Lithologic Reservoirs

Based on analysis and experiment data of fluid inclusions, hydrocarbon generation thermal simulation, TOC, physical properties and casting thin sections, combined with burial-thermal history, the geological condition, accumulation process, and main controlling factors of Miocene Sanya Formation in Yingdong slope area of Yinggehai Basin were systematically studied, and hydrocarbon accumulation models were established. The results show that: (1) The organic matter type of Miocene Sanya Formation source rocks in Yingdong slope area of Yinggehai Basin is dominated by humic kerogen, with average TOC values of 0.77% and 1.21% in the northern and southern sections, respectively. The average TOC value of Oligocene coal-bearing source rocks is 1.41%. The evolution characteristics of Oligocene and Miocene source rocks in Yingdong slope area are as follows: early shallow burial, long-term immaturity-low maturity stage, late rapid deep burial, short-term rapid entry into maturity-high maturity evolution stage. The evolution degree of source rocks in the near-sag area of the southern section is the highest, followed by the slope area of the southern section, the near-sag area of the middle section and the northern section, and the evolution degree of the slope area of the middle section is the lowest. The average porosity of reservoir in the northern section is 13.56%, and the main peak of permeability is 0.1-1.0 mD. The average porosity of the southern section is 11.53%, and the main peak of permeability is 1.0-10.0 mD, the permeability is significantly better than that of the northern section, and the reservoir space is mainly composed of dissolved pores. The composite transport system composed of continuous active strike-slip faults, derived fractures and large-scale sandbodies with relatively good physical properties ensured the efficient three-dimensional migration of natural gas.(2) The natural gas component of Sanya Formation is mainly CH4, with a median volume fraction of 83.16%, mainly coal-type gas. Natural gas of the northern section mainly comes from Sanya Formation and the underlying Oligocene, while the maturity of natural gas in the southern section is 1.3%-1.7%, significantly higher than that of the northern section, mainly from the underlying Oligocene.(3) Characteristics of Sanya Formation gas reservoir are"multi-stage continuous filling and late-stage accumulation". Both the northern and southern sections have undergone three-stage of oil and gas charging, with the main charging period being Pleistocene. The main charging time of oil and gas in the southern section(3.5-1.0 Ma)is earlier than that in the northern section(2.2-1.0 Ma). The filling abundance of the southern section is higher than that of the northern section.(4) Accumulation characteristics of Sanya Formation are"strike-slip fault controlling hydrocarbon, source superimposed tectonic activity controlling reservoir, superposition of strike-slip fault activity-fracture overpressure activation controlling transportation". The source rock evolution, transport efficient and reservoir features are the main controlling factors for natural gas accumulation.

Carboniferous volcanic reservoirs characteristics and favorable area prediction of the eastern Junggar Basin

CHEN Xuan, XU Xiongfei, ZHANG Hua, GOU Hongguang, ZHANG Yiting, YOU Fan, CHENG Yi, SUN Yufeng

2025, Vol.37(6): 13–27 Abstract ( 48 ) PDF (2215 KB) ( 68 )

doi: https://doi.org/10.12108/yxyqc.20250602

Using time-frequency electromagnetic method, residual magnetic force, and high-precision 3D seismic data, combined with data from drilling, logging, well testing, and laboratory analysis, Carboniferous volcanic reservoir characteristics of the eastern Junggar Basin were studied. And distribution zones of favorable reservoirs were predicted through numerical model analysis. The results show that: (1) Multiple thrust faults are developed in Carboniferous of the eastern Junggar Basin, presenting an overall tectonic framework of alternating uplifts and sags interconnected by faults. Denudation mostly occurs in the positions of uplifts. Volcanic reservoirs mainly distribute in Jimusar Sag, Jinan Sag, Fukang Sag, and Gucheng Sag. Lithologies are mainly basalt, andesite, rhyolite, and volcanic clastic breccia.(2) Carboniferous volcanic oil and gas reservoirs in the study area are characterized by a fissure-type volcanic eruption mechanism, with dominant lithofacies being explosive facies and effusive facies. The explosive facies mainly distribute in the central area, while the effusive facies mainly distribute in the eastern and northern areas, showing a linear or banded distribution in the plane, which has a good matching relationship with the fault distribution.(3) The development of volcanic reservoirs in the study area is controlled by weathering and leaching, lithofacies assemblage, and fracture development degree, with weathering and leaching being the main factor. The reservoirs are closer to the top interface of Carboniferous, their physical properties are better.(4) The favorable reservoirs in the study area are mainly volcanic breccia of nearvent explosive facies, andesite and basalt of effusive facies, mainly distributed in the western, central, and southeastern parts of the study area. Among them, the physical properties of volcanic reservoirs in the paleogeomorphic high-lying parts and slope zones in the western area are the best.

Formation mechanism of high-quality sand bodies caused by land floods: A case study of flood sediments of No. 2 dam in Tandonggou, Yaojie area, Lanzhou

LI Xiangbo, LIU Huaqing, HAO Bin, YANG Zhanlong, ZHANG Jing, LIU Zhenhua, LI Zhiyong, LI Zaiguang

2025, Vol.37(6): 28–34 Abstract ( 47 ) PDF (1411 KB) ( 60 )

doi: https://doi.org/10.12108/yxyqc.20250603

Through field geological investigation, and experimental analysis and testing, the characteristics of flood sediments in the debris flow prone areas of Tandonggou in Yaojie area, Lanzhou were clarified, and the formation mechanism of high-quality sand bodies was revealed. The results show that: (1) Flood sediments of Tandonggou in Yaojie area, Lanzhou are classified into four types: gravel(G), coarse sand containing gravel (C), medium fine sand(MS), and silty sediment with fine sand(clay)(FM). They distribute in an orderly manner from upstream to downstream. Medium fine sand(MS)continuously distributes in the downstream section of the catchment area, with good sorting, which is the high-quality sand body.(2) The ordered distribution of flood sediments in study area is related to the transformation of debris flow(non Newtonian fluid)into traction flow(Newtonian fluid)during fluid transport, which is jointly controlled by the"V"-shaped turning river channel and changes in terrain slope in the region.The mechanical differentiation effect of traction and the collision and fragmentation among high-energy flood particles are the main reasons for the formation of high-quality sand bodies in the study area.

Characteristics and main controlling factors of high-quality reservoirs in Cambrian Longwangmiao Formation of Penglai Gasfield, Sichuan Basin

LI Yong, ZHANG Ya, ZHOU Gang, QU Haizhou, LONG Hongyu, LI Chenglong, ZHANG Chi, CHEN Di

2025, Vol.37(6): 35–47 Abstract ( 50 ) PDF (1880 KB) ( 68 )

doi: https://doi.org/10.12108/yxyqc.20250604

In recent years, well Dongba 1 in Penglai Gasfield in central and northern Sichuan Basin has obtained industrial gas flow through testing in Cambrian Longwangmiao Formation. Based on relevant data such as core samples, thin sections, cathodoluminescence, conventional logging, imaging logging, and geochemical information, the reservoir characteristics, genesis, and distribution patterns of Longwangmiao Formation in Penglai Gasfield, northern central Sichuan Basin were systematically studied. The results show that: (1) The high-quality reservoir of Longwangmiao Formation in Penglai Gasfield are mainly composed of oolitic dolomite, followed by doloarenite. The reservoir space is primarily karst caves, needle-like dissolved pores, residual intergranular dissolved pores, and intragranular dissolved pores, accompanied by a few fractures. The overall porosity mainly ranges from 2% to 6%, and permeability is mainly 0.001-1.000 mD, characterized as a low-porosity and low-permeability reservoir. The reservoir types of Longwangmiao Formation can be divided into karst cave type(with an average porosity of 4.2% and permeability of 0.209 mD), dissolved pore type(with an average porosity of 3.6% and permeability of 0.052 mD)and pore type(with an average porosity of 3.0% and permeability of 0.034 mD), with the former two being high-quality reservoirs.(2) The development of high-quality reservoirs is mainly influenced by sedimentary facies, penecontemporaneous meteoric water dissolution, penecontem-poraneous dolomitization, shallow buried bedding karstification, and structural fractures. Among them, shallow buried karstification has significant impact on high-quality reservoirs in the western study area.(3) High-quality reservoirs are mainly distributed in the PS15 wellblock in the western region, with thickness generally over 10 m and locally exceeding 30 m. They are also distributed in the PS8-PY1 wellblock in the eastern region, with thickness generally ranging from 8 m to 15 m.

Characteristics of volcanic edifices and hydrocarbon accumulation models of the 6th and 7th blocks of Ke-Bai fault zone, Junggar Basin

QIU Zhengke, HOU Wenfeng, HUANG Huan, GAO Ruqi, ZHOU Lin, ZHANG Yuanmei, TIAN Jinshan, LI Hao

2025, Vol.37(6): 48–58 Abstract ( 35 ) PDF (1452 KB) ( 85 )

doi: https://doi.org/10.12108/yxyqc.20250605

In recent years, exploration efforts have yielded outstanding results in Carboniferous of Ke-Bai fault zone in the northwest margin of Junggar Basin, which shows that volcanic edifices are closely related to hydrocarbon accumulation. Based on the data of drilling core, thin section and logging, the evolution of volcanic edifice and the distribution of high-quality reservoirs were clarified through the analysis of volcanic edifice characteristics, and the oil and gas accumulation models were summarized. The results show that: (1) Carboniferous of the 6th and 7th blocks in Ke-Bai fault zone of Junggar Basin, primarily developed four types of volcanic facies: volcanic vent facies(porphyritic rocks), overflow facies(andesite), explosive facies(tuff), and volcanic sedimentary facies(conglomerate and sandstone). The areas along Nanbaijiantan Fault in the central of the 7th block and Kewu Fault in the east of the 7th block are volcanic vent facies. The dominant facies belts of the northern part of the central part, western part and eastern part of the 7th block are overflow facies. The dominant facies belts in the western part of the 6th block, the northern part of the 7th block, and eastern part of the 7th block are explosive facies and volcanic sedimentary facies.(2) Two north-south trending fissure volcanic eruption systems(the central part and eastern part of the 7th block)developed in the study area. Volcanic-related sediments can be divided into three stages: initial volcanic eruption phase-volcanic eruption intermission, renewed volcanic activity phase, and post-volcanic quiescence phase.(3) Reservoirs in the research area mainly develop secondary pores and fractures, and dissolution is the main controlling factor for the development of high-quality reservoirs. The dissolution zone is divided into dissolution highlands(volcanic vent areas in the central and eastern part of the 7th block), dissolution slopes(central part of the 7th block, west of western part of the 7th block, and north of eastern part of the 7th block), and dissolution depressions(the 6th block). The dissolution slope exhibits the strongest dissolution effect and the best physical properties, with an average porosity and permeability of 11.6% and 15.30 mD, respectively.(4) Hydrocarbons generated from Permian Fengcheng Formation source rocks in Mahu Sag migrated laterally along faults, fractures, and unconformities to the study area. The oil and gas migrated along fractures to the pore development area and accumulated. The dissolution slopes(central part of the 7th block and north of eastern part of the 7th block) are favorable exploration targets.

A method and application of identifying shale bedding structures based on FMI image micro-electrical conductivity curve time-frequency information: A case study on the first member of Cambrian Qiongzhusi Formation in Zizhong area of Sichuan Basin

YANG Yang, WANG Haiqing, SHI Xuewen, ZENG Yuting, GAO Xiang, LI Jinyong, ZHANG Xuanang, YAN Jianping

2025, Vol.37(6): 59–70 Abstract ( 46 ) PDF (1691 KB) ( 61 )

doi: https://doi.org/10.12108/yxyqc.20250606

With Cambrian Qiongzhusi Formation shale of well ZX01 in Zizhong area of Sichuan Basin as the case study, a new method was proposed to identify laminatedion developed intervals and bedding structures by extracting the equivalent micro-conductivity curve (EC) from FMI images to construct a lamination concentration curve(LC). LC curves response characteristics of shale bedding structures were discussed, and the application effectiveness of the LC curve in lithofacies identification and shale gas"sweet spot"evaluation was analyzed. The results show that: (1) An improved Criminisi algorithm was used to restore FMI dynamic images, extract the EC curve from the restored images, perform spectral analysis on the curve, compare the frequency distribution differences between laminated intervals and massive intervals, and perform Fourier band-pass filtering to obtain a laminar signal-enhanced curve. Absolute value and envelope processing were then applied to derive a curve (LC) reflecting the degree of laminar development.(2) Laminated intervals in the first member of Qiongzhusi Formation in the study area mainly distribute in sub-layers 1, 3 and 5, with LC values generally greater than 0.16. LC values of bedded structures are below 0.16, while LC values of massive structures are the lowest.(3) When using machine learning models for shale lithofacies identification, incorporating the LC curve as a feature input improved lithofacies recognition accuracy by 3%. The LC value exhibits positive correlations with TOC, brittleness index, free gas content, and adsorbed gas content, and exhibits a weak negative correlation with porosity. Higher LC values indicate more developed laminations, higher TOC content, and higher brittle mineral content. During hydraulic fracturing, intervals with higher brittleness index are more conducive to fracture propagation, and the development of superimposed laminations can form a complex fracture network system, which increase shale gas well productivity.

Hydrocarbon geochemical characteristics and source of Triassic Baijiantan Formation in Dabasong uplift, Junggar Basin

JIANG Mengya, JIANG Zhongfa, LIU Longsong, WANG Jiangtao, CHEN Hailong, WANG Xueyong, LIU Hailei

2025, Vol.37(6): 71–87 Abstract ( 37 ) PDF (1250 KB) ( 49 )

doi: https://doi.org/10.12108/yxyqc.20250607

Triassic Baijiantan Formation of Dabasong uplift in Junggar Basin has encountered large-scale highquality sand bodies and achieved industrial oil and gas flow, which show that oil and gas resources in the middle and shallow layers of Dabasong uplift have significant potential. Based on the analysis data of oil and gas samples from newly drilled wells, the hydrocarbon geochemical characteristics of Baijiantan Formation in Penbei 1 well area were systematically analyzed, and the sources of oil and gas were revealed. The results show that: (1) The crude oil of Baijiantan Formation in Penbei 1 well area of Dabasong uplift in Junggar Basin has relatively high viscosity and freezing point. The whole oil carbon isotope is relatively light, with the value of -29.38‰, and Pr/Ph of 0.69-1.29, and containing β-carotane and gammacerane, it is mature to high-mature light crude oil.(2) The natural gas composition of Baijiantan Formation in Penbei 1 well area of the study area is dominated by methane, with wet gas and dry gas coexisting. The ethane carbon isotope is relatively light, ranging from -31.34‰ to -27.83‰. Dimethylcyclopentane accounts for a large proportion of C7 light hydrocarbon compound, and oil-type gas and mixed gas are distributed.(3) The crude oil of Baijiantan Formation in Penbei 1 well area mainly originates from Permian Fengcheng Formation source rocks, with significant contributions from lower aquatic organisms in reducing environments. Natural gas mainly comes from Permian Fengcheng Formation source rocks, and part of it originates from Carboniferous source rocks.(4) Baijiantan Formation oil and gas reservoirs in Penbei 1 well area are lithologic or fault-lithologic oil and gas reservoirs with dual-source hydrocarbon-supply, multi-stage oil and gas charging, sedimentary facies belts controlling, and segmented by faults.

Fractal characteristics of pore throat structure and their influence on reservoir physical properties of tight sandstone reservoir: A case study of Triassic Chang 8 member in Fuxian area, Ordos Basin

SU Shuai, QU Hongjun, YIN Hu, ZHANG Leigang, YANG Xiaofeng

2025, Vol.37(6): 88–98 Abstract ( 32 ) PDF (1491 KB) ( 130 )

doi: https://doi.org/10.12108/yxyqc.20250608

Pore throat structure is a key factor that affects the reservoir and seepage capacity of tight sandstone reservoirs, and its fine characterization is very important for the exploration and development of tight reservoirs. The pore throat structure and fractal characteristics of the tight sandstone reservoir of Triassic Chang 8 member in Fuxian area of Ordos Basin were studied by various testing methods, such as casting thin section, physical property analysis, and mercury pressure. The influence of pore throat structure on reservoir physical property were clarified. The results show that: (1) Pore types of tight sandstone in Triassic Chang 8 member in Fuxian area of Ordos Basin are mainly dissolved intergranular pores and feldspar dissolved pores, while throat types are mainly lamellar and curved lamellar. According to the displacement pressure, average pore throat radius, and maximum pore throat radius, reservoirs are classified as three categories. From type Ⅰ to type Ⅲ reservoirs, pore sorting and connectivity gradually deteriorate, pore throat radius gradually decrease, and the pore throat full aperture is 0.001-10.000 μm.(2) The pore throat structures of the three types of reservoirs in the research area all have triple fractal characteristics, with large-scale pore throats (D1) > mesoscale pore throats (D2) > small-scale pore throats (D3). Larg-scale pore throats have complex pore throat networks and relative large fractal dimensions due to strong dissolution, while small-scale pore throats have regular morphology and relative small fractal dimensions due to strong compaction. According to the weighted results, the total fractal dimension(DT) of the pore throats ranges from 2.05 to 2.44, with an average value of 2.26. From type Ⅰ to type Ⅲ reservoirs, the average DT gradually increases, and the heterogeneity of the pore throats gradually strengthens.(3) The permeability of Chang 8 tight sandstone reservoir is mainly controlled by the average throat radius. DT, D1 and D3 are negatively correlated with average pore throat radius, reservoir porosity and permeability, and positively correlated with displacement pressure and sorting coefficient, indicating that the more complex pore throat structure results the poorer pore connectivity, sorting and reservoir physical properties. The correlation of D1 with porosity and permeability is the best, indicating that the physical properties of Chang 8 reservoir are mainly affected by large-scale pore throat. Reservoirs with larger average throats, higher proportion of large pores, and lower fractal dimension are of higher quality.

A fully automatic velocity picking method based on weighted K-means clustering

LIU Zhengwen, ZHAO Ruirui, CHEN Yangyang, XIE Junfa, ZANG Shengtao, QIN Long

2025, Vol.37(6): 99–106 Abstract ( 31 ) PDF (1380 KB) ( 58 )

doi: https://doi.org/10.12108/yxyqc.20250609

To improve the efficiency of seismic velocity picking, an improved weighted K-means clustering method was proposed based on the conventional K-means clustering algorithm. Both of the improved method and the conventional K-means clustering were applied to model data and actual data of TD block in Tarim Basin, and the picking results were analyzed. The results show that: (1) The weighted K-means clustering method eliminates weak amplitude velocity points by setting velocity spectrum amplitude threshold, then set the proportional coefficient to eliminate the outlier velocity points. Set a time window in the time direction and search for several velocity points with the largest amplitudes within the time window. The average velocity and average time of the found velocity points are taken as the initial values of the clustering centers. Based on the initial values, remove or merge some clustering centers, assign different weights to different velocity points, remove the velocity points at the edge of each cluster center, make the automatically picked cluster centers approach the energy group center. For picking results with velocity reversal, the first two picking results are used to make multiple wave judgments and eliminations. (2) The weighted K-means clustering method does not require prior velocity information, and achieves fully automatic velocity picking. In each iteration, some velocity points are eliminated, significantly reducing the number of required iterations. It not only speeds up the calculation but also enhances the picking accuracy. The weighted K-means clustering method was applied to automatically velocity picking on the model data and the actual data of TD block in Tarim Basin, compared with the conventional K-means clustering method, its computational efficiency was increased by approximately 7 times and the accuracy was improved by 1.7%.

Characteristics of strike-slip faults and their controls on hydrocarbon accumulation in Shunbei area, Tarim Basin

HUANG Cheng, ZHU Lianhua, BU Xuqiang, ZENG Jianhui, LONG Hui, LIAO Wenhao, LIU Yazhou, QIAO Juncheng

2025, Vol.37(6): 107–118 Abstract ( 48 ) PDF (1612 KB) ( 66 )

doi: https://doi.org/10.12108/yxyqc.20250610

In recent years, breakthroughs have been achieved in ultra-deep carbonate oil and gas exploration in Tarim Basin, and hydrocarbons have been discovered across multiple strike-slip fault zones in Shunbei area. Based on seismic profile interpretation, taking the southern section of Shunbei No.5 strike-slip fault zone as an example, the hydrocarbon sources connectivity, transport capacity, and reservoir modification capacity of the strike-slip fault zone were analyzed, and their controlling on hydrocarbon accumulation was discussed. The results show that: (1) Strike-slip fault zones in Shunbei area of Tarim Basin play three crucial roles in ultra-deep carbonate hydrocarbon accumulation: hydrocarbon sources connection, hydrocarbon transport, and reservoir modification. Integrated multiple factors, a semi-quantitative assessment criterion was established to categorize hydrocarbon source connectivity into three types: strong source connectivity, moderate source connectivity, and weak source connectivity. (2) The development of two sets of gypsum salt rock formations (Awatage Formation and Wusongge'er Formation) in Shunbei area has affected the across layer transport of oil and gas. The gypsum salt layer can be classified into three types: escape thinning type, fracture uplift type, and uplift thickening type. The thickness of the gypsum rock layer decreases at the location of strike-slip fault development. When the fault is active, oil and gas easily break through the blockage of the gypsum salt layer and migrate upward. Under the influence of compressive stress, the gypsum salt layer is prone to develop branch faults that intersect with vertical main strike-slip faults, resulting in strata fragment. Oil and gas can be injected into the upper strata of the gypsum layer through small-scale branch faults and fragmented strata, thereby facilitating oil and gas transport. (3) Reservoir spaces in deep carbonate rocks in Shunbei area are mainly caves, vugs, and fractures, which exhibit distinct seismic characteristics of fracture + "beaded reflection", fracture + "chaotic reflection", and fracture + "weak reflection". The reservoirs mainly consist of fractured zones formed by tectonic stress, and subsequently superimposed by deep hydrothermal fluid modification. Fractures can be classified into high-angle fractures, oblique fractures, irregular fractures, and induced fractures. (4) Three enrichment models can be identified in Shunbei area: "strong sourcing-efficient transport-superior reservoir-premium enrichment" "strong sourcing-weak transport-superior reservoir-moderate enrichment" "weak sourcing-weak transport-poor reservoirpoor accumulation".

Sedimentary evolution characteristics and paleogeomorphology-controlled sand distribution patterns of the upper Es4 sub-member of Paleogene in Linnan Subsag, Bohai Bay Basin

SUN Yuanfeng, CAO Aifeng, ZHOU Yong, GAO Chenxi, WANG Ke

2025, Vol.37(6): 119–130 Abstract ( 30 ) PDF (1873 KB) ( 55 )

doi: https://doi.org/10.12108/yxyqc.20250611

Based on the established sequence stratigraphic framework, the sedimentary evolution characteristics of the upper section of the fourth member of Shahejie Formation (Es4) in Linan Subsag of Bohai Bay Basin were analyzed through integrated utilization of core, well logging, mud logging, and seismic data. Combined with the activity analysis data of basin-controlling faults, the controlling effects of diverse paleogeomorphology on sedimentary systems and sandbody distribution were elucidated, and a tectono-sedimentary coupling model for the sedimentation period of sand group 2 in the upper Es4 sub-member was established. The results show that: (1) During the sedimentation period of sand groups 3 and 4 in the upper Es4 sub-member of Linnan Subsag, the climate was arid, primarily developing sedimentary systems of fluvial terminal fan. During the sedimentation period of sand groups 1 and 2, the climate gradually became humid, driving an evolution from fluvial terminal fan sedimentary to normal lacustrine sedimentation characterized by (fan) delta-shore shallow lacustrine beach-bar systems. (2) Paleogeomorphology in the study area control the distribution of sedimentary facies and sandbodies, which can be identified as four key patterns: broom-like faults, axial fault troughs, comb-like faults, and steep-slope parallel fault terraces. Axial fault troughs can serve as sand transport channels, guiding sandbody progradation along the trough axis. Syn-depositional fault-associated topography (comb-like faults, steep-slope parallel fault terraces, broom-like fault zones) provide significant accommodation space, controlling sandbody accumulation locations and defining favorable targets for sandstone reservoirs. (3) Tectonically, Linnan Subsag became the primary depocentre during the upper Es4 sub-member deposition due to subsidence driven by Xiakou and Linshang basin-controlling faults. Regionally, broom-like faults influenced sandbody migration via fault troughs towards the subsag in the north. Southwestern axial fault troughs served as a critical sediment pathway, promoting NE sand progradation. Comb-like faults controlled fan delta progradation and relative thick sandbody accumulation at fault-angle bases in Jiangjiadian area. Fan delta sediments developed at steep-slope parallel fault terraces in Wawu area are perpendicular to the boundary fault and exhibit retrogradational distribution. Sandbodies in Shanghe area have been influenced by alongshore currents, forming beach-bar systems.

Discovery of seismic anomalies in Silurian reefs in Jiange area of northwestern Sichuan Basin and their geological significance for oil and gas

YANG Liu, ZHU Yadong, LIANG Hong, DIAO Yongbo, PENG Xin, SI Guoshuai, XU Jiao, SUN Qingli

2025, Vol.37(6): 131–139 Abstract ( 29 ) PDF (1124 KB) ( 57 )

doi: https://doi.org/10.12108/yxyqc.20250612

Through the analysis of high-quality 3D seismic data of multiple blocks from northwestern Sichuan Basin, seismic reflection anomalous bodies of organic reefs were discovered at the bottom of Silurian. Combided with regional well-seismic calibration, seismic geological stratigraphy, curvature seismic attribute extraction, and paleogeomorphology characterization, the characteristics, distribution and sedimentary background of these anomalies were discussed. The results show that: (1) The Silurian reef anomalies in Jiange area of northwestern Sichuan Basin have a geometric shape resembling a reef mound on seismic profiles, belonging to Shiniulan Formation. They are widely distributed across Jiange area in varing size. (2) There are numerous near NS-NW direction basement faults developed in the underlying strata of Silurian organic reefs in the study area, mostly extending to Sinian-Cambrian, connecting the source rocks of Qiongzhusi Formation, Doushantuo Formation, and Longmaxi Formation. Source rocks of Qiongzhusi Formation and Longmaxi Formation, along with Silurian organic reef reservoirs, constitute a"lower-generation and upper-storage, lateral-source and side-storage"oil and gas accumulation model. The reef group mainly developed in northern part of Late Caledonian LeshanLongnvsi paleo-uplift in the enclosed slope area. During the sedimentary period of Shiniulan Formation, the enclosed area near the paleo-uplift source area was a mixed tidal flat deposit, with a large amount of terrigenous clastic, organic reefs are small scale, with severe erosion in the later stage, and few remnants. The central part of the enclosed slope area is a tidal flat edge/carbonate gentle slope deposit, reefs are large scale and often formed composite. The lower part of the enclosed slope area is composed of shallow water continental shelf sediments, with small scale anomalous bodies and mainly point reefs. (3) Jiange area is adjacent to Deyang-Anyue rift trough, and is the center of high-quality source rocks in Qiongzhusi Formation of Sichuan Basin. The organic reef reservoir of Shiniulan Formation is in direct contact with underlying Longmaxi Formation source rocks. The widely developed basement faults and associated faults in this area are conducive to oil and gas transportation. The overlying Liangshan Formation shale is a high-quality cap rock with superior reservoir conditions.

Seismic prediction technology for complex network fractures in fault-fracture reservoir of tight sandstones: A case study of Triassic Xujiahe Formation in northern Sichuan Basin

MIAO Zhiwei, LI Shikai, ZHANG Wenjun, XIAO Wei, LIU Ming, YU Tong

2025, Vol.37(6): 140–150 Abstract ( 38 ) PDF (1823 KB) ( 59 )

doi: https://doi.org/10.12108/yxyqc.20250613

Through a"three-step"complex network fracture seismic comprehensive prediction technology, the seismic quantitative prediction of fracture development intensity and scale in different orientations and phases of the tight sandstone"fault-fracture body"reservoir of Xujiahe Formation in northern Sichuan Basin was carried out.The results show that: (1) The technical workflow of seismic prediction is as follows: Utilize high-resolution frequency-division ant tracking based on deconvolution generalized S-transform, to predict fracture phases and orientations by constructing a discrete grid model. Establish QVAZ equation for azimuthal attenuation elastic impedance based on the theory of attenuation anisotropy, and combine group sparse inversion to achieve prestack quantitative prediction of fracture density. Integrating the above two technologies for complementary advantages and overlapping analysis, complete the spatial description of complex network fractures.(2) The fractures in the "fault-fracture body" tight sandstone reservoir of Triassic Xujiahe Formation in Tongjiang area of northern Sichuan Basin mainly develop near faults, and their direction align with fault trends. These fractures are mainly of tectonic origin, local anticlines strata display relatively stable development. The tensional fractures associated with the folding process are not the sweet spots of the "fault-fracture body"reservoir, but the intersection of multiple large-scale fractures is a favorable area for the development of complex network fractures.(3) This method can perform high-definition identification of low sequence level faults, reducing the impact of low signal-to-noise ratio and lithological mutations in complex structural areas, avoiding the false appearance of fractures that may be caused by local stratigraphic folds, reducing the dependence of traditional methods on seismic data signal-to-noise ratio, and predicted interlayer micro-fractures with high resolution. The predicted results are in good agreement with the FMI interpretation and testing productivity of actual drilling. Based on this method, the newly deployed well M15 obtained industrial gas flow of 10.35×104 m3/d in the fourth member of Xujiahe Formation during gas testing.

Current geostress logging evaluation of tight reservoir in the fourth member of Triassic Xujiahe Formation in Yuanba area, northeastern Sichuan Basin

LI Chunyang, WANG Boli, YAN Xiao, LI Kesai, DENG Hucheng, SU Jinyi, WU Yajun, YE Tairan

2025, Vol.37(6): 151–161 Abstract ( 29 ) PDF (1709 KB) ( 94 )

doi: https://doi.org/10.12108/yxyqc.20250614

Yuanba area in northeastern Sichuan Basin has been subjected to multi-stage tectonic stress since Triassic, with complex coupling characteristics of faults, folding and geostress. Accurate evaluation of current geostress has become one of the key factors for the efficient development of gas reservoir. Based on the data from dipole shear waves, electrical imaging, multi-caliper, and conventional well logging, the current geostress logging evaluation of the fourth member of Triassic Xujiahe Formation in Yuanba area was carried out, and the spatiotem-poral sequence of structural deformation was redefined. The results show that: (1) Since Yanshanian period, Yuanba area in northeastern Sichuan Basin has primarily experienced NW-SE compression and thrusting during LateMiddle Yanshanian, followed by NE-SW compression and thrusting during Early-Middle Himalayan. This tectonic history resulted in the current structure framework of NE-trending structure superposition, NW-oriented modification, and multiple stages fault development with diverse orientations.(2) In the fourth member of Triassic XujiaheFormation of Yuanba area, the maximum horizontal principal stress(σH)ranges from 110 MPa to 140 MPa, the minimum horizontal principal stress(σh)ranges from 80 MPa to 100 MPa, and the vertical principal stress(σV)mainly ranges from 105 MPa to 125 MPa. The relationship of these three principal stress(σH > σV > σh)exhibits a strike-slip stress state, with the regional principal stress direction being NWW-SEE.(3) The geostress is generally controlled by burial depth, and the release of fault stress adjusts the distribution characteristics of geostress.Vertically, mudstone in the middle section of the fourth member of Triassic Xujiahe Formation is developed, and the overall magnitude of geostress in the upper part is higher due to the creep deformation of the mudstone. The research results can provide reference for the selection of sweet spots in gas field geological engineering, analysis of the effectiveness of natural fractures, and artificial fracturing of reservoirs.

Hydrocarbon migration and accumulation characteristics of lithologic reservoirs in lower Minghuazhen Formation of Neogene in Qinhuangdao M-3 area, Shijiutuo uplift, Bohai Sea

CHENG Yan, ZHANG Tongyao, HAO Peng, YANG Jianghao, LIU Xuerui, ZHANG Weisen, HE Junhui, WANG Bo

2025, Vol.37(6): 162–171 Abstract ( 49 ) PDF (1202 KB) ( 79 )

doi: https://doi.org/10.12108/yxyqc.20250615

Through comparing and analyzing the geochemical characteristics of source rocks in Bozhong Sag and Qinnan Sag, the oil source correlation and hydrocarbon migration pathway of the middle part of lower Minghuazhen Formation in Neogene of Shijutuo uplift were studied, and the crude oil migration and accumulation characteristics of oil reservoir in Qinhuangdao M-3 area were analyzed. The results show that: (1) Source rocks in Qinnan Sag have high values of C19/C23 tricyclic terpane, C20/C23 tricyclic terpane, extended tricyclic terpane ratio (ETR) and gammacerane/αβ-hopane, while source rocks in Bozhong Sag have high values of C35/C34 22S homohopane and C27Dia/C27St.(2) Crude oil in the middle part of Shijutuo uplift in Qinhuangdao M-3 area exhibits characteristics of high density, high viscosity, narrow distribution range of δ13C value and relatively light saturated hydrocarbon isotopic, while crude oil in the northern and northeastern parts shows low density, low viscosity and wide distribution range of δ13C value.(3) Crude oil groups in Shijutuo uplift can be divided into three types: Type Ⅰ iscrude oil from the eastern oil reservoirs of Shijutuo uplift, with low values of C27Dia/C27St, medium ETR and low-medium values of C35/C34 22S homohopane, and the oil source is mainly from the Sha3 Member of Qinnan Sag. Type Ⅱ is crude oil from the northern and some middle parts of Shijutuo uplift, with high values of C27Dia/C27St, high values of C35/C34 22S homohopane and medium values of gammacerane/αβ-hopane, and the crude oil mainly comes from Shahejie Formation of Bozhong Sag, mixed with the crude oil from the Sha3 Member of Qin‐nan Sag. Type Ⅲ is crude oil from some middle parts of Shijutuo uplift, with high values of C27Dia/C27St, medium-high values of gammacerane/αβ-hopane and medium values of C35/C34 22S homohopane, and the crude oil mainly comes from the Sha3 Member of Bozhong Sag, mixed with the crude oil from the Sha1 Member.(4) The regular changes of parameters of 4-MDBT/1-MDBT, 2, 4-DMDBT/1, 4-DMDBT, 4, 6-DMDBT/1, 4-DMDBT, (Pr+Ph)/C30Hop and QGF index values of crude oil in the study area indicate that the oil and gas migration pathway of source rocks in Qinnan Sag is from southeast to the middle and then to the northwest, while the oil and gas migration pathway of source rocks in Bozhong Sag is from southeast to northwest.

PETROLEUM ENGINEERING AND OIL & GAS FIELD DEVELOPMENT

Minimum miscible pressure model of CO₂ flooding based on kernel ridgeregression multi-parameter optimization

LI Jiamin, ZHANG Yizhong, ZHANG Maolin, QIN Bowen, YANG Yuxin

2025, Vol.37(6): 172–179 Abstract ( 32 ) PDF (1274 KB) ( 53 )

doi: https://doi.org/10.12108/yxyqc.20250616

Based on slim tubes experiment data, the grey corelation method was employed to identify the main controlling factors affecting CO2 oil recovery efficiency and determine their weight assignment. Kernel ridge re‐gression(KRR)algorithm was used to train parameter sets, with model hyperparameters optimized through ge‐netic algorithm(GA)and grid search(GS), the minimum miscible pressure(MMP)prediction model was established. The results show that: (1) The primary factors influencing CO2 flooding are reservoir temperature, crude oil composition, and injection gas composition. Under pure CO2 injection conditions, the order of grey corelation grade as follows: T > x(C2—C4) > M(C7+) > x(C5—C6) > x(CH4+N2). Under the condition of CO2 injection containing impurities, the impact ranking of impurity type and content on MMP is: x(N2) > x(C1) > x(C2—C4)inj > x(H2S).(2) Compared with Ridge model and ElasticNet model, KRR model exhibits higher prediction accuracy and lower error. Among them, KRR-GA model demonstrates the best overall performance, with the mean absolute percentage error(EMAP) of 4.11%, root mean square error(ERMS) of 0.856 MPa, and coefficient of determination(R2) of 0.981 on the test set.(3) KRR-GA model demonstrates superior applicability for heavy crude oil reservoirs and conventional black oil reservoirs, while KRR-GS model is more suitable for light crude oil reservoirs with high H2S content in the injection gas.

Development characteristics and reasonable injection-production pressuredifference of SAGD under different injection-production well patternsin bottom water reservoirs

ZHAN Shengyun, TONG Jianxiang, WANG Zhendong, BAI Yuting, WANG Taichao

2025, Vol.37(6): 180–190 Abstract ( 26 ) PDF (1362 KB) ( 202 )

doi: https://doi.org/10.12108/yxyqc.20250617

SAGD production law of inclined dual horizontal well in the bottom water heavy oil reservoir of block A in Bohai Oilfield is complex, with high remaining oil saturation and high water cut.Through the physical simulation experiment, the characteristics of temperature field change and production laws of the forward and in clined horizontal wells during the SAGD development process were analyzed. Combined with the numerical simulation method, the influence of injection-production pressure difference on SAGD production efficiency is discussed, and the reasonable injection-production pressure difference range of horizontal well SAGD is clarified. The results show that : (1) SAGD steam chamber of the forward dual horizontal well extends to both sides of the model, and the oil drainage capacity of the inclined plane on both sides of the steam chamber is balanced.However, the expansion speed of the SAGD steam chamber and the oil drainage capacity of the inclined plane ofthe inclined dual horizontal well are unbalanced, resulting in a smaller steam chamber coverage area and lower recovery degree. The production process of dual horizontal well SAGD can be divided into three stages: oil production rate rising stage, stable production stage and falling stage. In the stable production stage, the steam chamber is in the lateral expansion stage, which is dominated by gravity drainage.(2) The SAGD production well in block A of Bohai Oilfield has a water avoidance distance of 10 m. Numerical simulation results show that: when the bottom water energy is less than 10 times and the bottom water has no effect on the production efficiency of horizontal well SAGD. In the stable production stage of dual horizontal well SAGD, with the increase of injection-production pressure difference, the steam injection and liquid production gradually increase, the oil production first increases and then gradually decreases, the cumulative oil-steam ratio first increases and then decreases, and both the sub-cool value and the height of steam-liquid interface decrease gradually. When there is no steam channeling in the production well, the oil production of the forward horizontal well is greater than that of the inclined horizontal well. The reasonable injection-production pressure difference of SAGD in forward and inclined horizontal wells is 20-30 kPa and 30-40 kPa, respectively.

Characteristics of oil reservoir seepage and formation mechanism ofdominant seepage channel after polymer flooding

CAO Ruibo, PI Yanfu, LIU Guochao

2025, Vol.37(6): 191–200 Abstract ( 38 ) PDF (1305 KB) ( 43 )

doi: https://doi.org/10.12108/yxyqc.20250618

In response to the widespread development of dominant seepage channels, low efficient circulation on invalid circulation in the oil reservoirs after polymer flooding in Daqing placanticline, physical modeling experiments, numerical simulations, and dynamic analysis of typical blocks were used to study the seepage capacity, development of dominant seepage channels and formation mechanism of oil reservoirs after polymer flooding of Daqing placanticline. The results show that: (1) The overall seepage capacity of heterogeneous oil layers decreases after polymer flooding, however, the seepage capacity gap between high and low permeability oil reservoirs further widens, and the relative liquid intake of high permeability layers gradually increases.(2) After polymer flooding, the dominant seepage channels of oil reservoirs in Daqing placanticline are mainly developed at the bottom of PⅠ2 and PⅠ3 units, with an average effective thickness of 3.8 m, accounting for 18.4% of the total well thickness. The average air permeability is 3 775 mD, and the oil saturation is 24.6%. The remaining reserves account for 10.9%, and the relative fluid intake exceeds 60%.(3) The formation mechanism of dominant seepage channels includes: difference in mud content between high and low permeability layers in heterogeneous oil reservoirs after polymer flooding leads to further widening of permeability max-min ratio, and difference of oil saturation and characteristic relative permeability curves of oil reservoirs with high and low permeability leads to a significant increase in water oil mobility ratio.