About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
The AAPG/Datapages Combined Publications Database
AAPG Special Volumes
Abstract
from:
Chapter 18
Velocity Estimation for Pore-Pressure Prediction
David W. Bell
Conoco Inc.
Ponca City, Oklahoma
ABSTRACT
The speed of propagation of compressional-wave energy in the subsurface, known simply as “formation velocity,” is strongly influenced by compaction, particularly in young clastic basins. Because pore pressures affect compaction, changes in velocity can be calibrated to changes in pore pressure. Velocities derived from surface seismic data provide indirect pressure measurements at undrilled locations. The accuracy depends on the validity of the relationship between pressure and velocity, the quality of the velocity measurements at enough points to perform the calibration and prediction, and the reliability of average velocities to correctly convert from seismic time to depth.
A key step is construction of a velocity profile with depth that simultaneously defines both the
compaction characteristics and a valid time-depth curve. A linear
fit to the logarithm of the sonic transit
time with depth is commonly assumed to represent the normal compaction trend. Such a velocity-depth
trend, however, does not produce a time-depth relationship that accurately converts seismic measurements
in time to depth. A
linear
fit of velocity with time provides a consistent fit to both time-depth
and velocity-depth data and is a better empirical representation of the normal compaction trend. The
linear
velocity-time model can be used to smooth through inaccuracies in seismic stacking-velocity picks
where applied to geologically consistent units.
This chapter illustrates relationships between velocity and the geologic setting and establishes an empirical model for the normal compaction trend. It then reviews various assumptions and techniques for converting seismic stacking velocities into representative formation velocities. It concludes with a step-by-step recommendation for estimation and calibration of velocity from seismic data.
View the First Page
A text abstract of this article is not available. The first page of the PDF appears below.
You may download the first page as a PDF.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
Watermarked PDF Document: $14 | |
Open PDF Document: $24 |