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01 February 2021, Volume 42 Issue 1 Previous Issue    Next Issue

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OIL AND GAS EXPLORATION

Development Tendency of Geological Theory of Total Petroleum System: Insights From the Discovery of Mahu Large Oil Province TANG Yong, CAO Jian, HE Wenjun, SHAN Xiang, LIU Yin, ZHAO Kebin 2021, 42 (1):  1-9.  doi: 10.7657/XJPG20210101 Abstract ( 751 )   HTML ( 33 )   PDF (826KB) ( 540 )   Save Petroleum system is a basic tool for strategic oil and gas exploration and the geological theory of petroleum system needs to be extended with the development of unconventional petroleum geology theory. Based on the review of the evolution of petroleum system theory and the analysis of its development tendency, the paper studies the discovery history of the large oil province of Mahu. The research results show that the discovery of the Mahu large oil province represents a microcosm of the development of petroleum system theory. The large oil province of Mahu where all kinds of reservoirs can be found has the basic conditions of source-reservoir coupling, providing empirical evidences for the establishment of the total petroleum system theory. Taking Mahu sag as a case, there are possibly four directions for the exploration of total petroleum system–from outer-source to inner-source, from conventional resources to unconventional resources, from shallow strata to deep ones, and from single traps to continuous geological bodies. Figures and Tables | References | Related Articles | Metrics

Sedimentary Facies and Controlling Factors of Shengjinkou Formation in Chepaizi Swell ZHU Yan, LI Yanran, YUE Xinxin, ZHANG Hui, LI Hengquan, ZHANG Chi, ZHANG Xinchao 2021, 42 (1):  10-11.  doi: 10.7657/XJPG20210102 Abstract ( 493 )   HTML ( 9 )   PDF (7598KB) ( 174 )   Save In Chepaizi swell of the Junggar basin, the sedimentary paleo-environment of the Lower Cretaceous Shengjinkou formation was restored according to the analysis of trace elements; the sedimentary characteristics of fan delta and braided river delta in the formation were compared and analyzed using drilling, logging, seismic and laboratory data; and the controlling factors on the distribution of the fan delta and braided river delta were determined after restoring the paleogeomorphology of the Shengjinkou formation. The result shows: (1) when the Cretaceous Shengjinkou formation deposited, Chepaizi swell was in oxygen-rich freshwater to brackish water environment under dry and hot climate, and the paleo-water temperature ranged from 27.3 ℃ to 29.2 ℃; (2) there were two sedimentary systems such as fan delta-lake and braided river delta-lake in the Shengjinkou formation; and several fan delta lobes were developed in the southwest of the study area, and many braided river delta lobes in the eastern regions. Transport channels, distance from sources and terrain slope are factors controlling the development of two types of deltas in the study area. Figures and Tables | References | Related Articles | Metrics

Diagenetic Evolution and Hydrocarbon Accumulation History in Reservoirs of Xishanyao Formation in Yongjin Oilfield, Junggar Basin REN Xincheng 2021, 42 (1):  21-28.  doi: 10.7657/XJPG20210103 Abstract ( 197 )   HTML ( 0 )   PDF (25029KB) ( 58 )   Save The Middle Jurassic Xishanyao formation in Yongjin oilfield is generally 5 600 m to 6 400 m deep in the hinterland of the Junggar basin, where the reservoirs are deep and ultra-deep ones with low porosity and low permeability. In order to reveal the relationship between the process of reservoir densification and hydrocarbon accumulation, the reservoir characteristics, diagenesis, diagenetic evolution sequence and hydrocarbon accumulation history of the Middle Jurassic Xishanyao formation were analyzed through core observation, casting thin section identification, fluid inclusion and asphalt fluorescent color analysis. The results show that the Xishanyao formation has undergone three stages of diagenesis-hydrocarbon charging, and each stage of diagenesis was terminated with hydrocarbon charging. The oil charged in the first stage was oxidized in the process of tectonic uplifting, and a large amount of carbonaceous asphalt was generated and occupied reservoir pores. At the end of the second stage of diagenesis, large-scale hydrocarbon charging took place, resulting in overpressure reservoirs. Hydrocarbon charging obviously inhibited reservoir cementation and pore reduction, dissolved the carbonaceous asphalt in the early pores and increased the reservoir space. That’s the key process of hydrocarbon accumulation and improvement and maintenance of reservoir physical properties. Reservoirs formed in the stage is the primary exploration target in Yongjin oilfield. In the third stage of diagenesis, rapid burying and compaction further worsened the reservoir physical properties, so that only a small amount of highly mature oil and gas accumulated in the stage. Figures and Tables | References | Related Articles | Metrics

Genesis of Densification of Low-Permeability Tight Sandstone Reservoirs: A Case Study of Lower Jurassic Badaowan Formation in Mobei-Mosuowan Swell, Junggar Basin SHAN Xiang, GUO Huajun, CHEN Xiguang, DOU Yang 2021, 42 (1):  29-37.  doi: 10.7657/XJPG20210104 Abstract ( 202 )   HTML ( 0 )   PDF (8109KB) ( 64 )   Save Based on the rock thin section, casting thin section and X-ray diffraction whole-rock mineral analyses, and the data of scanning electron microscopy and reservoir physical properties, the petrologic, physical and diagenetic characteristics of the tight reservoirs in the lower Jurassic Badaowan formation of the Mobei-Mosuowan swell in Junggar basin were studied, and the genesis of reservoir densification was analyzed. The results show that the reservoirs are characterized by low compositional maturity, low content of interstitial matter and high content of plastic debris, and that the reservoirs have experienced strong compaction, weak cementation and general dissolution. Strong compaction is the most important factor on the reservoir densification, which is caused by strong compaction from acid diagenetic fluid in coal measures and strong static rock compaction from the high content of plastic debris in the Badaowan formation. Due to the low plastic debri content, the medium-coarse sandstone and coarse sandstone have strong fluid compaction effect and weak static rock compaction effect, therefore the medium-coarse and coarse sandstone reservoirs in Badaowan formation have good physical properties and are favorable for oil and gas accumulation. Figures and Tables | References | Related Articles | Metrics

Characteristics and Reservoir Sensitivity of Jiucaiyuanzi Formation in Fudong Slope, Junggar Basin WANG Jian, MA Cong, LUO Zhengjiang, LYU Jian, LI Erting, ZHANG Baozhen, LIU Cuimin 2021, 42 (1):  38-45.  doi: 10.7657/XJPG20210105 Abstract ( 359 )   HTML ( 5 )   PDF (7040KB) ( 123 )   Save In order to investigate the characteristics and degree of reservoir sensitivity of the lower Triassic Jiucaiyuanzi formation in the Fudong slope of Junggar basin, the fracturing technology and injection-production development measures have been timely updated. The sensitivity of the conglomerate reservoirs in the Jiucaiyuanzi formation and its controlling factors on the sensitivity were systematically evaluated based on the analysis of reservoir lithology, reservoir space, pore structure and physical properties, and the data of SEM and whole-rock X-ray diffraction in the study area. The studies show that acid sensitivity of the reservoir is the strongest, followed by medium-strong salinity sensitivity, and the last are water sensitivity and velocity sensitivity, generally medium to weak. The location and occurrence of clay minerals are key factors that determine the reservoir sensitivity. Filamentous and flocculent illite/smectite formation among grains is the primary cause for water sensitivity. Meanwhile, water sensitivity and velocity sensitivity are also affected by filamentous illite. The salinity sensitivity is mainly caused by worm-like kaolinite. Furthermore, interstitial fillings rich in zeolite, calcite cements and comb-shaped and leaf-shaped chlorite are the main reasons resulting in the strong acid sensitivity in the study area. The integrated sensitivity evaluation method of dynamic flow and static immersion established through static immersion comparative experiments is introduced, which can eliminate the difficulty in obtaining sensitivity evaluating parameters due to loose cementation, strong expansion and dense lithology. This method can reflect the sensitivity mechanism of the reservoir more intuitively, and provides a new way for sensitivity evaluation of similar reservoirs. Figures and Tables | References | Related Articles | Metrics

Ordovician Fracture-Cavity Filling Sequence and Its Logging Responses in Tahe Oilfield LIU Jingjing, MAO Cui, WEI Hehua, QUAN Lianshun, LIU Zexuan 2021, 42 (1):  46-52.  doi: 10.7657/XJPG20210106 Abstract ( 348 )   HTML ( 5 )   PDF (1661KB) ( 249 )   Save Fracture-cavity filling in carbonate rocks has an important influence on fracture-cavity reservoirs. Accurately identifying the types of fracture-cavity fillings and establishing filling patterns are conducive to better identifying and evaluating the development situations of fracture-cavity reservoirs. By observing the core, the fracture-cavity fillings can be divided into sand-shale fillings, breccia fillings, chemical fillings and empty filling. The logging response characteristics of various fillings are calibrated by using logging information. Based on the main controlling factors of karst forming, the fracture-cavity fillings can be divided into three types, namely underground river type, fault-controlled karst type, and surface karst type, and then establish filling mode. On this basis, combined with core observations, the general filling sequence of different filling modes and its logging responses are summarized. It is found that large karst caves are easier to be drilled in the fillings of the underground river type, the fillings of fault-controlled karst type is conducive to migration of oil and gas, and dissolved cavities are developed in the fillings of surface karst type. Figures and Tables | References | Related Articles | Metrics

RESERVOIR ENGINEERING

Fracture Propagating Shapes in Gravel-Supported Conglomerate Reservoirs of Upper Wuerhe Formation on Manan Slope, Mahu Sag YU Tianxi, YUAN Feng, ZHOU Peiyao, HAO Lihua, ZOU Yushi, MA Xinfang, ZHANG Zhaopeng 2021, 42 (1):  53-62.  doi: 10.7657/XJPG20210107 Abstract ( 339 )   HTML ( 2 )   PDF (8202KB) ( 249 )   Save The tight conglomerate reservoirs with complicated lithofacies in the Wuerhe formation on the Manan slope are strongly heterogeneous, resulting in complicated fracture shapes after hydraulic fracturing, and insufficient theoretical basis for optimizing fracturing design. Taking the gravel-supported conglomerate as a research object, the mechanical properties of the gravel and the matrix were measured through nanoindentation experiments, and then hydraulic fracturing experiments were carried out to characterize the hydraulic fracture propagation and pressure curves after injecting different fracturing fluids. The research results show that, on a nanometer scale, the gravel underwent elastoplastic deformation, while the matrix underwent plastic deformation after injecting fracturing fluid; the elastic modulus, hardness, fracture toughness and stored elastic energy of the gravel are all higher than those of the matrix. With a wide gap in mechanical properties between gravel and matrix, the fracture propagation in the gravel-supported conglomerate is mainly controlled by gravel, and the extension around gravel is the main form of fracture propagation. Slick-water fracturing tends to initiate fractures at multiple points near wellbore, forming a radial propagation of multiple fractures. Guar-gum fracturing tends to induce tortuous double-wing vertical fractures, but the fractures are easy to branch when encountering gravels, forming tortuous fractures with horizontal and vertical branches communicating with each other. There is no obvious fracture initiating pressure on the bottom-hole pressure curve, but the extension pressure of guar-gum fracturing is higher and more fluctuant than that of slick-water fracturing. Figures and Tables | References | Related Articles | Metrics

Optimization of Water Injection Pressure in Developing Offshore Oil Reservoirs ZHANG Lijian, TIAN Panpan, REN Yiwei, YIN Yanjun, XING Chuanheng, LU Qiang 2021, 42 (1):  63-67.  doi: 10.7657/XJPG20210108 Abstract ( 533 )   HTML ( 6 )   PDF (516KB) ( 316 )   Save Over years of waterflooding development, the water injection pressure has been increasing and the water injection pressure has been decreasing while the effect of acidizing treatment becomes worse, resulting in long-term insufficient injection, large formation pressure drop and rapid production decline in Bohai B oilfield. In actual water injection process, near-borehole pollution may occur and cause additional pressure drop. The injection pressure limit available at present was designed at the early waterflooding development stage, which cannot adapt to the current conditions, so it is urgent to research how to optimize the injection pressure. In this study, after introducing the theory of additional pressure drop, the actual water injection pressure differential was calculated based on fluid mechanics, the theoretical dimensionless water injectivity index was derived, and finally the theoretical water injection pressure differential was obtained. The accuracy of the calculated additional pressure drop was tested in wells with the results of pressure-drop well testing and acidization, and the reasonable water injection pressure was optimized. The result provides basic data for later water injection while increasing pressure. Depending on field equipment conditions, 23 well-time of water injection while increasing pressure have been implemented in B oilfield, which on the one hand, has saved acidization cost, and on the other hand, maintained oil production. It is helpful to improve the ultimate recovery in the oilfield. Figures and Tables | References | Related Articles | Metrics

Dispersion Mechanism of Viscosity Reducer and Evaluation of Displacement Experiment for Cold Production of Heavy Oil XIONG Yu, LENG Aoran, SUN Yeheng, MIN Lingyuan, WU Guanghuan 2021, 42 (1):  68-75.  doi: 10.7657/XJPG20210109 Abstract ( 429 )   HTML ( 2 )   PDF (637KB) ( 284 )   Save Efficiently dispersed viscosity reducer is the key to cold production of heavy oil. Viscosity reducer not only has a static oil washing ability, but also can diffuse into the spaces between colloid and asphaltenes in heavy oil, and break the structure of heavy oil. Based on the research of microscopic viscosity reduction mechanism, experiments on static oil washing, microscopic oil displacement, single sand-layer displacement, double-layer commingling production and separate oil displacement were carried out with L-A viscosity reducer which is suitable for cold huff and puff production of heavy oil. L-A viscosity reducer has a good effect on cold production of heavy oil. The main mechanism is that the viscosity reducer can form strong hydrogen bonds among its molecules. After intercalating into the molecules of heavy oil, the viscosity reducer filtrates and diffuses into the space between the lamellate colloid molecules and the lamellate asphaltenes molecules, reducing the hydrogen bonding force among the heavy oil molecules. The static oil washing efficiency of the L-A viscosity reducer at a mass fraction of 3% can reach 11.3%, and on microscopic displacement level, the L-A viscosity reducer can peel the heavy oil from particle surface. Single-layer displacement experiments show that the optimum viscosity-reducing mass fraction is 2%-3%, and the oil displacement efficiency reaches 48% at a lower flooding rate (1 mL/min). Double-layer experiments show that if the permeability ratio is not greater than 2, the maximum oil displacement efficiency at a low flooding rate can reach 40%, and the overall oil displacement efficiency decreases with the increase of the flooding rate and the increase of the permeability ratio between layers. Figures and Tables | References | Related Articles | Metrics

Productivity Prediction and Influencing Factors of Low Permeability Reservoirs After Steering Fracturing Stimulation PU Xiao, GUO Dali, LAN Tian, HE Yong, ZHAO Yunxiang 2021, 42 (1):  76-80.  doi: 10.7657/XJPG20210110 Abstract ( 173 )   HTML ( 1 )   PDF (448KB) ( 75 )   Save Steering fracturing can expand the drainage area of low permeability reservoirs and achieve the effect of volume fracturing. However, the fractures induced by steering fracturing are complicated, and should be finely characterized to accurately predict the post-fracturing productivity. Based on the production data from Karamay oilfield, and in view of the characteristics of steering fractures, a mathematical model of single-phase flow was established, and a grid refinement technology was used to densify the steering fractures. Field application has proved that the oil production after steering fracturing was 5.3 times higher than that of conventional fracturing. The factors influencing the productivity after steering fracturing were evaluated and the result shows that the production is positively correlated with reservoir permeability, steering fracture length and conductivity of initial induced fractures, but not necessarily depending on steering fractures to get a high flow conductivity. Figures and Tables | References | Related Articles | Metrics

Physical Modelling of Artificial Fracture Conductivity of Glutenite ZHEN Huaibin, ZHAO Haifeng, WANG Chengwang, LAN Jianli, JI Liang, SUN Hang, WANG Xuan 2021, 42 (1):  81-87.  doi: 10.7657/XJPG20210111 Abstract ( 374 )   HTML ( 3 )   PDF (2386KB) ( 250 )   Save It is difficult to develop glutenite reservoir due to its complex structure, low porosity, strong heterogeneity and anisotropy. In order to realize the efficient exploitation of glutenite reservoir, the fracture conductivity of glutenite is studied. Through analyzing the factors affecting the fracture conductivity in glutenite, this paper starts from the experiments on proppant and gravel contents and studies the influences of fiber and proppant particle size on fracture conductivity. It is found that there are three contacts for proppants in fractures: contacting with gravel, contacting with gravel and matrix, and contacting with matrix. When the closure pressure is low, the fracture conductivity of glutenite is positively correlated with gravel content, at this time, the fiber has little impact on the conductivity; with the increase of the closure pressure, the fracture conductivity decreases with the gravel content, and the presence of fiber also decreases the conductivity. The conductivity is positively correlated with the content of proppant, and the greater the closure pressure, the weaker the fracture conductivity. If the content of gravel is fixed, the larger the particle size of proppant is, the stronger the flow conductivity will be. To sum up, under a certain closure pressure, the flow conductivity of fractures in glutenite is positively correlated with the contents of gravel and proppant. With the increase of closure pressure, the fracture conductivity tends to decrease. Figures and Tables | References | Related Articles | Metrics

Analysis on Produced Water Source in Well Gaotan-1 and How to Keep Stable Production BA Zhongchen, QIU Zigang, ZHANG Zongbin, CHEN Xinyu, KONG Chuixian, QIN Jun 2021, 42 (1):  88-93.  doi: 10.7657/XJPG20210112 Abstract ( 469 )   HTML ( 10 )   PDF (2219KB) ( 282 )   Save Well Gaotan-1, which is located in the Sikeshu sag in the southern margin of the Junggar basin, hit the high-yield record of more than one thousand tons of oil per day per well from onshore clastic reservoirs in China. During the second production test for getting the highest production, the water cut from the well increased from 0% to 18.17%. At present, only Well Gaotan-1 was put into production nearby. Without cores taken from the pay zone, or liquid production performance and long-term flowing pressure data, it is difficult to understand the produced water source and its mechanism. To identify the water source, water breakthrough features and mechanism, and to design a reasonable working system for long-term high and stable production, static and dynamic data were analyzed and wellbore simulation, dynamic analysis and reservoir numerical simulation were carried out to help logging interpretation and water diagnosis. Finally, Well Gaotan-1 realized stable water cut and sustainable stable production in combination with fine field adjustment. The findings are references to guiding formation test, production test and collection of dynamic data for other production wells, and help promote the process of exploration and development in the southern margin of the Junggar basin. Figures and Tables | References | Related Articles | Metrics

Characteristics and Development Strategies of Mound-Shoal Reservoirs With Bottom Water CHEN Pengyu, CHENG Muwei, CHEN Huailong, WEN Guangyao, ZHANG Liangjie, HE Yingxu, LI Yunzhu 2021, 42 (1):  94-99.  doi: 10.7657/XJPG20210113 Abstract ( 378 )   HTML ( 2 )   PDF (1759KB) ( 252 )   Save Carbonate gas reservoirs with bottom water are characterized by complex and diverse lithologies. Fractures are developed in these reservoirs, resulting in water production from gas wells and poor reservoir development effects. Taking the BTU carbonate gas field in the Amu Darya basin of Turkmenistan as an example, by analyzing the geology of the study area, the characteristics of the fractures were clarified, and the favorable factors for the high yield of gas wells were revealed. Based on the results of the water energy evaluation and the physical features of the reservoir, the water-invasion mound-shoal reservoirs were subdivided into different reservoir types, and the risks of water invasion were evaluated for different types of gas reservoirs. The water production performance and the production decline law were summarized through analyzing the production performances of different types of gas wells. Based on the water control and gas production experience at home and abroad, efficient development strategies for the reservoirs with different water invasion characteristics were proposed. Figures and Tables | References | Related Articles | Metrics

APPLICATION OF TECHNOLOGY

Near-Surface Azimuthal Anisotropy and Seismic Imaging in the Southern Margin of Junggar Basin LUO Yong, TAN Jia, YANG Xiaohai, DOU Qiangfeng, LIU Yiwen 2021, 42 (1):  100-106.  doi: 10.7657/XJPG20210114 Abstract ( 212 )   HTML ( 1 )   PDF (31384KB) ( 69 )   Save The Anjihai anticline in the southern margin of the Junggar basin is a typical complex oil exploration area where the near-surface heterogeneity is very strong, lithology changes fiercely, and the velocity of the weathered layer changes greatly. The complex near-surface shooting and receiving conditions change the path and velocity of seismic waves and result in serious near-surface azimuthal anisotropy, making effective seismic waves (events) not be superimposed. The accurate imaging of complex structure is the first problem to be solved in seismic processing. This study analyzed the characteristics of the first arrivals of original source points, and described the correspondence between gathers after NMO/static correction and source and receiver points based on geological outcrops and satellite images, and then built the close relationship with various gullies and near-surface medium lithology, and finally established the weighted coefficient fields of different azimuth through azimuthal NMO/static correction and azimuthal weighted pre-stack time migration imaging, so that the arcing phenomenon in pre-stack time migration can be obviously suppressed, and the final migration imaging quality can be significantly improved. Using the results of pre-stack time migration, the middle and lower trap combinations in the Anjihai anticline have been effectively identified. Figures and Tables | References | Related Articles | Metrics

Construction and Analysis of Pore-Fracture Network Model of Carbonate Rock LUO Yu, WANG Yin, WANG Rong, YUAN Wen 2021, 42 (1):  107-112.  doi: 10.7657/XJPG20210115 Abstract ( 463 )   HTML ( 13 )   PDF (7257KB) ( 149 )   Save In order to study the microscopic flow mechanism of dual-porosity carbonate rock which contains both pore and fracture, a dual-porosity model should be built which can accurately characterize the pore-fracture system. We first constructed a digital rock model with a real pore-fracture system based on CT images and image segmentation technique before separating the fractures from the pores. Then centerline extraction and maximal ball methods were applied to construct a fracture network model and merge it with a pore network model into a pore-fracture network model. The porosity and absolute permeability calculated on the pore-fracture network model shows good agreement with the results from conventional property experiments. The pore-fracture network model can accurately characterize the real pore-fracture system of dual-porosity carbonate rock, and can be used to study microscopic flow mechanism. Figures and Tables | References | Related Articles | Metrics

Selection and Application of Floating Datum in Seismic Data Processing in Loess Plateau Area XU Weiya, ZHAO Yanping, CHEN Shijun 2021, 42 (1):  113-119.  doi: 10.7657/XJPG20210116 Abstract ( 508 )   HTML ( 6 )   PDF (2744KB) ( 334 )   Save The loess plateau area in the southern Ordos basin is of “double complexity”, namely very rugged surface and super-thick LVL (low velocity layer). In order to reduce the error caused by static correction on a fixed datum, seismic data processing in time domain is often carried out on a floating datum which is selected in different ways. The comparison of how floating datums based on average statics, elevation and a fix value influence t0 reflections indicates that, in the area with rugged surface and thick LVL, an elevation floating datum is very helpful to reduce the influences of drastically changing elevation and thick LVL on seismic data processing. The actual seismic data processing also proves the advantages of an elevation floating datum in velocity analysis and NMO stretching and mute processing. Figures and Tables | References | Related Articles | Metrics

Field Application of Steam Foam Flooding in Foreign Oilfields GONG Yuning, WANG Yuhao, ZHU Zhouyuan 2021, 42 (1):  120-126.  doi: 10.7657/XJPG20210117 Abstract ( 408 )   HTML ( 6 )   PDF (504KB) ( 277 )   Save This paper reviews field applications of steam foam flooding in foreign oilfields, analyzes and summarizes the rules based on 18 oilfield cases. Specifically, we investigated how steam temperature, steam dryness, surfactant type, surfactant concentration, and timing and method of injecting surfactants influence the stimulation effect of steam foam flooding. Steam foam has been widely used to improve the sweep efficiency of steam flooding or cyclic steam stimulation, and consequently improving thermal recovery. The technology has been successfully piloted and applied on an industrial scale in many oil fields such as in the United States, Canada, and Venezuela. Finally, according to the field performances, we put forward some proposals for improving steam foam flooding, with the intent to provide referential support to field application of steam foam flooding. Figures and Tables | References | Related Articles | Metrics