新疆石油地质

Exploration Implications of Total Petroleum System in Fengcheng Formation, Mahu Sag, Junggar Basin

HE Wenjun, QIAN Yongxin, ZHAO Yi, LI Na, ZHAO Xinmei, LIU Guoliang, MIAO Gang

2021, 42 (zk(English)): 1-16.

摘要 ( 20 )

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As a globally typical total petroleum system, the Fengcheng formation in the Mahu sag of the Junggar basin has representative significance in terms of exploration. Taking the discovery of oil and gas reserves and key wells as the main line, and considering the improvement on exploration idea and theory, the oil and gas exploration history of the Fengcheng formation is reviewed and then divided into three major stages: conventional oil and gas exploration in the fault zone outside the source, multi-type risky exploration and inner-source total petroleum system exploration. Consequently, many implications have been obtained: the high-quality alkaline-lacustrine source rock in the Fengcheng formation can be considered as the key target for exploration; under the joint actions of terrigenous clast sedimentation, inner-source chemical sedimentation and volcanic activity, the all-type reservoirs with a stratigraphic sequence of orderly distributed sandy conglomerate-dolomitic sandstone-dolomitic mudstone and argillaceous dolomite are developed in the Fengcheng formation, and the stratigraphic sequence coexists with conventional volcanic rocks and fractured reservoirs; within the Fengcheng formation, controlled by facies sequence, all types of reservoirs including conventional oil reservoir, tight oil reservoir and shale oil reservoir coexist orderly. The total petroleum system in the Fengcheng formation is a typical example in the world. It reflects the concept of a total petroleum system, realizes the transformation from theory to practice, enriches and develops the theories of oil and gas systems in continental petroliferous basins, and guides the “inside sag” exploration of the hydrocarbon-rich sags in the Junggar basin. The review may be an important reference to oil and gas exploration in other major petroliferous basins in China.;

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Petroleum Exploration History and Enlightenment of Changqing Oilfield in Ordos Basin

ZHANG Caili, LIU Xinshe, YANG Yajuan, YU Jian, HAN Tianyou, ZHANG Yan

2021, 42 (zk(English)): 17-39.

摘要 ( 59 )

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This paper systematically analyzes the geological theories of hydrocarbon accumulation and summarizes the exploration achievements made by Changqing oilfield in the Ordos basin. The exploration process in the Ordos basin can be divided into five stages: (1) Oil and gas exploration for the structures in the basin and its surroundings from 1907 to 1969; (2) Oil exploration in the Jurassic paleogeomorphology from 1970 to 1979; (3) Oil and gas exploration in the Triassic delta and Ordovician karst paleogeomorphology from 1980 to 1999; (4) Oil and gas exploration for large lithological reservoirs from 2000 to 2012; (5) Exploration of tight and unconventional oil and gas since 2013. During more than 50 years of exploration practices, a number of innovative geological cognitions and theories have been developed, such as hydrocarbon accumulation in Jurassic paleogeomorphic oil reservoir groups, hydrocarbon accumulation in large delta reservoirs in continental lacustrine basin, shale oil accumulation in terrestrial freshwater lake basin, gas accumulation in tight sandstone, gas accumulation in karst paleogeomorphy and hydrocarbon accumulation in multiple series in the eastern Ordos basin, which promoted sustainable breakthroughs to oil and gas exploration in the Ordos basin.

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Hydrocarbon Accumulation of Ultra-Deep Ordovician Fault-Karst Reservoirs in Shunbei Area

YUN Lu

2021, 42 (zk(English)): 40-56.

摘要 ( 19 )

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In the Shunbei area of Tarim basin, Ordovician carbonate fault-karst reservoirs are controlled by strike-slip faults. These faults are distributed in rows and belts, and typically characterized by “laterally superimposed segments, vertically layered deformation and superimposed transformation”. On the plane, there are three types of fault systems: NE-SW, NW-SE, and NNE-SSW; and the faults of the Middle-Lower Ordovician can be divided into four styles: superimposed pull-out, superimposed indentation, linear translation, and composite graben. The different evolution of the Middle-Lower Cambrian source rocks in the east and west of the Shunbei area controls the present resource accumulation shown by “western oil and eastern gas”, and the plane segments of the fault zones control the internal structures of the reservoirs. The Ordovician fault-karst reservoirs have good source rock, reservoir and cap rock conditions. The faults communicate with the source rocks downwards, and the development of the fault-controlled fractured-vuggy reservoirs control the enrichment of oil and gas reservoirs. All these are mainly affected by the activity intensity, segmenting style, and the angle with the present principal stress direction in the fault zones.

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Controlling Factors on CBM Accumulation in Low-Rank Coal in Santanghu Basin

TU Zhimin, WANG Xinggang, CHE Yanqian, ZHANG Shizhao, LI Peng, CAO Zhixiong

2021, 42 (zk(English)): 57-63.

摘要 ( 23 )

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Industrial CBM (coalbed methane) flow has been obtained from the low-rank coal in the Malang sag, Santanghu basin. However, CBM accumulation there has been less researched. In order to get more understandings to guide future exploration, we studied the CBM geological characteristics through drilling and laboratory data analysis. The results show that the coal seams in the study area have large thickness, good coal structure, relatively high gas content, and good physical properties and enrichment conditions. By combining the hydrogeological characteristics with preservation conditions, it is concluded that the CBM in the low-rank coal belongs to a mixed genetic type. Water from melted snow and rain flowing along the slope of the basin margin provides good conditions for generating biogas and plays the role of a lateral seal; and at the same time, thermogenic gas generated continuously with structural subsidence accumulates in the favorable zone on the slope, which established a mixed genetic model of CBM accumulating in the low-rank coal on the basin margin. To sum up, a good configuration of hydrogeological and structural conditions with top and bottom sealing abilities controls the CBM accumulation in the low-rank coal in the basin.

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Sedimentary Characteristics of Jurassic Kalazha Formation in the Thrust Belt on the Southern Margin of Junggar Basin

SI Xueqiang, YUAN Bo, PENG Bo, JI Dongsheng, GUO Huajun, TANG Xueying, DOU Yang, LI Yazhe

2021, 42 (zk(English)): 64-73.

摘要 ( 27 )

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In order to clarify the characteristics of deep reservoirs in the thrust belt on the southern margin of the Junggar basin, the markers, types, distribution and models of sedimentary facies and source directions of the Jurassic Kalazha formation are analyzed based on the data of outcrops, mud logging, trace elements and heavy minerals. The result shows that the sedimentary facies of alluvial fan and braided river delta are mainly developed in Kalazha formation. Laterally, three large sedimentary systems are distributed from west to east, which are the alluvial fan-braided river delta in the middle section of the Qigu fault-fold belt, the braided river delta in the Toutunhe area in the eastern section of the Qigu fault-fold belt, and the braided river delta in the Fukang fault belt. Vertically, there are four sedimentary cycles which follow a prograding sequence. The types and planar distribution of the sedimentary facies are mainly controlled by the activities of the Tianshan orogenic belt during the late Jurassic period. Sandstone reservoirs of more than 200 m thick are developed on the three large sedimentary systems. Especially, the sandstone reservoirs in the braided river delta front are well sorted, thick and widely distributed, which match well with the deep large anticlines and can be favorable exploration targets.

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Classification and Genesis of Fine-Grained Sedimentary Rocks of Qingshankou Formation in Songliao Basin

DING Cong, SUN Pingchang, Rexiti·YALIKUN, WANG Chang, ZHANG Ying, ZHANG Qing

2021, 42 (zk(English)): 74-83.

摘要 ( 25 )

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The Qingshankou formation in the Songliao basin belongs to thick fine-grained sedimentary rock, and it is an important interval for shale oil and gas accumulation. The classification of the fine-grained sedimentary rocks is the key premise for exploring unconventional oil and gas. Based on field survey and systematic sampling analysis, we studied the types, sedimentary environment and geochemical characteristics of the fine-grained sedimentary rock of the Qingshankou formation in the Songliao basin. According to TOC and the contents of carbonate and terrigenous clastic minerals, the fine-grained sedimentary rocks in the study area can be classified into fine-grained terrigenous clastic rocks with extremely poor, poor, moderate and rich organic matters, and fine-grained terrigenous carbonate rocks with poor and extremely poor organic matters. The fine-grained terrigenous clastic rocks with rich and moderate organic matters and the fine-grained terrigenous carbonate rocks with poor organic matter were deposited in a semi-deep lake environment with stiller water; the fine-grained terrigenous clastic rock with poor and extremely poor organic matters and the fine-grained terrigenous carbonate rock with extremely poor organic matters were deposited in a shallow lake environment; and carbonate rock was mainly deposited in an open saline lake basin in temperate to subtropical zones. The primary type of organic matters in the fine-grained sedimentary rocks is Type Ⅱ1. The fine-grained sedimentary rocks are medium-good quality source rocks. The fine-grained terrigenous clastic rocks with rich and poor organic matters in deep formations are primary targets for shale oil and gas exploration.

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Diagenetic Evolution and Hydrocarbon Accumulation History in Reservoirs of Xishanyao Formation in Yongjin Oilfield, Junggar Basin

REN Xincheng

2021, 42 (zk(English)): 84-92.

摘要 ( 20 )

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The Middle Jurassic Xishanyao formation in Yongjin oilfield is generally at depth of 5600 m to 6400 m in the hinterland of the Junggar basin, where the reservoirs are deep and ultra-deep ones with low porosity and low permeability. In order to reveal the relationship between the process of reservoir densification and hydrocarbon accumulation, the reservoir characteristics, diagenesis, diagenetic evolution sequence and hydrocarbon accumulation history of the Middle Jurassic Xishanyao formation were analyzed through core observation, casting thin section identification, fluid inclusion and bitumen fluorescent color analysis. The results show that the Xishanyao formation has undergone three stages of diagenesis-hydrocarbon charging, and each stage of diagenesis was terminated with hydrocarbon charging. The oil charged in the first stage was oxidized in the process of tectonic uplifting, and a large amount of carbonaceous bitumen was generated and occupied reservoir pores. At the end of the second stage of diagenesis, large-scale hydrocarbon charging took place, resulting in overpressure reservoirs. Hydrocarbon charging evidently inhibited reservoir cementation and pore reduction, dissolved the carbonaceous bitumen in the early pores and increased the reservoir space. That is the key stage of hydrocarbon accumulation and improvement and maintenance of reservoir physical properties. Reservoirs formed in this stage are the primary exploration target in Yongjin oilfield. In the third stage of diagenesis, rapid burying and compaction of strata further worsened the reservoir physical properties, so that only a small amount of highly mature oil and gas accumulated in this stage.

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Genesis of Densification of Low-Permeability Tight Sandstone Reservoirs: A Case Study of Lower Jurassic Badaowan Formation in Mobei－Mosuowan Swell, Junggar Basin

SHAN Xiang, GUO Huajun, CHEN Xiguang, DOU Yang

2021, 42 (zk(English)): 93-100.

摘要 ( 17 )

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Based on the rock thin section, casting thin section and X-ray diffraction whole-rock mineral analyses, and the data of scanning electron microscopy and reservoir physical properties, the petrologic, physical and diagenetic characteristics of the tight reservoirs in the lower Jurassic Badaowan formation of the Mobei–Mosuowan swell in Junggar basin were studied, and the genesis of reservoir densification was analyzed. The results show that the reservoirs are characterized by low compositional maturity, low content of interstitial matter and high content of plastic debris, and that the reservoirs have experienced strong compaction, weak cementation and general dissolution. Strong compaction is the most important factor on the reservoir densification, which is caused by strong compaction from acid diagenetic fluid in coal measures and strong static rock compaction from the high content of plastic debris in the Badaowan formation. Due to the low plastic debris content, the medium-coarse sandstone and coarse sandstone have strong fluid compaction effect and weak static rock compaction effect, therefore the medium-coarse and coarse sandstone reservoirs in Badaowan formation have good physical properties and are favorable for oil and gas accumulation.

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Vertical Layered Structure of Shunbei No.5 Strike-Slip Fault Zone and Its Significance on Hydrocarbon Accumulation

HAN Jun, KUANG Anpeng, NENG Yuan, HUANG Cheng, LI Qiqi, CHEN Ping, SHEN Zhuoyi

2021, 42 (zk(English)): 101-108.

摘要 ( 24 )

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As the largest strike-slip fault zone in Shunbei area, Shunbei No.5 structure is vertically layered and deformed, and has been proved to play an important role in controlling fault-karst reservoirs. The study carried out the interpretation of 3D seismic data of the Shunbei No.5 strike-slip fault zone, analyzed its structure, and established vertical layered structure model to clarify the control of the strike-slip fault zone on reservoir development and hydrocarbon migration and accumulation. The results show that: (1) The Shunbei No.5 strike-slip fault zone can be divided into four layers in the vertical direction, namely a Cambrian sub-gypsum fault system, a Cambrian gypsum-related fault system, an Ordovician carbonate fault system, and an Ordovician-Carboniferous clastic fault system; (2) The difference between stratum mixing competence is the basic condition of the layered deformation, and the staged activities of strike-slip faults caused by the changes of regional tectonic movement is the primary reason for the layered deformation; (3) The vertical layered structure of the strike-slip fault zone controls the hydrocarbon migration and accumulation: the sub-gypsum faults control the distribution of source rocks, the faults penetrating gypsum interval control hydrocarbon migration, the faults inside the Ordovician carbonate rock control the scale and connectivity of reservoirs, and the faults inside the Late Ordovician-Carboniferous clastic rock control hydrocarbon accumulation. According to the strength of the strike-slip fault movement, the strike-slip fault zone can be classified into three categories such as strong activity and dominant superimposition, strong activity and differential superimposition, and weak activity and weak superimposition.

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Division and Application of Gas/Water Occurrence Models in High⁃Rank Coal Reservoirs

LIU Zhong, WANG Ning, ZHANG Yongping, LU Xiuqin, LI Zheng, GAO Yan

2021, 42 (zk(English)): 109-115.

摘要 ( 42 )

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By analyzing the factors controlling hydrocarbon accumulation in Zhengzhuang block and Mabidong block in the southern Qinshui basin, and using molecular simulation technology, the microscopic laws of gas/water occurrence in the coal reservoirs were studied, then the occurrence models of methane in microscopic pores were demonstrated, and finally dynamic balance occurrence models considering the dynamic boundary effect of low-permeability fractures were established based on evaluation well data (i.e. measured gas content, fracturing stimulation and production data), microfracture models and boundary layer effects. The results show that anhydrous methane mainly adsorbs to the pores with a diameter of 2 nm, and as the gas saturation increases, the competition among water molecules weakens. The balance relationship among viscous force, gas/water phase pressure and capillary force is defined. The gas/water pressure balance models are divided into escaping and occluding models. After analyzing the influences of 4 types of gas/water occurrence models on later production, it is believed that the gas output of Type III and Type IV models is relatively higher.

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Imbibition Law of Shale Oil Reservoirs in the Lucaogou Formation in Jimsar Sag

MA Mingwei, ZHU Jian, LI Jiacheng, LIAO Kai, WANG Junchao, WANG Fei

2021, 42 (zk(English)): 116-122.

摘要 ( 22 )

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Shale oil reservoirs with middle-low porosity and low-ultra-low permeability are present in the Lucaogou formation in Jimsar sag, and the reservoirs are also the source rocks. These oil reservoirs have been developed with dense horizontal wells and high-strength volume fracturing stimulation. In the case of a long-term well shut-in after fracturing, the flowback rate of fracturing fluid is low, but the oil production is high. In comparison, in the case of a short-term well shut-in, the flowback rate of fracturing fluid is high, but the oil production is low. In order to understand the law of fracturing fluid imbibition displacement in the soaking period after fracturing, the reservoir wettability was evaluated using contact angle, and the spontaneous imbibition experiment was carried out using real downhole cores and NMR. The results show that the wettabilities of the upper sweet spot interval and the lower sweet spot interval in the Lucaogou formation in Jimsar sag are quite different, which are closely related to the imbibition displacement capacities. The upper sweet spot interval is hydrophilic, where small pores are dominant during the imbibition process. Initial imbibition is a rapid process and reaches equilibrium after about 160 h, and the average imbibition recovery is 31%. The lower sweet spot interval is lipophilic, where large pores are dominant during the imbibition process. The imbibition rate is slow and reaches equilibrium after about 400 h, and the average imbibition recovery is 22%. It is proposed to appropriately extend soaking time for the upper sweet spot interval, and choose fracturing fluid with surfactants for the lower sweet spot interval, so as to give full play to imbibition displacement to improve the recovery of the shale oil reservoirs.

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Feasibility of Supercritical CO2 Huff⁃Puff Development of Tight Conglomerate Reservoirs

PU Wanfen, WANG Yangsong, LI Longwei, GAO Haiming, SHAN Dongbai, WANG Wenke

2021, 42 (zk(English)): 123-129.

摘要 ( 18 )

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CO₂ huff-puff development has unique mechanisms such as dissolution, extraction and miscibility and supercritical CO₂ has better injectivity, penetrability and extraction of light components. In order to further understand the feasibility of supercritical CO₂ huff-puff in enhancing oil recovery of tight conglomerate, based on supercritical CO₂ crude oil interaction, supercritical CO₂ crude oil extraction experiment and supercritical CO₂ huff-puff indoor physical simulation, oil property changes and stimulation mechanism during huff-puff process were revealed, and the recovery factors obtained with different injection parameters were determined. The results show that supercritical CO₂ can effectively supplement formation energy, reduce viscosity and density of crude oil, and improve mobility of crude oil. The recovery factor was improved by 22.16% after injecting 0.50 PV of supercritical CO₂; with the increase of supercritical CO₂ injection rate, the recovery factor increased but the replacement ratio decreased. Compared with the single round stimulation, the recovery efficiency of the four-round huff-puff can be increased by 20%-24%. The recovery factor was 22.16% after soaking for 120 minutes, but changed little after soaking for 240 minutes. The findings demonstrate that it is feasible to enhance the recovery by implementing supercritical CO₂ huff-puff development after depletion development in tight conglomerate reservoirs, which provides a reference to the development of tight conglomerate reservoirs.

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A New Method for Evaluating the Productivity of Oil Wells in Fault-Karst Reservoirs in Shunbei Oil & Gas Field

HU Wenge

2021, 42 (zk(English)): 130-134.

摘要 ( 22 )

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There are two problems in the understanding of oil well productivity in the high-productivity pilot block of fault-karst reservoirs in Shunbei oil & gas field: First, the formation pressure fluctuates obviously after well testing, so the conventional method for well test interpretation is no longer applicable;; second, the productivity index curve determined based on well test data is nonlinear, so the oil production index method is unsuitable for quantitatively evaluating the oil well productivity. In order to realize quantitative evaluation of the productivity of the oil wells in Shunbei oil & gas field, based on the correction to well test data for estimating the fluctuating productivity in the systematic well test stage, we proposed a new method for evaluating the productivity of the oil wells, which includes exponential productivity equation, comprehensive oil production index, and productivity division standard. Field application has proved the systematic well test data correction method and the productivity evaluation method are suitable for quantitatively evaluating the productivity of the oil wells in Shunbei oil & gas field, which provide a theoretical basis for the quantitative understanding of the productivity of the oil wells in Shunbei oil & gas field.;

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Fluid Phases and Gas Reservoirs of Qingshuihe Formation in Well Hutan-1

WANG Qixiang, LIANG Baoxing, LIU Huan, SHI Feng, JIN Jun, ZHOU Wei, TUO Hong

2021, 42 (zk(English)): 135-139.

摘要 ( 22 )

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After characterizing the gas reservoir of the Qingshuihe formation in Well Hutan-1 as a condensate gas reservoir, the fluid phase behaviors around the well were studied through a series of experiments of one-time degassing, fluid composition, constant-mass expansion and constant-volume depletion. The research results show that the formation fluid compositions are characterized by high contents of light components and low contents of medium and heavy components, indicating a typical gas reservoir containing less condensate oil. Due to a few condensate fluid and a big difference between formation pressure and dew point pressure, it is not necessary to supplement energy in the early production stage. In addition, re-injecting associated gas can inhibit retrograde condensate and increase the recovery of Well Hutan-1. Based on the production data, fluid phase behavior, pressure-temperature phase diagram of the formation fluid, triangular ternary phase diagram and empirical discrimination, the reservoir of the Qingshuihe formation in Well Hutan-1 is deemed as a condensate gas reservoir with a large oil ring.

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Productivity Prediction and Influencing Factors of Low Permeability Reservoirs after Steering Fracturing Stimulation

PU Xiao, GUO Dali, LAN Tian, HE Yong, ZHAO Yunxiang

2021, 42 (zk(English)): 140-144.

摘要 ( 21 )

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Steering fracturing can expand the drainage area of low permeability reservoirs and achieve the effect of volume fracturing. However, the fractures induced by steering fracturing are complicated, and should be finely characterized to accurately predict the post-fracturing productivity. Based on the production data from Karamay oilfield, and in view of the characteristics of steering fractures, a mathematical model of single-phase flow was established, and a grid refinement technology was used to densify the steering fractures. Field application has proved that the oil production after steering fracturing was 5.3 times higher than that of conventional fracturing. The factors influencing the productivity after steering fracturing were evaluated and the result shows that the production is positively correlated with reservoir per permeability, steering fracture length and conductivity of initial induced fractures, but not necessarily depending on steering fractures to get a high flow conductivity.

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Full-Diameter Physical Simulation of Oxygen-Reduced Air-Assisted Gravity Drainage: A Case Study of Gasikule E¹₃ Reservoir in Qinghai Oilfield

LONG Anlin, QI Qingshan, CHEN Xiaolong, LI Yiqiang, LU Shanshan, ZHANG Pei, LI Xin

2021, 42 (zk(English)): 145-150.

摘要 ( 22 )

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Compared with conventional gas injection methods, the gas-injection assisted gravity drainage has the advantages of restraining gas channeling and expanding swept volume. In this study, a static low-temperature oxidation experiment was conducted to investigate the adaptability of the oxygen-reduced air-assisted gravity drainage in the Gasikule E¹₃ reservoir. Oxygen-reduced air-assisted gravity drainage experiment was carried out with the help of natural full-diameter long core, so as to study the influences of oxygen volume fraction, gas injection rate and core inclination angle on the oxygen-reduced air-assisted gravity drainage. The results show that the oxygen-reduced air with low oxygen volume fraction (5%) plays a significant role in low-temperature oxidation in the Gasikule E¹₃ reservoir, and the oxygen consumption rate can reach 2.19 mol/(h·mL). For the oxygen -reducing air-assisted gravity drainage, under the conditions of the Gasikule E¹₃ reservoir, the ultimate recovery increases with an increased oxygen volume fraction of the injected air. The incremental recovery factor of the core experiment ranges from 1.2% to 6.9%. From the perspective of recovery ratio and safety, oxygen-reduced air with the oxygen volume fraction slightly lower than 10% can be applied as the displacement medium. Viscous fingering may occur when the gas injection rate is more than 1.0 mL/min, while capillary retention may occur when the oxygen injection rate is less than 0.1 mL/min, resulting in relatively low recovery factor. When the gas injection rate is 0.3 mL/min, it is a stable oil and gas flooding with a higher recovery factor. The process of the oxygen-reduced air-assisted gravity drainage is relatively sensitive to gravity. For the reservoirs with small inclination angles, the oxygen-reduced air-assisted gravity drainage is still feasible to some extent. The factors that affect the oxygen-reduced air-assisted gravity drainage in the Gasikule E¹₃ reservoir are gas injection rate, core inclination angle and oxygen volume fraction in sequence according to their sensitivities.

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Near-Surface Azimuthal Anisotropy and Seismic Imaging in the Southern Margin of Junggar Basin

LUO Yong, TAN Jia, YANG Xiaohai, DOU Qiangfeng, LIU Yiwen

2021, 42 (zk(English)): 151-157.

摘要 ( 18 )

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The Anjihai anticline in the southern margin of the Junggar basin is a typical complex oil exploration area where the near-surface heterogeneity is very strong, lithology changes fiercely, and the velocity of the weathered layer changes greatly. The complex near surface shooting and receiving conditions change the path and velocity of seismic waves and result in serious near surface azimuthal anisotropy, making effective seismic waves (events) not be superimposed. The accurate imaging of complex structure is the first problem to be solved in seismic processing. This study analyzed the characteristics of the first arrivals of original source points, and described the correspondence between gathers after NMO/static correction and source and receiver points based on geological outcrops and satellite images, and then built the close relationship with various gullies and near surface medium lithology, and finally established the weighted coefficient fields of different azimuth through azimuthal NMO/static correction and azimuthal weighted pre stack time migration imaging, so that the arcing phenomenon in pre stack time migration can be obviously suppressed, and the final migration imaging quality can be significantly improved. Using the results of pre stack time migration, the middle and lower trap combinations in the Anjihai anticline have been effectively identified.

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Application of Vertical P⁃Wave Slowness in Porosity Evaluation of Shale Gas Reservoirs in Highly Deviated or Horizontal Wells

ZHENG Jian, FU Yongqiang, CHEN Man, JING Cui, ZHANG Jing, ZHOU Hao, ZHANG Jiahao

2021, 42 (zk(English)): 158-164.

摘要 ( 22 )

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In Changning Shale Gas Pilot Development Area of Sichuan basin and based on vertical wells, a parameter model is built by using density, neutron, P-wave slowness, GR and resistivity logging data and core porosity and saturation to evaluate the resources. Horizontal well is used to develop the shale gas in the area. A parameter model is established with the same logging data from horizontal wells and core porosity and saturation from vertical wells to evaluate reservoirs in horizontal wells. P-wave slowness is the basic data for building the porosity and rock mechanical parameter model. The results show that the P-wave slowness measured in vertical wells is greater than those measured in highly deviated wells and horizontal wells in the Changning shale gas area. The P-wave slowness is greatly affected by well deviation, and the larger the well deviation, the greater the influence because of obvious velocity anisotropy in vertical and horizontal directions. In the same horizon and the same well interval, the porosity calculated from the model in highly deviated or horizontal wells is significantly different from the core porosity. In this study, we analyzed the relationships between P-wave slowness and well deviation in the same interval of the vertical, highly deviated and horizontal wells in the study area, and compared the P-wave slowness and porosities calculated by direct fitting method and anisotropic elliptic model method. It is considered that both of the two methods can reduce the influences of anisotropy and the anisotropic elliptic model method works better. Finally, the anisotropic elliptic model method has been widely used in porosity evaluation of shale reservoirs and good results have been gained in the study area.

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Current In-Situ Stress Field and Efficient Development of Bozi-1 Gas Reservoir in Kelasu Structural Belt

XU Ke, YANG Haijun, ZHANG Hui, WANG Haiying, YUAN Fang, WANG Zhaohui, LI Chao

2021, 42 (zk(English)): 165-173.

摘要 ( 22 )

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In order to improve the development effect of the Bozi-1 gas reservoir in the Kelasu structural belt in the Kuqa depression, Tarim basin, multiple information and methods were used, and logging interpretation and three-dimensional numerical simulation were carried out to study the current spatial distribution and its influencing factors of the in-situ stress field. The findings are basic data for locating development wells. The Bozi-1 gas reservoir is deeper than 6,500 m and still in a strike-slip in-situ stress field. Current in-situ stress is high, the horizontal stress difference is large and the heterogeneity is strong. The current max. horizontal principal stress may deflect horizontally and longitudinally, with a max. deflection of 90°. Complicated geological boundary conditions and differences in rock mechanical properties are important factors on the strong heterogeneity of the in-situ stress field. The development of the gas reservoirs obviously disturbs the in-situ stress state around wellbores. To locate wells in the ultra-deep reservoirs, it is necessary to consider the current in-situ stress and the disturbance caused by adjacent wells. It is suggested to drill highly-deviated wells and expand reservoir contact to eliminate the risk of the strong reservoir heterogeneity on drilling safety.

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Thin Reservoir Prediction Under Strong Reflection Shielding Background in Chunguang Area

XIE Qi, LI Hengquan, LI Lei, ZHANG Xinchao, GUO Jiayu, YANG Xingxing, JIA Xiurong

2021, 42 (zk(English)): 174-180.

摘要 ( 23 )

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In the Chunguang exploration area, the Carboniferous strata show strong seismic reflections, while the Cretaceous reservoir above and vertically close to Carboniferous is thin and laterally superposed, and completely shielded by the strong reflections from the Carboniferous. Vertically, we used forward modelling to get the dominant frequencies of AC and GR curves, and reconstructed the acoustic impedance curve to improve reservoir identification effects. Horizontally, the distribution of thin reservoirs shielded by strong reflections is predicted using high-resolution seismic inversion with waveform indication. Twelve lithologic traps has been identified, and commercial oil and gas flows have been obtained from one preliminary exploration well and one evaluation well. It has been proved that the technology can effectively predict thin reservoirs shielded by strong reflections, and it is also of great significance for predicting thin reservoirs on other similar complex background.

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