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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Integrated Geological and Geophysical
Characterization of Gulf Coast
Reservoirs
for Incremental Natural Gas Recovery
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Incremental recovery of natural gas beyond standard
development practices in structurally simple, conventional
permeability reservoirs
is dependent on understanding of
reservoir heterogeneity. Such heterogeneity, where not
structural, is a function of the original depositional system
modified by diagenesis. Investigations focusing on Frio
fluvial
reservoirs
of Seeligson and Stratton fields in South
Texas, supported by the Gas Research Institute, the U.S.
Department of Energy, and the Bureau of Economic
Geology, illustrate how facies and diagenetic variability can
result in boundaries or baffles to gas flow. Recompletions
and strategic infield drilling are means of overcoming such
compartmentalization and producing gas from untapped or
incompletely drained
reservoirs
.
At Seeligson field, reservoirs
tend to have better lateral
connection than at Stratton field and have been more
intensively completed. Fluvial and splay sandstone
reservoirs
tend toward a multilateral geometry at Seeligson.
Nevertheless, 3-D seismic data show discrete, meandering
channel thalwegs and AVO analysis illustrates a distribution
of gas reflecting the channel form in an analysis of the
19C-04 reservoir in that field. Careful use of zero-offset VSP
data have allowed the optimum tie of stratigraphy to the
geophysical data for seismic surveys completed at different
times. Recompletions made in Seeligson have been based
on cased-hole logging and have encountered pressures of
about 1,000 psi that were 2 to 3 times reservoir fieldwide
average. Five recompletions in bypassed reservoir compartments
made 1.4 Bcf of incremental gas in about 18
months and are projected to recover about 4 Bcf of gas.
At Stratton field, greater vertical separation of reservoirs
has allowed aggressive incremental development by
the operator, mostly in the late 1980's. Analysis of publicly
available data shows33 Bcf of shallow (<7,000 ft) and 15 Bcf
of deeper gas reserve growth in an area of about one-third
the area within the field. Fieldwide production decline was
reversed beginning about 1987.
Reservoirs
in the F series,
for example, have seen new completions in the 1980's with
static bottom-hole pressures (BHP) of 1,800-2,300 psi in the
same reservoir where previous completions have been
abandoned with BHP's of 200-300 psi. Single-well transient
tests and interference tests are underway to characterize
the nature of the reservoir compartmentalization involved.
Two 3-D seismic grids with VSP's for velocity control have
been designed to further determine the nature of reservoir
variability at Stratton field. Evidence such as that from
Seeligson and Stratton fields demonstrates that strategic
targeting of heterogeneous
reservoirs
using new approaches
can lead to economic recovery of incremental gas resources
from the Frio and other major Gulf Coast fluvial-
deltaic
reservoirs
.
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