Articles | Volume 4, issue 2
Research article
28 Oct 2015
Research article |  | 28 Oct 2015

Thermal-plume fibre optic tracking (T-POT) test for flow velocity measurement in groundwater boreholes

T. Read, V. F. Bense, R. Hochreutener, O. Bour, T. Le Borgne, N. Lavenant, and J. S. Selker

Abstract. We develop an approach for measuring in-well fluid velocities using point electrical heating combined with spatially and temporally continuous temperature monitoring using distributed temperature sensing (DTS). The method uses a point heater to warm a discrete volume of water. The rate of advection of this plume, once the heating is stopped, equates to the average flow velocity in the well. We conducted thermal-plume fibre optic tracking (T-POT) tests in a borehole in a fractured rock aquifer with the heater at the same depth and multiple pumping rates. Tracking of the thermal plume peak allowed the spatially varying velocity to be estimated up to 50 m downstream from the heating point, depending on the pumping rate. The T-POT technique can be used to estimate the velocity throughout long intervals provided that thermal dilution due to inflows, dispersion, or cooling by conduction does not render the thermal pulse unresolvable with DTS. A complete flow log may be obtained by deploying the heater at multiple depths, or with multiple point heaters.

Short summary
The monitoring and measurement of water flow in groundwater wells allows us to understand how aquifers transmit water. In this paper we develop a simple method, which we call T-POT, that allows flows to be estimated by tracking the movement of a small parcel of warmed water. The parcel is tracked using fibre optic temperature sensing - a technology that allows detailed measurements of temperature, and therefore flow using the T-POT method, to be made in the well.