沁水盆地南部煤层气井排采储层应力敏感研究

Study on stress sensitivity of coal reservoir during drainage of coal-bed methane well in Southern Qinshui Basin

为分析煤层气排采不同阶段煤储层应力敏感性及渗透率变化的影响因素,采集沁水盆地南部煤样,开展了不同实验条件的应力敏感实验。结果表明:有效应力从0增加到10 MPa时,煤样渗透率减少了50%~70%;有效应力从10 MPa增加到20 MPa时,损失量仅约占初始渗透率的10%;有效应力低于2.5 MPa时,应力敏感性较强;有效应力增加到3.5 MPa的过程中,渗透率损害系数急剧上升,渗透率损耗为20%~30%;有效应力从2.5 MPa增加到9 MPa时,应力敏感性最强,有效应力从3.5 MPa上升至9 MPa时,渗透率损害系数快速下降,渗透率损耗约60%;有效应力自9MPa之后,渗透率损害系数缓慢下降,渗透率损耗约10%;渗透率损害率介于30%~65%,临界应力为7~11 MPa。有效应力较低且不变时,煤样渗透率随孔隙压力增加而增加。围压不变时,随有效应力下降和孔隙压力增加,煤样渗透率下降,这与有效应力和孔隙压力变化引起的煤储层渗透率变化量有关。

Coal samples from Southern Qinshui Basin were sampled,and experimental study on stress sensitivity under different experimental condition was performed,in order to analyze stress sensitivity and affecting factors on permeability of coal reservoir at different stage of coal-bed methane drainage. The results show that permeability of coal samples decline 50%- 70% when the effective stress increase from 0 to 10 MPa,and the loss of coal reservoir permeability is about 10% when the effective stress increase from 10 MPa to 20 MPa. The stress sensitivity of coal samples are relatively stronger when the effective stress is below 2. 5 MPa. The damage coefficient of permeability increase quickly and the loss of permeability is about 20%- 30% of the initial permeability from coal samples when the effective stress increase to 3. 5 MPa. The stress sensitivity is strongest when the effective stress increase from 2. 5 MPa to 9 MPa. The damage coefficients of permeability decrease quickly and the initial permeability from coal samples lose 60% when the effective stress increases from 3. 5 MPa to 9 MPa. The damage coefficient of permeability decrease slowly and the lossof permeability is about 10% of the initial permeability from coal samples when the effective stress beyond 9 MPa. The damage rate of permeability from coal samples is between 30% and 65%,and the critical stress is 7 MPa to 11 MPa.The permeability of coal samples increase with increase of pore pressure,when the effective stress is relatively lower and constant. The permeability of coal samples decrease with the decline of effective stress and increase of pore pressure when the confining pressure is constant,which is related to the variation of permeability caused by the variation of effective stress and pore pressure on coal reservoir.