Numerical Simulation on Key Parameters for Wellbore Strengthening by Bridging Fracture

ABSTRACT: Wellbore strengthening (WBS) technology is a common method to alleviate lost circulation. It mainly uses lost circulation materials (LCMs) to bridge drilling-induced or natural fractures to artificially enhance fracture gradient and formation pressure-bearing capacity. In this work, a fully wellbore-fracture-bridge coupled numerical model is established by the finite element method (FEM) and finite volume method (FVM). The factors of bridge permeability, bridge location and bridge length are studied to improve the WBS treatment scientifically. Numerical simulation results indicate that a decrease in the bridge permeability leads to a continuous reduction in fracture width or the fracture to close. This result verifies the WBS theory of 'stress cag'. In addition, reducing the bridge permeability helps to enhance the fracture gradient and reduce the fracture internal pressure so that expanding mud weight window (MWW). Moreover, the results quantified the relationship between the enhanced fracture gradient and the geometry and physical properties of the bridge. For bridges with the same permeability, reducing the distance between the bridge and the fracture entrance and the bridge length is also beneficial to improve the WBS treatment. The research results can provide theoretical guidance for improving the design of LCMs and WBS treatment.