Simulation of Injection Water Supply Wells in Central Arabia

Abstract

Abstract Seventeen wells were drilled in an aquifer to supply water for injection in an oil field in central Saudi Arabia. Although these wells produced high volumes of clear water on initial completion, during field start-up most wells produced poor quality water, and only at much reduced rates. A stimulation program to restore the productivity of water supply wells was initiated. The program included injection of 15 wt% HCl along with a friction reducer and a corrosion inhibitor. Samples of all injected and produced fluids were collected to analyze the solid particles present in the samples, and measure the concentration of key ions in the acid returns. The results of these analyses have been used to determine the mechanism by which damage to the wells occurred. In this paper we present conclusive evidence, drawn from analyses of the returned acid cleaning fluids, which indicates that biomass and microbial corrosion products, produced by active sulfate-reducing bacteria (SRB) populations during shut-in periods, were responsible for much of the damage experienced by these wells. The investigation has highlighted an absolute requirement for an effective downhole SRB control program to prevent subsequent damage to water supply wells which have been restored by the cleaning program. Based on the results of this investigation, an optimized cleaning procedure which will restore water productivity, and at the same time will minimize casing corrosion, has been developed. This program includes acid additives to minimize precipitation of calcium sulfate, elemental sulfur and ferric hydroxide, which can damage the formation and reduce the productivity of water supply wells.