Quantifying Seismic Reflectivity
Fred HiltermanDistinguished Research Professor – University of Houston
Chief Scientist – Geokinetics Data Processing and Interpretation
April 28, 2010
Based on UH Dissertation by Dr. Jenny Zhou – Former AGL RA
A Second Look at the Fluid Factor
Birth of Fluid Factor
George Smith & Maurice Gidlow South Africa - 1986
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 incidenceNIS = S-wave normal incidence
Class 1 AVO
Fluid Factor Review
2.9
3.0 Stack
NIP
NIS
2.9
3.0
2.9
3.0
Class 1 AVO
NIP NIS
Fluid Factor: F = NIP - 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
Fluid Factor Review
Can F discriminate oil from gas ?
Gas Oil
Calibrating Fluid Factor toWell-Log Data
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
-0.12 -0.08 -0.04 0 0.04 0.08
NI WET
NI
We
t, G
as
an
d O
il
(NIGAS-NIWET)
Fluid Factor from Normal Incidence
NI varies significantly for gas- and brine-saturated sand … but
(NIGAS-NIWET) changes little.
Wet
Oil
GasNIHYDROCARBON-NIWET Fluid Factor
NIOIL - 1.09 NIWET = - 0.052
NIGAS - 1.14 NIWET = - 0.088
NIOIL = -0.052 + 1.09 NIWET R2 = .94
NIGAS = -0.088 + 1.14 NIWET R2 = .83
Regression Equations
Reservoir porosity: 10-33 %Encasing shale: 2600-4200 m/s
How is Fluid Factor extracted from seismic data?
151 wells from South Marsh Island
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
F(t) ≡ NIP(t) – 0.72 NIS(t) + 0.03 therefore … E{FWET} = 0
Based on horizon pore-fluid projection
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
-0.16 -0.08 0.00 0.08 0.16
NIS
NIP
Linear Equation NIP=0.72NIS-0.03
Wet
OilGas
Fluid Factor = NIP - 0.072NIS + 0.03
-0.16
-0.08
0.00
0.08
0.16
-0.15 -0.10 -0.05 0.00 0.05
NIP - 0.72 NIS + 0.03
NIS
WetOilGas
151 wells in South Marsh Island
Unique Properties of Fluid Factor
Fluid Factor: Boundary or Layer Property?
F relates to gas/water contact -NIGWC … not encasing shale.
NIGWC = (AIWET SAND–AIGAS SAND)
(AIWET SAND+AIGAS SAND)
NIGAS – NIWET = F
- -Wet Sand
Gas Sand
S R
F - NIGWC
Wet Sand
Shale
S R
NIWET
Gas Sand
Shale
S R
NIGAS
Fluid Factor: 9-m Wet Thin Bed
NIP
NIS
y = 0.5511x - 0.0195
R2 = 0.99
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.1 0.2 0.3 0.4 0.5 0.6
NIS
NIP
VP = 2280 m/s
VP = 2280 m/s
VP= 2250 m/s
VP = 3600 m/s
VP = 3490 m/s
VP = 2280 m/s
Seismic Section: Fluid Factor = NIP – 0.55 NIS
F
Fluid Factor: 9-m Gas Thin Bed
NIP
NIS
y = 0.5511x - 0.0195
R2 = 0.99
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.1 0.2 0.3 0.4 0.5 0.6
NIS
NIP
VP = 2280 m/s
VP = 2280 m/s
VP= 1628 m/s
VP = 3370 m/s
VP = 3490 m/s
VP = 2280 m/s
11.1 ms
Two-way time
5.3 ms
Two-way time
109% increase in two-way time
Seismic Section: Fluid Factor = NIP – 0.55 NIS
F
Approximately 109% increase in amplitude
Thin Bed: Fluid Factor vs. NI
NI = f( VP1, VP2, Rho1, Rho2) * 2 t/T t = thin-bed traveltime T = wavelet period
Wet ……..… F = 0 * 2 t/TOil, Fizz…… F = -.058 * 2 t/T
Gas ……….. F = -.088 * 2 t/T
Fluid Factor
Normal-Incident Reflectivity
Fluid factor independent:• shale properties• reservoir porosity • upper shale lower shale
Field Data
GOM Oil and Gas Reservoir
Seismic data from Fairfield Industry, Inc.
Well Production: Early 1970sSeismic Data: 1996 as OBSSeismic Processing: 2008
7.5 km
Oil Gas
1 s
2 s
3 s
-3000 m
Reservoir exhibits fault shadowvelocity anomaly
AVO Inversion –NIP & NIS
4.2
m
iles
4.6 miles
FaultFault
400
-200
-800
1500
0
-1500
Seismic NIP Seismic NIS
WET WET
Zhou 2009
Producing gas wellAbandoned oil wellProducing oil well
Fluid-Factor Projection Line
Producing gas wellAbandoned oil wellProducing oil well
FaultWet areaWhole survey
0.02
0
-0.08
-0.04
NIP(2)=0.3266 NIS(2)+0.0022R2=0.8408
Calibrated Fluid Factor
Zhou 2009
Fluid Factor = NIP -.33 NIS - .002
NIP = 0.33 NIS + .002R2 = 0.84
Calibrated NIS
Cal
ibra
ted
NIP
Fluid Factor Prediction of Pore Fluid
Producing gas wellAbandoned oil wellProducing oil well
- 0.066
- 0.02
Wet sand
Oil sand
Gas sand
9900
12 3 4
5 6
7
8910Fault
Depth Contours
Fluid Factor
3 producing wells correctly located Gas zone correctly located
Zhou 2009Calibrated fluid factor is an accurate pore-fluid discriminator.
Gas and oil zones generally tie depth contours
Summary: Fluid-Factor Properties
5. … function of thin-bed traveltime and pore fluid.
2. … independent of reservoir porosity.
4. … related to NI of hydrocarbon/water contact.
1. … independent of shale properties above or below reservoir.
3. … independent of wavelet shape.
Field Study Conclusions
1. NIP vs. NIS horizon crossplot provides … E{FWET} = 0.
3. With questionable wavelet and low-frequency control, F was better pore-fluid discriminator than PI or .
2. Regional well-log curves provide … Seismic to well-log amplitude calibration.