Water-Alternating-Steam Process Improves Project Economics at West Coalinga Field

Abstract

The water-alternating-steam process (WASP) was applied to vertical expansion (VE) sands in the pilot area of Section 13D, West Coalinga field to stop wasteful steam production and to improve vertical conformance of injected steam. Before the WASP application, steam breakthrough in the VE sands caused well sanding, cutting of downhole tubulars, and high-temperature-fluid handling problems. To alleviate these problems, pumps had to be raised in five wells and one well had to be shut in, reducing oil production from the VE sands and the lower waterflooded zones. A WASP field test, based on a numerical simulation study, was implemented in July 1988 with alternating slugs of water and steam, each injected over 4 months. The WASP eliminated steam production, allowing the pumps to be lowered and the one shut-in well to return to production. Oil production remained constant through the first WASP cycle and increased during the second cycle. Sales oil (total production minus oil used to generate steam) increased as a result of saving generator fuel during the water leg of each WASP cycle, resulting in improved project economics.

Evolution of Field Rejuvenation

“…The water alternating steam process (WASP) had shown itself to be a viable method of operating a mature flood economically 5 . At Petrotrin there are several mature steamfloods, which exhibit high steam oil ratios, high water cuts, and high flowline temperatures.…”

Reservoir Characterization, Production Characteristics, and Research Needs for Fluvial/Alluvial Reservoirs in the United States

“…These techniques include waterflood after steamflood (Hong 1987;, steam-foam (Patzek and Koinis 1990;Mohammadi et al 1989), and water-alternating-steam processes (Hong and Stevens 1992;Bautista and Friedmann 1994). Chevron and Texaco implemented the waterflooding after steamflood process in California in the early 1980s, but discontinued the practice due to adverse production problems and questionable benefits .…”

“…One major benefit of WASP is the reduction or elimination of steam breakthrough (Blevins 1990). Chevron has implemented this mobility control technique at the West Coalinga and Cymric Fields, California, and claims to have succeeded in eliminating steam breakthrough problems and in improfig sweep and recovery efficiency (Hong and Stevens 1992;Bautista and Friedmann 1994). In addition, cost-effective high temperature polymer gels have been developed and successfully applied in California steamflood projects to mitigate steam channeling and premature steam breaktlwough (Hunter et al 1992;Littleiield et al 1992).…”

Coupling Smart Seawater Flooding and CO2 Flooding for Sandstone Reservoirs: Smart Seawater Alternating CO2 Flooding (SMSW-AGF)

“…WASP reduces or eliminates steam breakthrough because water that is injected after steam causes the steam zone to collapse while tending to pass the reservoir. In turn, more vertical thermal fronts are formed . In addition, we developed a new method of coupling steam with low-salinity (LS) water flooding to avoid the aforementioned steam flooding problems. , However, steam flooding is still an expensive and environmentally unfriendly source of improved oil recovery (IOR) …”