Abstract
<title>Abstract</title> <p>Flow profiling is needed to evaluate stimulation effectiveness and reservoir connectivity in enhanced geothermal systems (EGS), but repeated conventional flow logging can require equipment mobilization, wellhead reconfiguration, and well intervention. At the same time, fiber-optic distributed temperature sensing (DTS) is increasingly deployed in geothermal wells, creating an opportunity to estimate flow profiles from thermal transients without repeated logging-tool runs. We present an isotherm-slope flow-profiling method for estimating wellbore gains and losses from DTS thermal-front migration during injection and subsequent production or backflow. The method tracks a selected thermal front in depth-time space and estimates through-wellbore flow changes from ratios of fitted isotherm slopes above and below perforations. Because the calculation uses local slope ratios within a flow phase, it does not require calibrated thermal properties of the wellbore or formation. Synthetic DTS responses generated with a transient wellbore heat-transmission model were used to validate the workflow before application to a huff-puff test in Utah FORGE EGS well 16B(78)-32. The synthetic tests recovered monotonic injection losses and non-monotonic production profiles containing gains and losses. In the field example, the isotherm-slope analysis estimated losses from the wellbore to the formation in resolved intervals during injection, but both gains and losses during production, indicating near-wellbore inter-stage flow. These results show that DTS thermal-front migration can estimate stage-scale flow partitioning in EGS wells. The method provides a practical approach for repeated evaluation of stimulation effectiveness and evolving reservoir connectivity from DTS data, without requiring repeated flow-logging interventions or calibrated wellbore heat-transfer modeling.</p>