A fracture-mechanics-based model for wellbore strengthening applications

Wellbore strengthening is an effective method to mitigate lost circulation, a major non-productive-time drilling complication, which utilizes lost circulation materials (LCMs) to bridge small preexisting, drilling-induced, or natural fractures on the wellbore wall. Although a number of successful field applications have been reported, the fundamental mechanisms of wellbore strengthening are still not fully understood. Based on linear elastic fracture mechanics, this paper illustrates an analytical solution for investigating geomechanical aspects of wellbore strengthening operations. The proposed solution (1) provides a fast procedure to predict fracture-initiation pressure before and after bridging a preexisting fracture in wellbore strengthening; (2) considers effects of wellbore-fracture geometry, in-situ stress anisotropy, and LCM bridge location. The solution is validated by comparison with available fracture mechanics examples, then used to investigate and quantify the effect of several parameters on wellbore strengthening with a sensitivity study. Results show that the wellbore can be effectively strengthened by enhancing fracture-initiation pressure with wellbore strengthening operations, but the magnitude of strengthening is affected by LCM bridge location, in-situ stress anisotropy, and formation pore pressure. The proposed solution illustrates how wellbore strengthening works, and provides useful considerations for field operations. (C) 2016 Elsevier B.V. All rights reserved.