The Steam-Foam Process

Abstract

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. Summary The steam-foam process was developed to improve the sweep efficiency of thesteamdrive and steam-soak processes. Steamdrives that are not stabilized bygravity can have a poor vertical sweep efficiency as a result of (1) gravityoverlay in a thick sand with vertical communication and/or (2) channeling in alayered formation with poor vertical communication between sand members. Thereduced mobility of steam foam increases the pressure, and gradient in thesteam-swept region to displace the heated oil better and to divert steam to theunheated interval. Surfactants reduce the steam mobility by stabilizing theliquid lamellae that cause some or all of the steam to exist as a discontinuousphase. The propagation of surfactant is retarded by ad sorption. In the phase. The propagation of surfactant is retarded by ad sorption. In the case of ionexchange of divalent ions from the clays, the surfactant is also retarded byprecipitation and/or partitioning into the oil. The rate of propagation of foamis also determined by the mechanisms that generate and destroy foam. Thegeneration mechanisms include leave-behind, snap-off, and division. Thedestruction mechanisms include condensation and evaporation, coalescence by alimiting capillary pressure, and coalescence resulting from the presence ofoil. The foam texture can be predicted from a population balance that includesthese mechanisms. predicted from a population balance that includes thesemechanisms. Introduction Scope. This paper reviews the steam-foam process. It is not an exhaustivesurvey of the literature, and I apologize to the many contributions that had tobe omitted because of length limitations. The types of field application ofsteam foam are discussed first. Examples are taken from reported pilot results. The remainder of the paper focuses on process mechanisms. Understanding of themechanisms for foam flow in porous media is still in the formative stage, andmany advances can be expected. It is hoped that this paper will help thepracticing engineer apply the process more efficiently and will challenge theresearcher to advance the knowledge of the process and to develop moreefficient formulations. History. The concept of using foam for mobility control in petroleumrecovery was first suggested in 1958 by Bond and petroleum recovery was firstsuggested in 1958 by Bond and Holbrook. The first research on the mechanisms ofthe foam-drive process was the contribution of Fried. The research in thisfield was pioneered by Bernard and Holm of Union Oil Co. and Marsden and hiscolleagues at Stanford U. during the 1960's. In a 1986 literature survey, Marsden gives a history of foam in porous media. The first process patent forthe steam-foam process was a 1968 patent granted to Needharn, describing aprocess to plug high-permeability strata so that steam may be diverted into theless-permeable strata. The application of steam foam to improve the injectionprofiles of steam-soak wells was reported by Fitch and Minter. The descriptionof a steam-foam-drive process to control gravity override and the results ofthe first process to control gravity override and the results of the firstfield test of the process were described in a 1978 patent granted to Dilgren etal. The 1990's saw a large number of field test reports and research results. Many of the early field tests are reported in U.S. DOE reports. A survey wasgiven by Peterson and Schwartz in 1984. Marsden prepared a survey of theliterature on foam in porous media through 1985. A survey of the foam rheologyliterature was prepared by Heller and Kuntamukkula in 1987. The Proceedings ofa 1987 symposium on surfactant-based mobility controls is directed to miscibleprocesses, but the basic research applies to steam foam as well. Application of the Steam-Foam Recovery Processes Gravity Override. The steamdrive process is very efficient and there islittle potential for foam when the effect of gravity makes a large contributionto the flux of the heated oil from the injecter to the producer (downdip)and/or from the gas/oil contact (GOC) to the perforated interval or pumpoff-take level. The gravitational flux from the injecter to the producer islarge for a reservoir with a large dip angle and/or permeability and alinedrive with updip steam injection. permeability and a linedrive with updipsteam injection. An example of such a reservoir is the Mount Poso field, wherethe dip angle is only 6 degrees but the permeability is 20 to 30 darcies. Thegravitational flux from the GOC to the pump off-take level is large for athick, high-vertical-permeability reservoir such as that described by Matthewsand Lefkovits. For such a reservoir, Vogel suggests injecting just barelyenough steam after steam breakthrough to maintain the heat requirements withoutproducing steam. Steam will override the reservoir, and poor vertical sweepwill result, if a reservoir (or a sand unit of a multizone reservoir) hasnonzero vertical permeability and does not have high enough dip and/orhorizontal permeability. Such a reservoir has a good potential for theapplication of foam. This override and poor sweep is similar to the bypassingdescribed by Dietz for a low-density, high-mobility fluid and by van Lookerenfor a steamdrive. An example of such a case is the steamdrive in the MeccaPilot of the Kern River field (3 1/2 dip angle), where steam breakthroughoccurred early and oil production declined as a result of (1) poor pumpefficiency because of the produced steam and (2) reduced pressure gradient forhorizontal oil displacement as the steam-zone thickness increased. P. 449