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贵州省过饱和煤层气藏产气规律研究

Study on gas production laws of supersaturated CBM reservoir in Guizhou Province

  • 摘要: 基于过饱和煤层气藏的排采过程兼具游离气与吸附气的生产特征,为弄清此类过饱和气藏产气特征的内在原因和机理,探索影响其高产、稳产的主控因素,为后期此类气藏的勘探选区、井位部署、压裂及排采工程设计提供指导, 通过深入剖析游离气与吸附气的产出机理,将等温吸附曲线划分为2种经典类型,并结合现场生产实例,系统阐述了各自的产出特征及产能主控因素。研究结果表明:煤储层的等温吸附特征决定吸附气快速解吸释放的时间及储层导流能力的变化趋势,从而影响压力降的传播及游离气与吸附气的有效产出;过饱和煤层气藏具有排采初期见气快,产气增长快的特征,中后期的稳产气量、稳产期及衰减速率主要取决于产层的等温吸附特征、煤体结构及排采制度的合理性,其中等温吸附特征为主控因素。

     

    Abstract: The discharge process based on supersaturated CBM reservoirs has the characteristics of production of free gas and adsorbed gas. In order to understand the inherent causes and mechanisms of gas production characteristics of such supersaturated gas reservoirs, and explore the main controlling factors affecting high yield and stable production, and provide guidance for the exploration and selection of wells, well location, fracturing and drainage design of such gas reservoirs, the production mechanism of free gas and adsorbed gas are deeply analyzed and the isothermal adsorption curves are therefore divided into two classic types. Combining with the on-site production examples, their output characteristics and capacity control factors are wholly described respectively. The results of the study show that the isothermal adsorption characteristics of coal reservoirs determine the time of rapid desorption of adsorbed gas and the trend of reservoir diversion capacity, thus affecting the propagation of pressure drop and the effective output of free gas and adsorbed gas. The supersaturated CBM reservoir has the characteristics of rapid gas production and fast growth of gas production in the early stage of drainage. The stable gas production, stable production period and decay rate in the middle and later stage of drainage mainly depend on the isothermal adsorption characteristics of the production layer, the structure of coal and the rationality of the drainage system, among which the isothermal adsorption characteristics are the main controlling factor.

     

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