Lithologic Reservoirs

The marine shale of the Upper Permian Wujiaping Formation in Sichuan Basin is a hotspot for shale gas exploration and development. Based on X-ray diffraction，thin section identification，scanning electron microscopy，organic geochemistry，and low-temperature nitrogen adsorption，the distribution of sedimentary facies，characteristics of source rocks and reservoirs of the second member of Permian Wujiaping Formation （P2w2）shale in the northeastern Sichuan Basin were conducted. The main controlling factors of reservoir development were clarified，and distribution of favorable reservoir zones was also analysed. The results show that：（1）The deposition of the P2w2 in the northeastern Sichuan Basin is influenced by the rise of sea level and the development of rifts，and is dominated by deep-water shelf facies，displaying a banded distribution in the areas of Dazhou-Kaijing-Wanzhou-Zhongxian.（2）The mineral composition of the P2w2 shale in the study area is complex with a high content of brittle minerals（67.9%）. They are similar to the Silurian Longmaxi Formation shale in Sichuan Basin，displaying biogenically influenced quartz with flocculated and framboids pyrite with small grains（2w2 shale is 4.11%，with pore types including organic matter pores，intragranular pores，intergranular pores，and micro-fractures. The shale pore structure is dominated by mesopores，with a minor presence of micropores and macropores，where contribution rate of mesopore to pore volume is the largest. （3）The source rocks of P2w2 exhibit high TOC content and high maturity，with an average TOC content of 4.8% and an average Ro of 2.53%，reaching an over-mature stage，predominant type Ⅱ kerogen，indicating high hydrocarbon generation potential. It generally meets the criteria for a Class Ⅰ shale gas reservoirs.（4）P2w2 shale reservoir is mainly controlled by sedimentary environment and diagenetic transformation. The sedimentary environment of deep-water shelf is conducive to the formation of shale reservoirs. Quartz on resisting pressure and retaining pores，hydrocarbon generation from organic matterrs play a critical role in the formation of shale reservoirs. There is a positively correlated relationship between the quartz content，TOC content to porosity. It is considered that the Kaijiang-Liangping and Wanzhou areas should be favorable distribution areas for the P2w2 shale reservoirs.

Logging identification and application of lacustrine dolomite in the fourth member of the Shahejie Formation in the Bamianhe area of Dongying Sag

HU Xinling, RONG Huanqing, YANG Wei, ZHANG Zaichang, QI Zhixian

2025, Vol.37(1): 13–23 Abstract ( 94 ) PDF (11835 KB) ( 137 )

doi: https://doi.org/10.12108/yxyqc.20250102

The rock composition and structure of lacustrine dolomite reservoirs are complex and diverse，and the use of logging data is of great significance for identifying dolomite lithology. In order to solve the problems of heavy workload and low recognition accuracy in traditional logging methods，a method of integrating spider web plot intersection plot principal component analysis is proposed to construct a lithology sensitive factor intersection plot and carry out comprehensive identification of lacustrine dolomite lithology. The results indicate that：（1）The fourth member of the Paleogene Shahejie Formation（Sha 4 Formation）in the Bamianhe area of Dongying Sag is mainly composed of granular dolomite，microcrystalline dolomite，mud crystalline dolomite， sandstone，and shale. Among them，granular dolomite，microcrystalline dolomite，and shale are the main rock types.（2）Selecting 6 types of feature parameters to analyze the differences between spider web diagrams and intersection diagrams of different rock types，among which GR and AC can effectively distinguish granular dolomite，and SP has a good distinguishing effect on sandstone. Based on the results of spider web diagrams and intersection diagrams，principal component analysis is applied to standardize the logging parameters，and principal components F1 and F2 with a cumulative variance contribution rate of 90.75% are constructed. A lithology discrimination model is established to comprehensively identify lithology.（3）Through the verification of production capacity and coring wells，the accuracy of lithology identification is as high as 85.4%. It is clear that the granular dolomite is distributed in a strip like pattern in the west along the SW-NE direction， transitioning to microcrystalline dolomite and mud crystal dolomite in the south and north，while irregularly distributed sandstone is dominant in the east. This fusion method can efficiently identify the lithology of dolomite and has strong guiding value for subsequent favorable reservoir evaluation and oil and gas exploration.

Characteristics，formation environment and enrichment model of Triassic Chang 7 shale oil reservoir in Huachi area，Ordos Basin

LIANG Feng, CAO Zhe

2025, Vol.37(1): 24–40 Abstract ( 85 ) PDF (6686 KB) ( 126 )

doi: https://doi.org/10.12108/yxyqc.20250103

Through the petrological characteristics and elemental geochemical testing and analysis of cores from Triassic long 7-layer drilling in Huachi area of Ordos Basin，the paleoenvironmental characteristics were analyzed by using V（/ V+Ni），Ni/Co，U/Th，Sr/Cu，CaO（/ MgO*Al2O3），Sr/Ba，Fe/Mn，Mn/Ti，Babio values and P/Al values，combined with the content of total organic carbon，to analyze the paleoenvironmental. Paleoenvironmental characteristics such as Ancient climate，paleosalinity and paleoredox conditions. The results show that：（1）The rocks of Triassic Chang 7 member in Huachi area of Ordos Basin are mainly dark gray mudstone，dark gray gray mudstone，silty mudstone containing carbon debris and silty mudstone rich in organic matter. Intercrystalline pores and intergranular pores of clay minerals are the main pore types. In addition，a small number of dissolution pores and fine fractures can be seen.（2）In the study area，the organic matter productivity was significant during the deposition period of Chang 7，and the environment was mainly freshwater with low oxygen content，which was in a state of poor oxygen to hypoxia，while in the Chang 72 and 73 periods，some areas with deep water bodies had extremely strong reduction conditions，mainly warm and humid climate. Overall，it indicates a deep-water environment. And Chang 72 is located in the boundary zone of the deep-water area，and its water environment are obviously different from the adjacent Chang 71 and Chang 73 members，showing relatively low water depth conditions. The P/Al value and Babio value generally change in the Chang 7 member，from Chang 73 to Chang 71，they all show a process of increasing from bottom to top.（3）The paleosedimentary environment of the Chang 7 member in this area has suitable temperature and salinity conditions，coupled with the deep water and strong reduction，which jointly promote the extensive development，enrichment and preservation of organic matter. The source rock and the reservoir are interconnected through fractures，and the oil generated in the source rock is more easily transported to the reservoir layer through fractures. In addition，when the distance between the source rock and the reservoir is relatively close，the process of crude oil migration and accumulation will be more efficient，and finally form a high-quality source rock system. Source rock and reservoir configuration laid a solid foundation for large-scale enrichment of shale oil and created extremely favorable conditions.

Geochemical characteristics and source of crude oil of Cretaceous Tongbomiao Formation in Urxun Depression，Hailar Basin

HE Xing, JIN Wei, ZHANG Fan, HUO Qiuli, LI Yue, BAO Junchi, LIU Lu, ZENG Qingbing

2025, Vol.37(1): 41–52 Abstract ( 71 ) PDF (7023 KB) ( 108 )

doi: https://doi.org/10.12108/yxyqc.20250104

The Cretaceous Tongbomiao Formation in Urxun Depression of the Hailar Basin has achieved exploration breakthroughs，it is a new layer with great potential for resources. On the basis of dividing the Tongbomiao Formation into three layers，the abundance，type，and maturity of the source rocks in each small layer of the trough in the study area were evaluated trough analysis and laboratory data such as TOC，pyrolysis，Ro，group composition，chromatography，color quality，and carbon isotopes. The geochemical characteristics of the crude oil in the Tongbomiao Formation were analyzed in depth，and the source of the crude oil was quantitatively calculated，and the favorable exploration direction was predicted. The results show that：（1）The overall development of the Tongbomiao Formation in Urxun Depression is a medium source rock with a TOC mean of about 1%， mainly of type Ⅰ-Ⅱ2. The mudstone of the Tongbomiao Formation（t2）is source rock of type Ⅰ，and the Ro in the trough is 0.6%-1.5%，which is in the mature stage.（2）The crude oil of the Tongbomiao Formation in the research area can be divided into three categories. The crude oil of the third section of the Tongbomiao Formation（t3）in north Urxun，the crude oil of the third section of the Tongbomiao Formation（t3）in south Urxun，and the crude oil of the second section of the Tongbomiao Formation（t2）in south Urxun. T3 crude oil of North Urxun has high saturation hydrocarbons content，high ratio of Pr to Ph，heavy carbon isotopes of saturated hydrocarbons and aromatic hydrocarbons，and high content of C27 rearranged steranes and tricyclic terpenes. T3 crude oil of South Urxun has high saturation hydrocarbons content，light carbon isotopes of saturated hydrocarbons and aromatic hydrocarbons，and moderate content of C27 rearranged steranes and tricyclic terpenes. T2 crude oil of South Urxun has low saturated hydrocarbon content，high OEP value，light carbon isotopes of saturated hydrocarbons and aromatic hydrocarbons，and low content of C27 rearranged steranes and tricyclic terpenes.（3）All three types of crude oil in the Tongbomiao Formation are binary mixtures of the mudstone of first section of the Nantun Formation（n1） and the mudstone of the Tongbomiao Formation. The first type of crude oil is closer to the source rock of n1 in north Urxun，and the mixed source ratio calculation shows that its contribution from the mudstone of n1 in north Urxun is 62.9%. The second type of crude oil is closer to the source rock of n1 in south Urxun，and the mixed source ratio calculation shows that its contribution from the mudstone of n1 in south Urxun is 59.5%. The third type of crude oil is closer to the source rock of t2 in south Urxun，and the mixed source ratio calculation shows that its contribution from the mudstone of t2 in south Urxun is 75.4%.（4）The dark mudstone with a depth of over 200 m is developed in the north Urxun and south Urxun troughs，which can be used for exploration of oil reservoirs of t3 with mainly external hydrocarbons supply and oil reservoirs of t2，respectively. The north Urxun trough and east Urxun slope zone can be regarded as favorable areas for further exploration of the Tongbomiao Formation in Urxun Depression.

Geological characteristics and enrichment model of Ordovician oil and gas in Tazhong Uplift

XIONG Chang, WANG Peng, LIU Xiaoyu, WANG Wei, ZHAO Xingxing, SUN Chong

2025, Vol.37(1): 53–67 Abstract ( 81 ) PDF (17808 KB) ( 135 )

doi: https://doi.org/10.12108/yxyqc.20250105

Based on the data of structural analysis，fault distribution，production dynamics，and geochemistry，an analysis is conducted on the characteristics of oil and gas properties as well as productivity distribution in the Tazhong area during the Ordovician period. The factors contributing to oil and gas accumulation are examined from three perspectives：oil and gas charging，transport system，structure，and the relationship between migration and accumulation. Consequently，an accumulation model is established. The results show that：（1）The crude oil found in the Tazhong area during the Ordovician period is predominantly light crude oil with low density，viscosity， and sulfur content. Its density ranges from 0.75 to 0.85 g/m3，while the gas-oil ratio varies between 119 and 82， 367 m3/m3. This region contains multi-phase oil and gas reservoirs where there is no distinct boundary between the oil and gas phases. The dryness coefficient of natural gas ranges from 0.70 to 0.98，and the carbon isotope composition of methane in natural gas shows a wide variation ranging from -35.7‰ to -61.4‰. Different regions exhibit amantane index（MDI）values ranging from 0.33 to 0.64. The eight major oil and gas charging points exhibit characteristics such as low crude oil density，high gas-oil ratio，and elevated levels of methane carbon isotope and MDI. Moving along the strike-slip fault zone towards the south or away from it results in an increase in density，while the gas-oil ratio，methane carbon isotope，and MDI all decrease. Variations in gas penetration intensity across different blocks may lead to localized differences in these patterns.（2）The distribution pattern of oil and gas in the study area is primarily influenced by localized oil and gas charging. Oil and gas wells surrounding the 8 charging points typically exhibit high production rates，due to reservoir development scale， there may be occasional occurrences of low-producing wells near the charging points. The regional distribution of filling points' production capacity can be categorized into three types：“northern dominance in natural gas，southern abundance in crude oil，”“central prevalence of natural gas with flanking areas rich in crude oil，”and“generally abundant natural gas with localized presence of crude oil”. However，low-producing wells and those located far from the charging points are dispersed over a wide range.（3）The oil and gas enrichment mode in the study area during the Ordovician period is characterized by tension-torsional large faults controlling vertical hydrocarbon charging，unconformity and strike-slip faults governing lateral hydrocarbon migration，interlayer karst within fracture zones providing reservoir space for hydrocarbon accumulation，and local structural highs and platform areas serving as favorable directions for hydrocarbon accumulation.

Carboniferous structural characteristics and hydrocarbon accumulation regularity of Chepaizi Uplift in Junggar Basin

CHEN Peng, WU Xiaoning, LIN Yu, ZHONG Houcai, ZHANG Jie, HUANG Youhua, YUE Wen, LENG Ping

2025, Vol.37(1): 68–77 Abstract ( 78 ) PDF (55456 KB) ( 133 )

doi: https://doi.org/10.12108/yxyqc.20250106

The Chepaizi Uplift of Junggar Basin has favorable reservoir conditions for dual source hydrocarbon supply，with low exploration level and great potential. Based on the newly collected 3D and reprocessed 2D seismic data，the structural characteristics of the area were clarified through fine structural interpretation. The research results indicate that：（1）Controlled by four northwest thrust faults in the Late Carboniferous-Early Permian and multiple north-south faults in the Early Carboniferous，the Chepaizi Uplift Carboniferous system is divided into three zones from south to north：southern，central，three stripes in northern，and three steps in the east-west direction. The eastern second step and the western Aika fault are shallowly buried on the hanging plate， adjacent to the main source rock stove，and are the most favorable locations for reservoir formation.（2）A series of fault blocks formed by the cutting of north-south faults in the northwest southeast direction control the distribution of oil and gas in the Carboniferous system，and have the characteristics of fault block controlled reservoirs.（3）When the degree of fracture development is comparable，reservoir is a key factor in controlling oil and gas production，among which volcanic eruption facies reservoirs have good matrix properties，which are most conducive to oil and gas enrichment.（4）The four major faults，namely the Shamenzi Fault，Chepaizi Fault，Chepaizi South Fault，and Aika Fault，have developed explosive facies on the hanging wall，with shallow burial depth. Also connected to the two major source rocks of the Fengcheng Formation in the Shawan Depression and the Jurassic in the Sikeshu Depression over a large span，and have superior reservoir conditions， making them favorable areas for further exploration.

Study on the difference of petroleum accumulation between Paleogene and Neogene in the western Bozhong Sag，Bohai Bay Basin

LIU Zhifeng, ZHU Xiaoer, LIU Guangdi, WANG Xiang, LI Zekun, WU Xuan, LIANG Yuyang

2025, Vol.37(1): 78–89 Abstract ( 73 ) PDF (6581 KB) ( 132 )

doi: https://doi.org/10.12108/yxyqc.20250107

Through the simulation of hydrocarbon generation and expulsion history of source rocks，oil-source correlation，petroleum filling history，and fault analysis of the western Bozhong Sag，Bohai Bay Basin，combined with the structural evolution history and controlling fault activity history，the petroleum origins，accumulation time，and the fault migration pathway system in the Paleogene and Neogene reservoirs in western Bozhong Sag were analyzed. The results shows that：（1）The Paleogene petroleum in the western Bozhong Sag is mainly concentrated in the reservoirs of the Oligocene Dongying Formation Mbrs 2 and 3（E3d2 and E3d3）of the northern steep slope zone，while the Neogene petroleum in the western Bozhong Sag is distributed in the shallow Guantao Formation and Minghuazhen Formation reservoirs of the northern steep slope zone，western gentle slope zone，and central structural zone. The petroleum reserves of the Neogene in the central structural zone and western gentle slope zone are significantly higher than those in the northern steep slope zone.（2）The significant source rocks of the western Bozhong Sag are the Shahejie Formation Mbrs 1 and 3（E2s1 and E2s3），while the source rocks of the E3d3 also contribute to the petroleum reservoirs in the northern steep slope zone. The accumulation of petroleum in the western Bozhong Sag can be divided into three stages. The discovered petroleum reservoirs mainly formed in two stages. The discovered petroleum reservoirs are mainly formed in the second stage（10-5 Ma）and the third stage（since 5 Ma）. The petroleum generated by the source rock of Shahejie Formation in the first large amount of hydrocarbon generation and expulsion period，between 30 and 20 Ma ago，remains undiscovered. The fault crossing layer and formation time of the fault have a significant controlling effect on the differential enrichment of petroleum in the deep and shallow layers.（3）The shallow Neogene oil and gas reservoirs in the research area are mainly controlled by the communication of shallow，medium，and deep through-source faults formed by neotectonic movements. Mature oil and gas generated by the Shahejie Formation source rocks are transported through multiple long-term active faults and other transport systems；The oil reservoirs of the Paleogene Dongying Formation are mainly controlled by a fault system that only extends to the Dongying Formation，and their oil and gas mainly come from the underlying source rocks of the Shahejie Formation and the third member of the Dongying Formation; The deep Shahejie Formation may develop self generating and self storing oil and gas reservoirs，but no exploration discoveries have been made yet.

Genesis and exploration significance of calcareous intercalation of Jurassic Xishanyao Formation in Luliang area，Junggar Basin

HE Yan, XU Weina, DANG Sisi, MOU Lei, LIN Shaoling, LEI Zhangshu

2025, Vol.37(1): 90–101 Abstract ( 72 ) PDF (14830 KB) ( 99 )

doi: https://doi.org/10.12108/yxyqc.20250108

Based on core description，cast thin slice，scanning electron microscopy，conventional logging，CT， XRD，production dynamics and other data，the development characteristics，genesis，distribution pattern and 3D model of calcareous intercalation of Jurassic Xishanyao Formation in well 9 area of Luliang Oilfield are studied by means of hierarchical structure analysis，multi-dimensional interactive reservoir configuration characterization， 3D embedded intercalation modeling and reservoir numerical simulation. The results showed that：（1）The calcareous intercalations are mainly distributed in the densified medium and fine sandstone，and are typical physical intercalations. Its physical properties are characterized by extremely low porosity and low permeability，and it is a typical physical intercalation with“three low and two high”logging response characteristics.（2）The abundant sediment supply from underwater distributary channels and the mineralization process of bioclastic debris at the delta front，where dissolved Ca2+ and CO32- are converted into solid calcium carbonate，provide the sedimentary material basis for the formation of calcareous layers. Calcareous layers primarily form during the diagenetic stage. Based on their genesis，they can be divided into two main types：one type is the cementation of thin sand layers within the proximity of mudstone formations，and those are calcareous cementation of diagenetic evolution；the other type develops in river channel sand bodies with good physical properties and connectivity，specifically at the base and overlapping areas of the channels，where secondary porosity is filled and cemented in pores. （3）It is mainly distributed of calcareous intercalation，with a thickness of about 0.25-2.00 m，a length of about 200-1 300 m and a width of about 100-900 m. The planar distribution is relatively continuous，and the direction of vertical material source varies greatly，and it is thin layer lenticular.（4）The calcareous interlayer has obvious control over the distribution of residual oil，forming residual oil-rich zones in the form of lenses and strips，etc. The residual oil in the study area is mainly distributed in J2x41-3 and J2x42-1 layers.

Overpressure-generating mechanism and its evolution characteristics of Cretaceous Shahezi Formation in Xujiaweizi Fault Depression，Songliao Basin

CHEN Hongguo, ZHANG Fengqi, JIANG Qingchun, LIU Hongyan, SUN Lidong, LIU Gang

2025, Vol.37(1): 102–114 Abstract ( 66 ) PDF (2191 KB) ( 124 )

doi: https://doi.org/10.12108/yxyqc.20250109

Using the data of drilling，logging，pressure testing and analysis test，the current overpressure characteristics and the formation mechanism of overpressure of Cretaceous Shahezi Formation in Xujiaweizi fault depression of Songliao Basin were analyzed The overpressure evolution of source rocks with different structural units and different lithology is quantitatively restored by numerical simulation method，and the contribution of each overpressure to total overpressure is calculated. The results show that：（1）The present pressure of Cretaceous Shahezi Formation in Xujiaweizi fault depression are normal pressure-weak overpressure system， and the overpressure in the uplift is largest in the sag. Overpressure in the source rock is mainly driven by hydrocarbon generation and its second origin is undercompaction，while overpressure in the reservoir is the overpressure transfer effect from source rock overpressure，which is closely related to the formation and development of faults and anticlines.（2）The overpressure of source rocks in the Shahezi Formation in the study area is mainly caused by hydrocarbon generation of coal seam and organic-rich mudstone. Generally，the contribution ratio of hydrocarbon generation to total overpressure is the largest in coal seam，followed by organicrich mudstone，and organic-poor mudstone is lower，while the contribution ratio of hydrocarbon generation to total overpressure in the organic-rich mudstone is higher than that of coal seam in the sag and its periphery. The contribution ratio of hydrocarbon generation to total overpressure in the sag is higher than that in the slope zone and the uplift.（3）The evolution of overpressure in Shahezi Formation in the study area can be divided into three stages. The early to middle Cretaceous period is a slow pressurization stage. Overpressure was generated by undercompaction and slow hydrocarbon generation of source rocks，and was transmitted to the reservoir through active faults and anticline formation in Shahezi and Yingcheng formations，and overpressure in the reservoir increased slowly. The late Cretaceous period was a stage of rapid pressurization，with a large amount of gas generation in source rocks. In this stage，continuous transfer of overpressure caused by hydrocarbon generation and undercompaction make the overpressure in the reservoir be rapidly increased. The overpressure in the reservoir in this stage accounted for 90% of the total overpressure at present. The early Paleogene to the present is a stable stage. During this period，the tectonic is stable，overpressure induced by the hydrocarbon generatation and undercompaction in the source rock basically unchanged. Otherwise，the overpressure in the reservoir increases steadily. （4） The differential evolution of overpressure in different lithologic strata of Shahezi Formation in the study area controls the distribution of natural gas，overpressure difference between source and reservoir provides dynamic conditions for oil and gas migration，and the overpressure developed by organic-poor mudstone cap layer provides overpressure sealing conditions for the underlying reservoir.

Reservoir characteristics and high yield control factors of Permian Fengcheng Formation shale oil reservoir in Mahu Sag

QIAN Yongxin, ZHAO Yi, LIU Xinlong, LIU Hong, LIU Guoliang, ZHU Tao, ZOU Yang, CHEN Fangwen

2025, Vol.37(1): 115–125 Abstract ( 78 ) PDF (40862 KB) ( 123 )

doi: https://doi.org/10.12108/yxyqc.20250110

Based on the experimental results of rock slices，scanning electron microscopy，low temperature nitrogen adsorption，high pressure mercury injection，core fluorescence，laser confocal microscopy and liquid production profile，the characteristics and high yield control factors of Permian Fengcheng Formation shale oil reservoir in Mahu Sag were detailed studied. The results show that：（1）The shale oil reservoirs of Permian Fengcheng Formation in Mahu Sag can be divided into sandstone，dolomite and mudstone. Siltstone reservoirs are dominated by terrigenous clastic sediments，mudstone reservoirs are dominated by terrigenous and endogenous mixed deposits，and dolomite（calcite）reservoirs are dominated by endogenous chemical deposits. The throat size distribution ranges of sandstone，dolomite and mudstone reservoir of Fengcheng Formation in Mahu Sag decrease successively，and the pore connectivity of the three lithologic reservoirs deteriorates successively. （2）Siltstone reservoirs have the best oil content，followed by mudstone reservoirs，dolomite reservoirs are the worst of shale oil reservoirs of Permian Fengcheng Formation in Mahu Sag. The proportion of free oil is higher in the larger pores and micro-fractures，and the proportion of adsorbed oil is higher in the smaller pores.（3）High quality source rock and high quality reservoir control the high production area and high production interval of Fengcheng Formation in Mahu Sag，respectively. The shale oil reservoirs with high felsic content，effective porosity，free oil porosity，fracture density and brittleness index are the favorable interval for high production.

Main controlling factors and hydrocarbon accumulation model of Carboniferous reservoir in Chepaizi Uplift，Junggar Basin

GUI Shiqi, LUO Qun, HE Xiaobiao, WANG Qianjun, WANG Shichen, WANG Liang

2025, Vol.37(1): 126–136 Abstract ( 125 ) PDF (28996 KB) ( 139 )

doi: https://doi.org/10.12108/yxyqc.20250111

Using seismic，logging，oil test，core，casting thin，physical property analysis and physical simulation experiments，the configuration relationship of hydrocarbon accumulation elements，enrichment law research and main controlling factors of hydrocarbon accumulation of Carboniferous reservoir in Chepaizi Uplift of Junggar Basin were discussed. The results show that：（1）The reservoir lithology in the study area is mainly tuff，andesite and breccia，and the reservoir space is mainly secondary pores and fractures. The porosity mostly less than 8%， and the permeability is concentrated in 0.1-10.0 mD，which belongs to ultra-low porosity and ultra-low permeability reservoir.（2）The enrichment，migration and accumulation elements of the reservoir are controlled by the union of three elements of“fault-reservoir-shell”：Deep and large faults are the channel of vertical migration of oil and gas；Weathering and leaching can improve reservoir physical properties and provide effective storage space for oil and gas enrichment；The Carboniferous itself and its overlying mudstone are generally relatively tight，form a good reservoir-cap combination with the fracture volcanic reservoirs；The configuration relationship between strike-slip faults and cap rocks plays an important role in controlling the vertical and lateral migration of oil and gas.（3）It is concluded that the reservoirs in the study area as a whole have the characteristics of “dual source hydrocarbon supply，multi-system transport，multi-type caprock，multi-layer oil-bearing，multireservoir type，and compound oil-bearing area”. There are significant differences in reservoir accumulation models in different regions and different depths. Horizontally，the near source is“fault blanket transport，lateral filling， near source weathering crust accumulation model”，and the far source is“dual source hydrocarbon supply， multiple transport types，hard shell sealing，far source fault shell accumulation model”. Vertically，the shallow part is“dual-source hydrocarbon supply，multiple transport types，hard shell sealing，shallow weathering crust accumulation mode”，and the deep part is“dual-source hydrocarbon supply，fault transport，tight rock sealing， deep fault body accumulation mode”.

Characteristics and main controlling factors of tight gas reservoirs in the second member of Triassic Xujiahe Formation，central Sichuan Basin

YANG Jie, ZHANG Wenping, DING Chaolong, SHI Cunying, MA Yunhai

2025, Vol.37(1): 137–148 Abstract ( 87 ) PDF (17322 KB) ( 132 )

doi: https://doi.org/10.12108/yxyqc.20250112

In order to clarify the characteristics，genesis and distribution of favorable reservoir in the second member of Xujiahe formation，comprehensively utilizing the thin sections，scanning electron microscopy， nuclear magnetic resonance，mercury injection and CT testing，the main controlling factors of tight gas reservoirs were analysed. And based on the macro and micro parameters，classify the tight gas reservoirs quantitatively and distribute foe different kinds of reservoirs according to Q-cluster analysis. The results show that：（1）The reservoirs in the second member of Xujiahe formation in Hechuan area of central of Sichuan Basin are lithic feldspar sandstone and feldspar lithic sandstone，with an average porosity and permeability of 6.58% and 0.21 mD， which is typical ultra-low porosity and low permeability reservoir. The reservoir space in the second member of Xujiahe Formation is mainly residual intergranular pore and intragranular dissolved pore，secondly is intergranular dissolved pore and fissure，the pore and throat radius range from 1.31 μm to 55 μm and 0.05 μm to 1.14 μm， classifying them as micrometer pores and millimeter-micrometer throats.（2）The granularity and shale content is controlled by the sedimentary，which is the basic for primary pore and its evaluate，while the pore distribution by compaction and cementation is 14.6%-20.1% and 9.8%-15.1%，which is the significance reason for the reservoir densification. The dissolution and chlorite formed lots of intragranular dissolved pore，and protect some intergranular pore，which is helpful to the improve the tight reservoir into favorable reservoir.（3）Multiple parameters such as reservoir quality and pore structure was selected to divide the tight gas reservoirs into 4 kinds of different reservoirs，the reservoir quality and pore structure are different from each other in different kinds of reservoirs. TheⅠ-type and Ⅱ-type reservoirs have a greater reservoir quality and pore structure，which is the main“sweet spot”in tight gas reservoirs and favorable development target in study area. TheⅠ-type and Ⅱ-type reservoirs are development in H1，H3 well in the central and H125 well in the east，and they concentrated development in the third and second layer in the upper of the second member of Xujiahe Formation.

Fracture development characteristics and geological significance of tight sandstone of Cretaceous Bashijiqike Formation in Keshen area，Kuqa Depression

WEI Huan, SHAN Changan, ZHU Songbai, HUANG Zhongxin, LIU Hanguang, ZHU Bing, WU Changtao

2025, Vol.37(1): 149–160 Abstract ( 93 ) PDF (17731 KB) ( 114 )

doi: https://doi.org/10.12108/yxyqc.20250113

Based on the data of core，cast slice and laser confocal scanning electron microscopy，the fracture development characteristics and main controlling factors of Cretaceous Bashijiqike Formation in Keshen area of Kuqa Depression are analyzed，and their influence on reservoir physical properties and hydrocarbon accumulation effect is discussed. The results show that：（1）The rock type of Cretaceous Bashijiqike Formation in Keshen area of Kuqa Depression is dominated by lithic feldspar sandstone，which is a typical tight sandstone reservoir. Shear and tension fractures are mainly developed，and high angle and vertical fractures are mainly developed，and unfilled and semi-filled fractures occupy a relatively large proportion. The difference of fracture plane distribution in Keshen A and B gas reservoirs is mainly caused by the difference of structural location and stress evolution，and the fracture effectiveness of A gas reservoir is better than that of B gas reservoir.（2）There are differences for the fracture density and effectiveness in the different structural location. The fracture effectiveness is highest at the high point of the anticline，while the fracture density is high but the effectiveness is low at the saddle and wing near the fracture. The fracture effectiveness in sandstone is higher than that in mudstone. There is a nonlinear relationship between the thickness ratio of sand and mudstone and the fracture density，and the fracture density reaches its maximum value when the thickness ratio of sand and mudstone reaches 6.1，beyond which the fracture density gradually decreases.（3）Fracture development significantly increases the permeability of tight sandstone reservoirs；The fracture network can effectively connect the low permeability reservoir， improve the accumulation efficiency and migration ability of oil and gas，increase the reservoir reserves and enhance the resource development potential of the reservoir. This study has certain guiding significance for the migration and enrichment of oil and gas in the same type reservoir and the productivity of single well.

Characteristics and reservoir control effects of the fault system in Kongqueting area of Xihu Sag，East China Sea Basin

XUE Yuheng, LI Kun, SHANG Yamin, CHEN Qiutong, SHENG Liehao, LIU Jianbin

2025, Vol.37(1): 161–169 Abstract ( 77 ) PDF (9665 KB) ( 112 )

doi: https://doi.org/10.12108/yxyqc.20250114

Based on the fine interpretation of 3D seismic data，the characteristics of the fault system in Kongqueting area of Xihu Sag in the East China Sea Basin were analyzed using methods such as structural profile reconstruction and fluid inclusion analysis. The evolution characteristics and reservoir control effects were studied. The results show that：（1）The fault system in Kongqueting District of Xihu Sag has obvious differences in east and west zoning，and showing different zoning. On the plane，there are three sets of main extensional faults developed in the east，mainly in the NNE direction，followed by the NE direction and near NS direction，and two sets of main extensional faults developed in the west，mainly in the NE direction，followed by the NNE direction； On the profile，the eastern part is dominated by a domino shaped oblique structure style，while the western part is dominated by syndromic fault terraces；From west to east，it can be divided into 5 fault zones，with 2 reverse fault zones developed in the east and 3 syndromic fault zones developed in the west.（2）The fault system in the research area has gone through four evolutionary stages：fault depression period，fault depression conversion period，depression inversion period，and regional subsidence period. The fault activity shows differential evolution characteristics of“early strong and late weak in the east，early weak and late strong in the west”.（3）The research area has developed reverse fault groove-local self enclosed oil and gas reservoir in the east，as well as forward fault terraces and lithological pinch out oil and gas reservoirs in the west. The reservoirs in the east are dual source hydrocarbon supply，which are favorable for oil and gas accumulation zone. Especially，the F2 and F3 faults have strong activity，large fault displacement，large controlled trap area and height. They are rich in oil in the Pinghu Formation and rich in gas in the lower section of the Huagang Formation，making them favorable exploration areas.

Shale rock-reservoir collocation and hydrocarbon enrichment rule of Triassic Chang 7 member in Yan’an area，Ordos Basin

WU Jia, ZHAO Weiwei, LIU Yuchen, LI Hui, XIAO Ying, YANG Di, WANG Jianan

2025, Vol.37(1): 170–181 Abstract ( 71 ) PDF (6613 KB) ( 120 )

doi: https://doi.org/10.12108/yxyqc.20250115

The continental shale of member 7 of Yanchang Formation in Ordos Basin is rich in oil and gas resources and has great potential for exploration and development. Through core observation，well logging and logging data analysis，geochemical data，X-ray diffraction analysis and on-site analytical gas and other specific test data，in-depth analysis of the shale oil and gas source-reservoir characteristics of the three sub-member of Chang 7 member，and establish the source-reservoir division standard，compare and analyze the relationship between different source-reservoir combination characteristics and oil and gas enrichment rules. The results show that：（1）The organic matter types of Chang 7 member of Yanchang Formation of Triassic in Yan’an area of Ordos Basin are mainly type Ⅱ1 and type Ⅱ2，followed by type Ⅰ；the average organic carbon content（TOC） of the three substrata are 3.39%，4.35% and 5.57%，respectively. And value of vitrinite reflectance（Ro）are 0.69%， 0.97% and 1.31%. Chang 71、Chang 72 and Chang 73 sub-members are poorly developed，medium source rocks and high quality source rocks，respectively.（2）The shale mineral composition of Chang 73 sub-member of Yanchang Formation in the study area is rich in clay，and the clay mineral content of Chang 72 sub-member is better than that of Chang 71 sub-member. The pore space types of Chang 71，Chang 72 and Chang 73 sub-members are dissolution pore，intergranular pore-solution pore and intergranular pore fracture，respectively，and the developed reservoir characteristics are type Ⅲ（poor），type Ⅱ（medium）and type Ⅰ（excellent），respectively. （3）Six kinds of source reservoir characteristics are mainly developed in the study area，such as high quality hydrocarbon source rock high quality reservoir，medium hydrocarbon source rock medium reservoir，poor source rock medium reservoir，high quality source rock medium reservoir，poor source rock poor reservoir and so on. The enrichment degree of high quality source rock is the highest，which is mainly distributed in Chang 73 sub-member. The second is medium source rock high-quality reservoir，medium source rock medium reservoir， high-quality source rock medium reservoir，mainly developed in Chang 72 sub-member，Chang 71 sub-member with poor distribution and other poor source rock reservoirs，which is not conducive to shale oil and gas accumulation.（4）Shale with high organic matter abundance and high organic matter maturity has better hydrocarbon generation potential. High clay mineral content and good pore connectivity are conducive to oil and gas migration and accumulation. Source and reservoir characteristics control the enrichment position of shale oil and gas in this area.

Shale gas enrichment law of Ordovician Wufeng Formation to Silurian Longmaxi Formation in Anchang syncline of Zheng’an area，northern Guizhou

WU Song, FENG Bing, YU Jiliang, LAN Baofeng, LI Long, WANG Sheng, SHEN Jianing, LI Gangquan

2025, Vol.37(1): 182–193 Abstract ( 72 ) PDF (4552 KB) ( 103 )

doi: https://doi.org/10.12108/yxyqc.20250116

There are good prospects for shale gas exploration and development in northern Guizhou area on the outer edge of Sichuan Basin. Based on wire-logging，mud-logging，and analytical data，the characteristics and enrichment law of shale gas reservoirs of Ordovician Wufeng Formation to Silurian Longmaxi Formation in Anchang syncline of Zheng’an area in northern Guizhou were analyzed. The results show that：（1）The lithologies of Ordovician Wufeng Formation to Silurian Longmaxi Formation in Anchang syncline of Zheng’an area in northern Guizhou are mainly composed of siliceous shale and siliceous rock，and the pore types are mainly organic pores， intergranular pores，intragranular dissolved pores，intercrystalline pores，as well as bedding fractures，structural fractures and micro-fractures. The total organic carbon（TOC）content in rocks ranges from 0.34% to 6.65%， with an average of 3.69%. It shows an overall trend of first increasing and then decreasing from bottom to top in the vertical direction. On the plane，it is higher in the syncline core and decreases in a circular band. The mass volume of gas in the rock core ranges from 1.6 to 6.2 m3/t，with an average of 3.9 m3/t. The total gas content of Longmaxi Formation increases vertically with depth，and gradually decreases from the middle of the syncline to the north and south ends in the plane，and from the syncline core to the two sides. The overall brittleness index of minerals is relatively high，indicating good fracturing ability.（2）The Wufeng Formation to Longmaxi Formation in the study area has a unique geological background of“shelf margin，reformed residue，and shallow syncline burial”. Its favorable sedimentary environment and paleoproductivity laid the foundation for shale gas enrichment and accumulation，good preservation conditions avoided the large-scale escape of natural gas in shale reservoirs，and the overlying Xintan Formation and the underlying Baota Formation formed a sealing combination of“upper cap and lower seal”.（3）The residual synclinal shale gas outside the basin is obviously enriched in the synclinal center， the core is a favorable location for shale gas accumulation，the low-angle reverse faults on both wings are also favorable enrichment areas for shale fas，and the development of micro-fractures is favorable for shale gas accumulation and stable production. Therefore，the core site of“wide，gentle and deep”should be considered first for the deployment of wells in middle-shallow residual synclines.

PETROLEUM ENGINEERING AND OIL & GAS FIELD DEVELOPMENT

Calculation method for reasonable oil-water well ratio in the edge water drive offshore sandstone oilfield

CHEN Xiao, MIAO Yun, LI Wei, XIE Mingying, SHI Hao, WANG Weifeng

2025, Vol.37(1): 194–200 Abstract ( 64 ) PDF (3852 KB) ( 95 )

doi: https://doi.org/10.12108/yxyqc.20250117

Based on the calculation formulas for reasonable oil-water well ratio and reasonable formation pressure in oil fields considering the influence of edge water energy were derived through material balance and extreme value principles. This method was applied to reservoir A，which is developed in Neogene the Pearl River Formation of the Pearl River Mouth Basin. Meanwhile，the variation law of reasonable oil-water well ratio with water content in edge water reservoirs has been analyzed through the new method. The results show that：（1）Compare with natural energy supplementation，the new method can determine the reasonable oil-water well ratio for different water content stages of edge water reservoirs and the calculation results are closer to field practice.（2）The reasonable ratio of oil-water wells is subject to the comprehensive influence of multiple factors. The coefficient of edge water invasion has the most significant impact on it. The larger water invasion coefficient，the greater the calculation error of traditional methods.（3）To meet the conditions of high liquid yield and high utilization of natural energy，the current reasonable oil-water well ratio was 1.97 for reservoir A of the Pearl River Mouth Basin. Under this condition，the daily water injection volume was 18 878 m3/d. The natural water influx was 1 693 m3/d. The formation pressure was 21.27 MPa. The calculation results were similar to the numerical simulation results.