Flow profiling by distributed temperature sensor (DTS) system - Expectation and reality

Permanent downhole monitoring can provide valuable information for production decisions in real time without the need to perform an intervention to collect data. One of the commercial permanent monitoring technologies is the fiber-optic DTS, which can record the wellbore temperature profile in real time with decent accuracy and resolution. A key potential application for DTS data is to profile injection or production for wells, which is the primary motivation and focus of this project. In the present paper, a thermal model recently developed for single-phase- and multiphase-fluid flow along a vertical, deviated, or horizontal well will first be briefly described. The model can be applied for both wellbore temperature prediction (forward modeling) and for flow profiling using a measured temperature profile (inverse problem). The model has successfully been applied for investigating key thermal characteristics of single-phase- and multiphase-fluid flow along a wellbore. In particular, the dependence of wellbore temperature upon phases, flow profile, fluid type, fluid properties, well deviation, and Joule-Thomson effect will be demonstrated in the paper. The model has further been adapted for directly predicting production and injection profiles (i.e., flow profiling) based on a given wellbore temperature profile. The potential impact of noise in the DTS measurement on flow profiling has been explored. It is found that the wellbore temperature does not change significantly along horizontal or near-horizontal sections because of the small variation in geothermal temperature. Therefore, based only on steady-state DTS data, the amount and the location of each fluid entry would be difficult to identify. The current study shows that a maximum wellbore deviation of 75 degrees should be honored to appropriately estimate flow profile directly through steady-state DTS data. The study has also led to an observation that under certain circumstances such as multiphase flow, a production profile may be determined through DTS temperature measurement with extra data or information provided. The types of the extra measurements and the appropriate approaches will be recommended.