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.