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The Permian Admire "650-ft" sandstone reservoir occurs at shallow depths (650 ft; 197 m), is thin (11 to 23 ft; 3 to 7 m), and has produced 48.7 million bbl of oil through primary and conventional secondary-recovery methods in the El Dorado field, Kansas. A micellar-polymer tertiary oil-recovery pilot project being conducted by Cities Service Oil Co. and DOE is aimed at recovering half of the 71.5 million bbl of oil still in the reservoir.
The 51-acre (20 ha.) block being tested for enhanced recovery at El Dorado field was initially assumed to be a generally homogeneous reservoir. A Phase 1 geologic analysis of seven slabbed and polished cores indicated the reservoir was, instead, heterogeneous and that it contained at least two vertically stacked layers with variable production characteristics. Considerable areal variability was also observed.
In Phase 2, a total of 24 cores was used to build a detailed geologic model. Various facies associated with a delta system were defined. Reservoir facies are distributary-channel sandstones, splay sandstones, and natural-levee deposits. Interdistributary-bay (in part intertidal), silty shales are present below, interbedded with and lateral to the sandstones. A classic subdelta model similar to that described by J. Coleman for West Bay in the Mississippi delta is demonstrated for the Admire. The deltaic model developed through geologic interpretation of cores allows prediction of the effectiveness of the tertiary oil recovery.
Pressure-transient analysis has been used to define sandstone trends further and to analyze directional properties of the reservoir. Interference tests yield directional pressure:transient ratios ranging up to 14 in areas of definite sandstone lineation. The high pressure:transient ratios result from strongly contrasting, mutually perpendicular transmissibility values. Many areas of strong, preferred transmissibilities are confined within geologic-facies boundaries.
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