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01 April 2024, Volume 45 Issue 2 Previous Issue   

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OIL AND GAS EXPLORATION

Exploration Practice and Total Petroleum System in Residual Marine Sag，Eastern Junggar Basin ZHI Dongming, CHEN Xuan, YANG Runze, LIU Juntian, YU Haiyue, MA Qiang 2024, 45 (2):  127-138.  doi: 10.7657/XJPG20240201 Abstract ( 91 )   HTML ( 22 )   PDF (6277KB) ( 76 )   Save The Shiqiantan sag in the eastern Junggar basin is a residual marine sag. In recent years, high-yield natural gas have been obtained from many wells in the Shiqiantan formation, and oil and gas shows have been observed in different strata across the sag, indicating its excellent exploration potential and characteristics as a total petroleum system. Based on seismic, drilling, logging, and organic geochemical data, the formation and evolution of the Shiqiantan sag, the conditions for the formation of the total petroleum system, and the models of hydrocarbon accumulation are studied. The results show that during the Late Carboniferous the north Tianshan oceanic crust subduction and seawater intrusion in the region led to the development of terrigenous, marine, medium- to high-quality source rocks which are now in the mature- to high-mature stage. The reservoir contains volcanic rocks in the Carboniferous strata, marine clastic rocks in the Shiqiantan formation, and continental clastic rocks in the Permian Jingou formation, in all of which hydrocarbons were accumulated. Controlled by the hydrocarbon generation and evolution in the source rocks of the Shiqiantan formation and the characteristics of multiple types of reservoirs, a distribution pattern of shale gas reservoir in the sag-tight oil and gas reservoir in the slope-conventional oil and gas reservoir in the high position is formed, showing a total petroleum system featured with orderly symbiosis of unconventional and conventional oil and gas reservoirs. According to the theory of total petroleum system, the exploration in the Shiqiantan sag should focus on tight oil and gas reservoirs in the near-source slope area, structural-lithological oil and gas reservoirs and volcanic weathering-crust oil and gas reservoirs in the above-source fault-terrace area and structural high, and marine shale gas reservoirs within the source. The Carboniferous near-source favorable lithofacies belts, piedmont thrust fault-concealed structures, intra-basin palaeouplifts, and slope areas are favorable exploration zones in northern Xinjiang. Specifically, exploration efforts should be made towards shale oil and gas reservoirs within the sag, tight sandstone oil and gas reservoirs around the sag, conventional oil and gas reservoirs in the structural highs, and volcanic weathering-crust oil and gas reservoirs in uplifted areas. Figures and Tables | References | Related Articles | Metrics

Breakthrough and Implication of Oil and Gas Exploration in Permian Upper Wuerhe Formation in Fukang Sag, Junggar Basin LIU Chaowei, LI Hui, WANG Zesheng, WANG Qiuyu, XIE Zhiyi, HUANG Zhiqiang, ZHANG Rong 2024, 45 (2):  139-150.  doi: 10.7657/XJPG20240202 Abstract ( 51 )   HTML ( 5 )   PDF (9344KB) ( 41 )   Save The confirmation of 100-million-ton reserves in the Permian upper Wuerhe formation in the Kangtan-1 well area of Fukang sag, Junggar basin, demonstrates the excellent hydrocarbon accumulation conditions and huge exploration potential of the deep layers in the sag. Summarizing the exploration experience and theoretical understanding of the upper Wuerhe formation in the Fukang sag will be significant to guide the exploration of clastic reservoirs in other hydrocarbon-rich sags. Using the data of drilling, reservoir rock thin section, porosity-permeability analysis and formation testing, a systematic analysis was conducted on the exploration breakthrough of the upper Wuerhe formation in the Fukang sag. It is indicated that the oil and gas in the uplift and slope zones around the Fukang sag are mainly products of source rocks in the early maturity stage, and the hydrocarbons generated in the high maturity stage of source rocks are mainly found in the sag area. Controlled by the paleogeomorphology during deposition, retrogradational sand bodies in lowstand systems tract （LST） were developed in the upper Wuerhe formation in the Fukang sag, forming superimposed continuous large-scale reservoirs in the paleo-trough area. Overpressure is commonly found in the sag, which is conducive to the preservation of primary pores in deeply buried sandstones and also to the formation of microfractures, enhancing the permeability of reservoirs and making the deep reservoirs more effective. The upper Wuerhe formation in the Fukang sag has large exploration potential for achieving reserves increment due to the late-stage charging of hydrocarbons generated from highly mature sources rocks in the Lucaogou formation, the large-scale retrograditional sedimentation, and the pore preservation and permeability increasement caused by overpressure. Figures and Tables | References | Related Articles | Metrics

New Understanding of Hydrocarbon Accumulation Model of Upper Wuerhe Formation on Western Slope of Shawan Sag, Junggar Basin XIONG Ting, LIU Yu, CHEN Wenli, ZHONG Weijun, JIA Chunming, JIANG Tao, SHANG Chun 2024, 45 (2):  151-162.  doi: 10.7657/XJPG20240203 Abstract ( 40 )   HTML ( 6 )   PDF (11143KB) ( 30 )   Save In 2018, based on a detailed characterization of paleogeomorphology, the sedimentary facies of the upper Wuerhe formation on the western slope of Shawan sag, Junggar basin, were identified, and a breakthrough was achieved by deploying Well ST 1 according to the hydrocarbon accumulation model of “trough-controlled sandbody, facies-controlled reservoir”. However, due to insufficient research on sedimentary facies and reservoirs, the reservoirs encountered by Well ST 1 didn’t meet the expectation in scale, with the hydrocarbon accumulation model to be clarified. In this paper, using the seismic, logging, core, and geochemical data, the sedimentary facies and reservoirs of the upper Wuerhe formation on the western slope of the Shawan sag were systematically investigated. The results show that two sedimentary systems, i.e., Xiaoguai fan and Shamenzi fan, are developed in the Shawan sag. Shamenzi fan which is larger in scale is characterized by retrogradational fan delta sedimentary facies. The upper Wuerhe formation (P3w) can be divided into three members such as P3w1, P3w2 and P3w3 from bottom to top. The thin sand layers in P3w2, and the glutenites in the lower part of the upper P3w1 and the upper part of the lower P3w1 are the main reservoirs. Dual-porosity reservoirs are developed in the upper Wuerhe formation, and the faults connected to source rocks provide dominant pathways for oil and gas migration. A hydrocarbon accumulation model of “fault-connected source, fan-controlled reservoir, and fracture-controlled production” was established. Accordingly, fault-lithologic reservoirs and fault-stratigraphic reservoirs have been discovered on the western slope of the Shawan sag, expanding the exploration area in the upper Wuerhe formation. Figures and Tables | References | Related Articles | Metrics

Genesis of Differential Bonding Between Zeolite Cements and Clastic Particles in Sandy Conglomerates in Shawan Sag，Junggar Basin KUANG Hao, ZHOU Yuandong, LIU Hao, PAN Lang, ZHOU Runchi, WANG Junmin, TAN Xianfeng 2024, 45 (2):  163-171.  doi: 10.7657/XJPG20240204 Abstract ( 36 )   HTML ( 3 )   PDF (20351KB) ( 18 )   Save Through thin section and scanning electron microscopy （SEM） observations and energy spectrum analysis, the types and characteristics of zeolite cements in the Permian sandy conglomerate reservoirs in the Shawan sag of Junggar basin were identified, and the mechanism of differential bonding between zeolite cements and clastic particles was clarified. The results show that in the Upper Permian upper Wuerhe reservoirs, the plastic deformation of rock fragments and alkaline formation water result in strong bonding between laumontites and clastic particles and in the Lower Permian Fengcheng reservoirs, laumontites are lowly bonded with clastic particles under the conditions of abnormally high pressure, and acidic fluids, while heulandites are highly bonded with clastic particles due to their crystal characteristics. The differential bonding between zeolite cements and clastic particles in the upper Wuerhe and Fengcheng reservoirs are mainly related to rock composition, abnormal pressure, mineral type, crystal structure, and the degree of late diagenetic fluid alteration. Figures and Tables | References | Related Articles | Metrics

Development Characteristics and Main Controlling Factors of Reservoir Space in Northern Yujiang Strike-Slip Fault Zone BAO Dian, HU Wenge, CAO Fei, PENG Xiaoping, LIAO Shixi, PAN Lin, WANG Xiao 2024, 45 (2):  172-180.  doi: 10.7657/XJPG20240205 Abstract ( 39 )   HTML ( 7 )   PDF (7961KB) ( 19 )   Save In order to understand the development characteristics and formation mechanism of reservoir space in the crushed zone of a strike-slip fault, based on the field outcrops, remote sensing images, and core testing data, the reservoir space in the northern Yujiang strike-slip fault zone was identified and quantified, and its main controlling factors were discussed. The results show that the crushed zone of the northern Yujiang strike-slip fault zone can be divided into a northern tenso-shear segment and a southern compresso-shear segment in a plane view. The two segments are different in the reservoir space development characteristics. The tenso-shear segment has larger fracture aperture, while the compresso-shear segment has larger fracture length, fracture density, fractured area, and cave area. Overall, the compresso-shear segment has larger reservoir space. The tectonic stress of the strike-slip fault zone is the external factor determining the development of dominant reservoir space, while the thickness and mineral composition of rocks are the internal factors controlling reservoir space development. The carbonate rocks with a thickness greater than 1 m and a calcium carbonate content of less than 70% can be reworked by compresso-shear process to form favorable areas for the development of fractured-vuggy reservoirs. Figures and Tables | References | Related Articles | Metrics

RESERVOIR ENGINEERING

Sensitivity Analysis of Injection-Production Parameters for CO2 Huff-n-Puff Flooding and Storage in Tight Oil Reservoirs：A Case From Typical Tight Reservoirs of Chang 7 Member，Ordos Basin DING Shuaiwei, ZHANG Meng, LI Yuanduo, XU Chuan, ZHOU Yipeng, GAO Qun, YU Hongyan 2024, 45 (2):  181-188.  doi: 10.7657/XJPG20240206 Abstract ( 59 )   HTML ( 6 )   PDF (1331KB) ( 31 )   Save CO2 huff-n-puff in tight oil reservoirs can enhance oil recovery and store CO2. The existing researches on CO2 huff-n-puff flooding and CO2 storage in tight oil reservoirs rarely take parameters related to CO2 storage capacity as evaluation indicators. Taking typical tight reservoirs in the seventh member of Yanchang formation (Chang 7 member) in the Ordos basin as an example, through numerical simulation, six injection-production parameters (huff-n-puff timing, injection rate, injection time, soaking time, production time and huff-n-puff cycle) and three evaluation indicators (oil exchange rate, CO2 retention coefficient, and flooding-storage synthesis coefficient) were selected. Using single-factor control variable method and multi-factor orthogonal experimental design, together with range analysis method, the sensitivities of the six injection-production parameters to three evaluation indicators were analyzed. The results suggest that in the CO2 flooding-dominant stage, it is recommended to set an injection time of 30-60 d, injection rate of 0.001 0-0.003 0 PV/d, and huff-n-puff timing of less than 0.5 a; in the CO2 storage-dominant stage, it is recommended to set a production time of 30-230 d, injection rate of 0.007 5-0.010 0 PV/d, and injection time of 145-180 d; and in the synergistic optimization stage of CO2 flooding and storage, it is recommended to set an injection time of 30-65 d, huff-n-puff timing of 6 months earlier, and soaking time of 10-20 d. Figures and Tables | References | Related Articles | Metrics

Architectures of and Remaining Oil Potential Tapping in Heavy Oil Reservoirs of Panyu Oilfield Group TU Yi, DAI Jianwen, YANG Jiao, WANG Yahui, WANG Hua, TANG Zhonghao, LI Qi 2024, 45 (2):  189-198.  doi: 10.7657/XJPG20240207 Abstract ( 70 )   HTML ( 31 )   PDF (1918KB) ( 45 )   Save Due to the low oil recovery percent of reserves, developed barriers/interlayers, and difficult remaining oil prediction in the heavy oil reservoirs in the Panyu oilfield group, it is urgent to improve the accuracy of reservoir architecture analysis and prediction. Based on geological, seismic and logging data, together with GR return rate and big data statistical technologies, the 3rd-, 4th-, and 5th-order architecture boundaries in the reservoirs were identified, the distribution patterns of interlayers were studied, the internal structure of reservoir architecture units and the distribution of interlayers were quantitatively characterized, the main controlling factors and occurrence patterns of the remaining oil were analyzed, and the control of architecture boundary on remaining oil was clarified. The results show that the 3rd-order oblique progradational interlayers in the reservoirs can slow down vertical fluid flow, and the 4th-order superimposed horizontal interlayers can prevent vertical fluid channeling. The energy and direction of remaining oil migration are mainly constrained by the 3rd- and 4th-order interlayers and the rhythm differences. Ten ineffective and inefficient wells were sidetracked, which revealed an initial cumulative oil production of 680.00 m3/d, five times that before sidetracking. Figures and Tables | References | Related Articles | Metrics

Optimized Laboratory Experiment on Interlayer Interference in Heterogeneous Reservoirs WANG Jie, LI Hongyu, LYU Dongliang, QIAN Chuanchuan, ZHOU Qunmao 2024, 45 (2):  199-204.  doi: 10.7657/XJPG20240208 Abstract ( 44 )   HTML ( 3 )   PDF (869KB) ( 14 )   Save During the development of multi-layer heterogeneous reservoirs through commingled injection and production, interference between layers occurs due to various factors such as reservoir lithology, petrophysical properties, formation pressure, and fluid properties. The previous laboratory experiments on parallel displacement failed to effectively simulate fluid exchange between layers during the commingled production of multiple layers, and the physical meaning of the defined interference coefficient does not align with the flow process in water injection development. In this paper, an experimental model of series-parallel combined displacement was established to simulate the variation of lithology within the reservoir layers. The oil production, water cut, and recovery rate of cores with different permeabilities in the experiments were investigated to verify and re-understand the interference coefficient. The results show that interlayer interference is essentially a phenomenon that the variation of flow resistance of reservoir layers with time leads to alteration in flow distribution within the layers. Reservoir heterogeneity is identified as a key factor in forming dominant flow channels during commingled production. The research results provide a reference for designing interlayer interference experiments and developing heterogeneous reservoirs rationally and efficiently. Figures and Tables | References | Related Articles | Metrics

Genesis of Tilted Oil-Water Contact of Heavy Oil Reservoir in Shawan Formation, Chunfeng Oilfield, Junggar Basin ZHANG Deyao 2024, 45 (2):  205-212.  doi: 10.7657/XJPG20240209 Abstract ( 51 )   HTML ( 11 )   PDF (3330KB) ( 22 )   Save The oil-water relationship of the heavy oil reservoir in the first member of the Neogene Shawan formation （Sha 1 member） in Chunfeng oilfield is complex and cannot be explained from the traditional viewpoint of oil-water contact （OWC）, which affects the exploration and development process of the oilfield. Taking the P601-20 block with prominent contradiction in oil-water relationship as an example, researches on seismic-geology and pool-forming dynamics were conducted, and combining with the reservoir performance during development, the oil-water relationship of the heavy oil reservoir in Sha 1 member and its genesis were analyzed. It is found that the complex oil-water relationship in this oilfield is caused by the presence of a tilted OWC in the reservoir which is a structural-lithological reservoir with bottom/edge water. In terms of reservoir physical property, fault, formation pressure, tectonic movement, etc., the presence of the tilted OWC should be attributed to the adjustment of the reservoir due to tectonic movements, and the crude oil densification and flat strata intensified the lag of OWC adjustment. This reservoir can be classified as an unsteady oil and gas reservoir. Figures and Tables | References | Related Articles | Metrics

Comprehensive Determination of Oil-Water Boundary in Eastern Transitional Zone of Daqing SN Oilfield LIANG Yu, YANG Huidong, FU Xiandi, CAI Dongmei, WANG Yanhui, SUN Yanmin 2024, 45 (2):  213-220.  doi: 10.7657/XJPG20240210 Abstract ( 38 )   HTML ( 11 )   PDF (4907KB) ( 15 )   Save In order to determine the oil-water contact in the eastern transitional zone of the Daqing SN oilfield, based on the drilling, logging, and seismic data, together with the core oil occurrence analysis and the reinterpretation of oil/water layers in existing wells, a comprehensive method for determining the oil-water boundary in the extension zone of structural reservoirs was discussed by using the techniques such as hydrocarbon detection through post-stack seismic attributes based on dual-phase medium theories and fluid identification based on pre-stack seismic waveform indication inversion. The oil-water interface in the study area exhibits the following characteristics: (1) oil patch or higher level occurs in cores; (2) oil layers or oil-water layers are extrapolated on the basis of logging interpretation; (3) in post-stack attributes, the energy ratio of low frequency to high frequency is greater than 0.85; and (4) the predicted water saturation from pre-stack inversion is less than 75%. Therefore, following the principle of “depth of oil-water contact determined by well data, boundaries of oil and water distribution determined by seismic data, and validation by well performance”, and through comprehensive analysis from point to line, plane, and then space, the final position of the oil-water interface was determined. The research results effectively guide the extention deployment and evaluation in the study area, and are referential for delineating the oil-water boundaries in similar structural reservoirs. Figures and Tables | References | Related Articles | Metrics

Regulation of CO2 on Physical Properties of Heavy Oil Reservoir and EOR of CO2-Assisted Steam Flooding WEI Hongkun, WANG Jian, XU Tianhan, LU Yuhao, ZHOU Yaqin, WANG Junheng 2024, 45 (2):  221-227.  doi: 10.7657/XJPG20240211 Abstract ( 46 )   HTML ( 5 )   PDF (862KB) ( 16 )   Save It is necessary to improve development efficiency of heavy oil reservoirs in the late stage of steam flooding. In this paper, considering the application of the technology of carbon capture, utilization and storage, and enhanced oil recovery （CCUS-EOR）, and taking the J6 block of Karamay oilfield as an example, four components of heavy oil were analyzed before and after CO2 treatment, and the changes in saturation pressure, expansion coefficient, viscosity, and density were tested to investigate the regulation of CO2 on physical properties of heavy oil. Parallel core physical simulation experiments were performed to understand the performance of CO2-assisted steam flooding in improving oil recovery. The results show that the viscosity of heavy oil is mainly affected by the contents of resin and asphaltene. As the volume of CO2 dissolved in heavy oil increases, the saturation pressure rises from 2.08 MPa to 11.11 MPa, and the expansion coefficient shows an upward trend, with an increase of 7.6%; meanwhile, the viscosity and density of the heavy oil decrease by 30.5% and 3.5%, respectively. This indicates that CO2 can effectively improve the physical properties of heavy oil by optimizing the expansion coefficient, viscosity, and density while increasing the saturation pressure. In addition, the application of CO2-assisted steam flooding enables the recovery of heavy oil to increase from 38.55% to 46.46% under the effect of CO2 dissolution for viscosity reduction and demulsification, representing an increase of 7.91% compared to pure steam flooding. This study provides a theoretical and experimental basis for the application of CO2-assisted steam flooding in enhancing the recovery of heavy oil, offering insights for similar heavy oil reservoirs. Figures and Tables | References | Related Articles | Metrics

Study on Water Flooding With Self-Emulsification in Heavy Oil Reservoirs SHI Lanxiang, TANG Wenjun, ZHOU You, WANG Bojun 2024, 45 (2):  228-234.  doi: 10.7657/XJPG20240212 Abstract ( 37 )   HTML ( 4 )   PDF (1281KB) ( 16 )   Save Influenced by crude oil properties, water flooding with self-emulsification in heavy oil reservoirs is different from conventional water flooding, and the conventional theories for light oil water flooding are not applicable to heavy oil reservoirs. Taking a heavy oil reservoir with self-emulsification water flooding and the reservoir fluid parameters in China as cases, the water flooding with heavy oil self-emulsification was studied through laboratory experiments and numerical simulations to clarify key mechanisms and main influencing factors. The new numerical simulation method reveals that the stable displacement stage of the self-emulsification water flooding is a quasi-piston oil displacement pattern. The development process can be divided into four stages, namely pure oil, transition, plateau and rapid WOR increase. Permeability ratio and crude oil viscosity are the main factors affecting the water cut in self-emulsification water flooding, followed by permeability and water injection rate. Figures and Tables | References | Related Articles | Metrics

APPLICATION OF TECHNOLOGY

High-Resolution Processing Technology for Restoring Weak Signals Based on Harmonic Decomposition MA Zhaojun, HU Zhiquan, ZHANG Jianfei 2024, 45 (2):  235-243.  doi: 10.7657/XJPG20240213 Abstract ( 29 )   HTML ( 2 )   PDF (16866KB) ( 19 )   Save Improving the resolution of seismic data processing is an effective means for predicting thin reservoirs. The primary objective of high-resolution processing is to effectively recover high- and low-frequency information of seismic data, broaden frequency bandwidth, and maintain signal-to-noise ratio and fidelity of seismic data. Using the high-resolution processing technology for restoring weak signals through harmonic decomposition, and based on compressed wavelet transform, the high- and low-frequency weak seismic signals were restored according to harmonic components. Firstly, the seismic signals within effective frequency bands were decomposed into various baseband signals by using the compressed wavelet transform. Then, the high-order and low-order harmonics of each baseband signal were calculated and added to the wavelet transform coefficients. Finally, inverse wavelet transform was performed to restore the high- and low-frequency weak signals. In this process, only the baseband signals within the effective frequency band are estimated, which helps to maintain the signal-to-noise ratio. The wavelet transform coefficients of seismic signals are consistent with the stratum reflection coefficients, verifying that the technology has high fidelity and good relative amplitude preservation. The actual application of the high-resolution processing technology shows that it can maintain the signal-to-noise ratio and significantly widen the seismic bandwidth, resulting in clearer seismic profile breakpoints, higher resolution, and better identification of thin reservoirs of about 40 m thick at the depth below 6 000 m. Figures and Tables | References | Related Articles | Metrics

Application of True Surface Velocity Modeling Technology to Imaging of Seismic Data in Complex Mountainous Areas PENG Gengxin, GU Xiaodi, DUAN Wensheng, GONG Ting, ZHAO Ruirui, WANG Qing 2024, 45 (2):  244-252.  doi: 10.7657/XJPG20240214 Abstract ( 30 )   HTML ( 3 )   PDF (15543KB) ( 15 )   Save Conventional pre-stack depth migration imaging techniques separate the migration imaging and static correction processing. In the processing of seismic data from complex mountainous areas, due to the factors such as complex surface condition, drastic lateral velocity variation near the surface, and exposure of high-velocity interval, the static correction based on the assumption of surface consistency may cause wave field distortion. This distortion leads to big errors in calculation of travel time, affecting the effects of depth migration imaging. To solve this problem, a full-depth modeling and imaging technique based on true surface migration was proposed. This technique starts with velocity modeling and travel time calculation from the surface elevation, and addresses static correction implicitly in the migration imaging process. It has been satisfactorily applied in the processing of complex mountainous data. Figures and Tables | References | Related Articles | Metrics