韩城地区煤储层孔渗应力敏感性及其差异

Stress sensitivity and difference of porosity and permeability in coal reservoirs in Hangcheng CBM block

以韩城煤层气区块3号、5号和11号煤层为例,进行不同围压条件下的煤心孔渗实验,探讨了该区煤储层物性与应力之间的耦合关系,建立了相应的数学模型。结果表明,煤心孔渗随围压的增加而不断下降,渗透率应力伤害远强于孔隙度应力伤害,但各煤层的应力敏感性各不相同:在实验围压从4.14 MPa(600 psi)增加到12.42 MPa(1 800 psi)条件下,11号煤层孔渗应力敏感性最强,孔隙度应力伤害达76.5%,渗透率应力伤害达93.3%;3号煤层孔渗应力敏感性最弱,孔隙度应力伤害38.5%,渗透率应力伤害77.9%;5号煤层孔渗应力敏感性较强,孔隙度应力伤害约45%,渗透率应力伤害达83.9%。分析认为,裂隙发育状况是造成各煤层间孔渗应力敏感差异的主要原因。从实验数据的拟合情况看,幂函数模式比指数函数模式更能准确地获取测试围压范围内的孔渗内插值。

In order to discuss the relationships between the physical properties of coal reservoir and the stress, the stress sensitivity experiments of the porosity and permeability of the coal samples from No.3, No.5 and No. 11 coal seams in Hancheng coalbed methane （CBM） block were carried out under various pressure and the corresponding mathematical models were established. The results showed that the porosity and permeability of the samples de- crease as the confining stress increases and the stress damage for permeability is much larger than that for porosity. However, the stress damage is different for different coal seams. When the confining stress increased from 4.14 MPa （600 psi） to 12.42 MPa （1800 psi）, the stress damage of the sample from No.ll coal seam was highest in the samples from three coal seams, with the porosity damage of 76.5% and permeability damage of 93.3%, that from No.3 coal seam was lowest with the porosity damage of 38.5% and permeability damage of 77.9%, and that from No.5 coal seam is relative high with the porosity damage of about 45% and permeability damage of 83.9%. It was suggested that the occurrence of the fractures in coal is resulted mainly from the stress damage difference among the coal seams. Additionally, the power function is more accurate than exponential function for fitting the measured value of porosity and permeability in the range of test stress.