Maria Jimenez Edgar Castillo Juan Carlos Chavez · Models without coupling with reservoir and/or...

Maria Jimenez Edgar Castillo Juan Carlos Chavez Senergy Senergy GDF Suez EP

May 2010

Objectives

!  To review various approaches used for water injection modelling and their implications on the outcomes and decision making process

!  To highlight the relevance of the coupled fluid flow -

geomechanics modelling for water injection (WI) and produced water re-injection (PWRI) processes

!  To share experiences and views on the topic

2

Outline

!  Background

!  Coupled Reservoir(flow)-Geomechanics Modelling for Water Injection

!  Modelling approaches

!  A comprehensive and pragmatic workflow

!  Final Comments

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Geomechanics in the reservoir

!  Compaction –Subsidence !  Faults reactivation

!  Stimulation

!  Depletion

!  Sanding

!  Hole stability

!  Casing Integrity

!  Injection: Gas and water

4

What is coupled fluid flow - geomechanics

reservoir modelling ?

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Coupled reservoir stress/strain-fluid flow modelling …is not something new

Public Material (Internet)

“Here we will suggest that it means interaction between a fluid flow

prediction model (traditional reservoir simulator) and rock

deformation model (geomechanics simulator) that is more advanced

than currently found in standard reservoir fluid flow simulators”

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Coupled reservoir fluid flow-stress/deformation modelling

Pressure

Reservoir Modelling

Fluid Flow

Pressure, Temperature

Flowrate

Reservoir Modelling

Stress-deformation

Pressure, Stresses Deformations

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From SPE 126159, Abass, Sierra & Tahini !

PI performance for various scenarios without the effect of stress (left) and with stress effect (right)!

Coupled reservoir fluid flow-stress/deformation modelling

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Why coupled fluid flow – geomechanics modelling for

Water Injection?

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What do we want to know when modelling water injection?

ü  Forecast of Injection Rates ü  Surface pressures

ü Are the fractures reaching the production zone?

ü  Swept area ü  Production Forecast ü  Are fractures generated?

The injection of water for pressure maintenance, waterflooding and disposal,

has been and will continue to be an important aspect in the definition of

reservoir development strategies

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Water Injection – Thermal fracturing

In situ stresses February 1985

Society of Petroleum Engineers Journal

Shear Failure

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!  Fracture or multiple fractures

!  Large leak-off

!  Poro-elastic and thermo-elastic effects on stresses and permeability

!  Large time-scale

!  Low viscosity fluids

!  Formation Damage

!  Fault reactivation

Water Injection - characteristics

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Water Injection - Characteristics

!  In water injection, formation damage due to particles suspended in the injection water can significantly change the fracturing pattern and therefore the injection profile

!  Fracturing creates a large surface area

for leak-off and it could re-propagate if it becomes plugged. Fractured injectors experience less injectivity decline over t ime and are more tolerant to suspended solids

!  To really see the impact of formation

damage at long term, comprehensive modelling is required

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Tp

ref Pσσσσ

ασσ

Δ−Δ+=

−=

0

Background – Water Injection and fracturing

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How is Water Injection Modelled?

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How is Water Injection Modelled

The volumes injected into hydraulic fractures are at

least 1000 times less than in water injection cases

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Stress gradient

The stress gradient changes with time are insignificant and not accounted when designing

hydraulic fractures

One hour later 17


Thermal and Poro-

elastic effects

One hour later

The rate of fracture propagation is also different. A hydraulic fracture propagates 100’s of feet in an hour while a typical injection-induced fracture

propagates 100’s of feet in months or years

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After 45 minutes of injection

~50 m

After 6 years of injection

The fluids used for hydraulic fracturing have much higher viscosity compared to the water used in injection wells. The so-called fluid efficiency for hydraulic fractures

treatments is high (low leak-off); the leak-off for water injection is very high.

+ leak-off

+ heat transfer

stresses decrease

+ leak-off

+ pressure

stresses increase

minimum leak-off à No need to consider

stresses change

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!  Non-coupled analytical models for 1 injector

!  Pseudo steady-state

!  2D analytical fracture mechanics.

!  Analytical leak-off on the third direction

!  Poro-elastic and thermo-elastic effects considered

!  The pressure is constant over the simulation period

!  Stress effect on permeability and porosity not considered

Injection

Leak-off 2D Fracture

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!  4D Reservoir simulator (pseudo-steady state). Production and injection are accounted for

!  The stress field is not numerically modelled is calculated through analytical correlations (non-coupled model)

!  It may or may not include fracture mechanics

!  Stress effect on permeability and porosity at reservoir level not considered or not accurately considered

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Shear failure and hysteresis can be

considered

Finite difference grid for flow calculations

Simplified fracture mechanics

Finite Element grid for stress-deformation

calculations

Stress-dependant permeability &

porosity

Likelihood of multiple fractures can be evaluated (deviated/horizontal wells)

Formation damage due to particle plugging can

be modelled

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SPE 110379 Shell

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SPE 107952

SPE 71614 U. Of Texas at Austin internal Coupled model UTWID - UTCHEM

U. Of Alberta internal Coupled model ATH2VIS

!  Models without coupling with reservoir and/or geomechanics can be fixed to some extent but ultimately are not suitable (SPE Hydraulic Fracturing Workshop – 2009)

!  The programs used for designing hydraulic fractures treatments are simply not suitable for studying fracturing due to water injection.1D or 2D leak-off modelling is not adequate. These convent ional tools general ly overestimate fracture growth

!  Requires geomechanical approach – Reservoirs are

geomaterials (Tony Settari at the SPE Hydraulic Fracturing Workshop – 2009)

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A comprehensive workflow is required

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A comprehensive workflow

Water

Injection

Coupled

Model

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Structural Model

Reservoir Model (Flow)

Understanding

Grid Manipulation for Geomechanics

Over/Under/Sideburden

Faults

Geomechanical data

Production and PWRI

Coupled model


Permeability Multiplier

1.0E+00

2.0E+04

4.0E+04

6.0E+04

8.0E+04

1.0E+05

1.2E+05

1.4E+05

1.6E+05

-1200 -1000 -800 -600 -400 -200 0 200 400 600

Effective Stress (psia)

Mul

tiplie

r

Shear Failure

Shear failure Tensile failure

Tensile Failure

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SPE 79695

Well!


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Fracture

Enhanced permeability

(Shear Failure)

Blocks adjacent to the fracture plane are in

shear failure.This shows that enhanced leak-off is

likely.

Effective Stress

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Shear failure

Tensile failure (frac open)

1 hour of injection

Effe

ctiv

e S

tress

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Red dotted lines: original cell

dimensions x &y

3 planes for evaluating probable multiple

fractures generation at each point

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psia

Effective Stress

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Plane 1

Plane 2

Plane 3

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f(p)

f(Smin’)

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Final comments

!  Prediction of injectivity for water injectors requires a geomechanical approach (coupled fluid flow - geomechanics). Reservoirs are geo-materials

!  Single well models which consider fracture mechanics, do not capture a comprehensive view of the system. It is required to account for the interdependence between extraction, production and the associated stresses acting on the structure

!  The importance of this coupled modelling is usually disregarded as current industry practice generally ignores this workflow for reservoir engineering

!  This type of modelling it is an excellent opportunity to understand the system, the boundaries of its responses and to design the optimum sand-face completion.

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Cost / expertise / specialised data requirements

Acc

urac

y of

ans

wer

/

glo

bal a

pplic

abili

ty

!  Reservoir characterization uncertainties !  No model is 100% accurate

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Final comments

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Final comments

We are evolving to a more comprehensive view

Points of view

Viewing points

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Final comments

There is a growing realization that almost all the water injection wells

develop injection induced fractures at some point in their life

(SPE 124857 and 95% of attendees to the SPE Water Injection Workshop in

Portugal – 2008)

Maria Jimenez Edgar Castillo Juan Carlos Chavez · Models without coupling with reservoir and/or...

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