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01 October 2019, Volume 40 Issue 5 Previous Issue    Next Issue

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Research Progress on Oil and Gas Geology and Exploration Practice in Qaidam Basin ZHANG Daowei1, MA Dade1, CHEN Yan1, WU Kunyu1, CAI Zhihong1, ZHAO Jian1, WANG Jiangong2 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190501 Abstract ( 189 )   PDF (300KB) ( 325 )   Save Since the 13th Five-Year Plan, in accordance with the guiding ideology of “marching toward unconventional oil and gas and prospecting oil and gas in deep strata”, the Qinghai oilfield has vigorously promoted the exploration of unconventional and deep oil and gas resources and the studies on related theories. Over several years of research, a series of new progresses and new understandings have been achieved：the hydrocarbon-generating parent material in saline-lacustrine source rocks and its hydrocarbon generation mechanism have been identified; a hydrocarbon generation model including interactions among soluble organic matter, kerogen and minerals has been established, which is so called “three-factor controlling” hydrocarbon-generation model; the characteristics and forming mechanisms of fine-grained carbonate reservoirs, deep clastic reservoirs and basement reservoirs have been summarized; and the hydrocarbon accumulation patterns of mixed carbonate reservoirs and deep clastic reservoirs have been built. Guided by these theoretical understandings, a series of exploration targets such as the deep mixed carbonate reservoirs in the Yingxiongling structural belt, deep clastic gas reservoirs in the north Lenghu slope, and basement gas reservoirs in the piedmont of Altyn Tagh mountain have been proved and significant discoveries have been gained. As of April 2019, the cumulative incremental proved OOIP is 2.5×108 tons of equivalent crude oil Related Articles | Metrics

Effects of Fracture Systems During Oil and Gas Accumulation in Yingxi Area, Qaidam Basin CUI Jun, LI Yanan, MAO Jianying, ZHAO Quan, GAO Shufang, DENG Wen 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190502 Abstract ( 95 )   PDF (300KB) ( 195 )   Save A significant breakthrough has been gained in petroleum exploration of Yingxi carbonate reservoir of the lower Ganchaigou formation in Yingxi area of Qaidam basin recently. Based on the core observation, experimental analysis and logging data, the forming mechanism of Yingxi carbonate reservoir and its effects during oil and gas accumulation are researched in this paper. The research indicates that the reservoir was formed in a deep-water sedimentary environment, and the sediment is a set of fine-grained carbonates with some features of diamictite. The reservoir spaces are dominated by dolomite intercrystalline pores, the fracture systems are very developed in the reservoir. The complicated fracture systems are made up of various scales of fractures and play important roles in hydrocarbon accumulation and migration. During the deposition of the upper Ganchaigou formation, the source rocks in the upper member of the lower Ganchaigou formation entered the threshold of oil generation and continuously generated oil and gas. During the late deposition period of Shizigou formation, Himalayan movement resulted in the folding inversion and the Yingxiongling structure gradually formed. The formation process of Yingxiongling structure is not only the formation process of the fracture systems in Yingxi carbonate reservoir, but also is the process of hydrocarbon redistribution in the fracture systems, during which a lot of separate petroleum systems formed Related Articles | Metrics

Evaluation of Effective Reservoirs in Mixed Carbonate Rocks in Yingxi Area LI Yafeng1,2, WU Kunyu1, GAO Shufang1, LI Guimei1, LI Qingbo1, ZHANG Di1 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190503 Abstract ( 82 )   PDF (300KB) ( 135 )   Save Compared with marine carbonate rocks, Yingxi lacustrine carbonate rock is characterized by mixed sediments, variable lithologies and diverse minerals. There are various types of reservoir spaces including intercrystalline pores and fractures as well as dissolved pores, leading to extremely high reservoir heterogeneity. It is hard to get accurate information about mineral content, porosity and pore structure only by using conventional logs, and effective reservoirs are difficult to be identified. In this paper, based on the data of FMI logging, lithoscanner logging, conventional logging and core analysis, the matrix porosity is accurately calculated by using variable skeleton method according to rock mineral components, the factors of matrix reservoir are constructed, and the integrated reservoir classification chart and classification standard for mixed lacustrine carbonate reservoirs are established by combining with test data, fracture parameters, FMI structure and apparent surface proportion of fractures and pores. The actual application result of the classification standard in Yingxi area is pretty good, providing references for logging evaluation of the complicated carbonate reservoirs in other areas Related Articles | Metrics

Formation and Evolution of Cenozoic Basins in the Middle Part of Altyn Tagh Fault Zone SUN Songling1, ZHANG Zhenggang1, RONG Guanglai2a, SHI Yajun1, HOU Suli2b, WANG Wenzhuo2b 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190504 Abstract ( 89 )   PDF (300KB) ( 129 )   Save Altyn Tagh fault zone is a large NE-SW trending transforming fault located in the northwestern China. Various basins formed in the both sides of the fault zone due to different regional stress at different times and different fault movement directions. Based on the studies of the Cenozoic basins and surface outcrops in both sides of the fault and previous research results on strike-slipping of the Altyn Tagh fault, the paper analyzes the evolution process, basin type, sedimentary environment and the relationship between the Altyn Tagh fault zone and the evolution of peripheral basins by combining with a structural model related to right-lateral divergent fault. According to the relationships among the outcrop, basin shape and lithofacies of the Cenozoic basin in both sides of the fault zone, it is considered that the left-lateral slipping distance of Altyn Tagh fault is about 350 km since Cenozoic; the comparison of the experimental model of mud cake right-lateral slipping with the Cenozoic prototype basin in the middle part of Altyn Tagh fault zone shows good structural matching relations on the basin forming environment and basin type. The study on the distribution of Cenozoic prototype basins after the restoration of the strike slip of Altyn Tagh fault has important significance for understanding current Cenozoic basins and for petroleum exploration in the basins Related Articles | Metrics

Identification and Prediction of Effective Source Rocks for Tight Oil in Zhahaquan Area, Qaidam Basin TIAN Mingzhi1, LIU Zhanguo1, SONG Guangyong1, LI Chang1, TIAN Han1, LI Yafeng2, XIA Xiaomin2 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190505 Abstract ( 85 )   PDF (300KB) ( 136 )   Save Since 2013, large-scale tight oil reservoirs have been discovered in the upper Ganchaigou formation of Neogene in Zhahaquan area of Qaidam basin. In order to evaluate the availability of the source rocks in the area and to effectively support the well deployment, a core-calibrated logging method to identify effective source rocks is established on the basis of core observation, whole rock analysis, geochemical analysis, sedimentary environment analysis and log response comparison. The logging response characteristics of the source rocks in study area are not very typical, and the TOC is poorly correlated with logging parameters such as interval transit time, natural gamma ray, resistivity and density. It is found that the TOC is well correlated with the difference between total natural gamma ray and de-uranium natural gamma ray and the ratio of thorium to uranium, respectively; and then a formula is built to calculate TOC. The method is simple and effective. The vitrinite reflectance of the source rocks in study area is 0.624%~1.265%, which is in the mature stage and is conducive to oil generation. After identifying the effective source rocks of 24 wells in study area, it is found that the effective source rock development zones in the Ⅳ toⅠ sand member gradually migrate from the northwest to the southeast. Furthermore, the source rocks and the beach bar overlap each other vertically in shallow lake area, forming a good source-storage configuration. The method can be a guidance for source rock evaluation and tight oil exploration and deployment Related Articles | Metrics

Logging-Based Debris Identification of Oil Member in Lower Section of Lower Ganchaigou Formation in Block Qie12, Kunbei Oilfield JIA Fengjuan1, ZHAO Wenkai2, MOU Zhonghai3, LIN Changqing1, SHI Qi1, ZHENG Yubao1, ZHANG Fengying1 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190506 Abstract ( 83 )   PDF (300KB) ( 119 )   Save Regarding the difficulties in identifying the sandy conglomerate and high-resistivity layers in the Ⅲ oil member of the lower section of lower Ganchaigou formation in the Block Qie12 of Kunbei oilfield, Qaidam basin, using the data of core, thin section, formation test, logging and a geology-logging combined analysis method, the paper discusses the logging responses of rock debris content and its quantitative calculation methods, and then applies these methods into identifying sedimentary source orientation, major distributary channel and high-resistivity aquifer and lithology-induced induction resistivity correction in high-resistivity layers. Log responses are related to debris contents, based on which, an equation of debris content calculated from interval transit time and induction resistivity, and an induction resistivity correction equation have been established based on the relationship between interval transit time and induction resistivity variation. The high induction resistivity after correction can be used to solve the problems in identifying high-resistivity aquifer and correcting the oil saturation errors caused by high-resistivity debris. Related Articles | Metrics

Gas Invasion and Its Main Controlling Factors of Oil and Gas Reservoirs in Ziniquanzi Formation of Horgos Anticline TANG Xueying1, YANG Qiang2, YUAN Bo1, YAN Guihua1, WEI Lingyun1 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190507 Abstract ( 87 )   PDF (300KB) ( 194 )   Save In order to identify the gas invasion and its main controlling factors in the oil and gas reservoirs in Ziniquanzi formation of Horgos anticline, using the methods of geochemical property analysis, inclusion testing and seismic analysis, this paper studies the oil and gas reservoirs in which fractionation of gas invasion occurs, and analyzes the influences of the fractionation on the reservoirs. The study result shows that the source rocks have high organic matter abundance and persistent gas generation capability; a large number of faults and a good matching of geological conditions such as oil and gas charging time in the study area cause the large scaled gas invasion fractionation in the study area; formation pressure and vertical depth are the main factors controlling the intensity of gas invasion fractionation; the gas invasion fractionation is the direct cause of the formation of complex crude oil types such as heavy oil, low waxy condensate oil and high waxy oil Related Articles | Metrics

Brittleness Analysis and Characterization of Deep Marine Shales ZHANG Chenchen1, LIU Zi1, DONG Dazhong2, WANG Yuman2, JIANG Shan3, GUAN Quanzhong4 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190508 Abstract ( 70 )   PDF (300KB) ( 120 )   Save Aiming at the challenges of deep-marine shale gas development in the southern China, and taking the Wufeng-Longmaxi shale in the Sichuan basin as the research object, the paper focuses on the brittleness analysis and characterization of deep marine shale, establishes a quantitative assessment index of shale brittleness based on the complete stress-strain curve, and uses the peak strain and steepness of post-peak slope as indicators to express the degrees of brittle failure complexity and adequacy, respectively. Then according to the results of high-confining-pressure triaxial compression tests for main shale lithofacies including siliceous shale, calcareous-siliceous shale, calcareous shale and clay-siliceous shale, the paper analyzes the influence of confining pressure on shale brittleness, establishes a brittleness evaluation method for deep marine shales and compares the brittleness of deep and shallow shale reservoirs. The results show that under low confining pressure, the pressure mainly enhances the compressive strength of the shale and the shale brittleness increases with the enhancement of the confining pressure; while under high confining pressure, the pressure mainly restrains the initiation and propagation of fractures and the shale brittleness decreases with the weakening of the confining pressure; using elastic parameters as the indicators of lithology and fracture toughness as an indicator of confining pressure, a mechanical brittleness index is established, which can be effectively used in the brittleness evaluation of the deep shale reservoirs below 3 500 m as the supplementary of the mineral method and elastic parameter method; the siliceous shale and calcareous-siliceous shale still have the potential to be favorable reservoirs at the depth of 4 500-5 000 m. However, the deep marine shales have thinner “sweet spot” layers and lower development potential due to the brittleness weakening Related Articles | Metrics

Carboniferous Igneous Reservoir Distribution and Its Controlling Factors in Mahu-Dabasong Area, Junggar Basin Ablimiti YIMING1,2, ZHA Ming1, YANG Fan3, YIN He2, DING Xiujian1, BIAN Baoli2 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190509 Abstract ( 101 )   PDF (300KB) ( 142 )   Save In recent years, oil and gas exploration of Carboniferous igneous reservoirs in Junggar basin has gradually shifted from basin margin to basin center. In order to more accurately determine the oil and gas reservoir distribution in the hinterland of the basin, a study on Carboniferous igneous reservoir distribution, reservoir development characteristics and its controlling factors is carried out in Mahu-Dabasong area based on aeromagnetic, seismic and logging data. The study results show that the Carboniferous strata are dominated by intermediate-basic igneous rock and volcanic sedimentary rocks and the igneous rock spreads out like a strip with the NNE-SSN direction. The reservoir spaces of the igneous rocks are mainly composed of secondary pores and the reservoir belongs to low porosity, low-extra low permeability reservoirs; The forming of effective reservoir is mainly controlled by igneous rock lithology and lithofacies, weathering time and diagenesis at the late stage; the igneous reservoirs of weathering crust are mainly developed in the explosive facies near craters and the effusive facies on the flanks of volcanoes Related Articles | Metrics

Study on Seepage Mechanism and Development Simulation of Commingled Production for Multi-Layered Gas Reservoirs: A Case of Sebei Gas Field, Qaidam Basin MA Yuankun, CHAI Xiaoying, LIAN Yunxiao, GU Duanyang, YU Xue, LIU Guoliang 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190510 Abstract ( 123 )   PDF (300KB) ( 242 )   Save Sebei gas field in Qaidam basin is a typical sandstone gas reservoir with multiple thin layers and loose sands. There are nearly 100 reservoirs from shallow to deep in the gas field. In order to realize efficient development and to improve reserves producing degree, multi-layer commingled production technology is applied in the gas field. In terms of the problems like interference between layers and unbalanced reserves producing resulted from the commingled production, a physical simulation method is proposed for the commingled production in this paper. Combined with numerical simulation, the main factors influencing the reserves producing degree of the gas reservoir during commingled production are discussed and the production performance under different formation pressures and different physical properties are systematically analyzed. Based on which, the favorable conditions for the commingled production are studied and a series of charts is established by taking permeability multiple ratio and pressure multiple ratio as evaluation parameters, which can be used to judge physical property and formation pressure of different gas zones, then to evaluate the interference degree of the commingled production and finally to provide a basis for the perforation combination optimization in the multi-layered gas reservoirs Related Articles | Metrics

Factors Influencing Productivity in CBM Fractured Horizontal Wells SUN Renyuan1, YAO Shifeng1, MEI Yonggui2, SUN Ying1, SUN Xiaofei1, ZHANG Xianmin1 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190511 Abstract ( 113 )   PDF (300KB) ( 189 )   Save Coalbed methane is an important unconventional resource and its productivity evaluation is very significant for the efficient development of coalbed methane. Based on the data of formation pressure, permeability, initial gas content and Langmuir pressure, etc. in Qiyuan Coal Mine of Shouyang block, the software COMET3 is used to evaluate the production capacity of CBM fractured horizontal wells, and the factors influencing well productivity such as horizontal section length, horizontal well spacing and fracture parameters are studied in this paper. The results show that the horizontal section length, horizontal well spacing, fracture amount, fracture half-length and fracture conductivity can significantly affect the productivity of horizontal well. When the horizontal section length is less than 600 m, the variation of gas production of CBM well is sensitive; the heterogeneity of coal bed is very important for the high yield of CBM well; the fracture amount is the main factor controlling cumulative gas production, followed by fracture conductivity and fracture half-length; with the decrease of horizontal well spacing, the cumulative gas production will increase, but too small well spacing does not work well Related Articles | Metrics

Production Prediction Methods for Carbonate Reservoirs in Tarim Oilfield LI Zhenhua, GU Qiaoyuan, ZHANG Dapeng, TONG Kejia, WEI Hua, PI Qiumei 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190513 Abstract ( 114 )   PDF (300KB) ( 251 )   Save Carbonate reservoir is characterized by strong heterogeneity and rapid production decline at the early stage, and the conventional production prediction methods can’t meet the production demands. The paper optimizes the conventional production prediction methods and discusses the basic models and matching methods of both exponential decline prediction and stretched exponential decline prediction. After the main factors influencing the production are identified, the producing wells are classified and an exponential decline model is used to match the production data of oil wells, thus the production prediction for producing wells during programming can be well guided. The stretched exponential decline model is applicable for the reservoirs with rapid production decline such as carbonate reservoirs. Taking the stretched exponential decline laws of producing wells in some similar reservoirs as references, the production of newly-drilled wells can be predicted. The combination of the 2 prediction methods can further improve the reliability of production prediction for carbonate reservoirs and guide the production practices of the similar reservoirs in the future Related Articles | Metrics

Feasibility Study of Reservoir Volume Fracturing in Complex Geostress State in Yingxi Area XIONG Tingsong, ZHANG Chengjuan, ZHAO Endong, LIU Youmin, XIE Jing, Liu Huan 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190512 Abstract ( 68 )   PDF (300KB) ( 177 )   Save The shale oil in the E23 reservoir of Yingxi area is characterized by the oil distributed in the whole area and high oil yield in local districts. Limited by geological understanding and engineering technology, efficient development of the reservoir hasn’t been realized over 30 years of progressive exploration and evaluation due to the poor effect of vertical wells and low natural productivity. The paper aims to research volume fracturing technology in horizontal wells and its application to realize the efficient development by increasing stimulated volume and drainage area and reducing differential pressure. Based on the reservoir geological analysis, the paper performs feasibility evaluation of volume fracturing technology and simulation of crack propagation under complex geostress conditions. The study results show that microfractures are very developed in the E23 reservoir of Yingxi area, the reservoir rock is brittle, the reservoir space is complex and the fluidity ratio is low and the ground stress condition is complex. The volume fracturing technology in horizontal wells with “large displacement, large fluid volume, high slickwater content and temporary plugging in fractures” has been adopted and complex fracture systems form. The application of the process has achieved the goals of increasing single well production and improving development effect, proving that the volume fracturing technology in horizontal wells is an effective way to efficiently develop the oil shale in the E23 reservoir of Yingxi area Related Articles | Metrics

Performance and Oil Displacement Effect of Polymer Microsphere Additive System REN Hao1, ZHANG Zuowei2, WANG Jian3, GUAN Dan1, QUE Tingli1, YU Heng4 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190514 Abstract ( 111 )   PDF (300KB) ( 196 )   Save In order to improve the effects of waterflooding and polymer flooding in Pu125 block of Pubei oilfield, it is proposed to use polymer microsphere additive system to improve the technology. Under the simulated reservoir conditions, the performance of the additive system was evaluated, and its microstructure was analyzed to study its oil displacement effect. The experimental results show that the polymer microsphere additive system under the reservoir condition has a viscosity of 114.3 mPa·s, which has good temperature adaptability, mineralization adaptability and long-term stability. Its shear resistance is better than that of polymer solution; the microstructure of the additive system is that the microspheres are dispersed and adsorbed on the branches of the polymer network structure, which not only improves the viscosity of the polymer, but also enhances the dispersion of the microspheres; the efficiency of the additive system is better than that of polymer system. After the injection of the additive system, the distributing rates of the high and low permeability layers are about 50%, respectively. Compared with polymer-only flooding, the additive system can better improve the development effect and the recovery factor of high watercut reservoirs Related Articles | Metrics

Study on Sedimentary Facies Based on FMI logging and LS loggingA Case Study of Huangguamao Area, Qaidam Basin ZHANG Yongshu1, ZHANG Shenqin1, WU Yanxiong1, YANG Zhi2, SHI Qi1, MA Fengchun1 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190515 Abstract ( 140 )   PDF (300KB) ( 285 )   Save There are three types of lithologies such as carbonate rock, clastic rock and mixtite in Huangguamao area of Qaidam basin and conventional logging curves can’t be used to effectively identify the lithologies because the reservoirs in the study area are very thin. By using lithoScanner logging (LS) and imaging logging (FMI), mineral compositions and structures of the rocks can be identified, and then the reservoir rock type can be determined. Based on the well core, LS logging, FMI logging and comprehensive calibration of conventional logging, this paper identifies four categories of sedimentary microfacies and summarizes the corresponding logging characteristics of different microfacies. Firstly, for alga mat, LS logging shows that the calcite content of the alga mat is generally more than 80%, FMI logging is characterized by highlight and disorder or flocculent reflections and the conventional logging curve has the characteristics of ultra-low GR and low SP. For calcareous dolomitic flat, LS logging shows that its carbonate mineral content is more than 50%, FMI logging indicates that it is a weak-strong layer, while the conventional logging exhibits low GR, low SP and medium-high resistivity. For sand flat, LS logging shows that its felsic mineral content is higher than 50%, FMI logging indicates it has a blocky structure and the conventional logging exhibits a feature of medium-low GR and medium-low resistivity. The mineral compositions of marlstone (dolomite) flat are very complex, sandstone and marl are interbedded with each other, for this microfacies, a serious toothed LS logging curve is noted, FMI logging shows a strong stratification and the toothed conventional logging curve exhibits a feature of medium-high GR. Based on the logging facies analysis, detailed characterization is carried out for the spatial distribution of the sedimentary microfacies and the study results can be a guidance for the determination of the effective reservoir distribution in the area Related Articles | Metrics

Application of Characteristics of Seismic Frequency Spectrum Attenuation in Classification and Evaluation of Gas Wells in Basement Gas Reservoirs: A Case of Dongping Basement Gas Reservoir CHEN Fangfang1a, JIANG Yue2, LIU Jingun1b, LI Chengcheng1a, FENG Jun1c, TAN Zhiwei1d 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190516 Abstract ( 77 )   PDF (300KB) ( 181 )   Save As a kind of basement gas reservoir in the inland basins of China, Dongping basement gas reservoir is characterized by complex lithologies, developed fractures and greatly different development effects in single wells. Affected by basal water invasion, the gas yield of Dongping basement-rock gas reservoir decreases, and the reservoir enters the stage of large-scale adjustment. In order to realize the potential tapping targets and to rapidly deploy risky wells, it is necessary to qualitatively evaluate the standard of high-yield gas wells. Seismic frequency spectrum attenuation reflects the strong absorption of the high frequency energy of seismic waves by gas-bearing intervals and can better predict the gas distribution in the formation. Based on which, Discrete Fourier Transformation method is used to perform spectral decomposition of the seismic time-frequency data for the favorable gas-bearing areas in Dongping basement gas reservoir, and the frequency spectrum attenuation of gather profile is analyzed. The results show that the phenomena of high frequency attenuation and low frequency enhancement exist in the areas penetrated by high-yield gas wells. By combining well production and lithologies, a set of standards for gas well classification and evaluation is established for Dongping basement gas reservoir with the coincidence rate of 83.3% in single wells, which verifies the reliability of the classification and evaluation standards. Related Articles | Metrics

Comparison of Deterministic Modeling and Stochastic Modeling for Interlayers in Clastic Reservoir Development LIAN Zhanggui1, LI Jun1, WANG Xiao2, WANG Kaiyu1, SHAO Guangqiang1, ZHANG Shuzhen1 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190517 Abstract ( 97 )   PDF (300KB) ( 152 )   Save The conventional method of clastic reservoir interlayer modeling aims at simple interlayer description, which is lack of systematic understanding about remaining oil distribution. Four virtual wells are designed and stochastic and deterministic models are established for between-layer and within-layer interlayers. Reservoir numerical modeling regarding production modes of natural energy, water injection and gas injection is performed for the different models, the corresponding models are established by increasing area and expanding well numbers, respectively and comparisons of the models are carried out. The comparison results show that the result obtained from the stochastic modeling is of significant heterogeneity and large uncertainty, and the result obtained from the deterministic modeling is in accordance with the geological understanding. Different interlayer modeling methods lead to obvious differences in cognitions about the remaining oil distribution with the same production mode, and result in different controls on oil and water movement, remaining oil distribution and water injection and gas injection. During the middle-late stage of oilfield development, the geological understandings should be fully used to establish a deterministic interlayer model and a corresponding facies-controlled reservoir model, and to accurately quantify the remaining oil distribution, then providing basis for well allocation Related Articles | Metrics

Seismic Fluid Prediction in Caved Carbonate Reservoirs in Wellblock ZG8, Tarim Basin ZHANG Yuanyin1, 2, SUN Zandong2, YANG Haijun3, Ahmatjan ABUDRAHMAN4, JIANG Kunpeng1 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190518 Abstract ( 99 )   PDF (300KB) ( 189 )   Save Regarding the characteristics of complicated pore types and strong heterogeneity of carbonate reservoirs and based on the exploration status of fluid properties difficult to be predicted in Tarim basin, DEM-Gassmann rock-physics model which not only considers the influence of pore shapes on velocity but also diminishes velocity dispersion by differential method was employed for fluid substitution in the carbonate reservoirs in Wellblock ZG8, Tazhong area. It was concluded that the elastic properties of the water in the reservoir were different from those of oil and gas. Based on the comparison of elastic parameter crossplots, P-impedance vs. Vp/Vs and Poisson ratio vs. P-impedance were selected to identify fluid properties, and according to AVO inversion results, fluid property prediction was carried out for the carbonate reservoir in Yingshan formation of Wellblock ZG8. The predicted results were in accordance with the geological understanding obtained from 24 wells. Theoretical and case analysis in this paper provide some applicable methods and corresponding standards for the fluid prediction in the caved carbonate reservoirs in Tarim basin. Related Articles | Metrics

Tight Oil Reservoir Brittleness Index Prediction Based on Petrophysical Experiments: A Case from Yuehui 101 Area of Qaidam Basin ZHANG Ping1, XIA Xiaomin2, CUI Han2, CHEN Yuanyuan2, WANG Wenzhuo2 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190519 Abstract ( 74 )   PDF (300KB) ( 186 )   Save The Ⅳ oil member of the upper section of the lower Ganchaigou formation in the Yuehui 101 area of the southwestern Qaidam basin belongs to tight lacustrine carbonate reservoirs, which lacks of quantitative characterization basis for its brittleness evaluation. The key technology for tight oil reservoir brittleness evaluation is discussed based on the tight reservoir brittleness prediction. At first, based on the whole rock mineral analysis by core X-ray diffraction, the brittleness index of rock sample is calculated qualitatively by using mineral content. Based on high-temperature high-pressure triaxial mechanical tests and acoustic triaxial experiments for rocks, the brittleness index of the sample is calculated quantitatively and furthermore, the transforming relations between the static and dynamic Young’s modulus and between the P-velocity and S-velocity are determined. Secondly, the simultaneous inversion technology of pre-stack elastic parameters is used, the P-impedance, S-impedance and density data are obtained. Then Young’s modulus and Poisson’s ratio are calculated, and the dynamic and static Young’s modulus relations are used to convert them into the static Young’s modulus, so as to complete the calculation of static brittleness index. Finally, the distributions of brittleness and lithology in the target zone are analyzed to identify the key areas for tight oil exploration, and the effectiveness of the method has been verified by subsequent well drilling Related Articles | Metrics

Application of Lithology-Electrical Property Rendezvous Method in Studying Water Invasion in Unconsolidated Sandstone Gas ReservoirsA Case Study from Tainan Gas Field, Qaidam Basin GU Duanyanga, CHAI Xiaoyinga, SUN Yongb, LIU Guolianga, YAN Huandea, QIN Caihonga 2019, 40 (5):  1-1.  doi: 10.7657/XJPG20190520 Abstract ( 78 )   PDF (300KB) ( 146 )   Save Tainan gas field in Qaidam basin is a typical unconsolidated sandstone reservoir, which is characterized by loose stratum, sandstone interbedded with mudstone, surrounded by edge water and complex gas-water distribution. During the mid-late development period of gas reservoirs, the changes of formation resistivity are not obvious after edge water invasion, resulting in the difficulties of fluid identification in the reservoir. Based on the logging data normalization and logging interpretation technologies for water invasion, the lithology-electrical property relations are used to study water invasion mechanism. The electrical property curves obtained from conventional logging and production logging are used to identify water invasion zones qualitatively, a method to identify water invasion characteristic is proposed on the basis of lithology-electrical property rendezvous, quantitative parameter identification and horizon calibration are performed for water invasion zones, and a set of water invasion evaluation technologies has been established and the difficulties of water invasion identification in low-resistivity gas zones can be overcome. The established logging interpretation mode and evaluation method for water invasion zones are put into use in some newly-drilled wells and the interpretation coincidence rate is 84.2%, which proves that the lithology-electrical property rendezvous method can be the references for water invasion zone identification and interpretation in other unconsolidated gas reservoirs Related Articles | Metrics