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10 September 2021, Volume 17 Issue 3

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OIL AND GAS EXPLORATION

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Analysis of Wellbore Blocking Substances in Yuanba High-Sulfur Gas Field

LIU Zhendong, SUN Tianli, Zhu Guo, XIONG Xindong, WAN Liping, ZENG Dezhi

2021, 17(3):  1-6. 

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Yuanba Gas Field is a large-scale marine sour gas field with deep burial and great development difficulty. Wellbore blockage occurs from time to time during its production. In order to know the main components and sources of blocking substances,methods such as thermogravimetric analysis,scanning electron microscopy,X-ray diffraction,and high-temperature simulated distillation carbon number distribution analysis were resorted to. Analysis results show that the blocking substances mainly consist of asphaltenic organic components in well H1,inorganic components such as FeS₂ and BaSO₄ in well H2,and BaSO₄,CaCO₃,a small amount of S elemental substance and SiO₂ in well H3. There are some differences in the blocking substances between different gas wells in Yuanba area. Asphaltenic organic components are mainly the asphalt separated out of formations and the high-temperature pyrolysis products of inflowing fluid,while the occurrence of inorganic components is related to sand production and barite and other additives.

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Quantitative Characterization of Microscopic Pore Structures for the High-Yielding Shale Gas Reservoir of Longmaxi Formation in Zhaotong Demonstration Zone

XIE Qingbin, WANG Jia, SONG Shuyu, ZHU Yixiu, WANG Yuhan, ZHANG Jiehui

2021, 17(3):  7-16. 

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In this study,the high-yielding shale gas reservoir of Longmaxi Formation in Zhaotong Demonstration Zone is addressed. The microscopic pore structures of high-yielding shale gas reservoir were quantitatively characterized by field emission scanning electron microscopy,nitrogen adsorption experiment,X-ray diffraction (XRD),nuclear magnetic resonance experiment,nano-CT scanning technology and Image J image processing software. The study findings show that the rocks of shale gas reservoir mainly consist of greyish black - black shale rich in organic matters and with a porosity greater than 2% and a permeability greater than 0.01 ×10^-3 μm². Most of the pores are organic ones with good connectivity,and there are also some intergranular and intragranular pores,as well as a small number of micro-cracks. The pore size is in the range of 5~50 nm. The three types of pore structures are different in pore type,total organic content (TOC) and pore size. Type I pores are mainly organic ones,with high TOC and good reservoir quality. Type II pores have moderate organic content,which are mainly composed of micropores-mesopores provided by organic matters and clay minerals. Type III pores have low organic content,which are mainly composed of some micropores and mesopores provided by clay minerals.

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Study and Application of Ultra-High Temperature and Ultra-High Density Cement Slurry System in Deep and Ultra-Deep Wells at Southern Margin of Junggar Basin

MA Jiang, SU Hongsheng, XU Xinniu, QI Jing, ZHENG Yongsheng, ZHANG Wei, DENG lin, DI xinye, WEI Ruihua

2021, 17(3):  18-24. 

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Targeted at the geologic characteristics of deep and ultra-deep wells at the southern margin of Xinjiang Oilfield,this paper expounds the main technical difficulties of cementing,especially the technical problems in respect of cement slurry technology,and proposes solutions. On this basis,an ultra-high temperature and ultra-high density cement slurry with the temperature up to 200 ℃,density up to 2.70 g/cm³,and all performance indicators meeting the requirements of cementing technology was designed. Thus,the technical problems existing with ultra-high density cement slurry when being applied in ultra-high environment,such as poor stability,poor rheological property,slow-to-function compressive strength and poor compatibility,have been solved. This system has been successfully applied to blocks at the southern margin of Xinjiang Oilfield.

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Ecological Utilization and Development Trend of Environment-Friendly Drilling Fluid

YE Cheng, LU Tiemei, LIU Xiang, LIU Kecheng, YAO Xuyang, GONG Jiaqin

2021, 17(3):  25-29. 

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Environmental issues are key problems to be solved urgently during oil and gas exploration and development,and minimizing the pollution by drilling fluid is a top priority among the solutions to the environmental pollution caused by oil and gas development. For a long time,the research of environment-friendly drilling fluid has focused on individual treatment agents. As a result,only the core chemicals are environment-friendly. It is hard to have a nontoxic drilling fluid system,and the progress to achieve this purpose is slow. However,the currently available toxicity assessment methods for drilling fluid are limited to unused product or its waste,ignoring the functions of drilling fluid waste in ecological restoration and utilization,and lacking effective tracking and evaluation means after the waste is disposed. Regarding the ecological restoration and utilization of drilling fluid,exploration is currently limited to some local fields only,restricted by fundamental mechanisms,environment-friendly drilling fluid technology and application environment. Therefore,it helps realize the comprehensive environment-friendly development and utilization of underground hydrocarbon resources and surface land resources to build a whole-link environmental protection mechanism (treatment agent - drilling fluid system - recycle - discard - ecological restoration and utilization),eliminate the disadvantages of traditional environment-friendly drilling fluid,and take the ecological restoration and utilization of saline-alkali land as breakthrough point.

OIL AND GAS DEVELOPMENT

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Characteristics and Control Methods of Wellbore Integrity Failure for Jimsar Shale Oil

LI Jun, WU Jiwei, XIE Shiyuan, CHEN Liang, LIAN Wei

2021, 17(3):  37-43. 

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The casing deformation problem in the process of multistage fracturing in Jimsar shale oil is prominent. Based on an analysis of its development status,casing deformation in shale oil wells in the demonstration area was counted to give a clear picture on the forms of casing deformation,as well as the characteristics of its temporal and spatial distribution. The influencing factors of casing deformation were analyzed from the perspective of engineering and geology. The analysis results show that the casing deformation in shale oil wells is characterized by shear deformation. Casing deformation points are located near target A,middle section and target B accounts for 50.0%,32.2% and 17.8%. Casing deformation mostly occurs in the process of fracturing. Formation lithologic interfaces,natural fractures and fault development degree are the main influencing factors,while cementing quality,casing wall thickness and rigidity have little influence. Reducing pump rate and pump pressure is conducive to mitigating casing deformation. Finally,the control methods of wellbore integrity are put forward which can provide reference in controlling the wellbore integrity failure for shale oil.

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Study on the Flow and Oil Displacement Characteristics of Associating Polymers of Different Molecules under Conditions with Different Permeabilities and Max-to-Min Permeability Ratios

LIANG Yan, WANG Yi, ZHANG Xinmin, CAO Miao, HU Jun, ZHANG Wei, LUO Pingya, GUO Yongjun

2021, 17(3):  44-52. 

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By establishing a long sand-packing model with satisfactory reproducibility for porosity, permeability parameters and sand-packing stability, the flow characteristics and oil displacement effect of associating polymers with different hydrophobe contents at a similar shear viscosity were investigated under conditions with different permeabilities and max-to-min permeability ratios. The results show that, in the permeability range of 0.55~6.93 μm², the polymer without hydrophobes (DM-0) always exhibits an identical "equal resistance" pattern; while the associating polymers DM-1~DM-3 respectively demonstrates a flow pattern of "equal resistance" and "increasing resistance" before and after a certain critical permeability, and the critical permeability notably increases with increasing hydrophobe content. Moreover, the combination pattern of "increasing resistance + increasing resistance" can achieve the best oil displacement effect, and the higher hydrophobe content the greater max-to-min permeability ratio. The synergetic oil displacement of associating polymers with different flow patterns can provide important technical reference for heterogeneous reservoirs to enhance recovery factor significantly.

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Study and Application of Microseismic Monitoring and Interpretation Technology in Unconventional Oil and Gas Reservoirs

LIANG Xueli, LIU Hailong, CHENG Ning, ZHANG Rongli

2021, 17(3):  53-58. 

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This paper focuses on the study of the response characteristics of unconventional oil and gas reservoirs,such as tight sandstone,carbonate,rock with coal luster and shale. In addition,it also describes the microseismic monitoring results of reservoirs with different lithologies,and comprehensively interprets the microseismic monitoring results with the actual conditions of fracturing and seismic geology taken into account,achieving satisfactory results.

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Finite Element Analysis for Vibration Mechanical Behavior of Tubing String in Gas Wells under Extreme Conditions

LIAN Zhanghua, MOU Yisheng, ZHANG Qiang

2021, 17(3):  59-66. 

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In order to systematically and quantitatively analyze the vibration mechanical behavior of tubing string in gas wells under extreme conditions,two finite element mechanical models were established according to the tubing string structures and sizes of an oilfield in Xinjiang for the vibration of tubing string with packers under the said conditions using finite element method. APDL finite element program was compiled,by which the vibration problems of such tubing string were systematically analyzed and studied. Study findings show that ① After comparing the first 15th modes and frequencies of two string structures,it was found that the improved structure could mitigate the damage of vibration to tubing string. ② In respect of transient dynamic response,the improved structure made the average stress in high-risk string section (4 200-5 500 m) reduce by about 104 MPa,and the neutral point moved down by 231 m,which are conducive to improving the safety and fatigue life of string. It is concluded that the established model can be used to analyze the string vibration mode,inherent frequency,and stress,velocity and displacement that change with time,providing quantitative basis for the fatigue life prediction,neutral point change and vibration mechanical mechanism of tubing string in gas wells under extreme conditions,as well as theoretical basis for tubing string design of new wells.

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Research Progress and Development Direction of Hydrofracturing Design Models

ZHANG Shicheng, CHEN Ming, MA Xinfang, ZOU Yushi, GUO Tiankui

2021, 17(3):  67-73. 

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Hydrofracturing model is the basis of hydrofracturing design,and also the crux where current bottlenecking problems lie. In order to promote the development of fracturing design models and softwares in China,fracture propagation models,numerical methods and popular commercial softwares for hydrofracturing are systematically analyzed,and their future development orientations are predicted. Research findings show that (1) Planar and complex fracture models are different in application conditions and accuracy. Most commercial softwares are planar fracture models-based,and most complex fracture models are pseudo-three-dimensional ones. (2) It is the focus of fracturing design softwares to develop models with satisfactory accuracy and efficiency. (3) Artificial intelligence data-driven fracture analysis,and fracture parameter inversion based on micro-seismic and fiber optic logging are the development orientation of fracturing design models.

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Optimization and Application of Crude Oil Transportation and Distribution System

XIONG Xiaoqin, YANG Jun, CHENG Mengmeng, LI Yang, HE Lijun

2021, 17(3):  74-78. 

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As a key link for the production and operation of oilfield enterprises,crude oil transportation and distribution system is complex and variable,covering a vast area and involving many stakeholders,through which commercial oil is exported and marketed. It is the primary goal for oil scheduling to optimize oil transportation and marketing allocation patterns,and maximize marketing profit under the premise of ensuring pipeline transportation safety. In this paper,the oil transportation and distribution system of Xinjiang Oilfield is studied,and oil production,supply,marketing and storage are integrated together. By setting up an optimization and allocation system for regional resources and determining performance evaluation factors,simulation model for long-distance oil transportation pipeline operation,mathematical model for oil density and viscosity calculations,and mathematical model for the optimized allocation of multiple stations and storages were built to optimize the flow direction for oil marketing and allocation,oil blending ratio,and the operation patterns of oil transportation stations and pipelines. After optimization,the annual oil marketing benefit has increased by hundreds of millions yuan.

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Study on A Highly Efficient Anti-Swelling and Salt-Resistant Slickwater Fracturing Fluid System

SUN Xize, XU Chengjun, LUO Teng, GUO Yongjun, REN Hongda, LUO Pingya

2021, 17(3):  79-83. 

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A study on a highly-efficient anti-swelling and salt-resistant slickwater fracturing fluid system was conducted based on the wastewater from fluid preparation in an oilfield. This study was designed to solve the blockage problem of induced fractures and matrix pores and throats due to the hydration expansion and even rock skeleton collapse after fracturing fluid system contacts a readily loose reservoir with high clay content,strong water sensitivity,and weak cementation. The experimental results show that a highly efficient anti-swelling and salt-resistant slick water fracturing fluid system prepared from 0.05% KY-2 （salt-resistant drag reducer ）,0.4% FP-3 （organic amine compound anti-swelling agent）,0.1% ZP-2 （cleanup additive）,and the said waste water with a TDS of 15 548.96 mg/L has an anti-swelling rate （96.2%） equivalent to 4% KCl,which means a satisfactory anti-swelling performance. After washing with tap-water for 10 times,the anti-swelling rate is still as high as 89.87%,which means a satisfactory long-acting anti-swelling performance. Besides,with a drag reduction rate of 78.45%,this system has a satisfactory drag reduction performance. Field test results have validated that the new system can effectively alleviate the problems of high KCl consumption,high cost,and inability to use mixing-free process in strong water-sensitive reservoirs,as well as the decrease in drag reduction rate due to high TDS.

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Analysis Method Study on the Influence of Wellbore Flow Pressure Drop on the Productivity of Commingled Production Wells for Testing

XU Xiaohui, GAO Han, LIU Tao, XU Yiwen, XIN Xiaozhi

2021, 17(3):  91-94. 

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In the testing process of exploratory and evaluation wells, single-layer testing is mostly used to measure the productivity of each layer. It is necessary to adopt reasonable calculation, evaluation and analysis methods to predict productivity, which is impacted by such factors as interlayer pressure, fluid supply capacity, workstring size, and fluid properties during commingled production. Well DN5 is studied in this paper as an example. Commingled production was analyzed and studied by establishing a vertical pipe flow model for wellbore, and using a systematic analysis method, which provides a reliable analysis method for the well testing of commingled production and development.