Formation Damage from Workover and Completion Fluids

Abstract

Abstract Wellbore damage that occurs during initial well completion or workover operations is the subject of this paper. The linear and radial fluid flow equations are reviewed in relation to this problem and in relation to the laboratory procedures used to test for such damage. procedures used to test for such damage. Return permeability testing methods are discussed, as are the results of such tests. Several commonly used completion and workover fluid systems were compared and these comparisons are included. The merits of the relatively new and almost nondamaging systems are given. Several cases of their application are discussed in the form of field case studies. Introduction A subject that has received a great deal of attention in recent years is that of formation or skin damage around a wellbore. Most of this attention has been directed to the problem of skin damage caused by drilling and cementing productive zones. Such damage normally is of a productive zones. Such damage normally is of a shallow penetrating nature and good perforating, stimulating and completion practices overcome much of the problem. However, poor completion and workover fluids and practices may cause considerable damage to a formation long after the formation was drilled, cemented and perforated. The damage to producing formations caused by workover and completion fluids is the subject of this paper. Many forces tend to change the natural virgin permeability of producing formations during initial completion and/or workover operations. The net result is usually a reduction in permeability in the vicinity of the wellbore or perforations, and a decreased ability of a well to produce. Operations considered here to be completion or workover functions include the following: perforating casing, under-reaming pay zones for perforating casing, under-reaming pay zones for gravel-packing, under-reaming injection zones for gravel-packing for disposal purposes, gravel packing, plastic sand consolidating, all workover packing, plastic sand consolidating, all workover operations in which a producing zone must be killed, all workover or completion operations in which wellbore fluids are lost to the formation and drilling into a pay zone after casing has been set on top of the zone.