Lithologic Reservoirs

By means of core observation, thin section identification, electron backscattering, secondary imaging and energy spectrum analysis, the micron pores and micron fractures in shale oil reservoirs of Cretaceous Qing‐ shankou Formation in Gulong sag of Songliao Basin were studied. The results show that:（1）The lithologies of shale oil reservoirs in Gulong sag are fine-grained clastic rocks dominated by shale, and the mineral composition is mainly clay and felsic, showing the characteristics of mudstone or shale in structure, and the whole reservoir is felsic shale. Micron pores and micron fractures are developed in reservoirs with various types.（2）The diameter of micron pores in the study area is generally 1-2 μm, and the maximum can reach 70 μm, and they are nearly round, oblate, polygonal and irregular. According to the genesis, they can be divided into six types:compaction stress shielding pores, diagenetic authigenic pores, dissolved pores, hydrocarbon generation and expulsion expansion pores, organic matter pores and diatom residual pores. Compaction stress shielding pores are mostly developed on both sides of rigid minerals. Diagenetic authigenic pores are often developed in authigenic minerals such as dolo‐ mite, chlorite and illite, mainly intergranular pores. Dissolved pores are mostly developed in carbonate minerals, and secondary mycelial floccules can be seen inside. Hydrocarbon generation and expulsion expansion pores are mostly produced in vertical or nearly vertical rows, which is related to the secondary hydrocarbon generation and expulsion formed by light oil. Organic matter pores develop in organic matter and are related to residual cells of plants and filling of light oil and natural gas. Diatom residual pores mainly develop in the interior and edge of dia‐ toms, with large sizes ranging from several microns to tens of microns.（3）The micron fractures in the study area are mainly bedding, with a width of 1-10 μm and a maximum of 100 μm, and a length of several microns to tens of microns. They can be divided into four types:diagenetic shrinkage fractures, dissolved fractures, hydrocarbon generation and expulsion expansion fractures and structural/shear fractures. The diagenetic shrinkage fractures are mainly tensile fractures, with curved fractures and uneven fracture wall. The width of dissolved fractures can reach 60-70 μm, authigenic clay can be seen in the fractures, and authigenic minerals such as pyrite, apatite and dolomite can be found on both sides of the fracture. Both sides of hydrocarbon generation and expulsion expan‐ sion fractures are jagged and uneven, bypassing rigid minerals. Structural/shear micron fractures are generally straight, accompanied by other fractures related to shear.（4）The connectivity between pores and fractures of dif‐ ferent scales in the study area is good, forming a three-level reservoir and transport system of“nano-pores + nanofractures, micron-pores + micron-fractures, millimeter-pores + millimeter-fractures”.

Cyclostratigraphy analysis and stratigraphic division of lower Sha-3 member of Paleogene in Zhanhua Sag，Bohai Bay Basin

FANG Xuqing, ZHONG Qi, ZHANG Jianguo, LI Junliang, MENG Tao, JIANG Zaixing, ZHAO Haibo

2024, Vol.36(3): 19–30 Abstract ( 3 ) PDF (8205 KB) ( 9 )

doi: https://doi.org/10.12108/yxyqc.20240302

Lacustrine fine-grained sediments often have continuity and can record and preserve significant astronomical cycle signals, making them ideal strata for astronomical cycle analysis. MTM spectrum analysis and FFT evolutionary harmonic analysis were conducted for natural gamma data of the lower Sha-3 member of key wells in Zhanhua Sag, Bohai Bay Basin, a“floating”astronomical timescale was established, astronomical cyclostratigraphic division of single well and well-tie stratigraphic correlation were carried out, and the stratigraphic frame-work was established. The results show that:（1）Significant astronomical cycle signals were recorded in the lower Sha-3 member in Zhanhua Sag, and the optimal sedimentation rate was matched to be 9.0×103 cm/Ma. The cycle thicknesses corresponding to long eccentricity, short eccentricity, obliquity and precession cycle are 42.3 m, 9.0 m, 2.4-4.7 m and 1.3-1.9 m, respectively.（2）Six long eccentricity cycles and 25 short eccentricity cycles were stably recorded in the lower Sha-3 member, and the short eccentricity curves can be used as the stratigraphic division interface for high-precision stratigraphic correlation.（3）The application of astronomical cycle theory to predict the development patterns and spatial configuration relationships of lithofacies can provide a basis for the precise exploration of geological“sweet spots”of shale oil and gas in the sedimentary

Low resistivity response characteristics and main controlling factors of shale gas reservoirs of Ordovician Wufeng Formation-Silurian Longmaxi Formation in Changning area，southern Sichuan Basin

CHENG Jing, YAN Jianping, SONG Dongjiang, LIAO Maojie, GUO Wei, DING Minghai, LUO Guangdong, LIU Yanmei

2024, Vol.36(3): 31–39 Abstract ( 3 ) PDF (7440 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240303

Taking low resistivity shale gas reservoirs of Wufeng Formation-Longmaxi Formation of well NX22 in Changning area in southern Sichuan Basin as an example, the data of core mineral composition, scanning electron microscope, total organic carbon（TOC）content, water saturation test and logging curves were used to establish a rock volume physical model of low resistivity shale gas reservoirs. A three-dimensional digital core model was constructed by random method, and the resistivity response characteristics were simulated under different mineral components content, water saturation and organic matter graphitization by finite element numerical simulation method, and the main controlling factors were analyzed. The results show that:（1）The rock volume physical model of low resistivity shale gas reservoirs of Wufeng Formation-Longmaxi Formation in Chang-ning area consists of six parts:skeleton（quartz, feldspar, calcite and dolomite）, clay minerals, pyrite, ungraphitized organic matter, graphitized organic matter and pores.（2）The 3D digital core is of 100×100×100 pixels in length, width, and height, respectively. It integrates the six parts of the physical model mentioned above, and uses different colors to identify the conductive components. It can display slices in different directions to characterize the composition characteristics of low resistivity shale gas reservoirs.（3）An increase in clay mineral content, pyrite content, water saturation and organic matter graphitization degree can cause a decrease in the resistivity of shale gas reservoirs. However, the high degree of organic matter graphitization（25%）and high water saturation （88.0%）cause the resistivity of shale gas reservoirs to decrease from normal resistivity（greater than 15 Ω·m）to low or even ultra-low resistivity（less than 5 Ω·m）, which are the two core factors leading to the ultra-low resistivity response of shale gas reservoirs in the study area.

Application of improved U-Net network small faults identification technology to Triassic Baijiantan Formation in Mazhong area，Mahu Sag

SONG Zhihua, LI Lei, LEI Dewen, ZHANG Xin, LING Xun

2024, Vol.36(3): 40–49 Abstract ( 5 ) PDF (48240 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240304

The small faults of Triassic Baijiantan Formation in Mazhong area of Mahu Sag in Junggar Basin were identified by using the improved U-Net network small fault identification technology. The results show that: （1）Construct-guided filtering preprocessing can effectively improve the quality of seismic data and increase the accuracy of fault identification. The U-Net network, which incorporatesskip connections, relay supervision, normal standardization, and focused mean square loss function, has improved its fine identification ability of small faults（. 2）Using 200 training sample sets and 20 validation sample sets, the seismic data of the model were generated by convolution of reflection coefficients and Ricker wavelet, and faults were manually labeled. Optimal network model parameters were selected to test on the synthesized noisy seismic data by using coherent attributes, conventional U-Net network methods, and the improved U-Net network method. Construct-guided filtering effectively highlighted the boundaries of faults and enhanced the lateral continuity of the same phase axis. The improved U-Net network method can effectively identify faults with a fault distance of more than 7 meters.（3）The improved U-Net network method has significantly higher accuracy than coherent attributes and conventional UNet network methods in identifying high-angle strike-slip faults and associated secondary faults with small fault throw of Triassic Baijiantan Formation in Mazhong area of Mahu Sag. The No. 3 and No. 4 sand bodies in the northern Dazhuluogou fault in the study area are favorable areas for efficient exploration of Triassic Baijiantan Formation in MZ4 well area.

Main controlling factors and distribution of reservoirs of the second member of Sinian Dengying Formation in Penglai gas field，central Sichuan Basin

XIA Maolong, ZHANG Benjian, ZENG Yiyang, JIA Song, ZHAO Chunni, FENG Mingyou, LI Yong, SHANG Junxin

2024, Vol.36(3): 50–60 Abstract ( 0 ) PDF (57347 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240305

Based on data of rock cores, thin sections and analysis tests, a detailed study was conducted on the main controlling factors and distribution of the second member of Sinian Dengying Formation in Penglai gas field in central Sichuan Basin. The results show that:（1）The reservoirs of the second member of Sinian Dengying Formation in Penglai gas field are mainly composed of thrombolite dolomite, foam spongy dolomite and doloarenite. The reservoir space includes pores, caves and fractures, dominated by residual framework pores and small and medium-sized caves. The pores are mostly developed in microbial bonded dolomite and grain dolomite. The porosity of the reservoir in the upper Deng 2 member is 2.0%-11.0%, with an average of 4.43%, and the permeability is 0.005-10.000 mD, with an average of 1.19 mD. The porosity of the reservoir in the lower Deng 2 member is 2.00%-6.98%, with an average of 3.64%, and the permeability is 0.030 9-2.600 0 mD, with an average of 0.950 0 mD（. 2）The distribution and quality of reservoirs of Deng 2 member in the study area are jointly controlled by the distribution of microbial mound shoal, quasi syngenetic karstification and supergene karstification. High-quality reservoirs are mostly developed in the upper and middle parts of the upper Deng 2 member and the top of the lower Deng 2 member.（3）The lower Deng 2 member in the study area is generally a product of semi cyclical marine transgression, with vuggy-fractured reservoirs only developed in the upper part and reservoir undeveloped in the middle and lower parts. The upper Deng 2 member is mostly a product of regression and semi cycle. No. 1 sublayer developed in a secondary transgression background, with thin mound shoal, dominated by porous reservoir. No. 2 sublayer developed contiguous mound shoal under regression, with thick reservoirs mainly composed of vuggy reservoirs（mostly type Ⅱ reservoirs）, which is the main gas producing zone in the study area. The No. 3 sublayer is overall shallow water platform deposit in the late stage of regression, with well-developed botryoidal-lace shape structures and obvious karst transformation, dominated by karst reservoirs with superimposed fractures and caves（type Ⅲ reservoirs）.

Key factors and favorable exploration directions for oil and gas enrichment in back margin sag of thrust nappe in Lower Yangtze

SHAO Wei, ZHOU Daorong, LI Jianqing, ZHANG Chengcheng, LIU Tao

2024, Vol.36(3): 61–71 Abstract ( 2 ) PDF (15328 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240306

Through systematic analysis of structural characteristics, sedimentary environment and hydrocarbon enrichment law, on the basis of newly discovered drilling data, the oil and gas enrichment law and favorable exploration direction of the back margin sag of thrust nappe in northern margin of Lower Yangtze were studied. The result shows that:（1）The oil and gas in the sag is characterized by“three gas and two oil”, namely, shale gas of Permian Dalong Formation and Gufeng Formation, coalbed methane and tight sandstone gas of Longtan Formation, shale oil of Dalong Formation and limestone fracture oil of Triassic Yinkeng Formation.（2）The oil and gas enrichment in the sag, represented by Xuancheng Sag, is controlled by three key factors:The sag is a stable block and the formed oil and gas system has a good preservation environment；The sedimentary environment of Dalong Formation（P3d）and Gufeng Formation（P2g）in this area is a deep-water shelf environment, which is a favorable sedimentary facies zone, with two sets of organic matter rich source rock series developed；The effective sealing conditions of the top and bottom are good, with the upper part of the source rocks covered byTriassic marl formation, and the lower part being of bioclastic limestone of Qixia Formation, controlling the longitudinal oil and gas escape.（3）The Lower Triassic to Upper Permian strata in the study area are enriched in marl fracture oil, shale oil, shale gas, coalbed methane and tight sandstone gas from top to bottom, showing the characteristics of“upper oil and lower gas”multiple unconventional oil and gas coexisting together, forming a special oil and gas enrichment pattern.（4）Xuancheng sag has similar geological conditions to Nanling sag, Jurong sag and Changzhou sag, making it the preferred favorable area for next shale oil and gas exploration.

Source-reservoir characteristics and accumulation rules of shale gas of Permian Shanxi Formation in Yan'an area, Ordos Basin

DUAN Yifei, ZHAO Weiwei, YANG Tianxiang, LI Fukang, LI Hui, WANG Jianan, LIU Yuchen

2024, Vol.36(3): 72–83 Abstract ( 5 ) PDF (9417 KB) ( 2 )

doi: https://doi.org/10.12108/yxyqc.20240307

Permian Shanxi Formation has great exploration potential for shale gas in Yan’an area of Ordos Basin.By analyzing drilling, mud-logging and wire-logging data, combined with the analysis and laboratory data of shale samples, the source-reservoir characteristics and accumulation process of shale gas of Permian Shanxi Formation in Yan’an area were analyzed, and the accumulation mechanism of shale gas was discussed. The results show that:（1）The organic carbon（TOC）content of shale of Permian Shanxi Formation in Yan’an area of Ordos Basin is relatively high, with an average mass fraction of 2.12%. The main type of kerogen is type Ⅲ, with Ro ranging from 2.0% to 3.7%. It is in the high to over mature stage and high-quality source rocks.（2）The mineral composition of the shale of Shanxi Formation in the study area seems to be rich in clay, with an average mass fraction of clay minerals of 56.7%, which is conducive to the occurrence of adsorbed gas. There are mainly three types of reservoir spaces:inorganic mineral pores, organic pores, and micro-fractures. The gas content of rocks varies greatly due to the influence of different lithology combinations. The Shan 2 member has a higher gas content than Shan 1 member（with an average mass volume of 1.38 m3/t）. According to different lithology combinations, the source-reservoir configuration of shale gas of Shanxi Formation can be divided into three types:thick shale interbedded with thin sand layer, shale interbedded with siltstone and fine sandstone, and shale mixed with coal seam. Different source-reservoir configurations have different gas-bearing characteristics.（3）The shale gas is mainly in adsorbed state and free state in the study area, and is in a dynamic equilibrium state during the accumulation process, continuously transforming with the change of formation conditions. The accumulation process can be divided into three stages:In Early Jurassic, organic matter began to generate gaseous hydrocarbons, and shale gas began to adsorb and accumulate；During Middle-Late Jurassic, a large number of gaseous hydrocarbons were generated and expanded, gaseous hydrocarbons were discharged, fractures closed, and cyclic migration and accumulation occurred；In Early Cretaceous, organic matter reached a high-over mature stage, entering the final stage of hydrocarbon generation and expulsion, until the formation uplifted and hydrocarbon generation ended. The good sealing effect of shale provides a solid guarantee for the formation of shale gas reservoirs.

Reconstruction of source-to-sink system of the third member of Paleogene Shahejie Formation in Miaoxibei area，Bohai Bay Basin

FENG Bin, HUANG Xiaobo, HE Youbin, LI Hua, LUO Jinxiong, LI Tao, ZHOU Xiaoguang

2024, Vol.36(3): 84–95 Abstract ( 1 ) PDF (69226 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240308

Based on drilling cores and 3D seismic data, the provenance characteristics and sedimentary facies distribution in Miaoxibei area in the Bohai Bay Basin were comprehensively analyzed from three aspects:source lithology identification, reconstruction of watershed river paleo-system and transport pathways, and the sourceto-sink system for the third member of Paleogene Shahejie Formation was reconstructed through the restoration of both paleo-geomorphological features within the sedimentary area and those within the denudation source area. The results show that:（1）A complete source-to-sink system of the third member of Paleogene Shahejie Formation has developed in Miaoxibei area, Bohai Bay Basin, with the provenance area located at Miaoxibei uplift and Bodong sag serving as the main sedimentary area. The source lithologies in Miaoxibei uplift comprise Mesozoic granite, Lower Proterozoic quartz schist, and Lower Proterozoic breccia. The primary watershed is distributed from south to north along the long axis of the uplift, with ancient water systems scattered within it. The main transport pathways consist of five ancient valleys and two ancient fault troughs. Fan delta-lacustrine facies deposits of the third member of Paleogene Shahejie Formation in Miaoxibei area are mainly characterized by rapid accumulation, mainly composed of gravel-bearing sandstone, fine sandstone and mudstone, with poor sorting and grinding degree. Rock composition and mineral association relatively match those found in quartz schist and granite located in Miaoxibei uplift. In northern Bodong sag, contiguous fan-shaped deltas dominate while isolated ones prevail in its southern part.（2）The denudation during the sedimentary period of Sha 3 member was pronounced in western Miaoxibei uplift and comparatively weaker in the eastern region, resulting in a gradual westward migration of the paleo-divide. The central and northern parts of Miaoxibei uplift exhibited a larger provenance area, significant vertical elevation differences, and a stronger supply capacity from the provenance. The thickness of the third member of Paleogene Shahejie Formation in Bodong sag varies between 100 to 600 m, with thinner deposits observed in the east and south, while thicker deposits are found in the west and north. The depositional center is located in the northern part of Bodong sag, where strata have undergone more extensive denudation reaching up to 3.2 km towards the east. The development location of fan delta is controlled by transport channels originating from provenance areas, while its scale is influenced by provenance size. Notably, fan delta deposition on a larger scale predominantly occurs in the northern and middle regions of Bodong sag which represent favorable areas for exploration.

Discovery and exploration enlightenment of Carboniferous volcanic condensate gas reservoirs in western well Pen-1 sag，Junggar Basin

BIAN Baoli, LIU Hailei, JIANG Wenlong, WANG Xueyong, DING Xiujian

2024, Vol.36(3): 96–105 Abstract ( 4 ) PDF (35127 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240309

Carboniferous volcanic reservoir in Junggar Basin is one of the key fields of oil and gas exploration. Based on logging data, geochemical analysis data and rock thin section identification, combined with geophysical methods, the main controlling factors of Carboniferous volcanic oil and gas accumulation in western well Pen-1 sag in Junggar Basin were clarified, the enrichment rules of deep volcanic reservoirs were summarized, and the favorable exploration directions were defined. The results show that:（1）The source rocks of Fengcheng Formation in western well Pen-1 sag of Junggar Basin are 100-300 m thick and cover an area of about 5 400 km2, and enter the stage of generating condensate oil and dry gas as a whole, with a gas generation intensity greater than 20×108 m3/km2, providing abundant natural gas sources for the sag.（2）The lithologies of the Carboniferous volcanic rocks in the study area are complex, and the andesitic volcanic breccias formed by volcanic eruptions are weathered and leached, which can form weathered crust-type reservoirs with high reservoir properties. The large unconformity between Carboniferous and Permian and widely developed deep and large faults are important transport systems. The mudstones of the upper Urho Formation of Permian serve as a regional cap rock, providing preservation conditions for condensate gas accumulation. Oil reservoirs are mainly developed in high position, while gas reservoirs are developed in low position.（3）Through the“WBH”（wide-azimuth, broadband, and high-density） technology, the accuracy of seismic imaging has been improved, and the timefrequency electromagnetic technology（TFEM）was combined to achieve fine characterization of Carboniferous volcanic rocks, providing a favorable support for the exploration of deep oil and gas reservoirs. The major breakthrough of well Shixi 16 has confirmed the great exploration potential of Carboniferous volcanic rocks in western well Pen-1 sag.

Spatial-temporal differential evolution model and reservoir control effect of Cenozoic extensional and strike-slip superimposed faults in Bodong Sag

DONG Rou, LI Kun, YIN Jihang, XUE Yuheng, JIANG Tao, XU Guosheng

2024, Vol.36(3): 106–116 Abstract ( 3 ) PDF (20929 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240310

Based on 3D seismic interpretation, the spatial-temporal differential evolution characteristics and reservoir control effect of Cenozoic extensional and strike-slip superimposed faults in Bodong Sag were systematically analyzed through structural profile restoration. The results show that:（1）Extensional and strike-slip superimposed faults with NNE trending as the main stem, NE trending as the derivative, and NW trending as the superposition, were widely developed in Cenozoic in Bodong Sag, and these faults can be divided into two types: strong extensional and weak strike-slip faults, strong strike-slip and weak extensional faults. The superimposed fault system has obvious characteristics of deep and shallow stratification and north-south segmentation. Vertically, the Paleogene mainly developed strong extensional and weak strike-slip faults, which are large and sparse, and the Neogene-Quaternary mainly developed strong strike slip and weak extensional faults, which are small and dense. On the plane, there are differences in the structural combination styles of the same fault in different segments.（2）The evolution of the Cenozoic extensional and strike-slip superimposed faults in the study area are manifested as early strong and late weak activity of the northern faults, inherited and continuous development of the central faults, and early weak and late strong activity of the southern faults. The evolution model can be divided into three stages:initial fault depression stage（Kongdian Formation-Sha 4 sedimentary period）, strong fault depression stage （Sha 3 member-Dongying Formation sedimentary period） and strike-slip depression stage （Guantao Formation-Pingyuan Formation sedimentary period）. In the initial fault depression stage, NNE-NE trending strong extensional and weak strike-slip faults superimposed, dominated by NE trending strong extensional and weak strike-slip faults, with NW trending pre-existing fault activation, dividing the depression. In the strong fault depression stage, NNE-NE trending strong extensional and weak strike-slip faults superimposed, dominated by NNE trending strong extensional and weak strike-slip faults, with NW trending fault activity weakened or stopped. In the strike-slip depression stage, NNE trending strong strike-slip and weak extensional faults superimposed, and the faults did not control the sedimentation, but has adjustment on stratigraphic distribution.（3）The development and evolution of the extensional and strike-slip superimposed faults in the study area are closely related to hydrocarbon accumulation, with the overall characteristics of early extensional faults control source, late strikeslip faults control migration, and multi-stage superimposed faults control traps. The eastern slope zone is a favorable area for hydrocarbon migration and accumulation.

Sedimentary model of fluvial fan of Permian He-8 member in Ordos Basin and its exploration significance

WANG Hongbo, ZHANG Lei, CAO Qian, ZHANG Jianwu, PAN Xing

2024, Vol.36(3): 117–126 Abstract ( 5 ) PDF (39745 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240311

Based on the analysis and laboratory data of field outcrops and drilling cores, combined with sourcesink system analysis, the paleoclimatic environment and sedimentary facies characteristics of the eighth member of Permian Shihezi Formation（He-8 member）in Ordos Basin were studied.The results show that:（1）The Sr/ Cu values of Permian He-8 member in Ordos Basin are mostly greater than 10, and the V/Cr values are mostly less than 2.0. The thickness difference of the strata is less than 30 m, and there is no obvious sudden change. The ancient sedimentary slope is 0.5°-1.0°, the paleotopography is open and flat without obvious slope breaks, and the sedimentary water is shallow. It is an event deposit dominated by flood transportation under the background of arid ancient climate and gentle paleotopography.（2）During the sedimentary period of He-8 member, there was no large catchment area in the basin, and the rivers in the sedimentary system did not enter the lake water body. Instead, they flowed out of the basin to the southeast or disappeared in inland arid areas. The entire basin was dominated by floodplain sedimentation, manifested as a sedimentation pattern of alternating distribution of rivers and floodplains, forming afluvial fan sedimentary model.（3）The lake water flows back and forth, with intermittent development in flood season and dry season. In flood season, the relay transport of multi-stage crevasses makes the coarse-grained sandstone extend to the lake basin for a long distance, while in dry season, thick muddy deposits can be used as regional caprocks, forming a good reservoir-cap assemblage with great exploration potential.

Tectonic evolution and hydrocarbon accumulation in northern Chenjia fault zone，Liaohe Depression

XI Zhibo, LIAO Jianping, GAO Rongjin, ZHOU Xiaolong, LEI Wenwen

2024, Vol.36(3): 127–136 Abstract ( 1 ) PDF (6336 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240312

The Chenjia fault zone in Liaohe Depression is rich in oil and gas resources and is one of the important oil and gas bearing zones in the west sag of Liaohe Depression. Based on structural evolution, combined with sand-box physical simulation experiments, the deformation mechanism and evolution process of Chenjia fault zone in Liaohe Depression were analyzed, and its control effects on hydrocarbon accumulation were analyzed. The results show that:（1）The Chenjia fault zone in Liaohe Depression has the evolution characteristics of segmented development and gradually becoming late from north to south during the activity period. Under the influence of fault segmentation, Chenjia fault zone mainly develops compression-torsion back-thrust and strike-slip com‐pression-torsion structural styles.（2）The results of physical simulation experiments show that under the influence of compression-torsion, compression-torsion en echelon small faults were first formed at the hanging wall of Taian-Dawa fault. As the displacement increases, the small faults were gradually connected, and finally the through-strike-slip fault zone, namely the Chenjia fault zone, was formed.（3）Taian depression is a depression formed by the superposition of multi-stage tectonic deformation in Cenozoic, and the main hydrocarbon source rock series is developed in deep layers, which has the material basis for the development of large-scale oil and gas reservoirs. The analysis results of drilling cores at the edge of the depression show that the TOC value of the source rock is 4.79%, and the Ro value is 0.3%-0.4%, belonging to good source rocks. It is speculated that source rocks in the depression center have larger thickness and bettwe quality. The fault nose structure is developed at the footwall of the central and northern Chenjia fault zone, which has the characteristics of dual source hydrocarbon supply in Chenjia depression and Taian depression, and is a favorable zone for oil and gas accumulation.

Fracture modeling of shale reservoirs of Silurian Longmaxi Formation in Luobu syncline in Zhaotong National Shale Gas Demonstration Area， southern margin of Sichuan Basin

JI Yubing, GUO Bingru, MEI Jue, YIN Zhijun, ZOU Chen

2024, Vol.36(3): 137–145 Abstract ( 3 ) PDF (32269 KB) ( 2 )

doi: https://doi.org/10.12108/yxyqc.20240313

Based on core analysis, imaging logging analysis and 3D seismic data, a multi-scale discrete fracture network modeling method was studied for Long-1 submember of Longmaxi Formation and Wufeng Formation in Luobu syncline in Zhaotong National Shale Gas Demonstration Area, southern margin of Sichuan Basin. The results show that:（1）Extracting the strong response part of ant tracking attributes as a surface can obtain a large-scale discrete fracture network model. Small scale fracture modeling can be established using the random discrete fracture network modeling method, which uses the trend of the fracture band shown by ant tracking properties along the layer slice, which reduces the uncertainty of small-scale fracture simulation.（2）The fractures of Long-1 submember of Longmaxi Formation and Wufeng Formation in Luobu syncline are mainly high angle shear fractures, mostly filled with calcite. The main direction of the fractures is northeast southwest, and the fracture direction explained by imaging logging is consistent with the fault direction explained by nearby seismic interpretation（. 3）The large-scale discrete fracture network model is consistent with the fault location of the drilling, and the development of small-scale fractures is consistent with the leakage of drilling fluid, indicating that the multi-scale discrete fracture network model can better represent the fracture development characteristics of Long-1 submember of Longmaxi Formation and Wufeng Formation in Luobu syncline.（4）The multi-scale discrete fracture network model was applied to optimize the hydraulic fracturing scheme for well Y12H in Luobu syncline, resulting in a high complexity of hydraulic fracturing network and nearly 41% increase in gas production compared to adjacent wells. The multi-scale discrete fracture network model after optimizing the small-scale fracture orientation has a good practical application effect.

Characteristics of deep source rocks and hydrocarbon accumulation model of Paleogene Shahejie Form ationin Qingshui subsag，Liaohe Depression

ZHU Kangle, GAO Gang, YANG Guangda, ZHANG Dongwei, ZHANG Lili, ZHU Yixiu, LI Jing

2024, Vol.36(3): 146–157 Abstract ( 2 ) PDF (47259 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240314

Based on the analysis of organic carbon, rock pyrolysis, chloroform bitumen“A”, saturated hydro‐carbon chromatography-mass spectrometry and fluid inclusions, the characteristics of deep source rocks and hydrocarbon accumulation model of Paleogene Shahejie Formation in Qingshui subsag of Liaohe Depression were analyzed. The results show that:（1）The deep source rocks of Paleogene Shahejie Formation in Qingshui subsag are mainly developed in E2s32 submember, E2s33 submember and E2s4 member, mudstone of sublayerⅡ of E2s32 submember is most developed, mainly dark gray thick mudstone, with an overall thickness of about 170 m.（2）The average TOC content of the deep source rocks in the study area can reach 1.60%, and the average hydrocarbon generation potential is 2.82 mg/g. The organic matters are mainly type Ⅱ1-Ⅲ, mainly contributed by the mixing of phytoplankton and higher plants, and are in a weakly oxidizing-weakly reducing lacustrine saline water sedimentary environment. With Ro value ranging from 0.5% to 1.5%, the source rocks have generally reached the stage of massive hydrocarbon generation, and some have reached the stage of highly matured evolution.（3）The deep source rocks in the study area entered the oil-generating window at 38 Ma, and a large amount of natural gas began to be generated at 20 Ma. Fluid inclusions show that there are two stages of oil and gas charging in the study area, namely 38-26 Ma and 20 Ma to present, matching the evolution history of hydrocarbon generation.

Characteristics and main controlling factors of interbedded shale oil reservoirs of Triassic Chang 7 member in Heshui area，Ordos Basin

CAO Jiangjun, WANG Xi, WANG Liuwei, LI Cheng, SHI Jian, CHEN Zhaobing

2024, Vol.36(3): 158–171 Abstract ( 2 ) PDF (28813 KB) ( 2 )

doi: https://doi.org/10.12108/yxyqc.20230315

Based on the data of cast thin sections, scanning electron microscopy, clay mineral X-ray diffraction, electron probe, cathodoluminescence, high-pressure mercury injection and physical properties testing, the cha- racteristics and main controlling factors of reservoir densification of the interbedded shale oil reservoirs of Triassic Chang 7 member in Heshui area of Ordos Basin were studied, a quantitative evaluation standard of the reservoirs was established, and favorable reservoirs distribution was predicted. The results show that:（1）The interbedded shale oil reservoirs of Triassic Chang 7 member in Heshui area of Ordos Basin are mainly composed of lithic feldsparthic sandstone and feldspathic litharenite, with low compositional maturity, high interstitial content, complex pore throat structure, high porosity and low permeability.（2）Cementation is the main controlling factor for the densification of the interbedded shale oil reservoirs of Chang 7 member in the study area, with an average apparent cementation rate of 86.3%, reaching a strong degree of cementation, and dominated by illite cementation in authigenic clay minerals. Compaction has relatively low effect on the reservoir densification, with an average apparent compaction rate of 46.0%, reaching medium compaction degree. Dissolution reduces the degree of the reservoir densification, but the reservoir seepage ability is low, making it difficult for acidic fluids to undergo large-scale dissolution. The average apparent dissolution rate is only 13.8%, indicating a weak degree of dissolution.（3）Due to the influence of medium compaction, weak dissolution and strong cementation, the reservoir heterogeneity is strong, and the diagenetic coefficients vary greatly. The type-Ⅰ reservoirs have a diagenetic coefficient greater than 2.4, the diagenetic coefficients of the type-Ⅱ1 and type-Ⅱ2 reservoirs range from 1.8 to 2.4 and 1.2 to 1.8, respectively, and the diagenetic coefficient of the type-Ⅲ reservoirs is less than 2.4. Among them, type-Ⅰ and type-Ⅱ1 are favorable reservoirs. The central mixed source area in the study area has the largest scale of favorable reservoir development, so it is the main target area for exploration.

PETROLEUM ENGINEERING AND OIL & GAS FIELD DEVELOPMENT

Characteristics of fracture interference between horizontal wells in tight reservoirs considering threshold pressure gradient

ZHONG Huiying, YU Chengzhi, SHEN Wenxia, BI Yongbin, YI Ran, NI Haoming

2024, Vol.36(3): 172–179 Abstract ( 6 ) PDF (4309 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240316

In view of the problems of fracture interference between horizontal wells during volume fracturing in tight reservoir development, based on the trilinear flow model, semi permeable boundary condition and interwell interference coefficient（α）were introduced to establish fracture interference percolation model of tight reservoir horizontal wells considering threshold pressure gradient in unreformed area, and the bottomhole pressure performance and production decline characteristics of horizontal wells under different interference conditions were studied. The results show that:（1）The larger the α, the more the number of fracture interference, the longer the duration of linear flow in the pressure dynamic curve transformation area, and the later the occurrence of cross flow and quasi stable flow in the transformation area. The larger the threshold pressure gradient in the unreformed area, the earlier the occurrence of quasi stable flow.（2）The larger the fracture conductivity, the earlier the linear flow of the main fracture occurs, and the closer the fracture conductivity of two wells. The influence of α on pressure dynamics is more obvious.（3）Horizontal wells with larger α and relatively lower bottom hole pressure have higher initial production, but in the later stage, the production decreases more significantly. The larger the dimensionless threshold pressure gradient, the faster the later production decline.（4）The smaller the fracture conductivity, the lower the production curves in the early stage. When the fracture conductivity of two wells is similar, α has a relatively large impact on production.

Mechanism and field practice of enhanced oil recovery by injection-production coupling in fault block reservoirs

LIU Renjing, LU Wenming

2024, Vol.36(3): 180–188 Abstract ( 5 ) PDF (3288 KB) ( 1 )

doi: https://doi.org/10.12108/yxyqc.20240317

Aiming at the problem of ineffective circulation of injected water caused by fixed streamline in the late stage of water drive development of Paleogene fault block reservoirs in Dongying Sag, Jiyang Depression, Bohai Bay Basin, based on seepage mechanics and reservoir engineering principles, the injection-production coupling development adjustment technology of“subdividing development layers, rotating injection and production”was proposed by means of indoor physical model simulation and reservoir numerical simulation, and the mechanism of enhancing oil recovery by this technology was clarified. The results show that:（1）The water absorption ratio model between high permeability channel and low permeability channel during injection and the oil production ratio model of mainstream line and non-mainstream line during oil production established by the injection-production coupling development technology reveal the injection-production coupling seepage mechanics mechanism of“changing pressure field to promote the adjustment of seepage field, achieving balanced injection and production, expanding sweep efficiency of water drive and increasing the oil displacement efficiency”. （2）The injection-production coupling technology can achieve remarkable development effect of“expanding sweep efficiency and increasing oil displacement efficiency”, that is, it plays a similar role of“profile control”. During the high water cut period, this technology can increase the diversion rate of low permeability cores from 1.0% to 18.6%, and the model displacement is more balanced. After two rounds of injection-production coupling adjustment, the oil recovery of high and low permeability cores increased by 10.3% and 16.1%, respectively. （3）The numerical simulation results of injection-production coupling development of Es236 oil-bearing sublayer of Paleogene Shahejie Formation in fault block D of the study area show that the displacement of mainstream line and non-mainstream line was more balanced, and the pressure gradient range between them decreased from 2.3 to 1.4. After three rounds of injection-production coupling development and adjustment, the average comprehensive water cut of the reservoirs in the third to the sixth sand layers of the second member of Shahejie Formation decreased by 3.2%, and the cumulative oil production increased by 1 760 t, which improved the oil recovery by 2.1%, and the effect of increasing oil production and dewatering was remarkable.