Theoretical Model and Numerical Investigation of Near-Wellbore Effects in Hydraulic Fracturing

Abstract

Abstract The high near-wellbore pressure drop which has frequently been reported in fracture treatments is indicative of ineffective communication between the wellbore and the fracture. Although numerous observations of such effects have been published, few attempts have been made to understand them. This paper describes three possible mechanisms of near-wellbore effects: perforation phasing misalignment-induced rock pinching, perforation pressure drop, and fracture reorientation (deviation tortuosity) – and their implementation in a numerical fracture simulator. Typical signatures of all three effects in fracture treatment records are shown, and a method proposed by which to distinguish them. Perforation phasing misalignment has been identified as a cause of near-wellbore restriction. Because the fracture does not always initiate at the perforation, the fluid must communicate with the fracture through a narrow channel (micro-annulus) around the casing. The paper describes this pinching effect and shows that it is related to the contact stress between the cement and the formation. Perforation pressure drop and deviation tortuosity, which have previously been proposed by other authors, have also been modeled. They have been incorporated in the simulator, together with the phasing misalignment effect, to allow investigation of the differences in response between the different mechanisms. Results of simulating the effects of erosion of near-well effects on treating pressure are also shown.