摘要
【目的和方法】吸附气、游离气产出过程及其产出效率的动态配分机制是深部煤层气勘探开发亟待解决的关键科学问题。基于探井取心测试化验数据,系统分析了深部煤层气资源的理论可动性,结合数学/数值模型构建、甲烷碳同位素监测和排采曲线解剖,揭示了排采诱导的储层压降扩展、吸附气解吸扩散、游离气渗流的时空演化过程及其产出效应,提出了深部富游离气煤储层多态甲烷协同供气机制和理论生产模式。【结果和结论】(1)深部煤层气井生产过程中,游离气和吸附气具备“连续-协同”的供气特点和“竞争产出”的配分关系,任意时刻产出气均为二者的混合气,不同赋存态甲烷的动态配分比例取决于不同生产阶段压力传播域内以“降压诱导解吸、压差驱动渗流”为核心的游离气传质效率和吸附气解吸补充效率的叠合。(2)深部煤储层将经历解吸全过程,降至关键解吸节点所需压力降幅较大,初期高储层压力-低解吸效率与后期高解吸效率-低压降空间的矛盾难以调和,压降漏斗内吸附气平均解吸率偏低且供气单元主要集中在高渗改造区,游离气供气半径可持续拓展并始终占据较大产量比重,高密度井组联采或气-水分布的强非均质性会导致吸附气-游离气产出占比发生调整,调整过程取决于供气单元拓展与流体供给能力的动态匹配关系。(3)游离气和吸附气分别具有“骤增-缓降或骤增-骤降-缓降”和“缓增-趋稳-缓降”的生产特征,总体产能存在快速上产、相对稳产和缓慢递减3个主要阶段,排采曲线形态受控于游离气量、原位渗透率、储层改造效果、排采降压制度等因素,部分井在相对稳产阶段存在先骤降后趋稳2个次级阶段。(4)增大改造体积、提高水平段长、寻找富游离气-高孔渗区段是增产核心,探索提高吸附气解吸效率和压降下沉幅度的工艺技术是增加下探深度的关键,兼顾气井生命周期和流体产出效率构建“动态调控排采制度”是产能充分释放的重要前提。(5)以地质-工程一体化原理为指导,合理确定深部不同地质单元煤层气产能目标及其所需井控面积,协同优化钻完井方式、井网密度、压裂参数、配产速率和生产周期,是深部煤层气效益建产的重要攻关方向。
[Objective and Methods] The production processes of adsorbed and free gases and the dynamic partitioning mechanism behind the production efficiency of both gas types are critical scientific issues to be addressed urgently in the exploration and production of deep coalbed methane(CBM).Based on the test and assay data of cores from exploration wells,this study systematically analyzed the theoretical production of deep CBM resources.By integrating the building of mathematical and numerical models,carbon isotope monitoring of methane,and the analysis of production curves,this study revealed the spatiotemporal evolutionary processes of production-induced pressure drop expansion,adsorbed gas desorption,and free gas seepage,as well as their production effects.Finally,this study determined the synergistic gas supply mechanism and theoretical production modes of methane with multiple occurrence states in free gas-rich deep coal reservoirs.[Results and Conclusions] During the production of a deep CBM well,free and adsorbed gases exhibited a continuous,synergistic gas supply characteristic and a partitioning relationship characterized by competitive production,with the produced gas identified as a mixture of both gas types at any given time.The dynamic partitioning ratios of methane with varying occurrence states depended on the superposition of free gas mass transfer efficiency and adsorbed gas desorption efficiency within the pressure propagation domain in varying production stages,with the efficiencies centering on pressure drop-induced desorption and differential pressure-driven seepage.Deep coal reservoirs would experience an entire desorption process,with substantial pressure drop required to reach critical desorption nodes.It is challenging to resolve the inherent contradiction between the high reservoir pressure and low desorption efficiency in the early stage and the high desorption efficiency and limited pressure drop in the late stage.The pressure drop funnel,adsorbed gas exhibited a relatively low average desorption rate,with gas supply units concentrated primarily in high-permeability stimulated zones.Free gas showed a continuously expanding supply radius and a consistently high production proportion.High-density well group co-production or the heterogeneity of gas-water distribution can lead to adjustments in the adsorbed and free gas proportion,and the adjustment process depend on the dynamic matching relationship between gas supply unit expansion and fluid supply capacity.Free and adsorbed gases demonstrated the production characteristics of sharp increase-gentle decline(or sharp increase-sharp decline-gentle decline) and gentle increase-stability-gentle decline,respectively.Their overall production capacity can be divided into three stages primarily:rapid addition,relative stability,and slow decline.The morphologies of production curves were influenced by free gas volume,in-situ permeability,reservoir stimulation performance,and pressure drop system.For some wells,the relatively stable production stage can be further divided into two substages:sharp production decline followed by stable production.The core strategies for production growth include increasing the stimulated reservoir volume,extending the horizontal sections of wells,and pinpointing free gas-rich zones with high porosity and permeability.Meanwhile,the key to an increase in the exploration depths of deep CBM is to explore technologies for enhancing both the desorption efficiency of adsorbed gas and the overall influential depth of pressure drop.Constructing a “dynamic regulation system for drainage and production” that balances gas well lifecycle and fluid production efficiency forms the critical foundation for fully releasing production potential.Furthermore,the first priority for commercial production capacity construction of deep CBM is determining rational production capacity targets and required well-controlled areas for varying deep geological units and synergistically optimizing well completion methods,well pattern density,fracturing parameters,production allocation rates,and production cycles under the guidance of geological and engineering integration.
作者
陈世达
张泰源
汤达祯
许浩
陶树
李松
唐淑玲
CHEN Shida;ZHANG Taiyuan;TANG Dazhen;XU Hao;TAO Shu;LI Song;TANG Shuling(School of Energy Resources,China University of Geosciences(Beijing),Beijing 100083,China;Coal Reservoir Laboratory ofNational Engineering Research Center of CBM Development&Utilization,Beijing 100083,China)
出处
《煤田地质与勘探》
北大核心
2025年第4期58-73,共16页
Coal Geology & Exploration
基金
国家自然科学基金项目(42130802,42102206)
中国石油集团公司科技专项项目(2023ZZ18,2023YQX10110)
长庆油田科技重大专项项目(2023DZZ01)
贵州省科技支撑计划项目(黔科合支撑[2025]一般062)。
关键词
深部煤层气
吸附气
游离气
产出机理
生产模式
deep coalbed methane(CBM)
adsorbed gas
free gas
production mechanism
production mode
作者简介
第一作者:陈世达,1991年生,男,山东莒县人,博士(后),副教授,博士生导师。E-mail:cugb_csd@126.com。
