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    01 April 2022, Volume 43 Issue 2 Previous Issue    Next Issue
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    OIL AND GAS EXPLORATION
    Petroleum Exploration Ideas and Discoveries in Upper Wuerhe Formation, Dongdaohaizi Sag, Junggar Basin
    LI Yanping, ZOU Hongliang, LI Lei, FU Jiyou, XIA Yu, XIE Junyang
    2022, 43 (2):  127-134.  doi: 10.7657/XJPG20220201
    Abstract ( 515 )   HTML ( 31 )   PDF (1730KB) ( 388 )   Save

    Dongdaohaizi sag is one of the important hydrocarbon-generating sags in the Junggar basin. Petroleum discoveries have been made in the Jurassic and Cretaceous in the uplift around the sag and in the Permian upper Wuerhe formation within the sag. Focusing on key wells with oil and gas breakthroughs in the upper Wuerhe formation within the sag, and combining with the changes in exploration ideas and theoretical understanding, the exploration of the upper Wuerhe formation in the study area is divided into three stages, namely, source-edge fault block exploration stage, in-sag fault block exploration stage, and above-source lithologic exploration stage. The changes in exploration ideas brought about the discovery of high-yield oil and gas reservoirs in the upper Wuerhe formation on the eastern slope of the sag. Also, insights in three aspects have been gained. First, the source rocks in the Pingdiquan formation have entered the stage of light hydrocarbon generation, contributing to the near-source hydrocarbon accumulation in the upper Wuerhe formation. Second, a large-scale retrograde fan delta sedimentary system is developed in the upper Wuerhe formation, where the fan delta front facies belt superimposed by the thick layers of lowstand system tract(LST) and the thin layers of transgressive system tract(TST) serves as favorable reservoirs, with a distribution area of 3 350 km2. Third, the hydrocarbon accumulation in the upper Wuerhe formation is characterized by sand enrichment in troughs, reserves controlled by facies belts, and production controlled by pores/fractures. Petroleum discoveries are concentrated in the eastern part, while no successful drilling result has been made in the western part of the sag. With these exploration ideas and geological understanding to guide the exploration deployment, there will be new discoveries of oil and gas in the Dongdaohaizi sag.

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    Paleo-Hydrogeomorphic Characteristics of EpisodeⅡof 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 (2):  135-144.  doi: 10.7657/XJPG20220202
    Abstract ( 340 )   HTML ( 9 )   PDF (7377KB) ( 241 )   Save

    In order to understand the mechanism that the karstification during the Episode Ⅱof 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 Ⅱof 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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    Development Characteristics and Model of Cili Longwang Karst Cave in Hunan Province
    XU Xinyu, CHEN Qinghua, JI Dongsheng, CUI Youwei
    2022, 43 (2):  145-152.  doi: 10.7657/XJPG20220203
    Abstract ( 417 )   HTML ( 10 )   PDF (1966KB) ( 256 )   Save

    To study the development characteristics and model of the Longwang Cave in the Cili area of Hunan province, a 3D model is constructed by using manual survey and 3D laser scanning technology to characterize the structure of the karst cave. The Longwang Cave can be divided into three sections. The western section is NEE-SWW trending and filled with chemical cements. The middle section is NNE-SSW trending and filled with collapsed cements. The eastern section is nearly EW trending, and filled with chemical cements and flowing water deposits. As for the filling degree, the middle section shows the highest, the western section is higher, and the eastern section is the lowest. Controlled by a NEE-SWW trending fracture zone, the Longwang Cave is a typical fracture-controlled karst cave which has undergone four development stages. First, a NEE-SWW fracture zone was formed along the Sanguansi syncline. Then the rock was dissolved along the fracture zone by karst water from west to east, and an initial karst cave formed. Second, the initial karst cave was dislocated by NNW-SSE trending strike-slip thrust faults and then differential dissolution occured, that is, the western section was dissolved to a higher degree than the middle and eastern sections. Third, due to different numbers and scales of fractures, differential dissolution made the carst caves in the western section further expand, and the karst caves in the eastern section gradually connected together. The dissolution of the western section was higher than that of the eastern section. Finally, the middle section inherited the previous dissolution characteristics, so it is weaker than the eastern and western sections in dissolution. After the four stages above, the Longwang Cave shows its present structure.

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    Fractal Characteristics and Main Controlling Factors of Wufeng-Longmaxi Formation Shale in Luobu Syncline, Southern Sichuan Basin
    DUAN Wengang, LIN Wen, TIAN Jijun, MA Jinghui, DU Meng, LUO Jinchang
    2022, 43 (2):  153-159.  doi: 10.7657/XJPG20220204
    Abstract ( 319 )   HTML ( 14 )   PDF (639KB) ( 174 )   Save

    In the Luobu syncline, southern Sichuan basin, the shale in the Upper Ordovician Wufeng formation (O3w)-Lower Silurian Longmaxi formation (S1l) is characterized by large thickness, high organic carbon content, wide distribution range and moderate thermal evolution of organic matter, making it an important target for subsequent shale gas exploration. In order to better characterize the heterogeneity of shale pore structure and clarify the influence of heterogeneity on shale gas enrichment in the study area, the fractal characteristics of the shale in layers of O3w-S1l11 in the study area were analyzed using the rock-mineral analysis, geochemical and well logging data, and CO2 and N2 adsorption analysis. The results show that the layers in the study area are very different in TOC content, mineral compositions and porosity, and the reservoir is highly heterogeneous. The fractal dimension of shale pores ranges from 2.711 0 to 2.794 8, with an average of 2.747 0; the value is relatively high for O3w and Layer #1 in S1l11, and the lowest for Layer #4 in S1l11. The organic carbon and bio-quartz can promote the development of shale micropores. The smaller the average pore size of shale, the more the pores, and the more complex the pore structure, and the larger the fractal dimension.

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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 (2):  160-168.  doi: 10.7657/XJPG20220205
    Abstract ( 334 )   HTML ( 14 )   PDF (1226KB) ( 223 )   Save

    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’alat formation in the piedmont at the northwestern margin of the Junggar basin. The volcanic rocks are generally calc-alkali-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’alat formation in the piedmont of the northwest margin.

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    Brittle Characteristics of Lucaogou Formation Reservoir in Jimsar Sag, Junggar Basin
    SHI Shanzhi, ZOU Yushi, WANG Junchao, ZHANG Shicheng, LI Jianmin, ZHANG Xiaohuan
    2022, 43 (2):  169-176.  doi: 10.7657/XJPG20220206
    Abstract ( 298 )   HTML ( 17 )   PDF (2337KB) ( 237 )   Save

    The lithology of the Lucaogou formation reservoirs in Jimsar sag is complex, and the rock brittleness has a significant impact on productivity. Based on the analysis of mineralogy, mechanical parameters and energy evolution characteristics, a new method for brittleness evaluation suitable for the Lucaogou formation reservoirs was proposed, which follows an analytic hierarchy process to compare the brittleness characteristics of different lithologies. The results show that the Lucaogou formation reservoir in the Jimsar sag has a low clay content and small differences in the contents of brittle minerals, so it is difficult to accurately evaluate the rock brittleness with the brittleness index; the reservoir is very heterogeneous, and the brittleness of different rocks varies greatly: the average comprehensive brittleness index of the argillaceous siltstone, sandy dolomite and mud shale is higher than 0.60, the average comprehensive brittleness index of the dolomitic siltstone and micrite dolomite is medium, ranging from 0.50 to 0.60, and the average comprehensive brittleness index of the dolomitic mudstone is relatively lower, only 0.49; for the rock samples taken from the same core, the brittleness in parallel bedding direction is larger than that in vertical bedding direction; and the development of beddings may easily lead to complex fracture patterns, which affects the brittleness evaluation results.

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    RESERVOIR ENGINEERING
    Numerical Simulation on Tilted OWC Controlled by Interlayers in Hade 4CⅢ Reservoir
    LIAN Zhanggui, BIAN Wanjiang, HAN Tao, LAO Binbin, WANG Kaiyu, ZENG Jiangtao
    2022, 43 (2):  177-182.  doi: 10.7657/XJPG20220207
    Abstract ( 284 )   HTML ( 6 )   PDF (3421KB) ( 151 )   Save

    The Hade 4CⅢreservoir is a marine sandstone reservoir with edge and bottom water, where there is a largely-tilted oil-water contact (OWC) with a height difference of nearly 100 m. The hydrocarbon accumulation mechanism and the origin of the tilted OWC are still controversial. According to the characteristics of beds, fluid and interlayers in the reservoir, a corresponding geological model was established. By adjusting the number, distribution, capillary pressure, and skylights of the interlayers, the process of secondary migration and accumulation of oil and gas in the reservoir was numerically simulated. The number and distribution of the interlayers have a significant impact on the formation of the tilted OWC and on the distribution of oil and water. The higher the capillary pressure of the interlayer, the greater the inclination of the tilted OWC. The longer the extension of the interlayer, the greater the inclination of the tilted OWC. If the number and location of interlayer skylights are different, the oil-water distribution and oil-water contact are also significantly different at the end of the hydrocarbon accumulation period. The great inclination of the tilted OWC in the Hade 4CⅢreservoir is mainly due to the shielding of interlayers and the differentiation of oil-water gravity during the hydrocarbon accumulation, followed by tectonic movement and unsteady hydrocarbon accumulation.

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    Development of Low-Permeability Heavy Oil Reservoirs by CO2 + Surfactant Combination Huff and Puff : A Case Study of Upper Wuerhe Formation Reservoir in Southern Block 5, Karamay Oilfield
    HUANG Weiqiang
    2022, 43 (2):  183-187.  doi: 10.7657/XJPG20220208
    Abstract ( 355 )   HTML ( 13 )   PDF (553KB) ( 230 )   Save

    The reservoir in the upper Wuerhe formation, southern Block 5, Karamay oilfield, is a heavy oil reservoir with low porosity and low permeability, indicating poor reservoir physical properties. When it was developed by water injection, the production decreased rapidly, and the formation energy kept low; as a result, all production wells were shut in or suspended. In recent years, some wells have been refractured to resume production and good effects have been gained in the initial stage, but the production declines rapidly. In order to solve the problems of low production and low efficiency of production wells, the CO2 + surfactant combination huff and puff technology was developed and tested for production enhancement. On the basis of experiment on stimulation mechanism, through multi-component reservoir numerical simulation, the method and parameters for injecting CO2 + surfactant were optimized. The relationship between the changes of the production increment and the parameters such as injection volume, injection rate, soaking period and production intensity in different cycles of huff and puff were established, and the optimal parameters for injecting CO2 + surfactant were determined for huff and puff. Field application reveals a natural flow of a sing well for 240 days and an incremental oil production of 630 t. It is concluded that the CO2 + surfactant combination huff and puff technology can effectively supplement formation energy and improve fluid mobility, which can be used as a reference for the development of similar reservoirs.

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    Connectivity Characterization of Fractured-Vuggy Carbonate Reservoirs and Application
    WU Meilian, CHAI Xiong, ZHOU Bihui, LI Hong, YAN Nan, PENG Peng
    2022, 43 (2):  188-193.  doi: 10.7657/XJPG20220209
    Abstract ( 353 )   HTML ( 12 )   PDF (5285KB) ( 327 )   Save

    Fractured-vuggy carbonate reservoirs are difficult to develop efficiently due to their strong heterogeneity, challenging connected unit identification, and unknown inter-well connectivity. In this paper, facies-controlled inversion and maximum likelihood attribute were used to characterize the fractured-vuggy aggregate and spatial distribution of large-scale fractures, so as to identify connected units and clarify the inter-well connection mode and the remaining oil potential. Based on dynamic data of wells, the connectivity was analyzed to verify the rationality of the connectivity characterization result obtained from static data. The technique was applied in the gas injection development of the Lungu 7-5 well group in the Lungu 7 wellblock, providing a basis for gas injection development strategy making to further improve the reservoir recovery performance.

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    Fracability Evaluation of Conglomerate Reservoirs in Baikouquan Formation in Ma-131 Well Block
    CAI Wenjun, FENG Yongcun, YAN Wei, JIANG Qingping, MENG Xianglong, LIU Kai
    2022, 43 (2):  194-199.  doi: 10.7657/XJPG20220210
    Abstract ( 308 )   HTML ( 7 )   PDF (5972KB) ( 294 )   Save

    For developing the tight conglomerate reservoirs in the Baikouquan formation in Mahu oilfield with small well-spacing, it is urgent to establish an appropriate fracability evaluation model. Based on the optimal parameters such as elastic modulus, Poisson’s ratio and minimum in-situ stress, and combined with the core, logging and seismic data, the 3D geomechanical modeling was carried out for Ma-131 well block. The spatial distribution of the fracability index (0.38-0.91) of the reservoir in the study area was determined. Coupling with the microseismic fracture monitoring and production data from 12 horizontal wells, it is found that the calculated fractability index is consistent with the fracture propagation direction and scale, and the actual production performance of the wells. The research results may provide a basis for developing the conglomerate reservoirs in the study area.

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    Enhancing Oil Recovery of Tight Conglomerate Reservoirs by Asynchronous CO2 Huff and Puff in Mahu Sag
    DENG Zhenlong, WANG Xin, TAN Long, ZHANG Jigang, CHEN Chao, SONG Ping
    2022, 43 (2):  200-205.  doi: 10.7657/XJPG20220211
    Abstract ( 371 )   HTML ( 11 )   PDF (2510KB) ( 198 )   Save

    CO2 can increase formation energy and reduce oil viscosity. Asynchronous CO2 huff and puff is becoming one of the effective methods for improving the recovery of tight oil reservoirs. The interaction among injection, production and soaking processes can significantly increase inter-well reserves producing degree, and this technology is expected to become an option for enhancing the oil recovery of the Mahu tight conglomerate reservoirs in the Junggar basin. According to the formation pressure, saturation pressure and minimum miscible pressure, an asynchronous CO2 huff and puff experiment with two cores in parallel was designed for clarifying the influence of reservoir physical properties, injection-production pressure difference and huff-puff timing on development effect. The results show that the crude oil recovery after asynchronous CO2 huff and puff is about 3-5 times higher than that of the depletion development; the better the physical properties of the reservoir, the smaller the flow resistance, and the more favorable for asynchronous CO2 huff and puff to improve oil recovery; the greater the injection-production pressure difference, the more significant the inter-well pressure change, and the more crude oil is produced; when the gas injection pressure is greater than the miscible pressure, it is beneficial for supercritical CO2 to play the role and to improve the recovery; when the formation pressure is higher than the miscible pressure, it is necessary to increase the pressure of the gas injection well and reduce the pressure of the adjacent production well through asynchronous CO2 huff and puff to increase the pressure difference of the injection-production system, expand the swept volume, and improve the inter-well reserves producing degree.

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    APPLICATION OF TECHNOLOGY
    ROP Improvement and Production Enhancement for Ultra-Deep Wells Based on Geology-Engineering Integration: A Case in Kuqa Depression, Tarim Basin
    CAI Zhenzhong, XU Ke, ZHANG Hui, WANG Zhimin, YIN Guoqing, LIU Xinyu
    2022, 43 (2):  206-213.  doi: 10.7657/XJPG20220212
    Abstract ( 388 )   HTML ( 8 )   PDF (1457KB) ( 405 )   Save

    The Kuqa depression in the Tarim basin is rich in oil and gas resources and has great potential for exploration. However, the geological setting in this area is complex and the target layers are generally buried deeper than 6 000 m, or even more than 8 000 m, making oil and gas exploration and development difficult. Considering the geological engineering characteristics and existing problems of ultra-deep wells in the Kuqa depression, a solution based on the concept of geology-engineering integration is proposed, and the successful practice of the first pre-salt highly-deviated well in Tarim oilfield is introduced. Research and practices show that geomechanical research is beneficial to reducing drilling complexities and increasing rate of penetration, can help select favorable reservoirs and optimize stimulation schemes, and finally support the ROP improvement and production enhancement. The geology-engineering integration is necessary for efficient development of complex oil and gas reservoirs. In this aspect, multiple disciplines will be collaborated in operations through the life cycle of each well to generate the maximum benefits and achieve overall progress from well location deployment, drilling engineering, well completion and stimulation to oil/gas production engineering, thereby facilitating the construction of large oil and gas fields.

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    Early Warning Model for Critical Sand Production in Horizontal Wells Based on Pressure Monitoring: A Case of H Gas Storage in Xinjiang
    WANG Quan, CHEN Chao, Hasyati SAYITI, ZHANG Yi, BAO Yingjun, WU Min
    2022, 43 (2):  214-220.  doi: 10.7657/XJPG20220213
    Abstract ( 307 )   HTML ( 5 )   PDF (594KB) ( 223 )   Save

    For H gas storage in Xinjiang, the largest gas-reservoir-type sandstone underground gas storage in China, the adjustment plan adopts full arrangement with horizontal wells. The single well is characterized by intensive injection and production as well as large-displacement huff and puff. If the production pressure difference is too large, the rock skeleton may be damaged, and the sand carried out may erode the production string or even block the wellbore, causing production suspension of gas wells and affecting the overall peak-shaving capability of the gas storage. This paper discusses the early warning on critical sand production in horizontal wells based on pressure monitoring. Based on the material balance equation, state equation and flow equation applicable to the H gas storage, a dynamic production pressure difference monitoring model of horizontal wells was established. Meanwhile, the field test on critical sand production pressure difference of horizontal wells was carried out, and the criterion “C” formula model determining rock solidity was defined to predict the critical sand production pressure difference. Finally, an early warning model for critical sand production in horizontal wells based on pressure monitoring was established. The coincidence between the model-derived pressure and the measured pressure exceeds 93%. The model can realize the real-time monitoring of the dynamic production pressure difference in horizontal wells and also lay a foundation for the evaluation of maximum peak-shaving capacity and subsequent peak-shaving and production allocation of the gas storage.

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    Methods for Separate-Layer Fracturing Optimization of Thin Interbeds in Fengcheng Formation, Mahu Sag
    PAN Liyan, RUAN Dong, HUI Feng, LIU Kaixin, ZHANG Min, PENG Yan
    2022, 43 (2):  221-226.  doi: 10.7657/XJPG20220214
    Abstract ( 304 )   HTML ( 11 )   PDF (609KB) ( 191 )   Save

    In Mahu sag, where there is abundant oil in place, the reservoirs in Permian Fengcheng formation are thick and have revealed good oil/gas show. However, the thin interbeds are complex in lithological assemblages and greatly variable in in-situ stress, so fine separate-layer fracturing must be done to recover the reserves. Based on the numerical simulation method, the factors influencing fracture propagation during multi-layer fracturing were analyzed, providing a basis for rational selection of layers for multi-layer or separate-layer fracturing. The results show that the reservoir stress difference influences fracture propagation the most, followed by fracturing fluid displacement and viscosity, and the reservoir thickness ratio influences the least. Based on the BP neural network algorithm, machine learning was carried out on the numerical simulation results, and a multi-factor fine separate-layer fracturing decision-making model that considers both geological and engineering factors was established. Using this decision-making model, multi-layer or separate-layer fracturing prediction and fracturing parameter optimization were made for 6 wells in the Fengcheng formation on the Manan slope. Post-frac flowing production tests demonstrated that the daily oil production of some wells reached 10.34-32.37 t, and the average single-well production was increased by nearly 50% compared with the traditional fracturing process. The study results can provide effective guidance for the optimization of the fracturing process of thin interbeds in the Mahu sag.

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    Numerical Simulation on Fracture Propagation in Conglomerate in Mahu Sag
    LIU Pengyu, JIANG Qingping, SHEN Yinghao, ZHAO Tingfeng, GE Hongkui, ZHOU Dong
    2022, 43 (2):  227-234.  doi: 10.7657/XJPG20220215
    Abstract ( 296 )   HTML ( 7 )   PDF (4324KB) ( 245 )   Save

    For the conglomerate in the Mahu sag, the law and controlling factors of fracture propagation are unclear. A numerical simulation model for conglomerate was constructed to analyze the law of fracture propagation in conglomerate with different material properties under different loading modes. The results show that the higher the gravel content, the lower the cementation strength and the greater the relative strength of gravel to matrix, the more complex the fractures created in the conglomerate. Influenced by loading mode, the most complex fractures are created in the conglomerate under the combined action of tensile and shear loads. The attracting and shielding effects of gravel on conglomerate fractures promote the formation of complex fracture network in the conglomerate.

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    REVIEW
    Development Countermeasures for Oil and Gas Industry Under the Background of “Carbon Peaking and Carbon Neutrality”
    CHANG Yuwen, FENG Naichao
    2022, 43 (2):  235-240.  doi: 10.7657/XJPG20220216
    Abstract ( 432 )   HTML ( 20 )   PDF (701KB) ( 393 )   Save

    As the measures are taken against global climate issues, more than 120 countries/regions have set the goal of “carbon neutrality”. The global energy transition is progressing rapidly, and the oil companies mainly engaged in traditional oil and gas businesses are facing pressures from both multiple environmental protection regulations and carbon emission reduction. Therefore, the low-carbon transition strategy has received extensive attention. On the basis of analyzing the global energy transition under the background of “carbon peaking and carbon neutrality”, the current situation and trend of the global oil and gas development were investigated from several aspects such as supply-demand pattern, exploration and development trends, business structure, international oil prices, and geopolitics. Finally, relevant countermeasures for the development of China’s oil and gas industry were put forward: (1) take both oil and gas as the main energy sources, put more efforts in exploration and development, and attach equal importance to “unconventional and conventional resources, offshore and onshore resources, deep and shallow resources”, in order to increase reserves, stabilize oil production and enhance gas production for purpose of national energy security; (2) combine carbon emission reduction with carbon utilization, and accelerate energy conservation and emission reduction, in order to realize green and low-carbon development; (3) keep the integrated development of oil, gas, and new energy, and promote the development of new energy step by step with a clear strategy by relying on the advantages (e.g. funds, technologies and talents) of oil/gas exploration and development; (4) follow the technological innovation strategy centered on theory/technology research, key technology R&D and supporting technology applications, in order to drive the oil and gas industry to achieve green transition and high-quality development

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    OIL AND GAS GEOLOGY ABROAD
    Genesis and Fluid Identification Method of Cretaceous Low-Resistivity Oil Layers in WTK Oilfield
    LI Fengling, XU Shipeng, LIU Tao, LU Zhiming, LI Xiang, Aini MAMAT
    2022, 43 (2):  241-251.  doi: 10.7657/XJPG20220217
    Abstract ( 345 )   HTML ( 6 )   PDF (1518KB) ( 181 )   Save

    The Cretaceous low-resistivity oil layers in WTK oilfield, South Turgay basin are widely developed and difficult to identify. In this paper, the genetic mechanism of these low-resistivity oil layers was analyzed using core analysis and logging data, and the method for identifying oil/water layers was stuided by combining formation testing data. According to the geological features of the study area, comprehensive research was carried out on internal factors and external factors. The internal factors include the reservoir lithology and clay mineral content during the deposition process, the pore structure characteristics and fluid distribution during diagenesis, and the oil-water differentiation during hydrocarbon accumulation, and the external factors include the accuracy of measurement methods during drilling, etc. The main controlling factors for the low resistivity of the oil layers in the study area are the additional conductivity of clay mineral cations and the conductivity caused by high irreducible water saturation and salinity, and the secondary controlling factors are low structural amplitude and thin oil layers. By analyzing the reservoir conductivity model and based on the model for calculating formation water and irreducible water saturations, the relationship between electrical characteristics and fluid saturation was established, the quantitative evaluation model of low-conductivity oil layers was constructed by stratification, and the lower limit standard for dividing each fluid type was made to realize accurate fluid identification. The practical application shows that the matching degree between the results of logging interpretation and actual production reaches 88.2%, suggesting a good application effect.

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