Productivity Improvement in Highly Unconsolidated Formation: Skin Characterization and Mitigation, Case History

Abstract

Abstract The productivity of highly permeable and unconsolidated sandstone reservoirs is expected to be high; however, the production seldom meets expectation as these reservoirs are more sensitive to the formation damage from the drilling and completion of the well. There are extensive publications regarding characterization and identification of formation damage and the total final skin of thick unconsolidated oil reservoirs, with or without sand control (Okoye et al., 1992; Benion et al., 1994). However, many of the currently producing unconsolidated reservoirs are thin formations, with poor defined barriers producing heavy oil with a high water cut and sand production. To optimize productivity in wells completed in multiple thin highly permeable sands it has proved necessary to develop a new completion optimization methodology. The methodology accounts for formation damage mechanisms and mechanical skin factors - completion, perforation and non-Darcy effects - to select the optimum production strategy and final completion, including sand control. The completion optimization methodology can also be applied to existing wells to identify the factors limiting productivity and so evaluate the technical and economic of alternative remedial actions. The methodology was applied in one field with 15 wells completed with gravel pack completions in thin laminated sandstone reservoirs ranging in height from 4 to 15ft. producing intermediate crude with an average rate of 2000 BFPD, despite a high positive skin. Initially the skin was attributed to formation damage - fines and scaling. However, the damage was correctly determined to be due to non-Darcy flow due to inadequate sand control. Recompleting these wells and changing the production strategy the final skin was reduced by an average of 60% and production increased by 35%. The completion optimization methodology has proved to be a versatile means of optimizing production in a number of different fields with wells completed in a number of thin highly permeable sands, producing intermediate crude and water.