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2026,53(2):1-12, DOI: 10.12143/j.ztgc.2026.02.001
Abstract:
Against the backdrop of the global energy transition and the in-depth advancement of China''s carbon peaking and carbon neutrality goals， unconventional geological energy has become a core alternative resource， and drilling coring is an important means to obtain accurate physical property parameters of its reservoirs. In view of the complex physical properties of unconventional reservoirs， the specific coring challenges associated with different energy types， and the current situation of existing studies-most of which are classified by energy type and lack a systematic summary of technical commonalities-this paper focuses on technical methodologies， systematically sorting out five major technologies： pressure-retaining coring， shape-preserving coring， large-diameter coring， sealed coring， and downhole freezing coring. The core principles and the current status of domestic and foreign technical applications of each technology are elaborated. The study shows that China has established a coring technology and equipment system with independent intellectual property rights and achieved engineering breakthroughs in scenarios such as deep sea and deep earth. However， the existing technologies still have some challenges， including limited adaptability of a single technology， insufficient capability in responding to extreme environments， and difficulty in balancing efficiency and cost. This paper further analyzes the core challenges in technological development and puts forward the development directions of technical integration， intelligent upgrading， environmental adaptation， green and high efficiency， and in-situ testing providing a systematic reference for technological innovation and engineering practice in this field.
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SHI Fangyu, NING Fulong, LI Wei, LIU Zhichao, HU Chen, SUN Yuxuan, LIU Zhihui
2026,53(2):13-24, DOI: 10.12143/j.ztgc.2026.02.002
Abstract:
Sidewall coring serves as a vital supplement to conventional coring. However， traditional rotary sidewall coring technology is prone to core loss， fragmentation， or coring failure under high-temperature， high-pressure， and high ground stress conditions， making it difficult to meet the demand for high-quality and efficient coring in deep wells and unconventional reservoirs. To address these challenges， this paper systematically reviews the technological progress of typical rotary sidewall coring tools both domestically and internationally， conducting a comparative analysis of their structural parameters and coring principles. It further delves into the influence mechanisms of factors such as formation conditions， coring tool performance， well deviation， filter cake quality， drilling fluid properties， and operational errors on sidewall coring quality. Based on field application data， a comprehensive evaluation is performed on various sidewall coring tools in terms of core recovery rate， integrity， suitability for core analysis， and reliability. The findings indicate that rotary sidewall coring technology holds significant advantages in complex formations and can provide reliable support in terms of petrophysical and geological parameters for the evaluation of deep and ultra-deep reservoirs， while large-size rotary sidewall coring technology markedly enhances sample representativeness. Domestic sidewall coring tools have reached maturity in conventional reservoirs but still have gaps in the lifespan of critical tool components， signal acquisition， and control accuracy. Future technological advancements should focus on key areas such as high-temperature-resistant materials， sealing and anti-contamination design， and multi-parameter adaptive control systems to improve operational precision and environmental adaptability， thereby offering more efficient engineering solutions for core acquisition in complex formations.
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YAN Liangliang, MU Zongyang, LIU Xiao, YAN Ping, ZHU Shaolong, AN Yuxiu
2026,53(2):25-34, DOI: 10.12143/j.ztgc.2026.02.003
Abstract:
Due to the unique “three-low characteristics” and dual-pore structure of coalbed methane （CBM） reservoirs， they are extremely prone to irreversible damage such as stress sensitivity， water sensitivity， and solid-phase invasion during drilling， and face severe risks of wellbore instability. This paper systematically analyzes the special physical and chemical properties of coal rocks and their specific requirements for drilling fluids， and deeply expounds the damage mechanism of drilling fluids on reservoirs and their impact on wellbore stability. The research progress in CBM drilling fluid technology is mainly reviewed： for reservoir protection， core technologies such as low-density drilling fluids， strong inhibition-plugging systems， low-solids/no-solids drilling fluids， and degradable drilling fluids have been formed； for wellbore stability， anti-collapse drilling fluid systems based on multi-component synergistic inhibition and high-efficiency plugging have been developed. The paper summarizes the current technical challenges and points out that future research should focus on geological adaptability， intelligent-responsive drilling fluids， high-efficiency environmental protection materials， etc.， to provide a reference for optimizing CBM drilling fluid technology and improving development benefits.
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XU Jiawei, WANG Sheng, XU Shiyi, TANG Fangjie, XIE Jie, ZHANG Jie, LAI Kun
2026,53(2):35-46, DOI: 10.12143/j.ztgc.2026.02.004
Abstract:
Under the backdrop of global energy restructuring and the exploration and development of unconventional resources such as shale gas， the water pressure test serves as a key in-situ testing technology for evaluating rock mass permeability， and its technological advancement is of great significance for ensuring energy and resource security. This paper systematically reviews the development history of the water pressure test from empirical qualitative analysis to digitalization and intelligence， and analyzes the co-evolution of its technical theories and testing equipment. Addressing the limitations of traditional techniques， such as frequent tripping， low efficiency， and data interpretation relying on inference， three innovative technical concepts are proposed： the non-tripping water pressure test system， the multifunctional integrated probe， and the multi-packer water pressure test device. Their working principles， technological processes， and technical advantages are elaborated. These concepts integrate core technologies including wireline coring， borehole imaging detection， and synchronous multi-packer isolation testing， aiming to achieve a leap towards "high efficiency， high precision， and visualization." This study provides a pathway reference for the evolution of water pressure testing from single-parameter testing to an integrated "geological-hydrological-engineering" diagnosis platform， offering technical support for energy resource exploration and major engineering construction in China.
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ZHANG Feifei, YANG Fuyuan, ZHANG Cong, WANG Jianlong
2026,53(2):47-56, DOI: 10.12143/j.ztgc.2026.02.005
Abstract:
With the continuous intensification of the exploration and development of unconventional energy resources in our country， drilling operations in deep and complex lithologic strata are becoming increasingly frequent. Against this backdrop， achieving efficient， economical and safe drilling operations has become a key issue in the industry， and the intelligent and precise improvement of drilling technology and equipment is the core driving force. The PDC cutter， as the core unit of the drill bit that directly participates in rock breaking， and its interaction mechanism with the rock is a key factor affecting the structural design of the drill bit， the decision-making of drilling parameters， and the overall drilling efficiency. Therefore， this paper focuses on the rock-breaking process of PDC cutters， and uses ABAQUS finite element software to establish a two-dimensional numerical model of the rock-breaking process of the PDC cutter， systematically exploring the influence of rock physical properties on the rock-breaking mechanism and the dynamic response of the cutter. By introducing the Drucker-Prager failure criterion and the Cohesive element model， the rock crack initiation， propagation and fracture behavior during the rock-breaking process of the cutter were simulated. The study analyzed the response characteristics of cutting force and vibration acceleration under different rock physical properties and lithology conditions. The results show that the compressive strength of the rock has the most significant influence on the cutting force and vibration response， followed by the internal friction angle， and the elastic modulus has a relatively small influence. The average cutting force of different lithologies is ranked as granite > conglomerate > limestone > sandstone， and the vibration acceleration is positively correlated with the average cutting force. This research provides a theoretical basis for the identification of rock physical parameters based on the dynamic response of drill bits， with important implications for the parameter optimization of deep drilling for unconventional energy resources， the identification of formation lithology and the development of intelligent drilling technology.
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ZHANG Chengkai, LIU Zihao, SONG Xianzhi, ZHU Zhaopeng, WANG Jianlong, JIA Yibo, ZHU Lin, LIU Muchen, WANG Zheng
2026,53(2):57-67, DOI: 10.12143/j.ztgc.2026.02.006
Abstract:
To address the frequent occurrence of stuck pipe incidents during drilling， the reliance on empirical diagnosis， and the lack of interpretability in intelligent models， this paper proposes a knowledge graph-based monitoring and analysis method for stuck pipe. Given the multi-source， heterogeneous， and highly specialized nature of stuck-pipe-related knowledge， a systematic workflow was established for knowledge graph construction， comprising： ontology design， multi-source data preprocessing， knowledge extraction， and graph visualization. Through a top-down ontology design， core entities such as stuck-pipe types， influencing factors， characteristic features， and mitigation measures were defined. Based on this framework， a BERT-BiLSTM-CRF model was employed to extract knowledge from unstructured texts， achieving an F1-score of 88.2%. Approximately 2000 structured entities were derived from 327 historical cases and integrated with structured time-series stuck-pipe sample data to construct a multimodal knowledge graph for stuck-pipe analysis. Furthermore， a stuck-pipe identification method combining data similarity computation and knowledge graph retrieval was introduced， significantly enhancing the interpretability of the diagnostic process. In addition， an intelligent question-answering system with strong human-machine interaction capabilities was developed for field applications. Adopting an "input parsing-intent classification-knowledge retrieval-answer generation" architecture， the system can quickly provide outputs including stuck-pipe types， causal analysis， and control recommendations. This research achieves effective integration of textual drilling knowledge and real-time monitoring data， markedly improving the intelligence and interpretability of stuck-pipe diagnosis. It offers a novel technical approach and engineering reference for the safe and efficient drilling of deep， ultra-deep， and unconventional oil and gas wells.
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HUANG Xiaocheng, SUN Pinghe, WANG Liang, XIA Yuhongye, DENG Yingying, LI Jiaxue, ZHANG Shaohe
2026,53(2):68-76, DOI: 10.12143/j.ztgc.2026.02.007
Abstract:
To address the challenges of lost circulation control in porous formations during unconventional geo-energy drilling， as well as the shortcomings of traditional plugging materials such as poor adaptability and difficult performance control， a shear thickening fluid （STF） was prepared using nano-SiO? as the dispersed phase and polyethylene glycol as the continuous phase. Experiments were conducted using an API static plugger and marble beds to simulate porous formations， systematically investigating the influence mechanisms of three key parameters-critical shear rate， shear thickening intensity， and shear thickening ratio-on the plugging performance of STF. The results indicate that the critical shear rate dominates the pressure response characteristics and the timing of thickening triggering. Within the marble bed pore size range of 0.15~1.66 mm， samples with a lower critical shear rate readily triggered the thickening effect under low pressure， reducing the leakage rate to below 2 mL/min. The shear thickening intensity determines the compactness and ultimate pressure-bearing capacity of the plugging layer； samples with high shear thickening intensity achieved a minimum leakage rate of 0.38 mL/min and maintained excellent plugging effectiveness even under high pressure. The shear thickening ratio affects the stability of the plugging morphology and pressure sensitivity. A high shear thickening ratio facilitated the formation of effective "throat-plugging" or "waist-plugging" structures， reduced a low leakage rate of 1.71 mL/min at pressures exceeding 3.0 MPa and demonstrating good pressure-bearing capacity. This study reveals the mechanisms by which the core thickening parameters of STF affect pore plugging performance， providing theoretical support and a technical basis for its engineering application in porous lost circulation formations.
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BING Xinguo, GUO Wei, ZHANG Pengyu, WANG Yuan
2026,53(2):77-87, DOI: 10.12143/j.ztgc.2026.02.008
Abstract:
Marine sediments serve as crucial repositories of oceanic information， and the accurate acquisition of undisturbed samples is essential for marine resource exploitation. Sampling is the primary method to obtain sediment samples， and its precision exerts a significant influence on resource exploration and analysis. Thus， acquiring low-disturbance soil samples constitutes the core objective of sampling operations. This study addresses the issue of soil disturbance during the drilling and sampling of submarine saturated soft clay. A three-dimensional numerical model of the sampler-soft clay interaction was established using Abaqus software with the Coupled Eulerian-Lagrangian （CEL） algorithm to systematically investigate the influence of the cutting shoe angle and penetration velocity on soil disturbance. Initially， sampler models with cutting edge angles of 5°， 10°， 15°， 20°， and 25° were adopted to analyze the effect of the cutting edge angle on soil disturbance and determine the optimal angle. Subsequently， various penetration velocities were simulated to further study the degree of soil disturbance under different velocity conditions. The results indicate that as the cutting edge angle increases， the disturbance range of the soil outside the sampling tube expands gradually， and the overall disturbance range of the samples inside the tube increases accordingly； compared with the 25° cutting edge angle， the 5° angle improves the sample recovery rate by approximately 4%. Furthermore， a higher penetration velocity results in a lower degree of soil disturbance： in comparison with 20 mm/s， a penetration velocity of 45 mm/s reduces the strain influence range of the soil on the inner tube wall by 34% and the maximum strain value by 11.2%. The combination of a small cutting edge angle and a high penetration velocity can effectively inhibit the plastic flow and structural damage of the soil. These findings provide a solid theoretical basis for the design of low-disturbance samplers and the selection of operational parameters for the sampling of submarine saturated soft clay sediments.
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DAI Chenli, QU Lili, WANG Yuan
2026,53(2):88-95, DOI: 10.12143/j.ztgc.2026.02.009
Abstract:
With the increase in global energy demand， marine natural gas hydrates have received widespread attention as a potential source of clean energy. However， methane leakage and marine ecological damage during hydrate extraction remain pressing challenges. In this study， a novel natural gas hydrate extraction method based on a freezing barrier is proposed， which aims to enhance the extraction efficiency and reduce the environmental risks. Through the formation of a solid ice barrier over the hydrate reservoir， the freezing barrier can effectively inhibit gas diffusion， enhance reservoir stability， and prevent seawater intrusion， while avoiding the ecological damage caused by traditional extraction methods. Numerical simulations comparing the SH7 site and the AT1 site show that in the low-permeability SH7 site， the freezing barrier increases the methane recovery rate by 16% and gas production by 17.89%， while the AT1 site does not show the same effect due to the difference in the barrier location. The results of the study show that the rational configuration of the freezing barrier provides effective technical support for the safe and environmentally friendly exploitation of natural gas hydrates and has good application prospects.
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LIN Baoxin, CHEN Zhilin, WANG Yuan
2026,53(2):96-101, DOI: 10.12143/j.ztgc.2026.02.010
Abstract:
To address the issues of environmental pollution and energy efficiency in the in-situ conversion and exploitation of oil shale， this study proposes an energy recycling method that involves recovering methane-rich waste gas generated from the downhole process and utilizing it as a fuel for a catalytic combustion heater. In this research， a combined approach of catalytic combustion and porous medium combustion was adopted， with methane as the fuel. A two-dimensional axisymmetric model was constructed to systematically simulate the effects of pore diameter， gas injection rate， and methane mole fraction on combustion performance. The results indicate that： reducing the pore diameter can significantly enhance methane conversion rate and exhaust gas temperature； variation in the gas injection rate has a negligible impact on combustion performance； under fuel-lean conditions， minor changes in methane concentration lead to limited improvement in the conversion rate. This study provides a theoretical basis for the resource utilization of methane from downhole waste gas in oil shale operations and the optimized design of combustion heaters， offering significant engineering reference value for advancing the green extraction of oil shale.
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CHEN Zhilin, SHUI Haoche, WANG Yuan
2026,53(2):102-107, DOI: 10.12143/j.ztgc.2026.02.011
Abstract:
In this study， for the methane-containing waste gas generated during the oil shale extraction process， an innovative technological solution， i.e.， catalytic combustion using methane cracking gas containing low concentration of methane to facilitate oil shale extraction， was proposed and analysed by means of detailed simulations with the help of Fluent and CMG software. In Fluent simulation， the role of pore size and length of porous media on the efficiency of catalytic combustion was explored. It is found that smaller pore size and increased catalytic section length could effectively enhance the methane conversion rate and combustion temperature. After model optimisation， the methane conversion rate can reach a high value of 92.4%， and the tail gas temperature can reach 1050 K. The CMG simulation results show that there are significant differences in the temperature field distribution and oil and gas production during the oil shale extraction process under different methane conversion rate conditions. The total oil production reaches the highest value of 20.5 m3 at a methane conversion rate of 92%. Meanwhile， the daily gas production shows an increasing trend with the decrease of the conversion rate， and the peak appears earlier. The study confirms that the scheme can effectively reduce the environmental burden while realising the recycling of waste gas and improving the efficiency of energy use， providing a brand new technical path and methodology for the green and efficient exploitation of oil shale.
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2026,53(2):108-114, DOI: 10.12143/j.ztgc.2026.02.012
Abstract:
Currently， the three-dimensional development of shale oil in China is still in the exploration stage. To construct an integrated and efficient production model of drilling， fracturing， and commissioning， it is necessary to carry out collaborative optimization of well group trajectory design and operation sequence. Taking an actual well pad in Minfeng Sag of Jiyang Depression as the research carrier， this paper focuses on two operating modes， namely "Vertical-Horizontal Push Tank" and "Horizontal-Vertical Push Tank". The closest approach method combined with Landmark software is adopted to systematically analyze the impacts of the position of kickoff points， the relative depth of kickoff points， and the build rate before target entry on collision risk， and targeted anti-collision measures are proposed. The research shows that the "Vertical-Horizontal Push" mode has lower overall collision risk and stronger adaptability through the design of trajectory plane staggering； while the "Horizontal-Vertical Push" mode has more complex anti-collision design and higher risk due to multiple trajectory crossings， and it is necessary to rely on the dual staggering optimization of kickoff points to reduce risks. The research results provide feasible technical support for the well group design of shale oil three-dimensional development and provide a reference for the well group optimization under different production models in the future.
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REN Zhenglian, JIAN Liming, WANG Sheng, CHEN Liyi, YUAN Jinke, TAN Huijing
2026,53(2):115-123, DOI: 10.12143/j.ztgc.2026.02.013
Abstract:
To address the severe mud loss and borehole wall instability encountered in deep drilling operations such as shale gas exploration in China， this study proposes a gelation time-controlled strategy for wellbore stabilization and leakage sealing. A corresponding gelation time-controlled cement-based wellbore protection and leakage sealing material was successfully developed by compounding Portland cement with organic acid， sodium fluoride， triethanolamine， and aluminum sulfate， enabling precise regulation of the slurry''s setting behavior. The formulation was optimized through factorial design， and predictive models were established for the pumpable period （PPD） and the interval between pumpable period and initial setting time （IST）. The hydration mechanism was elucidated using thermogravimetric （TG-DTG） analysis and scanning electron microscopy （SEM）. Results demonstrate that the material exhibits excellent gelation time-control characteristics and rapid setting response： the PPD can be precisely adjusted within 10~60 min， with a minimum IST of 12 min； the 7-day compressive strength ranges from 18.8 to 27.5 MPa， meeting engineering strength requirements. TG-DTG and microstructural analyses indicate that all four admixtures initially inhibit cement clinker hydration， later transitioning into a promoting effect， with a distinct inhibition-to-acceleration transition point. Their dynamic synergistic interaction establishes a dual-effect control mechanism characterized by "early inhibition and late promotion"， which confers the gelation time-control property. Notably， organic acid only temporarily retards hydration， leading to substantial formation of C-S-H gel and microstructural densification after 7 days， thereby ensuring long-term strength development. This research resolves the longstanding engineering challenge of balancing slurry loss control and setting efficiency in conventional cement-based sealing operations， providing a novel technical solution for wellbore stabilization and leakage sealing in deep shale gas drilling.
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ZHENG Xinghua, HONG Yi, WAN Yuhang, SONG Yongpeng, YAN Weichao, YANG Han, DU Yufei
2026,53(2):124-130, DOI: 10.12143/j.ztgc.2026.02.014
Abstract:
To address issues such as the susceptibility to failure and insufficient regulation accuracy of existing throttle valves under ultra-high pressure conditions in shale gas extraction in western Hubei， this study conducts structural optimization research on an ultra-high pressure cage-type throttle valve. The key geometric parameters of the throttle orifices were determined through theoretical fluid dynamics calculations. Utilizing ANSYS Fluent software and adopting the Reynolds Stress Model （RSM） for turbulence simulation， flow field simulations were performed to analyze different valve core surface profiles and throttle orifice arrangements. The results indicate that the semi-circular curved valve core exhibits the lowest pressure， superior erosion resistance， and ease of machining. Furthermore， the linear uniform arrangement of throttle orifices is identified as the comprehensive optimal scheme， offering uniform pressure distribution， effectively suppressing vortex generation， enhancing structural stability and regulation accuracy， and providing manufacturing convenience. The optimized throttle valve structure demonstrates excellent throttling performance and regulation accuracy under 100 MPa ultra-high pressure conditions， showing significant engineering application value and promising prospects for enhancing the reliability of key wellhead components in shale gas extraction.
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LI Kuan, SHI Shanshan, ZHANG Hengchun, YIN Hao, WANG Wen, WU Jixiu, GAO Pengju, WANG Yuewei
2026,53(2):131-139, DOI: 10.12143/j.ztgc.2026.02.015
Abstract:
Well GH-05 is an efficiency-enhancing well deployed for the hot dry rock pilot production project in the Gonghe Basin， Qinghai Province. It is a dual-target directional well with a designed depth of 4000 m. Based on the construction experience of adjacent wells， the running depth of the surface casing and technical casing was increased， the risk of block falling and sticking in the long open hole section was reduced， and the cementing quality of the production casing was improved. In addition， a shock-absorbing thruster and a drilling jar were added in the bottom hole assembly， which effectively reduced the adverse effects of severe vibrations on downhole tools. The service life of the motor was increased by 35%， and no accidents happened such as cone dropout， bearing failure， and drill string breakage， achieving safe drilling. Based on the theory of specific energy of rock fragmentation， taking both the rock fragmentation efficiency and roller cone bit life into account， meeting the upward return of cuttings， for the borehole diameter of ?311.2 and ?215.9 mm， the weights on bit were selected to be 203~291 and 131~186 kN respectively， the rotational speeds were 120~180 and 180~270 r/min respectively， and the displacements were 43.3~51.4 and 33~38.5 L/s respectively. Furthermore， strengthening the drilling parameters increased the rate of penetration （ROP） in the granite formation by 34%~47%， and the drilling cycle was shortened by over 20%. It has created the drilling records of 207.51 m with a ?311.2 mm bit and 183.42 m with a ?215.9 mm bit in the granite formation， basically achieving the economic indicators of “ROP of 4 m/h and bit life of 200 m”. Finally， a composite organic salt drilling fluid system with a temperature resistance of 220 °C was developed and applied， reducing the near-wellbore pollution in the geothermal reservoir， effectively reducing the directional sticking pressure， and cutting the drilling fluid maintenance costs by over 40%.
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ZHANG Jiazheng, LUO Weifeng, WANG Yufang, YANG Nankun, YANG Benzhao, LI Juan, CHI Huanpeng, XIANG Jie, ZHONG Jianwen, ZHANG Fujie
2026,53(2):140-148, DOI: 10.12143/j.ztgc.2026.02.016
Abstract:
To evaluate the resource potential of the Lower Sinian Doushantuo Formation shale and determine the lower limit of the shale productive horizon， this study focused on the Well Eyangye-2HF. Utilizing drilling data from the nearby Well Eyangye-1 （located 18 m from the Eyangye-2HF wellhead） and integrating multidisciplinary analyses in geology， geochemistry， geophysics， and rock mechanics， the shale gas sweet spots were identified， and geological steering methods were successfully applied within a complex structural setting. The high-quality shale thickness of the second member of the Doushantuo Formation in this well is 130.5 m. Revealed a maximum total gas anomaly of 10.32% during coring， with a cumulative thickness exceeding 2% gas content measuring 105 m. The TOC peaks at 2.57%， with an average exceeding 1.5%. The maximum desorbed gas content is 2.21 m3/t， while the maximum total gas content reaches 4.82 m3/t. This high-quality shale interval is subdivided into 10 sub-layers. Based on a comprehensive consideration of gas-bearing properties， drillability， and fracturability， the Layer 7 in the second member was identified as the optimal sweet spot. By employing precise 2D seismic interpretation and geo-steering modeling， the wellbore trajectory was effectively controlled through timely adjustments during horizontal geo-steering， significantly improving the drilling encounter rate of the sweet spot. Well Eyangye-2HF is the world''s first horizontal shale gas well drilled in the Sinian Doushantuo Formation. The horizontal section spans 1410 m and was stimulated and tested in 23 stages. The well achieved a high-yield gas flow with a stable production of 55300 m3/d and an open flow potential of 198200 m3/d. This achievement effectively defines the lower limit of the shale gas production horizon and opens up new frontiers for shale gas exploration and development.
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LIAO Ruojun, HU Yunfeng, WANG Jianbin, CUI Miao
2026,53(2):149-155, DOI: 10.12143/j.ztgc.2026.02.017
Abstract:
Under the three-layer three-dimensional development mode， the recovery rate of Fuling Shale Gas Field has significantly increased， and the recovery rate of Jiaoshiba block has increased from 12.6% to 23.3%. However， in the process of three-dimensional development of directional drilling， there are many problems： The wellhead spacing is small （6~8 m）， and the risk of collision prevention in the vertical section of the platform well is high； Large-scale fracturing leads to the dynamic reconstruction of the reservoir stress field， and the construction needs to take into account the identification of residual gas sweet spots and the control of fracturing interference； The three-dimensional track design and the superposition of high-density well pattern make it difficult to control the trajectory collision within the 300 m spacing of the horizontal section. In this study， a conventional infill well track optimization design method based on separation coefficient was proposed， and a dynamic adjustment technology for targets in the fracturing disturbance zone was established to form a three-dimensional obstacle drilling technology system suitable for complex stress fields. The engineering practice shows that the technical system effectively solves the problem of three-dimensional trajectory collision prevention under the condition of dense well placement， and provides important technical support for the efficient development of shale gas.
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TANG Weidong, YU Dongxue, LIU Haipeng, CAO Huilin, DENG Sunhua
2026,53(2):156-167, DOI: 10.12143/j.ztgc.2026.02.018
Abstract:
The Chang 7 Member of the Ordos Basin contains abundant low-to medium-maturity shale oil resources， with the Xunyi area exhibiting rich reserves and favorable potential for in-situ development. However， the thermal dynamic characteristics， reaction threshold temperature， and product evolution patterns of autothermal reactions in this reservoir remain unclear. To address this， low-medium maturity shale samples from the Chang 7 Member of the Yanchang Formation in the Xunyi area were investigated using thermogravimetry-Fourier transform infrared spectroscopy （TG-FTIR）， pyrolysis experiments， elemental analysis， SARA analysis， and gas chromatography-mass spectrometry （GC-MS）. The effects of pyrolysis atmosphere and preheating temperature on oxidation-assisted pyrolysis characteristics were systematically studied. Results show that an oxidative atmosphere significantly enhances organic matter reactivity， triggering a low-temperature oxidation-pyrolysis synergy that markedly reduces the initial decomposition temperature and promotes oxidative cracking of heavy components at high temperatures. The oxidative atmosphere exerts a chemical heat-promoting effect on the pyrolysis of low-medium maturity shale oil， with the apparent activation energy under air being 167 kJ/mol—about 30% lower than under nitrogen-indicating a distinct "pyrolysis-oxidation coupling" mechanism. The suitable preheating temperature range for oxidation-assisted pyrolysis is 230~390 ℃， which effectively activates the autothermal reaction and promotes hydrocarbon lightening. Excessive temperatures， however， lead to over-oxidation of some oil and gas， reducing oil yield and altering product composition. Thermodynamic analysis confirms that when the pyrolysis temperature is ≤530 ℃， the exothermic oxidation of residual carbon can maintain system energy balance， demonstrating the feasibility of autothermal in-situ conversion. This study clarifies the control ranges for key process parameters and provides theoretical support for the efficient in-situ development of low-medium maturity shale oil.
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2026,53(2):168-174, DOI: 10.12143/j.ztgc.2026.02.019
Abstract:
In the tight gas reservoirs of the northern Ordos Basin， the presence of fine pore throats， developed fractures， and strong sensitivity leads to severe formation damage caused by solid invasion and liquid phase trapping during drilling， which restricts efficient development. To resolve the conflict between reservoir protection and wellbore stability， this study conducts an in-depth analysis of the formation damage mechanisms and， consequently， develops targeted self-degradable temporary plugging agents and liquid-lock prevention agents. Based on this research， a novel low-damage reservoir protection drilling fluid system is innovatively constructed， integrating "physical particle self-degradable temporary plugging"， "interface modification for liquid-lock prevention"， and "multi-synergistic wellbore stabilization". This system is complemented by a horizontal well drilling acceleration technology. Field applications demonstrate that this technological system effectively reduces the depth of drilling fluid invasion and the extent of formation damage. It significantly improves the single-well production， with some wells achieving natural production without fraturing operation. This research provides robust engineering and technical support for the low-cost and efficient development of tight gas reservoirs in the Ordos Basin and similar tight gas reservoirs.
Volume 53,2026 Issue 2
综述
钻探理论与方法
钻探技术与装备
工程实践与应用
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Construction Technology for Restoration of Fluid Observation Well at a Volcanic Monitoring Station
zhaoshengqing, CHEN Haopeng, HUANG Yuxian, WANG Zhiyong, LIU Wei
Abstract:
To solve the complex repair problem of"accident plus accident"in a fluid observation well of a volcanic monitoring station,the construction team fully prepared a variety of drilling accident handling tools in the early stage,customized special casing milling tools with the manufacturer,and combined with on-site flexible tool processing to support the implementation of various accident handling methods such as"fishing,reversing,grinding,and casing milling".During the construction,the downhole TV system was used to accurately observe the conditions in the well,clearly grasping the position and state of the fallen objects;at the same time,the"mud non-landing"process was adopted to build a flushing fluid circulation system to avoid mud polluting the environment and realize green construction.Finally,the team successfully completed the repair of the observation well,fished out all the fallen objects in the well without causing secondary damage to the well wall.The repaired observation well can be used normally to place the probe monitoring instruments of the specified specifications into the well.This not only achieved significant economic benefits and restored nearly 2 million yuan from losses,but also ensured the subsequent development of volcanic monitoring work,with good social benefits.
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