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2021-12-25, Volume 17 Issue 4

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OIL AND GAS EXPLORATION

Study on Plugging Technology of Shizigou - Yingzhong Structural Belt in Qinghai Oilfield

LIU Fenghe , Liu Dezhi, Qiao Shijun , Xing Xing, Lei Biao, Bai Yang

2021, 17(4):  1-7. 

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Targeting the technical difficulties of well leakage in drilling Shizigou - Yingzhong structural belt of Qinghai Oilfield，geological analysis，operation difficulty summarization and study on plugging measurements are carried out. Taking well SX58 in Shizigou- Yingzhong structural belt as an example，it is found that the low pressure fracture leakage in deep E 3 2 formation is the main factor of well leakage. Based on E 3 2 formation logging data and drilling feedback，combined with 3D printing technology，a simulated fracture model has been designed and developed，and its plugging experiment evaluation method is established. Through laboratory experiments，the plugging material and plugging slurry formula are optimized，which can provide reference and guidance for the follow-up optimal and fast drilling in Qinghai Oilfield.


Rheological Properties of Water Based Micro Foam Drilling Fluids Considering the Wall Slip Effect#br#

LU Haiying, FENG Wei, ZHAO Jun, REN Tao, WANG Gui

2021, 17(4):  8-14. 

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In view of the wall slip phenomenon of water based micro foam drilling fluids，this paper develops a rheological property correction method considering the wall slip effect. The six-speed rotary viscometer was used to test the rheological properties of the drilling fluid system under different internal-external cylinder clearance conditions and Tikhonov regularization method was used to correct the experimental data to finally obtain the flow curve and slip velocity of water based micro foam drilling fluids，considering the wall slip effect. Comparison of the pre- and post- correction experimental results shows that when the shear stress exceeds a certain threshold，the slip velocity，no longer close to zero，grows with the further increase of the shear stress，and it is considered that wall slip occurs. Considerable differences are observed between the rheological parameters based on API and proposed methods—a minor difference is found in τ y ，and yet the K value declines and n value grows greatly after correction. It is indicated that the API method can accurately calculate the yield stress of water based micro foam drilling fluid，while the calculation of the n and K values shall incorporate the wall slip effect.


Study and Application of Fracturing Technology for Tight Reservoir in the Southern Margin of Junggar Basin with High Temperature，High Pressure and High Closure Stress

WEN Xianli, KONG Mingwei, LUO Yao, WANG Jian, ZHAO Chunyan, ZHAI Huaijian, WANG Rong

2021, 17(4):  15-20. 

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High-quality reservoir is developed in the deep layers of the lower assemblage of the southern margin of Junggar Basin, where embeds tremendous oil and gas resources. However，the reservoir there has a general burial depth greater than 5 700 m，a temperature greater than 130 ℃，a closure stress gradient greater than 0.02 MPa/m，an average porosity less than 10%，an average permeability less than 0.1×10 -3 μm 2 and strong heterogeneity. Due to the poor physical properties，high Young's modulus and high Poisson's ratio of the reservoir，fracturing faces great challenges in respect of fracture initiation，high pump pressure and efficient use，which present higher requirements for wellbore integrity，fracturing materials and technology. Through field study and practices，a fracturing technical system for tight reservoir with high closure stress has been developed，which is centered on the technology to reduce wellhead operating pressure and integrated with proppant combination and optimization technology and treatment parameter optimization technology. Thus，the bottleneck of the fracturing technology for deep reservoir with high temperature and pressure has been broken through. It has been successfully applied in 3 wells since 2020. After fracturing treatment，well-GQ6 has seen significant effect: the maximum daily oil production is 97.97 m 3 and the daily gas production is 2.03×10 4 m. This technical system provides new perspective for deep oil and gas exploration in the southern margin of Junggar Basin.


Study and Application of Rock Brittleness Evaluation Method Based on Compressive Deformation Characteristics

YAN Yinqiang, LI Ya , GUO Shenghao, YANG Xingyu, HAO Hongyong

2021, 17(4):  21-27. 

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There are many methods available to evaluate rock brittleness，but they are very different from each other. They are suitable for evaluating conventional sandstone reservoirs，but not for shale and conglomerate reservoirs with strong heterogeneity. Therefore，to evaluate the brittleness of strongly heterogeneous reservoirs，it is necessary to establish a static qualitative classification standard first for rock brittleness，and then to establish a connection with the quantitative brittleness characterization method. This study addresses the Permian shale oil reservoir in Jimsar area of Junggar Basin. The static Young's elastic modulus and Poisson's ratio of the cores were measured，and the curves and rock fracture forms obtained were analyzed using the crossplot method. As a result，the brittleness is divided into three types:good，moderate and poor. This study makes full use of the test data of rock mechanics to analyze the brittleness of the target interval，which provides technical support for selecting suitable fracturing fluid and technique in this area.


OIL AND GAS DEVELOPMENT

Recycle Technology of Fracturing Flowback Fluid in Sulige Gasfield

JING Jianglu, QU Gang, WEI Huiru, YAN Jie, CHEN Xiaoling, YU Wenjun, LI Shuaishuai

2021, 17(4):  36-40. 

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The fracturing flowback fluid in Sulige Gasfield is characterized by large volume，complex composition and great difficulties in treatment. After being treated by simple processes of oxidation，flocculation and sedimentation，the fracturing flowback fluid still fails to meet the standard for direct discharge or recycle. Besides，the need for storage of the treated fluid makes the operating cost increase. Therefore，more processes such as reduction and adsorption are added，so that the treated fluid can meet the standard for repreparing new fracturing fluid. Experimental results show that the concentrations of boron，calcium and magnesium ions which impair the performance of fracturing fluid in the treated fluid are obviously reduced and the quality of treated fluid is obviously improved. The re-prepared fracturing fluid system has a viscosity of 150 mPa∙s，satisfactory compatibility and gel breaking performance，and an average damage rate of about 17%. All of these indicators meet the requirements in relevant standards. In addition，the recycle technology of fracturing flowback fluid has been successfully applied in Sulige Gasfield.


Analysis of the Contact Effect Between Push-the-Rit Steerable Ribs and Sidewall

SHI Yucai, YUE Desheng, FU Chenglin, ZHANG Chen, CHEN Xuan

2021, 17(4):  41-46. 

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A theoretical analysis model of the contact between the steerable ribs of a static push-the-bit rotary steerable（SRS）drilling tool and sidewall was established on the basis of Hertz contact theory，and the distribution regularity of contact stress，as well as its relationship with different impacting factors were analyzed preliminarily. With the help of orthogonal test method，the impact of different factors in the model on the maximum contact stress was analyzed. Analysis results show that pushing force has the largest impact on the maximum contact stress，which increases almost linearly with the increase in pushing force；the impact of sidewall elastic modulus and rib curvature radius come the second，which increases with the increase in sidewall elastic modulus，and decreases with the increase in rib curvature radius；and the impact of sidewall Poisson's ratio and rib thickness are almost negligible. When SRS drilling tools are used in the field，the pushing force can be reduced properly or the curvature radius of steerable ribs can be increased properly to mitigate the risk of steerable ribs getting trapped in sidewall.


Study and Application of Trapezoidal Protection Technology for Low and Ultra-Low Permeability Reservoirs Subjected to Water Injection#br#

YOU Zhiliang, JIANG Guancheng, DONG Tengfei, HE Yinbo, SHI Haiming, ZHANG Jianguo

2021, 17(4):  47-54. 

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In the process of injecting water into low and ultra-low permeability reservoirs，serious damage to reservoirs often occurs，such as hydration swelling，water lock，and Jamin effect，increasing flow resistance and water injection pressure loss，and giving rise to high water injection pressure，rapid increasing in water injection pressure，low water absorption index，and even inability to get water injected into reservoir. As a result，reservoirs subjected to water injection have insufficient water injected into them for a long time，and the effectiveness of plugging removal measures cannot last long in such reservoirs，though they are effective. Consequently，beneficiary wells have low production and oil and gas recover percent. In order to solve this problem，it is a common practice to inject anti-swelling agent and surfactant into the injection water for a long time without interruption to mitigate the damage to reservoirs caused by hydration swelling and capillary effect. However，due to the demand for long-term injection of chemicals，production cost is high，and the effect is not so satisfactory. In this study，small cationic trapezoidal anti-swelling protectant A and trapezoidal wetting protectant B were developed and screened out based on the understanding that the hydration swelling of reservoirs is not only related to the TDS of foreign fluid，but also has a close relationship with the decrease rate of TDS. Both of them were injected into the injection water at a certain time interval and a concentration gradient from high level to low level until reservoirs were adapted to the properties of the injection water and demanded no more injection of protectants. This means that，at this point，hydration swelling and capillary effect of the reservoirs subjected to water injection were controlled. With the two

protectants，a lot of chemicals and costs have been saved，and cost-effective replenishment of reservoir energy and significant increase in the efficiency of water flooding have been achieved. This technology is referred to as trapezoidal protection technology for reservoirs subjected to water injection. Field application shows that，under the same water injection regime，the daily water injection volume of a single well was significantly increased at a lower cost，and the rise rate of injection pressure was significantly slowed down，which met the requirements of injection allocation，providing a key technology to replenish energy for low and ultra-low permeability reservoirs subjected to water injection.

Research on the Preparation of Civil Natural Gas from Oil Shale Retorting Gas by the Hydration Process

LIANGShuang, GAOFangxing, YUEGang, LIUZengqi, SUNQiang, WANGYiwei, LIUAixian, GUOXuqiang

2021, 17(4):  55-61. 

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Methane in retorting gas of oil shale is recovered and concentrated via the hydrate formation-based gas separation process to produce natural gas with the concentration satisfying the civil use standard. The optimum operating conditions of hydrate separation have been determined in the laboratory by the isothermal pressure search method using a self-built hydrate phase equilibrium experimental measurement system. Multi-stage hydrate separation experiments have been conducted under the found optimum conditions. The results show that compared with the traditional practice using a high dosage（10 wt%）of the accelerant tetrabutylammonium bromide（TBAB），a low concentration（2 wt%）of tetrahydrofuran（THF）is enough to significantly promote hydrate formation of oil shale retorting gas. The CH 4 content is improved from 15.2% to above 92% just by four-stage hydrate separation. The research results have provided the theoretical basis for the hydrate formation-based recovery of oil shale retorting gas.


The Application Status and Prospect of DTS/DAS in Fracturing Monitoring of Horizontal Wells#br#

LI Haitao, LUO Hongwen, XIANG Yuxing, AN Shujie, LI Ying, JIANG Beibei, XIE Bin, XIN Ye

2021, 17(4):  62-73. 

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The fractured horizontal well technology has been widely used in unconventional reservoir development in China，but there are still many technical problems in monitoring the fracturing performance of horizontal wells. The distributed optical fiber monitoring technology has been found with rapid progress over recent years，and developed the distributed temperature/acoustic sensing（DTS/DAS）technology，which has been widely applied to the fracturing performance monitoring of unconventional oil and gas reservoirs in the United States，Canada et al.，with good application results. In this paper，the basic principles of distributed optical fiber temperature/acoustic sensing are described，and the latest applications and research progress of DTS/DAS in fracturing monitoring of horizontal wells are summarized，including fracturing fluid distribution monitoring and leakage diagnosis，artificial fracture initiation and extension monitoring，effectiveness analysis of fracturing-based well completion，and quantitative fracture parameter interpretation. Also，the current technical limitations of the DTS/DAS technology in fracturing monitoring of horizontal wells are pointed out，and the development orientation of the distributed optical fiber monitoring technology for horizontal wells is reviewed. This paper is of great significance for accelerating the application process of the distributed optical fiber monitoring technology and improving the technical level for fracturing monitoring and evaluation of horizontal wells in unconventional oil and gas reservoirs in China.



Method for Determining Casing Confining Pressure Based on Field Casing Damage Analysis

HAN Guangyao, LIU Hailong, YU Tianxi, Li Yiqiang, HAO Lihua

2021, 17(4):  74-78. 

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Reservoir stimulation with large pump rate and high pump pressure by using production casing as injection channel is an indispensable means for the cost-effective development of shale and tight oil and gas. In order to accurately analyze the strength safety of casing during fracturing process，it is necessary to accurately determine the confining pressure load of casing. In view of the complicated situation of wells completed with production casing and the great difficulty in accurately determining the confining pressure load. field fracturing data are used to determine the confining pressure load factor of a specific section of casing by conducting inversion for the safety of production casing in wells with accidents. The analysis results show that the confining pressure load factor（MPa/100m）of
the casing in the section from intermediate casing shoe to the cement top in production casing is 0.97-1.04，which is equivalent to the pressure factor of fresh water column. Based on the study findings and considering that the effect of formation pressure on cement sheath is affected by time factor，fresh water column pressure rather than formation pressure is selected as the casing confining pressure in calculating the safety of casing under the fracturing conditions of cemented well section，which will yield a calculation result with morepractical guiding significance.


Study and Application of Quantitative Evaluation Method forExtended-Reach Well Trajectory

WANG Zan, WANG Xiaoqi, CHEN Liqiang, WU Zhanmin

2021, 17(4):  79-85. 

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At present，extended-reach well（ERW）drilling has become an important means for oil and gas exploration and development，and trajectory design optimization is the key to the successful drilling of ERW and the improvement of operating efficiency. With the continuous increase in horizontal displacement and horizontal length to vertical depth ratio，ERW drilling is facing many serious challenges. Therefore，it is necessary to comprehensively analyze and evaluate the factors affecting trajectory design，such as trajectory control ability and wellbore stability，so as to form an integrated technical thinking. In this study，a matrix of trajectory evaluation indicators was first established by analyzing the characteristics of ERW drilling technique，and then scores and weights of all indicators were determined based on expert experience. Consequently，quantitative evaluation was used to judge the selection of ERW trajectory，and applied to the ERW design in an oilfield. Drilling operations were carried out in the field strictly following the selected trajectory plan，and finally a high-quality trajectory was achieved for the whole well. The results show that the evaluation method is practicable and feasible，and provides a technical basis and guiding method for selecting the design plan of ERW trajectory.


Drilling and Completion Technology for Horizontal Well with Ultra-Long Horizontal Section in Tight Conglomerate Reservoir of Xinjiang Mahu Oilfield

LI Weixuan, SONG Lin, XI Chuanming, XIE Shiyuan, RONG Kesheng

2021, 17(4):  86-91. 

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Drilling a horizontal well with ultra-long horizontal section in conglomerate reservoir of Mahu Oilfield in Xinjiang is faced with a series of potential problems，including large drilling torque，difficult-to-control well trajectory，low ROP，weak wellbore stability and difficulty in running in completion casing. Systematic drilling and completion technology for horizontal wells with ultra-long horizontal sections in conglomerate reservoir of Mahu oilfield has been developed by means of casing program optimization，trajectory design and control，selection of featured PDC bit，high-performance oil-based drilling fluid，R&D of toughness cement，and safe casing running technique. This technology was applied to the drilling operation of Well Mahu029_H in Mahu15 Well Block，and achieved successful drilling of a horizontal section as long as 3 038 m，smooth running of casing，and satisfactory cementing quality that meets the requirements of large SRV fracturing. A new record has been created for the longest horizontal section in Mahu Oilfield，which accumulated experience for future drilling operations of horizontal wells with ultra-long horizontal sections in Mahu Oilfield，and provided references for the same type of wells in other areas of China.


TECHNOLOGY AND EQUIPMENT

Application of Running/Pulling Cable Type ESPCP in Shale Oil Production

CHU Haoyuan, ZHANG Liping, YAO Jinhang, ZHANG Jianwen, ZHANG Hui, LEI Derong, JIANG Li

2021, 17(4):  92-94. 

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Electric submersible progressive cavity pumps（ESPCP）were used in the preliminary test of Jimsar shale oil well area in Xinjiang Oilfield. The rodless pump lift technology has solved the problems of rod breaking and eccentric wear existing with rod pumps，and is well applicable to heavy oil wells with sand production. With this technology，however，it is difficult to bind cable and tubing together，and cable is readily to be damaged in the process of tripping string. Nonmetallic cable conduit and ESPCP can effectively solve the problems of difficult binding operation and cable damage，but they are difficult to run in，pull out and fish when the oil viscosity is too high. Therefore，a running/pulling cable type ESPCP lift technology was tested. During production，cable is run into well through tubing，and then connected with downhole cable connector. When the pump needs to be lifted，cable is pulled out of tubing.In this way，the tripping in and ou toperations of cable is realized by running in and pulling out through tubing.

This paper introduces the running/pulling cable type ESPCP lift system，and analyzes its field application effect. At present，this system is used in 23 wells in the shale oil well area of Xinjiang Oilfield，and the success rate of cable running，pulling and connecting is 100%. Due to its advantages of intelligent control，energyconservation，less consumption，safety and environment-friendliness，the application of this system is worth expanding.