新疆石油地质

Main Controlling Factors and Gas Enrichment Area Selection of Ma5₅ Gas Reservoir in Eastern Sulige gas field

BAI Hui, Yang Tebo, HOU Kefeng, MA Zhixin, FENG Min

2022, 43 (zk(English)): 1-7.

摘要 ( 52 )

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In order to improve the drilling rate of pay zones in the Ma5₅ gas reservoir in eastern Sulige gas field, the Ordos basin, using the drilling, logging, core and gas production testing data, and analyzing the main factors controlling pay zones such as sedimentary microfacies, diagenesis and paleotopography, the distribution law of dolomite in the Ma5₅ gas reservoir was clarified. Moreover, the reservoirs were comprehensively classified and evaluated, and the favorable gas enrichment areas in the Ma5₅ gas reservoir were selected. The research results show that the pay zones in the Ma5₅ reservoir are distributed as “lens” in local areas, with poor continuity. The most favorable reservoir rocks are granular dolomite and coarse powder crystalline dolomite, and the main storage space consists of intergranular pores, intergranular dissolved pores and structural fractures. Sedimentary facies and diagenesis are the main controlling factors of the Ma5₅ reservoir, and the grain beach is the most favorable sedimentary microfacies of the Ma5₅ dolomite. The pay zones are mainly controlled by quasi-contemporaneous dolomitization and buried dolomite diagenesis. The paleoslope on the relatively high position is a favorable area for the development of the Ma5₅ gas reservoir.

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Accumulation Conditions and Exploration Direction of Lower Jurassic Tight Sandstone Gas Reservoirs in Taibei Sag

CHEN Xuan, WANG Jufeng, XIAO Dongsheng, LIU Juntian, GOU Hongguang, ZHANG Hua, LIN Lin, LI Hongwei

2022, 43 (zk(English)): 8-16.

摘要 ( 38 )

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The Turpan-Hami basin has great potential of oil and gas resources in the Lower Jurassic Strata, with a large quantity of remaining resources. The discovered oil and gas reservoirs are mainly distributed in the positive structural belts around the Shengbei and Qiudong subsags in the Taibei sag, and they are primarily structural reservoirs. Less researches on the oil and gas resources in the hinterland of the subsags have been performed. Based on the dissection of known reservoirs, a systematic study was carried out on the depositional system, source rock, reservoir rock and accumulation conditions of three major hydrocarbon-rich subsags in the Taibei sag. The results show that the coal-measure source rocks are widely developed in the Shuixigou group in the Taibei sag and are in broad contact with the braided river delta sandstones, which is conductive to the formation of near-source tight sandstone gas reservoirs. There are two types of tight sandstone gas reservoirs in the Lower Jurassic, namely, trap-type and continuous-type. The hinterlands of the subsags are favorable areas for the formation of continuous-type tight sandstone gas reservoirs. Therefore, the exploration should be switched from the source-edge positive structure to the hydrocarbon-rich subsag, and from the above-source conventional oil reservoirs to the in/near-source tight sandstone gas reservoirs. The hinterlands of the Shengbei and Qiudong subsags have the conditions to form large gas reservoirs, so they are favorable areas for exploring near-source tight sandstone gas reservoirs in the Lower Jurassic.

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Lithofacies Paleogeography and Petroleum Exploration of Fengcheng Formation in Western Central Depression of Junggar Basin

HE Haiqing, TANG Yong, ZOU Zhiwen, GUO Huajun, XU Yang, LI Yazhe

2022, 43 (zk(English)): 17-31.

摘要 ( 33 )

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In order to evaluate the petroleum exploration prospects of the Fengcheng formation in the western Central depression of the Junggar basin, the lithology assemblages and sedimentary facies of the Fengcheng formation were studied by means of analyzing the trace element, core, rock thin section, paleomorphology, logging facies and seismic facies of the formation. The results show that the Fengcheng formation in the study area is fan delta-alkali lake deposition which was formed in an arid-semi-arid climate, foreland tectonic setting and geological environment with periodic changes in water salinity and water depth. From the margin to the center of the Central depression, basin-marginal fan-delta clastic rocks, outer-slope front dolomites, slope-highland volcanic rocks, low-uplift dolomitic calcareous beach-bar peperites, and the central lake-basin alkali rocks are found in sequence. According to the sedimentary characteristics, an evolution model for the fan delta-alkali lake deposition was established for the Fengcheng formation. Based on the sedimentary facies, lithofacies and petroleum exploration status, the Fengcheng formation in the study area can be divided into 5 areas such as conventional hydrocarbon area in basin-marginal ultra-denudation belt, tight hydrocarbon area in outer-slope front, shale oil/gas area in lake basin, conventional hydrocarbon area around low-uplift and conventional hydrocarbon area in highland volcanic rocks. The favorable exploration area with the depth less than 7 000 m reaches 1.2×10⁴ km², with hydrocarbon reserves of more than one billion tons, which demonstrates huge exploration potential of the total petroleum system of the Fengcheng formation in the study area.

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Hydrocarbon Accumulation Mechanism of Total Petroleum System in Permian Fengcheng Formation, Mahu Sag

HE Wenjun, SONG Yong, TANG Shiqi, YOU Xincai, BAI Yu, ZHAO Yi

2022, 43 (zk(English)): 32-43.

摘要 ( 38 )

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The exploration practice in the Fengcheng formation in the Mahu sag, western Junggar basin, has revealed the orderly coexistence of conventional and unconventional hydrocarbons. By finely dissecting the characteristics of the total petroleum system in the Fengcheng formation in the Mahu sag, and combining with the macro- and micro-analysis and production data of the reservoirs, the hydrocarbon accumulation mechanism of the total petroleum system was analyzed. The results show that conventional oil, tight oil and shale oil accumulate in an orderly pattern in the total petroleum system, which essentially complies with the hydrocarbon accumulation pattern of “source-reservoir coupling” and “dynamic sealing” of oil and gas. In the early diagenesis stage, the present tight reservoirs and shale reservoirs were conventional reservoirs with medium-large pore throats, where hydrocarbons accumulated because of buoyancy. In the middle-later diagenesis stage, the medium-large pore throats gradually evolved to micro- to nano-pore throats, the buoyancy was weakened, and the capillary force was strengthened. The hydrocarbon in the reservoir adjacent to or integrated with the source rocks underwent primary or micro migration continuously until the source-reservoir pressure difference resulted from hydrocarbon generation and expulsion and the capillary force originated from micro - to nano-pore throats reached a dynamic equilibrium, forming a “self-sealing” continuous unconventional oil and gas accumulation. The capillary force in the present conventional reservoirs is far less than the buoyancy, so “external sealing” is needed for hydrocarbon accumulation in traps. Generally, the hydrocarbon accumulation in the Fengcheng formation is represented by the space-time evolution of the pore throat structure in the reservoir and the dynamic coupling of source rock and reservoir on hydrocarbon generation-expulsion-migration-accumulation.

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Shale Oil Enrichment Mechanism and Sweet Spot Selection of Fengcheng Formation in Mahu Sag, Junggar Basin

JIN Zhijun, LIANG Xinping, WANG Xiaojun, ZHU Rukai, ZHANG Yuanyuan, LIU Guoping, GAO Jiahong

2022, 43 (zk(English)): 44-52.

摘要 ( 33 )

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The Fengcheng formation in the Mahu sag is an alkaline lake sediment, and is divided into Feng 1 member, Feng 2 member and Feng 3 member from bottom to top. In the Fengcheng formation, the lithology vertically changes rapidly, the mineral composition is complex, and the organic-rich shale source is integrated with the shale reservoir. The formation bears oil universally, but the sweet spots are scattered. The results of formation testing for single layers are not satisfied, showing an unclear production potential. According to core slices and geochemical analyses, the Fengcheng formation in the Mahu sag is dominated by lamellar silty shale intercalated with dolomite, which are mainly composed of terrigenous clastic minerals and carbonate minerals. With the variation of burial depth, the pore volume changes consistently with the variation of surface area of pores, and the pore volume is mainly contributed by macropores (pore diameter >50 nm). The source rock is dominated by Type II organic matter, and the vitrinite reflectance ranges from 0.85% to 1.40%, indicating a peak oil generation period. There are many shear fractures with middle to high angles in the Feng 2 member, and shear fractures with middle to high angles and structural fractures with low angles in the Feng 3 member, whose formation and development degree are controlled by lithology, mineral composition, rock mechanical properties, etc. Based on the characteristics of lithologic assemblage, reservoir property and oil-bearing property, four relatively concentrated sweet spots have been identified. When performing multi-interval formation testing and production testing in vertical wells, it is necessary to select sweet spots with good oil content and more fractures to conduct geological research and geology-engineering integration technology research, and to perform production improvement tests in horizontal wells, so as to realize comprehensive breakthrough for shale oil exploration and development in the Fengcheng formation in the study area.

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Oil-Bearing Properties and Hydrocarbon Occurrence States of Fengcheng Formation Shale in Well Maye-1, Mahu Sag

QIAN Menhui, WANG Xulong, LI Maowen, LI Zhiming, LENG Junying, SUN Zhongliang

2022, 43 (zk(English)): 53-62.

摘要 ( 31 )

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The oil-bearing properties and hydrocarbon occurrence states of shale are crucial to evaluating and selecting shale oil sweet spots. Through the analysis such as rock pyrolysis, multi-temperature-gradient pyrolysis and X-ray diffraction, the oil-bearing properties and hydrocarbon occurrence states of the shale in the Lower Permian Fengcheng Formation in Well Maye-1, Mahu Sag, were investigated, and then the optimal sweet spot intervals for shale oil in the Fengcheng Formation were defined. The results show that the Fengcheng Formation shale in Mahu sag is mainly composed of three lithofacies associations. The quality of source rocks is the best in the Feng 2 member, partially moderate in the Feng 1 member, and poor in the Feng 3 member. The macerals of organic matter in the rocks are mainly vitrinite and inertinite, indicative of a mature stage, showing a good material basis for shale oil accumulation. Vertically, the Fengcheng Formation shale can be divided into 6 sweet spot intervals with good oil-bearing properties. The lamellar felsic shale intervals at the top and in the middle of the Feng 2 member have the best oil-bearing property, and contain hydrocarbons mainly in free state, where free oil accounts for more than 80% of the total oil content and mainly occurs in intergranular pores and bedding fractures continuously, suggesting a good oil-bearing foundation and a good prospect of movable resource. The research results provide a theoretical basis and technical support for subsequent exploration and development of the shale oil in the Fengcheng formation

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Sedimentary Characteristics and Sandbody Architecture of Shallow Delta Front in Ordos Basin: A Case Study of Chang 9 Member in Shiwanghe Section in Yichuan

REN Yilin, ZHAO Junfeng, CHEN Jiayu, GUAN Xin, SONG Jinggan

2022, 43 (zk(English)): 63-72.

摘要 ( 27 )

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As an important reservoir for storing oil and gas, the sandbodies in delta front are found with enormous petroleum exploration potential. However, there are few studies on architecture of sandbodies in shallow delta front through field outcrops. Guided by sedimentology and reservoir architecture theories, the outcrop observation and sampling was combined with the results of laboratory experiments and statistical analysis to clarify the sedimentary characteristics and sandbody architecture of Chang 9 member in the Shiwanghe section in Yichuan, Ordos basin. The results show that during the deposition, the Chang 9 member in Shiwanghe section lied in a warm and humid environment, especially an oxidation to weak-reduction transitional freshwater environment that was not evidently stratified, and shallow delta front subfacies was mainly developed, including microfacies such as underwater distributary channel, estuarine bar, sheet sand and interdistributary bay. The single sandbodies of shallow delta front in Chang 9 member in the study area can be divided into two vertical stacking styles such as non-connected and connected, and two lateral contact styles such as butted and cut-stacked. The accommodation growth rate and sediment supply rate jointly controlled by terrain slope and lake level rise/fall are important factors affecting the spatial development style of the composite sandbodies. The gentle slope allows the channels to incise weakly and present the characteristics of plane intersection. The rise of lake level and the decrease of sediment supply increase the ratio of accommodation growth rate to sediment supply rate, which may lead to the weakening of sandbody connectivity. The architecture models of sandbodies like river-river cut stacking and river-bar cut stacking are favorable for hydrocarbon accumulation.

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Geological Age and Petrogenesis of Volcanic Rocks in Southern Chepaizi Oilfield

WANG Tao, XU Qian, LI Yongjun, KONG Yumei, ZHENG Menglin, GUO Wenjian

2022, 43 (zk(English)): 73-81.

摘要 ( 35 )

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The Carboniferous in southern Chepaizi oilfield is mainly composed of amygdaloidal basalt, basaltic andesitic agglomerate, andesitic breccia tuff and a small amount of basaltic andesitic breccia tuff. In order to determine the geological age of these rocks, isotopic and biofossil analyses were carried out, and then the analytical results were compared with the Carboniferous rocks in the outcrop area in the basin margin. It is found that there are abundant sporopollen fossils in the bottom of the Carboniferous sandstone in Well C47, and the zircon U-Pb age of the rhyolitic breccia-bearing vitric tuff from Well C68 is 314.6±2.1 Ma, suggesting that both the geological age and isotopic age of the volcanic rock are Late Carboniferous, which are comparable to the Hala'alate formation in the piedmont at the northwestern margin of the Junggar basin. The volcanic rocks are generally calcalkali-tholeiitic series and relatively rich in Al₂O₃, with a weak positive Eu anomaly. Moreover, the volcanic rocks are strongly short of high field-strength elements such as Nb, Ta, and Hf, and relatively rich in large ion lithophile elements such as Ba, Rb, and K. There exists an obvious Nb -Ta trough, and the magma source area may be the depleted mantle of spinel peridotite because of metasomatism, and formed in the subduction-related island arc tectonic environment. For the well blocks in southern Chepaizi oilfield, the Carboniferous in the northwest wall of the large fault can be compared with the Aladeyikesai formation, and the volcanic rock formation in the southeast wall can be correlated with the Hala'alate formation in the piedmont of the northwest margin.

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Sand Body Architecture of Chang 9 Member in Jiyuan Area, Ordos Basin

WU Zemin, KE Xianqi, ZHANG Pan, WEN Fengqin, TONG Qiang, LIU Linyu

2022, 43 (zk(English)): 82-98.

摘要 ( 42 )

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In order to clarify the spatial configuration of sand bodies under the dual-provenance background in Chang 9 member in Jiyuan area, Ordos basin, the sedimentary characteristics of Chang 9 member were determined by using the core, well logging, test and production data. On this basis, the sand body architecture of Chang 9 member was dissected level by level to understand the development of sand bodies under the dual-provenance background and to characterize the architectural elements and their assemblage and distribution. The results reveal that there are eight types of skeleton architectural elements in Chang 9 member, which are different from region to region: braided channel, abandoned channel and cross-bank deposits dominated by underwater distributary channel and interdistributary bay in the west; and estuary sand bar, front sheet sand and underwater natural levee in the east. On the plane, the architectural element of braided channel extends farther with continuous distribution, the architectural element of abandoned channel extends shortly with intermittent distribution, the architectural element of underwater distributary channel extends farther with discontinuous distribution, and the architectural element of estuary sand bar is usually in the side rear of the underwater distributary channel with poor continuity. Vertically, the superimposition and assemblage of the architectural elements of skeleton sand bodies become worse from bottom to top, and the architectural elements of braided river delta system in the west display better development scale and degree than those of meandering river delta system in the east.

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Paleo-Hydrogeomorphic Characteristics of Episode II of Middle Caledonian movement and Their Controls on Karst Cave Development in Western Slope Area of Tahe Oilfield

ZHANG Changjian, LYU Yanping, WEN Huan, WANG Zhen, MA Hailong

2022, 43 (zk(English)): 99-108.

摘要 ( 38 )

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In order to understand the mechanism that the karstification during the Episode II of the Middle Caledonian movement controlled the development of karst caves in the Upper Ordovician coverage area in the western slope area of Tahe oilfield, the paleo-hydrogeomorphic and underground karst cave system of the Episode II of the Middle Caledonian movement were precisely described using different methods. The results show that the karst platform is dominated by karst hills and depressions, the surface water system is dendritic, and the underground river-cave system is developed, forming an “open” underground river-karst system. The karst slope is dominated by hills and valleys, and deep incised valleys are developed because of strong vertical erosion, forming a “downward” buried fault-controlled karst system. The karst basin in the southern part of the platform margin is flat and the surface runoff is underdeveloped, with weak vertical erosion, but mainly horizontal dissolution, forming a “rising” buried fault-controlled karst system. Based on the paleo-hydrogeomorphic characteristics, the development model of karst caves under the control of special hydrogeomorphology of the Episode II of the Middle Caledonian movement was established for the Lianglitage formation coverage area in the western slope area of Tahe oilfield, which provides a geological basis for subsequent rolling development.

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Production Behaviors of Condensate Oil From Gas Reservoirs in Southeastern Area of Sulige Gas Field, Ordos Basin

GUAN Wei, LIU Chiyang, LI Han, WEN Yuanchao, YANG Qingsong, WANG Tao

2022, 43 (zk(English)): 109-115.

摘要 ( 40 )

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The Permian gas reservoirs in the southeastern area of the Sulige gas field in the Ordos basin are wet gas reservoirs developed from coal-measure source rocks. No condensate oil is produced just from the reservoir during development. However, when natural gas enters the wellbore and experiences the decreases in both temperature and pressure to below the critical values, condensate oil would appear. In order to increase the production of condensate oil associated with natural gas, the full-component analysis results of natural gas sampling and production data are used to analyze the geological conditions for reservoir forming and the factors such as temperature, pressure and gas production in the process of development. It's found that the condensate oil production is influenced by the stable balance separation time and the liquid carrying capacity. After analyzing the geological and production conditions, controlling factors on the production of condensate oil are compared, and according to the changes of gas production, the production of condensate oil can be predicted block by block. The result provides basis for updating the gas reservoir development plan in the study area.

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EOR Mechanism of Compound Gas Injection After Multiple Cycles of Oxygen-Reduced Air Huff and Puff in Heavy Oil Reservoirs

GUO Xiaozhe, ZHAO Jian, GAO Wanglai, PU Yanan, LI Chenggeer, GAO Neng

2022, 43 (zk(English)): 116-122.

摘要 ( 37 )

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For heavy oil reservoirs, the enhanced oil recovery (EOR) mechanism of injecting different gases or compound of gases after multiple cycles of oxygen-reduced air huff and puff following water flooding is unclear. In this paper, experiments were conducted with one-dimensional and three-dimensional physical models, and numerical simulations were performed on well pair model and inverted five-spot well pattern model. Based on the comparative analysis on production and components of oil recovered in different cycles of huff and puff and flow process research, the oil displacement and washing mechanisms during huff and puff with three gases, i.e. oxygen-reduced air, CO₂ and natural gas, in heavy oil reservoirs were discussed. The results show that the EOR mechanism of oxygen-reduced air huff and puff is dominated by water plugging, and the water front may readily break through after multiple cycles of operation and then huff and puff fail quickly. The huff and puff with CO₂ slug followed by oxygen-reduced air plays a synergy of water plugging and remaining oil displacement. The huff and puff with oxygen-reduced air injection followed by natural gas dissolves the heavy components of the oil in near-wellbore area, achieving multiple effects of increasing energy, reducing viscosity and dredging pores. EOR mechanisms of huff and puff with three gases and their compound have been clarified through the experiments and numerical simulations on 10 cycles of huff and puff, and have been verified by field wells. The conclusions are of guiding significance for enhancing oil recovery by gas huff and puff in similar reservoirs.

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Characteristics and Connectivity of Fault-Controlled Fractured-Vuggy Reservoirs: A Case Study of Unit T in Tuofutai Area, Tahe Oilfield

LI Jun, TANG Bochao, HAN Dong, LU Haitao, GENG Chunying, HUANG Mina

2022, 43 (zk(English)): 123-130.

摘要 ( 31 )

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Fault-controlled fractured-vuggy reservoirs are extremely heterogeneous and exhibit the diversity and complexity in inter-well connectivity. Clarifying the influence of faults and karsts on reservoirs is conducive to reservoir connectivity analysis and injection-production strategy adjustment. Taking Unit T in the Tuofutai area of Tahe oilfield as an example, the development characteristics of reservoirs were systematically analyzed based on the results of seismic interpretation and the analysis of overlying water system and production performance responses. It was clarified that the reservoir development is mainly controlled by faults and surface water systems; the difference in karstification intensity leads to different characteristics of the reservoirs, which makes development wells show different production behaviors and inter-well connectivity. Based on the analysis of dynamic and static data, inter-well connection models suitable for fault-controlled fractured-vuggy reservoirs were established, which can provide a basis for the adjustment of subsequent treatments.

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Establishment and Application of a Combined Production Decline Prediction Model for Tight Sandstone Gas Well

LI Xiaofeng, XU Wen, LIU Pengcheng, YUE Jun

2022, 43 (zk(English)): 131-135.

摘要 ( 32 )

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The Permian fluvial sandstone gas reservoirs in Sulige gas field are tight and contain most effective sand bodies that are mostly isolated or banded. After gas wells are put into production, reservoir fluid stays consistently in an unsteady flow state, and the boundary-dominated flow state occurs later. In this case, the traditional Arps production decline analysis method is not sufficient for field application. This paper analyzed the causes for the poor adaptability of the Arps production decline analysis method. On this basis, the variation law of the decline exponent of wells in tight gas reservoirs was identified by numerical simulation, and the relationship between the decline exponent and the flow period of fluid in gas wells was clarified. Finally, it was proposed to use the channel linear flow model to predict the production in the unsteady flow period and the Arps model to predict the production in the boundary-dominated flow period. For the gas wells in the unsteady flow period, the critical point time to attain boundary-dominated flow is determined by the theoretical formula; in the boundary-dominated flow period, the time of inflection point deviating from the linear flow is the critical point time. The field application shows that the proposed combined production decline model is accurate and effective in predicting the decline characteristics and indicators of gas wells.

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EOR of CO₂ Flooding in Low-Permeability Sandy Conglomerate Reservoirs

LI Yan, ZHANG Di, FAN Xiaoyi, ZHANG Jintong, YANGRuisha, YE Huan

2022, 43 (zk(English)): 136-142.

摘要 ( 36 )

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The low-permeability sandy conglomerate reservoirs of Benbutu oilfield in Yanqi basin was developed by water flooding in the early stage. While along with water flooding, the reservoirs were seriously damaged, it was even harder to inject water into the reservoirs and the recovery rate stayed in a low level, therefore, it is urgent to switch flooding agent to further improve the recovery rate. In order to determine the feasibility of CO₂ injection in the low-permeability sandy conglomerate reservoirs in Benbutu oilfield to enhance oil recovery, laboratory experimental researches were carried out. The research results show that the crude oil in the formation of the study area has good swellability, is easily miscible with the injected CO₂, and the viscosity of the crude oil is easy to be reduced. The minimum miscible pressure of the reservoirs is about 25 MPa, and near-miscible flooding can be achieved under the current formation pressure. The displacement efficiency of CO₂ flooding is relatively high, which can dramatically improve recovery rate. The CO₂flooding plan was optimized with numerical simulation, in which a five-spot well pattern and a continuous gas injection method were adopted, and the oil recovery is expected to increase by about 13.37% and the oil displacement ratio of CO₂ injection will be about 0.33 t/t. The numerical simulation results provide a theoretical basis for the next field application.

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Comprehensive Evaluation on Steam Chamber Position and Production Prediction of SAGD in Heavy Oil Reservoirs

GUO Yunfei, LIU Huiqing, LIU Renjie, ZHENG Wei, DONG Xiaohu, WANG Wuchao

2022, 43 (zk(English)): 143-150.

摘要 ( 36 )

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Production and steam chamber position are critical for steam assisted gravity drainage (SAGD) in heavy oil reservoirs. The existing prediction model only considers the lateral expansion of steam chamber and cannot predict the production of adjacent wells after steam chamber contact. According to the different characteristics of the steam chamber in the lateral expansion stage and the downward expansion stage, a parameter of thermal penetration depth was introduced, the flow potential function was modified, and a parabolic production prediction model was established. The results show that the production increases gradually in the initial lateral expansion stage of steam chamber, and then decreases due to the reduction of the inclination of the steam chamber interface; in the downward expansion stage of steam chamber, the production further decreases. The model analysis reveals that SAGD is more suitable for thick reservoir development, and the optimal well spacing needs to be determined depending on the oilfield conditions. The parabolic production prediction model takes the characteristics of the steam chamber into account in the downward expansion stage, and the accuracy of the model is verified by comparing with the previous experimental data.

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Mid-Late Development of Reservoirs With Narrow Oil Ring, Gas Cap and Edge Water

YUE Baolin, ZHU Xiaolin, LIU Bin, CHEN Cunliang, WANG Shuanglong

2022, 43 (zk(English)): 151-155.

摘要 ( 31 )

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The X sandstone reservoir in Jinzhou has a large gas cap, narrow oil ring and strong edge water. After entering its middle to late development stage, the reservoir faces the problems such as rapid formation pressure drop, severe gas channeling and difficult potential tapping, so it is urgent to optimize the development methods. Following the principles of geometric similarity, physical property similarity and production performance similarity, we optimized the profile model of the reservoir, and validated the feasibility of a barrier water injection scheme through 2D visualized physical simulation experiments. Then we proposed a barrier water injection scheme with horizontal wells in a parallel well pattern by combining with numerical simulation, and demonstrated the technical requirements for implementing the scheme. Considering the reservoir complexity, development risks, severe gas channeling, uneven vertical displacement and the ultimate goal for significant stimulation effects, a well group was selected for pilot test to improve the understanding of barrier water injection performance. The result provides a reference to the development of similar reservoirs.

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Reservoir Damage Mechanism for Upper Wuerhe Formation in Southern Mahu Area, Junggar Basin

ZHOU Wei, SHEN Xiulun, KOU Gen, WEI Yun, JIANG Guancheng, YANG Lili, ZHANG Yuankai

2022, 43 (zk(English)): 156-162.

摘要 ( 31 )

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The core of the conglomerate reservoir from upper Wuerhe formation of Permian is very easy to break after immersed in fluids, so that it is difficult to evaluate how gel-breaking fracturing fluid damages the reservoir, and it is impossible to determine the factors controlling reservoir damage in the southern Mahu area, Junggar basin. This study used X-ray Micro-CT technology to scan core samples and reconstructed the three-dimensional pore structure, and then characterized the pore changes on different sections by the ball-stick model and the threshold segmentation method. The results show that, after the reservoir was damaged by gel-breaking fracturing fluid, the average pore radius, average throat radius, average throat length, average pore-to-throat ratio, porosity and permeability were reduced by 42.1%, 32.7%, 19.1%, 45.3%, 7.7% and 33.8%, respectively. After fractured by gel-breaking fracturing fluid, the reservoir was damaged, resulting in reduced porosity and permeability, especially a significant change in permeability. Swelling montmorillonite in the clay minerals and particle migration are the factors that can cause damage to the reservoir, and the interaction between gel-breaking fracturing fluid and the reservoir is the primary factor causing reservoir damage.

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VSP Reverse Time Migration Technology and Its Imaging Effect

CHEN Keyang, YANG Wei, ZHAO Haibo, WANG Cheng, ZHU Lixu, LIU Jianying, LI Xingyuan

2022, 43 (zk(English)): 163-169.

摘要 ( 35 )

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In order to improve the precision of VSP seismic imaging, a VSP reverse time migration (RTM) operator with 16-order finite difference accuracy was constructed, and then the algorithm accuracy of VSP key links and the interchangeability of source and receiver points were analyzed by using impulse responses to verify the accuracy of the 3D VSP RTM operator. Based on the standard theoretical model of lava dome, the imaging effects of normalized VSP RTM and conventional cross-correlation RTM were compared. It is found that VSP RTM can describe the geological boundary and formation interface more clearly and more accurately, and can eliminate the uneven influence of folds to make energy distribution more uniform, with no borehole trace. The high-precision 3D VSP RTM technology was applied to the walkaway VSP data of Well L in the Songliao basin, and accurate and fine imaging of near-wellbore formations and small faults was achieved, which further verified the accuracy of the technology. The proposed VSP RTM technology can help improve the imaging accuracy of complex reservoirs around the wellbore.

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Seismic Prediction Method of Geological and Engineering Shale Oil Sweet Spots and Its Application in Fengcheng Formation of Mahu Sag

YU Jianglong, CHEN Gang, WU Junjun, LI Wei, YANG Sen, TANG Tingming

2022, 43 (zk(English)): 170-179.

摘要 ( 27 )

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In order to further accelerate the exploration and development of shale oil in the Lower Permian Fengcheng formation in the Mahu sag, Junggar basin, sweet spots of shale oil should be identified. Considering that lithology is the factor controlling geological sweet spots, and brittleness index and horizontal principal stress difference are the factors controlling engineering sweet spots, seismic methods of predicting geological and engineering sweet spots were established on the basis of prestack simultaneous inversion. In terms of geological sweet spots, by using core, experiment, drilling and logging data, the dominant lithology of shale oil sweet spots was identified to be dolomitic siltstone, the elastic parameters sensitive to the dominant lithology were selected, and the distribution of dolomitic siltstone was predicted by using prestack simultaneous inversion and lithofacies probability analysis. In terms of engineering sweet spots, using the Young's modulus and Poisson's ratio obtained from prestack simultaneous inversion, the brittleness index and in-situ stress in the study area were obtained through the Rickman brittleness index method and a combined spring model. The predicted results are consistent with the actual drilling results, demonstrating the accuracy of the prediction of geological and engineering sweet spots. The proposed methods can provide references for shale oil exploration and development in other areas.

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