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Abstract

El Dorado field, which is located in southeastern Kansas, was discovered in 1915 by Cities Service Company. The Admire 650’ sandstone reservoir (Permian Wolfcampian) is present at 650 ft (197 m), ranges in thickness from 11 to 23 ft (3 to 7 m) and has produced 36.5 million barrels of oil through primary and secondary recovery methods. A secondary waterflood was carried out in the field during the 1950s. A tertiary oil recovery project covering 51 acres (21 ha) was initiated in the Admire 650’ sandstone in El Dorado field in 1974. Deltaic facies are encountered at El Dorado field; the various deltaic facies are quite variable in reservoir quality. Documentation of the geometries and locations of reservoir and non-reservoir facies allows prediction of the distribution of flow units within the field.

Three types of sandstone reservoirs are recognized in the Admire 650’ sandstone. The major producing reservoir facies is the Distributary Channel Sandstone Facies, which includes High- and Low-Energy Subfacies.

The Admire 650’ sandstone was initially deposited from splay channels that prograded into a muddy interdistributary bay. Following deposition of some of the splays, distributary channels prograded into the enhanced oil recovery pilot project area (El Dorado Micellar-Polymer Demonstration Project). Some parts of the project area, however, contain substantially thicker distributary channel sandstones than others. In the southeastern corner no channel sandstones were deposited; the area remained an interdistributary bay environment. The final phase of deposition was one in which transgressive marine deposits spread over the whole area depositing limestones and shales.

The Distribuuiry Channel Sandstone Facies is most prevalent along the western margin of the northern (Chesney) and southern (Hegberg) leases, as well as across the center of the project area. Flow directions obtained from oriented cores indicate northward and northeastward paleocurrent flow within a distributary channel system which bifurcates within the lease areas.

Reservoir heterogeneities depicted on cross sections, fence diagrams, and isopach maps were recognized in cores, logs, and whole-core analysis. Abundant high quality geologic data were available for this project and were used to formulate detailed reservoir descriptions. The reservoir descriptions were utilized to some degree by engineers to better model the field.

One engineering parameter which strongly supports the presence of geologic heterogeneity in El Dorado was pressure-transient analysis. Pressure-transient ratios, as much as 14 in areas of recognizable elongate sandstone body deposition, indicate many areas of strongly preferred transmissibility.

Distributary Channel Sandstones average 436 md permeability and 28% porosity, whereas splay channel sandstones average 567 md and 27% porosity. Splay sandstones are thinner and discontinuous and, hence, do not contribute as much to overall production.

The variation in permeability and porosity of the Admire 650’ sandstone is affected by diagenesis. Permeability and porosity are reduced by clay laminae, deformation of ductile rock fragments, mica and micaceous laminae, quartz, the secondary leaching of feldspar, and calcite cement.

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