The El Dorado Steam Drive-A Pilot Tertiary Recovery Test

Abstract

Channeling is particularly detrimental to the recovery in a steam drive if the main recovery mechanism is oil distillation in the steam zone. The El Dorado pilot test suggests that a steam drive would not, in general, be economical for tertiary recovery in reservoirs where channeling occurs or where residual oil saturation is low in a zone swept by steam. Introduction The El Dorado 650-ft shallow sand is part of the El Dorado field, in the central part of Butler County, Kans. This sand is a member of the Admire group of sands, of Permian Age. Sand thickness varies from 10 to 20 ft, porosity ranges from 25 to 30 percent, and permeability varies from 20 to more than 1,000 md. Oil viscosity is 4 cp at formation temperature of 70 degrees F. Oil gravity is 37 degrees API. Irreducible water saturation indicated by laboratory waterflood tests is about 26 percent. Primary oil production started in 1915 and totaled 16 million bbl by 1926. Air injection was begun at this time and an additional 12 million bbl was produced. In 1947 waterflooding was started and about produced. In 1947 waterflooding was started and about 13 million bbl of additional oil was recovered by 1964. Field development reached a maximum of 5,000 acres in 1957. In 1964 about 3,000 acres was being flooded and there were 180 producing wells and 217 injectors. Production was marginal in many areas of the field. An apparently large amount of residual oil remaining after the waterflood motivated consideration of tertiary recovery. Of the various prospective tertiary recovery methods, steam drive prospective tertiary recovery methods, steam drive appeared the most promising and was chosen for initial field testing in 1961 Mechanism of a Steam Drive "Steam drive" refers to continuous injection of steam to displace oil to production wells. Numerous references have described the mechanisms that promote oil recovery. In general, there are three zones around a steam injection well: a steam zone, a hot-water (condensate) zone, and a cold condensate zone. The cold condensate bank moving ahead of the steam zone acts as a waterflood and lowers oil saturation to waterflood residual. Through viscosity reduction and thermal swelling, the hot-condensate bank may promote additional oil flow. The main mechanism in the steam zone is steam distillation, which may reduce oil saturation to a low value. The residual oil saturation in the steam-swept reservoir rock is essentially independent of the initial oil saturation. Marx and Langenheim published a solution to a heat balance that allows estimation of the heated area in a steam drive. This equation shows that the heated area is strongly influenced by heat loss to the cap and base rock. The thermal efficiency, or fraction of injected heat retained by the pay, depends partially on the thickness of the pay zone. For thin zones, thermal efficiency may be poor. Recently it has been shown that at some time after the start of injection the actual steam-zone area begins to lag behind the heat-bank area predicted by the Marx-Langenheim (M-L) equation. This time marks the beginning of a significant hot-water bank. In previously waterflooded reservoirs containing low-viscosity oil, the main recovery mechanism will be oil distillation in the steam zone. Distillation is particularly effective with high-gravity crudes. particularly effective with high-gravity crudes. JPT P. 1377