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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract:
Seismic
Pressure Prediction Method Addresses
Problem Common in Deepwater Gulf of Mexico
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By
Producing Technical Center,
Dallas, Texas
The analysis and interpretation
of calibrated
seismic
velocity
measurements plays a critical role in the
interpretation
of
the subsurface:
- Accurate pore pressure prediction is needed to optimize
drilling plans, avoid unscheduled events, and minimize
drilling costs. The pore pressure gradient, predicted using calibrated
seismic
velocities, and the fracture gradient are essential to well planning.
- Seal failure analysis, which relies on the accurate estimation of the pore pressure gradient, can be used to assess risk and prioritize exploration opportunities.
Seismic
processing methods designed to image targets in time or depth depend critically on the accurate determination of the velocity model from the
seismic
data
.
A method for predicting pore pressures from seismic
velocities
before drilling will be presented. The method overcomes a
problem common in the deepwater Gulf of Mexico (GOM)
where the deltaic model of a significantly thick, hydrostatically-pressured
section, followed by a rapid change into geopressure,
often does not hold.
Generally, geopressures start shallow below the mudline in the deepwater GOM subsurface. Conventional techniques for pressure prediction fail because these techniques require the normal interval travel time of a shale compaction trend, and such a "normal interval" is seldom drilled in the shallow section.
The new method for pressure prediction relates velocity measurements directly to effective stress, temperature, and gross lithology. This allows one, for the first time, to compute directly, simply, and repeatably the normal shale compaction interval travel time trend.
This presentation will discuss the preparation of the input
seismic
velocity
data
to improve pore pressure prediction before
drilling in wildcat areas, followed by a general overview of how
pore-pressures can be more reliably estimated from
seismic
velocities. Two published computational methods used to estimate
pore pressures from
seismic
velocities will be compared
using examples from the shelf and from the deepwater GOM.
Bibliography
Wilhelm, R., Franceware, L. B. and Guzman, C. E. (1998) Seismic
pressure-prediction method solves problem common in
deepwater Gulf of Mexico, Oil 8 Gas Journal, Sept. 14.
Guzman, C. E., Davenport, H. A., and Wilhelm, R. (1997)
Calibration method helps in seismic
velocity
interpretation
,
Oil 4 Gas Journal, Nov. 3, pp. 44-54.
http://www.oilvel.com
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