Discrete element analysis on the influence of drilling fluid pressure on core discing in pressure-preserved coring

Abstract

In the process of coring in a high in-situ stress environment, the rock core is damaged due to stress release, and core discing is a prominent manifestation of this damage. Pressure-preserved coring has no direct effect on in-situ stress, and its influence on stress release is related to drilling fluid pressure. Yet fluid pressure in the coring process was not considered in most former numerical simulation studies on core discing. In this paper, the discrete element method software PFC3D is used to conduct a numerical simulation of the coring process. According to the two conditions without drilling fluid pressure and with it, and different horizontal in-situ stresses of 5-160 MPa, fracture and discing of the core with drilling are observed. In addition, the law of fracture and discing in the process of coring was studied, and the function of pressure-preserved coring to prevent fracture and discing is explored. Simulation results show nonlinear trends in distribution of discs both in time and in space.