基于变孔隙压缩系数的深部低阶煤层渗透率实验

Experimental studies of deep low-rank coal reservoirs' permeability based on variable pore compressibility

深部低煤阶煤渗透率研究可为深部煤层气评价选区提供关键依据。基于应力-孔隙压缩系数-渗透率三者关系理论分析,利用高温覆压孔渗透实验数据,构建了变孔隙压缩系数下深部煤层渗透率预测模型。实验结果显示,变孔隙压缩系数下渗透率的预测模型较定孔隙压缩系数下渗透率预测模型能更为准确描述深部煤层渗透率,老君庙矿区的初始孔隙压缩系数为0.09 MPa^(-1),孔隙压力随有效应力变化的衰减系数为0.07 MPa^(-1),且初始渗透率随着温度升高而降低。根据孔隙压缩系数的定义,计算得到孔隙压缩系数。计算结果显示:实测孔隙压缩系数与拟合孔隙压缩系数之间的相关性较强;随着埋深增加,定孔隙压缩系数较变孔隙压缩系数模型下预测的渗透率偏低,揭示了该地区深部煤层渗透率并非如前所预期之悲观,仍存在一定可采潜力。

Studies on the deep low rank coal reservoirs＇ permeability can provide a key basis for evaluation and regional selection of deep coalbed methane （CBM）.Through theoretical analyzing the relationship among stress,permeability and pore compressibility,and using experiment data of porosity and permeability under high temperature and overlying pressure,a model is constructed to predict the deep low rank coal reservoirs＇ permeability based on variable pore compressibility.The results show that this model can predict permeability with variable pore compressibility more accurately than that with constant pore compressibility.The initial compressibility of coal mines in Laojunmiao area is 0.09 MPa^- 1,the attenuation coefficient of pore pressure changing with the effective stress is 0.07 MPa^- 1,and the initial permeability decreases with increasing temperature.The pore compressibility can be calculated according to its definition.The results demonstrate there is a strong correlation between measured pore compressibility and fitted pore compressibility; with an increase in buried depth,permeability predicted with constant pore compressibility is lower than that with variable pore compressibility.As a result,the deep coal reservoirs＇ permeability indicates there still exists a CBM exploitation potential in this area,not as predicted before.