Abstract: Reservoir Compartmentalization of the Morrow Sandstone at Sorrento Field, Southeastern Colorado

Sandra McDonald Mark, Roger M. Slatt

Sorrento field, in Cheyenne County, Colorado, contains an estimated 21 million barrels of original oil in place in Pennsylvanian Morrow Sandstone incised valley-fill. While the geophysical logs present a sandstone that is fairly uniform, the well performance and multiple fluid contacts indicate that the reservoir is very complex and compartmentalized. Several distinct flow units have been defined by geological and petrophysical properties; these flow units explain variable performance of wells in the field.

Core descriptions and analyses were used to determine representative geophysical log values for a variety of lithology types. These typical log values were used to generate a computed lithology log which defined the boundaries of flow units as discrete intervals and allowed correlation of the flow units throughout the field. The structural dynamics that control oil-water-gas contacts were also considered in correlating flow units. The ability of the computed lithology curve to differentiate flow units is confirmed by closely spaced pressure decay profile permeameter measurements of core. Flow units are also distinguished by unique log parameters, as illustrated by a clustering of points in neutron-density cross-plots.

Lateral boundaries of flow units are delineated by the geometry of the incised valley in which the sand was deposited, and isolated pods may be separated by multiple meander scrolls. Vertical boundaries of flow units are low permeability zones which display intense quartz cementation and may be the product of sub-aerial exposure between channel stacking cycles.

Accounting for the compartmentalized nature of Sorrento field may assist in reservoir management decisions and may demonstrate the necessity for additional wells.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994