Transcript Detection of Mobile Fluids in the subsurface

Detection of Mobile Fluids
in the subsurface
By
Dr. Kandiah [BALA] Balachandran
Kalamazoo, MI 49009-8015 Kalamazoo
Valley Community College
[email protected]
[email protected]
Experiments
• Comparatively strong horizontal
component signature was recorded at
near normal incidence at a field site near
Tulsa, Oklahoma which led to this
investigation.
• A simple set-up simulating a two-layer
medium was constructed using a thick
block of aluminum glued to a slab of Berea
sandstone.
Experiments (contd.)
• A P-transducer was placed on top of the Al
block to generate the waves that were
reflected at the interface. Both P- and SVreflected waves were recorded at various
offsets.
• The experiment was done with dry rock
first.
• It was repeated with the rock in a bath of
water.
SV- to P- amplitude ratios
• S-wave amplitudes and the corresponding
P-wave amplitudes were measured and
the ratios were calculated as a function of
offset
• The theoretical solution to the expected
amplitudes were obtained using solutions
to Zoeppritz equations made available on
the Web by the CREWES project of the
University of Calgary (Charles Ursenbach)
Observations
• The SV to P amplitude ratios were
significantly larger when the rock was wet
than when it was dry. This was more
noticeable at larger angles of incidence.
The following slides show the
experimental data and the theoretically
expected ratios of these amplitudes.
These results are preliminary.
Chart of SV-P amplitudes
Offset (cm) DRY ROCK 3 hrs soak Overnight 2 day soak
3
0.137
0.185
0.28
0.29
6
0.511
0.567
0.4
0.45
9
0.762
0.6
0.632
0.79
12
0.94
1.34
2.04
1.06
15
1
0.745
2.48
2.04
18
0.62
0.737
1.57
2.95
21
2.09
0.639
1.77
3.16
SV to P amplitude Ratios Vs Offset
3.5
3
Ratios
2.5
Series1
Series2
Series3
Series4
2
1.5
1
0.5
0
0
10
20
Offset (cm)
30
Theoretical Ratios using CREWES Zoeppritz Explorer Applet
Al on top: density = 2.7 g/cm^3, Vp+6.32 km/s, Vs = 3.13 km/s
Lower layer: density = 2.1 g/cm^3, Vp = 2.0 km/s, Vs = 0.7 km/s
Incidence Rpp
Angle(deg)
10
20
30
40
50
60
70
80
Rps
0.59
0.54
0.46
0.37
0.3
0.29
0.34
0.55
Rps/Rpp
0.22
0.42
0.56
0.64
0.64
0.59
0.46
0.29
0.372881
0.777778
1.217391
1.72973
2.133333
2.034483
1.352941
0.527273
Rpp,Rps,Rps/Rpp
rho=2.1,Vp=2.0,Vs=0.7 Al on top
2.5
2
Series1
Series2
Series3
1.5
1
0.5
0
0
50
Angle of Incidence (deg)
100
Further work
• July 2005: at Colorado School of Mines
• Repeated the experiment with some
measurement of saturation of the rock –
not very successful
• Repeat with light oil in the pores
• Repeat with heavy oil in the pores
• Improve the design of the experiment so
higher subsurface pressure environments
can be simulated…
Conclusions
• The observations suggest that the
presence of mobile fluids may be
determined by studying the ratios of the
amplitudes of the SV to P reflections and it
just may be possible to identify the fluid.
• Plans are being made to study these
variations with available data from 3Component surveys acquired in select
areas.