Borehole Geophysical Characterization Of Hydraulic Stimulation Of Fractured Bedrock Aquifers

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