Prospecting for
Gas
Hydrate Accumulations using 2D and 3D
Seismic Data, Milne Point, North Slope Alaska
The Milne Point
gas
hydrate prospect delineation study was
part of the U.S. Geological Survey (USGS) Alaska
gas
hydrate resource
characterization project in association with BP Exploration (Alaska) Inc. and
U.S. Department of Energy research that has helped answer questions about
gas
hydrate distribution and reservoir properties. The interval below the base of
ice-bearing permafrost (IBPF) to just below the base of the
gas
hydrate
stability zone (GHSZ) was analyzed. Theoretical seismic modeling of stratigraphic and fluid boundaries, including shale to
gas
hydrate reservoirs and shale to free
gas
reservoirs as well as transitional
gas
hydrate to free
gas
reservoirs have been used to understand the acoustic
properties of these complex systems. Petrophysical
analysis of known
gas
hydrates
show saturations of 60-90% and porosities of
30-40%. Reservoir thickness and saturation were the primary variables used in
modeling acoustic attributes and calculating potential resource volumes.
Prospective “intra”-
gas
hydrate-bearing reservoirs below the IBPF and within
the GHSZ and free
gas
-bearing reservoirs trapped below
gas
the GHSZ were
delineated by seismic attributes. Fault-bounded intra-
gas
hydrate prospects
were identified in areas that are structurally high, and that have acoustic
properties corresponding to high concentrations of
gas
hydrate.
The historical log analysis work conducted by the USGS in this area combined
with knowledge gained from 3-D seismic attribute analysis has helped us to
understand the geologic setting for these unconventional reservoirs. The Milne
Point area study has successfully delineated both intra-
gas
hydrate and sub-
gas
hydrate free-
gas
prospects that are appropriate for potential production
testing operations.