Rock Physics
Modeling is Critical for AVO Analysis – A
Hübert, Lars1, Karsten Müller1, Jack Dvorkin2 (1)
Rock Solid Images,
A thorough understanding of the geology
of an area, especially the underlying rock physics is critical for getting the
AVO right. The Lower Tertiary section of the Norwegian North Sea has proven up
AVO as a viable exploration tool, however, as this case study shows, using AVO
uncritically may lead to false positives, resulting in dry wells, or false
negatives thereby missing opportunities.
The results of rock physics, AVO and
seismic modeling in Block 24 and 25 indicate a complex system where the AVO
signature varies considerably as a function of, the stratigraphy,
depth and fluid content. This has an obvious effect on an exploration strategy
for the area. In Well A, the Heimdal sand provides
the reservoir. Here the AVO signature for hydrocarbons is Class III. Other
reservoir sands (Hermod and Balder) are not developed
in this well. In Well B we find reservoir quality sands in the Balder, Hermod and Heimdal formations.
Modeling indicates that hydrocarbons in the Balder sand should exhibit a Class
III AVO, in the Hermod sand a class IIP signature,
and the Heimdal sands should exhibit a Class I AVO
when hydrocarbon bearing. Note the contrast between Heimdal
sand in Well A and Well B. Interference effects, due to thin layers, further
complicate matters by clouding an expected AVO effect.
In conclusion, a thorough understanding
of the rock physics, particularly as it relates to burial, and a thorough
understanding of the stratigraphy of the area is
critical for using AVO as an effective exploration tool.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California