Identifying Fracture Interconnections Between Boreholes Using Natural Temperature Profiling: I. Conceptual Basis

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Abstract
In situ delineation of fracture characteristics is a difficult and often time‐consuming task. Several advantages would be gained from the development of simple field techniques which provide direct evidence of such parameters as fracture connectivity, fracture orientation, or fracture aperture. In this paper, such a technique for delineation of fracture connectivity between boreholes is introduced. The technique is based on utilizing the natural variation of water temperature within the subsurface as a natural ground‐water tracer. In this technique, thermal response in observation boreholes induced by local pumping or injection is related to the location of interconnected fractures. The technique provides several advantages including simple equipment and time requirements, direct evidence of fracture flow between boreholes, and the ability to test without contaminating a field site. The major limitations of the technique are related to the volume of fluid movement within an observation hole and are controlled by the geometry of the flow field in the vicinity of the pumping/ injection borehole. Two case studies are briefly outlined demonstrating application of the technique to both a fractured granite and a fractured dolomite. Part II of this paper (Robinson and Silliman, in preparation) contains a detailed discussion of the application of this technique to the second, fractured dolomite, case study.