AVO Sensitivity to Shale Reservoirs...Lab data X Shale Mancos Shale Results Two freq. (1 Hz & 21 Hz)...
Transcript of AVO Sensitivity to Shale Reservoirs...Lab data X Shale Mancos Shale Results Two freq. (1 Hz & 21 Hz)...
AVO Sensitivity to Shale Reservoirs
Hamad Alghenaim - NTNU
Outline
Objectives
Laboratory Experiment
Data and Model
Results
Conclusion
Next
Acknowledgment
Objectives
Examine unconventional shale reservoir sensitivity to:
Saturation
Stress
Frequency
Anisotropy
Cracks
Laboratory Experiments
• Two experiments:• Constant stress and
varying saturation. (done previously – data available)
• Constant saturation and varying confining and axial stresses. (April 2015 – data processing)
• Measured ultra sonic velocities and low frequency velocities calculated from strain measurements. (E, ʋ)
• Three different orientations in each expirement to calculate the stiffness tensor elements and anisotropy parameters.
Data and Model
Saturation Frequency Crack density
Stress
Saturation
Frequency
Crack density
Stress
Data and Model
Oveburden clay rich shale
Reservoir silt rich shale
Vp=3000 m/s, Vs =1500 m/s, ,density=2.4 g/cc, epsilon=0.2 and delta=0.1
Lab data
X Shale
Mancos Shale
Results
Two freq. (1 Hz & 21 Hz) while varying saturation
0 5 10 15 20 25 30 35 40 45 50-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1AVO Analysis
Offset (m)
Refe
ctivit
y
1 Hz S=01 Hz S=121 Hz S=12 Anis1 Hz S=331 Hz S=551 Hz S=751 Hz S=861 Hz S=86 Anis1 Hz S=10021 Hz S=021 Hz S=1221 Hz S=12 Anis21 Hz S=3321 Hz S=5521 Hz S=7521 Hz S=8621 Hz S=86 Anis21 Hz S=100
0-6 deg
6-20 deg
20+ deg
Increasing sensitivity to saturation
Shale samples measured at 1 Hz
0 5 10 15 20 25 30 35 40 45 50-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1AVO Analysis
Offset (degrees)
Refe
ctivit
y
1 Hz S=01 Hz S=121 Hz S=12 Anis1 Hz S=331 Hz S=551 Hz S=751 Hz S=861 Hz S=86 Anis1 Hz S=100
• Dimming with increasing saturation
• Trend starts at S=55
• Lower saturations are random
• Higher separation between isotropic and anisotropic curves with increasing saturation
Shale samples measured at 21 Hz
0 5 10 15 20 25 30 35 40 45 50-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1AVO Analysis
Offset (degrees)
Refe
ctivit
y
21 Hz S=021 Hz S=1221 Hz S=12 Anis21 Hz S=3321 Hz S=5521 Hz S=7521 Hz S=8621 Hz S=86 Anis21 Hz S=100
Similar observation to the previous slide but the whole curves are higher meaning brighter at low angles and dimmer at higher angles with increasing frequency
Data with measured anisotropic parameters
0 5 10 15 20 25 30 35 40 45 50-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1AVO Analysis
Offset (degrees)
Refe
ctivit
y
1 Hz S=121 Hz S=12 Anis1 Hz S=861 Hz S=86 Anis21 Hz S=1221 Hz S=12 Anis21 Hz S=8621 Hz S=86 Anis
• Higher zero crossing for higher saturation 17 deg vs 25 deg
• Dimming with angle:• Increasing S• Increasing Frequency• anisotropy
Data and Model
Oveburden clay rich shale
Reservoir silt rich shale
Lab data
Lab data
Pierre Shale
Mancos Shale
3 Freq. (1 Hz,21 Hz, 500kHz), 2 Sat. (12%,86%)
0 5 10 15 20 25 30 35 40 45 50-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3AVO Analysis
Offset (degrees)
Refe
ctivit
y
1 Hz S=121 Hz S=8621 Hz S=1221 Hz S=86500 kHz S=12500 kHz S=86
• Intercept separation
• Change in polarity
1 Hz and varying saturation
0 5 10 15 20 25 30 35 40 45 50-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25AVO Analysis
Offset (degrees)
Refe
ctivit
y
1 Hz S=121 Hz S=861 Hz S=01 Hz S=331 Hz S=751 Hz S=100
100
86
75
• Confirms Batzle 2010
Plots from Batzle and Sarker 2010
Sensitivity to Cracks
Tsvankin 1997Rathore 1995
Adding vertical cracks to 1 Hz, S=12% & 86%
0 5 10 15 20 25 30 35 40 45 50-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3AVO Analysis
Offset (degrees)
Refe
ctivit
y
1 Hz no crack 121 Hz with crack 12 y1 Hz with crack 12 x1 Hz no crack 861 Hz with crack 86 y1 Hz with crack 86 x
Varying crack density (1 Hz, S=12%,86%)
0 5 10 15 20 25 30 35 40 45 50-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3AVO Analysis
Offset (degrees)
Refe
ctivit
y
1 Hz no crack 121 Hz with crack 12 y 0.021 Hz with crack 12 x 0.021 Hz with crack 12 y 0.011 Hz with crack 12 x 0.011 Hz no crack 861 Hz with crack 86 y 0.021 Hz with crack 86 x 0.021 Hz with crack 86 y 0.011 Hz with crack 86 x 0.01
Adding 500 kHz
0 5 10 15 20 25 30 35 40 45 50-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3AVO Analysis
Offset (degrees)
Refe
ctivit
y
1 Hz no crack 121 Hz with crack 12 y 0.021 Hz with crack 12 x 0.021 Hz with crack 12 y 0.011 Hz with crack 12 x 0.011 Hz no crack 861 Hz with crack 86 y 0.021 Hz with crack 86 x 0.021 Hz with crack 86 y 0.011 Hz with crack 86 x 0.01500 kHz no crack 12500 kHz with crack 12 y 0.02500 kHz with crack 12 x 0.02500 kHz with crack 12 y 0.01500 kHz with crack 12 x 0.01500 kHz no crack 86500 kHz with crack 86 y 0.02500 kHz with crack 86 x 0.02500 kHz with crack 86 y 0.01500 kHz with crack 86 x 0.01
Conclusion
Sensitivity to saturation at angles higher than 20
Higher affect of anisotropy with higher saturation
Dimming reflectivity with increasing saturation for angles higher than 20
Lack of saturation trend for low saturations until ~S=55%
The higher the frequency the brighter the reflectivity at low angles and the dimmer it gets at higher angles
At higher saturations, larger separations between zero intercepts of the different frequencies
Small influence of cracks at angles higher than 30
Next
Include the stress varying data in the analysis after processing
Plot all the data on intercept-gradient for further analysis
Acknowledgment
PhD student: Dawid Szewczyk
Supervisors: Rune Holt / Per Avseth
Sintef