czerniak_geopressure_2011

HESS CORPORATION - Americas Offshore Exploration

1

Role of PermeabilityWeighting in

Centroid Positioning

Matt CzerniakOctober 3, 2011


2

Centroid Theory

Flemings, Stump et al., 2002


3

Centroid Modeling Concept –

Early application of centroid theory assumes simple basin flank or mini-basin setting (not complex structure)Permeability weighting in 3D centroid modeling workflow allows for complex structuring and lateral changes in formation pressure.


4

Flow into sand – Flow out of sand = 0

Sum{(map) αsand - (map) αshale}*{(map) kshale } = 0 over mapped area of sand on horizon

α : fluid potential in psik: permeability

Kilsdonk, 2003 AAPG


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Centroid Effect: FLOW IN = FLOW OUT

αsand = ∑ (αshale * kshale)∑ kshale

α: overpressure, psik: permeability, mDn: number of grid nodes


6

Assumptions / Scope

Existing 3D Pore Pressure Volume calculated from a pre-conditioned 3D Interval Velocity Model

• Corrected for Anisotropy• Properties include: pseudo-density, fracture gradient, porosity-permeability

Use 3D mapped horizons as a proxy for geobodies• Zero Sand Thickness• Geobody is contained within 3D Volume• Regular grid spacing (e.g., 500 x 500 ft.)• Correct for dip error

Transfer select properties from 3D Pore Pressure Volume to mapped horizonsPerform permeability-weighted centroid calculations through standard Gocad Scripting Editor


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Pre-Conditioned Velocity Model

Pseudo-density

Porosity

Permeability


8

Overpressure


9

Fracture Gradient


10

Өcos

Dip Correction


11

Convert dip angle to Radians

surface mode > compute


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Dip corrected OP script


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K * OP_dc script


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sumKxOP_dc script

Command Terminal

= n


15

Centroid OP script + hydrostatic

dc_sand_PPG.EMW


16

Hydrofrac


17


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SUMMARY

A framework is provided for advanced centroid modeling calculations in 3D, assuming an existing pre-conditioned seismic velocity-based 3D PPFG volume;Gocad provides an excellent platform for 3D centroid calculations using simple scripting editor, 3D permeability-weighted centroid calculations, corrected for dip, are capable of providing rubust predrill pore pressure forecasts.

Note: Special thanks to Bill Kilsdonk and Keith Katahara [Hess] for inspiration and suggestions regarding the permeability-weighting scheme and geobodydip correction workflows, respectively.

czerniak_geopressure_2011

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