David M. Wheeler¹, William A. Miller², Travis C. Wilson³

(1) Ensign Oil & Gas, Inc, Denver, CO
(2) Miller Consulting Services, Denver, CO
(3) Colorado School of Mines, Golden, CO

ABSTRACT: Reservoir Characterization and Development of Valley Fill Deposits with 3C3D Seismic and Horizontal Drilling, Eva South Morrow Sand Unit, Oklahoma

The Eva South Morrow Sand Unit (ESU) was selected as a demonstration site to test the ability of 3C3D seismic and horizontal wells to improve reservoir characterization and sweep efficiency in a waterflood unit. This project was supported in part by a grant from the U.S. Department of Energy under the Reservoir Class Field Demonstration Program-Class Revisit.

ESU produces from transgressive valley-fill deposits of the Morrow. The trap is formed by a convex up-dip bend in the valley system. Cores show that the reservoir is composed of very coarse grain, planar- to cross-bedded, fluvial sandstone. Non reservoir facies include mudstone and shale deposited in abandoned channel and flood plain environments. At least four compartments have been identified that interfere with reservoir sweep efficiency. Compartmentalization and reservoir heterogeneity is caused by faulting and abandoned channel-fill deposits.

A 4.25 square mile 3D seismic survey was obtained over the field. In addition to the standard P-wave data, mode-converted shear-wave data was recorded in an effort to improve resolution of the reservoir sandstone. The P-wave data provided excellent definition of the structure in the field, good definition of the valley-system and fair definition of the reservoir sandstone. The shear-wave data provided good definition of the faulting and a slight improvement over the P-wave data in the definition of reservoir sandstone. New processing techniques are being developed in an effort to improve the resolution of the shear-wave data. To date, one new horizontal well has been drilled with encouraging production results.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado