Fractured-bedrock aquifer studies based on a descriptive statistics of well-logging data: A case study from the Dajia River basin, Taiwan

A simple descriptive-statistical approach is proposed for evaluating the transmissivity of fractured-bedrock under field conditions. Based on standard well logging and identification of structural discontinuities from borehole televiewer, the approach consists of four steps: (1) determination of discontinuity properties, namely the frequency of discontinuities and the ratio of open fractures along the borehole; (2) ranking the three well logs and the discontinuity properties into tertiles (high-to-low); (3) performing statistical analysis (F-test) for the three well logs to assess the significance of open fractures on the water-transmitting potential and then assigned a weighting factor; and (4) a semi-quantitative indicator, RGVFO, is obtained by multiplying all predictive indexes and weighting factors. It is a multi-criteria evaluation procedure that elucidates the quantitative and qualitative importance of all selected geophysical indexes. A high cross-correlation between transmissivity to RGVFO value is found, which indicates that by a combined consideration of well logging and structural discontinuities, an appropriate estimate of bedrock water-transmitting potential can be derived.