Accurate reservoir modelling through optimized

integration of geostatistical inversion and flow

simulation. A North Sea case study.

A. Castoro1, L de Groot2, D. Forsyth3 & R. Maguire1

1Fugro-Jason UK, 2GDF SUEZ E&P Nederland B.V., 3Currently Saudi Aramco, Previously GDF SUEZ E&P Nederland B.V.

DEVEX 2009, 12 - 13 May, Aberdeen Exhibition and Conference Centre

2

Objectives and workflow

Input structural model, seismic data & well data

Geostatistical inversion > 20 reservoir models with range of properties

Prediction runs for well planning and field development

Engineering Data

History match & ranking of all reservoir models

Create robust reservoir model fit for prediction of field production

and development planning

Selection & fine tuning of final reservoir models

Business Decision

3

Outline

• Models from geostatistical inversion

• Initial history match and model selection

• Final models history match

• Geostatistical vs deterministic models

• Conclusions

4

Geostatistical reservoir modeling

� Interpolate between the wells

• Plausible details ����

• Accurate near wells ����

• Not elsewhere ����

Deterministic seismic inversion

� Optimize P-Impedance to minimize synthetic-to-seismic misfit

• Accurate within seismic bandwidth ����

• Unrealistically smooth ����

• Only one possibility ����

StatMod MC – FJ geostatistical seismic inversion

� Subsumes geostatistical modeling and deterministic inversion

� Does both, simultaneously and in a statistically rigorous way

� Multiple plausible realizations at high detail (e.g. 1ms × 25m)

� Yet also coherent “interpretations” of the seismic up to the km scale

Geostatistical inversion vs other modelling

techniques?

5

Reservoir properties

A1 A2 A3 A4 A5 A6 A7 A8 B3

Lithotype

Best

Good

Low

Non reservoir

LOWER RESERVOIR

UPPER RESERVOIR

6

Seismic data

Near stack seismic

Estimated wavelet

Seis

mic

-well

ties a

nd s

ynth

etics

Amplitude Phase

Seismic Synt Impedance

Seismic Synt Impedance

A2

B3

7

Geostatistical vs deterministic inversion

Impedance sections

Deterministic

(4ms)

Geostatistical

(1ms)

A8 A5 A2 A7A1 A6

8

Geostatistical inversion honours all inputs

Wells are honoured Seismic is honoured

Geostatistics are honoured

Deterministic Geostatistic

Input

Output

9

Blind well validation

• Single realization with wells overlaid

• Wells were not used as a constraint

P-Impedance

A8 A5 A2 A7A1 A6

Lithotype

Best

Good

Low

Non reservoir

1.5e+07

7e+06

1.1e+07

Lithology

Impedance

10

Outline

• Models from geostatistical inversion

• Initial history match and model selection

• Final models history match

• Geostatistical vs deterministic models

• Conclusions

11

Time

SM

3 /

da

y

• Models not matching

historical gas production

discarded

Model screening: historical field gas production

• Some models can fail

to match historical total

field gas production by

up to 2 % Historical

Model 9

Model 1

Model 4

Model 16

Historical

Model 9

Model 1

Model 4

Model 16

Simulated

Historical

Simulated

Simulated

Simulated

Time

SM

3

12

Outline

• Models from geostatistical inversion

• Initial history match and model selection

• Final models history match

• Geostatistical vs deterministic models

• Conclusions

13

Final models history match (bottom hole pressure)

Well A1

Well A3

Well A2

Well A6 Well B3

Well A7

14

Outline

• Models from geostatistical inversion

• Initial history match and model selection

• Final models history match

• Geostatistical vs deterministic models

• Conclusions

15

Geostatistical vs deterministic inversion models

Permeability (mD)

16

Geostatistical vs deterministic inversion: history match

• Historical

• Historical

Time

Pre

ssu

re (

bars

a)

Time

Pre

ssu

re (

bars

a)

Time

Pre

ssu

re (

bars

a)

Time

Pre

ssu

re (

bars

a)

Time

Pre

ssu

re (

bars

a)

• Historical

• Historical • Historical

• Historical

Time

Pre

ss

ure

(b

ars

a)

17

Outline

• Models from geostatistical inversion

• Initial history match and model selection

• Final models history match

• Geostatistical vs deterministic models

• Conclusions

18

Conclusions

• Creation of multiple equally probable reservoir models

given the geophysical and geological data

• Inverted impedance (→ porosity, etc) shown to be reliable by blind well

predictions

• Geostatistical character and correlations maintained

• History match achieved

� without the use of porosity or permeability modifiers

� without the incorporation of faults not substantiated by evidence from seismic

interpretation or well test analysis

• The reservoir model is considered robust and

suitable for use in forward simulation for well

planning and field development

19

Acknowledgements

• Thanks to GDF SUEZ E&P Nederland B.V. for permitting this study to be

shown

Questions?