Fractures / Faults Slip Potential

Fractures / Faults Slip Potential Apps

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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 two apps to perform critical stress analysis: one works on a single depth and multiple fracture orientations with graphic output (Slip Calculator) and the other for works for multiple [depth, orientation] pairs derived, for instance, from image logs interpretations in a certain interval (FracSlip). 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").

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

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.

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

Assumption:

Natural fractures are vertical. If this assumption is not valid for your particular case, contact us.

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

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)
Initial pore pressure gradient (psi/ft)
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.

Calculator

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

Not designed to work on mobile devices.

App 2 (FracSlip): Multiple [depth, orientation] pairs from image log interpretation

You must have a Google account to run this app. You will be required to grant permission for the App to read and write the Google Sheet that contains your input data. Google Sheets are saved on the Google Drive related to your account. We neither access any data in your Google Drive other than the one you indicate, nor we store or share your data in any form. For more information, read our Privacy Policy and Terms of Service.

Input parameters in HTML User Interface:

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)
Initial pore pressure gradient (psi/ft)
Coefficient of friction Mu

Input data in user provided Google Sheet:

[Depth, orientation] pairs saved on "Sheet1" of the Google Sheet
Here is an example:

Depth (ft) Orientation (deg)

5000 45

5230 52

5265 47

. .

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:

https://docs.google.com/spreadsheets/d/1HBVpWafqTCVD6wzsr73pROZPw_uYZFOfy3Jj0kBAhQE/edit#gid=0

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:

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:

Input depth
Input orientation
Effective normal stress (psi)
Shear stress (psi)
Shear stress to fail (or failure line for the given Mu)
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.

We recommend running the app from the button below to make sure you always use the latest version.

GoogleApp

Run FracSlip

App verification in progress....