四川盆地长宁示范区龙马溪组页岩岩石力学特性及脆性评价

Mechanical Properties and Brittleness Evaluation of Longmaxi Shale Rock of Changning Demonstration Area in Sichuan Basin

页岩的岩石力学特性对页岩气开发效果具有重要影响,因此以四川盆地长宁示范区志留系龙马溪组泥页岩层段为研究对象,分析其力学与脆性特性。采用矿物组分分析、地球物理测井分析和实验室力学实测相结合的方法,比较了龙马溪组龙一段和龙二段的脆性矿物含量、泊松比、杨氏模量、岩石脆性、三轴压力等力学特性。结果表明:龙二段比龙一段具有更高的脆性矿物含量,龙一段的泊松比明显高于龙二段,利用纵横波时差比可以反映泊松比的变化,纵横波时差关系图的斜率与泊松比具有相反的变化趋势。龙一段样品的杨氏模量低于龙二段样品,通过杨氏模量和泊松比关系图发现龙一段与龙二段发生分离,龙二段页岩段的脆性指数大于0.5,应力、应变曲线的负坡较陡。综合评价分析表明:龙二段具有较低的泊松比、纵横波时差比和较高的杨氏模量,龙一段比龙二段更易变形。因此龙二段脆性优于龙一段脆性,有利于后期的压裂改造。

Mechanical properties of shale rock play an important role in the development of shale gas. This paper focuses on analyzing the mechanical and brittle characteristics of shale rock by taking the Longmaxi Silurian shale clay of Changning demonstration area in Sichuan Basin as an example by the methods of min- eral composition analysis, geophysical log analysis and laboratory mechanics measurement. The mechanical properties （the content of brittle mineral, Poisson＇s ratio, Young＇s modulus, brittle rock, and triaxial stress） are compared between the Long 1 section and Long 2 section of Longmaxi Formation. The results show that Long 2 section has higher brittle mineral content than the Long 1 section, but the slope of aspect slowness diagrams and Poisson＇s ratio have the opposite trends, and the Young＇s modulus from the sam- ples of Long 1 section is lower than the Long 2 section. The Young＇s modulus-Poisson＇s ratio diagram in- dicates that the Long 1 and Long 2 section are separation. The shale brittle index of Long 2 section is grea- ter than 0.5 and the negative strain curve is very steep. The summary conclusions include the Long 2 sec- tion has a lower Poisson＇s ratio, lower aspect slowness ratio and higher Young model value, and the Long 1 section is more deformable than long 2. Therefore, the Long 2 section is more brittle than Long 1 which is better for press crack.