New Gas-Water Co-Injection Process Provides Solution for EOR in Unconventionals
A new Enhanced Oil Recovery (EOR) process, termed “Rapid-Switched, Stacked-Slugs (RSSS)”, has been developed and field tested. This process dramatically reduces surface injection pressures and compression costs/emissions for Huff & Puff EOR.
Low pressure gas injection is made possible via a patent-pending process that drops surface injection pressure in the range of 100-1,300 psig, thereby eliminating the need for large surface compressors. While surface pressure is reduced, the hydrostatic weight of the liquid, which is injected as precisely manufactured liquid slugs, allows the process to create pressures above the Minimum Miscibility Pressure (MMP) in the reservoir.
In addition, surfactant designed to alter wettability is delivered via the slugs of water. Thus, the recovery mechanism is not only due to multi-contact miscibility, but also surfactant assisted spontaneous imbibition (SASI) as a result of wettability alteration. Uniquely, this process can be delivered as a leased service, using a modular, self-contained surface system that can be quickly installed.
The first pilot of this new process was executed in the Bakken formation. The single injection cycle reached a bottomhole pressure of 4,600 psig, which was significantly greater than the approx. 2,450 psig MMP; a first for an EOR process in the Bakken. Over 46 MMscf of rich gas was co-injected along with 40,000 bbl of fresh water with surfactant. The pilot also demonstrated the ability of co-injection to reduce gas mobility in the reservoir and prevent gas breakthrough in adjacent wells.
The RSSS process resulted in approximately 10,000 barrels of incremental EOR recovery over a 1-year period for the pad, which translates into an impressive Gas Utilization Factor (GUF) of less than 5 Mscf/bbl EOR, a significant improvement when compared with most gas injection projects. While only one injection cycle was conducted in the pilot, this process is best applied in a round-robin fashion in a pad of 4-6 wells with each well experiencing multiple injection cycles.
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