Fault Definition Improvements in the West Abu El Gharadig Concession Using Prestack Depth Migration
By
Amir El Motany1, Moumir Diab1, Marwa El Badry2, Nabil El Kady2
(1) Agiba Oil Company, N/A, Egypt (2) WesternGeco Data Services Middle East Ltd -- Cairo Data Processing, N/A, Egypt
The West Abu El Gharadig concession is located in the Qattara depression in
the North of the Western Egyptian Desert. The surface geology is complex, Sabkha
deposits cover about 50% of the area of the study. Dyanamite was used to collect
the data in this areas. The rest of the area is flat rocky desert, where
vibroseis was used. We selected four lines, one of which was a strike line, for
prestack depth migration. The area presents a geologic structure affected by an
intense extensional faulting that deforms the sedimentary sequences. Faulting
induces strong lateral velocity variations, creating false pull-up and sags in
the seismic data which distort the true geologic structure. An exploratory well
was drilled from an interpretation of time-migrated data, but the well could not
confirm the interpreted fault locations. To reduce the risk of drilling, a
velocity model was built guided by the well information and the seismic data. A
3-D velocity model was built to unify seismic and well information, and to tie
the velocity model for the four lines. This velocity was used to run prestack
Kirchhoff
depth migration on the four selected lines. A second well was drilled
from a re_interpretation of the fault location using the depth images. The
second well confirmed the location of a major fault plane in the area. At the
target depth of about 4000 ft, there is a 2000 ft displacement across the fault.
Depths from the seismic data had a satisfactory tie with the well.