The Effect of Stratification, Fractures, and Dip on Steam Sweep Efficiency and Heat Requirements of Steamflood Operations

Abstract

Member SPE-AIME Abstract A one-phase, thermal simulator has been utilized to study the applicability of steamflooding in different reservoir geometries. Two and three-dimensional numerical models of homogeneous dipping (0 deg., 15 deg., 30 deg., 45 deg., and 60 deg.), heterogeneous dipping (0 deg., 30 deg., and 45 deg.), and fractured dipping (0 deg., 30 deg. and 45 deg.) reservoirs have been developed. The parameters investigated were heat utilization, steam vertical and areal sweep efficiency. The simulator was also utilized to generate temperature profiles for different reservoir types at different injection times. Results of this study show that dip and/or fractures should not be considered detrimental when screening reservoirs for steamflooding. Heat utilization and vertical swept efficiency are not significantly affected by dip. Formation heterogeneities tend to control steam displacement in a reservoir more-so than dip does. Natural or induced fractures improved the steam sweep efficiency but at the expense of heat utilization. Averaged (over the upper, middle, and lower section of the reservoir) steam areal sweep efficiency improves with dip and/or fractures, and for extended injection periods the observed differences become less significant. Introduction Steamflooding is without question the most widely applied enhanced oil recovery technique but has been applied almost exclusively to massive, horizontal, unconsolidated sandstone and high oil saturation reservoirs. Reservoirs that did not meet these standards were not given a second chance as potential candidates for steamflooding and were potential candidates for steamflooding and were considered unconventional steamflood when implemented. The literature reports few cases of unconventional steamflooding. Nolan et al reported results of physical and numerical simulation of steamflooding carbonates reservoirs. They predicted steam-oil ratios less than 5-1/2 and recoveries greater than 80 percent in the heated zones. They reported heat percent in the heated zones. They reported heat scavenging methods as drawing down the reservoir pressure by continued production after stopping steam pressure by continued production after stopping steam injection, thereby flashing hot water in the water zone. This reduced steam-oil ratios by about 1-1/2 units relative to continuous steam injection. Britton et al discussed the FAST process (fracture assisted steamflood technology) and its application in a South Texas tar sand deposit. This technique, as the Shell method, injects steam in a low injectivity tar sand deposit through pre-established fracture network. Tar recovery from the pre-established fracture network. Tar recovery from the steamed zone was 66 percent. Williams presented results of a three dimensional simulation model of steamflooding a massive (285') steeply dipping (40–60 deg.) reservoir that contained an undersaturated zone. He concluded that steamflooding this reservoir is economically more attractive than steam stimulation. He also recommended that no new up-dip producers should be drilled and that up-dip injectors are required to maximize oil recovery. Geshelin et al utilized a general thermal simulator (ISCOM) to study steam injection in fractured reservoirs. He showed that the time profiles of reservoir water saturation depend on the fracture orientation. Abad reported results of a steamflood pilot in a layered-dipping reservoir, and results of the numerical simulation performed to investigate the steam sweep efficiency in the Temblor reservoir which deg. (11 deg.) and is layered through the entire West Coalinga field. Most of the studies referred to in this paper and some others mentioned in the steamflooding literature have discussed specific situations and reservoir configurations, not attempting to generalize the effect that fractures, dip, reservoir heterogeneities or combinations may have on the applicability of steam. P. 215