Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Onshore U.S. Depth Imaging and 
Velocity
Model Building
(1) Wave Imaging Technology Inc., Houston, TX.
Prestack depth migration (PSDM) can produce accurate 3D images in situations where the earth’s seismic velocity exhibits complexity which hamper prestack and poststack time migration. Traditionally, PSDM has been treated as an exotic technology, and only applied in basins with extreme velocity complexity. However, significant increases in the performance-to-cost ratio of modern computers, and improvements in the industry’s ability to accurately estimate seismic velocity are creating significant momentum to adopt PSDM as the default imaging method in many onshore basins where operators traditionally have only used time imaging. Moreover, the most accurate, but most computationally demanding family of PSDM algorithms, generically known as “wave equation” PSDM techniques (including one-way wave equation migration and Reverse-time Depth Migration), are being applied increasingly to onshore datasets. This abstract highlights the application of wave equation depth imaging technologies on several onshore US examples. Below we list some of the benefits users of PSDM technology might expect to enjoy on their datasets:
A true depth picture - Local velocity anomalies create false time structures on a time image. Unless dense well control is available, PSDM (and the associated velocity model) provides the best connection between seismic reflection time and drilling depth.
The depth velocity model has interpretive value - Accurate velocity estimation is the key to PSDM success. But savvy prospectors may use the high spatial resolution velocity models now generated for PSDM to optimize drilling activities, perform fault seal analysis, and to generate petrophysical attributes such as pore pressure determination.
A better focused image - Even subtle lateral velocity variations cause a loss of clarity on time migrated images. Steep dips and faults are particularly sensitive to this effect, and PSDM usually produces a clearer image of these features, in almost any basin. Wave equation PSDM in particular can unravel subtle amplitude focusing effects.
More accurate attributes - Most AVO and azimuthal fracture attributes (fracture density and fracture orientation) are computed on prestack time data or time migrated data. Lateral velocity
variation causes focusing and refraction effects that may degrade the accuracy of these attributes. PSDM, applied in the true reflection angle domain, may allow attribute technologies to be applied even in complex geology.