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13 May 2022, Volume 41 Issue 2 Previous Issue   

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Study of Main Factors Controlling Deep-layer Reservoir and Exploration Practice in Qingshui Sag of Liaohe Depression Li Long, Li Yugang, Han Dong 2022, 41(2): 1-8.  DOI: 10.3969/j.issn.1002-302x.2022.02.001 Abstract ( )   PDF (13371KB) ( )   The middle and shallow layers of Liaohe Depression in the Bohai Bay Basin are now under the mature exploration and development stage. It is necessary to make detailed evaluation of the deep layers in order to identity the amount of the reserve and improve development performance. Block S229 is located in the northern part of Qingshui Sag. With a buried depth of 3750 to 4650 meters, it is the second member of Shahejie Formation. Exploration came to a standstill owing to the difficulty to predict the deep layers of the reservoir and understand the accumulation conditions. Based on the analysis of single-well data, this paper focuses on three areas of “establishing the intra-source depositional system, understanding the intra-source reservoir characteristics, and characterizing the sealing performance of the trap” and establishes the intra-source accumulating model of “hydrocarbon controlling by means of sourcing, reservoir controlling in formation of the depression, and compound transportation”. It is considered that the underwater branch channel was the favorable facies in formation of the reservoir with development of original pores. Erosion and low-degree secondary silicon increase created the favorable conditions for reservation of original pores, formation of secondary pores and improvement of permeability. As a result, favorable traps were found. Based on “integration of evaluation and development”, the 1-million-ton high-yield oil flow was acquired from three wells, providing the experiences for exploration and development of the in-source deep-layer sandstone oil reservoir.

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A Novel Bayesian-based Reservoir History Matching Method for 4D Seismic and Production Data Wang Zelong, Liu Xiangui, Li Zhiyong, Zhang Hui, Zhang Chuanjin 2022, 41(2): 9-22.  DOI: 10.3969/j.issn.1002-302x.2022.02.002 Abstract ( )   PDF (3522KB) ( )   To solve inefficiency, inaccuracy and inability to assimilating time-lapse seismic data by the existing history-matching methods, this paper focuses on the study and improvement of the Ensemble smoother with multiple data assimilation (ES-MDA), thus proposing a novel Bayesian-based history-matching method for 4D seismic and production data. First of all, the 4D seismic data are handled both coarsely and sparsely. Then, the mathematical model for reservoir and seismic wave response is established on the basis of the rock physics model to set up the reservoir fluid-seismic attribute coupling simulation program. Finally, the adaptability of the ES-MDA algorithm is improved to combine the P-wave impedance data acquired from 4D seismic survey with wellhead production data to bring about history matching between 4D seismic data and wellhead production data. The applied study of a certain marine-facies reservoir indicates that the reservoir history matching method based on 4D seismic data adds the constraint conditions for full coverage of the reservoir fluid status, thus apparently improving the credibility of the updated geological model.

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Numerical Simulation of Four-dimensional Stress Field for Tight Glutenite Reservoir in Mahu Sag, Junggar Basin Qin Yong, Li Baozhu, Hu Shuiqing, Zhang Jing 2022, 41(2): 23-31.  DOI: 10.3969/j.issn.1002-302x.2022.02.003 Abstract ( )   PDF (4693KB) ( )   The glutentite reservoir in Mahu Sag is characterized for its strong heterogeneity and complicated in-situ stress state. Therefore, it is a great challenge to design the horizontal well fracturing optimization and EOR plan. Based on the results from seismic prestack elastic parameters inversion of Mahu glutenite shale oil reservoir, the method for fluid-solid coupling simulation of multi-dimensional in-situ stress field is established to bring about accurate characterization of four-dimensional in-situ stress and dynamic update of geo-mechanical parameters at different scales from the whole area to a single well. With the principle for reasonable segmentation and clustering of fractured horizontal wells, the design technology to optimize variable density, segmentation and clustering of fractured horizontal wells is developed to effectively increase the fracture-controlled reserves. The on-site application indicates that the single-well production is raised by 20 to 30 percent after optimization of the perforation plan. The four-dimensional in-situ stress field simulation technology helps solve the bottleneck for dynamic coupling description of the reservoir “seepage field – stress field” and bring about characterization of dynamic in-situ stress field for fractured horizontal wells and prediction of the fracture propagation path for infill wells. The simulation technology can also support the later-on drilling and completion design and optimization of energy supplementation time/method. The research results are of important significance to full life-cycle development of Mahu glutenite shale oil reservoir and improvement of quality and economic performance.

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Decarbonization Paths in China’s Key Sector under Goals of Carbon Peak and Carbon Neutrality Li Jianqing, Jiang Xuefeng, Su Yinao, Dai Jiaquan, Wang Lining, Peng Tianduo 2022, 41(2): 32-38.  DOI: 10.3969/j.issn.1002-302x.2022.02.004 Abstract ( )   PDF (2504KB) ( )   The Es32+3 Reservoir in northern Liuzan Block of Nanpu Sag is complete in structure, stable in overlying mudstone stratum and good for trap sealing. The reservoir is favorable for gravity drive thanks to its large formation dip angle and good conductivity. The gas drive test indicates that natural gas is able for solubilization and expansion, effective reduction of crude oil viscosity, and increase of crude oil fluidity. Therefore, it can substantially improve the productivity. Based on the geological conditions of the reservoir in northern Liuzan, the study was carried out to focus on the key technology policy of natural gas gravity drive for EOR. The results indicated that the well pattern with alternation of high injection and low production, combination of horizontal wells with directional wells, the difference in the injection-production height between 100 meters and 120 meters and the injection-production well spacing between 100 meters and 150 meters can effectively produce the remaining oil in the top of oil formation and in the high position of the structure. Focusing on sweep volume and displacement efficiency, oil development was divided into three stages – mild gas injection for oil production, enhanced gas injection for oil production and water injection and gas production for higher efficiency – to optimize the key parameters of the development method, the injection-production method, the gas injection speed, the liquid production speed,the pressure-maintaining level, and the time for conversion of the stages. Based on the new model of natural gas gravity drive for EOR, the study of the technology path for water-drive development of oil reservoir during its later high water-cut period to keep sustainable development is of great significance to the oil reservoirs of the same type in the Bohai Bay Basin.

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Research on Line Injection and Line Production Energy Supplement Method for Horizontal Wells of Ultra-low Permeability Oil Reservoirs Liu Jian, Xie Qichao, Fan Jianming, Wang Jiwei, Sun Dong, Wang Di 2022, 41(2): 39-44.  DOI: 10.3969/j.issn.1002-302x.2022.02.005 Abstract ( )   PDF (2707KB) ( )   The “injection-on-points for areal production” method was used for the horizontal wells of the ultra-low permeability oil reservoirs in Ordos Basin. However, the horizontal wells under the five-point well pattern water injection development came across some problems, such as low efficiency and rapid declining. To enhance water injection for a higher water drive efficiency, the “line injection and line production” energy supplement technology for horizontal wells was proposed at the attempt to bring about inter-well mutual flooding, self-flooding between fractures and in-the-well imbibition. Based on the reservoir rock mechanical test, the fracture-network distribution prediction model was established to indicate the state of fractured seams under the different brittleness indexes and poor stress. The closer the brittleness is to 0.5 and the greater the two-way stress difference is, while the length-width ratio of the fractural belt is higher, flatter and more suitable to meet the requirements for line injection and line production. The Chang 63 oil reservoir of Heshui Oilfield was brought under fine geological study. The southern part of Z288 Well was selected as the experiment zone. The relative technological policies for well spacing, interval spacing, horizontal spacing and water-injection volume were formulated according to the fractural shape and reservoir characteristics. The well group test in Heshui area of the basin indicated that the single-well declining was reduced by 6.5 percent, confirming reasonability and operability of this method. Therefore, the technological method is effective to provide energy supplement for horizontal wells of ultra-low permeability oil reservoirs.

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Research and Application of Life-cycle Gas-lift Drainage and Production Technology for Shale Gas Fang Zhigang, Wang Zhensong, Ma Bin, Wang Wei, Qi Weilin, Li Nanxing 2022, 41(2): 45-52.  DOI: 10.3969/j.issn.1002-302x.2022.02.006 Abstract ( )   PDF (3519KB) ( )   The unconventional gas reservoir like shale gas is an important area for China’s natural gas production in the 14th Five-year Plan period. The main development process is “horizontal well + volumetric fracturing”. As for drainage and production technologies, gas lift is used for horizontal well because it is free from limitations of well deviation and well depth. Therefore, this paper put forward the gas lift drainage and production technology that runs through the full life cycle of the drainage and production period. This technology is concentrated on the multi-stage gas lift valve. Based on improvement of the design method and completion tools, continuous gas lift is integrated with intermittent gas lift, foam discharge, negative-suction gas recovery and jet gas lift. Equipped with the intelligent management platform, it is the gas lift compound drainage and production technology that can use one-trip completion string to keep the gas well producing until it is abandoned. The technological plan for full life cycle satisfies the demand for drainage and production technology of shale gas reservoirs at the different production stages, reduce workover services caused by change of the drainage and production method, lower the technological cost and reduce damage of reservoirs. The productivity is estimated to improve by 3 precent to 6 percent, substantially reducing the production cost of a shale gas well.

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Research and Practice of Tight Oil Drilling and Production Integration Plan Innovatively Designed for Higher Production and Cost-effectiveness in Northern Songliao Basin Jiang Guobin, Cai Meng, Zhao Ming 2022, 41(2): 53-61.  DOI: 10.3969/j.issn.1002-302x.2022.02.007 Abstract ( )   PDF (3017KB) ( )   Tight oil reservoirs in the northern Songliao Basin are geologically characterized for small thickness of a single layer, poor vertical concentration and poor horizontal continuity. To overcome the difficulties in development of the tight oil reservoirs, the drilling-production integration plan was studies and put into practice to increase production and cost-effectiveness. Based on the on-the-surface and underground characteristics, the drilling design was optimized as the platform-style well pattern. The horizontal well was changed to two layers from three ones with holes slimmed. As for the two-dimensional horizontal well, the build-up point was moved up to reduce the build-up rate, friction and torque. The three-dimensional horizontal well adopted the method of “first plane build-up in advance and then twist orientation”. The ultra-deep penetrating and equal-aperture perforation charges were preferred. Both vertical well and directional well were designed to have a density of 16 holes per meter and a phase angle of 135°, while the horizontal well was designed with a density of 20 holes per meter and a phase angle of 60°. The facies-controlled geological model was used to determine that the half length of the fracture was 250 meters to 300 meters, the fracture spacing was 10 meters to 15 meters, and the type of the proppant was quartz sand with a combination of particle sizes – 70 mesh to 140 mesh + 40 mesh to 70 mesh + 20 mash to 40 mesh. The research on the drainage and production system was based on the three stages of initial blowout, rapid drainage and normal production after fracturing to optimize the lifting process in the whole life cycle. Finally, the optimization method for an integration plan was formulated to meet the characteristics of northern Songliao Basin tight oil reservoirs, which were a combination of multi-layer thin inclined and vertical wells, horizontal wells for main layers and straight and flat wells for main thin layers. As a result, the design technology for higher production and cost-effectiveness focusing on large-platform drilling, ultra-deep penetration and other aperture perforation, compound high-efficiency fracturing and whole-life-cycle lifting was finalized to construct the cost-effective productivity of more than 1 million tons for the tight oil block.

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Research and Practice of Integrated Fracturing Design Technology for 3D Well Pattern of Permian Lucaogou Formation in Jimsar Depression in Junggar Basin Wang Junchao, Li Jiacheng, Chen Xi, Ma Mingwei, Tian Zhihua, Cheng Leiming, Chen Lu 2022, 41(2): 62-68.  DOI: 10.3969/j.issn.1002-302x.2022.02.008 Abstract ( )   PDF (3699KB) ( )   The conditions for shale oil accumulations are complicated in Jimsar Depression of the Junggar Basin. The reservoir is strong for heterogeneity and poor in sustainable productivity. The economic performance is unsatisfactory in development of the oilfield. Therefore, Xinjiang Oilfield has gradually stepped up exploration and development in the efforts to study the feasibility for a large-scale shale oil development in Jimsar Sag. Based on a decade of research and practice efforts and aiming at “fracture-controlled reserves” for transformation, Xinjiang Oilfield has pursued the cost-effective design conception and developed the volume fracturing technological system characterized in “high-density cutting + high-strength transformation + low-cost materials”. With development in transition to platform and multi-layer series mode, it is necessary to study integrated fracturing technology of 3D well pattern to improve the producing degree of reservoirs. The large-platform integrated transformation design method was developed on the basis of the engineering technological integration research. The optimization plan for large-platform service sequence was determined by means of the fine description of dynamic changes in fracturing time and stress field between segments. The classification prediction technology and control measures for casing deformation risks at the time of fracturing were developed on the basis of the detailed seismic interpretation. The on-site experiment of the first 3D development platform for integrated transformation was completed in 2021, meeting the fracturing safety targets of zero fracturing loss and unimpeded drill plugs. With substantial improvement of production, the fracturing technological system set a good example for constructing a high-quality productivity for Jimsar shale oil and effectively help construct the national demonstration zone for continental shale oil.

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Drilling Safety Technology for Complicated Deep Wells in Qaidam Basin Xing Xing, Liu Fenghe, Cheng Changkun, Qiao Shijun, Wu Yujie, Du Yubin, Zhong Yuan 2022, 41(2): 69-73.  DOI: 10.3969/j.issn.1002-302x.2022.02.009 Abstract ( )   PDF (2390KB) ( )   The drilling targets in Qaidam Basin have gradually extended into deep layers in recent years. Generally speaking, the ultra-deep wells are geologically characterized in complex pressure systems, complex stratigraphical lithology, complex reservoir fluid and complex engineering mechanics. Drilling engineering faces some technological bottlenecks, such as difficult optimization of design, high operational risks, slow drilling speed, and difficulty for engineering quality control. A systematic technology for drilling safety of complicated deep wells in Qaidam Basin was developed thanks to optimization of the drilling engineering plan, optimization of PDC bit, research on ultra-high temperature drilling fluid and high-temperature drilling mud, and high-pressure salt-water layer drilling safety study. The technology was applied to six wells on the field, achieving good results for well completion. The well depth was 6286.6 meters on average and the drilling period reached 236.3 days. The average mechanical drilling speed was 3.15 m/h while the complex timeliness was 10.8 percent, 45.6 percent shorter than the initial stage. Drilling and completion of the 7310-meter-deep Kun 1-1 Well set a record high for well depth in Qaidam Basin.

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Application of “Logging-Directional Drilling-Geosteering” Integration Technology for Shale Oil Horizontal Wells in Sichuan Basin Bai Aichuan, Ji Ren, Zhang Yu, Zhao Zhanzhao, Hou Yuwen, Liu Yuyan, Ding Haikun 2022, 41(2): 74-84.  DOI: 10.3969/j.issn.1002-302x.2022.02.010 Abstract ( )   PDF (4737KB) ( )   The Jurassic shale oil and gas reservoirs in Sichuan Basin are favorable for stereo exploration owing to their shallow buried depth, good preservation conditions, high formation pressure coefficient and development of multiple layers. It is difficult to use the conventional methods to bring the tight reservoirs in Da’anzhai Member and Lianggaoshan Formation under economic and effective development because of their ultra-low porosity and ultra-low permeability. The innovative “logging-directional drilling-geosteering” integration technology was practiced to improve the drilling success rate of high-quality shale oil reservoirs and lower the operational risks. Based on the core and cuttings data of the LA1 pilot well and analyzing the physical parameters of Da’anzhai Member shale reservoirs in the central Sichuan Basin, such as content of mineral components, porosity, TOC and permeability, the geological and engineering sweet point was determined. Combined with the well logging and seismic data, fine geological modeling, the efforts were made for studying the distribution law of high-quality shale reservoirs, optimizing the target box of horizontal well and optimizing the geosteering tools and drilling tools assembly plan. The horizontal well trajectory optimization design and control technology, combined with geological model and natural gamma data while drilling, was used for dynamic real-time tracing and drilling trajectory adjustment, thus effectively improving the wellbore quality of a horizontal well and the success rate of drilling into the box and laying a good foundation for segmentation and clustering fracturing. Application of the technology helped produce oil from Da’anzhai Member shale reservoir in Sichuan Basin.

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Leakage Characteristics of Shale Gas Wells Drilled in Southern Sichuan and Plugging Technology Research and Application Wan Fulei, Wang Peigang, Fan Shenglin 2022, 41(2): 85-91.  DOI: 10.3969/j.issn.1002-302x.2022.02.011 Abstract ( )   PDF (2517KB) ( )   The geological landform is complicated in the shale gas zone of Southern Sichuan with development of obvious fractures and cavities. Serious leakage of drilling mud frequently happened at various layers, causing difficulties for plugging work. The long period for treatment of the complicated conditions severely impaired acceleration of drilling rate. To solve those engineering geological bottlenecks, the efforts were focused to analyze the leakage characteristics of shale gas wells drilled in Southern Sichuan and evaluate the current conditions of leakage prevention technology, while systematically elaborating the effects of various technological process for well leakage, such as bridge-plug plugging, cement plugging, multiphase mixed injection plugging and rapid solidification plugging, and oil-based drilling fluid plugging. Leakage was mainly of the fractural property in the shale gas zone of Southern Sichuan, with the obvious characteristic of vertical “three segments”. Treatment of well leakage for the surface formation was difficult. It was still to be solved satisfactorily. As for the middle formations, bridge-plug plugging, cement plugging and clear water enhanced drilling process could achieve good results for leakage prevention. Plugging the leakage under pressure had no effect on the lower formation while spill and leakage co-existed for Longmaxi Formation. The study led to a comprehensive plugging process technology, such as compound bridge-plug plugging, bridge plug + high fluid loss plugging, bridge plug + cement slurry plugging, and gel + cement slurry plugging. The whole plugging success rate was brought up to 56 percent of the basis of integrated application, making a remarkable plugging achievement. Focusing on the existing problems for the surface formation, such as the limited process for treatment of well leakage, long duration for handling leakage, and lack of precise leaking formation diagnosis technology, it is proposed to make study of leaking formation diagnosis technology and develop the new plugging materials and tools suitable for the leaking channels as well as the series of the related processes.

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Fine Reservoir Description and 3D Geological Modeling Technology for Horizontal Wells for Bioclastic Limestone Reservoirs of Khasib Formation of Cretaceous, Iraq Deng Ya, Huang Tingting, Xu Jiacheng, Chen Mingjiang, Zhang Wenqi, Wang Junling, Tian Zhongyuan, Liu Dawang, Wang Yuning 2022, 41(2): 92-103.  DOI: 10.3969/j.issn.1002-302x.2022.02.012 Abstract ( )   PDF (8185KB) ( )   The porous bioclastic limestone reservoirs in Iraq was selected in this paper to accurately characterize the heterogeneous properties of carbonate rock reservoirs and predict the parameters of the reservoirs’ physical properties. The paper combines the static and dynamic data of the reservoirs, including the seismic, logging, geological, reservoir, drilling and production materials, to form a set of 3D geological modeling methods on the basis of horizontal wells. By analyzing the characteristics of cores and logging response, the logging response model was established for both intralayers and interlayers of a horizontal well. Based on the thickness-comparing method, a series of surface nodes were determined on the horizontal sections of the horizontal wells. The “seismic surface constraint+ trend line control + partial optimization of virtual well” method was adopted to fully couple vertical wells and horizontal wells, thus establishing the fine 3D structural model. The cores, slices, scanning electron microscope and logging data were used to establish the rock-type model of the target reservoir. The sequential Gaussian simulation method was used on the basis of the rock-type model. The seismic paleo-geomorphology was used as collaborative constraints to build the models of porosity and permeability for the different types of rock. The model was brought under verification on the basis of the actual drilling and dynamic production state. The results indicated that the actually measured permeability of the rock is highly in line with the predicted value. The depth of the structural top and parameters of physical property predicted by the model were highly in agreement with the actually-measured results, meeting the requirements for accuracy, the model can effectively help dynamic analysis of oil reservoirs, numerical simulation, prediction of remaining oil and adjustment of the development plan.

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Seismic Waveform Interpretation at Oilfield Development Stage Hao Jinjin, Shi Lanting, Zhang Yajun, Hong Liang 2022, 41(2): 104-112.  DOI: 10.3969/j.issn.1002-302x.2022.02.013 Abstract ( )   PDF (4302KB) ( )   The current fine seismic prediction technology, to a certain extent, is an extension of seismic interpretation technology at the exploration stage. Influenced by the research method and complex geological conditions, the prediction technology is dramatically limited in description of small-size reservoir structures at the oilfield development stage. The mindset for seismic data interpretation which is different from that at the exploration is established to settle the requirements and bottlenecks for interpretation of small-size layers and reservoir prediction. This paper puts forward the seismic waveform interpretation work process at the development stage, making seismic data interpretation detailed from analysis of the original large-size wave group characteristics to analysis of the waveform characteristics. It includes three steps: (1) establishing the relations between seismic waveform and lithology/reservoir structure and characterizing seismic phase variations on the top of layer; (2) dividing the zones and belts and changing the phases to interpret the sub-layers on the basis of the relations between combination of lithological properties and seismic waveform changes; and (3) making high-precision quantitative prediction of reservoirs by means of the depth domain seismic waveform instructions. The seismic waveform characteristics were fully taken into account in the above-stated study. The research results were used for Hartha oil reservoir of Halfaya Oilfield, using the seismic waveform to describe bioclastic beach, interpret restrained development sub-layers, and instruct reservoir inversion. The research results were in line with the requirements for high-precision reservoir prediction at the development stage.

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Optimization of Exploration Targets and Application Results on Trakes Slope of Termit Basin, Niger Wang Zhongfan, Sun Weizhao, He Jinsheng, Liu Qiang 2022, 41(2): 113-118.  DOI: 10.3969/j.issn.1002-302x.2022.02.014 Abstract ( )   PDF (5665KB) ( )   Trakes Slope in Niger is located in the southern part of the eastern terrace in Termit Basin and borders the oil-enriched Agadem area. The patterns of the fault assemblages were unclear owing to the poor quality of the 2D seismic data in the previous stage. The main controlling factors of accumulations and exploration directions remained unidentified while no breakthrough was made in the exploration area. To settle this problem, the 3D seismic surveys were made in this region. As a result, three fault assemblages of NNW-SSE, NW-SE and nearly S-N were found on Trales Slope. Controlled by the NW-SE strike-slip faults, six strike-slip structural belts developed on Trakes Slope, which controlled six oil and gas abundant zones. The NW-SE strike-slip faults controlled distribution of the Cretaceous-Paleogene traps in common with the nearly S-N strike-slip faults. The southern strike-slip was adjacent to the hydrocarbon-sourcing sag. The structure was appropriate in buried depth and abundant in oil and gas. It was the favorable exploration zone for conventional oil. The northern strikes-slip structural belt was buried shallowly, with part of caprock coming under denudation. It was the favorable exploration zone for heavy oil. A total of five oil and gas enriched zones in the southern part of Trakes Slope were optimized and selected for exploration. All fhe drilled and completed exploration obtained the industrial oil flow, laying the resources foundation for the second-stage productivity construction and maintenance of stable production on a long-term basis in Niger.

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Design of Auto-response DOC Controller on the Basis of Mechanism Research of Stick-slip Vibration He Zhenguo, Shi Libao, Nie Hongfang, Kong Lulin, Feng Jian, Qu Zhaofeng 2022, 41(2): 119-126.  DOI: 10.3969/j.issn.1002-302x.2022.02.015 Abstract ( )   PDF (3325KB) ( )   Stick-slip vibration has been one of the major problems during drilling operations in a basin, Chad. Hardness and brittleness of gneiss granite, the key lithology in basement reservoir has become the main cause of stick-slip vibration and further premature failure of drill bits and string, posing a serious threat to safe and cost-saving drilling and oilfield development. Hence, it is urgent to carry out the mechanism study of stick-slip vibration and structure design to manage the problem. Numerical simulations and lab experiments were run in this research to describe the micro dynamic rock cutting process, establishing the relation between depth of cut (DOC) and cutting performance or bit rotation. Lithological alternation and excessive DOCs are revealed as the root cause of stick-slip vibration, and furthermore, optimized DOCs for different rock layers are recommended. A novel design of auto-response DOC controller is proposed based on it to manage DOC and bit rotation in real time, followed by the modifications of structural features and parameters via numerical simulations. The controller was then machined and tested on mechanics and hydrodynamics. Results show that it has met the standards of satisfactory motion as it slowly retracts into the body by resisting the load and quickly extend outwards. The auto-response DOC controller has provided a sound theoretical basis for anti-stick-slip PDC bit and has profound application potential in increasing ROP and efficiently developing the ultra-deep and unconventional reservoirs.