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01 January 2019, Volume 38 Issue 4 Previous Issue    Next Issue

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Geochemical Characteristics and Genesis of Tight Oil in Lucaogou Formation of Jimsar Sag WANG Yutao1a, YANG Zuoming1a, MA Wanyun1b, PAN Changchun2, WANG Fei1a 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170401 Abstract ( 141 )   PDF (300KB) ( 399 )   Save The tight oil reservoir of Middle Permian Lucaogou formation in Jimsar sag, Junggar basin has characteristics of “4-high” physical properties (i.e. relatively high density, high viscosity, high pour point and high wax content). The study on saturated hydrocarbon chromatography shows that the distribution of n-alkanes in the crude oil is complete and the crude oil never suffered from biodegradation; the maturity indexes of light hydrocarbons and sterane demonstrate that the oil is in the low maturity stage. The oil and source rocks in Lucaogou formation show the same thermal evolution stage and geochemical fingerprint characteristics, indicating a good affinity between them and tight-oil reservoir forming characteristics of “source and reservoir integration”. The oil generation simulation experiment shows that the accumulative hydrocarbon generation and expulsion quantities and oil discharge rate of the source rocks in Lucaogou formation at low mature stage are almost the same with those of normal source rocks at mature stage. Half-deep and deep lacustrine facies sediments, salinized reducing-strong reducing environments and good parent materials of hydrocarbons (Type Ⅰ-Ⅱ1 kerogens) are the main causes for large quantities of hydrocarbon generation and expulsion, and low-maturity tight oil accumulation of the good-quality source rocks in Lucaogou formation of Jimsar sag at the early stage. Related Articles | Metrics

Characteristics and Genesis of Paleo-Karst Collapses in Ordovician Carbonate Rocks, Tahe Oilfield WANG Jianfeng1a, DENG Guangxiao1b, LI Tao1a, MEN Hongkun2, ZHANG Ziyi2 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170402 Abstract ( 53 )   PDF (300KB) ( 45 )   Save Fracture-caved reservoirs in Ordovician carbonate rocks are the main oil and gas reservoirs in Tahe oilfield and the collapse resulted from the subsidence of ancient cave systems is one of the important types of the late karst reformation. Using the data of core, conventional logging, imaging logging, seismic reflection configuration and production performance, the paper analyzes and studies the identification method and the genesis of the collapse in carbonate rocks, presents a set of identification methods applicable to the karst collapses of fracture-caved reservoirs and establishes the corresponding identification criteria for them. Based on the genetic analysis, the karst collapses in Tahe oilfield can be classified into 3 genetic types including fracture induced collapse, overlying stratum load collapse and late-stage hypergene karst collapse. The statistics of 122 collapses of the fracture-caved reservoirs in Tahe oilfield show that the late-stage hypergene karst collapse has the greatest potential for oil and gas development due to the developed fractures and caves within the reservoir. Related Articles | Metrics

3D Geological Modeling of Interlayers in Buried-Hill Dolomite Reservoirs of Block YM32, Tarim Basin YAN Xiaofang, DAI Chuanrui, CHEN Ge, CAO Peng, CHANG Shaoying, LUO Xianying 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170403 Abstract ( 70 )   PDF (300KB) ( 190 )   Save Regarding the characteristics such as complex spatial structure, large stratigraphic dip angle, low level of well control of buried-hill dolomite reservoir and its interlayers in the Block YM32 of Tarim basin, the paper classifies the interlayers in individual wells and establishes the stratigraphic framework by calculating true formation thickness; analyzes the relationships between various seismic attributes and zones with different lithologies by using dolomite lithofacies identification technology and multiple regression mehtod, and establishes a lithofacies model for dolomite with rock texture number and multiple seismic attribute constraint; builds a 3D attribute model for the study area through stacking actual measured core porosity and permeability, and inversion attributes of seismic porosity. The fitting ratio of numerical simulation results to the well production performance is more than 93.6%, providing effective basis for remaining oil distribution description, new-well placement and existing-well stimulation in the study area. Related Articles | Metrics

Geochemical Features and Paleoenvironment of Shales in Longmaxi Formation of Complicated Structure Area, Southwestern Sichuan Basin ZHANG Qian1,2, WANG Jian1,3, YU Qian1, WANG Xiaofei1, ZHAO Ankun1, LEI Zihui4 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170404 Abstract ( 73 )   PDF (300KB) ( 143 )   Save The paper studies the sedimentary environment of the shales in the Lower Silurian Longmaxi formation of the complicated structure area in the southwestern Sichuan basin, and provides guidance for shale gas exploration and development in the area. Based on the systematic sampling of shales in Longmaxi formation on Niba Mountain section in Yijing county, geochemical studies are carried out. The results show that the average value of Chemical Index of Alteration（CIA）in the study area is 68, which is slightly lower than that of the shales in the world (CIA=70), and the average Th/U ratio in the study area is 3.73, which is close to the average value 3.80 of the continental crust, indicating that the provenance suffered from weak-medium weathering. Relative high content of hydrolysable and ferrum and relative low content of sulfophilic elements show that the sedimentary water was shore-shallow sea environment. The redox indexes such as δU, U/Th, V/Cr and Ni/Co indicate a weak oxidation environment of the sedimentary water, and an even stronger oxidation environment at the late deposition stage of Longmaxi formation. The paleoclimatic indicator Sr /Cu indicates an arid climate during the deposition of the provenance and paleosalinity indicators Sr/Ba and B/Ga indicate Longmaxi formation is brackish marine deposition. The TOC in the study area is relatively low and well correlates with the indicators of weathering, redox, paleosalinity and paleoclimate, which indicates that the TOC is controlled by sedimentary environment. Longmaxi formation in the study area is a set of source rocks of deep water—shallow water shelf facies, and the lower Longmaxi formation is of good quality and the upper section is relatively poor due to the influence of sedimentary environment and tectonic uplift. Related Articles | Metrics

Forming Mechanism and Prediction of Structural Fractures in the Second Member of Jialingjiang Formation in Puguang Area ZU Kewei1, 2, ZENG Daqian3, CHENG Xiushen1, ZHUO Seqiang1, LI Songfeng1 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170405 Abstract ( 65 )   PDF (300KB) ( 108 )   Save In order to accurately predict structural fracture development in carbonate reservoirs, taking the second member of Jialingjiang formation in Puguang area for example, the paper studies the characteristics of fracture development by using field outcrop, core and thin section data; analyzes the forming mechanism of the fractures in the study area by combining with the test results of acoustic emission and inclusion homogenization temperature in the fractures. Based on which, fractures of different periods are predicted through stress field numerical simulation. It is concluded that the structural fractures were mostly formed under the NW-SE trending compression during the late Yanshan movement and the early Himalaya movement, and under the NE-SW trending compression during the late Himalaya movement. The development degree of shear fracture is higher than that of tension fracture in the second member of Jialingjiang formation in Puguang area. The structural fractures are mainly developed in the areas near fault zones, in the middle-western areas of Qingyangxi structure, in the main body of Puguang structure, in the northern parts of Dawan-Maoba and Fenshuiling structures and in the Tieshan structural belt. The rupture rate obtained from numerical simulation and the fracture development intensity have a good correlation with a relatively high correlation coefficient. Related Articles | Metrics

Using Discrete Element Numerical Simulation Method to Study Salt Tectonic Deformation Mechanism of Kelasu Structural Belt DUAN Yunjiang1, HUANG Shaoying1, LI Weibo2, ZHANG Huifang1, MA Xiaodan1, LIAO Feiran1 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170406 Abstract ( 93 )   PDF (300KB) ( 303 )   Save In order to research the tectonic compressional deformation and its main controlling factors of salt structures in Kelasu structural belt of Kuqa depression, the paper simulates the salt tectonic deformation process of the 3 major seismic sections of Awat, Dabei and Keshen segments by using discrete element numerical simulation method. The simulation results show that the salt bed exhibits plastic deformation under the compressional setting and has relatively strong fluidity. Post-salt, salt and pre-salt beds show some structural characteristics of overall compression and layered deformation. A series of NS trending thrust structures are developed in pre-salt beds, and fault propagating folds and detached deformation structures are developed in post-salt beds. Pre-existing fractures mainly control pre-salt tectonic deformation and stress propagation range, pre-existing salt diapirs mainly influence the tectonic uplifting range of post-salt beds; salt rock distribution and palaeohigh of basement mainly impact the tectonic deformation of post-salt beds. The study results reveal the dynamic evolution process of salt structures in Kelasu structural belt, which will benefit to improve the understandings on salt tectonic deformation mechanism and its evolution process. Related Articles | Metrics

Fine Extrapolation of Stratigraphic Oil-Gas Reservoir Boundary Based on Seismic Forward Modeling: A Case Study of the First Member of Dainan Formation in ShuaiduoChenjiashe Belt, Qintong Sag ZHOU Zhou, YANG Fei, LIU Jinshuai, ZHOU Qian, GONG Weicheng 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170407 Abstract ( 47 )   PDF (300KB) ( 104 )   Save Because the traps are complicated and the oil-bearing zones are relatively narrow in the stratigraphic oil-gas reservoirs of Qintong sag, there are big differences between the stratigraphic pinchout line obtained from seismic reflection tracing and the actual one, which results in the difficulties in stratigraphic oil-gas reservoir boundary identification and low success rate of drilling. A seismic model obtained from the forward modeling of a stratigraphic pinchout model, the advantages and disadvantages of various attributes in the seismic model are analyzed for the stratigraphic reservoir boundary identification, and the average trough amplitude and average instantaneous phase are selected due to their good recognition effects. The error between stratigraphic pinchout points with different frequency and included angles (i.e. the included angle between unconformity surface and stratum) and the pinchout points on the seismic sections can be obtained through analyses of a series of models at different frequencies. A functional relationship between the included angle and the error of stratigraphic pinchout point is established through matching and then the quantitative calculation of the included angle extrapolation can be realized. The boundaries of stratigraphic traps are characterized detailedly by the integrated use of semiquantitative description of the seismic attributes and quantitative calculation of the included angle extrapolation with seismic forward modeling. Related Articles | Metrics

Improvement and Application of Water Cut Forecast Models CUI Yinghuai, GAO Wenjun, HUANG Yu, WANG Qian, ZHAO Zhilong, LIU Wenrui 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170409 Abstract ( 71 )   PDF (300KB) ( 199 )   Save The Logistic model and Yu model are the most simple and commonly used models for water cut forecast, but both of the models have some flaws such as unclear seepage characteristics, the lack of model optimization technology, especially the uncertain relationships among the undetermined, dynamic and static parameters in the model, which could result in the unsufficient theoretical support to water control measures and irrigorous water cut forecast. Therefore, based on the Willhite oil-phase permeability formula and its modified formula, and combined with Эфрос’s experimental results, four water cut prediction models and the corresponding water-phase permeability formulas are derived. The improved water cut forecast models can be converted into Logistic model and Yu model under certain conditions, so they will be generalized to some extent. The analyses of water cut changes predicted by the 4 models show that the hyperbolic model is suitable for matching Г-shaped variations of water cut with production time; the exponential model is applicable for matching S-shaped variations of water cut with production time; the harmonic model and complex exponential model can match both Г-shaped and S-shaped variations of water cut with production time. The application results of the models in the developed block of Sabei transitional zone in Daqing oilfield, H2 reservoir in Pinghu oil and gas field and the reservoirs of Paleogene-Neogene in Yanmuxi oilfield show that the improved models for water cut forecast can make high-accuracy matching and get good effects, which could provide reference for other oilfields. Related Articles | Metrics

A Water Cut Prediction Model for Movable-Gel Profile Control and Flooding at High Water Cut Stage REN Hongmei1,2, WANG Ning1, ZENG Qingqiao1, CHAI Xuefeng1, WANG Yuting1, HUANG Wei1 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170410 Abstract ( 51 )   PDF (300KB) ( 99 )   Save After movable-gel profile control and flooding technology is carried out in the sandstone reservoirs at middle-high water cut stage, the changes of the water cut are quite different from those during waterflooding stage. Aiming at the problem of no analytical model for quantitative water cut prediction after displacement, the paper establishes a water cut prediction model for gel profile control and flooding. Based on the production performance data and general relative permeability formulas, a water cut prediction model for waterflooding is derived and the physical meaning of each parameter of the model is explained, then a watercut prediction model is established for movable gel profile control and flooding. The paper uses the volume-weighted iteration method to calculate the equivalent viscosity and residual resistance factor of the gel solution, characterizes the effects of oil yield increase and water cut decline during the gel profile control and flooding process and carries out sensitivity analysis on model parameters influencing water cut changes. The study shows that reservoir heterogeneity and injected pore volume of gel solution affect water cut decline range and funnel width, and the equivalent viscosity and residual resistance factor have the most significant impacts on water cut decline. A test area is selected from the western Menggulin sandstone reservoir of Erlian basin for model test, and the error of the predicted water cut is less than 2%, meeting the requirement of engineering, which proves the feasibility of the water cut prediction model for movable gel profile control and flooding. Related Articles | Metrics

Oil and Gas Distribution in Condensate Gas Reservoirs at Different Production Stages ZHANG Yongchang1,2, LI Xiangfang1, SUN Zheng1, MENG Ye1, ZHANG Yi1, LIU Wenyuan1 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170411 Abstract ( 104 )   PDF (300KB) ( 217 )   Save The percolation research of condensate gas reservoir has its particularity and is more difficult than that of conventional reservoir due to the intricate phase variations. The existing oil and gas distribution models for condensate gas reservoir are based on relative permeability curves measured with steady-state or unsteady-state methods, which does not consider the blocking of condensate liquid and may overestimate the filtration capacity of the condensate oil, resulting in certain deviations between the model results and the actual production status in the field, so the models can’t accurately describe the oil and gas distribution in reservoirs and evaluate the productivity of gas wells. Moreover, there are few studies on the oil and gas distribution in condensate gas reservoirs at different development stages based on reservoir microscopic heterogeneity so that there is no necessary theoretical basis for full-cycle production system making for gas wells. In view of this, a relative permeability measurement method of pseudo steady-state which can reflect the filtration capacity of fluids in condensate reservoirs is introduced to establish a set of full-process methods for oil and gas distribution description according to reservoir microscopic pore size and capillary pressure distribution and combined with the oil and gas filtration characteristics at different production stages in gas wells. The methods are applied in the optimal design of production parameters for condensate gas reservoirs and the results show that the influence of pseudo steady-state relative permeability on oil and gas production performance should be highlighted when large pressure difference is adopted in the condensate reservoirs at the late production stage, and finally the proposed methods are validated by the actual production performance in condensate gas wells. Related Articles | Metrics

Evaluation of Injected Water Utilization for Fractured-Vuggy Reservoirs in Tahe Oilfield ZHENG Songqing1, LIU Zhongchun1, QIU Lu2 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170412 Abstract ( 47 )   PDF (300KB) ( 77 )   Save Regarding the low utilization rate of injected water at the middle and late stages of water flooding in the fractured-vuggy reservoirs of Tahe oilfield, technological policy should be optimized and adjusted. The available evaluation indexes cann’t be used to effectively evaluate the injected water utilization due to the overflowing of injected water resulted from strong heterogeneity and developed fractures of the reservoirs. Based on the analysis of the characteristics of the injected water utilization in the fractured-vuggy reservoirs and according to the directions where the injected water goes underground, 4 evaluation indexes are presented such as pressure rising index, oil displacement index, channeling index and leakage index and a calculation method is proposed. The actual application in the Well group TK713 of Unit S80 in the District 6 of Tahe oilfield shows that the evaluation method can quantitatively characterize where the injected water goes underground and the evaluation result could guide adjustment program making. Related Articles | Metrics

Controlling Factors of Oil-Water Contact in M Layer of Heavy-Oil Field A, Bohai Bay Basin LI Hao, NIE Lingling, ZHANG Caiqi, PAN Guangming, XIE Yue 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170413 Abstract ( 57 )   PDF (300KB) ( 213 )   Save The oilfield A located at the southwestern end of Shijiutuo swell in the northern Bozhong depression of Bohai Bay basin, belongs to heavy-oil sandstone reservoirs featured with gentle and complicated nose-like structures. Drilling data shows that the oil-water contact (OWC) of M layer exhibits a SE-NW rising trend with the altitude difference of 5.0~22.0 m. Tracer data and production performance prove that the reservoir is continuous between wells with different OWCs. Analyses of capillary pressure and buoyance balance theory show that the differences of OWC in the connected sandbodies are mainly constrained by formation oil viscosity and reservoir physical properties; the larger the formation oil viscosity is, the poorer the reservoir physical properties are and the higher the OWC will be. Biodegradation of different levels results in the gradual rise of formation oil viscosity from southeast to northwest; the development of abandoned channel deposits and lateral accretion layers leads to worse and worse reservoir physical properties from southeast to northwest. Both the biodegradation and development of abandoned channel deposits and lateral accretion layers result in the SE-NW rising trend of the OWC. Related Articles | Metrics

Influence of CO2-Water-Rock Interactions on Wettability of Sandstone Reservoirs XIAO Na1, LI Shi2, LIN Meiqin3, ZHAO Chunxi4 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170414 Abstract ( 86 )   PDF (300KB) ( 299 )   Save The interactions among CO2, water and rock will result in wettability changes of reservoir rocks after CO2 is injected into formations, which will impact reservoir permeability. Contact angle and interfacial tension (IFT) measurements, and core displacement experiment are used to study the influence of CO2-water-rock interactions on the sandstone reservoir wettability under high pressure, and to investigate the relationship between rock wettability and permeability. The results show that the static water contact angle on the surface of quartz increases gradually with the increase of CO2 pressure and reaches the maximum when the pressure of CO2 is 7.2 MPa, then gradually reduces with the increase of CO2 pressure; water-CO2 interfacial tension and water adhesion work on the quartz surface gradually decrease with the increase of CO2 pressure and reach the minimum when the pressure of CO2 is 7.2 MPa, then increase with the increase of CO2 pressure. With the decrease of pH value of aqueous solution, the contact angle of water on quartz surface first decreases then increases, and reaches the maximum when the pH value reduces to 2.5. When the pH value continuously decreases, the contact angle reduces. With the decrease of the pH value of aqueous solution, the contact angle of water on sandstone surface first decreases and then increases, and the water permeability in the sandstone first decreases and then gradually increases. Related Articles | Metrics

Anti-Swelling Technology for Acidizing Pretreatment in Water Injection Wells in Wellblock Ji 7, Zhundong Oilfield XIE Jianyong, SHI Yan, LUO Hongcheng, LI Wenbo, XIE Junhui 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170415 Abstract ( 56 )   PDF (300KB) ( 186 )   Save Clay swelling is the main reason causing reservoir permeability reduction and water-injection pressure rising during waterflooding development of water-sensitive reservoirs. Though anti-swelling agents can be added to inhibit clay swelling and to reduce damage to permeability, water-injection pressure rising and insufficient water injection will occur in low permeability reservoirs. To achieve long-term and effective water injection and taking Wellblock Ji 7 for example, the study on anti-swelling technology for acidizing pretreatment is carried out for water-sensitive reservoirs. Compared with inorganic and organic anti-swelling agents, using acidizing pretreatment technology can get the minimum permeability loss, long-lasting and stable anti-swelling effects. Two injector groups with similar reservoir conditions in Wellblock Ji 7 are selected to carry out a contrast test. The results show that compared with the non-acidized pretreatment wells, the injectors with acidizing pretreatment before water injection are featured with low wellhead start pressure and slowly rising of water injection pressure, which can meet the demand of long-term water injection in low-permeability and water-sensitive reservoirs. Field applications of the pretreatment technology in 22 wells show that the technology can effectively slow down the rising of water injection pressure and good effects have been gained. Related Articles | Metrics

Application of NMR Logging in Low-Resistivity Reservoir Evaluation: A Case Study of Toutunhe Formation on the Eastern Fukang Slope, Junggar Basin LUO Xingping, SU Dongxu, WANG Zhenlin, WANG Gang 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170416 Abstract ( 53 )   PDF (300KB) ( 298 )   Save To solve the problem that conventional logging methods can’t be used to effectively identify low-resistivity reservoirs, taking Toutunhe formation on the eastern Fukang slope of Junggar basin, the paper uses the NMR logging technology to classify and evaluate low-resistivity reservoirs. Based on the data of NMR, cation exchange capacity, thin section and grain size analysis, the paper studies the genesis of the low-resistivity reservoirs. Based on which, NMR T2 spectrum is used to identify oil intervals and aquifers and to calculate porosity, permeability and water saturation. Although the reservoir of Toutunhe formation contains a small amount of mud and clay minerals, the special clay mineral constitution of the reservoir can generate relatively high additional electrical conductivity and high irreducible water content, which results in the resistivity of oil zones generally lower than 6 Ω·m and the oil zones showing a low-resistivity characteristic. According to the shape of NMR T2 spectrum and whether there is a peak spectral at 200 ms, oil interval, water-bearing oil interval, oil-bearing water interval and aquifer can be effectively classified. Taking 3 ms as the cutoff of T2 and combined with the porosity-permeability correlation obtained from core experiments, the porosity and permeability of the low-resistivity reservoirs can be calculated, finally the cation exchange capacity calculated from NMR logging is substituted into a W-S model to determine the water saturation of the low-resistivity reservoir. The qualitative identification and quantitative evaluation results of the method for the low-resistivity reservoirs well matche with the experimental results, showing a good applicability in oil production. Related Articles | Metrics

Sweet Spot Identification with Well-Logging Data and Production Prediction for Coalbed Methane: A Case Study from Southern Shizhuang Block in Qinshui Basin YU Jie1, QIN Ruibao1, LIANG Jianshe1, SUN Jianmeng2, WEI Xiaohan2, HUANG Tao1 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170418 Abstract ( 82 )   PDF (300KB) ( 302 )   Save The paper introduces a method to solve the problems in sweet spot identification and production prediction in coalbed methane wells by using conventional well logging data. Taking No.3 coal seam in southern Shizhuang block of Qinshui basin as an example and starting from the average daily gas production in individual CBM wells, the paper discusses the logging response characteristics of the coal seam and calculates the key parameters of the coal seam such as coal texture index, productivity index, gas content, gas saturation, critical desorption pressure and coal roof & floor features by using caliper, natural potential, gamma-ray, deep lateral resistivity and density logging curves. The paper establishes a composite coal-seam quality parameter by using coal texture index and productivity index, builds up criteria to identify CBM sweet spot with logging data by integrating the composite quality parameter, gas content, critical desorption pressure and coal roof & floor features, and predicts CBM production by using gas content and gas saturation in coal seams, and production scale coefficient. The application results from 97 CBM wells in the study area show that the accuracy rate of the prediction method can reach 84%. Related Articles | Metrics

Some Topics about Reservoir Sensitivity Evaluation LI Chuanliang1, ZHU Suyang1, WANG Fenglan2, DU Qinglong2, YOU Chunmei2, ZHU Lihong2, SHAN Gaojun2 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170419 Abstract ( 93 )   PDF (300KB) ( 276 )   Save Reservoir physical properties change with the changes of various conditions, and then the relative parameters will change, which is called sensitivity phenomena and will impact oil and gas production. Conventional evaluation methods and criteria are not in good accordance with production practice, which needs to be further discussed and improved. The study results of this paper shows that the level of reservoir sensitivity can be expressed by the loss ratio of rock permeability and the evaluation standards can be changed from 0.3 and 0.7 to 0.1 and 0.3, respectively. Water sensitivity is the extreme situation of salt sensitivity, so salt sensitivity evaluation includes water sensitivity evaluation. Stress sensitivity of tight reservoirs is quite weak, which causes negligible influences on production. Stress sensitivity of unconsolidated reservoirs is in favor of oil displacement, but its laboratory evaluation is very difficult. Velocity sensitivity is a false concept and belongs to experimental artifacts, which can not reveal the real sensitivity of reservoir rocks and may misguide the production practice. Permeability of rocks is very sensitive to the grain size of solid particles carried within the injected water, which must be evaluated properly. The conventional 5-item sensitivity evaluations can be changed to the 4-item sensitivity evaluations, namely sensitivities to salt, acid, alkali and grain size. Related Articles | Metrics

Review and Prospect of Acid Wormhole Modeling during Matrix Acidizing in Carbonate Reservoirs LI Xiaogang1, CHEN Yusong1, DENG Zhuang2, WANG Yiting3, WEI Zhuo4 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170420 Abstract ( 78 )   PDF (300KB) ( 211 )   Save Acidization is one of the main stimulation measurements to increase production of carbonate reservoirs. Once acid is injected into the reservoir matrix and fractures through a wellbore, selective chemical reactions are initiated between mineral rocks and acid, resulting in irregular earthworm-like holes, namely "acid wormholes". Many factors influencing the acid-rock reactions cause the diversity of wormholes. In order to break through the limitations of the existing wormhole modeling, this paper teases out the important achievements of both physical and numerical simulations of acid wormholes during the process of the matrix acidizing in recent decades, and demonstrates the latest progresses on the acid wormhole growth patterns and their shape distributions, 3D wormhole reconstruction technique and detailed wormhole characterization; then further summarizes the deficiencies of existing research ideas and methods on wormholes during matrix acidizing; finally presents some suggestions on experimental instruments and methods, mathematical simulation and characterization methods for acid wormholes. Related Articles | Metrics

Discovery of Lacustrine Condensed Layers and Prediction of Lithological Reservoirs: A Case Study of S Oilfield in the South Turgay Basin of Kazakhstan WU Guohai 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170421 Abstract ( 59 )   PDF (300KB) ( 101 )   Save During the study of the deposition characteristics of the Upper Jurassic Akshabulak formation of S oilfield in the South Turgay basin, Kazakhstan, a set of widely-distributed shale layers with high natural gamma values and low resistivities are found in almost the whole oilfield. With the viewpoint of sequence stratigraphy, the paper analyzes the shale layers and concludes that the shale layers are a set of condensed layers deposited during the maximum flooding period. According to the lateral distribution characteristics of the condensed layers and combined with geological and seismic data, a sedimentary model of the stratum is proposed. Analysis of the sedimentary characteristics of J0-0 sand member in Akshabulak formation above the condensed layer shows that the sedimentary thickness of the sand member varies greatly on the eastern slope of the oilfield due to the development of progradation delta facies during high-stand periods. The delta front is the most favorable stratigraphic-lithologic oil and gas reservoir development area, which has been well verified in wells S53 and S34. The paper provides a method of looking for lacustrine condensed layers and puts forward a new way to discover stratigraphic-lithologic oil and gas reservoirs. Related Articles | Metrics

Lithology Identification of Carboniferous Volcanic Rock with Logging Data in Xiquan Area, Junggar Basin ZHANG Lihuaa, ZHANG Guobinb, QI Yanpinga, LI Jinga 2017, 38 (4):  1-1.  doi: 10.7657/XJPG20170408 Abstract ( 73 )   PDF (300KB) ( 149 )   Save The Carboniferous volcanic rock in Xiquan area of Junggar basin is an important oil-bearing stratum, but the lithology identification of the volcanic rock is still a problem to be solved. Based on the optimization of gamma-ray and density logging curves sensitive to lithologies of the volcanic rock, the paper establishes a lithological composition identification chart for the Carboniferous volcanic rock in Xiquan area of Beisantai swell, Junggar basin, based on which the volcanic rock in the study area can be classified into 3 categories such as basic rock, intermediate rock and intermediate-acid rock; then the paper optimizes acoustic transit time and deep lateral resistivity logging curves sensitive to volcanic rock structures, and establishes a lithology identification chart for the volcanic rock in the study area, based on which the lithologies of the volcanic rock in the study area can be classified into 6 types. A 3D lithology identification chart combining gamma-ray, deep lateral resistivity and acoustic transit time logging curves can be used to effectively distinguish the overlaps of andesite and andesitic breccia lava. The 3 identification charts for the volcanic rock are used to identify the lithologies of volcanic rocks in 10 wells in the study area and the matching ratio of the identification results with the thin section analysis results can reach 75.8%, indicating that good application results of the 3 charts have been gained in the study area and the charts can provide new techniques for volcanic rock lithology evaluation with conventional logging data in the study area in the future Related Articles | Metrics