A New Evaluation Method for the Fracability of a Shale Reservoir Based on the Structural Properties

Table 1

Selected expressions of RQD.

Reference	Formula	Variable declaration
Palmstrom [39]		WJD is the weighted joint density; , , where is the angle between the joint and borehole; is the volumetric joint count
Palmstrom [39]
Shirouyeh Araghi [38]		nd is the number of discontinuities; CW is the length of the core washed segment; Fr is the length of the fragmented segment (with spacing of 15-50 mm); Cr is the length of the crushed segment (with spacing of 5-15 mm); VZ is the vuggy zone; is the cavity or core loss
Li et al. [40]		is the number of unbroken pieces; is the ratio of recovered cores in length: , where is the travel or run length and is the length of unbroken piece; is the function of the total number of unbroken pieces; , where is the material parameter
Azimian [38]		is the rating factor obtained from Table 2; CW is the length of the core washed segment; Fr is the length of the fragmented segment (with spacing of 15-50 cm); Cr is the length of the crushed segment (with spacing of <15 mm); is the length of the karstic segment (karstic zone including vuggy, cavity, core loss, and other karstic phenomena)