ABSTRACT

We have investigated the ability of low-frequency induction resistivity measurements to detect and appraise hydraulic fractures induced near vertical boreholes. Integral-equation-based simulations indicate that coplanar measurements can detect fractures when they are injected with electrically conductive proppant to increase their conductivity contrast with the shale background. Specifically, when a logging tool consisting of one transmitter and two receivers that are 1.2 and 1.5 m away is used to detect fractures with the effective electrical conductivity of 100  S/m in a homogeneous shale formation of 1/3  S/m conductivity, the measurements (1) can indicate the boundary of fractures intersecting with vertical boreholes by the signal spikes generated only when the tool enters/exits fractures, (2) can detect fractures as small as approximately 0.15 m and differentiate fractures up to approximately 10 m in width, (3) can detect fractures with height as small as 0.3 m, (4) can differentiate elliptical and rectangular fractures from each other if they exhibit the same width; e.g., they can discriminate if their widths are within approximately 0.4–10 m, and (5) are sensitive to the effective electrical conductivity of the fracture. A second logging tool consisting of one transmitter and two receivers that are 18 and 19.2 m away is found to be less useful in the detection and appraisal of hydraulic fractures induced near vertical boreholes.

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