ABSTRACT

The Lexington Field is situated in the Hugoton Embayment of Kansas in sec. 17, 18, 19, 20, and 29, T31S, R21W, and sec. 13 and 24, T31S, R22W of Clark County. Hydrocarbons are produced from both the Mississippian St. Louis Limestone Formation and the Lower Pennsylvanian Morrowan 'A' Sandstone operational unit.

The focus of this study is the Morrowan 'A' Sandstone, a carbonate and silica-cemented, glauconitic, pyritic, cherty quartz arenite to litharenite that displays silty shale intercalations. The sandstone was deposited in an estuarine environment on a mesotidal coast. Four subfacies of the Morrowan 'A' Sandstone were recognized and include: 1) a supratidal subfacies, 2) an intertidal subfacies, 3) a channel bank subfacies, and 4) a tidal channel subfacies.

The intertidal and channel bank subfacies exhibit the most petrologic homogeneity and have the highest porosity and permeability values. Most of the porosity was developed by secondary dissolution of carbonate (both calcite and ankerite) cement in the diagenetic realm. Three porosity zones in the Morrowan 'A' Sandstone exhibit mean porosity values of 17.1, 9.5, and 2.0 percent respectively.

Well log calculations indicate the original oil in place (OOIP) to be approximately 6,828,000 stock tank barrels (STBBLS). Macroscopic and microscopic examination of core samples, and related to well-log responses of uncored wells, suggests 50-55% of the OOIP ultimately might be recovered by primary, secondary, and tertiary techniques. Primary recovery has been estimated at 30 percent of the OOIP (2,048,000 STBBLS). As of September 1984, 2,104,767 barrels of oil has been produced from the Morrowan 'A' Sandstone. Mesa Petroleum Company has now initiated a pilot waterflood program with intentions to instigate a field-wide imbibition system. The geologic evidence suggests that the intertidal and channel bank subfacies are relatively homogeneous and capillary trapping of oil in these subfacies will not be so extensive as to render the reservoir uneconomic under the waterflood operation.