Geology Reference
In-Depth Information
a)
Dol.
L.S.
20000
10000
0
-10000
-20000
-3000
0
Intercept
3000
b)
Attribute cross section
Traces from P-wave (P)
Well B (dry limestone)
Well A (gas dolomite)
Dol.
L.S.
Figure 7.34
Detection of porous dolomite zones using AVO analysis; (a) intercept/gradient crossplot from small seismic window around
the top Black River Carbonate reflector, (b) red (tight limestone) and orange (porous dolomite) zones highlighted on intercept stack (after
Eissa et al.,
2003
).
(4) Fit a trend to the edited normalised ratios. For
example fit
amplitude distortion associated with land acquisi-
tion. Unfortunately confidence in the technique
may be reduced when the carbonates show strong
lateral lithological change. More recently several
authors have reported success in using simultan-
eous inversion techniques (
Chapter 9
)fordiscrim-
ination of porosity and fluid type in carbonates (e.g.
Pelletier and Gunderson,
2005
;Liet al.,
2003
;
Ishiyama et al.,
2010
).
A + Bx
2
, where A is the zero angle
intercept and B is a rate of change coefficient and
x is the offset distance.
(5) Derive the
¼
B/A*x
2
so that the AVO character can be mapped.
Effectively, increasing values of normalised
ratio give rise to positive AVO difference
values.
'
AVO difference
'
attribute
¼
In a comparison of AVO techniques for locating
zones of fractured dolomite within non-reservoir
limestone, Ho et al. (
1992
) determined that Chi-
buris
7.2.9 Fractured reservoirs
The exploration of fractured reservoirs using geo-
physics generally comprises azimuthal P wave AVO
and shear wave birefringence techniques. There are
numerous examples of
technique was the most robust. An appealing
aspect of the technique is that the ratio procedure
effectively accounts
'
147
fractures detected with
for most of
the causes of
