from the Mesozoic tectonic framework of this area, whose tectonic characteristics were completely controlled by two opposite strike-slipping faults, the trans-extensional or oblique rifting in the Paleogene, followed by extensional faulting and subsequent subsidence. Furthermore, the culmination of the decratonization of the North China Craton was also related to an eastward jump of Cenozoic subduction of the Pacific Plate and the far-field effect of eastward extrusion of Cenozoic subduction of the Indian Plate, and was not essentially restricted to the early Mesozoic processes. Therefore, the Cenozoic, especially ∼25Ma marks the time of cessation of the processes that led to lithosphere thinning and destruction of the Eastern Block of the North China Craton. [Copyright &y& Elsevier]

Rifting in the Gunsan Basin between China and Korea started in late Mesozoic times, due to large-scale interaction between the Pacific, Eurasian and Indian plates. To analyze the detailed tectonic evolution of this basin, backstripping the subsidence history of four representative units in the basin has been undertaken including sag and half-graben structures in the Central sub-basin as well as half-graben and graben structures in the SW sub-basin. Backstripping indicates that the subsidence history of the Gunsan Basin can be grouped into a Late Cretaceous-Oligocene a main subsidence phase and a Middle Miocene-present secondary subsidence phase. These phases were separated by an uplift and erosion phase during early Miocene times. The main subsidence phase comprised a rapid Late Cretaceous-Paleocene subsidence event and a slower Eocene-Oligocene subsidence event. These phases can be correlated to seismic sequence MSQ I, II and III, identified in the SW sub-basin from seismic stratigraphy, and can further be related to the convergence of the Pacific, Eurasian and Indian plates. Compared with the McKenzie (1978) lithospheric stretching model, this basin is relatively similar to the typical tectonic subsidence characteristics of intracontinental basins. [ABSTRACT FROM AUTHOR]

Abstract: Basin morphology and depositional stratigraphy of Lake Donggi Cona on the north-eastern Tibetan Plateau has been studied with echo depth sounding and shallow seismic sub-bottom profiling. The basin is a pull-apart structure situated at the highly active Kunlun fault. It is characterised by a 92 m deep graben structure in the western part of the lake basin, and a shallow eastern lake part, the latter filled up with fluvial sediments from a large alluvial plain. Three prominent morphological levels were identified at 24 m, 39 m and 57 m below present lake level. They were partly created by basin subsidence, while the deposition of prograding delta sediments primarily formed the morphological steps. The inherited tectonic structures control on-going neotectonic activity, which seems to have only minor influence on present basin morphology. The basin is filled by sediments of at least 30 m thickness in the depocentre. Three major depositional units can be distinguished. In comparison with lithological changes in a sediment core, they give evidence of pronounced lake-level fluctuations and dramatic changes in lake volume. A numerical age datum of ∼19 cal ka BP at the base of the sediment core allows a tentative reconstruction of Late Glacial to Holocene lake development. A very low base level preceded a time of delta formation during higher lake level, i.e. ∼26 m lower than present during Last Glacial Maximum, creating a lake of only 18% of its present size. At the transition to Holocene the lake-level rose very quickly changing to a deep lake environment. Thus, transgression may have promoted maximum lake stands. [Copyright &y& Elsevier]

Abstract: For Lake Nam Co, south-central Tibetan Plateau, geomorphological features and hydrological characteristics have been compiled to provide an overview of the landscape character. Information is based on primary data, collected during field campaigns in the summers of 2005 and 2006, and secondary data as available from satellite images. Nam Co is located at the intersection of the Westerlies, the winter monsoon, the South West Asian monsoon, and the East Asian monsoon. It is situated in a graben structure. Landforms of the drainage basin are highly influenced by tectonics, superimposed by fluvial and periglacial processes, and locally by glacial and aeolian processes. Its drainage basin is endorheic. Thus, lake level is primarily controlled by the balance between input through precipitation or inflow streams and evaporation as the output. The significance of lake water evaporation is evidenced by the salinity and measurable increase of 2H and 18O of the lake water when compared to the inflow streams and precipitation. Maximum conductivities total 431μSmm−1 for the inflowing river waters and 1920μSmm−1 for the lake water. Overall, the solute contents are low and characterise Nam Co as a pristine environment. Dominant ions are calcium and bicarbonate in river waters. Sulphate contents are relatively high in Nam Co, and the lake is also characterised by high boron values. A significant decrease in lake water salinity during the past two decades is likely related to increased freshwater input. [Copyright &y& Elsevier]

The petroleum systems of Chinese nonmarine rifted and depression basins, dominated by lacustrine strata, have distinctive source rocks, reservoir types and trap characteristics. The rifted basins are characterized by numerous faults and multiple structural salients and sags (half grabens). Sags include many subdivisions and smaller isolated sags. Most sags constitute relatively independent petroleum systems that have efficiently generated and expelled hydrocarbons, have excellent reservoir properties in a variety of sand-body types, and have multiple traps. These attributes impart a petroliferous character to the entire sag. Depression basins (intracratonic flexural basins) developed on large cratons and hosted large lacustrine systems. They feature very gentle structure, large deltaic sand-bodies, source rocks in extensive contact with sand-bodies, heterogeneous low-porosity-low-permeability reservoirs and large, widespread lithology-controlled pools. In recent years, large oil and gas reserves have been discovered in these two types of lacustrine-dominated basins, contributing significantly to the growth of reserves in onshore China, and stratigraphic oil and gas pools have become the major type of accumulation in nonmarine lacustrine basins. [ABSTRACT FROM AUTHOR]

The Miocene fluvial-deltaic system in the Bohai Bay Basin exhibits difficulties in favourable reservoir prediction in a complex strike-slip fault zone in the Tanlu fault system. On the basis of 3D seismic data and 12 wells, we utilize two different RGB colour-blending methods from various datasets. The first method is derived from the 3D stacked, −90° phase seismic volume, and the second method is generated from the root mean square (RMS) volume attribute, which is extracted from −90° phase seismic data. Combined with the linear combination analysis of user control, we attempt to better quantify reservoir thickness and evolution of the fluvial-deltaic system in the Guantao Formation. The results show that stratal slices of the second RGB colour-blending method have a much greater ability to characterize sedimentary facies evolution and to analyse sand-thickness variations, which can effectively decrease the disadvantageous influence of multiple fault blocks on stratal slice views. In the vertical section, the linear combination analysis and the first RGB colour-blending method, however, have greater utility and resolution, which can be used to characterize the sand body by the width of seismic events or display the various sand thicknesses in different colours. The high-resolution anatomy of the fluvial-deltaic system in the Bohai Bay Basin not only explains current exploration effects but also effectively predicts thick sandstones with the most production potential in this complex region. This study may also have great significance for other complex areas or strata. • Two different RGB colour-blending methods of three different-frequency panels/volumes from various data sets. •Integrated with user-controlled linear combination analysis to quantitatively identify and predict thick sandstone reservoirs. •The proposed methods can reduce the uncertain impact of manual interface interpretation within complicated zones. •This work can serve as a useful reference for reservoir-thickness prediction and sedimentary-facies analysis. [ABSTRACT FROM AUTHOR]

Active north-trending rifts in Tibet vary significantly in their character as a function of extension magnitude. Most rifts are characterized by internally drained basins bounded by high-angle normal faults with Paleogene or older rocks in the footwall. However, the central part of the Yadong-Gulu Rift (near Lhasa) and the newly documented Lunggar Rift in west-central Tibet are bounded by low-angle normal faults (detachments) with rocks and Miocene granites in the footwall, and exhibit active basin incision and intrabasin topographic highs in areas of inferred maximum extension. We suggest that Tibetan rifts initiate as high-angle normal fault and half-graben or graben basin systems and evolve in response to increasing extension and footwall isostatic rebound into detachment systems that are active at uppermost crustal levels and above which rift basin fi ll is being uplifted and eroded. [ABSTRACT FROM AUTHOR]

We use three-dimensional mechanical modelling with fault as Coulomb-type frictional surface to explore the active deformation of the Xianshuihe–Xiaojiang fault system in south-eastern Tibet. Crustal rheology is simplified as an elastoplastic upper crust and a viscoelastic lower crust. Far-field GPS velocities and Quaternary fault slip rates are used to constrain the model results. Numerical experiments show that effective fault friction lower than ∼0.1–0.08 leads to a high slip rate that fits well with geological estimates of the slip rate on the fault system. Associating with the modelled fault slip rate, strain in the surrounding crust distributes broadly, and is partitioned into strike–slip and thrust senses. This means that in the Indian-Eurasia convergence, accommodation of the large fraction of sinistral motion on the fault system is achieved mainly due to its lower fault friction. This in turn affects crustal deformation around the south-eastern Tibetan margin, resulting in negligible compression across the Longmen Shan. [ABSTRACT FROM AUTHOR]

Faults are important oil and gas reservoir spaces and seepage channels, and faults are hotspots in oil and gas geological research. A series of NE-trending strike-slip faults develop in the Tarim Basin. The structural evolution and formation mechanism of these faults need to be studied further. Based on the 3D seismic data in the Xiaotangnan area of the northern slope of Tazhong, the strike-slip fault structure characteristics, formation evolution and mechanism analysis were accomplished. The results are that: (1) Two sets of fault systems, namely deep strike-slip faults and shallow tensile torsional faults, are developed in the Xiaotangnan area. The deep strikeslip fault profile is a high-steep upright or regular flower-like structure, and on the plane, most of them show linear extensions and some branch faults develop at the intersection and the bend. The shallow transtensional faults have a negative flower-like structure on the cross section, and they are divided into three groups of faults: NW20°, NE10°, and NE30°. (2)The faults in the study area experienced two phases of activities: Late Ordovician strike-slip faults, and Early Carboniferous transtensional faults. The Late Ordovician strike-slip faults are transpressional strike-slip faults which are generated by horizontal displacement along the NE-preserved basement weak belts with the strong compression of the southwestern margin of the basin. The Early Carboniferous transtensional faults are syn-shear faults, tensile t-fractures and branch faults caused by block rotation which are generated by reactivation of deep strike-slip faults that are closely related to the oblique compression from the Algin tectonic domain in the southeastern margin of the basin. The result has certain guiding significance for the exploration of Ordovician fracture⁃ cavity oil and gas reservoirs in this area. [ABSTRACT FROM AUTHOR]

Discusses the neotectonics of the Thakkhola graben in the southern part of the Tibetan Plateau. Geologic setting of the central Nepal Himalayan Mountains; Basin-fill stratigraphy; Exposure of glaciolacustrine rocks; Development of river terraces in the Kali Gandaki valley in Nepal; Exposures and positions of faults.