Jean-Marc Chautru (Geovariances) *

Matthieu Bourges (Geovariances)

Hélène Binet (Geovariances)

Renaud Meunier (Geovariances)

Conditioning Static Models

with

Connectivity Information

Introduction

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• Connectivity is a key characteristics for Geomodels to be used in flow simulations

Not properly captured connectivity biased flow simulations Journel A., Alabert F. (1990), JPT 42

• Dynamic synthesis allows defining the hydraulic connection between wells and/or stratigraphic units

Production curves shape analysis (Pressure, produced fluids) Well tests Tracer tests

• Geomodels are expected to reproduce these connections If not, History Match will be very difficult

Connectivity is a critical parameter for flow simulations

How to honor wells connection?

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• No geostatistical simulation method honouring connectivity data available in commercial software

• Research algorithms are available Several authors

o Allard D. o Renard P. o Mariethoz G. o Straubhaar J. o Caers J. o Deutsch C. o Etc..

Different techniques.

o Based on Truncated Pluri-Gaussian facies simulation method o Based on MPS facies simulation method

How to honor wells connection?

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• In models built in commercial software

• For any facies simulation method

• Preserving the facies and Permeability simulation workflows

Post-processing approach

Checking wells connection

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Connections can be checked with “connected components”

• Continuous geobodies made of grid cells of similar properties that are connected by one face

• Similar properties = same facies or same permeability range

A B

1 geobody

A B

2 geobodies

A

3 geobodies

Geomodel QC with geobodies

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• Hydrocarbon volumes connected to the wells

o Volume of geobody * Porosity * N/G * (1-Sw)

o Must be consistent with production data

• Connection between wells

o Are observed connections between wells honored?

o What is the degree of consistency of the model with dynamic data?

o What are the characteristics of the connections in the model?

Geomodel QC must be done before flow simulations

Checking wells connection

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Connected wells

Two wells intersecting the same geobody are connected

Consistency with connectivity data

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Stochastic Connectivity Analysis

1. Test Connections on several realizations of the same model

Calculate the percentage of realizations

in which wells are connected o Low percentage model inconsistent

with dynamic data

o ~50% appropriate model, but

realizations have to be selected

o High percentage model consistent with

dynamic data

Consistency with connectivity data

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Stochastic Connectivity Analysis

2. Test sensitivity to model parameters Uncertainty on model parameters range of variation

Adjusting local VPC & ranges may solve connection inconsistencies

Geological models enhancement

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Three steps workflow

1. Calculate cells probability to be in a connecting geobody Calculated from stochastic realizations of the geological model

2. Select cells that are often in a connecting geobody

Probability of presence in connecting geobody Selection of cells with the highest

Probability of Presence

Geological models enhancement

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3. Define a random sampling in selected cells Connecting facies is assigned to random samples Random samples are added to well data for next model realization Random samples are updated for each realization

Cells most frequently in a connecting geobody

+

Additional random conditioning data (light color)

Additional samples help selecting realizations that work

Including Faults

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• If adjusting model parameters is not enough… Some parameters critical for fluid flow are missing

o Conductive faults o Fractures

• Including faults and fractures in calculations 1. Calculate the distance to faults or fractures 2. Select cells close to the faults 3. Merge this new selection with the connecting “facies” 4. Re-run the connection test

Distance to the closest fault

Dealing with complex structures

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In presence of faults with high throw

• Connection may exist between wells perforated in different stratigraphic units

• A global structural grid must be defined Cells on both sides of faults must be neighbours in I, J, K indexes Populated through an upscaling operation

• Connectivity calculations can be carried out within the global grid

Connections characterization

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• Connections must be characterized Connecting geobody shape may be regular or irregular

Connecting geobody shape impacts fluid flow

Connections characterization

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• Connections must be characterized Use erosion to progressively reduce the size of the connecting geobody

At each iteration, recalculate connected components on the eroded geobody

After erosion Initial geobody

Erosions help detecting baffles and narrow throats in geobodies

Upscaling issues

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• Connectivity check must be done on the geological model and on the reservoir model

The reservoir engineer will generally use only one realization for History Match

This realization, which has been upscaled, must preserve connections between wells observed in the geological model

• In case of contradiction, revisit the upscaling process or the reservoir grid resolution

Conclusion

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• Stochastic connectivity analysis improves Geomodels QC Facilitates communication between geologists and engineers

• Post-processing allows enhancing simulation results Can be used with all the geostatistical simulation methods Better calibration of geomodel parameters Preserves existing geomodeling workflows

• QC of connections to be done before any optimization process Enhances efficiency of Assisted History Match techniques

Honoring connections is required to speed-up and improve HM