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25 March 2022, Volume 18 Issue 1

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EXPERT VIEWPOINT

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Summary for Machine Learning Algorithms and Their Applications in Drilling Engineering

LI Hongbo, LUO Pingya, BAI Yang, LI Daoxiong, CHANG Shuang, LIU Xinguo

2022, 18(1):  1-13.  DOI: 10.12388/j.issn.1673-2677.2022.01.001

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In this era of Internet and Big Data，the application of machine learning，which is the core of artificial intelligence，in drilling engineering represents a general future development orientation. Drilling engineering is an essential part of hydrocarbon exploration and development technology. Machine learning-based drilling parameter optimization and accident prediction and warning are vital for economy，safety，efficiency，and environmental-friendliness. Given that it is hard to effectively guide the drilling operation for deep and ultra-deep wells using the previous experience and data，this research summarizes the present algorithms used in machine learning first，and gives a preliminary analysis for the benefits of machine learning in drilling engineering consequently. A review of global studies on applications of machine learning in drilling engineering is presented and the challenges are identified. Some suggestions are proposed，in an attempt to promote contributions of machine learning in the development of drilling engineering of China.


OIL AND GAS EXPLORATION

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Intelligent Prediction for Rate of Penetration Based on Support Vector Machine Regression

SONG Xianzhi, PEI Zhijun, WANG Pantao, ZHANG Gonglingyan, YE Shanlin

2022, 18(1):  14-20.  DOI: 10.12388/j.issn.1673-2677.2022.01.002

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Tarim Basin is rich in deep oil and gas resources. With the increase in well depth，however，formation drillability decreases
and abrasiveness increases，resulting in low rate of penetration (ROP) and high drilling cost. Therefore，there is an urgent need for drilling optimization technology. ROP prediction is a key technology to optimize drilling. Accurate ROP prediction provides important basis for drilling parameter optimization and drilling tool selection. This study establishes several intelligent prediction models based on decision tree regression algorithm，random forest regression algorithm，support vector machine (SVM) regression algorithm and deep neural network respectively，by using the mud logging data acquired in real time from the drilling field，which are then compared and analyzed in aspect of root-mean-square error，R square，maximum error and relative error，so as to select the optimum prediction model for ROP prediction. The results show that SVM prediction model is superior to other models regarding prediction accuracy and stability.
Key words:rate of penetration；machine learning；support vector machine；neural network


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General Algorithm and Programming to Determine the Rheological Parameters for Drilling Fluid

WEI Kai, YAN Liangzhu, FANG Qiongyao , SONG Bokai

2022, 18(1):  21-25.  DOI: 10.12388/j.issn.1673-2677.2022.01.003

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The determination of rheological parameters and the optimization of rheological pattern are the basis of drilling fluid design and circulating pressure loss calculation. For drilling fluid model of nonlinear rheological pattern，a regression model of nonlinear rheological pattern is established based on Gauss-Newton method and the readings of a six-speed viscometer. According to the relevant parameter R to measure the deviation relationship，matched computing software to select the rheological pattern for drilling fluid is developed with C# as the programming language，which outputs the rheological curve of each rheological pattern. Validation is also made by integrating with the measured data. The algorithm can determine the rheological parameters for drilling fluid of nonlinear rheological pattern，and select appropriate rheological pattern by comparing the correlation coefficient，which provides an effective tool for quickly selecting rheological pattern for drilling fluid.

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Wellbore Instability Mechanism and Countermeasures of High-Temperature Organic-Matter-Rich Reservoirs in the Southern Margin of Junggar Basin

2022, 18(1):  26-31.  DOI: 10.12388/j.issn.1673-2677.2022.01.004

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In the southern margin of Junggar Basin，wellbore instability has been perplexing the on-site drilling operation，because of the extremely complex geological conditions. In recent years，oil-based drilling fluid，characterized by its high shale/mudstone inhibition and good thermal stability，has been applied in the southern margin，which yet fails to effectively solve the wellbore instability issue. In this paper，the experimental methods such as X-ray diffraction and scanning electron microscopy are used to analyze the physical and chemical properties of rock samples in the unstable well section in the southern margin，including the bulk rock and clay mineral composition，organic matter characteristics，and microstructure characteristics. By doing so，the causes of wellbore instability of high-temperature organic-matter-rich reservoirs in the southern margin are identified and the wellbore instability mechanism in the case of oil-based drilling fluid is clarified. The unstable formation features high content of clay minerals and organic matter，and extensive development of beddings and micro fractures. Oil-based drilling fluid （with pH > 9） enters the formation，driven by the capillary force，which results in high-temperature alkali corrosion and a large number of dissolution pores. These corroded features lead to an uneven stress distribution in rock and the rock compressive strength degrades. Consequently，wellbore instability occurs and the borehole wall collapses. Given the aforementioned understanding，technical countermeasures are proposed.

OIL AND GAS DEVELOPMENT

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Analysis of Turbidity Testing Methods and Property Evaluation for Hydraulic Fracturing Proppants

LIANG Tiancheng, YANG Nengyu, CAI Bo, MENG Chuanyou, YI Xinbin, YAN Yuzhong, HUANG Xin, TANG Jianhua

2022, 18(1):  32-37.  DOI: 10.12388/j.issn.1673-2677.2022.01.005

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Hydraulic fracturing is one of the most effective technology for increasing production of uncoventional reservoirs. Turbidity is a key technical property for proppant evaluation. However，the current standard test method in China is different from the international test method，which impacts proppant optimization in hydraulic fracturing treatments in China. In order to improve proppant testing proficiency in China，this paper systematically investigates the influences of the procedures of sampling and sample preparation，liquid sampling position，and turbidity meter on the test value of turbidity. Moreover，considering the physical and chemical properties of suspended particles that affect proppant turbidity，the effects of turbidity on fracture conductivity and reservoir damage are studied. The influencing factors on conductivity and permeability during turbidity testing have been proposed.These studies have important implications for understanding proppant turbidity and proppant optimization and help to reduce costs for proppant manufacturers.

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Application of Cableless Intelligent Separate Injection Technology for Water Injection Wells in Subei Oilfield

CAO Liyuan, LIN Gang, LIU Xiaowen, HAN Chao, LIANG Zhen

2022, 18(1):  38-41.  DOI: 10.12388/j.issn.1673-2677.2022.01.006

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In order to improve the effect of separate water injection and the efficiency of testing，and reduce the volume of testing and adjustment jobs，cableless intelligent separate injection technology has been applied in Subei Oilfield for testing. This technology realizes remote cableless control for downhole intelligent water allocator，makes real-time and accurate testing and adjustment for separate water injection volume，and monitors separate injection pressure and other downhole data and parameters in real time，eliminating the job of running in instrument for testing and adjustment required by traditional concentric separate injection technology. The use of Y341 water injection packer，which allows backflushing of well，and inner anticorrosive coated tubing provides high reliability for the cableless intelligent separate injection string. The field testing in well N2-19 is successful with satisfactory application effect. The technology is worth spreading.

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Study on Geological-Engineering Sweet Spots Based on the Source Reservoir Configuration

WEI Zhipeng, HAO Pengling, LIU Zixiong

2022, 18(1):  42-47.  DOI: 10.12388/j.issn.1673-2677.2022.01.007

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Source rocks provide an important material basis for hydrocarbon accumulation. In particular，the favorable source-reservoir
configuration is one of the key factors for hydrocarbon accumulation of tight oil. In this paper，a case study is performed for the uncon ventional tight C8 reservoir in the HD area of Ordos Basin. Through the evaluation of the hydrocarbon generation capacity of source rocks and the investigation of the law of reservoir combination，four source-reservoir configuration models are identified. Moreover，the built models，combined with the engineering factors affecting productivity，are used to comprehensively identify the“source rock-geology-engineering-integrated”sweet spots and clarify the hydrocarbon enrichment regularity，in an attempt to provide guidance on the development and production.


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Research and Practice of Horizontal Wellbore Cleaning Technology

LI Zhenchuan , YAO Changshun , HU Kaili , LAN Zuquan

2022, 18(1):  48-53.  DOI: 10.12388/j.issn.1673-2677.2022.01.008

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In recent years，the large-scale development of unconventional oil and gas resources in China has led to a sharp increase in the number of horizontal wells. Due to the lack of scientific and systematic understanding on horizontal well bore cleaning，drilling process in horizontal section often appears stuck，completion ahead of schedule，disability of running casing to the predetermined well depth. In addition，poor wellbore cleaning can also cause very high implicit costs，including ROP controlling，increasing time consumption of reaming，circulation，and tripping. In this paper，by clarifying the mechanism of cutting migration in different sections of horizontal wells，analyzing the key elements of wellbore cleaning and proposing a method to evaluate wellbore cleaning by monitoring actual drilling friction，a set of efficient horizontal wellbore cleaning technology has been formed. Field practice in Mahu and Jimsar shale oil has verified the technical theory based on field data，which can guarantee the cleanness of horizontal section under the conditions of existing domestic equipments and instruments，and greatly ruduce inefficient production time consumption such as mud circulation and wiper tripping to increase speed and efficiency.

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Study and Test of Individualized Bit for the Horizontal Sections of Glutenite in Xinjiang Oilfield

WANG Xindong, WU Zhi, YAO Changshun, LI Yingxin, ZHANG Wutao, XIE Zhengsen

2022, 18(1):  54-58.  DOI: 10.12388/j.issn.1673-2677.2022.01.009

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Mahu tight conglomerate oil field in Junggar Basin is a key area for Xinjiang oilfield to increase production. In the horizontal sections of glutenite in Aihu well area of Xinjiang Oilfield with strong heterogeneity and poor drillability，a drill bit has only a short footage and a high decommissioning rate，giving rise to long-time drilling. In view of the long drilling period there，formation lithology，drill bit usage and drilling parameters of the drilled wells were analyzed and studied，and a new type of individualized PDC bit was designed and developed. Packaged with optimized drilling parameters and drill string assembly，a technical scheme based on the new bit to improve the drilling speed was formulated. After the application of this new bit to the drilling in glutenite horizontal sections，mechanical penetration rate increased by 137.46% and footage increased by 32.7~153.3%，compared with the average parameters per bit in this block. Field application shows that the new individualized PDC bit specially designed is highly targeted，and the packaged technical scheme to increase drilling speed is reasonable. With this scheme，mechanical penetration rate and footage for one run of bit were significantly improved，and drilling period and cost were reduced，laying a sound foundation for the development and application of individualized bits similar to this application.

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Study on the Application of Key Horizontal Well Drilling Technologies in Water-Sensitive Channel Sand Reservoir

CHENG Pengfei

2022, 18(1):  59-65.  DOI: 10.12388/j.issn.1673-2677.2022.01.010

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Reservoirs in well block Fudong5 are typical of highly water-sensitive channel sand bodies. The target Toutunhe Formation has a structure of sand-in-mud. With a clay mineral content as high as 27%～31% and a montmorillonite content as high as 56%～82%，the formation is highly water sensitive. Due to the strong water sensitivity，there is a high requirement for wellbore stability during drilling. Because of the high montmorillonite content，the rocks are very likely to become hydrated and swell，causing wellbore sloughing or collapse. The formation is likely to absorb water and swell，which changes the overall strength of mudstone，and causes wellbore instability. In the early stage of drilling，water-based drilling fluid was used，mudstone was very likely to swell，collapse，which caused sticking，backfilling，sidetracking and other drilling troubles many times. In this paper，the technical problem that has restricted the horizontal well drilling in the highly water-sensitive channel sand bodies in well block Fudong5 is solved by using such technogies as oil-based mud，borehole cleaning，real-time optimization and analysis of drilling parameters，and safe running of drillstring，which is of certain reference significance for accelerating the high-efficiency evaluation and massive development of water-sensitive channel. 

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Status and Prospect of Technologies to Reduce Cost and Increase Efficiency for Drilling in Bohai Oilfield

WANG Zan, WANG Xiaoqi, CHEN Liqiang, WU Zhanmin, SUN Lei

2022, 18(1):  66-72.  DOI: 10.12388/j.issn.1673-2677.2022.01.011

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Bohai Oilfield is an important support for increasing offshore oil and gas reserves and production in China. In view of the complex geological conditions，the coexistence of multiple pressure systems，poor wellbore stability，highly risky drilling operation，and the great difficulty in comprehensively improving inefficient wells in Bohai Oilfield，an analysis and study of the system of innovative technologies to improve drilling speed and efficiency are conducted with safe drilling operation as the criterion. These technologies have been applied successfully in field，which include the wellbore stability study-based extreme extending techology for ERW，the technology of twin holes in monobore to use the slot more efficiently，the well structure optimization technology to minimize casing stages and sizes，the dynamic comprehensive analysis and optimization technology for coated tubulars，and the decision-tree model-based refined sidetracking technology. The future development trend of reducing cost and increasing efficiency for drilling in Bohai Oilfield is also looked into in order to provide technical reference for the efficient development of Bohai Oilfield. 

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Productivity Model of Fractured Horizontal Wells in Shale Oil Reservoirs with Bedding Fractures Considered

CHEN Xi, LIU Ruining, XIE Bobo, PAN Yuting, HE Xiaodong

2022, 18(1):  73-79.  DOI: 10.12388/j.issn.1673-2677.2022.01.012

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Horizontal well fracturing is a key technolohy for the commercial exploitation of shale oil reservoirs，and the productivity after fracturing has always been the study focus of many scholars. A traditional shale oil productivity model ignores the influence of bedding fractures formed during fracturing on productivity. In response to this problem，the related theory of embedded discrete fracture model is introduced to establish a three-dimensional horizontal well productivity model for shale oil reservoirs with bedding fractures considered. The model is discretized based on finite-difference，and the pressure distribution and typical productivity curves in reservoir matrix and fractures are obtained by MATLAB programming. The influence of permeability and fracture density on shale oil productivity is analyzed. Studies show that productivity increases with the increase in the permeabilities of bedding fractures，and with the increase in the density of bedding fractures. When the permeability of bedding fractures is relatively high and developed，great error will be resulted in if no bedding fractures are included in the productivity model. The model in this paper is of important practical significance for accurately predicting the productivity of shale oil reservoirs after fracturing. 

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Exploration into and Practices of Low-Cost Volume Fracturing in Well Block X

LIU Kaixin, ZHENG Weijie, DAI Liya, PAN Liyan, ZHANG Long, CAI Guoqing

2022, 18(1):  80-85.  DOI: 10.12388/j.issn.1673-2677.2022.01.013

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The reservoir of Triassic Karamay Formation in well block X was developed by vertical well water injection in the early stage. As a result，the injection effect was insignificant，the production declined fast，and the overall recovery factor was low. In order to fully produce the remaining oil resources in the block，the original development mode was changed to horizontal well volume fracturing in 2018. The first well executed in 2019 was subjected to annulus fracturing using coiled tubing with a bottom packer，and the initial production of single well after fracturing was increased by 11.5 times compared with that of a vertical well. That validated the feasibility of increasing the production of horizontal wells. In order to satisfy market demands，field tests have been carried out in this block since 2020. Annulus fracturing using coiled tubing hydraulic jet has been gradually substituted by staged fracturing with bridge plug perforating，and the fracturing fluid has been changed from guar gum gel to guar gum slick water. A set of low-cost volume fracturing technologies has been developed. The application results show that: ①the 13 horizontal wells put into production using different technologies have all achieved design productivity; ②uneven fracture initiation can be improved by using bridge plug staged perforating + uneven distribution of perforations; ③insufficient sand-carrying capacity of guar gum slick water can be made up for by increasing the injection rate to ensure safe sand filling during field treatment; ④low-cost volume fracturing technology can reduce the fracturing cost by nearly 30%.

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Overview of Oilfield Microbial Technology Research and Application

REN Hongda, ZHAO Yongchang, MA Zehua, LUO Teng, SUN Xize

2022, 18(1):  86-89.  DOI: 10.12388/j.issn.1673-2677.2022.01.014

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The development of most oilfields in China is challenged by such problems as low recovery factor，serious wax formation in wellbore and pipelines，and insufficient gel breaking during stimulation for low-temperature reservoirs. Microbes are widely used in oilfield development due to the properties of their metabolic products. This paper makes an overview of the research of microbial technology and its application in oilfields in respect of enhanced oil recovery （EOR），wax removal and control，and fracturing fluid gel breaking. The paper explains the mechanism of microbial technology in three areas，summarizes the advantages and disadvantages of the application of microbial technology in oilfields，and makes an outlook for the research focus of microbial technology in future oilfield development.

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Discussion on the Feasibility of Applying GNSS Elevation Survey Technology to Oil and Gas Field Engineering

JI Changfei, JI Mo, WEI Tiancheng

2022, 18(1):  90-96.  DOI: 10.12388/j.issn.1673-2677.2022.01.015

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Aiming at the low accuracy of GNSS elevation survey in oil and gas field surface engineering，factors contributing the field survey errors when using satellite positioning technology are analyzed，and their attributes are briefly commented by describing GNSS static survey principle，GNSS dynamic survey principle and survey adjustment theory. With the help of the calculation principle for GNSS elevation conversion and the theory of survey error propagation，key error factors in the process of calculation are analyzed，and the empirical formula commonly used in oilfield survey engineering for elevation fitting is derived using the least-square method of mathematical inversion theory. Based on the experience in oil and gas field survey，and with relevant technical regulations referenced，measures for controlling error factors during survey are summarized. The source of GNSS elevation survey errors and their influence are verified through project cases，and the conclusions are analyzed. Views on the effectiveness and limitations of applying GNSS elevation survey to oil and gas fields are proposed to guide the smooth execution of similar jobs.