Permeability of Limestone-Dolomite Composite Fracture Surfaces Van de Reep, Peter John
The transport properties of fault zones are critically important in predicting subsurface fluid behavior in deformed rocks and understanding fold and thrust belts. Limestone-dolomite composite rocks are common components of fold and thrust belts and are also productive reservoir rocks for hydrocarbons. This study develops a methodology for measuring the permeability of experimentally induced fracture surfaces in limestone-dolomite composite rocks. Cores of rocks from the Mount Head Formation and the Fairholme Group of southern Alberta were deformed at a confining pressure of 25 MPa in a triaxial rock press. Fluid ports were drilled in the deformed cores to ensure direct fluid access to the fracture surface. The transient pulse decay method was used to determine the permeability of the fractures. Experimental difficulties resulted in only two permeabilities being derived from experimentation. Modeling of the transient pulse decay for the fracture surfaces shows permeabilities of 4•10-17 m2 for predominantly dolomite and 8•10-17 m2 for dolomitic limestone. Lower permeability in the dolomite end member is thought to be due to very fine comminution in the fracture gouge caused by highly focused strain with little distributed strain outside of the fracture itself. Increasing heterogeneity in a rock increases the distributed strain, causing an increase in permeability. This study serves as an initial development in the ability to measure the permeability of fracture surfaces. Increasing precision and accuracy of measurements is expected with further research.
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