Fault Seal Analysis in an Onshore Unconventional Gas Target, North Perth Basin

Area of Science:

• Geology
• Petroleum Geoscience
• Structural Geology

Background:

• Hydrocarbons were detected in aquifers during gas well drilling in the Woodada gasfield, North Perth Basin, Western Australia.
• The Kockatea Shale is a regional source rock and seal, with faults potentially influencing hydrocarbon migration.

Purpose of the Study:

• To test the hypothesis that reactivated faults in the Kockatea Shale are prone to leakage.
• To correlate fault integrity and stress conditions with hydrocarbon presence in aquifers.

Main Methods:

• Fault Seal Analysis Technology was employed to assess fault integrity.
• Fracture stability of faults was analyzed under different stress scenarios (normal and strike-slip).
• Hydrocarbon logs from wells proximal to faults were correlated with fault properties.

Main Results:

• Wells near faults with fracture stability >5 MPa only logged methane.
• Wells near faults with fracture stability ≤5 MPa logged both methane and condensate, confirming leakage.
• Uncemented Kockatea Shale faults with specific orientations and dips showed the lowest integrity under normal and strike-slip stress.

Conclusions:

• Hydrocarbon leakage is correlated with critically stressed faults in the Kockatea Shale.
• Fault rock properties (cemented vs. uncemented) significantly influence fracture stability and leakage potential.
• Hydraulic fracturing pressures may exacerbate existing fault leakage in areas like the Woodada gasfield.