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01 January 2021, Volume 41 Issue zk(English) Previous Issue    Next Issue

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Style and Evolution of Thrust Decollement in Miquan Area in Piedmont of Bogda Mountain YANG Yulong 2020, 41 (zk(English)):  1-9.  Abstract ( 129 )   PDF (9786KB) ( 57 )   Save To determine the structural style and stratum distribution in the Miquan area in the piedmont of Bogda Mountain, the paper establishes a typical thrust decollement style in the study area based on the study of the fault development characteristics and the controls of detachment layer on structure development. Restricted by the Upper Triassic mudstone and the detachment coal layer in the Lower Jurassic Badaowan formation, the basement fault which underwent a low-angle slip and thrust from south to north along the detachment layer at the early stage and a updip at the late stage incised into the strata and exposed on the surface, and displayed a unique deckchair-like shape. The secondary faults are of small scale, whose ends are located in the detachment layer. The piedmont of Bogda Mountain is divided into 3 large structural belts such as nappe belt (basement nappe), thrust belt and decollement belt. The Miquan area located in the thrust belt can be divided into 4 structural steps laterally and 3 structural layers vertically. Each structural layer is an active-roof duplex and the development degrees of the secondary faults are different from each other. The establishment of the thrust decollement style has overturned the preliminary understanding about the structures. It is considered that the strata under the nappe still belong to the lower reservoir-forming combination where favorable traps could be discovered. The understanding has great significance for petroleum exploration in the lower combination in the piedmont of the southern margin, Junggar basin. References | Related Articles | Metrics

Genesis of Oil and Gas in Sikeshu Sag in the Southern Margin of Junggar Basin REN Jiangling, WANG Feiyu, ZHAO Zengyi, ZHANG Yunpei, MI Julei, LIU Cuimin 2020, 41 (zk(English)):  10-15.  Abstract ( 107 )   PDF (687KB) ( 117 )   Save The oil found in Sikeshu sag in the southern margin of Junggar Basin is the light oil with associated wet gas, but the properties of the oil and gas in different regions are different and there are some disputes about the hydrocarbon sources. The samples of the Middle-Lower Jurassic and Middle-Upper Triassic source rocks obtained from the outcrops in the southern margin are selected. Based on the analysis of rock pyrolysis, choloroform asphalt A, gas chromatography and organic petrology and combined with geochemical analysis of the source rocks, the paper analyzes the geochemical properties of the source rocks of Triassic, Jurassic and Paleogene in Sikeshu sag, determines the organic facies of the source rocks and discusses the genesis and origin of the oil and gas. The study results show that the light oil and gas in Sikeshu sag mainly come from the source rocks of the Lower Jurassic Badaowan Formation, probably from the Middle-Upper Triassic source rocks; the oil in Dushanzi oilfield and the Neogene Xihu anticline mainly comes from Jurassic or Triassic source rocks, partial oil from the source rocks of the Paleogene Anjihaihe Formation. References | Related Articles | Metrics

Reservoir Characteristics and Main Controlling Factors of Cretaceous Qingshuihe Formation in the Southern Margin of Junggar Basin SI Xueqiang, YUAN Bo, GUO Huajun, XU Yang, CHEN Nenggui, PENG Bo 2020, 41 (zk(English)):  16-24.  Abstract ( 94 )   PDF (10888KB) ( 45 )   Save Profitable oil and gas flows of over 1,000 m3/d have been obtained from the sandstone reservoir of the Cretaceous Qingshuihe formation in the Sikeshu sag of the southern margin, Junggar basin, which proves that the formation belongs to a set of high-quality reservoir. Based on the analysis of outcrop sections and drilling data and using polarizing microscope, pore and permeability analyzer and confocal laser scanning microscope, the paper analyzes the rock mineral, physical property and pore structure of the sandstone samples from the Qingshuihe formation and carries out researches on diagenetic evolution by combining with its burial history. The results show that the sandstone of Qingshuihe formation mainly containing feldspar lithic sandstone and lithic sandstone is characterized by a little matrix, medium content of cements and developed residual intergranular pores, which is at the Phase A of the middle diagenetic stage with the compaction dominated by pore reduction. The comprehensive analysis shows that the formation of the high-quality reservoir in Qingshuihe formation is controlled by 3 key factors such as early long-term shallow burial and late rapid deep burial, developed fractures and abnormal high formation pressure. The early long-term shallow burial and the late rapid deep burial are favorable for preservation of primary pores in the reservoir; both intragranular microfracture and bedding fracture are developed, which is helpful for the formation of efficient flowing paths in the sandstone reservoir; and the abnormal high formation pressure contributes to the preservation of intergranular pores and the opening of fractures. References | Related Articles | Metrics

Prediction of Reef Reservoir in Changxing Formation of Damaoping Area, Eastern Sichuan Basin DING Chuanqi, ZHOU Lu, ZHONG Kexiu, WU Yong, ZHONG Feiyan, LIU Yi 2020, 41 (zk(English)):  25-32.  Abstract ( 97 )   PDF (4804KB) ( 122 )   Save The reefs of the Upper Permian Changxing formation in the Damaoping area of the eastern Sichuan Basin are distributed in the shape of ring and strip. Individual reefs are characterized by small scale, deep burial depth, multiple periods of vertical superimposition and strong heterogeneity, leading to difficulties in reef prediction. Regarding the characteristics of weak amplitude of in-phase axis, blank and disordered reflections within the reef reservoir, and based on the logging-seismic calibration and forward models to establish seismic response characteristics of the reef, clustering analysis is performed to fuse multiple seismic attributes which are sensitive to reef, and the reef distribution is predicted. Constrained by isochronal seismic amplitude slice through reefs, S-transformation-based spectrum decomposition amplitude slices are used to identify reef boundary. The combined method of fractional frequency and waveform clustering can get more accurate reef boundary and more detailed characteristics of the reef, which are highly consistent with the actual drilling results in the study area. References | Related Articles | Metrics

Genesis and Identification of Low Resistivity of Chang 2 Oil Layer in Heshui Area, Ordos Basin PAN Yiwen, ZUO Xiaohuan, ZHANG Shitao, ZHANG Yaohua 2020, 41 (zk(English)):  33-40.  Abstract ( 92 )   PDF (3407KB) ( 105 )   Save In order to determine the genesis of low resistivity of Chang 2 oil layer in Heshui area of Ordos basin, the paper analyzes the data of scanning electron microscope, casting thin section, mercury injection experiment, grain size, porosity and water quality. The results show that the low resistivity of the oil layer is attributed to high salinity of formation water, complex pore structure and high content of irreducible water. The high salinity of formation water is mainly caused by atmospheric precipitation which brings the ions from weathering and denudation of the overlying strata into the formation; CO2 carried by atmospheric precipitation reacts with feldspar in the formation and then kaolinite forms. The kaolinite with unsaturated electrical properties can adsorb cation and the cation exchange quantity increases, causing the enhancement of kaolinite additional conductivity. The metal ions such as K+ and Al3+ in medium are absorbed by smectite, which results in the rearrangement of the crystal and the substitution of isomorphism, leading to the low resistivity of the reservoir. In view of the characteristics of the oil layer in the study area, the paper proposes that a crossplot of resistivity and thickness can be used to identify low-resistivity oil layers, and to determine the upper and lower limits of each factor in the low-resistance oil layer, and establishes a chart to identify low-resistance oil layers for Chang 2 member with the coincidence rate between the identification result and the oil test result being more than 80%. References | Related Articles | Metrics

Comprehensive Prediction Model of Total Gas Content in the Shale of Yanchang Formation in Yanchang Petroleum Exploration Area DENG Changsheng, ZHANG Yi, XIE Xiaofei, MI Weiwei, QIANG Juan, SONG Jiaxuan 2020, 41 (zk(English)):  41-51.  Abstract ( 87 )   PDF (636KB) ( 137 )   Save Based on isothermal adsorption experiments of shale samples, the content of adsorbed gas in the shale of Yanchang formation is calculated, and the contents of free gas and dissolved gas in the shale of Yanchang formation are calculated by establishing formulas and logging interpretation. The calculation results show that the total gas content of the shale of Yanchang formation in Yanchang petroleum exploration area is 2.25-5.08 m3/t, among which the content of the adsorbed gas is 1.75-4.21 m3/t, the free gas content is 0.20-0.60 m3/t, the dissolved gas content is 0.05-0.52 m3/t. Based on the analysis of the correlation between shale gas in different occurrence states and geological factors, it is considered that the content of the adsorbed gas is mainly controlled by temperature, pressure, TOC and water saturation, the content of the free gas is mainly controlled by porosity and gas saturation, and the content of the dissolved gas is mainly constrained by residual oil content, temperature, pressure and relative densities of natural gas and crude oil. A comprehensive prediction model of total shale gas content in different occurrence states is established for Yanchang petroleum exploration area. The measured values of the total shale gas content obtained with in-situ desorption method are used to verify the comprehensive prediction model and the results show that the model is highly reliable. References | Related Articles | Metrics

Reservoir Characteristics and Sensitivity Evaluation of Chang 23 in N Area of Xifeng Oilfield HE Hui, LI Junjian, QI Zhao, XU Zhongyi, LIU Meirong, ZHU Yushuang 2020, 41 (zk(English)):  52-60.  Abstract ( 103 )   PDF (2180KB) ( 111 )   Save Based on the analysis of physical property testing, cast thin sections, SEM observation and high pressure mercury intrusion for the Chang 23 low-permeability sandstone reservoir in N Area of Xifeng oilfield, the paper describes the characteristics of the reservoir, classifies the reservoir according to petrologic features, physical properties and pore throat characteristics, evaluates the reservoir sensitivities and analyzes their influencing factors. The study results show that the Chang 23 reservoir in N Area of Xifeng oilfield is dominated by fine-grained feldspar lithic sandstone. The pore types are mainly intergranular pores and feldspar dissolved pores. The average porosity and permeability of the reservoir are 16.4% and 13.5 mD, respectively, which indicates the reservoir belongs to medium-low porosity, low permeability reservoirs. The reservoir can be divided into three types: the physical property and pore throat structure of Type I reservoir are the best, and those of Type II and Type III reservoirs become worse and worse. The reservoir in the study area is featured with moderate?weak velocity sensitivity, weak water sensitivity, moderate-weak salt sensitivity, moderate acid sensitivity, strong alkali sensitivity and moderate-strong pressure sensitivity. The sensitivities of the reservoir in the study area are influenced by clay minerals, partial clastic grains and pore throat structures. The velocity sensitivity of the reservoir is mainly related to kaolinite content, and water and salt sensitivities related to illite content and occurrence. The acid sensitivity is influenced by both chlorite and ferrodolomite contents, strong alkali sensitivity results from high contents of feldspar and quartz and pressure sensitivity is the result of the deformation of pore throats. The clay content, pore throat structure, physical property and sensitivity of the three types of reservoir are different. During the process of oilfield development, reservoir protection should be carried out according to the sensitivity controls and the differences of sensitivity of different reservoirs, so as to reduce the damage to reservoir. References | Related Articles | Metrics

Reservoir Characteristics and Hydrocarbon Accumulation Model in Chunguang Oilfield, Junggar Basin ZHANG Hui, YUE Xinxin, ZHU Yan, LI Yanran, GUO Juncan, YU Mengli, CHEN Feng 2020, 41 (zk(English)):  61-66.  Abstract ( 97 )   PDF (1187KB) ( 110 )   Save Chunguang oilfield is a multi-layer oil-bearing, multi-reservoir type, light oil and heavy oil co-existing complex oil-gas accumulation area. In order to determine the reservoir characteristics and hydrocarbon accumulation model in Chunguang oilfield, the paper analyzes the reservoir-forming factors and typical reservoirs. Double sag hydrocarbon supply, multiple reservoir-cap combinations, multiple reservoir sand bodies and compound transport system are the necessary conditions for the multi-layer oil-bearing and three-dimensional reservoir-forming of Chunguang oilfield, and the peripheral areas of stratigraphic overlap line, denudation line and sandbody pinchout line are favorable areas for oil and gas accumulation. Gypsum-salt-bearing regional caprock and high-porosity and high-permeability reservoirs are the key factors for high oil production of Shawan formation in Chunguang oilfield, biodegradation is the main reason for the thickening of Cretaceous crude oil and the distributions of light oil and heavy oil are mainly controlled by preservation conditions. The hydrocarbon accumulation model can be summarized as follows: double sag hydrocarbon supply, two-stage charging, compound transportation, three-dimensional reservoir forming and crude oil biodegradation and thickening, and the favorable areas are presented, which can provide references for the oil and gas exploration of the western uplift and its surrounding areas in Junggar basin. References | Related Articles | Metrics

Structural Deformation and Petroleum Exploration Potential of Subsalt Layer in Qiulitage Structural Belt, Kuqa Depression XIE Huiwen, LUO Haoyu, ZHANG Xueqi, DUAN Yunjiang, ZHANG Wen, XIE Yani 2020, 41 (zk(English)):  67-75.  Abstract ( 90 )   PDF (1437KB) ( 133 )   Save Qiulitage structural belt is located on the central part of Kuqa depression. Influenced by the orogenesis of the southern Tianshan Mountain, a series of thrust structures are developed in Qiulitage structural belt which has significant layered deformation characteristics. Based on the data of field survey and seismic interpretation, and taking the Paleogene Kumugeliemu group and the Neogene Jidike formation in Qiulitage structural belt as the main objectives, the Qiulitage structural belt is classified into above-salt layer, salt layer and subsalt layer. Due to the compression, the differential flow deformation of the gypsum-salt rock resulted in the forming of rows of linear folded belts on the surface, thrust nappe structures and recoil structures are developed in the above-salt layers, and the deformation of subsalt layer is mainly controlled by compressional stress and Paleozoic paleo-uplift, showing an obvious segmentation feature. In the central and eastern parts of Qiulitage structural belt which are located on the northern slope of Xinhe-Yaha paleo-uplift, the thrust structures similar to Keshen structural belt are developed in the subsalt layers where large-scale high-amplitude faulted anticline traps formed with great petroleum exploration potential. In the Jiamu-Western Qiulitage segment which is located on the Wensu-Western Qiulitage Paleozoic paleo-uplift, thrust structures cannot be found in the subsalt layer, and the subsalt traps are dominated by low-amplitude faulted anticline and fault block, showing relatively small exploration potential. References | Related Articles | Metrics

Exploration History and Enlightenment in Junggar Basin CHEN Lei, YANG Yiting, WANG Fei, LU Hui, ZHANG Yidan, WANG Xin, LI Yanping, LI Chen 2020, 41 (zk(English)):  76-83.  Abstract ( 125 )   PDF (5667KB) ( 213 )   Save To write the book of Petroleum Geology of China, first we summarize the petroleum geological theory, exploration targets and results, review the exploration history and analyze the drilling, seismic, reserves and other historical data, then divide the exploration history of the Junggar basin into five stages - surface geological survey and drilling in the southern margin (before 1954), discovery and expansion of Karamay oilfield (1955-1977), strategic development of eastern oil and gas fields (1978-1989), fast breakthrough to desert oil and gas fields in the hinterland (1990-2002) and large-scale development of hydrocarbon-rich sags (2003-), and finally based on the important exploration results and milestone data of all stages, point out the exploration enlightenment and accumulation models that have important influences on exploration, including structural oil-bearing model in overthrust fault zones, large-area above-source and fan-controlled accumulation model in sags, stepped outer-source, along ridge and fault-controlled accumulation model, inner-source self-generation and self-preservation accumulation model of volcanic rocks, and accumulation models with upper, middle and lower assemblages in the southern margin. These findings are expected to have important enlightenment for future exploration. References | Related Articles | Metrics

Characteristics and Genesis of Low Oil-Saturation Reservoirs in Taibei Sag, Tuha Basin ZHANG Hua, KANG Jilun, WANG Xinggang, LI Hongwei, JIA Xueli, ZHOU Yadong 2020, 41 (zk(English)):  84-91.  Abstract ( 107 )   PDF (887KB) ( 128 )   Save Low oil-saturation reservoirs are widely developed in the Shuixigou group in the Taibei sag of the Tuha basin, which are laterally concentrated in the positive structures in the sag, and vertically in the Xishanyao formation and Sangonghe formation. The oil reservoirs in the study area have low oil saturation and poor physical properties, so the natural productivity is low. Although the production is high after reservoir stimulation, both oil and water are produced for a long time. In order to understand the genesis of such oil reservoirs, the relationships among reservoir, structure, reservoir evolution and oil saturation were studied. The results show that the reservoir and structure are primary factors resulting in the low oil saturation. The reasons are as follows: the first is that the oil displacement by water is not complete due to compaction and pore reduction, fine pores and micro throats; the second is the existence of interlayers or barriers, which separate the oil layers and block the vertical migration of oil and gas; the third is that the low-relief structure provides an insufficient reservoir-forming dynamics which will bring impacts on oil saturation; and the fourth is that late tectonic activities destruct the ancient oil reservoirs. Comprehensive analysis shows that the low oil-saturation reservoirs in the Shuixigou group in the Taibei sag have a large amount of remaining hydrocarbon resources, which are important replaceable targets for oil and gas exploration in the Tuha basin. The overlapping areas of reservoir sweet spots and inherited positive structures are favorable for looking for the reservoirs with higher oil saturation. References | Related Articles | Metrics

Deformation Mechanism of Hutubi Anticline in the Southern Margin of Junggar Basin: Insights From Physical Simulation Experiment ZHANG Xichen, MA Delong, WEI Lingyun, WANG Hongbin, WANG Yanjun, LIU Wenqiang, YANG Xiulei 2020, 41 (zk(English)):  92-100.  Abstract ( 92 )   PDF (5740KB) ( 123 )   Save The fold-thrust belts in the southern margin of Junggar basin are characterized by multi-stage superimposition and deformation. The Hutubi anticline located in the front of the thrust is far away from the Tianshan Mountains and shows a double-layer structure, among which the deep layer is a Permian fault-depression-paleohigh and the shallow layer is a fault anticline of Jurassic with its overlying strata. To investigate the main controls on the shallow anticline formation and the vertical deformation mechanism of the Hutubi anticline, 5 groups of models are designed to perform physical simulation study by using control variable and comparative analysis methods on the basis of the identification of structural style and deformation laws. The study results show that the experimental result of the fault-depression-paleohigh model is similar to the seismic interpretation result. As the main controlling factor, the paleohigh in the fault-depression margin induced the overlying strata to deform into anticlines, which can prove the time-space coupling relations between the deep layer and shallow layer in the Hutubi anticline. The shape of the shallow anticline is also controlled by the combination of the scale of the underlying fault-depression, the overlying strata thickness and the syntectonic sedimentation. It is a scientific and effective method to reveal the correlation and deformation mechanism of vertical superimposed structures by using physical simulation experiments, which could provide more basis for petroleum exploration and production in the foreland area of the southern margin of Junggar basin. References | Related Articles | Metrics

High-Resolution Numerical Simulation for Gas Injection Gravity Drainage in Buried-Hill Reservoirs WANG Ruisi, ZENG Qingqiao, HUANG Pu, LIAN Liming, LI Junjie, CHENG Peng 2020, 41 (zk(English)):  101-105.  Abstract ( 104 )   PDF (4798KB) ( 108 )   Save The buried-hill reservoir in the Wumishan formation of Yanling oilfield is a massive carbonate reservoir with bottom water, in which field tests of nitrogen injection had been carried out in the past and a 44 m-high oil column was formed. At present, the reservoir has entered the late development stage of high water cut and high recovery factor, and the development mode needs to be changed. Based on the data of laboratory experiments, early nitrogen injection field tests and well logging interpretation, the paper optimizes the geological model and establishes a high-performance cloud computing platform for numerical simulation. The simulation model for dual porosity buried-hill reservoirs is optimized, a high-resolution numerical simulation is carried out based on the model with grid precision of 60 m×60 m×3 m and the total grid number of 97×104, and a gas injection gravity drainage plan has been made for the buried-hill reservoir in Yanling oilfield. It is predicted in the plan that the recovery factor will be improved by 11.8%, the ultimate recovery factor will reach 43.4% and good results will be obtained, which can provide references for the development of similar reservoirs. References | Related Articles | Metrics

Laws and Models of Water Invasion in Kela 2 Gas Field WU Yongping, YANG Min, LI Ming, SUN Yong, ZHANG Yongbin, WANG Hao 2020, 41 (zk(English)):  106-110.  Abstract ( 118 )   PDF (1280KB) ( 123 )   Save Kela 2 gas field in Tarim basin is a massive ultra-high-pressure dry gas reservoir with the largest proved reserves in China. Since 2010, water breakthrough due to geological conditions has been found in seven wells, which brings risks to the steady production of the gas field. Therefore, it is very important to understand the laws and to identify the models of water invasion in the gas field. This paper analyzes the general characteristics of water invasion in the gas field, and determines four regions with different water invasion models. Regarding the watered-out wells in the different regions, the fracture development degree, the relationship between high-permeable zone and interlayer and the distance from high-permeable zone to edge/bottom water are analyzed and the main factors controlling water invasion in watered-out wells are identified. The main direction of incoming water is determined through fault plugging capacity evaluation, dynamic tracking well test analysis and post-casing saturation time comparison. Combined with production performance and history matching of geological model, the water invasion models are determined and the model in single well can be divided into three types such as vertical channeling and lateral invasion of bottom water, lateral invasion of edge water and invasion upwards of bottom water. Based on the numerical simulation of the gas reservoir, the water invasion models in non-watered-out wells can be predicted and a detailed development strategy is proposed to ensure the continuous and efficient development of the Kela 2 gas field. References | Related Articles | Metrics

Characteristics of In-Situ Stress in Sandy Conglomerate Reservoir of Badaowan Formation in District No.7, Karamay Oilfield WANG Zhenyu, LIN Botao, YU Huiyong, SHI Shanzhi, KOU Xiangrong 2020, 41 (zk(English)):  111-115.  Abstract ( 89 )   PDF (1916KB) ( 104 )   Save The Badaowan Formation reservoir in District No.7 of Karamay oilfield is dominated by medium-coarse sandstone and conglomerate. The reservoir has been developed for a long time and remaining oil is widely distributed in the formation. In order to realize potential tapping in small layers and to reduce reservoir heterogeneity, separate layer fracturing has been carried out. In the process of reservoir stimulation, some fractures penetrated interlayers and connected with water layer, resulting in poor stimulation effect. In order to understand rock mechanical characteristics and regional in-situ stress distribution, the paper establishes a 3D stress field model for the reservoir on the basis of lab core experiments and field data analysis. The stresses are almost the same in the southwestern and central part of the reservoir, the stress in the southeastern part is greatly influenced by fault and that in the southwestern part is influenced by fault gently. Five reverse faults with large dip angle variations are developed in the study area and the stress mutation occurs at the junction of the faults, which will impact fracturing operation, therefore the operation parameters should be adjusted. The fractures in the southwestern and central reservoir extend upwards and downwards evenly. In the southeastern part of the reservoir, fractures tend to extend along the directions easily to stretch if encountering thick interlayers, so that the aquifer is connected, and fractures can easily penetrate thin interlayers. The fracture heights under the displacement of 2 m3/min and 3 m3/min are simulated and it is found that the fracture height under the displacement of 3 m3/min is hard to be controlled due to the fracture's large vertical extension and its connection with bottom water, and the fracture extension under the displacement of 2 m3/min can be controlled. References | Related Articles | Metrics

Dynamic Reserves Evaluation of Fractured-Cavity Reservoirs With Closed Water: A Case From Halahatang Oilfield, Tarim Basin LI Hongbo, WANG Cuili, NIU Ge, LIANG Hongtao, BU Lulu, GU Junying 2020, 41 (zk(English)):  116-121.  Abstract ( 102 )   PDF (712KB) ( 131 )   Save The fractured-cavity carbonate reservoirs are characterized by strong heterogeneity, complex connectivity, and non-uniform oil-water contact, which lead to difficulties in reserves evaluation and poor development effect. Using dynamic data, the paper improves the material balance equation according to the characteristics of the fractured-cavity carbonate reservoirs with closed water, the dynamic reserves evaluation method for this kind of reservoirs by combining with the predicted static reserves. The dynamic oil reserves and the water size can be accurately calculated with the method under the conditions without oil-water contact location and measured PVT data of reservoirs. Good application effects have been gained in Halahatang oilfield, Tarim basin. References | Related Articles | Metrics

Variations of Produced Polymer Concentration for Polymer Flooding in Conglomerate Reservoirs ZHANG Defu, LYU Jianrong, TIAN Mi, ZHANG Jing 2020, 41 (zk(English)):  122-126.  Abstract ( 102 )   PDF (589KB) ( 110 )   Save Over a long-term waterflooding development, the conglomerate reservoir of the lower Karamay formation in QD1 block of Karamay oilfield in Xinjiang is featured with strong heterogeneity, developed fracture and developed preferential pathway. But high produced polymer concentration in producers during subsequent polymer flooding affects the polymer flooding effect. In order to understand the variations of produced polymer concentration of polymer flooding in conglomerate reservoirs, taking the reservoir characteristics and fluids in QD1 block as research objects, the paper carries out studies related to production stage classification for the polymer flooding, rising law of the produced polymer concentration, charts of the produced polymer concentration limits and the lower injection pressure limits for polymer channeling control. The results show that the production stage of polymer flooding in conglomerate reservoirs can be classified into early stage of polymer injection, peak response stage, late response stage and subsequent water flooding stage. The peak response stage generally lasts for 2 or 3 years with the maximum produced polymer concentration of 737.2 mg/L, the maximum relative produced polymer concentration of 0.550 and the concentration rising rate of 2.3; when the well spacings are 140 m and 120 m, the reasonable rise rate of the relative concentration is 2.3-6.0, the corresponding relative concentration ranges from 0.276 to 0.720 and the produced polymer concentration is 414.0-1080.0 mg/L. The lower limits of injection pressure for polymer channeling control in wells dominated by preferential pathway, hydraulic fracture and fracture plus pathway are 8 MPa, 10.0 MPa and 9.5 MPa, respectively. The research results can provide references for production performance adjustment and well treatment during polymer flooding in conglomerate reservoirs in this area. References | Related Articles | Metrics

A Method to Predict Reasonable Reserve-Production Ratio Limit for Oilfields WANG Luchun, ZHAO Xin, LI Jindong, SUN Zhijie, XUE Rui 2020, 41 (zk(English)):  127-131.  Abstract ( 79 )   PDF (463KB) ( 102 )   Save In order to evaluate whether the reserve-production ratio of an oilfield is reasonable or not, according to the definition of reserve-production ratio, the relationship among production decline rate and liquid production and the relationship between production decline rate and water cut, the paper establishes the relationships between the reserve-production ratio and liquid production increasing rate, water cut increasing rate and reserve-production equilibrium coefficient, respectively, and predicts the trends of reserve-production ratio in different development modes. Additionally, the paper establishes an annual reserve-production ratio formula under the ideal conditions and charts of rapid prediction of reasonable reserve-production ratio, divides the reserve-production ratio at the limit water cut into 4 categories including reasonable, relative reasonable, unreasonable and extremely unreasonable reserve-production ratio and then determines the reasonable reserve-production ratio. Applying this method into a block and assuming that other conditions remain unchanged, the reserve-production ratio is already negative when the water cut reaches 96.2%, indicating a relatively low reserve-production ratio. Finally, the reasonable reserve-production ratio is determined as 8.2, which provides new references for reasonable reserve-production ratio limit determination in oilfields and countermeasures for development plan adjustment based on the rationality evaluation of the current reserve-production status of oilfields. References | Related Articles | Metrics

Analysis on Pseudo-Fault in Fault Shadow During Seismic Interpretation: A Case Study of Aogula Fault in Northern Songliao Basin LI Cao 2020, 41 (zk(English)):  132-136.  Abstract ( 97 )   PDF (3258KB) ( 108 )   Save The ascertain of Aogula fault and its nearby structures has important significance in exploration and development of Qijiagulong sag in the northern Songliao basin. During the seismic interpretation of the footwall of Aogula fault, from 4 aspects like regional structure, logging curve comparison, structural interpretation of dense well pattern and seismic forward modeling, it is proved that a previously interpreted near-upright fault is a pseudo-fault due to the inaccurate structural imaging and the existence of fault shadow. It is concluded that all or partial low-velocity intervals are broken in local areas and the interval velocities of the strata located on both sides of the fault abruptly change laterally, resulting in an inaccurate fault shadow in the footwall of the fault, both of which can be attributed to a large fault-throw normal fault passing through the low-velocity interval of the Lower Cretaceous Nenjiang formation in the northern Songliao basin. The paper proposes that the pre-stack depth migration technology based on high-precision velocity modeling can improve the phenomenon of the fault shadow. Regarding the seismic data in conventional time domain, structural interpretation can be carried out by using seismic forwarding modeling results and logging-seismic integration. The identification of the pseudo-fault in the fault shadow provides technical support for well allocation in Aogula oilfield. References | Related Articles | Metrics

Integrated Formation Pressure Testing by Logging and Genesis of Abnormal High Pressure in Gaoquan anticline XU Xinniu, LI Yujing, RUAN Biao, CAO Guangfu, HUANG Hong, YANG Hu 2020, 41 (zk(English)):  137-144.  Abstract ( 89 )   PDF (740KB) ( 99 )   Save There are many formation pressure testing methods by logging at home and abroad, but most of them are based on the undercompaction theory and limited to a single lithology of formations. Especially for the deep piedmont structures in the margin of the basin, logging interpretation with a single parameter will lead to large errors in formation pressure determination, and cannot give an explanation about more abnormal pressure mechanisms other than sedimentary compaction mechanism. Therefore, the logging parameters related to various abnormal high pressure mechanisms are comprehensively interpreted, a multiparameter model and several testing methods suitable for complex piedmont structures are established for formation pressure testing by logging and the formation pressure profiles of Well Gaotan-1 in Gaoquan anticline in the southern margin of Junggar basin are evaluated in detail. The calculated results are in good agreement with the measured data and the relative error is less than 3.00%. Meanwhile, based on the mechanical relationship of the original sedimentary loading-unloading processes, the forming mechanism of the abnormal high pressure in the deep strata of Gaoquan anticline is determined by using the multiple logging parameter analysis method. References | Related Articles | Metrics