Ultrahigh-Temperature/Ultrahigh-Pressure Scale Control for Deepwater Oil and Gas Production

Abstract

Summary Scale control in deepwater oil and gas production is often challenging not only because of the geological and mechanical limitations associated with deepwater wells, but also because of the high-temperature (>150°C) and high-pressure (>10,000 psi) (HT/HP) environment, which may be associated with brine containing high total dissolved solids (TDSs) (>300,000 mg/L). These extreme conditions make scale prediction, control, and testing difficult because of the requirements for special alloys, pumps, and control equipment that are not readily available. Therefore, few reliable ultrahigh-temperature/ultrahigh-pressure (ultra-HT/HP) data are available. To overcome such challenges, an efficient flow-loop method has been established to study both the equilibrium and the kinetics of scale formation and inhibition at ultra-HT/HP conditions. This paper will discuss (1) an efficient flow-loop method to study the solubility of scale minerals at ultra-HT/HP conditions, (2) solubility of barite at 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-HT/HP conditions. Specifically, the performance and thermal stability of some common scale inhibitors at the high-temperature conditions were studied in terms of barite-scale inhibition. The results to date indicated that (1) the solubility of barite at up to 200°C and 24,000 psi can be measured precisely by this newly developed flow-loop apparatus, (2) the rate of mineral scale formation at HT/HP 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 HT/HP apparatus for scale and inhibitor testing and information for better scale control at HT/HP conditions.