Perforating Skin as a Function of Rock Permeability and Underbalance

Abstract

Abstract Experimental tests were performed under simulated downhole conditions to determine the minimum underbalance necessary to obtain zero-perforation damage skin in two sandstones of different permeabilities. The objective of this paper is to study the transient cleanup resulting from the dynamic surge of fluid through the perforation immediately after perforating, prior to any postshot flow. Single-shot perforation flow tests were conducted in nominally 100-md Gold and 200-md Berea sandstone cores under various underbalances. Prior to shooting, the virgin whole core diametral and axial permeabilities were measured. Perforation damage skin was determined using analytical and finite element models. For each of the two basic rock permeabilities, (1) the minimum underbalance required to obtain zero-perforating skin without postshot flow was determined, and (2) a relationship of skin to perforating underbalance was obtained. The experimental results were used to establish a Reynold’s number criterion for zero-perforation damage skin. Using the Reynold’s number criterion, a simple equation can be employed to predict, as a function of formation and fluid properties, the minimum underbalance to achieve zero-perforating skin prior to any postshot flow.