Abstract and subjects
•We measured shale fracture permeability on a TDS system with X-ray CT and fluid flow.•Hydraulic aperture is greatly smaller than mechanical aperture for in-situ fractures.•Compressibility and surface roughness both affect stress sensitivity of fracture permeability.•Fracture closure can greatly affect gas production and optimal bottomhole pressure in some cases.
Stress-dependent fracture permeability could significantly affect oil and gas production, underground CO2 storage, and deep waste disposal containment. Yet, measurements to characterize these effects are lacking. To be most relevant to field conditions, measurements of stress-dependent fracture permeability should target pre-existing fracture features, be completed at high-stress conditions, and enable visualization of the fracture geometry to characterize the in-situ aperture profiles. Here, we employ triaxial direct-shear (TDS) tests, integrated with real-time X-ray imaging, to measure the stress-dependent fracture permeability of Marcellus shale and ‘Western Texas’ shale at subsurface conditions. Our results indicate that the studied shale fractures are characterized by large variation of compressibility factor. We also found that surface roughness can reduce fracture permeability more severely than what literature values would suggest. We then implemented our stress-dependent fracture permeability measurements in a formation-linear flow model to investigate the significance for shale gas production. The model uses the MIP-3H well at the Marcellus Shale Energy and Environment Laboratory (MSEEL) as a base case. The model results reveal a narrow stress-dependent permeability range over which fracture closure can be critical for production and that MSEEL appears to be close to this critical condition, which could be important for reservoir pressure management.