Lithologic Reservoirs

With the decarbonization of energy worldwide，natural hydrogen，as a primary energy，has gained widespread interest for its carbon-free emission and renewability. However，natural hydrogen has not yet to be explored in China. Through the review of the main geological settings and genesis of natural hydrogen with a high content（greater than 10%）discovered worldwide，the beneficial geological factors for natural hydrogen accumulation were systematically summarized，and the exploration prospects of natural hydrogen in China were evaluated based on the exploration and development status of natural hydrogen abroad. The results show that：（1）Global high content natural hydrogen is mainly developed in ophiolite belts，rift valley，and Precambrian iron-rich strata，mainly inorganic genesis，and the serpentinization process of iron-rich minerals is the most critical source of natural hydrogen，followed by degassing in the deep earth and water radiolysis.（2）High-quality hydrogen sources and good migration channels are the prerequisites for hydrogen enrichment，and the sealing ability of the cap rocks is a key element for the formation of natural hydrogen reservoirs. When natural hydrogen is used as associated gas，the traditional cap rocks can seal it，but may be difficult to form effective sealing when its content is high. The rift valley environment，ophiolite development areas，and the fracture-developed Precambrian iron-rich strata are the favorable areas for the exploration of hydrogen-rich gas reservoirs.（3）Many countries and regions abroad have formulated plans to explore，develop，and utilize natural hydrogen. Mali has realized commercial exploita‐tion of natural hydrogen，and the United States and Australia have also successfully drilled natural hydrogen ex‐ploration wells.（4）The areas with high hydrogen content in China are highly compatible with hydrogen-rich geological conditions，and the prospects of natural hydrogen exploration are good. The Tan-Lu fault zone and the peripheral rift basin areas，the Altyn fault zone and the basin areas on both sides，and the Sanjiang orogenic beltLongmenshan fault zone and peripheral basin areas have great natural hydrogen exploration potential. China should carry out the survey work of natural hydrogen as soon as possible，strengthen the research on hydrogen reservoir accumulation process and potential evaluation，and carry out research on exploration technology，ex‐traction and separation technology，and storage and transportation technology，to prepare technological reserves for large-scale development and utilization of natural hydrogen.

Heat transfer prediction of medium and deep coaxial casing based on BP algorithm

XIONG Bo, ZHU Dongxue, FANG Chaohe, WANG Shejiao, DU Guanglin, XUE Yafei, MO Shaoyuan, XIN Fudong

2024, Vol.36(2): 15–22 Abstract ( 193 ) PDF (1926 KB) ( 416 )

doi: https://doi.org/10.12108/yxyqc.20240202

By building a heat pump test bench and obtaining test data under multiple working conditions，a BP neural network coaxial casing heat transfer prediction model was established，and the simulation was carried out to predict the heat transfer of the coaxial casing. The results show that：（1）The heat pump system has the highest energy efficiency during stable operation at a water flow rate of 28 m3/h and a return water temperature of 10 °C， and the effective heat transfer of coaxial casing is 563 kW.（2）When the number of hidden layer nodes is 12，the BP neural network prediction model is optimal，with a maximum training mean square error（MSE）is 0.023%， and the basic structure of the optimal model is 9-12-1.（3）Comparing the simulation results of the predicted value and the test value of the coaxial casing，the average percentage error of the prediction of heat transfer of the coaxial casing of the BP neural network is 0.235%，and the prediction accuracy is 99.765%. The prediction model has high accuracy and reliability，and can accurately predict the change trend of heat transfer of coaxial casing，which has a wide range of application value for improving the energy efficiency and performance of heat pump systems.

Status and development trends of geothermal development and utilization in oilfields of China

WANG Shejiao, SHI Yizuo, FANG Chaohe, CAO Qian, REN Lu

2024, Vol.36(2): 23–32 Abstract ( 355 ) PDF (6672 KB) ( 345 )

doi: https://doi.org/10.12108/yxyqc.20240203

Based on the current situation of geothermal development in China，the characteristics of geothermal resource occurrence and distribution，and the comparison of different geothermal development methods，the potential for the development and utilization of geothermal resources in oilfields was analyzed，and the develop‐ment trends of China’s geothermal industry，especially oilfield geothermal，were discussed. The results show that：（1）China has abundant geothermal resources，mainly consisting of medium to low temperature geothermal resources. Shallow geothermal resources are distributed nationwide. Medium to low temperature geothermal resources are distributed in sedimentary basins，southeastern coastal areas，and uplift mountainous areas，forming a large area of thermal reservoirs containing geothermal water at different depths，which are hydrothermal geothermal resources. High temperature geothermal resources are concentrated in southern Xizang，western Sichuan，western Yunnan and Taiwan. China’s shallow geothermal energy resources（shallower than 200 m） have an annual mining output of 7×108 tons of standard coal.（2）Due to the environmental and efficiency issues in the development and utilization of shallow geothermal energy，the efficiency issues of direct heat exchange in deep wells，and the technical bottlenecks in the development and utilization of dry hot rocks，medium to deep hydrothermal geothermal resources will be the most important and practical field for the development and utilization of geothermal resources in China today.（3）A series of key technologies have been developed in the geothermal development of oilfields，including geothermal resource exploration and evaluation，sandstone formation reinjection，renovation of abandoned wells into geothermal wells，and high-temperature drilling and completion， all of which have been successfully applied in large-scale geothermal development projects. Oilfields have abundant produced water resources that can be directly utilized，and a large number of abandoned or inefficient oil wells can be transformed into geothermal wells through technological transformation for geothermal resource development，thereby reducing geothermal development costs and improving the economic efficiency of geothermal projects.（4）In addition to being used for energy consumption replacement and clean heating in oilfields， oilfield geothermal energy has great potential for development in the fields of medium-low temperature geothermal power generation，the production of associated resources such as helium，heat storage in depleted hydrocarbon reservoirs，and carbon dioxide sequestration. The comprehensive development and utilization of geothermal energy is the main direction for the future development of geothermal energy in oilfields.

PETROLEUM EXPLORATION

Sedimentary model of sublacustrine fan of the third member of Paleogene Dongying Formation and large-scale oilfield discovered in western slope of Liaozhong Sag

NIU Chengmin, HUI Guanzhou, DU Xiaofeng, GUAN Dayong, WANG Bingjie, WANG Qiming, ZHANG Hongguo

2024, Vol.36(2): 33–42 Abstract ( 147 ) PDF (6759 KB) ( 223 )

doi: https://doi.org/10.12108/yxyqc.20240204

Through stratigraphic sequence research，paleogeomorphological restoration，zircon dating and seismic data analysis，the sublacustrine fan development model of the third member of Paleogene Dongying Formation（Ed3）in western slope of Liaozhong Sag was discussed from the aspects of source system，paleogeomorphology and slope break system and lake level change，and the reservoir characteristics and accumulation model were studied. The results show that：（1）The sand bodies of the sublacustrine fan in the western slope of Liaozhong Sag are characterized by a sand-rich model controlled by“source-slope break zone-lake level”. The sources are mainly from Yanshan fold belt，followed by Liaoxi uplift. Large-scale source supply and parent rock area of metamorphic rocks provide clastic materials and high-quality reservoir sand bodies for the formation of the sublacustrine fan. Sedimentary slope break zones control the unloading position of gravity flow in the sublacustrine fan， and the micro paleogeomorphic changes formed by the fault slope break zones control the direction of local sand body transport and the degree of differential enrichment. The coupling of lake level changes and source system changes has resulted in the repeated stacking and development of delta，lake，and sublacustrine fan sediments in space，providing good preservation conditions for the formation of lithologic traps.（2）The lithologies of the sublacustrine fan in Lvda10-6oilfield are mainly medium to fine grained feldspar lithic sandstone，with smaller particle size and mainly composed of gravity flow sedimentation. The pore types are mainly primary intergranular pores and dissolved intergranular pores，with a small amount of intragranular dissolved pores. The pore development is average and the connectivity is poor. The development of the sublacustrine fan has the characteristics of vertical multi-stage overlap and planar continuity. The middle fan subfacies of the sublacustrine fan located in the middle of the slope have obvious collapse deformation structures，making them the most favorable exploration facies zone.（3）The sublacustrine fan reservoir in Lvda 10-6 oilfield is a major discovery in the western slope of Liaozhong Sag shifted from structural trap exploration to lithological trap exploration，achieving a significant breakthrough in the exploration field of Paleogene sublacustrine fan type lithologic reservoirs in the slope zone of Bohai Oilfield，with 11 oil reservoirs and 9 gas reservoirs developed. The oil and gas reservoirs are mutually independent，with large reserves，high abundance，a proven oil equivalent of 3 000×104 t，good physical properties of crude oil and high production capacity for exploratory well testing. The reservoir accumulation model is a ternary coupling of“convergence ridge-source fault-parallel sand body”.

Accumulation conditions of natural gas of Cambrian Xixiangchi Group in high-steep structural zones，eastern Sichuan Basin

BAO Hanyong, LIU Haotian, CHEN Miankun, SHENG Xiancai, QIN Jun, CHEN Jie, CHEN Fanzhuo

2024, Vol.36(2): 43–51 Abstract ( 258 ) PDF (4915 KB) ( 364 )

doi: https://doi.org/10.12108/yxyqc.20240205

Baased on cores，well-log and seismic data，combined with seismic interpretation，balanced crosssection and inclusion detection techniques，the structural evolution history of the high-steep structural zones in eastern Sichuan Basin was restored，and the natural gas sources，migration，accumulation and preservation conditions in Pingqiao，Jiannan and Zilichang structures were analyzed. The results show that：（1）Single reverse fault on the eastern flank of Pingqiao faulted anticlinal trap in eastern Sichuan Basin caused a lateral conjunction between Longmaxi source rocks on the footwall and Xixiangchi reservoir on the hanging wall，which enables the migration of gas through the fault zone to the reservoir on the hanging wall and，with good transport conditions. The cap rocks of the trap are not damaged by faulting，and the preservation conditions are good，which is condu‐cive to gas accumulation.（2）Although multiple parallel reverse faults in the flank of Jiannan faulted anticlinal trap result in source-reservoir conjunction，the combination of multiple faults reduces the gas lateral migration ability，causing natural gas to fail to accumulate on a large scale.（3）The Zilichang faulted anticlinal trap has good source-reservoir assemblages and transport conditions，but the sealing ability of the cap rocks is poor， mostly reduced by faults. Drilling indicates that the reservoir is water-bearing.（4）The main controlling factors for the natural gas accumulation of Cambrian Xixiangchi Group in the high-steep structural zones of eastern Sichuan Basin are source-reservoir assemblages controlled by fault or fault combination，lateral transport conditions，and the sealing ability of of cap rocks.

Geological characteristics and enrichment conditions of shale oil of Jurassic Lianggaoshan Formation in Yilong-Pingchang area，Sichuan Basin

BAI Xuefeng, LI Junhui, ZHANG Dazhi, WANG Youzhi, LU Shuangfang, SUI Liwei, WANG Jiping, DONG Zhongliang

2024, Vol.36(2): 52–64 Abstract ( 242 ) PDF (39075 KB) ( 328 )

doi: https://doi.org/10.12108/yxyqc.20240206

Based on the geochemical and other experimental analysis results of drilling cores，combined withproduction testing data，the geological characteristics and enrichment conditions of shale oil of Jurassic LianggaoshanFormation in Yilong-Pingchang area of Sichuan Basin were studied，and favorable exploration areas weredivided. The results show that：（1）The Lianggaoshan Formation in Yilong-Pingchang area is a sediment during the third lacustrine basin expansion stage of Jurassic，which has undergone the sedimentary environment changes of shore lake to shallow lake in the lower member of Lianggaoshan Formation，deep lake to semi-deep lake and shallow lake in the middle and lower part of the upper member of Lianggaoshan Formation，and delta front and shallow lake in upper part of the upper member of Lianggaoshan Formation.（2）The shales of Lianggaoshan Formation can be divided into felsic shales，calcareous shales and clay shales，with a high abundance of organic matter，TOC values ranging from 0.50% to 3.39% and an average of 1.30%. The organic matters are mainly type Ⅱ1 and type Ⅱ2，with a high degree of thermal evolution and vitrinite reflectance（Ro）ranging from 1.00% to1.90%，and indicating a high mature to over mature stage.（3）The shales of Lianggaoshan Formation have good physical properties，and the reservoir space types such as inorganic pores，organic pores and structural fractures are developed. The porosity ranges from 0.48% to 7.17%，with an average value of 3.61%. The oil-bearing capacity is good and mainly composed of light components，which is scattered and punctate in the whole，and locally concentrated in clumps. The lower part of the upper member of Lianggaoshan Formation is more developed with organic-rich shale，which is the focus of exploration at present.（4）The weak subsidence environment during the transitional period of foreland basin，widespread distribution of deep lacustrine sediments，the high degree of thermal evolution and widespread development of micro-fractures are favorable for shale oil and gas enrichment in Lianggaoshan Formation. The central and southern regions of the study area are shale oil and gas potential zones，with shale reservoir thickness generally greater than 15m，TOC value greater than 1.50%，porosity greater than 4.00%，Ro greater than 1.30%. Lianggaoshan Formation has 26.75×108t of shaleoilresources and 1.72×1012m3 of shale gas resources，which is expected to become themain layer for increasing oil production in Sichuan Basin.

A random forests prediction method for gas saturation based on feature variable extension

GUI Jinyong, LI Shengjun, GAO Jianhu, LIU Bingyang, GUO Xin

2024, Vol.36(2): 65–75 Abstract ( 226 ) PDF (4739 KB) ( 400 )

doi: https://doi.org/10.12108/yxyqc.20240207

A data-driven approach was proposed to predict gas saturation based on random forests machine learning algorithm. This method was applied to predict and analyze gas saturation in a complex natural gas reservoir in western China from single well data and two-dimensional seismic data respectively. The results show that：（1）The method extracts the pre-stack seismic inversion results of three elastic parameters from the uphole trace（compressional wave velocity，shear wave velocity，and density）from well log data as basic feature variables. It employs the boundary synthetic minority oversampling technique to balance the basic feature variables and corresponding gas saturation samples，generates a series of extended variables by combining the extended elastic impedance with mathematical transformations，and then uses random forests to rank the importance of the feature variables for gas saturation prediction，finally selects feature variables with higher importance for gas saturation random forests training.（2）This method significantly reduces the manual workload for feature variables extraction andselection，effectively reduces information redundancy and training bias caused by imbalanced gas saturation samples，and effectively enhances the capability of the random forests algorithm in predicting gas saturation. （3）In practical applications，the predicted gas saturation using this method shows a high correlation coefficient of 0.985 5 with the gas saturation by log interpretation. In the case of two-dimensional data，it achieves higher accuracy in gas saturation prediction compared to using 11 conventional unbalanced elastic parameters as inputs for random forests.

Micro-pore structure characteristics of coal seams of Jurassic Yan’an Formation in Shenmu area，Ordos Basin

LI Qihui, REN Dazhong, NING Bo, SUN Zhen, LI Tian, WAN Cixuan, YANG Fu, ZHANG Shiming

2024, Vol.36(2): 76–88 Abstract ( 147 ) PDF (21348 KB) ( 227 )

doi: https://doi.org/10.12108/yxyqc.20240208

The pore structure of coal seams has a significant influence on the adsorption and diffusion of coalbedmethane. By means of gas adsorption，nuclear magnetic resonance and scanning electron microscopy，a multiscale and multi-parameter joint characterization of coal seam pore structure of Jurassic Yan’an Formation in Shenmu area of Ordos Basin was carried out to clarify the law of desorption，diffusion and seepage of coalbed methane. The results show that：（1）The coal seams of Yan’an Formation in Shenmu area have average porosity and permeability of 6.89% and 4.82 mD respectively，which belong to typical ultralow permeability coal seams， mainly developing calcite，clay minerals and amorphous components，of which the average mass fraction is 54.8%，35.7% and 15.0% respectively.（2）The main reservoir spaces of coal seams in the study area are narrow‐slit shaped and ink bottle shaped，including stomata，interchip pores，cell pores，mold pores and a few microcracks. The pores are dominated by mesoporous pores with pore size of 2-50 nm，followed by macropores，with the least amount of micropores. However，micropores are the main contributors to the specific surface area and pore volume of pores，indicating that coalbed methane is mainly adsorbed in micropores.（3）The pore throat size of coal seams in the study area varies in nano-and micron-level，the contribution to permeability mainly comes from submicron to micro pore throats，indicating that the pore connectivity in this range is good. The movable fluid saturation of coal samples is 38.72%-65.06%，the mercury removal efficiency is 0.84%-44.30%，the homogenization coefficient is 1.86-10.95，and the contribution of pore throat radius to permeability at different depths were significantly different，indicating strong heterogeneity in this area.

Reservoir accumulation characteristics of the second member of Sinian Dengying Formation in Penglai-Zhongjiang area，Sichuan Basin

CEN Yongjing, LIANG Feng, WANG Lien, LIU Qianyu, ZHANG Xinzhe, DING Xiong

2024, Vol.36(2): 89–98 Abstract ( 144 ) PDF (5627 KB) ( 222 )

doi: https://doi.org/10.12108/yxyqc.20240209

Based on the comprehensive analysis of drilling，logging，seismic and core data，the reservoir accumulation characteristics of the second member of Sinian Dengying Formation in Penglai-Zhongjiang area were systematically studied. The results show that：（1）During the sedimentary period of Sinian Dengying Formation in Sichuan Basin，with the intrusion of seawater，the ancient land was mostly submerged or eroded and flat‐tened，and the basin gradually evolved into a carbonate platform. During the sedimentary period of the upper submember of the second member of Sinian Dengying Formation（upper Sinian Deng-2 member），platform margin shoal facies and platform margin mound facies were developed in Penglai-Zhongjiang area，and they can be further divided into six subfacies：shoal core，shoal edge，intershoal sea，mound core，mound edge，and intermound sea，which are favorable facies zones for reservoir development.（2）The reservoirs in the upper submember of the second member of Dengying Formation in the study area are mainly composed of algal dolomite and algal sand clastic dolomite，with four types of reservoirs developed：residual intergranular pore and intergranular dissolved pore type，intragranular dissolved pore and algal framework pore type，fracture type and pore type. The thickness distribution characteristics of the reservoirs are consistent with the sedimentary facies distribution characteristics，and the reservoirs located in the mound/shoal core of platform margin have a larger cumulative thickness.（3）The natural gas in the upper submember of the second member of Dengying Formaiton in the study area is mainly derived from the source rocks of Qiongzhusi Formation. The source rocks have a large thickness，high organic carbon content and high degree of thermal evolution. The gas reservoir has good hydrocarbon sources and sealing conditions，with two types of good assemblages：“upper source，lower reservoir and upper cap”and “side source，side reservoir，and upper cap”.（4）The oil and gas filling in the study area mainly occurred during Triassic-Cretaceous，which is multi-stage quasi-continuous. The gas reservoirs of the upper submember of the second member of Dengying Formation mainly mainly went through four stages：the accumulation stage of paleoreservoirs from Ordovician to Silurian，the paleo-reservoirs failure stage from Silurian to Carboniferous，the hydrocarbon regeneration and reaccumulation stage from Permian to Triassic，and the crude oil cracking and gas generation stage from Triassic to Jurassic.

Provenance analysis of Upper Triassic Xujiahe Formation in northeastern Sichuan Basin

BO Shangshang, TIAN Jixian, LI Yaoliang, WANG Yetong, WANG Hao, SUN Guoqiang

2024, Vol.36(2): 99–112 Abstract ( 185 ) PDF (6361 KB) ( 189 )

doi: https://doi.org/10.12108/yxyqc.20240210

Based on field investigation of geological profiles，determination of heavy mineral content and detrital zircon U-Pb ages of key samples，combined with regional tectonic setting，age of peripheral geological bodies，stratigraphic distribution and palaeocurrent，the provenance of Upper Triassic Xujiahe Formation in northeastern Sichuan Basin was analyzed. The results show that：（1）The provenance of the sediments during the deposition period of Upper Triassic Xujiahe Formation in northeastern Sichuan Basin was derived from the northeast and southeast directions. The sediments of Xujiahe Formation in Qilixiang area were sourced from the Daba Mountain Geological Park in the northeastern piedmont zone and Heitianchi of Fuping Town in the southeastern piedmont zone，and subsequently deposited in the basin. During transportation from the piedmont zone to the basin，the sediment grain size underwent a change from coarse to fine，accompanied by an increase in the ZTR index.（2）The sediments of Upper Triassic Xujiahe Formation in the study area are mainly derived from the Qinling orogenic belt in northeast and the Jiangnan orogenic belt in southeast. The ages of detrital zircons are 210- 282 Ma，400-500 Ma，650-850 Ma，1 500-2 000 Ma，and 2 265-2 600 Ma，with peak values of ～213 Ma，～427 Ma，～725 Ma，～1 694 Ma，～2 352 Ma，respectively. The sedimentary age of Xujiahe Formation should be no earlier than ～213 Ma.（3）～213 Ma corresponds to the formation of Mian-Lue suture zone，and the provenance of this stage is mainly from the south Qinling orogenic belt. ～427 Ma corresponds to the subduction and closure of Shangdan Ocean，and the provenance of this stage mainly originates from the north Qinling orogenic belt. ～725 Ma should be related to the breakup of Rodinia supercontinent，and the western Jiangnan orogenic belt is the most likely source of this age. Zircons of ～1 694 Ma age may have been formed during the amalgamation and fragmentation of the Columbia supercontinent，and the zircons of this age are mainly derived from the southern margin of the North China Plate and the western section of the Jiangnan orogenic belt. The zircons of ～2 352 Ma account for a small proportion and are derived from retrocyclic provenance.（4）The reservoirs of Xujiahe Formation in the study area are mainly developed in the braided river delta-shore-shallow lake depositional system under the northeast and southeast provenance supply systems，and the provenance in the two directions controls the rock types and pore development of the reservoirs，making it a strong regional character.

Connectivity of fracture networks of Carboniferous carbonate reservoirs in North Truva Oilfield，eastern margin of Precaspian Basin

LI Changhai, ZHAO Lun, LIU Bo, ZHAO Wenqi, WANG Shuqin, LI Jianxin, ZHENG Tianyu, LI Weiqiang

2024, Vol.36(2): 113–123 Abstract ( 179 ) PDF (30137 KB) ( 214 )

doi: https://doi.org/10.12108/yxyqc.20240211

Based on the data of core，imaging logging，and fracture network modeling，topology theory was applied to evaluate the connectivity of fracture networks of Carboniferous carbonate reservoirs in North Truva Oilfield，the eastern margin of Precaspian Basin，and its impacts on oilfield development were analyzed. The results show that：（1）The types of fracture cutting of Carboniferous carbonate reservoirs in North Truva Oilfield of eastern margin of Precaspian Basin can be divided into high-high cutting，high-low cutting，and low-low cutting. The fracture cutting in the sublayers A2，A3，G1，G2，G3，and G4 is relatively developed and mainly distributed in the high structural parts.（2）The connectivity of fracture networks can be quantitatively evaluated through four parameters：the proportion of connected area，fracture fracture volume density，average length of fractures，and average number of nodes. The connected area，fracture volume density，and fracture type can be used to qualitatively analyze and name the fracture connected units. The sublayer A2 in the study area mainly develops low-low large connected units，high-medium large connected units，and high-high large connected units. （3）The coupling effect of fracture network connectivity and reservoir properties is the origin of oilfield water channeling，and fracture network connectivity is mainly related to fracture length and fracture volume density.

Architecture characterization and 3D geological modeling of Ordovician carbonate reservoirs in Shunbei No. 1 fault zone，Tarim Basin

CHEN Shuyang, HE Yunfeng, WANG Lixin, SHANG Haojie, YANG Xinrui, YIN Yanshu

2024, Vol.36(2): 124–135 Abstract ( 193 ) PDF (39333 KB) ( 278 )

doi: https://doi.org/10.12108/yxyqc.20240212

Based on the seismic，logging，core and dynamic data，the internal architecture of fault-controlled carbonate reservoirs in Shunbei No. 1 fault zone of Tarim Basin was divided. Based on the hierarchical division， a 3D geological model was established through seismic data attribute extraction and conversion，deep learning， target-based schematic point process simulation，and discrete fracture network simulation（DFN）. Numerical simulation of oil and gas reserves and reservoirs was carried out with the model，and the fitting results were compared with the actual production data. The results show that：（1）The Ordovician fault-controlled reservoirs in the study area were categorized into five levels，from large to small，including strike-slip fault-influenced zones， fault-controlled bodies，cave-like，intra-cave-like cluster-filling and fracture zones.（2）The strike-slip faultinfluenced zones has segmentation due to stress differences，which can be subdivided into extrusion section， pullout section and translation section. The fault-control bodies develop six kinds of planar combination styles， including fault intersection type and single-branch slip type in the pullout section，double-fault staggered type and double-fault intersection type in the translation section，and double-fault twisted type and double-fault intersection type in the extrusion section. The cave-like is characterized by bead-like reflections on the seismic section. The intra-cave-like is divided into fenestration and inter-fenestration（bedrock），and the fenestration can be further divided into clusters（breccia zones）and inter-clusters（fracture zones），and the whole is characterized by fenestration structure，with better physical properties of the clusters. The fracture zones are the main reservoir space for cave-like structures，which are more developed within clusters than between clusters，and more developed in Yijianfang Formation than in Yingshan Formation. High-angle fractures are mainly developed in Yijianfang Formation and Yingshan Formation，while horizontal fractures are mainly developed at the joints between the two.（3）The error between the oil and gas reserves predicted by the geological model and the geological analysis reserves is 1.75%. The simulated production well formation pressure and cumulative liquid production results of the model are highly consistent with production performance，with a fitting error of less than 10%.

Characteristics and diagenetic evolution of Permian pyroclastic reservoirs in Jianyang area，Sichuan Basin

ZHANG Wenbo, LI Ya, YANG Tian, PENG Siqiao, CAI Laixing, REN Qiqiang

2024, Vol.36(2): 136–146 Abstract ( 157 ) PDF (10571 KB) ( 213 )

doi: https://doi.org/10.12108/yxyqc.20240213

As important unconventional reservoirs，pyroclastic reservoirs are of great significance for increasing oil and gas storage and production. Based on core observation，thin section identification，QEMSCAN scanning， X-ray diffraction，physical property analysis，inclusion temperature and carbon and oxygen isotope analysis，the characteristics and diagenetic evolution of Permian pyroclastic reservoirs in Jianyang area of Sichaun Basin were systematically analyzed. The results show that：（1）The rocks of Permian pyroclastic reservoirs in Jianyang area are mainly composed of volcanic breccia lava，tuff lava and melt-bonded volcanic breccia，with overall good physical properties，porosity ranging from 0.78% to 32.00%，average of 16.67%，permeability ranging from 0.001 to 2.680 mD，average of 0.125 mD，belonging to high porosity and low permeability reservoirs. The reservoir space is dominated by secondary pores and fractures，including devitrified pores，matrix dissolved pores and dissolved fractures.（2）Various diagenetic processes are developed in the study area，including fusion， compaction，devitrification，cementation and dissolution. （3）The study area experienced three diagenetic stages：syndiagenetic stage，epidiagenetic stage and burial diagenetic stage. The diagenetic evolution was influenced by deep hydrothermal fluids，atmospheric fresh water and organic acid fluids. On the one hand，fluid activities cause the precipitation of hydrothermal minerals or carbonate cements，which has a destructive effect on reservoir physical properties. On the other hand，hydrothermal fluids promote oil and gas migration，and the dissolution and transformation of acidic fluids play a constructive role in the development of reservoir pores.

Sandbody superimposition patterns and oil and gas exploration significance of Permian Shanxi Formation in Daniudi gas field，Ordos Basin

LEI Tao, MO Songyu, LI Xiaohui, JIANG Nan, ZHU Chaobin, WANG Qiao, QU Xuejiao, WANG Jia

2024, Vol.36(2): 147–159 Abstract ( 191 ) PDF (10417 KB) ( 269 )

doi: https://doi.org/10.12108/yxyqc.20240214

The reservoir configuration of fluvial facies sand bodies is of great significance for the distribution of high-quality tight sandstone reservoirs in tight sandstone and natural gas development. Through field geological profiles and drilling cores observation，combined with logging and core analysis testing data，the sand body con‐figuration elements，stacking patterns and oil and gas development significance of tight sandstones of Permian Shanxi Formation in Da 12 well area of Daniudi gas field in Ordos Basin were studied. The results show that：（1）The Permian Shanxi Formation in the study area developed six-level composite braided flow zones and five-level single braided flow zone，the single braided flow zone includes river bed（distributary channel）and river diffuse，the mid-channel bar contains three-level accretion bodies and siltation layers.（2）The four-level floodplain deposits in the five-level single braided flow zone of braided river delta plain are more developed than the river diffuse in the braided river，and the siltation layer in the mid-channel bar is less developed.（3）The sand bodies in the single braided flow zone of the braided river in Shan 2-2 sub-member of Shanxi Formation are continuously deposited in a pattern of“channel to mid-channel bar”，with undeveloped shale and high degree of sand body stacking （mostly in composite stacking），good connectivity，and many high-quality reservoirs.（4）In the delta plain deposits of Shan 1 member and Shan 2-1 sub-member of Shanxi Formation，the river channels in the west have good connectivity，and the sand bodies are mainly composite and side-jointed superimposed，with good connectivity and production effects，while the sand bodies in the east are mainly of isolated and side-jointed styles，with low sand body drilling rate and low single well production.

PETROLEUM ENGINEERING AND OIL & GAS FIELD DEVELOPMENT

Flow unit division based on SSOM and its production application： A case study of sublacustrine turbidity channels of middle Es₃ in F oilfield，Bohai Bay Basin

WANG Ya, LIU Zongbin, LU Yan, WANG Yongping, LIU Chao

2024, Vol.36(2): 160–169 Abstract ( 147 ) PDF (4910 KB) ( 147 )

doi: https://doi.org/10.12108/yxyqc.20240215

Based on the classification of reservoir architecture，the relationship between seepage barriers and architecture interfaces of the sublacustrine turbidity channels of the middle third member of Paleogene Shahejie Formation（Es3）in F oilfield of Bohai Bay Basin was summarized，a supervised self-organizing map neural network algorithm was used to quantitatively evaluate flow units，and the distribution of flow units under the control of architecture models was clarified. The results show that：（1）The reservoirs of middle Es3 in F oilfield of Bohai Bay Basin can be divided into four types of flow units，namely type Ⅰ，Ⅱ，Ⅲ and Ⅳ.（2）The flow unit recognition results based on SSOM algorithm show high prediction accuracy，with an overall accuracy of 82.81% for 256 training samples and 80.91% for 110 testing samples，which can meet the needs of geological reservoir research. （3）Vertically，the flow units developed in different types of single channels may vary greatly，resulting in difference of vertical distribution of flow units. The favorable typeⅠand Ⅱ flow units are developed in the middle stage of turbidity channel system evolution，mainly distributed in the category Ⅱ single channels. Type Ⅲ and Ⅳ flow units are developed in the early and late stages of turbidity channel system evolution. Among them，type Ⅲ flow units are widely distributed in category Ⅰ，Ⅱ and Ⅲ single channels，while type Ⅳ flow units are mainly developed in categoryⅠand Ⅲ single channels. Laterally，influenced by the sedimentary evolution stages of channels systems，the lateral division of flow units is different. The contact pattern between the flow units and the nonpermeable layers develops in the early sedimentary cycle of the turbidity channel system，with obvious contact interfaces，which belongs to category Ⅰ channel sand bodies. The contact pattern between the flow units develops in the middle and late sedimentary cycles of the channel system，which belongs to category Ⅱ and Ⅲ channel sand bodies. （4）Horizontally，due to the lateral migration and vertical accretion of single channels，the distribution of flow units in the composite channel was significantly different. The type Ⅲ flow units are developed widely in the single sand body with good continuity between wells，and they are developed in the main turbidity channels，turbidity channels and overflowing sand bodies. The distribution of typeⅠand Ⅱ flow units with good seepage capacity is limited with poor continuity，and they are distributed only in the direction of the main stream line of turbidity channels and the sand bodies of the main channels，showing discontinuous point or ribbon distribution. The Type Ⅳ flow units are distributed in a ring band along the outer edge of type Ⅲ flow units and developed in the area where the turbidity channels overflowed the sand bodies.

FORUM AND REVIEW

The past，present and future of intelligent geophysical technology

YANG Wuyang, WEI Xinjian, LI Haishan

2024, Vol.36(2): 170–188 Abstract ( 360 ) PDF (8588 KB) ( 409 )

doi: https://doi.org/10.12108/yxyqc.20240216

By reviewing the development history，main research progress，and development direction of artificial intelligence technology in the field of geophysical exploration（geophysical exploration）both domestically and internationally，the advantages and challenges of intelligent geophysical exploration were summarized，and solutions were proposed. The results show that：（1）Geophysical technology was integrated with artificial intelligence technology in the second wave of artificial intelligence development. Thanks to the exponential growth of data volume in the field of geophysical exploration，the rapid development of hardware computing power，and the emergence of new deep learning frameworks，intelligent geophysical technology has developed from early machine learning to current deep learning，and has achieved a large number of research results in seismic data processing and interpretation.（2）At present，intelligent geophysical technology is widely used in the construction of tag sets，denoising，fault detection，layer and sequence interpretation，seismic facies classification and anomaly detection，lithology identification and reservoir development，and seismic inversion imaging，greatly improving work efficiency，reducing work costs，overcoming the subjectivity and unreliability of manual interaction and experience，and helping to break the bottleneck of traditional geophysical technology.（3）The development of intelligent geophysical technology faces challenges such as a lack of publicly available label datasets，a lack of intelligent frameworks to solve problems in the field of geophysics，and the lack of an intelligent development platform suitable for sharing in the field of geophysics. These challenges can be addressed by addressing data infrastructure，building intelligent platforms，conducting basic research on network architecture，and combining it with application scenarios. In addition，the development direction of intelligent geophysical technology also includes the following aspects：research on intelligent seismic imaging methods，reservoir imaging methods，oil and gas big data mining，intelligent risk assessment and intelligent decision-making，and research and development of supercomputing software equipment.