Ultra-HTHP Scale Control for Deepwater Oil and Gas Production

Abstract

AbstractScale control in deepwater oil and gas production is often challenging due to not only the geological and mechanical limitation associated with deepwater wells, but also the high temperature (>150°C) and high pressure (>10,000 psi) environment, which may be associated with brine containing high total dissolved solids (TDSs > 300,000 mg/L or greater). These extreme conditions make scale prediction, control and testing difficult because of the requirements for special alloy, pumps and control equipments that are not readily available. Therefore, very few reliable ultra-HTHP data are available. To overcome such challenges, an efficient flow-loop method has been established to study both the equilibrium and kinetics of scale formation and inhibition at ultra-HTHP conditions. This paper will discuss (1) an efficient flow-loop method to study the solubility of scale minerals at ultra-HTHP conditions; (2) solubility of barite at a temperature up to 200°C and pressure up to 20,000 psi; and (3) scale control and inhibitor selection for deepwater oil and gas production at ultra-HTHP conditions. Specifically, the performance and thermal stability of some common scale inhibitors at the high temperature conditions were studied in terms of barite inhibition. The results to-date indicated that (1) the solubility of barite at up to 200°C and 24,000 psi can be precisely measured by this newly developed flow-loop apparatus; (2) the rate of mineral scale formation at HTHP may be considerably faster than previously projected from low temperature studies and hence, difficult to inhibit; (3) different scale inhibitors have shown considerably different thermal stability. The results and findings from these studies validate a new HTHP apparatus for scale and inhibitor testings and information for better scale control at HTHP condition.