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25 September 2022, Volume 18 Issue 3

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OIL AND GAS EXPLORATION

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Optimization and Application of Strength Criterion for Wellbore Mechanical Instability Evaluation in Drilling

YANG Hu, CHEN Hao, LI Yilin, SUN Weiguo, ZHOU Penggao

2022, 18(3):  1-5.  DOI: 10.12388/j.issn.1673-2677.2022.03.001

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There is a lack of theoretical guidance and practical optimization method for the selection of strength criteria in wellbore stability evaluation in field，which may lead to the deviation of the drilling fluid density used. The collapse pressure calculated by six strength criteria widely used in rock engineering had been compared. The results show that the collapse pressure calculated by D-Pi criterion is the highest，followed by M-C criterion，H-B criterion and D-Pc criterion；the collapse pressure calculated by LAm criterion and W-Cm criterion is in the middle. Through field practice，a set of method for strength criteria optimization and application has been summarized. Applying the optimized strength criterion to the wellbore stability evaluation in later drilling to optimize the design and use of drilling fluid density can not only ensure the wellbore stability，but also improve the drilling speed and oil and gas discovery. This method has been applied in some blocks and strata of Junggar Basin，and achieved good results，which is proved to be of popularization and application value.

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Bit Selection Based on PCA to Predict Drillability Level of Hard Rocks

KONG Xiangwei, CHEN Hao, YE Jiajie, LI Yadong, GAN Yifeng

2022, 18(3):  6-11.  DOI: 10.12388/j.issn.1673-2677.2022.03.002

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In the process of drilling through a hard formation，use of a bit unsuitable for the formation often leads to slow drilling speed and increased bit wear. Selecting a bit suitable for a formation is the key to reduce drilling cost and increase the rate of penetration. By applying such technical measures as principal component analysis （PCA），which takes the logging parameters of adjacent wells （such as natural gamma，well diameter and natural potential） as influencing factors for standard processing，and principal component reduced-dimension analysis，a mathematical model of drillability level was established for hard formation rocks. The results show that the acoustic time difference，formation density，natural gamma and resistivity are most closely related to the drillability level of rocks. It has been validated that the predicted drillability level value obtained using multivariate log-linear regression method is more than 95% in agreement with the testing result. The drill bit selected using this method was applied to the drilling operation in Fengcheng Formation. With it，the drilling footage per bit has been increased from 30 m to 150 m while maintaining the rate of penetration，thus reducing the non-operation time such as bit replacement.

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Development Status of key Technologies for Deepwater Drilling in Northern Basins of South China Sea 

WANG Yangfeng , LIU Zhiqin , LIU Xianyu , CHEN Li , AI Changming , HUANG Feiyu

2022, 18(3):  12-18.  DOI: 10.12388/j.issn.1673-2677.2022.03.003

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Due to the extremely rich oil and gas resources in deep-sea area, the deep-sea oil and gas exploration at home and abroad has been heated up in recent years. The actual drilling in northern basins of South China Sea proves that the oil and gas resources are abundant and the exploration prospect is bright. As an operator, CNOOC has completed a total number of 8 deepwater wells with the depth of 1500 m in northern basins of South China Sea, forming a complete set of key drilling and completion technologies, such as shallow disaster prevention and control, well structure design and optimization, surface conduit injection and running, formation pressure monitoring while drilling, narrow window safe operation, hydrate prevention and control, drilling and completion fluid and cementing. Mastering this set of technologies is important to promote the sustainable development of China's offshore oil industry. It is of great significance to increase oil and gas production and ensure energy security. Taking the first deepwater well completed by CNOOC as an operator in Lingshui Block as an example, this paper introduces the key technologies and application results of deepwater drilling and completion in this area. 

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Identification Method of Shale Deformation Structure Based on Whole Core CT Scanning：a Case Study of Permian Lucaogou Formation in Jimsar Sag，Junggar Basin

CHENG Leiming, LI Yifan, LU Ming, LIU Ruining, XIANG Yuankai, HAN Denglin, WANG Chenchen

2022, 18(3):  19-24.  DOI: 10.12388/j.issn.1673-2677.2022.03.004

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The development of deformed structures in shale oil reservoirs will change the physical characteristics of local rocks，resulting in flow barrier and inhibiting fluid flowing capacity，which further reduces the fracturing effect. The upper and lower sweet spots of Permian Lucaogou Formation are developed in Jimsar Sag of Junggar Basin，and contemporaneous deformation structures are widely developed in shale reservoirs. Traditional study methods are mainly based on the surface observation and the description of cores，but study on the extension mode of deformation structures in the strata and the information on adjacent strata is insufficient. In this study，a 134-meter whole shale core from a well section of Lucaogou Formation in Jimsar Sag was scanned using whole core CT to obtain its three-dimensional CT images，which were then observed for the development of deformation structure in the core，genetic type and distribution pattern. This method facilitates the identification and evaluation of geological and engineering sweet spots in shale reservoirs in the study area.

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Applicability of V150 High-Strength Drill Pipe in the Workover Jobs of Ultra-Deep Wells

PENG Xianbo, MA Dudu, WANG Feiwen, XIANG Zhipeng, MOU Yisheng

2022, 18(3):  25-30.  DOI: 10.12388/j.issn.1673-2677.2022.03.005

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As the number of high-temperature，high-pressure and ultra-deep oil and gas wells continues to increase，conventional G105 and S135 drill pipes can no longer meet the job needs of trouble wells. As a new type of high-strength drill pipe，V150 drill pipe has a performance superior to traditional steel drill pipe. To study the applicability of V150 drill pipe in the workover jobs of ultra-deep wells，basic performance parameters such as chemical composition，hardness and impact energy of V150 drill pipe samples were tested first. The test results show that all indicators of V150 meet industrial requirements. And then，the rotating bending fatigue test of V150 drill pipe in air and mud was carried out，and its S-N curve was obtained. The fatigue test results show that V150 drill pipe is highly sensitive to mud. The fracture analysis shows that the fracture of the V150 drill pipe sample is resulted from the combined action of oxygen corrosion and stress，as well as the accelerated corrosion rate due to the existence of Cl^- in mud. Finally，the actual use of V150 drill pipe was discussed in combination with the testing results. The results show that the maximum hook load to release stuck drill pipe has been reduced from 1 784 kN to 1 717 kN after the V150 drill pipe assembly was used，and the job safety factor has been increased from 1.16 to 1.41. The study in this paper can provide theoretical basis and guide for the safe use of V150 drill pipe in the workover jobs of ultra-deep wells. 

OIL AND GAS DEVELOPMENT

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Numerical Simulation for Controlling Fracture Propagation of an Infill Well with Radial Multilateral Wells

ZHANG Yupeng, SHENG Mao, WANG Bo, LI Jie, TIAN Shouceng, ZHANG Zhichao, LI Gensheng

2022, 18(3):  31-37.  DOI: 10.12388/j.issn.1673-2677.2022.03.006

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Fracturing of infill horizontal wells is one of the effective ways to improve the recovery factor of shale oil and gas. However，practices show that the production of an infill well after fracturing is generally lower than that of the parent well，and the fracturing effect is limited. The nature lies in that the fracture propagation of an infill well communicates with the pressure depletion zone of the parent wells，which makes it difficult to produce the remaining inter-well oil and gas resources. This paper proposes that radial multilateral wells be used to control the fracture propagation of an infill horizontal well，so as to increase the contact area between fractures and untapped oil and gas areas and prevent fractures from entering the pressure depletion areas of the parent well，which is expected to be a solution to the engineering problem of infill wells with poor fracturing effect. Therefore，a fracture propagation model of radial multilateral wells is established with the complicated uneven inter-well stress fields taken into account. The influence pattern of the uneven stress fields in different production phases of the parent well as well as the parameters of radial multilateral wells on the propagation of fractures are studied，and the optimal azimuth angle of a lateral borehole is selected. The results show that radial multilateral wells can effectively control the propagation of fractures in those untapped areas in different production phases of the parent well. The feasibility of controlling the fracture propagation of an infill horizontal well with multi-lateral wells is validated. The angle between a lateral borehole and the infill horizontal well is the main controlling factor affecting the forms of fractures.

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Uncertainty Analysis for the Testing Methods of Fracturing Proppant Performance

YANG Nengyu, LIANG Tiancheng, QIU Jinping, CAI Bo, YI Xinbin, YAN Yuzhong,

2022, 18(3):  38-43.  DOI: 10.12388/j.issn.1673-2677.2022.03.007

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Proppant is a key material to ensure the effect of hydraulic fracturing job and oil well production. Its quality is under the strict control of SY/T 5108-2014，an petroleum industrial standard of proppant testing. But this standard does not cover the final measurement of uncertainty. Uncertainty is of significant importance for the quality control of testing laboratories，the differences between laboratories and the differences in product characteristics. Therefore，the samples of four kinds of proppant were sent to more than 60 laboratories，and the test data obtained were used to calculate the standard deviation and uncertainty in standard repeatability and reproducibility. The results show that acid solubility and turbidity in SY/T 5108-2014 are highly uncertain，and the uncertainty increases with the increase in measured values. When the measured solubility is 7% of the critical value，and the measured turbidity is 150 FTU，the uncertainty can reach 1.5% and 13 FTU，respectively. The maximum uncertainty in crushing percentage is about 2.2%，and the uncertainty in roundness and sphericity is 0.1. The uncertainty decreases with the increase in measured values. The error of absolute density comes from systematic differences in the equipment of different manufacturers. This study provides technical support for revising the evaluation standard of proppant performance，as well as engineering and technical staff to correctly understand and apply the test results of proppant performance.

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Optimal Design of Anti-Inclination Bottom Hole Assembly in Mahu Area，Junggar Basin

WANG Ting, WANG Yingjie, MA Nengliang, WANG Yuezhi, LI Mingliang, LIU Yang

2022, 18(3):  44-53.  DOI: 10.12388/j.issn.1673-2677.2022.03.008

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Aiming at the complex formation conditions and deep oil layers in the Mahu area，the well deviation is prone to occur in the process of drilling vertical wells. Based on the two-dimensional vertical and horizontal bending beam method model and the principle of the equilibrium trend method，the author established an evaluation method for the anti-inclination and deviation-correcting ability of the anti-deviation BHA. The influences of BHA structural parameters，drilling parameters，formation parameters and bit anisotropy on the deviation correction capability of BHA are analyzed. The results show that the pendulum BHA and the tapered BHA are easily affected by the weight-on-bit；the single-bend PDM guided BHA has a relatively strong adaptability to the weight-on-bit；and the formation dip angle is the main controlling factor restricting the ability of passive anti-deflection BHA to "anti-deflect and hole straightening". Based on the analysis results，taking Well Ma52 as an example，the optimal design of the BHA was carried out to achieve the purpose of reducing the deviation，which has practical guiding significance for improving the drilling speed and saving costs in the Mahu area.

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The Effect of Active Substance in the Crude Oil of Block BW on Interfacial Tension During Chemical Flooding

LUO Teng, ABULIMITI Yiming, TUERXUN Matimu, HUANG Xinran, YIN Shuli, ZHAO Yongchang, HOU Junwei

2022, 18(3):  54-59.  DOI: 10.12388/j.issn.1673-2677.2022.03.009

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The active substance in crude oil has an important influence on the interfacial tension of chemical flooding formula. After active substance in the crude oil of Block BW in Xinjiang Oilfield was extracted，the interfacial tensions between it and petroleum sulfonate （KPS） and alkali were studied. The results show that the contents of resin and asphaltene in the crude oil are very low，and the interfacial active substance mainly exists in ethyl acetate eluent. Main components of the active substance include phenols，alcohols and carboxylic acids，which fall into two types of C_nH_2n-2O₂ and C_nH_2n-4O₂. With Na₂CO₃ added，the interfacial tension was reduced to 10^-2 mN/m. With KPS added，the interfacial tension was only reduced to 0.5 mN/m，showing a poor effect. After adding both KPS and Na₂CO₃ together，the interfacial tension was quickly reduced to 10^-3 mN/m. This is mainly because that alkali reacts with some components of ethyl acetate eluent，and an activator to enhance the performance of petroleum sulfonate is produced，which greatly reduces the interfacial tension.

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Application of Horizontal Well Conformal Coring Technology in Well Ma02

SU Tao, WANG Jiren, XIE Zhengsen, KANG Keli, CHENG Pengfei, DUAN Zhigang

2022, 18(3):  60-64.  DOI: 10.12388/j.issn.1673-2677.2022.03.010

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Well Ma02 is a horizontal monitoring well located in the fault block of well block Ma13 in Mahu Sag of the central depression of Junggar Basin. The conglomerate strata of Baikouquan Formation in this well block are broken after volume fracturing，and are very difficult for coring. For 270 m continuously coring in the horizontal section of well Ma02，there exist many uncertain factors，and it is difficult to control the trajectory. The horizontal well conformal coring technology developed by Research Institute of Engineering Technology，CNPC Western Drilling Engineering Co.，Ltd. was used，and the problem of loose and shapeless in target layer coring was satisfactorily solved^[1]. It has been proven by continuously multi-barrel coring practices that this technology can effectively improve the core recovery in horizontal sections，providing experience for coring in loose strata. The adopted tools，technical parameters，technical measures and actual application results of this coring technology are introduced in details.

Key words：conformal coring；horizontal well coring tool；trajectory control；volume fracturing

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Research Progress on String Erosion During Massive Sand Fracturing

ZHANG Sisong, ZENG Dezhi, PAN Yuting, TIAN Gang, YU Huiyong, SHI Shanzhi

2022, 18(3):  65-72.  DOI: 10.12388/j.issn.1673-2677.2022.03.011

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Massive sand fracturing is a necessary means for the development of unconventional oil and gas resources，as well as an important cause for the failure of downhole pipe strings and tools due to erosion wear. Targeted at this problem，the erosion theories and main research conclusions proposed by foreign scholars based on different materials are reviewed comprehensively，and the derivative researches into basic erosion theories conducted in China are summarized. Combined with the actual technological conditions，the main causes of serious erosion of pipe string in the process of sand fracturing are expounded. With respect to the pipe string structures and fracturing tools that are likely to be eroded in the process of massive sand fracturing，the research progress is introduced. Current research difficulties and future research direction of fracturing string erosion are pointed out，which is of important reference value and engineering significance for protecting the fracturing string against erosion and the wellbore integrity，and improving the development effect of unconventional oil and gas resources.

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Optimization of Rod-Tubing String for Rod-Pumped Wells under Polymer Flooding

WU Ruiqi, JIA Peng, XU Guangping, YANG Zhiqiang, DING Minghua

2022, 18(3):  73-76.  DOI: 10.12388/j.issn.1673-2677.2022.03.012

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In the process of polymer flooding，frequent injection and production adjustments have led to fluctuations in pay zone fluid supply and flowing pressure，and so it is necessary to adjust the pumping parameters in time acording to the working conditions of rod-pumped wells. Moreover，polymer is corrosive to rod-tubing string. The synergistic effect of corrosion and eccentric wear has led to seriously broken or disconnected of strings and shortened pump inspection period，preventive measures need to be taken. Since the start of polymer flooding in Block Qidong-1 of Xinjiang Oilfield，the downhole parameters of rod-pumped wells have been optimized by applying the self-developed calculating and analyzing computer system. A series of technologies to prevent tubing and rod corrosion and eccentric wear has been formed by independently developing anti-wear coupling，forced rotation centralizer and sucker rod connector，introducing lined tubing and providing bottom-weighted sucker rod according to wellbore trajectory. In addition，the rod-tubing string has been further improved and better protected with the development of anti-sticking，anti-leakage and anti-break oil well pump，anti-sand sticking gas separation device and new sucker rod connector. Through the application of string optimization technology，the average annual increase in oil production is 163241 t，and the average pump inspection period is extended from 235 days to 516 days，which ensures the normal and efficient production of rod-pumped wells under polymer flooding.

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The Characteristics of Water Cut Rise in Oil Wells of Narrow Banded Reservoirs and Their Influencing Factors

WANG Jijun, ZHOU Haiyan, SUN Qiang, LING Haochuan, YANG Lei, AO Lu

2022, 18(3):  77-81.  DOI: 10.12388/j.issn.1673-2677.2022.03.0013

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In view of the diversified patterns of water cut rise in a single well of narrow banded reservoirs and the difficulty in control，the regularity and main controlling factors of such water cut rise are studied by comprehensively using such approaches as statistics and gray correlation analysis based on the curve of water cut versus dimensionless recovery degree of a single well，and targeted control measures are proposed. The results show that there are mainly three patterns of water cut rise in narrow banded reservoirs：stepwise，convex and sloped rises. Among the three types，stepwise rise prevails. The duration of water-free oil production lasts long when the rise in water cut presents a convex pattern，but varies greatly when the rise presents a stepwise or sloped pattern. The innate and acquired factors affecting water cut rise mainly include oil-water viscosity ratio，channel width，formation coefficient，effective direction，fluid production intensity，and injector-producer spacing. It has been set out that the injector-producer spacing should be rationally designed according to the forms of river channels，and controlling the intensity of fluid production in the initial stage is the key to stablize oil production and control water. Moreover，different measures should be taken to stabilize oil and control water for different types of oil wells in different development stages. In 2021，measures to stabilize oil and control water were taken in wells for 22 times guided by this thinking，with an annual oil increase of 4.8×10⁴ m³ and an average water cut decrease of 1.5%. The study results can guide the execution of design for new wells，and provide a basis for the formulation of water control measures for narrow banded reservoirs. 

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Petroleum Fracturing Proppant Preparation from Industrial Solid Waste

WANG Tianxiang, WANG Sukai, ZHANG Guiyi, PU Songling, ZHANG Lipeng

2022, 18(3):  82-85.  DOI: 10.12388/j.issn.1673-2677.2022.03.014

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Under the trend of large-scale stimulated reservoir volume （SRV） fracturing，the cost of hydraulic fracturing proppants has already accounted for more than 50% of the total cost of fracturing materials. The cost of proppants for a single well has risen sharply. Nickel-iron slag is an industrial solid waste，which has a bulk density of 1.78 g/cm³，and a crushing rate of 21.8% at 52 MPa closure pressure. With adhesive agent，curing agent，modifier and other additives added，nickel-iron slag can be made into a new fracturing proppant with a bulk density of 1.62 g/cm³ and a crushing rate of 6.7% at 52 MPa closure pressure by applying multi-stage technologies for shaping，such as micro-powder processing，continuous grading granulation，and composite granulation coating. The new proppant made from solid waste not only adds an additional choice to the types of fracturing proppants，but also contributes to the control of environmental problem caused by industrial waste and the increase of its comprehensive utilization rate by breaking through the restriction of traditional hydraulic fracturing proppants to the efficient development of oil and gas fields.

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Application of Seismic-Based Casing Deformation Prediction Technology in Xinjiang Oil Field

ZHANG Liping, DU Jinling, TIAN Zhihong, XU Wenli, ZHAO Yunfeng, Aliyaha ASLIBAIK, ZHANG Yong

2022, 18(3):  86-91.  DOI: 10.12388/j.issn.1673-2677.2022.03.015

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With the application of horizontal well and hydraulic fracturing technology in the development process of shale oil in Xinjiang Oilfield，there have emerged more and more casing deformation cases，which bring huge economic loss. In addition，other problems such as abnormal fracturing operation，missing well sections and low individual well production also arise. In this paper，a relevance model is established by analyzing the geophysical response characteristics where casing deformation occurs，so that casing deformation can be predicted using the three-dimensional seismic attributes to optimize the fracturing program before a horizontal well is subjected to fracturing. Consequently，early warning for casing deformation during fracturing becomes possible after combing with monitoring results of microseismic to guide fracturing operation，which minimizes the occurrence of casing deformation，improves the effect of reservoir fracturing，and enhances the production of individual wells.

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Main Points on Engineering Design of Liquid Ethane Mother/Daughter Tank

YANG Zhaoyan, SHEN Ying, YANG Zhong, YANG Lihui

2022, 18(3):  92-96.  DOI: 10.12388/j.issn.1673-2677.2022.03.016

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In order to improve the energy utilization rate and prolong the life cycle of Xinjiang Mahe Gas Field，its processing plant has switched to adopt the cryogenic technology of "refrigeration by expander + RSV" to recover ethane. This is the first natural gas processing plant that produces liquid ethane in China. At present，there is no guidance specification on the storage of liquid ethane available in China. By drawing on the engineering experience in designing cryogenic tanks of LNG plant，and integrating actual engineering conditions，the key design points of mother/daughter tank process flow is justified and analyzed，and a series of engineering issues such as the cold insulation materials and indicators of mother/daughter tank and piping，and the calculation of safety radius for the plan layout of mother/daughter tank are made clear. Moreover，design framework is summarized，and practical engineering problems are solved effectively. This study provides guidance and reference for the application of medium-small-sized cryogenic tanks in the development construction of gas fields.