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06 March 2024, Volume 20 Issue 1

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EXPERT VIEWPOINT

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Research Status and Development Proposal of ROP Improvement Technology with Percussion Rock-Breaking Method

LI Gensheng, MU Zongjie, TIAN Shouceng, HUANG Zhongwei, SUN Zhaowei

2024, 20(1):  1-12.  DOI: 10.12388/j.issn.1673-2677.2024.01.001

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Enhancing the rate of penetration （ROP） is crucial for optimizing the efficiency of oil and gas development and deep exploration in China and ensuring national energy security. The percussion rock-breaking drilling technology has been applied in oil fields at home and abroad，resulting in significant improvements in ROP. Further research efforts are expected to address the technical challenges of low drilling footage and limited ROP enhancements encountered during deep exploration of hard rock formations with high temperature and pressure. This paper presents and analyzes the practice and development trends of the drill bit percussion rock-breaking drilling technology assisted by axial percussion，torsional percussion，and axial-torsional coupled percussion. It illustrates that the percussion-assisted drill bit rock-breaking mechanism is the core of percussion rock-breaking ROP improvement technology. This paper also reviews the scientific advancements made by domestic and overseas research scholars in physical experiments，theoretical modeling，and numerical simulation of percussion-assisted drill bit rock-breaking. In addition，it offers relevant proposals for the development of percussion rock-breaking ROP improvement technology，i.e. advancing research on material structure optimization design，intelligent control，integration of multiple technologies，and optimization of well applications. This is expected to provide valuable insights for enhancing the drilling efficiency in energy development of our country.

OIL AND GAS EXPLORATION

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A Machine Learning-Based Bridging Particle Size Recommendation Method for Lost Circulation Control

LIU Fan, LIU Yushuang, ZHANG Zhen, LI Yongjian, LIU Ce, MA Zhihu,

2024, 20(1):  13-20.  DOI: 10.12388/j.issn.1673-2677.2024.01.002

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Lost circulation is a key technical challenge in oil and gas exploration，and bridge plugging is the most commonly used method for lost circulation control. As an important parameter，the size of bridging particles directly affects the plugging. At present，the size selection mainly relies on experience，lacking a scientific and effective method. In light of this，this paper investigates a particle size recommendation method for lost circulation control based on machine learning algorithms. The basic data used for this method are well-logging，mud logging，and lost circulation control data from 126 completed wells in Kuqa piedmont area of Tarim Basin. The input layer adopts 23 main parameters screened based on the Pearson algorithm，and the output layer is in 4 bridging particle size ranges of 0-750 μm，750-1 500 μm，1 500-4 000 μm and＞4 000 μm. 10 commonly used machine learning algorithms are trained and tested to determine the accuracy of three types of datasets：well logging data，mud logging data，and combination of the former two types. It is found that the scores of each algorithm for the well logging + mud logging dataset are generally higher than those for the well logging and mud logging datasets. For the combined dataset，the support vector machine and extremely randomized trees algorithms have the highest F1 scores of above 0.9. The bridging particle size recommendation model based on the support vector machine and extremely randomized trees algorithms is validated twice on a well in Kuqa piedmont area. The predicted results of bridging particle size of the two algorithm models are consistent with the actual bridging effect in the field. This method exhibits good application prospects in the scientific optimization of bridging particle size.

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Prediction of Bedding Fractures in Shale Reservoirs Based on Two-Step Matching Core-Logging-Seismic Information

LI Jiacheng, TIAN Gang, WANG Junchao, ZHANG Teng, TONG Liang

2024, 20(1):  21-30.  DOI: 10.12388/j.issn.1673-2677.2024.01.003

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The key to breakthroughs in shale oil exploration and development lies in the characterization and prediction of reservoir bedding fractures. The complexity of its genetic mechanism and the diversity of influencing factors have led to bottlenecks in the prediction technique. Based on the identification of bedding fractures at core and thin section scale （~ mm），and evaluation of bedding fractures through resistivity imaging and at conventional logging scale （~ m），it is found that the bedding fractures in the sweet spot section of Lucaogou Formation in Jimsar Sag are the most developed in dolomite reservoirs，followed by dolomite siltstone and argillaceous siltstone. These fractures are predominantly found in the distribution area of tight reservoirs and exhibit a significant negative correlation with reservoir matrix porosity. Furthermore，combined with the lithology distribution predicted by 3D seismic data and the porosity distribution from inversion，this study investigates the technique for predicting bedding fractures in shale reservoirs by advancing sequentially through core-points，logging-lines，and seismic-surfaces using the well-seismic information scale matching technology. This method integrates the advantages of accurate core identification，high longitudinal resolution of logging curves，and strong lateral continuity of 3D seismic data. The verification conducted on 27 wells in the sweet spot section of the Lucaogou Formation in Jimsar Sag shows an average relative prediction error of 8%，indicating a satisfactory application effect. This technology can provide robust support for the exploration and development of shale oil in the Lucaogou Formation，and it also holds significant reference value for the evaluation of shale oil reservoirs in other basins.

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Nonlinear Propagation and Influencing Factors of Perforation Detonation Waves in Ultra-Deep Wells

LIU Huailiang, LIU Xianbo, LIU Yu, LI Jun , XI Yan, LIAN Wei

2024, 20(1):  31-37.  DOI: 10.12388/j.issn.1673-2677.2024.01.004

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As oil and gas wells are gradually extended to deep and ultra-deep layers，the safety of completion strings during perforation has attracted more attention. Based on the principles of computational fluid dynamics，a perforated interval-packer detonation wave propagation model was established，revealing the detonation wave propagation and reflection rules in the wellbore completion fluid and clarifying the characteristics of the influence of completion fluid on detonation wave propagation. Research shows that the detonation wave propagation process demonstrates extremely strong non-periodicity and irregularity. When the detonation wave propagates to the packer position，the amplitude of the detonation wave pressure is reduced by up to 75.65%. The detonation reflected waves show better periodicity，and the amplitude of the detonation pressure waves is reduced by 23.4% when it propagates to the perforated interval. The density of the completion fluid not only has a great influence on the amplitude of the detonation waves during propagation，but also has a great interference on the waveform characteristics of the detonation waves. The viscosity of the completion fluid has almost no impact on the waveform characteristics of the detonation waves during propagation，and has a small impact on the amplitude of the detonation waves. With the impact of detonation waves on the completion string considered only，priority should be given to selecting a completion fluid system with low density and high viscosity to reduce the impact of detonation waves on the downhole completion string. The research results of this article provide a reference for the design of on-site completion fluid parameters for oil and gas wells.

OIL AND GAS DEVELOPMENT

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Numerical Simulation of Nitrogen-Assisted VHSD Development in Old Super-Heavy Oil Reservoirs

WANG Pan, LIU Yang, LIANG Xiangjin, ZHENG Aiping, QIN Ninghan, FENG Zhijun

2024, 20(1):  38-43.  DOI: 10.12388/j.issn.1673-2677.2024.01.005

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Changing over to Vertical-Horizonal well Steam Drive （VHSD） development pattern is becoming an important means for improving block production rate and recovery rate in old super-heavy oil reservoirs. Nitrogen-assisted VHSD can increase energy and pressure and form a heat insulating top layer，effectively solving the problems of pressure maintenance，low displacement pressure，and low steam chamber temperatures following huff-puff operations in old heavy oil reservoirs，saving steam volume，improving oil production levels and oil-steam ratio，and reducing carbon consumption. This paper examines a VHSD development unit in the Ninth Block of Karamay Oilfield. Numerical simulation is used to determine the influences of different parameters （nitrogen injection timing，injection pattern，injection amount） on pressure and energy increase，and on the establishment of heat insulating layers. Variations in recovery rates and accumulated injection-production indicators during VHSD development are also analyzed. The results show that nitrogen injection by slug can help to build a heat insulating layer in the initial stages of the transition to displacement and drainage. In field tests of this nitrogen-assisted VHSD approach，the oil-steam ratio of the study well group was increased by 0.025，and daily oil production was increased by 0.7 t，which are favorable results. This study provides a technical reference for efficient development using nitrogen-assisted VHSD in similar old heavy oil reservoirs.

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CO2 Flooding Connectivity Characteristics of the Strong Water-Sensitive Conglomerate Reservoir in Xinjiang Oilfield

CHEN Shengen, XU Jinshan, ZHANG Xin, WANG Rui, ZHANG Liwei, LI Haifu

2024, 20(1):  44-51.  DOI: 10.12388/j.issn.1673-2677.2024.01.006

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Clarifying the connectivity characteristics between injection and production wells in CO₂ flooding reservoirs can provide essential support for the subsequent implementation of CO₂ flooding technology to improve sweep efficiency. With a strong water-sensitive conglomerate reservoir in Xinjiang Oilfield as the research object，this paper specifies the key parameters for determination of injection and production connectivity through the analysis of injection and production data. It designs the evaluation coefficient C after presetting the proportion of key parameters，and confirms the connectivity between injection and production wells under different ranges of C value，thus establishing a connectivity evaluation method for the strong water-sensitive conglomerate reservoir. This method can be used to judge weak，medium，or strong connectivity between injection and production wells in this area and analyze the main controlling factors of different connectivity characteristics to form targeted treatment measures. The study shows that the key parameters for determination of injection and production connectivity are oil production rate，tubing pressure，and the gas component of production wells. When the C value is greater than 8，the injection and production wells have strong connectivity；between 3 and 8，the injection and production wells have medium connectivity；and when less than 3，the injection and production wells have weak connectivity. According to the statistical injection and production data of the whole area and the C value，the connectivity between injection and production wells in the block presents two apparent characteristics. First，the connectivity between injection and production wells has directionality. The medium and strong connectivity is mainly northwest，but the local connectivity has specific differences，primarily affected by the structure and early water flooding. Second，the connectivity has regional characteristics and is better in the northeast region of the block center. Among the 22 wells in the area，14 wells show strong connectivity，accounting for 63.6%，mainly affected by the difference in formation permeability and the amount of carbon injection. According to the results of injection and production connectivity，it is suggested to implement classified management of the various connected wells in the area，huff and puff for wells with weak connectivity in the marginal area，small-scale fracturing for wells with weak connectivity in the core area，and channeling sealing and profile control for wells with strong connectivity. This study can provide a reference for the efficient development of strong water-sensitive conglomerate reservoirs by CO₂ flooding after water injection.

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Research Progress on Capture of CO2 by Alcohol Amine Absorption Method

YANG Tianmeng, YANG Fan, REZEY Rehemtuli, GOU Guolei, LI Xiuhui, HOU Junwei

2024, 20(1):  52-60.  DOI: 10.12388/j.issn.1673-2677.2024.01.007

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CO₂ capture，utilization，and storage are the main technologies to cope with the greenhouse climate，achieve the strategic goal of carbon peak and neutralization，lead the transformation and upgrading of the global energy system，and promote the green and sustainable development of energy. The chemical absorption methods have the characteristics of high absorption efficiency and large processing capacity，most suitable for large-scale carbon capture in various industries. Among them，the alcoho lamine method is the most widely used and the most effective. After absorbing CO₂，the alcoholamine solution becomes an alcoholamine-rich solution，which can be recovered by desorption treatment for cyclic utilization. However，in the process of CO₂ capture by the existing alkanolamine absorbent，there are some disadvantages such as high energy consumption and great loss of absorbent，and it is necessary to improve the alcoholamine absorber to realize high absorption efficiency and a feasible process with low regeneration energy consumption. To solve the problems of large loss of absorbent and low regeneration rate，a new mixed alcoholamine absorber was developed for improvement. For the problem of high energy consumption for regeneration，the traditional thermal desorption process is improved and microwave desorption technology is selected. This paper introduces the mechanism and characteristics of CO₂ absorption by alcoho lamine method，summarizes the basis for improving the mixed alcoholamine absorber，and expounds on the principle and characteristics of CO₂ capture through microwave-assisted alcoholamine，providing a reference for industrial carbon capture and environmental protection.

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CO₂-CH₄ Gas Throttling and Hydrate Generation Characteristics

XIONG Xiaoqin, AN Guoyu, LIAO Tao, LI Xinze

2024, 20(1):  61-67.  DOI: 10.12388/j.issn.1673-2677.2024.01.008

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In the process of CO₂ flooding production and oil lifting，with the decrease of pressure，a large amount of associated gas will be separated from the produced liquid. In the associated gas，the content of CO₂ is as high as 50%-90%. Compared with CH₄，gaseous CO₂ has a stronger throttling cooling effect，which may cause the generation of hydrate to block the pipeline，threatening the operation safety of the gathering and transportation system. The influence of CO₂ content on the CO₂-CH₄ gas throttling and hydrate generation characteristics was studied using a high-pressure sapphire reactor. The results show that：When the initial pressure is high （16 MPa），the throttling effect coefficient D_i of the mixture gas with the same CO₂ proportion is about 1.3-5.4 ℃/MPa，and the incorporation of CH₄ will enhance the throttling effect of the mixture gas，indicating that the high pressure section is mainly affected by the throttling effect of CH₄；when the initial pressure is low （5 MPa，4 MPa），the throttling effect coefficient D_i is about 3.4-11.9 ℃/MPa，and the incorporation of CH₄ will weaken the throttling effect of the mixture gas，indicating that the low pressure section is mainly affected by the throttling effect of gaseous CO₂. The higher the pressure at which CO₂-CH₄ gases with the same CO₂ content are，the higher the temperature at which hydrates are generated，and the easier it is to generate hydrates. At the same pressure，the lower the CO₂ content is，the lower the temperature at which hydrates are formed. When the CO₂ content is 8%-100% and the pressure is 1.5-5 MPa，the hydrate generation temperature is 0.5~10 ℃. The comparison results between the experimental and software simulation data show that the PR equation of state has a high correlation for the calculation of CO₂-CH₄ throttling and hydrate generation characteristics. The research results can provide a reference for the selection of safe gathering and transportation process parameters.

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Applicability Evaluation of Tight Oil Reservoir Gas Channeling and Sweep Control System

LI Junjian, XI Yilin, ZHANG Miao, ZANG Chuanzhen

2024, 20(1):  68-76.  DOI: 10.12388/j.issn.1673-2677.2024.01.009

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Tight oil reservoirs are widely distributed in China，with a large proportion of reserves and great development potential. These reservoirs have low matrix permeability and porosity，with fractures acting as main oil and gas flow channels，and gas injection is often used to recover such reservoirs. However，due to the cross-scale development of reservoir fractures and the influence of reservoir heterogeneity and viscous fingering，the technology of gas injection to improve oil recovery has limits. Gas channeling can easily occur in the presence of fractures and high permeability bands，causing many issues related to the energy supplement of formation. In this paper，foam and CO₂-responsive gel were selected to prepare the gas channeling and sweep control system，and their performance and applicability in tight oil reservoirs were evaluated by physical experiment simulation. Commercial numerical simulation software was used to characterize CO₂ huff-n-puff and underground gelling reaction. Through the numerical simulation of a tight oil reservoir in China，it is proved that the CO₂-responsive gel has an obvious stimulation effect during huff-n-puff treatment，resulting in an increase in recovery rate by 3.1%. This research validates the promising application prospects of the CO₂-responsive gel system in the development of tight oil reservoirs.

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Numerical Simulation of Three-Dimensional Vertical Fracture Propagation Model under the Influence of Bedding

WANG Bo, WANG Qianren, ZHOU Hang, ZHANG Li, XIE Ziqi

2024, 20(1):  77-87.  DOI: 10.12388/j.issn.1673-2677.2024.01.010

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The reservoirs at a block of Xinjiang Oilfield have the characteristics of high heterogeneity，and uneven natural bedding plane development and stress distribution. The vertical fracture propagation mode of such reservoirs with bedding planes under complex stresses has an impact on the layer-penetrating fracturing effect. Based on the finite element method and cohesive zone model，a three-dimensional fluid-solid fully coupled numerical model with bedding planes has been established. The vertical propagation patterns of hydraulic fractures under the influence of different stress conditions and bedding planes were studied. the layer-penetrating fracture propagation mode of reservoirs with beddings was also clarified，forming a prediction diagram of fracture penetrating patterns under complex stresses. The model’s simulation results are consistent with the published results of physical modeling experiments，validating the model’s reliability. The research results show that the smaller the vertical stresses，the easier the fractures activated along the bedding planes. When the vertical stresses are less than 18 MPa，the fractures propagate along the bedding planes. The greater the horizontal stress difference，the greater the barrier effect applied on the fractures by the bedding planes. When the horizontal stress difference is greater than 3 MPa，the fractures are more easily captured by the bedding planes and propagate along the bedding planes. The greater the tensile strength of the bedding planes，the more likely the fractures are to propagate through the bedding planes. The research results will provide theoretical guidance for layer-penetrating fracturing design of layered reservoirs.

NEW ENERGY

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Energy Conservation and Consumption Reduction Technology of Gas Extraction System in Hutubi Gas Storage

MA Zenghui, ZHAO Yida, CHEN Ligang, HE Lin, ZHU Huan, BAI Bofeng

2024, 20(1):  88-94.  DOI: 10.12388/j.issn.1673-2677.2024.01.011

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Given the current situation that some operating parameters of the gas extraction system in Hutubi gas storage deviate from the optimal value to cause low energy-saving efficiency，the energy efficiency of the gas extraction system is analyzed through pinch analysis and exergy analysis methods. A simulation study is performed based on HYSYS software，giving rise to the scheme of energy conservation and consumption reduction. The scheme mainly includes the selection of the gas-gas heat exchanger，the optimization of the glycol-rich liquid inlet temperature，the optimization of the reflux ratio of the regenerator，and the optimization of the phase-change furnace. The calculation model between the inlet pressure and J-T valve back pressure and the theoretical KA value of the gas-gas heat exchanger is established to optimize the selection of the heat exchanger. The optimum inlet temperature of the glycol-rich liquid is determined to be 67 ℃，and the reflux ratio of the regenerator is 0.06. During the operation of the top condenser of the regenerator，the consumption of glycol can be reduced by 84.6%. The energy consumption of the system can be reduced by 9.0% by using the waste heat of the exhaust gas from the regenerator to preheat the external transmission gas. This optimization scheme effectively reduces the total energy consumption of the gas extraction system with minimum alteration.