煤层气藏开发降压解吸气运移机理  

Transport mechanism of desorbed gas in coalbed methane reservoirs

作　　者：李相方[1] 石军太[1] 杜希瑶[1] 胡爱梅[2,3] 陈东[2] 张冬玲 

机构地区：[1]中国石油大学(北京)石油工程教育部重点实验室 [2]中联煤层气国家工程研究中心有限责任公司 [3]中石油煤层气有限责任公司

出　　处：《石油勘探与开发》2012年第2期203-213,共11页Petroleum Exploration and Development

基　　金：国家基础研究发展规划(973)项目"煤层气井间干扰机理及开发方式优选"(2009CB219606);国家科技重大专项"煤层气数值模拟与开发综合评价技术"项目(2011ZX05038)

摘　　要：气液两相流体流动与传质原理表明:浓度差驱动的扩散仅发生在单相流体中;气液易溶两相流体之间通过溶解进行扩散;气液不溶或微溶两相流体通过压差驱动渗流。据此认为基质孔隙解吸气应为压差驱动下的渗流,并不满足Fick定律。研究了降压解吸的气分子溶解、扩散、成核及成泡过程,对气泡和气柱进行了受力分析,建立了基质孔隙解吸形成的游离气进入割理及裂缝的非线性渗流模型。研究表明:煤基质孔隙中少量解吸气溶解扩散,而大部分成核及成泡,并在压差驱动下进入煤层割理及裂缝系统;考虑基质孔隙与割理压差时,基质孔隙压力下降较慢、传播距离较近,并会出现解吸气产出滞后现象;计算动态储量时需采用基质孔隙压力而非割理压力;注CO2提高煤层气采收率为驱替机理而非置换机理;提高煤层气采收率需优化开采压差而非地层压力越低越好。The gas-liquid two-phase flow and mass transfer principle shows that the diffusion caused by concentration difference only happens in a single-phase fluid;gas-liquid two-phase diffluent solution happens in the way of dissolution;and gas-liquid two-phase insoluble or semisoluble solution flows under differential pressure driving.These facts demonstrate that the transport of desorbed gas through matrix pores is the flow,and it doesn’t conform to Fick law.The dissolution,diffusion,nucleation and bubble processes of desorbed gas through depressurization are studied,and the nonlinear flow model of free gas from matrix pores to the cleat and fracture system is established based on force analyses of the gas bubble and the gas column.Research shows that a small amount of desorbed gas diffuses by dissolution;most of them becomes nucleation and bubble,and then flows to the coal cleat and fracture system under the pressure difference driving;considering the existence of the pressure difference between the matrix pores and cleats,the pressure in coal matrix will reduce more slowly,the investigated radius will be shorter,and the outflow lag phenomenon of desorbed gas will appear.The dynamic reserve should be calculated not by using cleat pressure but by the pressure in coal matrix.The mechanism of enhanced methane recovery by CO2injection is not replacement but displacement.Improved methane recovery can be obtained by optimizing the production pressure difference,it is not reasonable that the lower formation pressure gives higher methane recovery.

关 键 词：煤层气 扩散 解吸 渗流 开发 

分 类 号：TE37[石油与天然气工程—油气田开发工程]