Rock strength and stress dependence of local flow-path connectivity within faults or fractures; A Preliminary overview of virtual and in-situ hydraulic tests

Ishii, Eiichi   ; Ozaki, Yusuke  ; Aoyagi, Kazuhei  ; Sugawara, Kentaro*

This study performed virtual packer tests on modeled single fractures on computer and derived the relationship between flow dimension and mappable indicator, DI, which is defined by the mean stress, groundwater pressure, and rock tensile strength. The greater DI results in the smaller flow area in faults or fractures, subject to fracture-normal closure. Comparing the derived relationship with results from in situ hydraulic tests on natural faults in rock with few fracture-mineral-fillings revealed that flow-path connectivity is high (flow dimension 1.5) when DI was 2.0 while was low (flow dimension 1.5) when DI was 2.0. This relationship was valid even when DI was varied, or faults were sheared, during injection tests on faults, and even in rock with abundant fracture-mineral-fillings. However, flow-path connectivity in minor fractures far from faults could be also low even when DI was 2.0 probably due to poor connection to the main fault network or sealing effects of fracture-mineral-fillings. When the permeability of intact rock is high, flow-path connectivity in fractures was high even when DI was 2.0. These findings can be helpful to map the spatial distribution of flow-path connectivity in faults or fractures from limited borehole data.