Fracture
Detection Using Multi-Azimuthal AVO At Y107, Jizhong Depression,
Pan, Renfang1 (1)
Y107, located in Jizhong
Depression, is a faulted block with conglomeratic reservoirs in Formation Shahejie IV. There are 22 wells drilled, 18 are producers
and 4 are injectors. Current produced volume is about 5%. It's inferred that,
by the fact that injected water break through the reservoir no late than
injection, fractures occur in the production zone between faults. Therefore, 30
km2 of 3D seismic dataset was selected to be reprocessed involving pre-stack
time migration. Then, two sets of CRP gathering were sorted by azimuth ranges
that are fan shaped centrally both in inline and crossline
directions. Azimuthally, two angle gathering sets were extracted after super
gathering by rolling 3×3 inlines and crosslines, from which AVO anomalies were extracted,
respectively. Comparatively, two sets of velocity and amplitude coherence were
derived from 3D volume stacked after migration. The study demonstrates that
coherence is adequate to illustrate faults but fractures between them, and that
the difference of shear velocity anomalies by AVO (Intercept minus Gradient) in
two directions is consistent to the fracture zone revealed by drilling, and the
fracture prediction from multi-azimuthal AVO is
consistent to the data from 20 wells. Consequently, an animation made by
step-slicing along with horizon interpretation clearly shows up fracture's
orientation and vertical occurrence. It concludes that seismic coherence
indicates only faults that are in large scale and visible changes in seismic
wave traveling time, and the difference of azimuthal AVO's anomalies can
indicate fractures that are in relatively small scale and affect seismic wave
dynamically.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California