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Fractures / Faults Slip Potential Apps

slipExplore

#### Natural fracture reactivation or fault slip potential after fluid injection

Propensity of existing, closed natural fractures to get reactivated after increased pore pressure due to fluid injection depends mostly on the relative orientation of the fracture plane with respect to the orientation of maximum stress and the coefficient of friction. Fractures whose orientations are closer to the angle of friction are more likely to get reactivated (critically stressed) with increased pore pressure and therefore, more likely to flow. Further increases in pore pressure may reactivate other orientations effectively creating a "network" of reactivated fractures.

What these apps do

We have three apps to perform critical stress analysis:

2) FracSlip2D works for multiple [depth, orientation] pairs derived, for instance, from image logs interpretations in a certain interval.  Assumes vertical fractures. Depths are needed to calculate stress from a given stress gradient.

3) FracSlip3D works for multiple [depth, orientation, dip] triplets derived, for instance, from image logs interpretations in a certain interval. This app generalizes FracSlip2D. Depths are needed to calculate stresses from given stress gradients.

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Under the assumption of vertical fractures, both apps determine which natural fractures from a given set are critically stressed under the given stress state. If they are not, the apps determine the additional pore pressure needed to reactivate them. Reactivated fractures will determine the preferential orientations of flow. For more details, see Enderlin, M.B. (2010) ("A method for evaluating the effects of stress and rock strength on fluid along the surfaces of mechanical discontinuities in low permeability rocks"). For a more recent reference, see Zoback, M.D. and Lund Snee, J-E. (2018) ("Predicted and observed shear on pre-existing faults during hydraulic fracture stimulation").

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â€‹Interested in generalizing this concept using 3D seismic data to estimate recovery? Take a look at this presentation

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Click here to see an example of how to use Slip Calculator taken from our fracture modeling class for the problems of fracture reactivation and fault slip potential due to increase fluid pressure.

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Change the pore pressure or friction coefficient to see which natural fractures get reactivated for your given stress state.

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Calculator

App 1 (Slip Calculator): Single depth, multiple fracture orientations

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Input:

• Minimum horizontal stress gradient (in psi/ft)

• Maximum horizontal stress gradient (in psi/ft)

• Orientation of maximum horizontal stress Shmax in degrees (measured from North)

• Coefficient of friction Mu

• Depth(s) (ft)

• Fracture strikes in degrees (measured from North)

Output:

• Minimum horizontal stress at given depth (in psi)

• Maximum horizontal stress at given depth (in psi)

• Pore pressure at given depth (in psi)

• Indicator of whether each input fracture orientation is critically stressed (Yes or No)

• Additional pore pressure required to reactivate fractures that are not critically stressed

• Plot of extra pore pressure needed to reactivate fractures vs fracture strike (zero means "reactivated"). If fractures are cannot be reactivated under the current stress state, they are indicated as "Impossible".

• Plot of orientations of reactivated fractures and Shmax strike.

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Assumption:

Natural fractures are vertical.

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JAVASCRIPT MUST BE ENABLED IN YOUR BROWSER FOR THIS APP TO WORK PROPERLY

Not designed to work on mobile devices.

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Input parameters:

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• URL of input Google Sheet with [depth, orientation] pairs. Make sure the sharing parameters are set to "Anyone with the link" and "Editor".

• Minimum horizontal stress gradient (in psi/ft)

• Maximum horizontal stress gradient (in psi/ft)

• Orientation of maximum horizontal stress Shmax in degrees (measured from North)

• Coefficient of friction Mu

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Input data in user provided Google Sheet:

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• [Depth, orientation] pairs saved on "Sheet1" of the Google Sheet

• Here is an example:

Depth (ft)       Orientation (deg)

5000                      45

5230                      52

5265                      47

.                               .

.                               .

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Use this Google Sheet to test the app using the default parameters. and to check how you should prepare your own data.  Here is the actual URL of the test Google Sheet:

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Remember that this Google Sheet can be accessed by anyone with this link. You won't be able to modify the input data. If you want to run the app with your own data, prepare a separate Google Sheet.

Output results in user provided Google Sheet:

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The App creates a Sheet2 on the user's Google Sheet to save the results. Sheet1 is left untouched. The new Sheet2 has 6 columns:

1. Input depth

2. Input orientation

3. Effective normal stress (psi)

4. Shear stress (psi)

5. Shear stress to fail (or failure line for the given Mu)

6. Additional pressure needed to fail (psi). Yellow cells in column 6 indicate fractures that are critically stressed. Orientations marked as "Impossible" are those that cannot be reactivated under any additional pore pressure increase.

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App 3 (FracSlip3D): Multiple [depth, orientation, dip] triplets from image log interpretation

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Input parameters:

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• URL of input Google Sheet with [depth, orientation, dip] triplets. Make sure the sharing parameters are set to "Anyone with the link" and "Editor".

• Principal stress gradients S1, S1, and S3 (S1 ≥ S2 ≥ S3)

• Trend of S1, Plunge of S1, Rake of S2

• Coefficient of friction Mu

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Input data in user provided Google Sheet:

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• [Depth, orientation, dip] triplets saved on "Sheet1" of the Google Sheet

• Here is an example:

Depth (ft)       Orientation (deg)     Dip(deg)

5000                      45                             80

5230                      52                             75

5265                      47                              85

.                               .                                    .

.                               .                                    .

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Use this Google Sheet to test the app using the default parameters. and to check how you should prepare your own data.  This example is designed to reproduce the results of the example of FracSlip2D above with vertical fractures. Here is the actual URL of the test Google Sheet:

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Remember that this Google Sheet can be accessed by anyone with this link. You won't be able to modify the input data. If you want to run the app with your own data, prepare a separate Google Sheet.

Output results in user provided Google Sheet:

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The App creates a Sheet2 on the user's Google Sheet to save the results. Sheet1 is left untouched. The new Sheet2 has 6 columns:

1. Input depth

2. Input orientation

3. Input dip

4. Effective normal stress (psi)

5. Shear stress (psi)

6. Shear stress to fail (or failure line for the given Mu)

7. Additional pressure needed to fail (psi). Yellow cells in column 7 indicate fractures that are critically stressed.

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