Modeling Fluid Flow Through Single Fractures Using Experimental, Stochastic and Simulation Approache

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Modeling Fluid Flow Through Single Fractures
Using Experimental, Stochastic and Simulation
Approaches

• Dicman Alfred
• Masters Division

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Introduction

• A NFR with extensive
• fractures
• Poor ultimate recovery

Reserves 10B bbls
Recovery lt 10
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Why study fracture flow?

• Improve prediction of sweep in Naturally
  Fractured reservoirs
• Improve modeling of tracer studies

Shale
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Getting the basics right!
Knowledge of the nature and mechanics of flow
through a fracture becomes critical.
Starts from basic understanding of core studies.
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Historical perspective
Fractures as parallel plates
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Historical perspective
Fracture Model
Constant permeability fracture surface
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Historical perspective
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Reality ?
Fractures cannot be assumed as parallel plates.
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Reality ?
Fractures cannot be assumed as parallel plates.
A real fracture surface is rough and tortuous.
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Issues
The flow through a fracture follows preferred
paths because of the variation in fracture
aperture.
Witherspoon (1980)
Iwai (1976)
Neuzil(1980)
Tracy (1980)
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More issues
The friction associated with the rough fracture
surface affects the flow performance.
TsangTsang(1988)
Brown (1987)
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The story so far
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The objective

• How do we obtain fracture aperture width?
• How do we simulate flow through fractures
  effectively?

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The approach
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The approach
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Motivation

• Information from experiments?
• Fracture permeability
• Fracture aperture
• Matrix and fracture flow contributions
• How these properties change with overburden
  stress

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In the past
Apertures measured physically
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New perspective
To quantify the change in aperture with
overburden pressure
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Experimental setup
km
Hydraulic jack
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Experimental setup
Core Berea
km
Hydraulic jack
kav
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Permeability Changes at Variable Overburden
Pressure
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Fracture aperture?
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Average aperture equation
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Fracture aperture
5 cc/min
10 cc/min
15 cc/min
20 cc/min
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Matrix flow rate
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Fracture flow rate
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Motivation

• Is it possible to create an entire aperture
  distribution from a single value of mean aperture?

Yes !
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Aperture distribution
Apertures distributed log-normally
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Generation of apertures
Through a mean and a variance
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Application?
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Application?
Slightly rough fracture surface
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Application?
Highly rough surface fracture
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Stochastic analysis
Creation of the aperture map

• Variogram

• Kriging

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Aperture distribution map
Outcome of Kriging
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Good enough?
Comparison
Not the real picture but effective
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Motivation

• Tackle the issue of surface roughness
• Match the experimental results, namely flow and
  pressure drop across the core

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Surface roughness
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Surface roughness
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Surface roughness
Modified cubic law
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Effect of friction?
Permeability modification of the fracture surface
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Simulation
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Flow on a smooth fracture surface
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Flow on the distributed fracture
surface follows preferred flow paths
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Results
Parallel Plate Theory
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Flow match
Parallel Plate Theory
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The new approach
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The new approach
Flow match
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Limitation?
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Applications
Gravity Drainage Experiment
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X-ray ct scan
Rotating During Scan
X-Ray Source
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Applications
Parallel-Plate Theory
Gravity-Drainage Experiment
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Applications
Gravity-Drainage Experiment
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The new approach
Gravity-Drainage Experiment
Simulation
X ray CT Scan
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Conclusions
How do we obtain fracture-aperture width ?
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Conclusions
How do we simulate flow through fractures more
effectively ?

• Distribute fracture apertures
• Consider effect of friction caused by rough
  fracture surfaces

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Conclusions
What other factors affect flow through fractures?

• Tail of frequency distribution impacts flow
  performance
• Tortuosity dominates fracture flow at high
  overburden pressures

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Conclusions
Why study rugosity in fractures?

• Improve prediction of sweep in naturally
  fractured reservoirs
• Improve modeling of tracer studies