Abstract: Since 2019, a major breakthrough has been made in the exploration of deep coal-rock gas and coalbed methane in the Daning-Jixian block on the eastern margin of Ordos Basin in China. The cumulative proven reserves of the main productive layer, i.e., the No.8 coal seam of Carboniferous Benxi Formation, have reached 3 063×10⁸m³, and also achieved a production capacity of 30×10⁸m³/a. Taking Daning-Jixian coal-rock gas field as a case study, this paper focuses on the goal of enhancing the estimated ultimate recovery (EUR) of individual wells throughout the full lifecycle of deep coal-rock gas, and systematically summarizes four key technologies: identification and evaluation of black-gold reservoirs, precise drilling, hydraulic fracturing, and production regime optimization. These technologies are discussed in detail as below. (1) Based on microscopic pore structures and well-logging response characteristics of different macroscopic coal-rock types, a quantitative identification system for black-gold reservoirs was established, incorporating two main categories of indicators, i.e., reservoir geological evaluation and logging parameters. It has been confirmed that black-gold reservoirs constitute the primary gas-producing intervals, and with every 1 % increase in the penetration rate of these reservoirs, the EUR per well can be improved by 1 %. (2) By innovatively integrating five types of gamma-ray curve crossover relationships with X-ray diffraction (XRD) mineralogical analysis, a precise geosteering technology for black-gold reservoirs in horizontal wells was developed. This approach effectively overcomes the influence of microstructures on wellbore trajectory control, achieving a penetration rate of over 80 % for black-gold reservoirs. (3) A black-gold reservoir dense fracture network fracturing technology system was developed, integrating the techniques such as bottomhole pressure-controlled fracturing, multi-cycle temporary plugging and diversion, and multi-size proppant synergistic placement. This system enables the optimized regulation of fracture height, fracture network density, and proppant intensity, thereby establishing a well-connected and fully-integrated fracture network. (4) Through studies on the post-fracturing shut-in for imbibition displacement, water-rock interaction, and production characteristics, the optimal shut-in period was preliminarily determined to be 7 to 10 days. An innovative "three-stage" drainage and production model was proposed, consisting of the primary stage dominated by native free gas and imbibition displacement-induced desorbed gas, the coexistence stage of free gas and desorbed gas, and the stage dominated by desorbed gas. Corresponding pressure control and production regulation techniques were developed, including pressure control with natural flow liquid unloading, pressure control with assisted liquid removal, and artificial lift. These innovations allow 25-day extension of the flow period, 455-day extension of the stable production period, a reduction in decline rate from 50 % to 30 %, and an increase in the average EUR per well by 8.64 %. The establishment of a key technology system for the efficient development of Daning-Jixian coal-rock gas field has become a successful paradigm for the development of deep coal-rock gas in Ordos Basin and even across China.

Key words: deep coal-rock gas, black-gold target zone, precise drilling, efficient fracturing, pressure control, cost-effective development technology

摘要： 自2019年以来,鄂尔多斯盆地东缘大宁—吉县(大吉)区块率先实现中国深层煤岩气(亦称深层煤层气)勘探重大发现,石炭系本溪组8号煤层(主力产层)的累计探明储量达3 063×10⁸m³,建成了30×10⁸m³/a的产能规模。以大吉区块煤岩气田为例,围绕深层煤岩气全生命周期单井估算最终采收量(EUR)提升目标,系统总结了黑金靶体的识别与评价、精准钻遇、压裂改造和生产制度优化四大关键技术:①基于不同宏观煤岩类型的微观孔隙结构和测井响应特征,建立了包含储层地质评价和测井参数2大类指标的黑金靶体定量识别体系,明确黑金靶体为主要产气贡献段,证实黑金靶体的钻遇率每提升1 % ,单井EUR可提高1%;②创新融合5种自然伽马曲线交切关系和X射线衍射矿物分析结果,形成水平井黑金靶体的精准钻遇技术,克服了微构造对井眼轨迹控制的影响,黑金靶体的钻遇率达80% 以上;③研发"黑金靶体密织缝网"压裂技术体系,集成控底压裂、多轮暂堵转向和多粒径协同支撑等工艺,实现了缝网高度、缝网密织度和缝网支撑度的优化调控,构建了充分弥合的压裂缝网;④通过分析压后焖井渗吸置换、水-岩作用及生产特征,初步明确合理的焖井时间为7~10 d,并创新提出了"原生游离气+渗吸置换解吸气"主导阶段、游离气+解吸气共存阶段、解吸气主导阶段"三段式"排采模式及配套的"控压+自喷携液—控压+辅助排液—人工举升"调控技术,使得气井的自喷期延长25 d、稳产期增加455 d,产量递减率由50 % 降至30 % ,单井EUR平均提升8.64 % 。大吉区块煤岩气田效益开发关键技术体系的建立为鄂尔多斯盆地乃至全国深层煤层气的开发树立了成功的范式。

关键词: 深层煤岩气, 黑金靶体, 精准钻遇, 高效压裂, 控压, 效益开发技术