1. Twin Wavefield (Pump-Probe*) Exploration
G. Quiroga-Goode*
-We are always looking for better ways to define not only the geological macrostructure but also petrophysical properties such as porosity, permeability, fluid type, etc. Actually, it’d be better if we could tell first if there’s hydrocarbons and then focus our resources to define the macrostrucure later to place the geometry in its right place.
-It is clear however that if we based our models as if the multiphase porous reservoir rocks behaved as single-phase solids, meeting those goals is going to be a very tough job.
-Here I’m presenting the basis of a novel approach for direct hydrocarbon detection which uses a couple of wavetrains, as opposed to single wavefields used in conventional seismic exploration.
-It is still in the early stages of development and there are lots of things yet to be done. The theoretical and numerical results that I’ll be showing here clearly reflect this. Nevertheless, there is one thing I’m sure of: the evidence appears to indicate that the method could work.
-The preliminary numerical modeling I’ve done so far provides inconclusive evidence.
-As you will see further ahead, it turns out that this method is very similar to Seismic Time-Lapse.
-I’d love to get feedback from you.
Instituto de Investigacion en Ingenieria
Universidad Autonoma de Tamaulipas
Tampico, Mexico
*formerly IMP, Mexico, *from Ursenbach & Stewart, 2004

2. The basic idea
In viscoelasticity, the material properties change with strain
Material properties are attached to fluid content
Can we use two different waves (strain sizes) to determine fluid-related properties?

3. t t c2 t TRANSIENT MECHANICAL BEHAVIOUR elastic viscoelastic f theory
relaxation
creep t
viscoelastic
strain
stress
stress t
Pilot Wave f c2 r MR MU
Velocity Dispersion
Tracking Wave
strain MR r MU
Tracking Wave + MU + MU t

4. 2D P-SV Biot poroelastic theory (1956, 1962)x s
= R 22 [ xx + xy
] - R 12
+ B 2 f -
], (1) y yy ],
(2) v x f
= -R 12 [ s xx + xy
] + R 11
+ B 1 - ],
(3) y yy
(4) t
[ho (v f - v s ) ] s
= ( Q + R )
Ñ · v
+ R / h o
(8) t xx
= ( P + Q )
- 2 N y
+ Q /
(5) yy x
Ñ · [ho (v f - v s ) ]
(6) xy
= N ( + ) ,
(7) R ij = r
ij / ( 11
22 - 12 ),
i, j
= 1,2 B 1 h o m f
( R
+ R ) 2 22
______ _____ k

5. ] TEST MODEL: geology distance (m) depth (m) ho = 0.05 K = 10 mD
homogeneous porous background
ho = K = 10 mD ]
pseudo-fractured porous media
ho = 0.60 K = 10 D
depth (m)
Whole model is saturated with water
except within the ellipse, which is
permeated with
gas.

6. TEST MODEL: geometry . . reflection data transmission data
512 X 512 square cells (Dh = m) .
distance (m) .
transmission data
reflection data 1 85
receivers
depth (m)

7. Center of mass velocity
ho rfo vf + (1 - ho) rso vs r
Pore fluid pressure
Fluid content s ho y y
pf = -
x = -Ñ· [ho (vf - vs ) ]
vy=
4.0
5.0
6.0
7.0
8.0
0.0
1.0
2.0
3.0
distance (m)
depth (m) + +
fluid increase - -
fluid decrease

8. CREWES Collaboration
Viscoelastic modeling to have a priori knowledge of Q attenuation
Analytical solution considering twin waves in a homogeneous
and in a heterogeneous viscoelastic medium
Investigate exactly how to implement
Analyze converted waves