摘要
目前人们普遍认为，在煤层气开发过程中，基质孔隙的解吸气主要呈游离态，受分子浓度差的作用，以气相扩散方式运移至割理。现有的扩散理论忽略了基质孔隙中水的存在及其对解吸气运移的影响。文中从煤层气成藏机理出发，分析认为甲烷、水、基质微孔同时生成，基质微孔中存在着自生水；然后对基质-割理的压差和基孔毛细管力进行了分析，在此基础上探讨了基质孔隙水的可驱动性和解吸气的运移方式。研究表明，基质孔喉中的水能否被驱动，取决于该孔喉的尺度、埋深、温度、压力、煤阶、距井筒的距离及排采的时长。当该孔喉中的水能被驱动，则解吸气以渗流的方式向割理运移；当不能被驱动，则解吸气以溶解相扩散或表面扩散。无论基孔中的水能否被驱动，解吸气都不能通过气相扩散的方式运移。
Abstract
It is widely believed that during CBM development, the adsorbed methane becomes free gas and moves to cleats by the mean of gas phase diffusion under the effect of molecular concentration difference. However, in fact, this ignores the presence of water in coal matrix pores, as well as the influence of water on the desorbed gas migration. In this paper, according to the forming mechanism of CBM reservoir, it is proposed that the methane, water and matrix micro-pores generate at the same time and micro-pores are filled with the autogenous water. Then the pressure difference between matrix and cleat, as well as the capillary force in micro-pore are analyzed. Based on this, the displace-ability of micro-pore water and the mean of desorbed gas migration are discussed. It is concluded that the micro-pore water mobility is influenced by pore size, temperature, pressure, coal rank, distance from gas well and duration of production. When the water is displaceable, the desorbed gas moves to cleat by flow. If not, the desorbed gas moves by flow dissolved phase diffusion or surface diffusion. Whether the pore water is displaceable or not, the desorbed gas can not migrate to cleat by gas phase diffusion.
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