煤层气合采地质研究进展述评

煤层气合采是提高多煤层区煤层气开发效率的重要途径，但成藏作用的特殊性决定合采方式与产能效果复杂多变，高效开发面临较大挑战。我国煤层气地质工作者围绕多煤层煤层气成藏与合采可行性开展大量基础研究与工程实践，取得丰富的阶段性成果，为深化煤层气开发地质理论、推动产业发展提供有力支撑。从叠置煤层气系统成藏机理、合采地质约束条件、合采可行性判识方法、合采储层伤害4个方面，系统分析评述我国煤层气合采地质领域的最新研究进展，以期为后续研究开展、工程实施与产业建设提供参考。主要认识可概括为:(1) 深化了叠置煤层气系统成藏的层序控气机理以及成岩作用与地应力的后期改造效应；构建了煤系地下水环境化学封闭指数，为判识含气系统叠置性及流体动力条件提供了新的参数，结合流体压力剖面识别出3类含气系统叠置地质模式(增长型、衰减型和稳定型)；进一步将叠置煤层气系统理念扩展到煤系气范畴，提出煤系复合储层叠置含气系统“共采兼容性”理论与方法体系，并应用于煤系气合采先导示范工程，取得初步应用成效；(2) 华北石炭?二叠系(太原?山西组)与黔西?滇东上二叠统(长兴?龙潭组)是煤层气合采研究与工程实践的热点区域(层域)，压力系统及渗透性差异是合采中最受关注的地质因素。华北山西组、太原组的水动力系统与供液能力差异是制约合采效果的重要因素，黔西?滇东地区合采煤层的最大层间跨度、累计煤厚、煤体结构受到更多关注，表层水干扰是制约织金区块煤层气合采效率的关键；(3) 产能分析、物理模拟、数值模拟、产出水地球化学分析是煤层气合采可行性与干扰判识的重要方法，提出了基于产出水地球化学解析合采井产出水源和判识干扰程度的基本思路、技术图版和评价流程及基于产能曲线分峰剥离的产层贡献分析方法，技术方法的不断成熟、创新为煤层气合采方案、工艺优化与效率提升提供了有力支撑；(4) 煤层气合采对地质条件与工程扰动更为敏感，易诱发储层伤害，涉及产层暴露诱发的贾敏效应与气锁伤害，压力系统与渗透性差异诱发的应力与速度敏感伤害。均一化储层改造、分压力系统开采(分时间或分空间)、精细化排采设计与管控是降低储层伤害的有效途径。 

Review of the progress of geological research on coalbed methane co-production

Coalbed methane (CBM) co-production is an important way to improve the efficiency of CBM development in multi-seam areas, but the special nature of reservoir formation makes the co-mining method and production effect complex and variable, which presents challenges for efficient development. Experts in the field of CBM from China have carried out a lot of basic research and engineering practice on CBM reservoir formation and the feasibility of co-production in multiple seams, which have gained fruitful results, providing strong support for deepening the CBM geological theory and promoting industrial development. To provide reference for subsequent research, engineering implementation and industrial construction, this paper systematically analyzes and reviews the latest research progress in the field of CBM co-production geology in China from four aspects: reservoir formation theory of stacked CBM systems; co-production geological constraints; co-production feasibility identification method; and co-production reservoir damage. The main understandings can be summarized as follows. (1) The sequence gas control mechanism of the accumulation of the stacked CBM systems and the later modification effect of rock formation and ground stress are deepened. The hydrogeochemical closed index of coal-measure groundwater environment is constructed, which provides a new parameter to identify the stacked gas-bearing systems and hydrodynamic conditions, and three types of stacked geological patterns of gas-bearing systems (growth type, decay type and stable type) are identified by using fluid pressure profiles. The concept of stacked CBM system is further extended to the category of coal measure gas, and the theory and method system of “co-mining compatibility” of stacked gas-bearing systems based on coal-measure composite reservoirs is proposed and applied to the pilot demonstration project of coal-measure gas co-production, which has a chieved preliminary results. (2) The Carboniferous-Permian (Taiyuan-Shanxi Formation) in North China and Late Permian (Changxing-Longtan Formation) in Western Guizhou and Eastern Yunnan are the hotspot areas for CBM co-production research and engineering practice, and the fluid pressure system and permeability differences are the most concerned geological factors in co-production. The difference in hydrodynamic conditions and fluid supply capacity of Shanxi Formation and Taiyuan Formation is an important factor limiting the CBM co-production in North China. The maximum inter-seam span, cumulative thickness, coal body structure of the coal seam in co-production in Western Guizhou and Eastern Yunnan have received more attention, and interference from shallow groundwater is the key restricting the efficiency of CBM co-production in the Zhijin Block. (3) Productivity analysis, physical simulation, numerical simulation, and geochemical analysis of produced water are important methods to identify the feasibility and interference of CBM co-production. The basic idea, technical template and evaluation process for analyzing the produced water source and identifying the degree of fluid interference in the co-production wells based on the geochemistry of produced water, as well as the production layer contribution analysis method based on the peaking and identification of the gas-production curve, have been proposed. The continuous maturity and innovation of technical methods provide strong support for the optimization and efficiency improvement of CBM co-production engineering. (4) CBM co-production is more sensitive to geological conditions and engineering disturbances, and is prone to induce reservoir damage, involving Jamin effect and airlock damage induced by production layer exposure, as well as stress-sensitive and velocity-sensitive damage induced by the pressure system and permeability differences. Homogenized reservoir reconstruction, separated-pressure system development (separated-time or separated-space), and refined drainage design and control are effective ways to reduce reservoir damage.