Table of Content

01 January 2024, Volume 44 Issue zk(English) Previous Issue    Next Issue

For Selected:

Download Citations EndNote Reference Manager ProCite BibTeX RefWorks

Toggle Thumbnails

OIL AND GAS EXPLORATION

Exploration Progress and Potential Evaluation of Deep Oil and Gas in Turpan-Hami Exploration Area ZHI Dongming, LI Jianzhong, CHEN Xuan, YANG Fan, LIU Juntian, LIN Lin 2023, 44 (zk(English)):  1-13.  Abstract ( 57 )   PDF (2253KB) ( 22 )   Save To realize the shift of oil and gas exploration from shallow-middle to deep strata, and from conventional to unconventional resources, and then to promote the exploration of deep oil and gas resources in the Turpan-Hami exploration area, the tectonic-lithofacies palaeogeographical evolution of Turpan-Hami basin, Santanghu basin, and Zhundong block of Junggar basin were analyzed, the characteristics and exploration potential of the petroleum systems in these basins were evaluated , the main exploration targets were determined, and the fields for strategic breakthrough were selected. In the Carboniferous-Permian period, the Turpan-Hami exploration area was a unified sedimentary basin with similar sedimentary environments and structures. In the Triassic-Jurassic period, the study area was separated into several independent foreland basins. With the tectonic-lithofacies palaeogeographical evolution, three sets of source rocks (transition facies of Carboniferous, lacustrine facies of Permian, and lacustrine-coal measure of Jurassic) were formed, contributing to three major petroleum systems. The change in exploration ideas has promoted significant progress in petroleum exploration in deep strata. Significant breakthroughs have been made in the exploration of Shiqiantan formation marine clastic oil and gas reservoirs, Permian shale oil reservoirs and conventional sandstone oil reservoirs in the Zhundong block, and the Middle-Lower Jurassic large-scale tight sandstone gas reservoirs in the Turpan-Hami basin, which enables the discovery of large-scale high-quality reserves and the orderly succession of strategic resources. Future exploration should be carried out at three levels: strategic preparation, strategic breakthrough, and strategic implementation, with a focus on 10 favorable directions. References | Related Articles | Metrics

Sedimentary Characteristics and Controlling Factors of Hyperpycnal Flow in Triassic Depressed Lake Basin, Northern Tarim Basin ZHONG Mihong, TANG Wu 2023, 44 (zk(English)):  14-21.  Abstract ( 60 )   PDF (2627KB) ( 27 )   Save Previous studies on hyperpycnal flow mainly focused on modern marine environment and paid little attention to sedimentary characteristics and controlling factors of hyperpyenal flow in ancient continental depressed lake basins. In this paper, taking Tabei area as an example, the hyperpycnal flow deposits of the Triassic TII oil member are analyzed by using core, drilling, logging and 3D seismic data. The results show that during the deposition of lacustrine transgressive system tract (TST)-highstand systems tract (HST), the TII oil member in the study area developed two typical hyperpycnal flow sedimentary sequences, and each sequence is a compound of a basal coarsening-upward unit and a top fining-upward unit, with climbing ripples and ripple cross lamination. In one sequence, an erosive surface is developed between the two units, while in the other sequence, the two sedimentary units present a trend of gradual change, reflecting different flooding energy. The hyperpycnal flow in the study area mainly comes from two directions such as southwest and northeast, among which the hyperpycnal flow from southwest is the dominant with wide distribution, long extending distance and vertical superimposition of hyperpycnal flow deposits of multiple periods. The hyperpycnal flow in the study area has the characteristics of flood gravity flow, and its formation is closely related to flooding and controlled by multiple factors such as climate, tectonic activities, lake level, and provenance. References | Related Articles | Metrics

Spatial Distribution of Architectures of Braided River Reservoirs in He 8 Member, Sulige Gas Field LIU Jinku, HU Yang, WU Yi 2023, 44 (zk(English)):  22-28.  Abstract ( 44 )   PDF (3937KB) ( 13 )   Save In order to determine the spatial distribution of the architectures of the multi-stage superimposed braided-river tight sandstone reservoirs in the He 8 member, Sulige gas field, by using well logging and core data and referring to modern rivers, the architecture division scheme of the braided river reservoirs in the study area was determined, and the reservoir architecture units were dissected hierarchically. Through the joint simulation based on pixel and target methods, a 3D architecture model of the braided river reservoir including multi-level architecture units was established to finely depict the spatial distribution of different reservoir architectures. The reservoirs in the He 8 member formed due to the vertical or lateral cutting and stacking of multi-phase sandbodies of braided channel. The mid-channel bar of a single braided belt appears in form of lens. The interior of mid-channel bar is separated by discontinuous fall-silt seam, and the braided channels are distributed around the mid-channel bar. According to the 3D architecture model, the reservoir can be divided into different hierarchical architectures, among which the favorable reservoir interval is He 84 sublayer which is mainly distributed in two major braided belts extending north-south in the east and west of the study area, and high-quality sandbodies are distributed in a lenticular shape inside the braided belt. The research results were applied to horizontal well deployment and geosteering drilling, and the drilling results show a high coincidence rate with model predictions. References | Related Articles | Metrics

Characteristics of Alkaline Minerals and Logging Evaluation of Trona in Fengcheng Formation of Mahu Sag MAO Rui, ZHAO Lei, SHEN Ziming, LUO Xingping, CHEN Shanhe, FENG Cheng 2023, 44 (zk(English)):  29-35.  Abstract ( 45 )   PDF (1591KB) ( 14 )   Save The Fengcheng formation of the Mahu sag in the Junggar basin is primarily composed of alkaline lake sediments. A large number of alkaline minerals are developed near the center of the alkaline lake. As a major type in these alkaline minerals, trona is an important industrial resource worthy of development. Currently, the trona intervals are mainly qualitatively evaluated by using the crossplot method, and a quantitative evaluation method is required. Based on core analysis and thin-section identification on alkaline minerals, together with previous research findings, the alkaline minerals in the Fengcheng formation are classified into four categories: trona, shortite; huntite, and searlesite, and their physical properties and impacts on both reservoir properties and oil-bearing property are identified. The influence of trona content on logging responses is analyzed, and a predictive model for trona content is developed by using the deep-to-shallow resistivity ratio. Core data uninvolved in the modeling are used for verifying the prediction model. It is found that the trona content predicted by the model and the trona content measured from cores are in better agreement, with an average relative error of 5.67%, meeting the requirements for precise mineral content calculations. Finally, based on the logging evaluation results of trona content from eleven wells, the distribution of trona in the Fengcheng formation is clarified. The research results may provide a theoretical and technical support for trona resource evaluation. References | Related Articles | Metrics

Controlling Factors and Models of Hydrocarbon Accumulation in Tight Oil Reservoirs of Yao 1 Member in Gulong Sag LIU Ping 2023, 44 (zk(English)):  36-46.  Abstract ( 61 )   PDF (838KB) ( 14 )   Save Based on the seismic, geological, geochemical, and production testing data, the types and distribution patterns of the tight oil reservoirs in the first member of Yaojia formation (Yao 1 member) in the Gulong sag were analyzed, and then the controlling factors and models of hydrocarbon accumulation in these reservoirs were clarified. The results show that five types of tight oil reservoirs are developed in the Yao 1 member such as lenticular sandstone reservoir in the Gulong syncline, updipping pinch-out lithologic reservoir, fault-lithologic reservoir, fault-block reservoir, and fault-anticline reservoir at the top of the nose-like bulge. The formation of tight oil reservoirs is jointly controlled by source rock and overpressure distribution, traps, oil-source faults, and high-quality reservoir beds. The lacustrine mudstones in the first member of Qingshankou formation (Qing 1 member) serve as the material basis for tight oil reservoirs and also create abnormally high pressure that drove oil charging into the Gulong syncline. Before extensive hydrocarbon accumulation, various traps had been formed, including structural traps and structural-lithologic traps at high positions on both sides, which act as the tight oil migration destinations and favorable accumulation sites. The reversal-stage faults that opened during the main oil accumulation phase serve as the primary pathways for vertical oil migration, and high-quality distributary channel reservoir beds are favorable for tight oil accumulation. The structural units are different in controlling factors and models of hydrocarbon accumulation. In the Gulong syncline, the hydrocarbon accumulation model is “driven by overpressure, vertical migration along faults, and enrichment in local sweet spots”. In the Xinzhan nose-like bulge, the hydrocarbon accumulation model is “first driven by overpressure then by buoyancy, vertical migration along faults, and accumulation in favorable traps”. In the Xinzhao slope, the hydrocarbon accumulation model is “driven by overpressure + buoyancy, fault-sandbody relay-migration, and accumulation in favorable reservoir beds”. References | Related Articles | Metrics

Stratification and Segmentation Characteristics and Tectonic Evolution of Shunbei No.5 Strike-Slip Fault Zone in Tarim basin CHEN Ping, NENG Yuan, WU Xian, HUANG Cheng, WANG Laiyuan, GUO Man 2023, 44 (zk(English)):  47-56.  Abstract ( 39 )   PDF (21141KB) ( 14 )   Save The ultra-deep fault-karst reservoirs in the Tarim basin are mainly distributed along strike-slip fault zones, and the oil and gas exploration effects are poor in the areas far away from fault zones, that is, the activity scale of strike-slip fault zones control the scale of hydrocarbon accumulation. The Shunbei No.5 strike-slip fault zone is a super-large strike-slip fault zone, which is characterized by deep burial, complex internal structure, and evident stratification and segmentation. Based on high-quality 3D seismic data, the geometry, kinematics and dynamics of the Shunbei No.5 strike-slip fault zone were systematically analyzed. It is recognized that the Shunbei No.5 strike-slip fault zone is evidently stratified (including 5 structural layers), and also segmented, with the southern and northern segments demonstrating different kinematic characteristics. The former has experienced 5 stages of evolution, and the latter has experienced 4 stages of evolution. References | Related Articles | Metrics

Controls of Continental Shale Lithofacies on Pore Structure of Jurassic Da'anzhai Member in Central Sichuan Basin KONG Xiangye, ZENG Jianhui, LUO Qun, TAN Jie, ZHANG Rui, WANG Xin, WANG Qianyou 2023, 44 (zk(English)):  57-67.  Abstract ( 43 )   PDF (11045KB) ( 19 )   Save The hydrocarbon storage capacity of shale reservoirs depends on their complex pore structures, which vary by lithofacies of shales. In order to clarify the control of shale lithofacies on the pore structure, the lithofaices of the shales in the Da'anzhai member of Jurassic Ziliujing formation in central Sichuan basin were determined based on total organic carbon and X-ray diffraction analyses, and the pore structure characteristics of the shales were identified by means of thin section observation, and analysis on scanning electron microscopy, low-temperature nitrogen adsorption and high-pressure mercury injection. The results show that six shale lithofacies (organic-rich clayey shale, organic-moderate clayey shale, organic-poor clayey shale, organic-moderate mixed shale, organic-poor mixed shale, and organic-poor calcareous shale) are mainly developed in the Da'anzhai member, with parallel plate-like and slit-like pores dominantly. Clayey shales mainly contain clay mineral interlayer pores, organic matter pores, and fractures induced by hydrocarbon generation pressurization; mixed shale mainly contains residual intergranular pores; and calcareous shale mainly contains a small amount of dissolution pores. For all these lithofacies, the clay mineral content is positively correlated with pore volume and specific surface area, and the TOC is positively correlated with the macropore volume of organic-rich clayey shale. The organic-rich clayey shale exhibits the largest macropore volume and trimodal pore-size distribution, making it the most favorable lithofacies for shale oil storage in the Da'anzhai member in central Sichuan basin. References | Related Articles | Metrics

Distribution and Potential Tapping Strategies of Remaining Gas in Tight Sandstone Gas Reservoirs, Sulige Gas Field SHI Yaodong, WANG Liqiong, ZANG Yicheng, ZHANG Ji, LI Peng, LI Xu 2023, 44 (zk(English)):  68-76.  Abstract ( 55 )   PDF (1742KB) ( 13 )   Save The Su 36-11 block in the central area of Sulige gas field has been developed for 17 years, with high degrees of development and reserves producing. The strong reservoir heterogeneity in this block leads to uneven producing of reserves and complex distribution of remaining gas. Distribution determination and potential tapping of the remaining gas are crucial for maintaining stable production in the gas field. By accurately characterizing the reservoir architecture, the main factors influencing remaining gas distribution were identified, the distribution patterns of different types of remaining gas were determined, and corresponding strategies for recovering the remaining gas were proposed. The research results show that the gas-bearing sand bodies in the study area are mainly distributed in the 4th-order architecture units, such as channel bar and point bar, these sand bodies are significantly affected by various levels of flow barriers, with small overall scale, poor connectivity, width of 150-500 m and length of 300-800 m. The main NE-SW sand belt in the block has been developed the most, with low formation pressure, and the remaining gas is mainly distributed in the lower He 8 member in the northwestern part of the block. Remaining gas, whose distribution is mainly influenced by reservoir heterogeneity and uneven development, can be divided into five types: gas uncontrolled by well pattern, gas in composite sand body flow barrier, gas in secondary pay zone unexploited by horizontal well, gas in unperforated gas-bearing layer in vertical well, and gas unproduced. Four potential tapping measures were proposed, including well infilling, reperforation, sidetracking and potential tapping in existing wells. According to the adjusted development plan, it is predicted that stable production can be maintained for 7 years with the recovery efficiency reaching 45%. References | Related Articles | Metrics

RESERVOIR ENGINEERING

Reasonable Productivity Optimization Methods and Application in Ultra‑Deep Fault‑Controlled Fractured-Vuggy Reservoirs GU Hao, KANG Zhijiang, SHANG Genhua, ZHANG Dongli, LI Hongkai, HUANG Xiaote 2023, 44 (zk(English)):  77-83.  Abstract ( 54 )   PDF (2619KB) ( 12 )   Save In this paper, the geological and development characteristics in the FQ oilfield in the Tarim basin were analyzed, and then the productivity test method, choke flow method and reservoir numerical simulation method were developed to optimize the reasonable productivity in ultra-deep fault-controlled fractured-vuggy reservoirs. The results show that the primary oil recovery of ultra-deep fault-controlled fractured-vuggy reservoirs can be divided into early stage, middle stage and late stage, which differ greatly in development characteristics. The ultra-deep fault-controlled fractured-vuggy reservoirs in the FQ oilfield exhibit four types of productivity test curves: convex, linear, upturned and stepped. For wells showing the convex curves, the productivity at the inflection of the curves is the reasonable productivity. For wells showing the linear and upturned curves, the maximum test productivity is the reasonable productivity, but the choke testing productivity needs to be continuously expanded until the inflection of the curves appears. For wells following the stepped curves, the maximum test productivity after reaching the step will be the reasonable productivity. When the well productivity is optimized by the choke flow method, the productivity at the inflection of the choke flow curves is the reasonable productivity. The reservoir numerical simulation method is applicable in optimizing the well productivity in the middle and late stages of primary oil recovery, that is, the reasonable productivity is determined by optimizing the key indicators such as water breakthrough time, cumulative oil production, and recovery rate. References | Related Articles | Metrics

Productivity Evaluation of Condensate Gas Wells With Water and High Condensate Oil Content in Shunbei Oil and Gas Field LI Dongmei 2023, 44 (zk(English)):  84-89.  Abstract ( 45 )   PDF (482KB) ( 11 )   Save The wells drilled in the fault-karst condensate gas reservoirs in Shunbei oil and gas field of Tarim basin exhibits significant formation pressure fluctuations, making conventional well testing interpretation methods based on constant formation pressure inapplicable. Additionally, due to the presence of water and high contents of condensate oil in gas wells, the evaluation results of open flow rates of the wells deviate significantly. Based on systematic well testing data that are corrected with elastic productivity in the well testing stage, this paper presents a productivity evaluation method for the condensate gas wells with water and high content of condensate oil. The field application validates that this evaluation method is applicable for assessing the open flow rate of condensate gas wells in the Shunbei oil and gas field to provide a quantitative understanding on the productivity of condensate gas wells with water and high content of condensate oil in Shunbei area. References | Related Articles | Metrics

Development Characteristics of Solution-Gas Drive in Fault-Karst Reservoirs in Shunbei-1 Block LIU Xueli, TAN Tao, CHEN Yong, XIE Hui, ZHU Suyang, WU Haoqiang, XIANG Dongliu 2023, 44 (zk(English)):  90-97.  Abstract ( 40 )   PDF (2293KB) ( 11 )   Save In order to confirm whether there is solution-gas drive in the fault-karst reservoirs in the Shunbei-1 block, reservoir numerical simulation was performed to characterize the solution-gas drive in the fault-karst reservoirs. Based on the reservoir engineering method, the solution-gas drive characteristics of the fault-karst reservoirs in the Shunbei-1 block were analyzed. The study shows that due to the large thickness of the fault-karst reservoirs in the study area, component gravity differentiation occurs simultaneously near the bottom of the well and at the top of the reservoir, leaving a large amount of solution-gas unproduced and forming a secondary gas cap. Under the action of the elastic energy of solution-gas, the decline of bottomhole flow pressure slows down, and the dynamic reserves of a single well increase to a certain extent. This process is accompanied by the decline in oil-phase driving index. With the further development of solution-gas drive, the secondary gas cap invades the bottom of the well, resulting in a rapid decline of oil production. Therefore, during the depletion development of the fault-karst reservoirs in the Shunbei-1 block, the solution-gas drive can be used to a certain extent together with development under pressure. References | Related Articles | Metrics

Water-Gas Ratio and Early Warning of Water Invasion in Unconsolidated Sandstone Gas Reservoirs in Sebei Gas Field, Qaidam Basin CHAI Xiaoying, WANG Yan, LIU Junfeng, CHEN Fenjun, YANG Huijie, TAN Zhiwei 2023, 44 (zk(English)):  98-104.  Abstract ( 42 )   PDF (519KB) ( 16 )   Save The Sebei gas field in the Qaidam basin is an anticline shallow unconsolidated sandstone gas field driven by weak edge water, and is developed with a depletion pattern. According to the water-gas ratio, the production process of the gas reservoirs in the gas field can be divided into four stages: low water-cut steady production stage, stage of initial water invasion, stage of edge water breakthrough, and stage of strong water invasion. The occurrence of water invasion can be accurately monitored based on the water-gas ratio. The stage of edge water breakthrough can be used as a time window for predicting the extensive water invasion of edge water, and duly adjusting the development plan can prolong the steady production period. The stage of strong water invasion with high water cut corresponds to a long production period, so it is an important stage for enhanced oil recovery while producing with water. References | Related Articles | Metrics

Characterization of Hydraulic Fractures in Tight Conglomerate Reservoirs in Baikouquan formation, Mabei Slope LI Xiangyang, JI Hancheng, BIAN Tengfei, CHEN Liang, CHEN Liang, GUO Xinshu, LI Mengkai 2023, 44 (zk(English)):  105-110.  Abstract ( 49 )   PDF (4660KB) ( 11 )   Save Hydraulic fracturing is a main technique for developing oil and gas in tight conglomerate reservoirs. Currently, hydraulic fractures are mainly studied by means of physical experiments and numerical simulation. The study results can provide a theoretical basis for optimization of development plans, but they are not verified with field data, bringing great uncertainties to the design of stimulation measures. In order to describe the shape of hydraulic fractures for confirming the effective stimulation in tight conglomerate reservoirs, a coring well was drilled on the north slope of Mahu sag for obtaining hydraulic fractures. Based on the observation and analysis of the tight conglomerate cores, the shape, occurrence, and density of hydraulic fractures were characterized by using the core, image logging and CT scanning data. It is found that the tight conglomerate is characterized by large grain size, poor sorting, grain support, and strong heterogeneity. A total of 335 hydraulic fractures were identified in the core with the length of 323 m. Principal fractures propagate in the direction perpendicular to the wellbore; branch fractures are few and nearly perpendicular to the main fractures; crushed zones and asymmetrical double-wing fractures are observed in some intervals. The fractures propagate in two modes: gravel bypassing and gravel penetrating, which are formed due to tension and shear action, respectively, and are thus classified as tensional fractures and shear fractures. The tensional fractures and shear fractures are consistent in occurrence, both with a high dip angle close to 90° and a nearly south-north trending. The density of shear fractures is generally greater than that of tensional fractures. References | Related Articles | Metrics

Development Characteristics and Potential Tapping Strategies of Massive Sandstone Reservoirs With Bottom Water in Tahe Oilfield LIU Lina, CAO Fei, LIU Xueli, TAN Tao, ZHENG Xiaojie, LIU Rui 2023, 44 (zk(English)):  111-116.  Abstract ( 56 )   PDF (617KB) ( 14 )   Save The massive sandstone reservoirs with bottom water in the Tahe oilfield are characterized by relatively thin oil layers. After oil wells are put into production, water breakthrough, water-cut rise, and production decline occur rapidly, posing challenges for stable production. Through the analysis of reservoir development characteristics, the water-cut rise patterns of wells were classified, and the remaining oil distribution and its influencing factors were determined. The results indicate that the main factors affecting the distribution of remaining oil in bottom-water reservoirs are structure, interlayer, reservoir heterogeneity and development methods. Based on the distribution of remaining oil in bottom-water reservoirs in the high water-cut stage, effective potential tapping strategies were proposed to improve development efficiency, including flow adjustment by controlling fluid, natural gas flooding, and CO2 flooding. Numerical simulations and field practices have demonstrated satisfactory results of these strategies, which provide valuable references for the development of similar reservoirs. References | Related Articles | Metrics

Adaptability Evaluation of Gas Huff-n-Puff in Heavy Oil Reservoirs in Tuha Exploration Area XIA Zhengchun, ZHAO Jian, LIU Feng, QIN Enpeng, CAI Bijin, WANG Qi 2023, 44 (zk(English)):  117-122.  Abstract ( 49 )   PDF (467KB) ( 12 )   Save The performance of gas huff-n-puff in heavy oil reservoirs in the Tuha exploration area are declining. Gas huff-n-puff experiments were conducted by using PVT analysis technology to simulate high-temperature and high-pressure environment in the heavy oil reservoirs. CO2, natural gas, and nitrogen were injected respectively into the reservoirs, and then evaluated for adaptability in terms of viscosity reduction, swelling effect, foamy oil range, and residual heavy oil properties. The results show that CO2 huff-n-puff is best performed in viscosity reduction, swelling, and foamy oil range, but the injected CO2 has a significant impact on the residual heavy oil properties by increasing the residual heavy oil viscosity and decreasing the gas dissolution capacity, which is not conducive to multiple rounds of gas huff-n-puff. The natural gas huff-n-puff effect is slightly inferior to that of CO2 huff-n-puff, while the nitrogen huff-n-puff exhibits the worst performance but has a little impact on residual heavy oil properties. References | Related Articles | Metrics

APPLICATION OF TECHNOLOGY

Prediction of Present-Day In-Situ Stress in Ultra-Deep Tight Sandstone Reservoirs in Bozi Gas Reservoir, Kuqa Depression ZHANG Hui, JU Wei, XU Ke, NING Weike, YIN Guoqing, WANG Zhimin, YU Guodong 2023, 44 (zk(English)):  123-128.  Abstract ( 45 )   PDF (1173KB) ( 12 )   Save The ultra-deep formations in the Kuqa depression are rich in oil and gas resources, with strong reservoir heterogeneity and obvious well-to-well productivity difference. The present-day in-situ stress plays an important role in wellbore trajectory design, horizontal well operation, and fracturing design, but the current research methods are disadvantageous in many aspects. On the basis of the measured present-day in-situ stress, the relationships between in-situ stress and logging parameters were constructed, and the prediction of the present-day in-situ stress in the ultra-deep tight sandstone reservoirs in the Bozi gas reservoir of Kuqa depression was realized by using BP neural network. The results show that BP neural network is an effective method for predicting in-situ stress, with just a smaller error between the predicted and measured in-situ stress values, which is generally less than 10%. In the Lower Cretaceous of the Bozi gas reservoir, the maximum horizontal principal stress is the largest, followed by the vertical principal stress, and the minimum horizontal principal stress is the smallest. Generally, the strike-slip stress mechanism is universal, and the maximum horizontal principal stress is predominantly NE-SW trending in the east and NW-SE trending in the west of the Bozi gas reservoir. Compared with sandstone intervals, the sandstone-mudstone interbedding interval exhibits a stronger fluctuation of in-situ stress and a sudden high in-situ stress locally. The horizontal wells drilled along NE-SW direction in the east of the Bozi gas reservoir and along NW-SE direction in the west are relatively stable, while the vertical wells are prone to collapse. References | Related Articles | Metrics

Leakage Pressure Model of Natural Fractures in Igneous Rocks in Kelameili Gas Field YANG Hu, XUE Xiaojun, CHEN Xianghui, LI Xiubin, XIE Junyu, ZHANG Wei 2023, 44 (zk(English)):  129-135.  Abstract ( 49 )   PDF (1917KB) ( 10 )   Save Fractures are developed in the igneous strata of the Kelameili gas field. The composite structure consisting of natural fractures and pores or cavities in such fractured formations may result in a large difference between the leakage pressure and the formation fracture pressure during drilling. The leakage mechanism was investigated according to the fracture-pore occurrence and the fracture opening/closing, connection and filling of the igneous rocks in different well sections, the leakage pressure models under different fracture states were constructed, and the layered leakage pressure profile was plotted depending upon pore pressure, in-situ stress and other parameters, so as to determine the leakage law of natural fractures in the igneous rocks in the Kelameili gas field. The results show that the leakage pressure of closed fractures in the igneous rocks is controlled by in-situ stress, and the leakage pressure of open fractures is affected by formation pore pressure and filling state. Furthermore, combining with the drilling parameters from typical wells, the variation law of fracture leakage pressure under different well trajectories was analyzed, and the safe density window of drilling fluid was determined to ensure drilling safety. References | Related Articles | Metrics

Productivity-Based Classified Logging Evaluation of Carbonate Reservoirs: A Case Study on Yijianfang Formation in Tuofutai Area, Tarim Basin TANG Jun, HE Ze, SHEN Wei, QI Gewei, GUO Weimin 2023, 44 (zk(English)):  136-142.  Abstract ( 43 )   PDF (2304KB) ( 13 )   Save The diversity of pore types is the main cause for strong heterogeneity of the carbonate reservoirs in the Yijianfang formation in Tuofutai area of Tarim basin, making it challenging to evaluate the reservoir effectiveness. On the basis of core and thin section observations, and according to the imaging logging data, the vugs in the carbonate rock are divided into dissolved vug and cavity, and the fractures are divided into structural fracture, dissolution fracture and pressolution fracture. According to the pattern of vug-fracture association, the pore spaces of the Yijianfang formation carbonate reservoirs in the study area are classified as fracture, fracture-vug and vug. The quantitative classification criteria for the reservoirs were established by combining electrical conductivity, fracture porosity and deep lateral resistivity variation. To be specific, the reservoir with the electrical conductivity less than 0.008 and the fracture porosity less than 0.13% is considered as vuggy reservoir; the reservoir with the electrical conductivity ranging from 0.008 to 0.024 and the fracture porosity of 0.13%-0.60% is considered as fractured-vuggy reservoir; and the reservoir with the electrical conductivity greater than 0.024 and the fracture porosity higher than 0.60% is regarded as fractured reservoir. According to the cumulative effective pore thickness, average effective porosity and productivity, the classification and discrimination charts for fractured-vuggy type reservoirs and vug-type reservoirs were established. The vuggy and fractured-vuggy reservoirs in the Yijianfang formation in Tuofutai area are mainly Category Ⅱ reservoirs, with the daily liquid production of more than 50 t and 55 t, respectively. References | Related Articles | Metrics

Methods for Calculating Oil Column Height in Reservoirs Controlled by Deep and Large Faults WANG Rujun, WANG Peijun, NIU Ge, WANG Huailong, ZHANG Jie, LIANG Ruihan, ZHAO Xinyue 2023, 44 (zk(English)):  143-147.  Abstract ( 52 )   PDF (497KB) ( 11 )   Save The reservoirs controlled by deep and large faults are generally thick and deep. Therefore, a well cannot penetrate completely through an entire reservoir. For calculating the oil column height in fault-controlled reservoirs, a physical model of oil column height in fault-controlled reservoir was established. On this basis, the idea of the wellbore temperature profile extrapolation method was discussed, a formula for calculating oil column height with the conversion method of oil-water column pressure coefficient was derived, and the dynamic reserves inversion method considering the cuboid drainage area and the equivalent flow resistance method considering the influence of gravity were proposed. The four methods were applied to two wells drilled into a fault-controlled reservoir in Fuman oilfield of the Tarim basin. The results show that the oil column heights calculated by the four methods are consistent, and the average oil column heights of the two wells are 675.39 m and 634.60 m, respectively. References | Related Articles | Metrics

High-Precision Seismic Imaging of Western Qiulitag Structural Belt in Kuqa Depression ZHANG Xiangquan, GU Yongxing, LIU Jun, PEI Jiading, GU Xiaodi 2023, 44 (zk(English)):  148-155.  Abstract ( 50 )   PDF (11111KB) ( 10 )   Save The western Qiulitag structural belt is an important successive area for oil and gas exploration in the Kuqa depression, Tarim basin. Its complex surface and underground geological conditions bring challenges to seismic survey. It has been less explored in the main structural belt, where the high steep structural features and complex fault systems cannot be depicted by using previous 2D (single-line and wide-line) seismic data. To address this problem, a combination of wide-frequency band, wide-azimuth and high-density 3D seismic survey and high-density cable 3D seismic survey is used to increase the effective folds in the complex, high, steep structural areas. The microlog-constrained shallow surface velocity modeling is conducted to improve the static correction accuracy in complex mountainous areas and thick gravel-covered piedmont areas. The six-division method for denoising is adopted to improve the signal-to-noise ratio of seismic data in inter-salt and pre-salt structures. The five-dimensional interpolation and regularization technique is applied to mitigate the impact of irregular observation system in mountainous areas on pre-stack depth migration imaging. Moreover, two-way wave reverse time-migration is performed to increase the migration imaging precision of highly steep formations. Through acquisition-processing integration and seismic-geological fusion, the seismic imaging precision in the western Qiulitag structural belt can be significantly improved. References | Related Articles | Metrics