Table of Content

01 January 2025, Volume 45 Issue zk(English) Previous Issue    Next Issue

For Selected:

Download Citations EndNote Reference Manager ProCite BibTeX RefWorks

Toggle Thumbnails

OIL AND GAS EXPLORATION

Exploration Practice and Total Petroleum System in Residual Marine Sag, Eastern Junggar Basin ZHI Dongming, CHEN Xuan, YANG Runze, LIU Juntian, YU Haiyue, MA Qiang 2024, 45 (zk(English)):  1-13.  Abstract ( 15 )   PDF (5546KB) ( 2 )   Save The Shiqiantan sag in the eastern Junggar Basin is a residual marine sag. In recent years, high-yield natural gas has been obtained from many wells in the Shiqiantan formation, and oil and gas shows have been observed in different strata across the sag, indicating its excellent exploration potential and characteristics as a total petroleum system. Based on seismic, drilling, well logging, and organic geochemical data, the formation and evolution of the Shiqiantan sag, the conditions for the formation of the total petroleum system, and the models of hydrocarbon accumulation are studied. The results show that during the Late Carboniferous, the north Tianshan oceanic crust subduction and seawater intrusion in the region led to the development of terrigenous, marine, medium- to high-quality source rocks which are now in the mature- to high-mature stage. The reservoir contains volcanic rocks in the Carboniferous strata, marine clastic rocks in the Shiqiantan formation, and continental clastic rocks in the Permian Jingou formation, in all of which hydrocarbons were accumulated. Controlled by the hydrocarbon generation and evolution in the source rocks of the Shiqiantan formation and the characteristics of multiple types of reservoirs, a distribution pattern of shale gas reservoir in the sag-tight oil and gas reservoir in the slope-conventional oil and gas reservoir in the high position is formed, showing a total petroleum system featured with orderly symbiosis of unconventional and conventional oil and gas reservoirs. According to the theory of total petroleum system, the exploration in the Shiqiantan sag should focus on tight oil and gas reservoirs in the near-source slope, structural-lithological reservoirs and volcanic weathering-crust oil and gas reservoirs in the above-source fault-terrace area and structural high, and marine shale gas reservoirs within the source. The Carboniferous near-source favorable lithofacies belts, piedmont thrust fault-concealed structures, intra-basin paleouplifts, and slope are favorable exploration zones in northern Xinjiang. Specifically, exploration efforts should be made towards shale oil and gas reservoirs within the sag, tight sandstone oil and gas reservoirs around the sag, conventional oil and gas reservoirs in the structural highs, and volcanic weathering-crust oil and gas reservoirs in uplifted areas. References | Related Articles | Metrics

Multilayer Superimposition Patterns of Strike-Slip Fault Zones and Their Petroleum Geological Significance in Platform Area, Tarim Basin YANG Haijun, NENG Yuan, SHAO Longfei, XIE Zhou, KANG Pengfei, YUAN Jingyi, FU Yonghong 2024, 45 (zk(English)):  14-27.  Abstract ( 17 )   PDF (32998KB) ( 2 )   Save In recent years, with the progress of oil and gas exploration in the Tarim basin, large-scale strike-slip fault systems have been discovered in the Paleozoic strata of the platform area in the basin and a new type of fault-karst reservoir has been identified. Due to multiple tectonic movements in the basin, these strike-slip faults exhibit multilayer structures featured with multiple phase superimposition. Based on high-quality 3D seismic data, drilling data, and petroleum geological data, the multilayer superimposition of large-scale strike-slip faults in the basin and its controls over hydrocarbon accumulation were investigated. The research results show that the strike-slip fault zones in the platform area of the Tarim basin primarily develop five structural layers in the Paleozoic: Lower Cambrian pre-salt structural layer, Middle Cambrian salt structural layer, Upper Cambrian-Middle Ordovician carbonate structural layer, Upper Ordovician-Carboniferous clastic structural layer, and Permian magmatite structural layer. Affected by multiple tectonic movements and strike-slip fault activities, these layers exhibit characteristics of banded spatial distribution, vertical superposition, and differential superimposition. The superimposition patterns can be broadly categorized into four types: connection, overlapping, inverse superimposition, and inverse reformation. These superimposition patterns have significant impacts on hydrocarbon accumulation, and three types of reservoirs such as Type Ⅰ (Ordovician carbonate reservoirs), Type Ⅱ (Ordovician carbonate, Silurian clastic, and Permian magmatite reservoirs), and Type Ⅲ (Cambrian pre-salt dolomite reservoirs) are formed. References | Related Articles | Metrics

Research Progress and Trend of Ultra-Deep Strike-Slip Fault-Controlled Hydrocarbon Reservoirs in Tarim Basin WANG Qinghua, CAI Zhenzhong, ZHANG Yintao, WU Guanghui, XIE Zhou, WAN Xiaoguo, TANG Hao 2024, 45 (zk(English)):  28-36.  Abstract ( 12 )   PDF (4637KB) ( 3 )   Save Ultra-deep strike-slip fault-controlled hydrocarbon reservoirs have been discovered as a new frontier for exploration and development in the Tarim basin. However, the complexity of these reservoirs poses a significant challenge for profitable development, necessitating enhanced foundational geological research. The strike-slip fault-controlled hydrocarbon reservoirs are commonly characterized by strong heterogeneity, intricate reservoir and fluid distribution, significant variations in hydrocarbon production, and low recovery. The great differences in faulting, reservoir characteristics, hydrocarbon accumulation, and fluid dynamics of these reservoirs between different areas present a series of exploration and development challenges. A series of models for strike-slip fault zones of different genesis and their controls on reservoirs have been established, and the mechanisms of reservoir formation along strike-slip fault zones including combined reservoir control by microfacies, strike-slip fault and dissolution, and contiguous, differential and extensive development have been revealed. Furthermore, the strike-slip fault-controlled reservoir models with “source-fault-reservoir-caprock coupling” and “small reservoir but large field” are constructed, unveiling the mechanisms of the hydrocarbon accumulation and preservation of ultra - deep strike-slip fault-controlled reservoirs. This research breaks through the limitations in theory that weak strike-slip faults in cratonic basins are difficult to form large-scale strike-slip fault-controlled reservoirs and large oil/gas fields. Finally, the genesis of large-scale strike-slip fault systems, the differential reservoir formation mechanisms within strike-slip fault zones, and the hydrocarbon enrichment patterns in cratonic basins have been clarified. References | Related Articles | Metrics

Main Controlling Factors of Shale Oil and Gas Enrichment in Chang 7 Member, Southeastern Ordos Basin SONG Haiqiang, LIU Huiqing, WANG Jing, SI Shanghua, YANG Xiao 2024, 45 (zk(English)):  37-44.  Abstract ( 10 )   PDF (611KB) ( 2 )   Save In order to clarify the main controlling factors of shale oil and gas enrichment, the degree and mechanisms of shale oil and gas enrichment in the Chang 7 member in southeastern Ordos basin were analyzed using the data of drilling, logging, and core. Desorbed gas content is positively correlated with the total organic carbon content (TOC) of source rocks, the organic matter content controls the total content of shale oil and gas, and abundant pores are developed in organic matter, and shale oil and gas exist in both adsorbed and free states in these organic pores. The pore structure and porosity of the reservoir affect the content and occurrence state of shale oil and gas. Adsorbed oil and gas mainly exist in micropores, while free oil and gas in mesopores and macropores. The content of free gas in mesopores is higher than that in macropores, and the larger the porosity, the higher the absolute content of oil and gas in shale. The configuration between sandstone interlayers and organic-rich shale controls the enrichment positions of shale oil and gas. Based on the distribution of siltstone, fine sandstone and shale in the reservoir, the shale oil and gas in Chang 7 member can be classified into two types: near-source and in-source. The in-source shale oil and gas can be further divided into hydrocarbons from sandstone interbedded with shale, shale intercalated with sandstone, and pure shale. Sand bodies underlying the organic-rich shale and lenticular sand bodies exhibit the best potential of oil and gas, followed by sand bodies overlying the organic-rich shale or those tongue-shaped or finger-shaped ones in contact with shale. References | Related Articles | Metrics

Identification and Modeling of Micro-Minor Fractures in Thin Biolimestones in Wangxuzhuang Oilfield LI Yunpeng, LIN Xuechun, YU Xingchen, KANG Zhihong, LI Peijing, WANG Yajing, QI Aiping 2024, 45 (zk(English)):  45-53.  Abstract ( 15 )   PDF (4785KB) ( 2 )   Save Micro-minor fractures represent a key type of reservoir space in the thin biolimestones of the Shahejie formation in the Wangxuzhuang oilfield. Due to the lack of effective measurement methods and characterization techniques, it is challenging to understand these fractures, thereby hindering accurate prediction of fluid flow capacity during oil and gas development. By integrating the data of core samples, thin sections, CT scanning, formation micro-resistivity imaging (FMI) logging, and conventional logging, the development of micro-minor fractures was investigated. With a PSO-BP neural network, the fracture development and distribution in the fractured reservoirs of the study area were predicted. Then a discrete fracture network modeling approach was proposed to simulate the spatial distribution of these fractures. The results show that the biolimestone with developed micro-minor fractures exhibits significant amplitude differences between shallow and deep lateral resistivity readings. Micro-minor fractures are well developed in the biolimestones in the study area, which play a crucial role in improving reservoir physical properties and waterflood response directions. These fractures are controlled by fault zones and sedimentary microfacies of the biolimestone. Numerical simulation confirms that the dual-porosity dual-permeability model incorporating micro-minor fractures can provide a better fit for the dynamic behavior of oil-water relations. References | Related Articles | Metrics

Optimization of Geological Sweet Spots for Shale Oil in Fengcheng Formation in Well Maye-1, Mahu Sag LI Na, LI Hui, LIU Hong, CHEN Fangwen, YANG Sen, ZOU Yang 2024, 45 (zk(English)):  54-60.  Abstract ( 15 )   PDF (787KB) ( 2 )   Save The Fengcheng formation in the Mahu sag is a typical alkaline lacustrine deposit characterized by mixed provenance, complex lithology, overall oil possibility, and scattered sweet spots. To efficiently explore and develop the shale oil, it is necessary to optimize geological sweet spots for the shale oil. Based on the results of high-pressure mercury injection and rock pyrolysis experiments, the reservoir and shale oil mobility of the Fengcheng formation in Well Maye-1 were evaluated, a model for optimizing geological sweet spots for the shale oil was constructed, and the vertical distribution of geological sweet spots for the shale oil was assessed. The results show that porosity, total organic carbon content, brittle mineral content, and difference between free hydrocarbon content and 100 times of total organic carbon content are parameters for respectively evaluating the reservoir performance, oil-bearing property, brittleness, and shale oil mobility of the Fengcheng formation. A model for optimizing geological sweet spots for the shale oil was constructed by using these four parameters, with sweet spot factors for Class Ⅰ, Ⅱ, and Ⅲ shale oil geological sweet spots in Well Maye-1 being greater than 0.282 3, ranging from 0.011 1 to 0.282 3, and less than 0.011 1, respectively. Class Ⅰ shale oil geological sweet spots in the Fengcheng formation in Well Maye-1 are mainly distributed in the upper part of the second member of Fengcheng formation and in the third member of Fengcheng formation, with lithology dominated by mudstone and dolomitic mudstone. References | Related Articles | Metrics

Establishment of Geological Model of Ancient Pockmarks in Fuman Oilfield, Tarim Basin LI Mohan, LI Xiangwen, DU Zhongyuan, ZHANG Yintao, JIN Meng, WANG Ziao 2024, 45 (zk(English)):  61-69.  Abstract ( 13 )   PDF (17547KB) ( 2 )   Save For the pockmarks between major faults and in deep marginal-platform beaches in the Fuman oilfield, a seismic geological model was established based on the detailed interpretation of 3D seismic data and the analysis of the drilling and seismic data in the oilfield. This model enabled a simulated analysis of the variations in seismic response characteristics of the ancient pockmarks in the oilfield by altering the factors such as pockmark scale and fracture density. Consequently, seismic-based pockmark identification models were proposed, along with an understanding of the distribution, genesis and hydrocarbon potential of the pockmarks. The study results provide a foundation for the effective prediction of Ordovician ancient pockmark reservoirs in the Fuman oilfield, Tarim basin. References | Related Articles | Metrics

Thermal Evolution History of Shale in Da’anzhai Member and Its Petroleum Geological Significance in Central Sichuan Basin JIANG Qijun, LI Yong, XIAO Zhenglu, LU Jungang, QIN Chunyu, ZHANG Shaomin 2024, 45 (zk(English)):  70-78.  Abstract ( 11 )   PDF (652KB) ( 2 )   Save The Da’anzhai member of the Lower Jurassic Ziliujing formation is the most favorable layer for the development of continental shale oil in the Sichuan basin, with immense potential for shale oil exploration. However, systematic research on the thermal evolution history of this formation remains scarce. Using a petroliferous basin simulation system, this study comparatively analyzes the differences in thermal evolution and hydrocarbon generation of the shale in Da’anzhai member between the northern and central parts of the Sichuan basin and discusses their impacts on shale oil enrichment. The thermal evolution degree of the Da’anzhai shales in the study area increases gradually from southwest to northeast, with the shales categorized into a highly matured zone and a matured zone. The highly matured zone, located in the northern part of the study area, exhibits vitrinite reflectance values ranging from 1.3% to 1.7%, primarily developing Type III organic matter. Hydrocarbon generation began in the early Late Jurassic, peaked at the end of the Late Jurassic, and experienced two phases of hydrocarbon generation. The matured zone, located in the central to southern parts of the study area, shows vitrinite reflectance values ranging from 0.9% to 1.3%, primarily developing Type II1 to II2 organic matter. With relatively smaller Jurassic sedimentary thickness, organic matter in this region matured later, entering early oil generation by the Late Jurassic and peaking in hydrocarbon generation during the Early Cretaceous, with only one phase of hydrocarbon generation. Compared to the northern region, the central region contains large deposits of organic-rich shales, forming a robust foundation for Da’anzhai shale oil. However, tectonic uplift and stratum erosion since the Paleogene have somewhat impaired oil and gas preservation in this region. References | Related Articles | Metrics

Ordovician Differential Deformation Mechanism of Northern Section of FⅠ17 Strike-Slip Fault, Tarim Basin CAI Zhenzhong, LI Bing, LUO Xiao, LI Huiyuan, LI Mengqin, LI Zhengyang, WANG Qinghong 2024, 45 (zk(English)):  79-86.  Abstract ( 10 )   PDF (7332KB) ( 2 )   Save To understand the role of strike-slip faults in hydrocarbon accumulation in carbonate reservoirs, based on 3D seismic data, the development characteristics and tectonic deformation processes of the northern section of the FI17 strike-slip fault in the Tarim basin were analyzed, and a sandbox physical simulation was performed on the formation and evolution of strike-slip faults by using natural prototypeing. The FI17 strike-slip fault is divided into two sections. The southern section, nearly NE-SW trending, is characterized by en echelon faults, with the Yijianfang formation showing an uplifting feature and significant vertical deformation during the Ordovician period. The northern section, nearly NNE-SSW trending, is dominated by linear strike-slip faults, with the Yijianfang formation exhibiting weak deformation and slight subsidence in local areas during the Ordovician period. Sandbox physical simulation results show that a series of uplift zones formed along the main displacement zone of linear strike-slip faults, while the deflected strike-slip faults formed a series of uplift zones in the southern section and presented strata subsidence in the northern section. Under identical stress conditions, differences in the initial strikes of strike-slip faults lead to the changes in the stress put on the faults, thereby influencing their evolution processes. The southern section of the FI17 strike-slip fault is found with more concentrated stress in compressional uplift zone and more developed fractures and vugs locally, containing richer hydrocarbons. The southern section is expected to be superior in exploration to the northern section. References | Related Articles | Metrics

Development Characteristics and Main Controlling Factors of Reservoir Space in Northern Yujiang Strike-Slip Fault Zone BAO Dian, HU Wenge, CAO Fei, PENG Xiaoping, LIAO Shixi, PAN Lin, WANG Xiao 2024, 45 (zk(English)):  87-94.  Abstract ( 10 )   PDF (7487KB) ( 2 )   Save In order to understand the development characteristics and formation mechanism of reservoir space in the crushed zone of a strike-slip fault, based on the field outcrops, remote sensing images, and core testing data, the reservoir space in the northern Yujiang strike-slip fault zone was identified and quantified, and its main controlling factors were discussed. The results show that the crushed zone of the northern Yujiang strike-slip fault zone can be divided into a northern tenso-shear segment and a southern compresso-shear segment in a plane view. The two segments are different in the reservoir space development characteristics. The tenso-shear segment has larger fracture aperture, while the compresso-shear segment has larger fracture length, fracture density, fractured area, and cave area. Overall, the compresso-shear segment has larger reservoir space. The tectonic stress of the strike-slip fault zone is the external factor determining the development of dominant reservoir space, while the thickness and mineral composition of rocks are the internal factors controlling reservoir space development. The carbonate rocks with a thickness greater than 1 m and a calcium carbonate content of less than 70% can be reworked by compresso-shear process to form favorable areas for the development of fractured-vuggy reservoirs. References | Related Articles | Metrics

RESERVOIR ENGINEERING

Establishment and Application of Type II Generalized Gas-Water Miscible Flooding Characteristic Curve CHU Fujian, GOU Tuobin, HAN Yuetao, GAO Wenjun 2024, 45 (zk(English)):  95-100.  Abstract ( 11 )   PDF (487KB) ( 2 )   Save Based on the Type II generalized water flooding characteristic curve, the concept of underground gas-water cut was introduced, and the Type II generalized gas-water miscible flooding characteristic curve was established on the basis of analogy. The mathematical model of gas-water cut corresponding to the Type II generalized gas-water miscible flooding characteristic curve can be transformed to describe the S-shaped gas-water cut variation and also the convex, S-convex, S-concave, concave, and other shapes of gas-water cut variations, when the characteristic values n and m take different values. This provides additional methods for evaluating development effects of gas-water miscible flooding. The paper put forward a general formula for the Type II gas-water miscible flooding characteristic curve and corresponding methods for solving the mathematical model of gas-water cut, and evaluated the development effects of the water-alternating-gas miscible flooding in the reservoir of Sanjianfang formation in Pubei oilfield and the gas cap + edge water miscible flooding in S31 reservoir in Jinzhou oilfield, respectively, showing a high fitting accuracy. This work provides a valuable reference for developing other oil reservoirs. References | Related Articles | Metrics

Genesis of Barriers/Interlayers in Braided-River Reservoirs and Its Controls on Remaining Oil Distribution: A Case of N1g3Ⅱ in Liuguanzhuang Area of Dagang Oilfield LI Hang, LI Shengli, ZHOU Lianwu, MA Shuiping, HUANG Xiaodi, HAN Bo, LI Ning 2024, 45 (zk(English)):  101-108.  Abstract ( 12 )   PDF (2137KB) ( 3 )   Save In order to clarify the controls of barriers/interlayers on the distribution of remaining oil in the braided-river reservoirs, taking the sand set II in the third member of the Guantao formation (N1g3Ⅱ) in the Liuguanzhuang area of Dagang oilfield as an example, and using the data of core, testing, logging, and production performance, the criteria for quantitative identification of barriers/interlayers were established for the target interval in the study area, and the hierarchy, genesis of barriers/interlayers and their controls on remaining oil distribution were determined. In the study area, the barriers/interlayers in the target interval can be divided into 3 categories such as barriers between sand sets, interlayers between sand bodies, and interlayers within a sand body, which are developed near the architecture boundaries of the 7th-, 8th-, and 9th-order sand bodies, respectively. The barriers between sand sets are dominated by floodplain mudstones and silty mudstone, with thickness ranging from tens of centimeters to several meters. They can efficiently seal oil and gas vertically and allow the edge water to advance preferentially along the formation during development, leading to severe water flooding, and thus the remaining oil is mostly distributed in the upper parts of the complex mid-channel bars and braided channels far from injectors. The interlayers between sand bodies are mainly composed of fine-grained sediments in abandoned channels and gullies, with thickness typically ranging from 0 to 2 meters. They locally hinder vertical fluid migration and laterally control the distribution of remaining oil in different sand bodies, leading to two remaining oil distribution patterns: one is controlled by abandoned channel and the other by gully. The interlayers within a sand body are primarily associated with lateral accreted and interchannel mud deposits, and fall-silt seam, with the thickness reaching tens of centimeters, leading to three remaining oil distribution patterns, which are controlled by laterally-accreted mudstone, fall-silt seam, and interchannel mudstone, respectively. References | Related Articles | Metrics

Comprehensive Determination of Oil-Water Boundary in Eastern Transitional Zone of Daqing SN Oilfield LIANG Yu, YANG Huidong, FU Xiandi, CAI Dongmei, WANG Yanhui, SUN Yanmin 2024, 45 (zk(English)):  109-116.  Abstract ( 15 )   PDF (4529KB) ( 3 )   Save In order to determine the oil-water contact in the eastern transitional zone of the Daqing SN oilfield, based on the drilling, logging, and seismic data, together with the core oil occurrence analysis and the reinterpretation of oil/water layers in existing wells, a comprehensive method for determining the oil-water boundary in the extension zone of structural reservoirs was discussed by using the techniques such as hydrocarbon detection through post-stack seismic attributes based on dual-phase medium theories and fluid identification based on pre-stack seismic waveform indication inversion. The oil-water interface in the study area exhibits the following characteristics: (1) oil patch or higher level occurs in cores; (2) oil layers or oil-water layers are extrapolated on the basis of logging interpretation; (3) in post-stack attributes, the energy ratio of low frequency to high frequency is greater than 0.85; and (4) the predicted water saturation from pre - stack inversion is less than 75%. Therefore, following the principle of "depth of oil-water interface determined by well data, boundaries of oil and water distribution determined by seismic data, and validation by well performance", and through comprehensive analysis from point to line, plane, and then space, the final position of the oil-water interface was determined. The research results effectively guide the extension deployment and evaluation in the study area, and are referential for delineating the oil-water boundaries in similar structural reservoirs. References | Related Articles | Metrics

Thermally Recovered Reservoir Management and EOR for a Multi-Layered Sandstone Oilfield LYU Xiaoguang, LI Wei 2024, 45 (zk(English)):  117-124.  Abstract ( 13 )   PDF (518KB) ( 2 )   Save This paper presents the characteristics and development history of the multi-layered sandstone heavy oil reservoirs in the Kern River field, USA, and specifically discusses the practices of thermally recovered reservoir management and enhanced oil recovery (EOR). The Kern River field is a monocline reservoir of hydrodynamic trap. In the late stage of steam flooding, the practices such as C/O spectral logging, 4D time-lapse dynamic surveillance during thermal recovery, injector-producer performance monitoring, isolated single-channel sandbody identification and tracking, and full-field 3D geological modeling and numerical simulation lay a basis for identifying remaining oil and enhancing oil recovery. Artificial intelligence, steam foam flooding, and layered steam injection through dual-tubing completion are proved technologies for expanding the swept volume of steam flooding. Infill drilling, horizontal well drilling, and horizontal sidetracking in shallow oil reservoirs provide additional opportunities for significantly increasing the recoverable reserves. These technologies enable the production of horizontal well to be more than three times that of adjacent vertical wells. To exploit “cold reservoirs” near the oil-water contact in the downdip zone of the reservoir, water producers are drilled in the downdip aquifer zone to release reservoir pressure, allowing the remaining oil in this zone to be effectively swept by steam. References | Related Articles | Metrics

Water Production Mechanism in Tight Sandstone Gas Reservoirs After Fracturing in Linxing Gas Field SHI Xuefeng, YOU Lijun, GE Yan, HU Yunting, MA Litao, WANG Yijun, GUO Sasa 2024, 45 (zk(English)):  125-131.  Abstract ( 16 )   PDF (514KB) ( 2 )   Save The tight sandstone gas reservoirs in Linxing gas field, Ordos Basin, are key targets for onshore gas development. Due to the structural complexity, reservoir physical properties, and complicated gas-water relationship, most gas wells produce water continuously after fracturing, and their water production rates are very different. Understanding the reasons for irreducible water saturation variation after fracturing is of great significance for formulating effective water control and gas recovery measures to increase well productivity. In this study, representative tight sandstone samples from Linxing gas field were tested by using the gas displacement method to clarify how reservoir properties, production pressure difference, and fracturing fluid affect irreducible water saturation. The results show that the difference in the irreducible water saturation between matrix and fractures is 13.32%-18.36% for Type Ⅰ reservoirs, 28.28%-34.19% for Type Ⅱ reservoirs, and 39.10%-48.15% for Type Ⅲ reservoirs. Hydraulic fractures can significantly improve the water flow capacity of reservoirs, and provide additional water flow pathways. The increased production pressure difference, reduced flow pressure loss and weakened hydrophilic degree are the main mechanisms leading to the weakening capacity of the reservoir in irreducible water and water production of gas wells after fracturing. To control water and produce gas efficiently in tight sandstone gas reservoirs with high water cut after fracturing, measures such as controlling fracturing scale, optimizing production systems, and adjusting fracturing additive amount can be implemented, which will help delay the onset of water breakthrough in gas wells and reduce the overall water production. References | Related Articles | Metrics

Numerical Simulation of Grid-Like Fragmented Structure of Fault-Karst Reservoirs in Southern Tuoputai Block ZHANG Rujie, YUE Ping, ZHANG Ying, LI Xiaobo, HUANG Nan, ZHAO Liming, FAN Qingzhen 2024, 45 (zk(English)):  132-137.  Abstract ( 14 )   PDF (2911KB) ( 2 )   Save The fault-karst reservoirs in the southern Tuoputai block of the Tahe oilfield exhibit a high initial production capacity, but a sharply declining production in the late development stage due to serious water flood and rapid water breakthrough occurred in many wells. There is no efficient simulation method for this phenomenon. Based on the karst features, seismic characteristics, actual well-reservoir configuration, and three-zone structure of fault-karst reservoirs, a grid-like fragmented structure of the fault-karst reservoirs was proposed. Accordingly, by combining the automatic fault extraction (AFE) technology with the ant body attributes, the fracture indicator was derived for characterizing the grid-like fragmented reservoir. Tensor attributes were used for characterizing the karst-vug reservoir, and a dual-porosity compositional model was established for numerical simulation. The results indicate that the grid-like fragmented structure serves as the primary flow channel in fault-karst reservoirs. The fracture indicator is better applicable to characterize the grid-like fragmented structure than AFE and maximum likelihood, and it is highly compatible with tensor attributes in water source zone but poorly compatible in other areas. Compared to single-porosity model, the dual-porosity model based on the grid-like fragmented structure can offer higher matching accuracy and better reflect the production performance of the fault-karst reservoirs. References | Related Articles | Metrics

APPLICATION OF TECHNOLOGY

Application of Scattered Wave Field in Identifying Fractured Reservoirs CHEN Keyang, ZHOU Hui, YANG Wei, WANG Cheng 2024, 45 (zk(English)):  138-145.  Abstract ( 13 )   PDF (10483KB) ( 2 )   Save Fractured reservoirs are important exploration and development targets for increasing oil and gas reserves and production. Conventional post-stack seismic data is not effective for fractured reservoir identification. This paper proposes a relative separation technique of reflected wave field from scattered wave field based on diffusion filtering. This method predicts fractured reservoirs by taking optimal diffusion coefficient and iterations to separate post-stack seismic data into reflected wave field and scattered wave field, and then extracts seismic attributes such as coherence, curvature, and ant body from the scattered wave field. Application for predicting the fractured reservoirs of bedrock weathered crust in the Songliao Basin and the fractured reservoirs in the Maokou formation in the Sichuan Basin has obtained good results, demonstrating the method has higher resolution in predicting fractured reservoirs. The coincidence rate between the predicted result and the actual drilling data from two wells is 67% on the bedrock weathered-crust fractured reservoirs in a Daqing exploration block. It provides a reference for exploration, development, and well deployment in similar reservoirs. References | Related Articles | Metrics

Dynamic Reserves Calculation Method for Fault-Controlled Carbonate Reservoirs GENG Jie, YUE Ping, YANG Wenming, YANG Bo, ZHAO Bin, ZHANG Rujie 2024, 45 (zk(English)):  146-151.  Abstract ( 11 )   PDF (842KB) ( 2 )   Save Fault-controlled carbonate reservoirs are highly heterogeneous, with interweaving development of pores, fractures, and vugs of various sizes. For this kind of reservoirs, the dynamic reserves calculated using conventional material balance methods may be larger than the static reserves. By incorporating water-oil ratio and considering rock compressibility coefficients for different pore-fracture-vug media, a comprehensive compressibility coefficient suitable for the fault-controlled reservoirs was derived. On this basis, a new flow material balance equation was established for the fault-karst reservoir, and its accuracy and applicability were verified using numerical simulation. The research results show that the dynamic reserves calculated by the new equation have an error of only 0.1099% with the static reserves obtained from numerical simulation, confirming the new equation’s reliability and accuracy. In the Halahatang area, the relative error between the dynamic reserves calculated using the new equation and the static reserves derived from geological modeling for multiple wells ranged from -4.82% to -0.15%, which is significantly lower than that calculated using the conventional material balance equation. The results obtained from the new equation are closer to actual conditions, making it more suitable for calculating the reserves of the fault-controlled carbonate reservoirs in the Halahatang area. References | Related Articles | Metrics

OVT-Domain Wide-Azimuth Seismic Forward Modeling of Glutenites in Dongying Sag LOU Fengqin, YU Jingqiang, ZHANG Yunyin, LIU Haining, WU Mingrong, GUO Zhiyang 2024, 45 (zk(English)):  152-157.  Abstract ( 13 )   PDF (7729KB) ( 2 )   Save Considering the varying lithofacies and lithology of the near-source glutenites in the Dongying sag, a three-dimensional geological model of the glutenites was established for wide-azimuth seismic forward modeling. Using the simulated data, and through azimuthal stacking of gathers in OVT-domain, the effects of azimuth variation on parameters such as seismic travel time and amplitude were analyzed, and the relationships between azimuth/amplitude and favorable reservoirs were established. The results show that the variation in the sedimentary direction of the glutenites causes azimuth differences in seismic wave propagation, leading to azimuthal anisotropy in seismic reflections. The data cube obtained from azimuthal stacking at the azimuth perpendicular to the sedimentary boundaries is more sensitive to the responses of the top and internal boundaries of the glutenite,with stronger amplitudes. It more effectively reveals the contacts between glutenites of different periods,thereby facilitating the accurate identification of glutenite and fine prediction of favorable reservoir distribution. Wide-azimuth OVT-domain seismic data are proved effective in glutenite prediction,and have been successfully applied in predicting glutenite reservoirs in the steep slope zone of the northern Dongying sag,with the prediction results in good agreement with actual drilling results. References | Related Articles | Metrics

Seismic Frequency Enhancement Processing Based on Multi-Layer Residual Network and Its Application to Identification of Thin Reservoirs ZHANG Wenqi, LI Chunlei 2024, 45 (zk(English)):  158-164.  Abstract ( 15 )   PDF (4638KB) ( 2 )   Save The seismic frequency enhancement processing method based on multi-layer residual network combines high-frequency well logging information with seismic data through an intelligent network. This method effectively improves vertical resolution while maintaining lateral continuity, facilitating the identification of thin reservoirs. In the AMH area, seismic data processed by conventional techniques enable only the identification of carbonates thicker than 30 m. The seismic frequency enhancement processing method based on multi-layer residual network was proposed and applied in this area. First, training was performed using a multi-layer residual network, a deep learning network with near-wellbore seismic amplitude as training data and the relative wave impedance data from well logging curves as label data. A predictive model for relative wave impedance curve was obtained. Using seismic data as input, the deep network model calculated relative wave impedance data, and the reflection coefficient based on the frequency-enhanced seismic data. According to the geological conditions of the target area, appropriate wide-band wavelets were selected convolved with the reflection coefficient to obtain frequency-enhanced seismic data. The inversion results based on the frequency-enhanced seismic data are of high resolution vertically, and identifiable and traceable laterally, and well matched the target beds. They can identify the thin beds in the AMH area. The seismic frequency enhancement processing method based on multi-layer residual network together with corresponding high-resolution model inversion can identify beds thicker than 10 m in the AMH area. This method can effectively identify thin beds that can’t be identified using low-resolution seismic data, and improves the accuracy in predicting thin beds. It is referential for identifying similar thin beds. References | Related Articles | Metrics