Integrating
Geology and Velocity
Data to Constrain Pressure Prediction in Foldbelts
Couzens-Schultz, Brent A.1,
Chris A. Hedlund1 (1) Shell International E&P, Inc,
This paper focuses on the first drilled
prospect in the Perdido fold belt, deepwater velocity
analysis
and
data from previous deepwater wells suggested near hydrostatic pressures. To
drill a second well, the problem of finding an optimal well location that
avoided low drilling margins was addressed. The work involved re-picking of
seismic
velocity
, trend
analysis
, and developing end-member rock models for
pore pressure prediction
using
constraints from a mechanical seal failure
analysis
.
Areas of higher velocity
, and lower
predicted overpressure were identified in the same stratigraphic interval where
the first well was lost. The second well was drilled successfully through one
of these higher
velocity
areas. The
velocity
results, combined with constraints
from top seal failure were used to construct drilling margin maps. These
indicated that beneath the stratigraphy where the first well was lost, drilling
margin would increase. Once a path was found through the shallow hard
pressures, the well would be drillable to objective. Results from the second
well show that pressure prediction
using
seal failure arguments is a good first
approach. The methodology is limited by assumptions on sand continuity from top
seal failure locations and by
velocity
fidelity.
Hard overpressures and top seal failure
are common aspects of deepwater fold belts. These prospects can be difficult to
drill and can be under-filled. Deepwater foldbelts often have little well
control to constrain predictions within them. The techniques presented here can
be adapted to other foldbelts, and were used to evaluate and rank other Perdido
prospects.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California