Subsea Water Treatment and Injection to Optimize Production and to Reduce Cost

Abstract

Abstract Water injection is normally used as the preferred drainage mechanism and to optimize oil recovery. Moving water treatment and injection close to the subsea wellhead, as close to the reservoir as possible, enables flexible, cost-efficient, and robust field development. The short distance the water travels and the unique approach to water treatment make the subsea solution attractive, with reduced energy and chemical consumption. Moving water treatment and injection to the seabed saves significant weight and space topside and enables unmanned or low-manned operations. The subsea approach and technology offer new ways to develop and optimize existing fields. Implementing and expanding water injection on existing fields are possible with minimal interruption to ongoing operations and practically no production shutdown required. The modular approach and flexibility enable more freedom to manage the subsurface uncertainties, mitigate risk, and pursue upsides throughout the life cycle of the field. Subsea water treatment and injection, combined with subsea chemical storage, enable an all-electric solution for sophisticated injection water for enhanced oil recovery with a high potential to increase value on brown and green fields. Treating seawater at the seabed has several inherent advantages, such as effective disinfection through long-time chlorine soak and removal of particles via sedimentation without topside processing equipment. SWIT is a modular system that can be adapted to all water requirements and is based on Seabox as the initial conditioning step where microbes are killed and particles are settled out. The quality of water injected into an oil reservoir impacts the water produced together with the oil and gas. Thorough disinfection to mitigate reservoir souring and H2S generation is a prerequisite. Further tailoring of the chemistry of the injection water to mitigate any compatibility issues between raw seawater and formation water is critical for many reservoirs and operations to avoid precipitation of solids and scaling. The subsea seawater treatment technology offers some unique capabilities to improve this. Subsea water treatment enables processing capacity increases without impacting the existing topside. This reduces weight, avoiding topside modification and associated shutdowns, cost, and environmental footprint compared to a traditional topside solution. Long-term maintenance-free and unmanned operations reduce logistics and hence improve safety. This paper discusses conceptually how the quality of water injected into the reservoir impacts oil recovery and overall flow assurance from a life-of-field perspective. Subsea chemical storage and pigging are also discussed and may play an important role in flow assurance and production optimization.