不同岩性火山岩孔隙度压力敏感性及其影响因素--以长岭断陷火山岩为例

Analysis on Porosity Stress Sensitivity of Volcanic Rocks with Different Lithology and Its Influencing Factors:Taking Volcanic Rocks in Changling Fault Depression as an Example

为了解不同岩性火山岩孔隙度的压力敏感性,笔者选取长岭断陷安山岩、角砾凝灰岩和凝灰岩的代表性岩样,分别进行3.4、8.3、13.1、17.9、22.8、27.6、32.4、37.2MPa多个覆压条件下的气体法孔隙度测量.结果表明,随着压力的增大,3种岩性岩样的孔隙度呈不同幅度的减小,幅度减小程度由大到小的岩性依次为凝灰岩、角砾凝灰岩、安山岩;说明凝灰岩的孔隙压力敏感性较强、角砾凝灰岩的孔隙压力敏感性居中、安山岩的孔隙压力敏感性最弱.经X射线衍射全岩分析、偏光显微镜下岩石薄片鉴定、高压压汞仪实验和基于CPMG脉冲序列的核磁共振实验分析显示,岩石组份、颗粒分选、孔径分布是影响孔隙压力敏感性的关键因素;塑性矿物体积分数越大、颗粒越小、孔径越小,相应孔隙度的压力敏感性越强.

In order to understand the pressure sensitivity of porosity of volcanic rocks with different lithology,the representative rock samples of andesite,breccia tuff and tuff in Changling fault depression were collected to measure porosity by gas method under the overburden pressures of 3.4,8.3,13.1,17.9,22.8,27.6,32.4 and 37.2 MPa respectively.The results show that with the increase of pressure,the porosity of the three lithological types of samples decreases in different ranges,and the decreasing level is tuff,breccia tuff and andesite from large to small,whichindicates that the pore stress sensitivity of tuff is the strongest,breccia tuff is in the middle,and andesite is the weakest.The analyses of whole rock X-ray diffraction,rock slice identification under polarizing microscope,high-pressure mercury porosimeter experiment and nuclear magnetic resonance experiment based on CPMG pulse sequence show that rock composition,particle sorting and pore type are the key factors affecting pore pressure sensitivity;The larger the volume fraction of plastic minerals,the smaller the particles and the smaller the pore size,the stronger the pressure sensitivity of the corresponding porosity.