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The AAPG/Datapages Combined Publications Database
Indonesian Petroleum Association
Abstract
2-D and 3-D Prestack Depth
Migration
for Complex Geologic Structures Offshore Indonesia
Abstract
Unocal Indonesia is using 3-D prestack depth migration
to better image Indonesian prospects in difficult seismic areas. The goal is to delineate the deep fault geometry beneath image-distorting carbonates. Previous 2-D prestack depth
migration
has resulted in significantly better structural imaging, which is motivating the 3-D work.
Lateral velocity variations of 2 to 3 km/s within distances of less than 1 km make conventional time migration
methods inadequate to accurately image structures and faulting. Iterative 2-D depth
migration
has provided better structural imaging in depth due to more accurate interval velocities and structural geometry resolution. 3-D prestack depth
migration
provides better
migration
velocity analyses and superior structural imaging, especially in comparison to 2-D lines acquired in directions oblique to major faults.
The most important step in depth migration
is construction of a 3-D interval velocity model. All available data are used in constructing the model: Dip Moveout (
DMO
) stacking velocities, poststack time
migration
, well logs, check-shot surveys, gravity and magnetic data, seismic interpretations, and the 3-D prestack depth
migration
velocity analyses. The model is developed iteratively from the surface downward. Modeling packages such as GOCAD assist the data integration and 3-D visualization quality control. The 3-D
migration
algorithm is a Unocal proprietary Kirchhoff
migration
with ray - trace traveltimes and
migration
computed on a 3 Gigaflop, 10 CPU Silicon Graphics Power Challenge.
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