This study explores the application of multiphase pumps as an alternative to conventional separation using rigorous steady-state simulation models incorporating a newly developed multiphase pumping model. The simulation results show that multiphase pumps are advantageous in not only reducing facilities, but can also increase production rates by lowering the backpressure on wells. Additionally, the complexities associated with multiphase flow through a single pipeline are compared to running dual single-phase pipelines and important considerations observed with the steady-state simulation are highlighted.
Following it's emergence from research labs a decade ago, multiphase pumping has become a viable solution to a wide number of field development plans. While the technology is seen to be particularly beneficial in remote locations such as the deepwater Gulf of Mexico, pumps have also been deployed to a number of onshore locations ranging from Alaskan North Slope to Columbia and from West Africa to the Middle East. Multiphase production systems require the transportation of a mixture of oil, water and gas, often for many miles from the producing well to a distant processing facility. This represents a significant departure from conventional production operations in which fluids are separated before being pumped and compressed through separate pipelines. By eliminating this equipment, the cost of a multiphase pumping facility is about 70% that of a conventional facility (Dal Porto, 1996) and significantly more savings can be realized if the need for an offshore structure is eliminated altogether. However, multiphase pumps do operate less efficiently (30-50%, depending on Gas volume fraction and other factors) than conventional pumps (60-70%) and compressors (70-90%). Still, a number of advantages in using multiphase pumps can be realized, including:
Increased production through lowering backpressure on wells;
elimination of vapor recovery systems;
reduced permitting needs;
reduction in capital equipment costs; and,
reduction in "footprint" of operations.
Interest in the subsea deployment of multiphase pumps has grown as operators search for methods to improve recoveries and economics for subsea completed wells. While subsea completed wells enable development of deepwater resources as well as marginal fields in normal water depths, without some form of subsea processing, these wells are expected to experience poor ultimate recoveries due to the high backpressures. For example, conventional production operations routinely drawdown wellhead pressures to 100-200 psig. A subsea completed well, however, may have abandonment wellhead pressures of 1,000-2,000 psig due to the backpressure added by the long multiphase flowline. In addition, operating as such a continual high backpressure has been shown to have a direct impact on production decline behavior, acting to reduce ultimate recovery (Martin & Scott, 2002). Maintaining a high backpressure can be viewed as a production practice that wastes reservoir energy. Energy that could be used to move reservoir fluids to the wellbore and out of the well is instead lost to flow through a choke or a long flowline.