Interpreting Distributed-Temperature Measurements in Deepwater Gas-Well Testing: Estimation of Static and Dynamic Thermal Gradients and Flow Rates

Abstract

Summary In typical drillstem testing (DST), transient pressures are gathered downhole while rate measurements occur at the surface. Effects of heat transfer on pressure, particularly during a buildup test in a gas well, necessitate the close proximity of pressure measurements to the point of fluid entry. While pressure measurements are reliable with sufficient resolution in most settings, rate measurements often lack synergy with pressure because of the sensor resolution and the frequency of monitoring. The reduced-rate sensor resolution and rate-monitoring frequency may precipitate significant uncertainty in transient-test interpretations. This paper presents a case study for a deepwater asset in Western Australia, where, in addition to the traditional downhole-pressure and surface-rate measurements, temperatures were recorded at various depth stations in four wells, each in a different reservoir, before, during, and after transient testing. These temperature data allowed estimation of gas-flow rates. The computational accuracy of flow rates increased at shallower depths because increased heat transfer, leading to larger temperature difference, enhanced the fidelity of measurements. Overall, the distributed-temperature data allowed the estimation of temperature gradients, including their nonlinear trends, for both the static geothermal and dynamic flows.