Determining Sand-Body Geometries for Waterflood Reservoirs: Examples from Oklahoma
R. D. Kreisa, E. Pinero
Waterflood projects require an accurate knowledge of reservoir geometry and well-to-well continuity. However, sandstones with thin, multiple-pay zones can be extremely difficult to correlate with confidence. Two case studies of Pennsylvanian sandstones in Oklahoma illustrate how a model for the depositional history of such reservoirs can be an effective tool for determining reservoir continuity. In contrast, correlation criteria such as similar wireline log signatures and relative sand-body thicknesses are not reliable in many situations.
In Southwest Logan field (Beaver County), 5 to 15-ft thick reservoir sands formed as shallow marine sand ridges. Their dimensions were approximated from height-to-width ratios of modern sand ridges. Then the reservoir sands were mapped using wireline logs and core data. Individual reservoir sands were approximately 1-2 km wide and stacked en echelon vertically. Thus, a line-drive waterflood pattern oriented parallel to the axes of the ridges is recommended.
Tatums field (Carter County) consists of 5 to 50-ft thick sandstones deposited in various deltaic environments. Distributary channel sands have good continuity downdip, but are narrow and lenticular across depositional strike. Crevasse splay and other bay-fill sands were deposited marginal to the channels and are extremely discontinuous. This depositional model can be used to improve flood patterns for these sands, leading to improved sweep efficiency.
In both examples, for effective mapping, the depositional facies models have been used to register reservoir quality and wireline log signatures.
AAPG Search and Discovery Article #91037©1987 AAPG Southwest Section, Dallas, Texas, March 22-24, 1987.