Mesoscale numerical study on the evolution of borehole breakout in heterogeneous rocks

Abstract

Inherent heterogeneity of a rock strongly affects its mechanical behavior. We numerically study the mechanisms governing the initiation, propagation, and ultimate pattern of borehole breakouts in heterogeneous rocks. A twodimensional finite element model incorporating material heterogeneity is established to systematically examine the effects of several key factors on borehole failure, including borehole diameter, far-field stress, and rock heterogeneity. The inherent heterogeneity of a rock is explicitly characterized by prescribing the rock mechanical properties of mesoscale elements statistically obeying the Weibull distribution. Elastic damage mechanics is used to represent the constitutive law of the mesoscale element. We find that borehole diameter reduction remarkably changes the crack failure from tensile to shear and elevates the critical hydrostatic pressure. Far-field stress anisotropy strongly affects the shape of the borehole breakout. Rock heterogeneity dictates the location of the preferred crack under the hydrostatic stress, which leads to local stress concentration, and determines the types of breakouts around the borehole. Our findings facilitate in-depth understanding of the classic borehole stability problems in heterogeneous rocks. K E Y W O R D Sborehole breakout, borehole diameter, rock heterogeneity, Weibull distribution

Discrete Element Simulation of Fracture Evolution around a Borehole for Gas Extraction in Coal Seams

“…The shape and size of the borehole and the stress state have a great influence on the mechanical properties of the rock sample. Li et al 13 have systematically studied the influence of several key factors, such as borehole diameter, far-field stress, and rock heterogeneity, on borehole failure. Lu et al 14 and Yang et al 15 have studied the mechanical properties of specimens with holes under true triaxial loading and the failure behavior and fracture evolution mechanism of nonsustained jointed rock masses with round holes, respectively.…”

Experiment Analysis of Drilling Feedback Signal from Simulation of Roadway Roof

“…The state of rock strata can be judged by vibration signals [4,5]. However, in the research of identifying roof strata by vibration signals, insufficient data volume, low recognition accuracy, and the need for manual processing of vibration signals are all factors that restrict the identification of roof lithology by vibration signals [6][7][8]. Therefore, this study takes the analysis algorithm of vibration signals as the core and generates the corresponding computer program, so that the input vibration signals can be automatically converted into information about the rock strata.…”