Quantifying Seismic Reflectivity
A Second Look at the Fluid Factor
Based on UH Dissertation by Dr. Jenny Zhou – Former AGL RA
Fred Hilterman
Distinguished Research Professor – University of Houston
Chief Scientist – Geokinetics Data Processing and Interpretation
April 28, 2010
Birth of Fluid Factor
George Smith & Maurice Gidlow
South Africa - 1986
Fluid Factor Review
Class 1 AVO
2.9
3.0
Stack
Smith and Gidlow; Fatti et al.
Generate NIP and NIS from AVO inversion
RC()  NIP/cos2() – 2 NIS sin2()
NIP = P-wave normal incidence
NIS = S-wave normal incidence
Fluid Factor Review
Class 1 AVO
NIP
2.9
3.0
NIS
Stack
2.9
Fluid Factor: F = NIP -  NIS
3.0
NIP
2.9
3.0
NIS
Brine saturated: F = 0
Gas Saturated: F = NIPGAS- NIPWET
Fluid Factor Review
2.9
3.0
Stack
2.9
3.0
NIP - 0.56 NIS
Gas
Oil
Can F discriminate oil from gas ?
Calibrating Fluid Factor to
Well-Log Data
Fluid Factor from Normal Incidence
151 wells from South Marsh Island
0.10
Regression Equations
(NIGAS-NIWET)
NI Wet, Gas and Oil
0.05
0.00
-0.05
NIOIL = -0.052 + 1.09 NIWET
R2 = .94
NIGAS = -0.088 + 1.14 NIWET
R2 = .83
Wet
NIOIL - 1.09 NIWET = - 0.052
Oil
NIGAS - 1.14 NIWET = - 0.088
Gas
NIHYDROCARBON-NIWET  Fluid Factor
-0.10
-0.15
-0.20
-0.12
-0.08
-0.04
0
0.04
0.08
NI WET
Reservoir porosity: 10-33 %
Encasing shale: 2600-4200 m/s
NI varies significantly for gasand brine-saturated sand … but
(NIGAS-NIWET) changes little.
How is Fluid Factor extracted from seismic data?
Fluid Factor from NIP & NIS
F(t) ≡ NIP(t) -  NIS(t) (Smith and Gidlow)
F  0
In wet zones
F  (NIP,GAS-NIP,WET)
At top of reservoir
Based on horizon pore-fluid projection
F(t) ≡ NIP(t) – 0.72 NIS(t) + 0.03
therefore … E{FWET} = 0
0.1
0.16
Gas Oil
Linear Equation NIP=0.72NIS-0.03
Wet
0.05
0.08
NIS
NIP
0
-0.05
-0.1
0.00
Wet
-0.08
-0.15
Oil
Gas
-0.2
-0.16
-0.08
0.00
-0.16
0.08
0.16
NIS
151 wells in South Marsh Island
-0.15
-0.10
-0.05
0.00
0.05
NIP - 0.72 NIS + 0.03
Fluid Factor = NIP - 0.072NIS + 0.03
Unique Properties of
Fluid Factor
Fluid Factor: Boundary or Layer Property?
NIGAS – NIWET = F
S R
Shale
Gas Sand
S R
-
NIGAS
S R
Shale
Wet Sand
 -
NIWET
NIGWC =
Gas Sand
Wet Sand
F  - NIGWC
(AIWET SAND–AIGAS SAND)
(AIWET SAND+AIGAS SAND)
F relates to gas/water contact -NIGWC … not encasing shale.
Fluid Factor: 9-m Wet Thin Bed
VP = 2280 m/s
VP = 2280 m/s
VP= 2250 m/s
VP = 3600 m/s
VP = 2280 m/s
VP = 3490 m/s
0.3
NIP
y = 0.5511x - 0.0195
0.25
2
R = 0.99
NIP
0.2
NIS
0.15
0.1
0.05
0
F
-0.05
0
0.1
0.2
0.3
NIS
Seismic Section: Fluid Factor = NIP – 0.55 NIS
0.4
0.5
0.6
Fluid Factor: 9-m Gas Thin Bed
Two-way time
VP = 2280 m/s
VP = 2280 m/s
Two-way time
11.1 ms
VP= 1628 m/s
VP = 3370 m/s
5.3 ms
VP = 2280 m/s
VP = 3490 m/s
0.3
NIP
y = 0.5511x - 0.0195
0.25
2
R = 0.99
NIP
0.2
NIS
0.15
0.1
0.05
0
F
-0.05
0
0.1
0.2
0.3
NIS
Seismic Section: Fluid Factor = NIP – 0.55 NIS
109% increase in two-way time
Approximately 109% increase in amplitude
0.4
0.5
0.6
Thin Bed: Fluid Factor vs. NI
Normal-Incident Reflectivity
NI = f( VP1, VP2, Rho1, Rho2) * 2 t/T
t = thin-bed traveltime
T = wavelet period
Fluid Factor
Wet ……..… F =
0 * 2 t/T
Oil, Fizz…… F = -.058 * 2 t/T
Gas ……….. F = -.088 * 2 t/T
Fluid factor independent:
• shale properties
• reservoir porosity
• upper shale  lower shale
Field Data
GOM Oil and Gas Reservoir
Oil
Gas
1s
Reservoir exhibits fault shadow
velocity anomaly
2s
-3000 m
3s
7.5 km
Well Production:
Early 1970s
Seismic Data:
1996 as OBS
Seismic Processing: 2008
Seismic data from Fairfield Industry, Inc.
AVO Inversion –NIP & NIS
Seismic NIP
Seismic NIS
400
4.2 miles
WET
1500
WET
0
-200
-1500
-800
4.6 miles
Producing oil well
Zhou 2009
Abandoned oil well
Producing gas well
Fluid-Factor Projection Line
Calibrated Fluid Factor
(2)=0.3266 NIS(2)+0.0022
NIP
NIP
= 0.33 NIS + .002
R2=0.8408
R2 = 0.84
0.02
Calibrated NIP
0
-0.04
Wet area
Whole survey
-0.08
Fluid Factor = NIP -.33 NIS - .002
Calibrated NIS
Producing oil well
Zhou 2009
Abandoned oil well
Producing gas well
Fluid Factor Prediction of Pore Fluid
Depth Contours
Wet sand
1
- 0.02
2 3
4
5
Oil sand
6
7
10
- 0.066
9
8
Gas sand
Fluid Factor
Producing oil well
Abandoned oil well
Producing gas well
3 producing wells correctly located
Gas zone correctly located
Gas and oil zones generally tie depth contours
Calibrated fluid factor is an accurate pore-fluid discriminator.
Zhou 2009
Summary: Fluid-Factor Properties
1. … independent of shale properties above or below reservoir.
2. … independent of reservoir porosity.
3. … independent of wavelet shape.
4. … related to NI of hydrocarbon/water contact.
5. … function of thin-bed traveltime and pore fluid.
Field Study Conclusions
1. NIP vs. NIS horizon crossplot provides
… E{FWET} = 0.
2. Regional well-log curves provide
… Seismic to well-log amplitude calibration.
3. With questionable wavelet and low-frequency control,
F was better pore-fluid discriminator than PI or .