Characterization of Transmissive Fractures by Simple Tracing of In‐Well Flow

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Abstract
Under‐exploration of complex hydrogeologic settings may lead to the occurrence of short‐circuiting internal flows in monitoring wells. Susceptible settings include fractured formations with large thickness and monotonous lithology. The occurrence of internal flow may distort flow pattern and induce contaminant migration. Monitoring data from the affected wells may be misinterpreted if the flow is unaccounted for. In order to identify and measure well bore flow in several deep monitoring wells at a site, a technique of in‐well tracing was used. The vertical movement, dispersion, and dilution of an injected saline slug was tracked by periodic electrical conductivity logging.Combining internal flow measurements with baseline conductivity and temperature logs provided estimates of the quality and origin of water entering well bores from major transmissive fractures. Identified locations of these fractures coincided with locations of larger fractures seen on video logs; only a few fractures were significant for the flow. Relative distributions of heads and fracture permeabilities in a well with internal flow could be evaluated easily, but determination of their absolute values would require measurement of static heads. In data quality, cost, and feasibility, the in‐well slug tracking compares favorably with conventional fracture characterization methods, such as coring, packer permeability testing, flowmeter and other specialized geophysical logging.