中高煤阶煤岩弹性模量及其影响因素试验研究

Experimental study on elastic modulus of medium- high rank coals and its influencing factors

煤层气勘探开发中煤岩弹性模量是重要的力学参数之一,针对取自沁南和鄂尔多斯盆地东南部的25个中高阶煤岩心,开展了变围压条件下煤岩应力-应变关系测试。根据应变曲线直线段计算出不同围压下的煤岩弹性模量,并对影响弹性模量因素进行了分析。结果表明:煤岩弹性模量具有较强的非均质性,受孔-裂隙、煤岩煤质、围压以及流体介质等因素的综合影响。煤岩孔-裂隙等固有缺陷越发育,弹性模量越低;煤岩镜质组、微镜煤和固定碳含量的增加使弹性模量降低,煤岩惰质组、微惰煤和灰分的增加则相反;煤岩孔-裂隙受围压作用而压密闭合,致使弹性模量增加;水介质的吸附作用和体积力反作用,削弱了煤岩抵抗变形的能力,导致弹性模量降低。综合考虑以上因素,可准确预测地层条件下的煤岩弹性模量分布。

Elastic modulus of coal is one of the most significant mechanical parameters. In this paper,a total of 25 cores from the southern Qinshui and southeastern Ordos Basins were carried out on the stress- strain at different confining stress conditions. Based on the stress-strain curve,the elastic modulus of coal was obtained. Furthermore,the controlling factors of elastic modulus of coal were comprehensively analyzed. The results showed that the elastic modulus of coal had a strong heterogeneity and is affected by pore- fracture,coal compositions,coal quality,confining stress and fluid media etc. The elastic modulus of coal reduced due to the development of pore- fracture within coal. With the increase in vitrinite,vitrite and fixed carbon contents,the elastic modulus decreased. However,the elastic modulus would increase with incremental inertinite and inertite contents and ash yield. The elastic modulus increases resulting from the compression and closure of pore- fracture caused by the increase in confining stress. The resistance of coal deformation is induced by the adsorption and volume force from water,which results in the decrease in the elastic modulus. Based on the multiple influencing factors,the elastic modulus distribution of coal reservoir in- situ can be predicted.