气水两相流阶段煤基质收缩量预测方法

为了尽量避免实验室对煤中甲烷气体解吸时煤基质收缩量测试结果的局限性,综合考虑煤层气井排采时气、水两相流阶段煤储层中气、水产出时引起的煤基质压缩变形与解吸收缩,构建具有一定普适性的力学预测模型显得很有必要。基于有效应力、损伤等力学理论,结合煤储层孔隙结构特征,构建了有效应力压缩煤基质的压缩效应模型;根据吉布斯公式、Bangham理论和Langmuir方程,构建了气体解吸引起的煤基质收缩解吸效应模型;基于表面自由能和煤基质弹性能等能量理论、断裂力学理论,建立了压缩效应与解吸效应相互影响下煤基质收缩数理模型。以沁水盆地樊庄区块为实例对气、水两相流阶段的煤基质收缩量进行了计算。结果表明:对基质收缩量的贡献方面,压缩、解吸效应及2者相互影响的4种效应贡献能力处于同一数量级。其中解吸效应影响最大,解吸效应的收缩量计算结果与其他学者实验室的测试结果基本相符。所建煤基质收缩量数学模型能对不同储层地质条件下气、水两相流阶段煤基质收缩量做出较准确的预测。

Prediction of coal matrix shrinkage in gaswater twophase flow stage

In order to avoid the limitations of laboratory experimentalresults about coal matrix shrinkage in gas desorption process，it is necessary to establish a universal mathematical model of coal matrix shrinkage in gas water twophase flow stage，the mathematical model can fully consider on both the coal matrix deformation and shrinkage.Based on the effective stress and damaging stress relevant theory，combined with pore structure characteristics of coal reservoir，the coal matrix shrinkage mathematical model under the effective stress was established.According to the Gibbs formula，combined with the Bangham’s theory and Langmuir gas adsorption/desorption equation，the coal matrix shrinkage mathematical model under the gas desorption was established.Based on the surface free energy and coal matrix flexibility energy and fracture mechanics analysis，the coal matrix shrinkage mathematical model considered on the mutual influences between the effective stress and gas desorption was established.The calculation results case of the Fanzhuang block show that：the contribution ability of stress desorption effect，and the mutual influences to matrix shrinkage are in the same order of magnitude.The desorption effect is the biggest one to the influences of the coal matrix shrinkage，and the calculation results about the coal matrix shrinkage under gas desorption are basically correspond with other scholars’ testing results.The mathematical model of the coal matrix shrinkage in gaswater twophase flow stage can make accurate prediction to different geologies and reservoir conditions.