TIME-LAPSE GRAVITY INVERSION USING GENETIC ALGORITHM (2 BIT)

EKO JANUARI WAHYUDI

Supervised by:Dr. Wawan Gunawan A Kadir

Dr. Hendra Grandis

• INTRODUCTION• 4D MICROGRAVITY• FLUID SUBSTITUTION• GENETIC ALGORITHM• PERFORMANCE TEST• REAL DATA INVERSION• CONCLUSION

OUTLINE

INSTITUT TEKNOLOGI BANDUNG

INSTITUT TEKNOLOGI BANDUNG

• As technology advance gravimeter also improve in accuracy and give the possibility to monitor pore fluids redistribution in permeable layer.

• Especially in Indonesia, 4D microgravity becomes considerable choice because: (1) relatively cheaper, (2) strong response (in many cases), (3) fast in acquisition, (4) less social and environmental conflict.

• Focus of this study is inversion programming using genetic algorithms (GA's).

• This study was inspired by publication Krahenbuhl & Li (2008). They used binary formulation to inverse borehole and surface gravity data.

INTRODUCTION

INSTITUT TEKNOLOGI BANDUNG

INSTITUT TEKNOLOGI BANDUNG

• Pore fluids (gas, oil, & water) are subject in gravity forces, because they have different densities.

• Mass redistribution will cause changes in the gravity attraction.

4D MICROGRAVITY

INSTITUT TEKNOLOGI BANDUNG

INSTITUT TEKNOLOGI BANDUNG

Δρmax = 00.060 0.297 0.237 (in g/cc)

Assumption:Porosity = 30%Water Density = 1.00 g/ccOil Density = 0.80 g/ccGas Density = 0.01 g/cc

FLUID SUBSTITUTIONINSTITUT TEKNOLOGI BANDUNG

INSTITUT TEKNOLOGI BANDUNG

• GA is optimization method that combines biology genetic concept with optimization function maximize fitness through artificial evolution process

• Genetic algorithm using the principal of survival for the fittest

GENETIC ALGORITHM

INSTITUT TEKNOLOGI BANDUNG

INSTITUT TEKNOLOGI BANDUNG

Krahenbuhl (2005)

• GA does not need any derivatives or curvature information• GA's strongly can handle non-linier inversion and give sharp

characterization of fluid contact movement in permeable layer.

GENETIC ALGORITHM

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INSTITUT TEKNOLOGI BANDUNG

The objective function

GA’s RESULTS

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INSTITUT TEKNOLOGI BANDUNG

Inversion Result

Krahenbuhl & Li (2009)

Data Observation

Inversion Performance

1 BIT, 2 BIT

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INSTITUT TEKNOLOGI BANDUNG

1 bit Inversion

n=2 bit Inversion

PERFORMANCE TEST

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INSTITUT TEKNOLOGI BANDUNG

Inversion ResultSynthetic Model

REAL DATA INVERSION

INSTITUT TEKNOLOGI BANDUNG

INSTITUT TEKNOLOGI BANDUNG

Inversion Result

Data Observation

• Genetic algorithm can be applied in 4D gravity inversion• Using 2 bit GA inversion give the possibility to characterize 3 type

density changes in reservoir• Inversion results from real data show the characterization of mass

increase, mass decrease, and stable zone in permeable layer

CONCLUSION

INSTITUT TEKNOLOGI BANDUNG

INSTITUT TEKNOLOGI BANDUNG

THANKS