HYDRAULIC HEAD APPLICATIONS OF FLOWMETER LOGS IN KARST AQUIFER STUDIES

Borehole flowmeters are routinely used to identify inflow zones and estimate relative zone hydraulic conductivity in karst aquifer studies. However, radially convergent flow into or out of boreholes causes viscous flow losses to be concentrated within a few borehole diameters of the measurement point. Hydraulic conductivity estimates made in this way represent only a single local sampling that is unlikely to be representative of a heterogeneous flow conduit. Furthermore, ambient hydraulic conditions act to disguise the flow response of the most permeable conduit in boreholes with more than one flow zone. Hydraulic head estimates (h) can be derived from flowmeter logs and are more likely to indicate the character of large-scale flow paths than transmissivity (T) values. Such head estimates are made by simultaneously fitting flow model solutions to flow profiles obtained under ambient and stressed conditions to solve for two unknowns (T and h). Multi-well flowmeter studies can expand the method to provide estimates of storage coefficient and vertical leakage between flow zones. Several karst aquifer studies are presented, verifying the effectiveness of flow logs in estimating hydraulic head in multi-zone aquifers, and demonstrating the presence of otherwise undetected aquitards isolating flow paths in heterogeneous carbonate environments.