As one of the most convenient conveyance tools in shale gas horizontal wells, the well tractor plays a crucial role in conveying downhole tools. With the emergence of ultra-long horizontal sections in shale gas wells in recent years, traditional tractors may face challenges related to insufficient pull force. As the well inclination increases and the length of horizontal well section increases, the required pull force also increases. Research on the force characteristics of tractor conveyance revealed that when the well inclination reaches 120 degrees and the section length reaches 4500 m, the required pull force can reach 10555 N, far exceeding the pull force provided by traditional tractors. To address this situation, this study investigated two aspects to improve pull force: improving the friction of drive wheels and optimizing the tractor's power system. The research shows that the friction force can be changed by controlling the normal force through the hydraulic system, which can effectively improve the pull force. When the normal force is between 0 and 10 MPa, pull force steadily increases, reaching a maximum of nearly 10000 N. When the normal pressure exceeds 10 MPa, pull force begins to decline. Therefore, setting the hydraulic pressure (normal force) provided by the hydraulic system to a continuously adjustable range between 0 and 10 MPa ensures efficient pull force output. Second, replacing the triangular-shaped teeth drive wheel with a conical tooth drive wheel can increase pull force by 12 %-14.9 %. Furthermore, with respect to the drive power system, the efficiency of the tractor can be improved by using reducers with varying reduction ratios. The higher the reduction ratio, the greater the tractor's power output. Finally, the feasibility of the proposed methods is validated through case studies, offering valuable insights and references for the development of tractor conveyance technologies for horizontal wells.

During the development of shale gas fields, horizontal wells drilling through highly fractured shale formations are prone to drilling abnormal conditions such as borehole collapse and lost circulation, which significantly increase drilling risks and operational complexity. Therefore, this study investigates the shale of the Wufeng-Longmaxi Formations in the Sichuan Basin to identify the specific intervals where highly fractured shale develops and their development characteristics by analyzing data from drilling, logging while drilling (LWD), wireline logging, and core analysis. Furthermore, it analyzes the generation mechanism of highly fractured shale and the induced causes of drilling abnormal conditions, and develops a real-time drilling identification method based on LWD technology. The study shows that the top interval of the Wufeng Formation belongs to highly fractured shale, characterized by frequent abnormal conditions and a low gas production contribution rate. Moreover, bedding fractures at the top of the Wufeng Formation are more developed than those in the overlying Longmaxi Formation, and the Wufeng Formation exhibits stronger heterogeneity relative to the Longmaxi Formation. This leads to discontinuous or uneven rock strength where fractures develop or lithology changes drastically, making the rock mass susceptible to fracturing when the external environment changes, thereby forming highly fractured shale. Based on the LWD response characteristics of highly fractured shale, a mechanical specific energy (MSE) evaluation model can be established using drilling engineering theory. Combining this model with near-bit and far-bit γ ray (GR) and gas show parameters can effectively identify highly fractured shale, and the feasibility of this method is verified through field cases. The study results can meet the needs of field engineers for real-time evaluation, providing a new method and technical approach for the evaluation of highly fractured formations.

Carbon sequestration in shale gas operations represents a crucial pathway to achieve Geological Negative Emissions, which is essential for global 1.5 °C targets. However, the emissions reduction potential and economic viability of this approach in China’s shale gas value chain remain unclear. This study quantifies the potential for transforming China’s shale gas value chain from an emission source to a carbon sink, while revealing spatial heterogeneity in economic feasibility. Results demonstrate that synergistic deployment of CO2-based technologies can achieve Geological Negative Emissions across the value chain, with national carbon sink potential reaching 66 billion tonnes of CO2-equivalents and shale gas production increasing by 4,518 billion cubic meters. Multi-scenario economic assessments reveal that marine shale in the Sichuan Basin exhibits inherent profitability, whereas continental reservoirs require carbon credit integration or optimized production. Current Chinese carbon market prices provide insufficient incentives, implementing region-specific subsidies and enhancing carbon pricing frameworks could unlock this potential, thereby contributing to national carbon neutrality goals and multiple Sustainable Development Goals. China’s shale gas value chain can achieve net-negative carbon emissions through geological sequestration, offering a viable pathway for large-scale decarbonization in the energy sector.

The heterogeneity of overmature shales is a research hotspot, but there is a lack of deep understanding of its origins. Taking the Wufeng–Longmaxi shales as an example, this study investigates the controlling factors of reservoir and petrological heterogeneity in systems. The transgressive systems tracts (TST) are the sweet-spot intervals of shale gas. Their sedimentary processes were controlled by volcanism and glaciation. Both processes directly/indirectly injected nutrients into the ocean, causing the high primary productivity. The produced organic matter (OM) and siliceous skeletons were preserved well in anoxic water. The siliceous skeletons were transformed into authigenic quartz through diagenesis, which filled interparticle pores to resist compaction and maintain pore connectivity. OM migrated and accumulated in the interconnected pore network and formed abundant OM pores. The early highstand systems tract (EHST) was deposited during the regression, and productivity was weakened, resulting in reduced siliceous skeletons. Moreover, dysoxic-oxic water was not conducive to OM preservation. Extrabasinal quartz and feldspar significantly increased, becoming the main brittle particles resisting compaction. These factors made the number of full-scale pores was far smaller than that of TST. During the late highstand systems tract (LHST), further regression occurred, and extrabasinal clay rapidly increased. Oxic water facilitated oxidation of OM, making it more difficult to accumulate. Clay aggregates undergo continuous compaction during diagenesis to form a dense structure, resulting in the lowest porosity. The results suggest that the good compaction resistance of authigenic quartz may be the key to the hydrocarbon potential of deeply buried overmature shales.

China, holding the world's largest shale gas reserves, lacks precise data on methane emissions from its rapidly expanding production. We introduce a two-tiered mobile measurement approach, using a mobile laboratory to measure methane concentrations across 125 well pads (approximately 750 wells) distributed among four major production blocks (Changning, Weiyuan, Fuling, and Luzhou). These blocks contributed 84% of China's total shale gas production in 2023, providing the first comprehensive ground-level measurements. Stationary downwind monitoring of well pads revealed emission rates from 0.002 to 98.86 kg/h, validated through mobile observations of methane concentrations across the region. Notably, emissions were highly concentrated, with 89% originating from just 10% of the well pads. For 2023, the extrapolated methane emissions from China's shale gas production were estimated at 16,842 t (6,444-29,991 t, 95% CI), corresponding to a methane leakage rate of 0.10% (0.04%-0.17%, 95% CI). This rate is lower than major U.S. fields and similar to that of U.S. dry gas fields. Our research identifies gas lift venting, incomplete combustion from compressors, and process venting as significant sources of super-emissions in China's shale gas upstream production chain. The methodology employed, based on comprehensive and targeted field measurements, demonstrates its effectiveness in providing a scientific basis for formulating precise and effective regulatory policies on methane emissions.

As global efforts to mitigate climate change intensify, CO2 storage in shale oil reservoirs presents a promising avenue for reducing greenhouse gas emissions while enhancing oil recovery. However, accurate assessment of storage potential remains challenging, particularly in China's diverse shale oil basins. This study introduces the Storage Index-Well Layout (SI-WL) method, a novel approach for evaluating CO2 storage potential in shale oil reservoirs, and applies it to 12 major basins in China. Comparing this method with traditional and improved US-DOE methods demonstrates its superior reliability in estimating storage capacity under current technological conditions. Our analysis reveals a cumulative CO2 storage potential of 5.69 x 108 t of liquid CO2 across the studied basins, with the Bohai Bay Basin showing the highest capacity at 1.87 x 108 t. Scenario analysis from 2025 to 2060 identifies key factors influencing storage potential, including the proportion of wells using CO2 fracturing and fracturing fluid performance. While current practices in China's shale oil CO2 fracturing achieve effective results, improving liquid CO2's viscosity and sand-carrying performance remains a significant challenge. This research provides valuable insights for shale oil CO2 fracturing development and CO2 emission reduction strategies, suggesting that technological advancements could significantly enhance CO2 storage in the shale oil industry.

The gas-production potential of shale gas is a comprehensive evaluation metric that assesses the reservoir quality, gas-content properties, and gas-production capacity. Currently, the evaluation of gas-production potential is generally conducted through qualitative comparisons of relevant parameters, which can lead to multiple solutions and make it difficult to establish a comprehensive evaluation index. This paper introduces a gas-production potential evaluation method based on the Analytic Hierarchy Process (AHP). It uses judgment matrices to analyze key parameters such as gas content, brittleness index, total organic carbon content, the length of high-quality gas-layer horizontal sections, porosity, gas saturation, formation pressure, and formation density. By integrating fuzzy mathematics, a mathematical model for gas-production potential is established, and corresponding gas-production levels are defined. The model categorizes gas-production potential into four levels: when the gas-production index exceeds 0.65, it is classified as a super-high-production well; when the gas-production index is between 0.45 and 0.65, it is classified as a high-production well; when the gas-production index is between 0.35 and 0.45, it is classified as a medium-production well; and when the gas-production index is below 0.35, it is classified as a low-production well. Field applications have shown that this model can accurately predict the gas-production potential of shale gas wells, showing a strong correlation with the unobstructed flow rate of gas wells, and demonstrating broad applicability.

Block H, located in western Hubei-eastern Chongqing, remains at a low exploration degree. Characterized by its complex structural attributes, the area presents adverse conditions such as a thin thickness of high-quality shale reservoir, rapid lateral formation occurrence, and poor stratigraphic correlation, challenging conventional geosteering methods. The primary shale gas reservoir in Block H corresponds to the Upper Permian Wujiaping Formation. To ensure that the shale gas horizontal wells in this block effectively penetrate high-quality gas reservoirs, this study delves into the geological characteristics of this stratigraphic unit, identifies principal challenges faced by current geosteering techniques, and introduces a tailored technical solution. This solution encompasses the application of real-time 3D geological modeling to track while drilling, identification of steering marker layers, optimization of steerable tools, and optimization of the steering trajectory while drilling. In the technology of optimization of the steering trajectory while drilling, a trajectory control calculation model based on the average angle technique was established for the first time. Additionally, a sectional control chart for marker layers and well inclination under different deflecting constraints was established. These methods have solved the problems of large error in target prediction and poor trajectory control effects by using the equal thickness method alone. The findings from this study can significantly enhance target prediction and trajectory control accuracy in complex structural areas, offering pivotal insights for the proficient development of analogous shale gas reservoirs in the future.

Shale gas extraction in China often faces inadequate reservoir stimulation after initial fracturing of the wells, leading to production challenges despite abundant residual gas. Refracturing is an effective approach to enhance gas recovery; however, its impact on water consumption remains understudied. This study analyzes two refracturing techniques employed in China's largest shale production field, Fuling: temporary plugging and diverting refracturing (TPD) and wellbore reconstruction refracturing (WR), focusing on fracturing efficiency and water consumption. The results demonstrate that WR refracturing exhibits superior fracturing performance but consumes 1.3 times more water than initial fracturing. Considering 315 wells that required refracturing from 2013 to 2017, this study reveals, for the first time, that the lifecycle water consumption for shale gas production with refracturing is more than twice that without refracturing. The estimated total water consumption for the Fuling shale gas field over the next decade, incorporating refracturing, is approximately 7594.53 × 104 m3. By including the water consumption of refracturing, this study provides a more comprehensive evaluation of water usage throughout the entire lifecycle of shale gas development. The findings offer new insights for assessing water consumption in global shale gas development and highlight the importance of considering refracturing when evaluating the environmental impacts and resource management strategies associated with shale gas extraction.

总有机碳含量(total organic carbon,TOC)是确定烃源岩质量的最重要参数.为解决传统ΔlogR方法应用于沉积环境较复杂的海相页岩气储层精度低的问题,以桂中坳陷A区B组海相页岩气储层为研究对象,在分析研究区低阻原因的基础上,对测井曲线按照扩径范围进行井径校正,并利用自然伽马能谱测井中Th/K数据,与ΔlogR建立多元拟合关系,提出基于井径校正和自然伽马能谱测井的改进ΔlogR方法.结果表明:声波时差曲线经过校正后,降低了井径扩径带来的测井数据失真的影响,同时结合自然伽马能谱测井,能够适应研究区复杂的地质背景和较强的非均质性,大大提高总有机碳质量分数的预测精度,具有较好的推广性和适用性.该方法可以为桂中坳陷A区B组海相页岩气储层评价提供参考.

The Wufeng-Longmaxi Formations are the focus of shale gas exploration in China. Their sedimentation is affected by global and regional geological events, and the resulting heterogeneity hinders the expansion of exploration results. This study combines logging, mineralogy, and geochemistry to reconstruct the sedimentary mechanisms of shale in the southern Sichuan Basin and discusses its implications for exploration. The shale can be divided into third-order sequences, in which the Wufeng Formation and lower Long-1 Member are transgressive systems tracts (TST1 and TST2), and the Guanyinqiao Member and the middle-upper Long-1 Member are highstand systems tracts (HST1 and HST2). Volcanic eruption and glaciation evolution are the driving factors of the sedimentary environment during the TST. The area is in a cold-warm climate, characterized by anoxic conditions, slow sedimentation, booming productivity, and low terrigenous influx, thereby depositing four types of siliceous shale. The siliceous shale is rich in biogenic microcrystalline quartz and high TOC, which are the keys to becoming the "sweet spot" of shale gas. Microcrystalline quartz fills the intergranular pores to support the entire pore network framework. The organic matter undergoes thermal evolution to produce abundant organic matter pores, which constitute the main place for adsorbed gas and free gas. For the highstand systems tract, HST1 is the product of the peak of glaciation, mainly composed of calcareous shale and carbonate rocks. The sedimentation of HST2 is affected by turbidity currents and violent orogeny. The area is in a warm climate, characterized by high terrigenous influx, dysoxic-oxic conditions, medium productivity and rapid sedimentation rates. The lithofacies gradually changed from siliceous shale to mixed shale and argillaceous shale. Excessive clay minerals and low TOC make it difficult for HST2 to realize the commercial development of shale gas.

鄂西渝东红星地区勘探程度较低,存在优质页岩储层厚度薄、横向地层产状变化快,且对比性差等不利条件,对地质导向技术提出了挑战.为了保证该区块的页岩气水平井能有效穿越优质气层段,从红星地区二叠统吴家坪组目的层地质特征入手,分析地质导向面临挑战的主要问题,提出了运用三维地质建模随钻跟踪、确定导向标志层(点)、优选导向工具、优化随钻导向轨迹控制等一系列有针对性的技术方案.首次建立了平均角法轨迹控制计算模型和不同造斜率约束条件下标志层(点)与井斜分段控制图版,能够解决单纯利用等厚法预测靶点误差大和轨迹控制效果不理想的难题,显著提高了靶点的预测和轨迹控制精度.应用试验8 口井,取得了平均优质页岩储层钻遇率93.0%和钻井提速29.7%的成果,实现了有效提高储层钻遇率、优快钻井的目的.

Shale oil resources are abundant in China, and their large-scale development plays a critical role in the national energy strategy. Hydraulic fracturing is widely employed for shale oil extraction, but the large-scale water consumption in this process poses serious environmental concerns. In recent years, CO2 fracturing has been proposed as an alternative method to improve fracturing effectiveness, reduce water consumption, and simultaneously store CO2 underground. This is the first field-testing study in China to systematically analyze the CO2 fracturing technology and quantitatively evaluate its recovery efficiency and CO2 storage capacity in the shale oil wells in Jianghan Basin. We designed and conducted a comparative investigation of hydraulic fracturing, CO2water fracturing, and CO2 methanol-based fracturing techniques in terms of the effectiveness of fracturing, water saving, and CO2 storage. The results showed that CO2 methanol-based fracturing was most effective in eliminating the need for freshwater consumption on site and storing CO2, with an effective CO2 storage rate as high as 82.5%, suggesting a promising direction for carbon offset in the oil and gas industry. CO2-water fracturing reduced freshwater consumption and also effectively stored CO2 at an effective storage rate of up to 79.5%, making it more efficient than hydraulic fracturing but less so than CO2 methanol-based fracturing. The research provides a valuable reference for the development and practice of waterless fracturing for shale resources, and also sheds light on the potential of carbon storage in the oil and gas industry to achieve the carbon neutrality goal of China.

Geothermal resources are green and environmentally friendly renewable energy. An accurate evaluation of geothermal resources will help subsequent efficient exploitation. However, to save costs and improve efficiency, core-free drilling and without mud logging are adopted in the actual exploration, which results in an inability to directly obtain the relevant evaluation parameters of a geothermal reservoir for exploration and evaluation. Well logging technology can effectively delineate the geothermal reservoir and determine the location of the major aquifer, while also allowing for the accurate measurement of key reservoir evaluation parameters, such as the shale content, porosity, and well temperature. Moreover, coupled with the calculated logging parameters, a volumetric method can be used to determine the regional geothermal reserves. This research takes the geothermal wells of the Guanghuasi Formation in the Qianjiang sag, Jianghan Basin as an example to conduct the application research. The findings can be of reference for similar geothermal wells in China and facilitate the development of "carbon neutrality."

The Upper Triassic Ma'antang Formation is not only an important set of source rocks in the Sichuan Basin but may also be a successor for shale gas in China. In this study, the provenance, tectonic setting, chemical weathering, environment and productivity of the middle–late Carnian (Tuvalian) are reconstructed from petrological and geochemical data to determine the origin of the Ma'antang shales. The brachiopod-dominated fossil composition, type II-dominated organic matter, and fluctuating water salinity reflect that the shale formed in a marine environment influenced by terrestrial influx. TiO2 vs. Zr and La/Th vs. Hf diagrams, as well as the combination of major elements indicate that the Sichuan Basin was a collisional setting in the Tuvalian, and the provenance was felsic igneous source rocks. Redox-sensitive elements indicate dysoxic–anoxic conditions. Samples with Cd/Mo < 0.1 and Co*Mn > 0.4 show normal levels of Cd and relative enrichment of Mn and Co, which supports that the shale is more likely to be a product of anoxic preservation mode associated with the restricted basin. In contrast, the moderate productivity conditions reflected by Babio and P/Ti are also positive factors for organic matter accumulation. Based on the reconstruction of these environmental parameters, several driving factors that promote the formation of high TOC shales are explored. It is believed that the rapid tectonic subsidence in the early stage of foreland basin evolution (undercompensation period) created accommodation space for the shale, and the deep water also promoted anoxic bottom water, which facilitated the preservation of organic matter. The Carnian Pluvial Episode (CPE) increased global weathering and rainfall, allowing the oceans to receive more terrestrial nutrients, and freshwater influx caused stratification due to differences in salinity between the surface water and bottom water. Volcanic ash from the Wrangellia Large Igneous Province (W-LIP) and volcanic ash from local volcanoes were transported over long distances in the Late Triassic megamonsoons. Both were able to stimulate marine productivity, maintain and expand oceanic anoxia, and were beneficial for organic matter accumulation.

Hydrothermal fluid is one of the factors controlling Archean buried hill reservoirs in Bozhong 19-6. However, there are no clear studies focusing on the influence of hydrothermal alteration products and their lithological characteristics on reservoirs. Through characterization of the alteration reservoir and construction of a new subtraction model of the logging-rock mechanical alteration degree, the comprehensive uses of core, thin section, and electrical imaging logging data are considered as the research objects with metamorphic and igneous rocks. Thus, the relationship between lithologies with different alteration degrees and reservoir quality is revealed. The study shows that feldspar chloritization and sericitization are the main factors controlling the hydrothermal alteration of the reservoir; the overall alteration degree of igneous rocks is high, and the overall alteration degree of metamorphic rocks is low; the reservoir with strongly altered igneous facies is prone to forming dissolution pores, with strong reservoir inhomogeneity and poor reservoir performance (alteration degree is greater than 15%); the reservoir with weakly altered metamorphic facies is prone to developing fractures and a high reservoir productivity (alteration degree is 0); The reservoirs with altered metamorphic facies are numerous in the formation, spatially diverse in type, and second in reservoir quality only to those in the weakly altered metamorphic facies (alteration degree of 0–15%). This method is expected to provide a reference for quickly finding advantageous reservoirs in the Bohai Sag.

After more than seven years of commercial development in the Fuling shale gas field, most old wells in the main block are confronted with significant pressure decline, so shale gas production is lower than the critical fluid-carrying flow rate and considerably reduced production. Pressure-boosting stimulation technology can increase the pressure difference between flow pressure and transmission pressure, which improves gas transmission capacity, maintains production and subsequently improves the recovery. This study analyzes the pressure-boosting stimulation pattern and prediction method of the remaining recoverable reserves in the Fuling shale gas field. The findings show that the pressure-boosting stimulation pattern of a gas-gathering station can reduce the abandonment pressure of a gas well to the maximum extent and fulfill the requirements for the new adjustment wells in the gas-gathering station; therefore, it is a pressure-boosting pattern suitable for the Fuling shale gas field. Blasingame analysis method can effectively predict the production change of continuous recovery over the next ten years. In addition, the influence of water production in shale gas wells on pressure-boosting stimulation technology is discussed. The research results can provide experience and direction for the continuous improvement of gas recovery in the Fuling and the same type shale gas fields.(c) 2022 Elsevier Ltd. All rights reserved.

为克服涪陵地区五峰组—龙马溪组页岩气储层低阻导致Archie类电法测井饱和度模型计算的含气饱和度不准确的问题,根据页岩气储层含气饱和度与偶极阵列声波测井和常规测井参数之间的关系,以及含气饱和度与总有机碳质量分数(TOC)之间的关系,建立了2种非电法测井含气饱和度计算方法,并通过实例井验证了2种方法的可行性及精确度.研究表明:涪陵地区焦石坝区块五峰组—龙马溪组页岩气储层低阻现象的主要成因是页岩石墨化,并且黄铁矿发育及黏土矿物附加导电也会对储层低阻现象产生一定的影响;利用横纵波时差比和岩性密度(DEN)拟合含气饱和度的方法具有一定的地区经验性,基于TOC计算含气饱和度的方法具有较好的普适性.这2种新方法适用于低阻页岩气储层的含气饱和度评价,具有一定的推广价值.

为加强具有国际领先水平的中石化电缆测井牵引器技术专利保护,详细探讨寻求国际专利保护PC T策略、申请美国专利的有效途径及把握基本专利优先策略、重视专利抢先申请策略等系措施,对深层次研究与实施牵引器技术专利保护和实现防御最终目标具有重要指导作用,供广大石油工程技术创新同行借鉴与参考.