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

摘要

We develop an approach for measuring in-well fluid velocities using pointelectrical heating combined with spatially and temporally continuoustemperature monitoring using distributed temperature sensing (DTS). Themethod uses a point heater to warm a discrete volume of water. The rate ofadvection of this plume, once the heating is stopped, equates to the averageflow 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 atthe same depth and multiple pumping rates. Tracking of the thermal plume peakallowed the spatially varying velocity to be estimated up to 50 m downstreamfrom the heating point, depending on the pumping rate. The T-POT techniquecan be used to estimate the velocity throughout long intervals provided thatthermal dilution due to inflows, dispersion, or cooling by conduction doesnot render the thermal pulse unresolvable with DTS. A complete flow log maybe obtained by deploying the heater at multiple depths, or with multiplepoint heaters.