Borehole Geophysical Characterization of Hydraulic Stimulation of Fractured Bedrock Aquifers

Paillet, Frederick; Hanscomb, Harry

Portions of abstract are copied below: 'Changes induced by typical hydraulic stimulation procedures were monitored in two adjacent boreholes at a site in northeastern Maine by comparing geophysical well logs run before and after stimulation. Caliper and acoustic televiewer logs run before stimulation indicated a few faint, impermeable-looking horizontal and vertical fractures, but inflow before treatment was too weak to detect with a heat-pulse flowmeter. Caliper and televiewer logs run after stimulation showed no significant differences comparedto the pre-stimulation logs. Flow logs run after stimulation demonstrate that inflow in both boreholes is associated with a faint horizontal fracture on the televiewer logs near 60 m in depth, which appears no different from several other similar fractures. A cross-borehole flow experiment confirms that the stimulated zone is a single horizontal fracture connecting the two boreholes. These results demonstrate that the hydraulic stimulation produced at least a 10-fold increase in well capacity from less than 0.5 to more than 5.0 liters per minute. The results also agree with previous studies where fractures affected by stimulation: 1) were present before treatment; 2) showed no obvious changes in the imediate vicinity of the borehole after stimulation; and 3) experienced a 10 to 20 fold increase in permeability attributed to the treatment.' /STUDY LOCATIONS:/ /MOUNT DESERT ISLAND/