The Investigation of Scale Inhibitor Performance at High Temperature, High Pressure (HTHP), and High Salinity Conditions

Abstract With the development of drilling in deep water areas, chemical treatments encounter more and more challenging operational conditions, including high temperature (>300°F), high pressure (>5,000 psi), and high salinity (>100,000 mg/L) as well as potential seawater breakthrough due to waterflood operations. To choose a best-fit scale treatment program, a primary step is to conduct laboratory testing for chemical performance evaluation. A deepwater well operation was expected in the near future. A chemical treatment program was requested for scale prevention and control under both primary depletion and waterflood stages. To qualify the scale treatment under the conditions of HTHP and high salinity, selected inhibitors needed to pass several criteria: 1. Thermal stability at >300°F; 2. Good tolerance to high levels of calcium and iron/compatibility with formation brine; 3. Good inhibition performance. Product evaluation including this qualification testing with formation water and sea water/formation water mixture was conducted in the laboratory for scale inhibitor product selection. High temperature vessels and/or dynamic scale loops are typically used to evaluate the performance and compatibility of inhibitors at HTHP. However, these testing approaches only allow observation of the initial and final scale status, not the scale formation process itself. In this study, a see-through autoclave was used for in-situ visual observation at HTHP. By using this technology, the scale formation and inhibitor performance can be observed over time with changes in temperature and pressure. It was found that scale formation and/or inhibitor-brine compatibility changed with temperature during the test, e.g., some scale formation and/or incompatibility was present in at high temperature but disappeared at lower temperatures. By using a see-through autoclave combined with other testing approaches, scale formation kinetics and mechanics can be better understood, and the interactions between inhibitors and brines were thoroughly studied to improve the understanding of inhibitor performance with specific water compositions for inhibitor selection at HTHP and high salinity formation brine conditions.