Lithologic Reservoirs

Based on analogies from modern sedimentary satellite imagery，integrated with core，well-logging， and production dynamic data，the microfacies types and distribution characteristics of anastomosing rivers from Member 4 of Miocene Guantao Formation in Lindong area of Dongying Sag were analyzed. The reservoir sandbody was characterized，and a multivariate classification model was established. The results show that：（1）The anastomosing rivers in Lindong area can be divided into four microfacies： channel，natural levee，crevasse splay，and interchannel. In plan view， channel sandbodies exhibit an anastomosing network with low-sinuosity single channel segments， while confluences form moderate-to-high-sinuosity interconnected channels. In crosssection，sandbodies exhibit flat-topped and convex-based lenticular geometries，locally superimpose to form “sand walls”，exceeding 10 m in thickness. Natural levee sandbodies distribute on both sides of the river channels， with width of 18-430 m；in cross-section，display as wedge-shaped， with thickness less than 3 m. Crevasse splays develop sparsely，showing fan-shaped geometry in plan view，and in cross-section they form wedgeshaped thin layers， with thickness of 3-5 m. Interchannels extensively develop，accounting for 43%-70% of the study area.（2）Guantao Formation anastomosing rivers share similarities with the modern Nenjiang anastomosing river in terms of sedimentary environment，microfacies，hydrodynamics，and geomorphic evolution. Its channel sandbodies exhibit NW-SE direction of long-axis and display contiguous distribution with favorable continuity in plan view.（3）Single channels in the study area are small-scale，with width of 65-170 m and thickness less than 5 m，developing two types of architectural splicing patterns： channel-channel connectivity and channel-natural levee contact.（4）Production performance post-waterflooding and tracer dynamic analyses show that singlechannel sandbodies are developed in injection-production well along the NW-SE provenance direction，preferential waterflooding/tracer migration paths aligned with paleochannel orientation. Interchannel mudstones and lowpermeability natural levees act as flow barriers.

Reservoir formation conditions and exploration potential of Jurassic coal-rock gas in Qaidam Basin

TIAN Jixian, SHI Zhenghao, LI Jian, SHA Wei, JIANG Zhengwen, YANG Lei, YU Xue, PU Yongxia

2025, Vol.37(4): 17–25 Abstract ( 27 ) PDF (32143 KB) ( 45 )

doi: https://doi.org/10.12108/yxyqc.20250402

The exploration of Jurassic coal-rock gas in Qaidam Basin is in its early stage and has great exploration potential. Based on outcrop，drilling，seismic，and experimental analysis data，the distribution and quality characteristics of Jurassic coal rock were analyzed. The reservoir formation conditions were evaluated from four aspects： gas generation capacity，reservoir conditions，reservoir-cap assemblages，and gas-bearing properties. And reservoir formation models and resource potential were clarified. The results show that：（1）Jurassic coal rocks in Qaidam Basin are mainly distributed in Middle-Lower Jurassic Hushan Formation，Xiaomeigou Formation，and Dameigou Formation，with large thickness，wide distribution area，distributed from the surface in front of the mountain to the hinterland of the basin（buried at a depth of nearly 10 000 meters），strong gas generation capacity，providing good material foundation for the generation of coal rock gas. The coal rocks are mainly semi-bright coal and bright coal，with high vitrinite content（average volume fraction of 65.5%）. Characterized by high volatile matter and ultra-low moisture content ，the coal rocks have good quality（. 2）The lithologies of Jurassic coal seams in the research area are mainly mudstone，carbonaceous mudstone，and coal rock， with coal rock thickness of 1.0-80.0 m，an average TOC value of 57.60%，an average hydrocarbon generation potential（S1+S2） of 79.9 mg/g，hydrogen index reaching up to 165 mg/g，and burial depth of over 4 500 m in the basin hinterland. Ro is generally greater than 1.5%，and can reach up to 3.5%，indicating strong overall gas generation capacity.There are four types of pores，such as pores，microcracks，residual tissue pores，and mineral intergranular pores. High proportions of meso-macropores provide reservior conditions rich in free gas. Two types（coal slurry and coal sand）of reservoir-cap assemblages are formed in the lacustrine sedimentary environment（3）Jurassic coal seams in the research area develop two types of reservoir formation models： self-generation and self-storage， and lower-generation and upper-storage. The preliminary estimate of coal-rock gas resources is 2.32×1012 m3， with great exploration potential. Middle Jurassic in Yuka-Jiulongshan area and Lower Jurassic in Niudong-Lenghu area represent the most favorable exploration targets for deep coal-rock gas in Qaidam Basin.

Characteristics and exploration prospects of coal-rock gas reservoirs in Permian Longtan Formation in Suining-Hejiang area，Sichuan Basin

WANG Qing, TIAN Chong, LUO Chao, ZHANG Jingyuan, YANG Xue, WU Wei, TAO Xiayan

2025, Vol.37(4): 26–37 Abstract ( 21 ) PDF (22062 KB) ( 47 )

doi: https://doi.org/10.12108/yxyqc.20250403

Coal-rock gas in Permian Longtan Formation of Sichuan Basin exhibits a wide distribution range， with great resource potential. Based on macro-distribution of coal rock，and comprehensive analysis of organic geochemical，physical property-pore structure，and isothermal adsorption experiments of rock cores，the reservoir characteristics of coal-rock gas in Permian Longtan Formation of Suining-Hejiang area were studied，and its exploration prospects were evaluated. The results show that：（1）Coal rock of Longtan Formation in Suining-Hejiang area is deposited under shore-swamp environment. The coal rock is characterized by large total thickness， multiple layers， and thin single layer thickness. The main coal group is C17-20 coal， with a thickness of 1.0-5.9 m， and the single layer thickness of the main coal seam is 1.0-4.5 m.（2）Coal rock in the study area is mainly bright coal and semi-bright coal， with good coal structure， high vitrinite content and low ash content.（3）The physical properties of the coal-rock reservoirs are good，and the organic pores and inorganic pores are synergistically developed. A lot of micropores and microcracks are beneficial to the adsorption of coal-rock gas， reservoir transformation and gas seepage. The total gas content of coal rock in the study area is high，with a mass volume of 16.4-30.5 m3/t，and of which free gas accounts for 25.8%-37.1% of the total gas content. Within a certain range of buried depth， both the total gas content and free gas proportion increase with the increase of buried depth.（4）The coal-rock reservoir-cap assemblages of Longtan Formation in the study area develop well， mainly develop coal-mud assemblage and coal-sand assemblage. The coal-mud assemblage is with the best reservoir formation condition. Highyield wells have confirmed that the study area has good exploration prospects for coal-rock gas exploration. It is predicted that the favorable area of coal-rock gas is 6 431 km2， with the resource of 2.53×108 m3.

Multi-level sparse regularization inversion method for seismic frequency division： A case study from the second member of Paleogene Dongying Formation in Shijiutuo Uplift，Bozhong Sag

WANG Jian, WU Yaning, WANG Tao, JIA Wanli, BAO Yifan, LIU Lifeng

2025, Vol.37(4): 38–49 Abstract ( 14 ) PDF (36026 KB) ( 31 )

doi: https://doi.org/10.12108/yxyqc.20250404

Conventional inversion techniques yield low prediction accuracy for reservoirs with low well density， thin single-layer thickness，and strong heterogeneity. A multi-level sparse regularization inversion method based on seismic frequency division was proposed using matching pursuit and Wigner-Ville distribution time-frequency methods，sparse theory，and Bayesian theory. The model data was tested and the inversion method was applied in the reservoir prediction of the second member of Dongying Formation in Shijiutuo Uplift of Bozhong Sag.The results show that：（1）The main idea of seismic frequency division multi-level sparse regularization inversion is to use the Matching Persuit Wigner-Ville distribution technique（MP-WVD）to decompose seismic signals into large，medium，and small scale frequency bands. Based on that，Bayesian theory is employed to construct a multi-scale sparse inversion objective function，applying L2，L1，and L0 norm constraints to the large，medium，and small scale inversion processes，respectively.A hierarchical iterative strategy is adopted： the largescale inversion results as prior constraints for the medium-scale inversion，and then the medium-scale inversion results as prior constraints for the small-scale inversion，with the final inversion result derived from the smallscale inversion.（2）The model data testing results show that： MP-WVD time-frequency spectrum exhibits stronger energy concentration than continuous wavelet transform（CWT）and S-transform time-frequency spectra， with higher resolution in both time and frequency directions，effectively overcoming the cross-term interference issue present in the WVD transform.（3）The application of seismic frequency division multi-level sparse regularization inversion in the reservoir waves of the second member of Paleogene Dongying Formation in Shijutuo Uplift of Bozhong Sag shows that： the results of the P-wave impedance inversion are in good agreement with the sonic log-derived acoustic impedance. It also provides higher resolution than the sparse pulse inversion results， with superior vertical resolution， offering more accurate characterization of thin layers.

Reservoir characteristics and main controlling factors of carbonate rock of Cambrian Xiannüdong Formation in Micangshan area， northern Sichuan Basin

XING Qian, LI Yangfan, LI Xiang, WAN Ziqian, LI Yalan

2025, Vol.37(4): 50–62 Abstract ( 17 ) PDF (181380 KB) ( 47 )

doi: https://doi.org/10.12108/yxyqc.20250405

Cambrian marine carbonates in Sichuan Basin host high-quality source rocks and widely develop reservoirs，making resource potential there a key point for hydrocarbon exploration and development. The reservoir characteristics and main controlling factors of Cambrian Xiannüdong Formation in northern Sichuan Basin were systematically studied through sedimentology and geochemical analyses. The results show that：（1）During the sedimentory period of Cambrian Xiannüdong Formation in northern Sichuan Basin， a sedimentary system of mixed tidal flat-platform depression-carbonate platform was developed. The carbonate dominated reservoir rocks are oolitic limestone and microbial rocks，all of which have undergone varying degrees of dolomitization. The reservoir spaces are intergranular（dissolution）pores，intragranular（dissolution）pores，intercrystalline（dissolution）pores，dissolution pores，fractures，and biological skeleton pores. The regional physical property data show that Xiannüdong Formation in northern Sichuan Basin is a low-porosity and low-permeability porous reservoir.（2）With the continuous development and northward migration of the paleo-rift zone in central and northern Sichuan Basin，Xiannüdong Formation inherited the paleogeographical framework of low in the center（rift zone）and high on both sides，and developed a sedimentary system of mixed tidal flat-platform depressioncarbonate platform. The geomorphology of the paleo-rift and paleo-uplift controlled the distribution of favorable facies zones and the development of high-quality reservoirs.（3）The sedimentary environment of high-energy oolitic shoals and microbial reefs（mounds）is the material foundation for the reservoir formation in the study area. Oolitic limestone，oolitic dolomite，and dolomite are relatively high-quality reservoirs，with stable layer distribution and wide lateral distribution，preserving a small amount of primary pores and developing a large number of dissolution pores and intergranular pores.（4）Multi-stage dissolution and dolomitization are the primary drivers of reservoir space creation in the study area. The dissolution of atmospheric freshwater during the syndiagenetic stage and the dissolution of pore fluids during the diagenetic stage，create intergranular dissolution pores，intragranular dissolution pores，intercrystalline dissolution pores，and dissolution fractures.The formation of microcrystallinefine crystalline anhedral dolomite by syndiagenesis seepage-reflux mechanism，the selective replacement of oolites by powder-crystalline rhombic dolomite developed in shallow-buried mixed-water condition，the fog-centered bright-edged euhedral dolomite and coarse-crystalline saddle dolomite formed in deep buried or tectonic hydrothermal environments， develop a large number of pores and promote the formation of reservoir space.

Characteristics and hydrocarbon accumulation process of karst reservoir in the third member of Permian Maokou Formation，Hechuan-Tongnan area，central Sichuan Basin

WANG Jingzhao, JIN Wei, CHANG Lipeng, DONG Zhongliang, WANG Gaowen

2025, Vol.37(4): 63–72 Abstract ( 19 ) PDF (9450 KB) ( 30 )

doi: https://doi.org/10.12108/yxyqc.20250406

Based on the latest core well data， characteristics and hydrocarbon accumulation process of karst reservoir in the 3rd member of Maokou Formation（Ma3）in Hechuan-Tongnan area of central Sichuan Basin were determined through analysis of carbonate rock petrology， inclusion petrography and fluid inclusion homogenization temperature. The controlling factors of reservoir development was clarified，and favorable exploration areas were preliminarily predicted. The results show that：（1）In Hechuan-Tongnan area，the reservoir lithology of Ma3 is dominated by bright crystalline-muddy microcrystalline bioclastic limestone，with reservoir spaces characterized by structural enlarged dissolution fracture-vug and pore. Formed fracture-vug karst reservoir is characterized by ultra-low porosity and ultra-low permeability，mainly composed of fractures，with an average porosity of 2.04% and an average permeability of 0.210 mD.（2）Three stages of mineral filling are developed in Ma3 of the research area，from early to late，which are intergranular cemented powder-fine crystal calcite，fracture-vug filling finemedium crystal calcite，and fracture-vug filling medium-coarse crystal calcite. The homogenization temperatures of fluid inclusions developed in the three stages mineral filling are 90-106 ℃，111-136 ℃ and 173-193 ℃，respectively. There are three stages of hydrocarbon filling and accumulation，including the Late Triassic paleo-oil reservoir formation period，early Jurassic paleo-hydrocarbon reservoir formation period，and Middle-Late Jurassic cracked paleo-gas reservoir formation period.（3）The development of karst reservoir in Ma3 is jointly controlled by epigenetic karstification and tectonic fracture activity. The favorable area of karst and tectonic overlap in reservoir development is 2 139 km2， mainly distributed in the central part of the study area.

Multi-phase fluid activities and hydrocarbon accumulation process of Permian Qixia Formation，southwestern Sichuan Basin

YAN Weitao, LIAO Yun, HUANG Wenming, ZHANG Benjian, HU Xin, LI Wenzheng, WU Juan, DENG Bin

2025, Vol.37(4): 73–83 Abstract ( 15 ) PDF (5309 KB) ( 21 )

doi: https://doi.org/10.12108/yxyqc.20250407

Based on core observation，thin section identification，cathodoluminescence analysis，fluid inclusion testing，and U-Pb dating technology，the characteristics of petrology and fluid activities of Middle Permian Qixia Formation in southwestern Sichuan Basin were analyzed.The mineral filling sequence and stages of hydrocarbon accumulation were systematically revealed，and the reservoir formation models were clarified.The results show that：（1）The reservoirs of Permian Qixia Formation in southwestern Sichuan Basin mainly distribute in the Qi-2 Member，mainly composed of fractured-vuggy dolomite reservoirs formed through dissolution modification，followed by limestone reservoirs. The reservoir space is predominantly composed of inherited dissolution pores and fractures，which are mostly filled with calcite（2）Qixia Formation reservoirs in the study area exhibit three stages of mineral filling within the pores and cavities，sequentially developed as follows： The first stage is fine-medium crystalline dolomite（Late Permian，253.0±12.0 Ma），characterized by the development of saline fluid inclusions，reflecting low-temperature hydrothermal activity during Late Permian tectonic uplift. The second stage is saddle shaped dolomite（Early Triassic，244.2±9.5 Ma），coexisting with medium to high maturity blue-green fluorescent hydrocarbon inclusions and saline fluid inclusions，with homogenization temperature of 110-115 ℃， indicating hydrothermal fluid and crude oil joint filling during the early stage of Indosinian movement. The third stage is medium-crystalline calcite（Late Jurassic，158.0±38.0 Ma），accompanied by high maturity blue fluorescent oil inclusions and high-temperature saline fluid inclusions，with homogenization temperature of 180-185 ℃，corresponding to the secondary migration of deep crude oil driven by Yanshanian tectonic thermal events. （3）Qixia Formation hydrocarbon reservoir in the study area are mixed-source supply of hydrocarbons formed by two sets of source rocks from Cambrian Qiongzhusi Formation and Middle Permian. The hydrocarbon accumulation process have experienced two key charging stages，namely the initial charging of hydrocarbons in Early Triassic to form the paleo-oil reservoir and the re-charging of deep crude oil in Late Jurassic to adjust and shape the paleo-oil reservoir.

Distribution law of remaining gas in condensate gas reservoirs in fault-controlled body of No. 4 fault zone in Shunbei Oilfield， Tarim Basin

JIANG Shan, TANG Yongjian, JIAO Xiarong, LI Wenliang, HUANG Cheng, WANG Ze

2025, Vol.37(4): 84–94 Abstract ( 10 ) PDF (6989 KB) ( 23 )

doi: https://doi.org/10.12108/yxyqc.20250408

Carbonate condensate gas reservoirs in Ordovician fault-controlled bodies of No. 4 fault zone in Shunbei Oilfield of Tarim Basin are with low recovery efficiency and rapid decline in formation pressure. The characteristics of remaining gas distribution and main controlling factors of Ordovician condensate gas reservoirs in No. 4 fault zone of Shunbei Oilfield were studied by numerical simulation methods， and the remaining gas distribution patterns of condensate gas reservoirs were summarized. The results show that：（1）Shunbei Oilfield has developed various small-scale strike-slip fault zones， which have formed fault-controlled reservoirs with relatively large burial depths. The effective storage space is mainly composed of fault cavities and fractures. Fault-controlled reservoirs are distributed in strip along the strike-slip fault zone， and develop multiple sets of fracture-cavity assemblages consisting of an orderly arranged of bedrock-fracture zone-cave zone-fracture zone-bedrock zone in the direction vertical to the fault zone，known as grid cluster structure.（2）The remaining gas in the reservoirs developed by a single well in the study area has sporadically distributed. When two fault surfaces of the reservoirs are not connected，the condensate gas from one fault surface is utilized while the other surface forms remaining gas. When the reservoirs consist of multiple isolated fault-controlled bodies， the remaining gas distribute in blocks.When the reservoirs are strongly affected by bottom water， the remaining gas is sealed off by the bottom water and distribute at the top of the reservoir. The remaining gas in the reservoirs developed by multi-well has the distribution characteristic of being patchy.When there are obvious high-speed gas drive channels within the reservoir， there is a large amount of trapped remaining gas along the channel edges.When the connectivity between injection and production wells is good， the injected gas advances in a piston manner， with remaining gas distributed around the production wells in sheet shape. The distribution of remaining gas from single well development is mainly controlled by geological factors and hydrodynamic conditions， while that from multi-well development is primarily influenced by injection and production conditions as well as geological factors.（3）The distribution of remaining gas in fault-controlled condensate gas reservoirs in the study area is characterized by seven models，which are isolated type，structural control type，sealing plugging type， bottom water plugging type of single wells， and isolated type， trapped near gas drive channels type， and injection-production control type of multi-well.

Sand control patterns of fault-landforms-sedimentary slope break and their significance for oil and gas exploration： A case study of the northern section of Baochu slope zone in Xihu Sag，East China Sea Basin

ZHENG Xin, JIANG Donghui, LI Kun, ZHUANG Jianjian, ZHANG Chuanyun, YANG Chao, YUAN Zhongpeng, WANG Jiaqi

2025, Vol.37(4): 95–104 Abstract ( 8 ) PDF (49951 KB) ( 41 )

doi: https://doi.org/10.12108/yxyqc.20250409

Sequence characteristics and structural combination characteristics of faults of the oil and gas bearing strata of Paleogene Pinghu-Baoshi Formation in the northern section of Baochu slope zone of Xihu Sag in East China Sea Basin were studied by using drilling core，logging and 3D seismic data. The paleogeomorphology was restored through DepoSpace sedimentary domain modeling and sequence stratigraphic boundary difference method. Based on the dip attribute of paleogeomorphology，the types of slope breaks were quantitatively classified，and the sand control mechanisms of different types of slope breaks were explored. The results show that：（1）Paleogene Baoshi-Pinghu Formation in the northern section of Baochu slope zone in Xihu Sag was divided into three structural zones from west to east： the Jinlong Mountain，Longyi Mountain，and Yuanlong Mountain. 7 thirdorder sequences have been identified，with 3 in Baoshi Formation and 4 in Pinghu Formation. In the research area，faults develop and can be divided into 5 fault combination patterns， such as sliding fault step，parallel fault step，graben barrier combination，flower like structure，and“Y” -shaped combination.（2）The slope break in the research area can be classified into fault slope break（level Ⅰ），landforms slope break（level Ⅱ）and sedimentary slope break（level Ⅲ）. The sand control mechanisms of the 3 types of slope break are different. Fault slope break is significantly affected by structural fault，landforms slope break is affected by both structural bending and sedimentary transformation，while sedimentary slope break is mainly affected by sedimentary erosion. （3）4 types of sand control patterns develop in the research area，including fault-landforms slope break broom shaped sand control pattern of the graben barrier fault combination of Jinlong Mountain，landforms-sedimentary slope break sand control pattern of Longyi-Yuanlong Mountain，multi-stage broken step fault slope break sand control pattern of Longyi-Yuanlong Mountain，parallel fault trough fault slope break sand control pattern of Jinlong-Yuanlong Mountain.（4）In the research area， the slope breaks control the development of sedimentary bodies. The footwall of level Ⅰ slope breaks often develop landslide deposits with distant landslides，the footwall of level Ⅱ slope breaks develop steep slope deposits，and the footwall of level Ⅲ slope breaks develop gentle slope deposits. Branch waterways often flow through the area with smaller slope angles on level Ⅱ and Ⅲ slope breaks， and they are prone to form slope fans at the foot of level Ⅰ and Ⅱ slope breaks when flow through them.

Fault development characteristics and controlling on hydrocarbon accumulation of medium-shallow layers in Yuzijing area of southern Songliao Basin，NE China

ZHANG Ziwei, LIU Junqiao, LI Jiaona, HU Xinlei, WU Hao, LYU Yanfang, JIANG Fei

2025, Vol.37(4): 105–114 Abstract ( 11 ) PDF (45013 KB) ( 39 )

doi: https://doi.org/10.12108/yxyqc.20250410

Petroleum resources in southern Songliao Basin mainly distribute in oil-bearing series in mediumshallow layers，and faults are the primary migration pathways for vertical multiple layers hydrocarbon enrichment. Fault development characteristics and their controlling on medium-shallow layers of southern Songliao Basin was studied based on 3D seismic interpretation，drilling analysis data and distribution characteristics of oil and gas reservoirs. The results show that：（1） During the fault-depression stage of Songliao Basin ， the faults exhibit large-scale and tense activity，mainly composed of tensional normal faults. The internal structural style of the fault intensive zone in the depression stage inherits the basic pattern of the fault-depression stage，profiles appear V-shaped and stepped ，showing typical characteristics of tension and torsion. During the inversion stage， intense folding，uplifts，and tectonic inversion were generated，and reverse faults were developed. Oil-source faults can be classified as segmented growth fault and through-going fault.（2）Hydrocarbon migration through faults includes four forms： vertically upward along the fault，vertically downward along the fault（backflow transport），crossing the fault plane（lateral transport），and along the fault direction. In Fuyu oil layer， hydrocarbon migration is dominated by lateral transport and backflow transport，controlled by the fault-displaced formation thickness and sand to mud ratio.Lateral transport forms FⅠ and FⅡ oil group in upper Fuyu oil layer，with minority hydrocarbon transported to FⅢ oil group. Backflow transport is suitable for segmented growth oil-source faults，controlling hydrocarbon distribution across all four oil groups of Fuyu oil layer（. 3） In Gaotaizi oil layer and Putaohua oil layer，hydrocarbon migration is dominated by upward and lateral transport. The oil layers formed by upward transport widely distribute，while the oil layers formed by lateral transport mainly distribute within the fault zone.

Characteristics and resource potential of source rocks of Carboniferous Shiqiantan Formation in Shiqiantan Sag，eastern Junggar Basin

LI Zhenming, JIA Cunshan, WANG Bin, SONG Zhenxiang, QIU Qi, WANG Jiyuan, XU Chenjie, CUI Yuyao

2025, Vol.37(4): 115–126 Abstract ( 9 ) PDF (18401 KB) ( 27 )

doi: https://doi.org/10.12108/yxyqc.20250411

Several wells in Shiqiantan Sag of eastern Junggar Basin have obtained industrial oil and gas flow， which shows good exploration potential. The organic matter type，abundance，maturity，sedimentary environment and parent material of Carboniferous source rocks in Shiqiantan Sag，eastern Junggar Basin were analyzed based on organic petrology characteristics，pyrolysis parameters，and biomarker characteristics. The hydrocarbon generation potential of Shiqiantan Formation source rocks was evaluated through simulation experiment for hydrocarbon-generating. The controlling factors for the development of effective source rocks were identified， the distribution range of large-scale source stoves was delineated，and the resource quantity was calculated. The results show that：（1）The kerogen macerals of Carboniferous Shiqiantan Formation in Shiqiantan Sag，Junggar Basin are mainly vitrinite and inertinite，and the pyrolysis parameters and stable carbon isotopes have the characteristics of type Ⅱ-Ⅲ. The organic matter abundance is relatively high，with an average pyrolysis TOC value of 2.79%，an average hydrocarbon generation potential value of 0.96 mg/g，and vitrinite reflectance（Ro）ranging from 0.70% to 1.66%，all of them have entered the hydrocarbon generation threshold，and the deep subsag area has reached the stage of condensate oil-wet gas. The edge of the sag is deposited in a weakly reduced to weakly oxidized freshwater environment，and the parent material is mainly composed of higher plants，while the center of the sag is a reduced brackish water environment and the parent material is mainly a mixture of higher plants and aquatic organisms.（2）Controlled by the maturity and quality of the original samples，the hydrocarbon yield ratio of Shiqiantan Formation source rocks in a semi-closed system is relatively lower than previous research results. Combined with the theory of kerogen hydrocarbon generation，it is believed that the peak value of the original oil generation yield of the source rocks is about 150 mg/（g·TOC），and the peak value of the original gas generation yield is about 250 mg/（g·TOC）.（3）The tectonic activity and sedimentary background control the development and distribution of effective source rocks. The thickness of the source rocks in the center of the sag can be 500 m，and the TOC value can be up to 3.0%. The maximum oil generation intensity in the center of the sag can be over 500×104 t/km2，and the maximum gas generation intensity can be over 150×108 m3/km2. There are about 6 600×104t oil resources and 730×108 m3 natural gas resources in place of Shiqiantan Formation，which has the potential to form medium-sized oil and gas fields，and it exhibits target direction and successor field of Carboniferous oil and gas exploration in eastern Junggar Basin.

Geophysical identification and distribution prediction of weathered crust reservoirs in Lower Paleozoic of Longdong area，Ordos Basin

WANG Yonggang, DU Guanghong, HE Run, QU Chang, SHE Yuwei, HUANG Cheng

2025, Vol.37(4): 127–135 Abstract ( 15 ) PDF (41603 KB) ( 19 )

doi: https://doi.org/10.12108/yxyqc.20250412

Based on core data，well logging and seismic data，the well logging response and seismic reflection features of weathered crust reservoir of Lower Paleozoic in Longdong area of Ordos Basin were analyzed. Using impression method and seismic image enhancement， the paleogeomorphology features， fault-fracture system characteristics and the spatial distribution of weathered crust reservoir in pre-Carboniferous of the study area were clarified. The results show that：（1）The reservoir lithology in Longdong area mainly composed of mud crystalmicrocrystalline dolomite ， with an average porosity of 4.44% and an average permeability of 0.29 mD， belonging to tight reservoir. Based on genesis，they can be clasified into 3 types such as fracture-dissolved pore， fracture-dissolved vug，and dissolved pore，with fracture-dissolved pore as the main type.（2）Different types of reservoirs of the study area exhibit significant variations in well logging response and seismic reflection： fracturedissolved pore and dissolved pore display high acoustic transit time，high neutron， low resistivity，low gamma ray，and low density，and dark spots can be seen in imaging logging. However， imaging logging of fracturedissolved pore reservoirs shows high dip angle or reticular dark bands，and seismic profiles exhibit weak amplitude，high frequency，and discontinuous reflection characteristics. The seismic events has“truncation”feature. While dissolved pore reservoirs have strong continuity，medium-weak amplitude，and medium frequency reflection characteristics on seismic profiles，and the“truncation”feature is not obvious.The amplitude variation of fracture-dissolved vug reservoirs is small on conventional logging curves，and irregular intermittent dark bands are observed on imaging logging. On seismic profiles，they exhibit high-frequency，strong amplitude，and continuous reflection，and the seismic events has“truncation”feature.（3）The pre-Carboniferous paleogeomorphology of the study area can be classified into 3 subunits： karst highlands，karst slopes，and karst basins. Fracturedissolved pore and fracture-dissolved vug reservoirs are mainly sporadically distributed in a strip like along the peripheries of the karst highlands or slopes. The intersection area of NW and NEE faults serves as the primary development zone，while dissolved pore reservoirs are primarily found within karst basins. The weathered crust reservoirs developed at the tops of Ordovician Majiagou，Cambrian Sanshanzi Formation and Zhangxia Formation are distributed in a ring-shaped pattern along the inner side of structural closures. Based on comprehensive evaluation，12 favorable areas for gas-bearing weathered crust reservoirs of Class Ⅰ with an area of 208.47 km2 and 10 favorable areas of Class Ⅱ with an area of 745.45 km2 have been selected.

Crude oil filling characteristics and hydrocarbon accumulation model of the second member of Paleogene Kongdian Formation in the deep subsag zone of Cangdong Sag，Bohai Bay Basin

CHEN Jiaxu, CHEN Changwei, LIU Guoquan, ZOU Leiluo, DONG Xiaowei, LIU Chuan, YANG Fei, ZHONG Wei

2025, Vol.37(4): 136–146 Abstract ( 15 ) PDF (12726 KB) ( 23 )

doi: https://doi.org/10.12108/yxyqc.20250413

With the continuous improvement of exploration ，the exploration direction of Cangdong Sag in Bohai Bay Basin gradually convert from positive tectonic unit to the deep subsag zone，searching for oil reservoir in the deep subsag zone will be the trend for future exploration and development. Based on analysis of hydrocarbon generation evolution， such as crude oil filling time，filling intensity，and filling process of the source rocks in second member of Paleogene Kongdian Formation （Ek2）in the deep subsag zone of Cangdong Sag， hydrocarbon accumulation model in the deep subsag zone of the Cangdong Sag was discussed. The results show that：（1）The oil samples from the Ek2 reservoir in the subsag zone of Cangdong Sag mainly derived from terrigenous organic matter，deposited under brackish lacustrine with redox condition，and sourced from the Ek2 source rocks.（2）The Ek2 source rocks in the deep subsag zone of Cangdong Sag entered intense oil generation from the late Ek1 sedimentation to the sedimentary period of Dongying Formation.The large-scale crude oil filling period was the sedimentary period of Shahejie Formation. The GOI（oil inclusion abundance index）values of the Ek2 reservoir range from 60% to 90%，and the pressure coefficient of the reservoir was 0.99-1.59.（3）The hydrocarbon system in the deep subsag zone of Cangdong Sag is characterized by fast burial rate，early timings of hydrocarbon generation，and high intensity of crude oil injection. Under the background of stable tectonic and source-reservoir interbedded，crude oil is mainly injected from near source，which is conductive to the formation of large-scale lithologic reservoirs.

Characteristics of sequence stratigraphy and main controlling factors for reservoir development of Lower Ordovician in Xishui area， southeastern Sichuan Basin

CHEN Yuhua, SHI Zejin, LI Wenjie, YI Yongjie, LIU Heng, TIAN Yaming, TAN Qian

2025, Vol.37(4): 147–158 Abstract ( 11 ) PDF (71784 KB) ( 20 )

doi: https://doi.org/10.12108/yxyqc.20250414

Based on the observation of field outcrops and thin sections，the types of rock microfacies of Lower Ordovician Tongzi Formation and Honghuayuan Formation in Xishui area of southeastern Sichuan Basin were identified. The sedimentary environment was determined by rock microfacies assemblages，and the characteristics of sedimentary evolution were revealed. Controlling effects of sedimentary environment and different levels of sea-level changes on reservoirs were discussed. The results show that：（1）Thirteen rock microfacies types are developed in Lower Ordovician Tongzi Formation and Honghuayuan Formation in Xishui area of southeastern Sichuan Basin，which can be divided into five sedimentary subfacies： tidal flats，lagoons，shoals，intershoal seas， and intra-platform depressions.（2）There are three third-order sequences（SQ1-SQ3 from bottom to top）in Lower Ordovician Tongzi Formation and Honghuayuan Formation，each of which consists of one retrogradational and three progradational fourth-order sequences. During SQ1 period，the environment gradually changed from open platform to restricted platform，with three sedimentary sequences： shoals-intershoal seas，lagoonstidal flats-shoals，and tidal flats-shoals. During SQ2 period，it was restricted platform environment，with two sedimentary sequences： lagoons-shoals and lagoons-shoals-tidal flats. During SQ3 period，it was open platform environment，with three sedimentary sequences： shoals-intra-platform depressions，intra-platform depressionsshoals，and intershoal seas-shoals.（3）Shoals and tidal flats in the restricted platform of Lower Ordovician in the study area are the most favorable sedimentary subfacies for reservoir development. Influenced by the dissolution and dolomitization of syngenetic-early diagenetic stage under different levels of sea-level，multiple sets of reservoirs are vertically superimposed and concentratedly developed in the second to third progradational fourth-order sequences of SQ1 highstand systems tract and the first to third progradational fourth-order sequences of SQ2 highstand systems tract，especially in the upward-shallowing cycles where the shoals and tidal flats are superimposed in the restricted platform.The study areas can form large-scale reservoirs and has certain exploration potential.

Paleogeomorphological characteristics of Oligocene Dongying period in southern Liaozhong Sag and its control on sedimentary system

LIU Xiumei, XIN Renchen, LIU Hao

2025, Vol.37(4): 159–168 Abstract ( 9 ) PDF (59058 KB) ( 40 )

doi: https://doi.org/10.12108/yxyqc.20250415

Paleogeomorphology is the foundation of the study of sedimentary filling process and dynamic background in basins. Based on the data of core， well logging， master logging and 3D seismic， the structural sedimentology and seismic sedimentology were applied to reconstruct the paleogeomorphology and analyze the sedimentary facies of Oligocene Dongying Formation in southern Liaozhong Sag，and the control of paleogeomorphology on sedimentation was clarified. The results show that：（1）Dongying Formation in southern Liaozhong Sag develop four types of structural geomorphic units： uplift zone，slope zone，shallow subsag zone and deep subsag zone. The geomorphic units are controlled by fault slope-break zones，showing an overall feature of“east-west zoning and north-south blocking”.（2）Dongying Formation in the study area mainly develops braided river delta，meandering river delta，anastomosing river delta，sublacustrine fan and lake.The types and distribution of sedimentary facies are obviously controlled by paleogeomorphology： During the sedimentary period of ESTd3-ESTd2，the rifting process was strong. During the lacustrine expansion period，the Liaoxi low uplift and the south bulge rise were the main provenance areas，and the subsag area received near-source deposits，which controlled the development of braided river delta. During the sedimentary period of HSTd3，along with the elevation of lake level，the uplift area transformed into underwater low uplift，and shore-shallow lake beach-bar sand deposits were developed. During the sedimentary period of HSTd2-SQd1，the fault activity weakened，and the pre-existing paleo-uplift transformed into underwater low uplift. The two strip-shaped subsag zones in northeast-southwest direction provided important geomorphic background for the development of the distal meandering river delta.

Development characteristics and oil-gas accumulation condition of the aulacogen in Dnieper-Donets Basin

LI Gengtong, HE Dengfa

2025, Vol.37(4): 169–183 Abstract ( 7 ) PDF (17124 KB) ( 14 )

doi: https://doi.org/10.12108/yxyqc.20250416

The geological structure，formation and evolution of the aulacogen， and its control on the accumulation and distribution of oil and gas are the key issues in the study of rift basins，which are of great significance for deep and ultra-deep oil and gas exploration in craton basins. Based on the study of the geological structure and oil-gas geological conditions of the typical aulacogen in Dnieper-Donets Basin（DDB），combined with statistics of oil and gas fields in the basin， the oil-gas accumulation conditions of the DDB were explored by using seismic and drilling data. The results show that：（1）The syngenetic rift period in the DDB controlled the development of the source-reservoir combination.The folds and faults developed in the post-rift period are the key to the trap formation.The salt structures（salt diapir and salt flow movement，etc.）not only facilitate the migration and accumulation of oil and gas，but also ensure the sealing of the cap rock.There are two oil-gas accumulation models： fault-controlled oil（gas）migration and accumulation； salt structure-related oil（gas）accumulation.（2） The oil and gas resources in the basin are mainly stored in Carboniferous-Lower Permian.Horizontally controlled by faults，it is concentrated in the central fault zone of the basin，while it is more scattered in the north-south fault terrace zone. On the whole，oil and gas are distributed in a belt along the fault zone and its surrounding areas， showing the distribution characteristics of gas production in the southeast and oil production in the northwest. （3）The syngenetic rift period sedimentary structure of the aulacogen has great potential. The fault zone has strong controlling effects on hydrocarbon migration and accumulation， and spatial distribution of oil and gas. As an important area of deep to ultra-deep oil and gas exploration in craton basin，the aulacogen can be a key direction for future research and exploration.

PETROLEUM ENGINEERING AND OIL & GAS FIELD DEVELOPMENT

Oil-gas two-phase flow well testing model of horizontal well considering stress sensitivity and changing wellbore storage effects

NIE Renshi, ZHANG Yuqing, ZHOU Jie, YUAN Anyi, CAI Mingjin, ZHANG Tao, LU Cong, ZENG Fanhui

2025, Vol.37(4): 184–191 Abstract ( 16 ) PDF (2378 KB) ( 23 )

doi: https://doi.org/10.12108/yxyqc.20250417

In consideration of homogeneous reservoirs with stress sensitivity and changing wellbore storage effects of wellbore fluids，oil-gas two-phase flow well testing model of horizontal wells was established， typical well testing sample curves were drawn， and the sensitivity of related parameters was analyzed. The results show that：（1）Applying mathematical methods such as Laplace transform，Duhamel principle，perturbation transform and Stehfest numerical inversion to seek the solution of establied model， numerical solution in real space was obtained.（2）According to well testing theory curves obtained from established model，four main flow stages can be identified： changing well storage and skin effect influence stage，early-time radial flow stage，horizontal well linear flow stage，and late-time pseudo-radial flow stage.（3）Changing wellbore storage effects influence the early-time seepage stage， total conductivity capacity becomes greater as changing wellbore storage coefficient increase. The length of horizontal well influences the early-time linear flow stage， the discharge area enlarges and the bottomhole pressure drop amplitude decreases when the horizontal well becomes longer. The stress sensitivity influence the late-time radial flow stage，as the stress sensitivity coefficient increases，the drop amplitude in permeability also increases. The flow resistance of oil and gas two-phase flow increase while oil saturation become bigger.（4）Using established model to match the measured pressure buildup well testing data，with high fitting accuracy and good consistency between the interpreted reservoir parameters and geological knowledge， the accuracy of the established model is verified.

Experiment on damage of fracturing fluid in strong water-sensitive tight conglomerate reservoir

LIU Sai, LOU Qingxiang, LIU Wenwen, WEI Yun, ZHOU Hao, SHI Feng

2025, Vol.37(4): 192–200 Abstract ( 11 ) PDF (2732 KB) ( 13 )

doi: https://doi.org/10.12108/yxyqc.20250418

The distance and influencing factors of fluid resistance damage in strong water sensitive tight glutenite reservoirs，as well as the reservoir damage pattern after fracturing fluid invasion，were simulated and studied through a combined measurement method of long core，conventional core displacement experiments，and nuclear magnetic resonance. Based on the experiment，a multivariate nonlinear regression prediction model was established to quantitatively predict the degree of fluid resistance damage. The results show that：（1）Reservoir properties play a decisive role in the distance of liquid resistance damage. The lower the permeability，the smaller the distance of liquid resistance damage，and the more likely it is to cause reservoir damage. When the permeability is the same，gravel bearing coarse sandstone cores are more prone to liquid resistance damage than gravel bearing fine sandstone cores，but the difference is small. After fracturing fluid invades the formation，it has obvious“three zones”characteristics，such as“pressing into the liquid resistance zone”， “imbibition resistance zone”，and“original stratigraphic zone”. And“pressing into the liquid resistance zone”is the main factor controlling the degree of liquid resistance damage.（2）The physical properties，lithology，and content of expansive clay minerals together constitute threshold that determines the variability of liquid resistance damage in tight conglomerate reservoirs. The lower the permeability of similar multimodal sandstone cores，the closer the variability threshold of liquid resistance damage is near 1. The initial liquid resistance damage rate of bimodal gravel coarse sandstone cores is higher，which is relieved after soaking，and the initial damage rate of bimodal gravel fine sandstone cores is lower，which increases after soaking. The damage rate of cores with higher clay mineral content tends to shift towards 1.（3）The accuracy of the established multiple nonlinear regression prediction model for the degree of liquid resistance damage and porosity，permeability，and clay mineral content is greater than 80%，this model can be used for quantitative prediction of the degree of liquid resistance damage in oilfield exploration and development processes when there is a lack of core samples or when indoor displacement simulation experiments are difficult to conduct.