This paper discusses the initiation and performance of a shallow zone steamflood project in the Loco performance of a shallow zone steamflood project in the Loco Field, Stephens County, Oklahoma. The flood has been conducted in two thin Permian Sands, at depths of 200 feet and 500 feet. The zones are 18 feet and 12 feet thick, respectively. Each sand is 74% oil saturated and has negligible gas saturation. At reservoir conditions the oil viscosity is over 798 cSt in the 200 foot zone and 254 cSt in the 500 foot zone. The heavy 200 API oil is immobile under natural conditions and earlier enhanced recovery projects have proven unsuccessful.
Three, 2.5 acre, inverted 5-spot patterns have been steamflooded thus far. Pattern response has been greatly influenced by a unique hydraulic fracturing program. Before steam injection was initiated, program. Before steam injection was initiated, horizontal fractures were induced in the formation, communicating the injection wells with each producer. Steam was injected above formation parting pressure and was then followed by cold water injection. Other parameters significantly influencing pattern response parameters significantly influencing pattern response have been the amount of heat input and areal confinement of the patterns.
Results indicate that steamflooding in the Loco Field is mechanically feasible. Oil recovery from steamflooding has been 90,500 bbls. or 645 BO/Ac. Ft. This represents an average pattern recovery of 46.4% of the original oil in place. The cumulative producing water/oil ratio was 4.77 to 1. producing water/oil ratio was 4.77 to 1
The Loco Unit covers approximately 2300 acres in Stephens County, Oklahoma. It is underlain by several productive Permian formations from 55 feet to 1200 feet. The zones are named alphabetically (i.e., "A"-deep, "C"-deep, "J"-shallow, etc.). When many of the wells were drilled in the late 1940's and early 1950's, oil production was established in the sands below 500 feet. Although at least four sands above that depth have good oil saturation, greater than 65%, and several of these shallow zones were perforated in original completion programs, there is no perforated in original completion programs, there is no evidence that any had appreciable primary recoveries. High oil viscosity and low reservoir pressures were the reasons for low primary production from the shallow sands.
Tables No. 1 and 2 indicate the reservoir properties of two of the shallow sands and of the properties of two of the shallow sands and of the oil from two of these zones. As is listed, the oil has a viscosity range of from 195 - 798 cSt at 70 deg. F. The oil viscosity in the deep formations, below 500 feet, range as low as 80 cSt. Here the less viscous oil and a solution gas producing mechanism allowed primary production. It is estimated that as much as 15% of the original in place was produced by primary means in the lower zones. These reservoirs have been successfully waterflooded with recoveries on the order of 15% of the original oil in place.
PREVIOUS RECOVERY ATTEMPTS PREVIOUS RECOVERY ATTEMPTS Effors were begun early in the operation of the Unit to develop a method to recover the immobile oil in the shallow zones. Cold waterflooding was attempted from 1953 through 1957 in eight contiguous 2 1/2 acre patterns. The zones of interest were the A-shallow patterns. The zones of interest were the A-shallow and C-shallow at 525 and 475 feet respectively. Production was commingled in the producers. Although Production was commingled in the producers. Although sands were separated by packers in the injectors, no separate records were kept for determining individual zone injection rates. The cumulative oil recovery from secondary operations was 42,800 BO or 9.1% of the oil in place.
In 1961 a hot waterflood was initiated in the same area as discussed above. The zone of interest was the A-shallow. This particular area of the unit was chosen for this experiment for the following reasons: the availability of wells, the five spot 2 1/2 acre patterns would yield quick response, the fluid and formation characteristics were typical of other Loco sands and the zone had already been cold waterflooded to its economic limit.
