Abstract:
The accuracy of brittleness evaluation critically influences the effectiveness of hydraulic fracturing in deep coal reservoirs; however, conventional methods, largely developed for shale, are inadequate for coal rocks owing to their complex cleat systems and pronounced sensitivity to confining pressure. To address this, triaxial compression tests were conducted to obtain the stress-strain curves of coal rocks. A damage variable was introduced to quantify the nonlinear impact of pre-peak crack evolution on energy distribution, formulating a dual-parameter pre-peak brittleness index, Bpre, based on damage and energy. Incorporating the dynamic constraint effect of confining pressure, a post-peak brittleness index, Bpost, was established by coupling the stress drop rate with confining pressure. Subsequently, a comprehensive coal brittleness index, Bcoal, was derived by employing the harmonic mean method, integrating both pre- and post-peak energy characteristics and confining pressure constraints. Experimental results demonstrate that Bcoal effectively differentiates the brittleness of coal rocks across varying confining pressures, demonstrating reliable evaluation within the confining pressure range of 5 to 20 MPa, and exhibits superior sensitivity and reliability over traditional methods. This study enhances the accuracy of coal brittleness evaluation, thereby providing crucial theoretical support for the optimization of coalbed methane fracturing strategies.
点击查看大图
下载:
