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20 June 2023, Volume 19 Issue 2

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Advances in Study on Rheology Modifier for Water-Based Drilling Fluids

SUN Jinsheng, , YANG Jie, , RONG Kesheng , WANG Ren, , QU Yuanzhi, , LIU Fan,

2023, 19(2):  1-16.  DOI: 10.12388/j.issn.1673-2677.2023.02.001

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The global oil and gas exploration is gradually moving from shallow layer to deep layer，conventional hydrocarbon resources to unconventional hydrocarbon resources，medium and high-permeability to low-permeability and low-grade，and shallow seas to deep seas. With the increasing drilling workload，fit-for-purpose drilling fluid technology is needed to provide support for high-performance drilling. High-performance drilling fluids are the key to safe，efficient，economical，and green drilling，and the drilling fluid rheology is the core parameter for evaluating the performance of the drilling fluid system. As an essential treatment agent for building the drilling fluid systems，rheology modifiers can enhance viscosity and shear，improve the yield point-plastic viscosity ratio and optimize shear thinning，so as to control the rheology of drilling fluids. In order to drive the research and development of new rheology modifiers for drilling fluids，this paper investigates and classifies the rheology modifiers for water-based drilling fluids at home and abroad，and summarizes the research results，application，and existing problems of various rheology modifiers. The future direction of rheology modifiers for water-based drilling fluid was also analyzed to facilitate the technical improvement of water-based drilling fluids.

OIL AND GAS EXPLORATION

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Study on Penetration Depth and Rock Breaking Mechanism of PDC Cutter in Different Percussion Drilling Methods

LIU Wei, XI Yan, ZHA Chunqing, GUO Qingfeng, XU Zhaohui, Wang Wei

2023, 19(2):  17-23.  DOI: 10.12388/j.issn.1673-2677.2023.02.002

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Based on actual engineering applications of conventional drilling and percussion drilling，and considering the material parameters and intrinsic model of rock dynamic mechanics，a numerical model of rock breaking of the cutters of Polycrystalline Diamond Composite（PDC） bit was established. The penetration depth，damage area，size of rock debris particles and rock breaking volume of PDC cutters under different percussive drilling models were compared and analyzed. The results show that the rock cutting pattern is very similar between the numerical simulation results and the laboratory physical experimental model of single-cutter. The penetration depth of single tooth of rotary，torsional，and combined percussive drilling increased by 19.8%，6.6% and 26.9% respectively compared with that of conventional drilling，and the combined percussive drilling saw the most significant increase in rate of penetration. When there is axial impact load during percussive drilling（such as combined percussive drilling or rotary percussive drilling），it will cause visible damage to the rocks below the cutting surface，which facilitates the “second cutting” after the drilling cutters turn 360 °，but large rock debris particles can be produced，so it is necessary to optimize the drilling fluid parameters to keep the wellbore clean. The fluctuation range of penetration depth of the cutter in torsional percussive drilling is small，which indicates that this method helps reduce the risk of bit stick-slip，and the rock debris particles produced are small which makes it easy to keep the wellbore clean. The research results are of great significance for the selection of different types of percussion drilling tools and tool parameters optimization. 

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Progress and Application of the Key Technologies of Deep and Ultra-Deep Well Cementing

YU Yongjin, XIA Xiujian, WANG Zhiguo, LIAO Fuguo, LIU Binhui, DING Zhiwei,

2023, 19(2):  24-33.  DOI: 10.12388/j.issn.1673-2677.2023.02.003

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Deep and ultra-deep reservoirs are strategic alternatives for increasing reserves and production of hydrocarbons. Recently，significant progress has been made in deep well cementing，especially for special cementing working fluid systems(such as high temperature-resistant cementing additives，cement slurry tolerant of high temperature and large temperature deferences and ultra-high temperature cement slurry)，high temperature-resistant spacer，cementing tools，and cementing technology such as precise managed-pressure cementing，gradual wellhead pressure-holding and prestressed cementing. The cement slurry and cementing technology developed independently in China have been applied to deep well cementing operations in Sichuan，Tarim and Bohai Bay and other basins，and present remarkable performance in the successful cementing operations of Well Pengshen 6，the deepest vertical well in Asia，and Well Hongxing 1，the first well in China featuring 8-section-and-8-completion，and Well Qiantan1，the well with the highest temperature in Dagang Oilfield. Nowadays，the increasing complexity of targets of hydrocarbon exploration and development leads to a series of new challenges for cementing deep and ultra-deep wells. Consequently，it is necessary to strengthen the research on the basic theory，key materials，working fluid system，functional tools and technologies for cementing deep and ultra-deep wells，so as to provide more powerful technical support for deep and ultra-deep oil and gas exploration and development.

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A Global Review of Technical Status and Development Trend of Drilling Fluids for Deep and Ultra-Deep Wells

LIU Fengbao, SUN Jinsheng, WANG Jianhua

2023, 19(2):  34-39.  DOI: 10.12388/j.issn.1673-2677.2023.02.004

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Drilling fluid is the core technology of deep and ultra-deep drilling and completion，and is one of the key technologies determining the success of a drilling operation. In this paper，the difficulties facing drilling fluids of deep and ultra-deep wells were analyzed，including wellbore instability，failure of drilling fluids at high-temperature and high-salinity conditions，high friction and environmental protection. Moreover，the latest technical progress of water- and oil-based drilling fluids in both China and other countries was reviewed. It was concluded that there are still large technical gaps in temperature and salinity resistance of drilling fluids between domestic drilling fluid systems and foreign advanced technologies，and therefore，it is urgent to strengthen research and development  efforts in terms of failure mechanisms of drilling fluid agents，anti-ultra-high-temperature drilling fluid agents and supporting technologies for special formations.

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Integration of 1D Geomechanics and 3D In-Situ Stress Numerical Computation：Methodology and Application

SHEN Xinpu, XIANG Dongmei, WU Xingyong

2023, 19(2):  40-48.  DOI: 10.12388/j.issn.1673-2677.2023.02.005

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There are two major difficulties in safe drilling of a new block in the southern margin of Junggar Basin：the first is the lack of logging data，which makes it impossible to calculate pore pressure values using a conventional method；the second is that the anticline structure has complex stress variations locally and it is hard to give accurate stress values through a single-well in-situ stress analysis. In order to overcome the two difficulties，this paper puts forward a method for pore pressure and drilling fluid weight window predictions based on 3D in-situ stress numerical solutions. It has been successfully applied in the drilling operation of LT1，a high-pressure gas well in Tugulu anticlinal block in the south margin of Junggar Basin. The structural details derived from the seismic formation data were introduced into the calculation model of the 3D in-situ stress field of the block to obtain the accurate numerical solution of its 3D in-situ stress. The predicted formation pore pressure values and drilling fluid weight windows were calculated accordingly. The predicted formation pore pressure data covering LT1's total depth of 8，000 m were given according to the numerical results of the 3D in-situ stress field with the velocity data of intervals，and the corresponding drilling fluid weight windows for safe drilling were calculated，thus providing theoretical guidance and accurate reference data for performing the drilling operation of this well safely，quickly，and excellently. The successful drilling operation of LT1 shows that the method proposed here is effective and the predicted pore pressure and drilling fluid weight window data are accurate.

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Application of Deflection Control While Fast Drilling in Kuqa Foreland Area

LIANG Hongjun, LIU Hongtao, YAN Hui, CHEN Kaifeng, YANG Junqi, ZHOU Zhi

2023, 19(2):  49-55.  DOI: 10.12388/j.issn.1673-2677.2023.02.006

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The main geological characteristics of the Kuqa Piedmont area are thrusting nappe structure，featuring wide changes of stratum lithology and many interbeds. Traditional drilling assembly delivers low rate of penetration and make it difficult to achieve deflection control while fast drilling. After the vertical drilling system was introduced，many problems occurred，for example，the tools had no signals in downhole operation，the deflection control effect was poor and the daily cost was very high. In order to solve these problems，high-efficiency Polycrystalline Diamond Compact（PDC） bit + high-torque bending screw were used in Bozi 34 well. Compared with the PDC bit + PowerV rotary vertical drilling used in adjacent Bozi18 well，the footage of a single bit was increased by 74% and the average rate of penetration rose by 116%. Combined with MWD real-time monitoring，it improves rate of penetration and reduces well deflection，while also significantly cuts drilling costs，contributing to the efficient exploration and development of oil and gas resources in the Kuqa foreland area.

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Application of High-Temperature Resistant and High-Density Oil-Based Drilling Fluid in Well DS1

CUI Xiaobo, ZHANG Jiaqi, YAN Lili, ZOU Jun, YANG Haijun, LIU Zheng

2023, 19(2):  56-61.  DOI: 10.12388/j.issn.1673-2677.2023.02.007

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Well DS1 is a 6-interval exploratory well on DS buried structure in the Southern Sichuan Basin，with bottom hole temperature as high as 197 ℃. The well had some technical problems with the oil-based drilling fluid used，such as the difficulty in controlling its rheology and stability under high-temperature and high-density conditions，the difficulty in carrying cuttings under high-temperature and low-density conditions，and high risk of wellbore instability. A high-temperature resistant and high-density oil-based drilling fluid system has been formed by developing nano high-temperature resistant suspension agent，and combining with emulsifier，shear strength-improving agent，fluid loss reducer and other treatment agents. Experiments show that nano high-temperature resistant suspension agent can form a three-dimensional network structure in oil-based drilling fluid due to its "emulsification effect" and "small-size effect"，and significantly improve the stability of oil-based drilling fluid at high temperatures. The oil-based drilling fluid system has no obvious precipitation after standing at 200 ℃ for 7 days，and its settling stability and cuttings-carrying capacity have been significantly improved at high temperatures. The system has been successfully applied in well DS1. Because of its excellent settling stability at high temperatures and satisfactory slim hole cuttings-carrying capacity，the system has broad prospect for popularization and application in high-temperature deep wells. 

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Advances in Study on Temperature-Resistant and Salt-Tolerant Fluid Loss Reducers for Water-Based Drilling Fluids

YUAN Yuehui, QU Yuanzhi, GAO Shifeng, RONG Kesheng, YE Cheng, LIU Kecheng

2023, 19(2):  62-68.  DOI: 10.12388/j.issn.1673-2677.2023.02.008

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The high-temperature and high-salinity environment in deep well drilling can lead to failure of drilling fluid performance，causing well collapse，lost circulation and other accidents，resulting in reduction of drilling safety and efficiency. As one of the most important additives in the drilling fluid system，the fluid loss reducer can reduce filtration through gel protection，viscosity increase and plugging，minimize damage to the formation and maintain the stability of the wellbore. With the continuous increase of deep and ultra deep well operations in China，more and more high-temperature and high-pressure formations，salt gypsum formations and other harsh formations have been encountered during drilling. The research and development of temperature-resistant and salt-tolerant fluid loss reducers has become the key to addressing the challenges in enhancing the drilling fluid technology for high-temperature and complex wells. Three types of water-based drilling fluid loss reducer were described in this paper，including the fluid loss reducers made of natural polymers and modified materials，synthetic polymers and inorganic/organic composites. It summarizes the recent research results of temperature-resistant and salt-tolerant fluid loss reducers for water-based drilling fluids in terms of raw material composition，synthesis（modification） method and product performance，discusses the future development direction of temperature-resistant and salt-tolerant fluid loss reducers for water-based drilling fluids in China，and provides theoretical guidance for the development and application of temperature-resistant and salt-tolerant fluid loss reducers. 

OIL AND GAS DEVELOPMENT

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Experimental Research and Application of VHSD Dilatation Stimulation in Shallow Heavy Oil Reservoirs

ZHANG Liwei

2023, 19(2):  69-74.  DOI: 10.12388/j.issn.1673-2677.2023.02.009

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In the late development stage of heavy oil reservoirs by steam injection huff and puff，the vertical well + horizontal well pattern steam drive （VHSD） is considered an effective way to sustain the recovery of mature heavy oil blocks. However，due to the interlayer distribution，low formation pressure coefficient，and the presence of steam channels in mature heavy oil blocks，the resultant oil gain of this method is unsatisfactory. The SAGD dilatation stimulation technology for heavy oil recovery can effectively break through the interlayers between injection well and production well and improve the overall production degree of the reservoir. Therefore，it is necessary to perform in-depth investigation of the dilatation technology for heavy oil reservoirs in the context of the VHSD. A one-dimensional core dilatation experiment was carried out，and the results showed no considerable post-dilatation variation of the core porosity and yet，an increase in the effective permeability by about 200 times. Based on large scale three-dimensional physical modeling，a dilatation experiment under the VHSD well pattern mode was carried out. The experiment shows that：（1） When the horizontal well trajectory is parallel to the direction of the maximum principal stress，the dilatation area is larger；（2） The distance of less than 35m between the vertical well and horizontal well is conducive to the formation of the combined dilatation zone；（3） After the high-permeability channels are plugged，an effective dilatation zone can still be formed. The experimental results are applied to the field practice，which shows that the recovered degree of the horizontal section of the production horizontal well is increased by more than 15% and the well production is effectively improved. This research provides effective references for the optimization of key parameters of the dilatation stimulation of heavy oil reservoirs，and is of great significance for the continuous efficient development of mature heavy oil blocks.




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The Law of Gas-Liquid Two-Phase Seepage for Workover Gas Injection Huff and Puff Production Recovery in Low-Pressure Gas Wells

LIU Lili, XIE Yingming, LI Yuzhan, Cao Yi, Zeng Shunpeng

2023, 19(2):  75-81.  DOI: 10.12388/j.issn.1673-2677.2023.02.010

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For the gas injection huff and puff process used for the workover and production recovery in low-pressure gas wells，accurate prediction of the law of gas-liquid two-phase seepage is the key to efficient production recovery. Based on the development status and production recovery of gas wells in the Longhuishan-Tieshan block，the pore type and pore-fracture type reservoir short cores from the Member 3 of the Feixianguan Formation were selected to conduct core flooding experiments and study the law of gas-liquid two-phase seepage. The experimental data were normalized to form a standard chart of the gas-liquid two-phase seepage curve. A hypothesis was established for the seepage characteristics of pore-fracture reservoirs，and a correction method for the gas-liquid two-phase seepage curve was proposed by considering anisotropy，and corrections were made to the corresponding chart. The corrected gas-liquid two-phase seepage curve of fractured carbonate reservoirs better mirrors the gas-liquid two-phase seepage pattern. The saturation of the bound water in pore-fractured reservoirs is lower than that in the pre-corrected curve，with a larger actual co-infiltration range and higher displacement efficiency. This research provides the theoretical basis for the development of pore-fracture carbonate gas reservoirs.

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Design Method and Implementation of Oil and Gas Supply Chain System for Digital Economy Web 3.0

WEI Liyao, LI Yichang

2023, 19(2):  82-87.  DOI: 10.12388/j.issn.1673-2677.2023.02.011

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Digitalization is a new trend in the development of human society today，and digital economy has become a key differentiator in the new landscape of international competition. The volume of oil and gas trading between China and the countries along the "Belt and Road" routes is huge，but the management model for cross-border oil and gas supply chain is rather outdated，handicapped by high cost，low efficiency，long cycle and high risks. To solve these problems，this paper proposes a blockchain-based oil and gas supply chain system designed for massive heterogeneous supply chain data. The prototype system based on Springboot framework and Thymeleaf engine template was implemented，which verified the effectiveness of the system. The experiment shows that the storage overhead of massive heterogeneous supply chain data in this system is about 16.7% of the conventional blockchain storage overhead. This paper provides reference for relieving the storage pressure of blockchain nodes and building a large-scale supply chain system that meets the needs of cross-border oil and gas trade. 

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Application of Differential Pressure Power Generation Technology in Shallow Cooling Treatment of Natural Gas

RONG Shaojie, CHEN Pu, WANG Huaibo, LIU Baichun, CHEN Yuntao

2023, 19(2):  88-94.  DOI: 10.12388/j.issn.1673-2677.2023.02.012

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Some gas fields with lean gas（i.e. lean gas fields） usually use dew-point controlled shallow cooling process in early-stage development. During shallow cooling，the J-T valve is used for throttling refrigeration，and at least 2.5~3.0 MPa of pressure energy is wasted on the J-T valve. In order to make full use of the pressure energy of natural gas and improve energy utilization，this paper explores the application of differential pressure power generation technology in the shallow cooling unit of natural gas based on the application of natural gas differential pressure power generation technology and the key equipment，taking the shallow cooling unit of Kelameili Gasfield of Xinjiang Oilfield as an example. It also demonstrates the feasibility of using turbine expander to generate electricity in natural gas shallow cooling unit. The results show that：according to the calculation results of power generation potential，a 150×10⁴  m³/d shallow cooling equipment can generate 350 kW·h per hour and 280×10⁴ kW·h per year，saving 1.092 million yuan by using a turbine expander to generate electricity with the pressure difference of 2.0 MPa of wet gas. The total project investment is estimated to be 4 million yuan，and it can be paid back in 3.6 years. It is concluded that using the pressure difference in the shallow cooling process of natural gas for power generation can not only fully utilize the pressure energy of natural gas，but also supplement the power supply for the site. It demonstrates good energy saving and emission reduction results and sets an excellent example，which can be promoted in the upstream oil and natural gas fields.