Estimating rates and electrical conductivities of borehole inflows using a logging/two-level pumping technique

Abstract

AbstractVertical variations in borehole inflow rate and inflow conductivity can be calculated from temperature-conductivity borehole logs obtained during two pumping phases, one phase having the pump intake at a lower level than the other. Although promising results were obtained by previous workers for sites in Bahrain, the method has attracted little attention in the literature. Here the theory is reviewed, and two direct and one inverse calculation procedure outlined. Simple sensitivity analysis shows that under certain circumstances, predicted inflow rates and conductivities are very sensitive to data error. Three field trials show the method to be potentially very useful, although detailed inflow calculations are difficult to quantify accurately. Analysing the data using the direct method can produce erratic predictions as forecast by the sensitivity analysis. The inverse method introduces a degree of hydrogeological control into the interpretation thus eliminating the artifacts produced by data error; however, the inverse method does tend to increase the possibility of non-uniqueness in the solution. These problems appear to be in part avoidable, and work will continue.