Reservoir Description and Production History; Bell Creek
Field, Muddy Sandstone, Barrier
Island, and Valley Fill Deposits
Roderick W. Tillman, M. Szpakiewicz, M. M. Honarpour, S. R. Jackson
Improved sedimentologic and stratigraphic reservoir descriptions of
barrier
-island sandstones and genetically related deposits allow better
reservoir management. Few published geologic models of ancient barriers contain
sufficient detail to predict the distribution of heterogeneities on a variety of
scales. The study described involves a 4-mi2 area of Bell Creek
production Unit A in which 15 cores were described and interpreted and 70 wells
were utilized in constructing detailed cross sections and maps.
Production in Unit A is primarily from several stacked shallowing-upward
barrier
-island sandstones. Within the
barrier
, facies recognized are foreshore,
upper shoreface, lower shoreface, transition, washover, and perhaps a backshore.
Two periods of post-
barrier
erosion and shale and sandstone valley fill are
related to two falls in sea level. Earlier valley incisions are broad and
relatively shallow and commonly involve reworking of the top of the
barrier
.
Younger valley fill deposits along the west side of Unit A are 30 ft thick where
erosion has cut completely through the
barrier
.
A wide variety of scales of heterogeneities occur within the field: large-scale heterogeneities (facies changes, valley fills, sand-shale boundaries, and faults), moderate-scale heterogeneities (clayey beds, cemented zones, e.g., clay and calcite), and high-permeability channels (perhaps fractures); small scale-diagenetic clay; compaction effects; leaching of minerals; and cementation.
The production history over the 20-year life of the field indicates the
effect of various heterogeneities on oil production. The secondary oil
production history indicates that as additional fluids were injected, areas of
peak production within the field migrated irregularly to the east (updip).
Mapping of changes of the percentage of water produced in individual wells over
the waterflood history indicates that local heterogeneities within the barrier
cause significant local production/injection anomalies.
AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.