Prediction of Temperature Changes Caused by Water or Gas Entry into a Horizontal Well

Abstract

Summary With the recent development of temperature measurement systems such as fiber-optic distributed temperature sensors, continuous temperature profiles in a horizontal well can be obtained with high precision. Small temperature changes with a resolution on the order of 0.1°F can be detected by modern temperature-measuring instruments in intelligent completions, which may aid the diagnosis of downhole flow conditions. Since in a producing horizontal well fluid inflowing temperature is not affected by elevational geothermal temperature changes, the primary temperature differences for each phase (oil, water, and gas) are caused by frictional effects. While gas production usually causes a temperature decrease, water entry results in either warming or cooling of the wellbore. Warmer water entry is a result of water flow from a warmer aquifer below the producing zone (water coning). In contrast, produced water can be cooler than produced oil because of differences in the thermal properties of these fluids. If both oil and water are produced from the same elevation, oil is heated more by friction while flowing in a porous medium than water is resulting in the produced water having a lower inflow temperature than the oil. Water entry by coning is relatively easy to detect from the temperature profile because of its warmer inflow temperature, but water breakthrough from the same elevation as the oil may not be obvious. In this paper, we illustrate the range of inflow conditions for which water-or-gas entry locations can be identified from the temperature profile of a well from measurable temperature changes. Using a numerical wellbore-temperature-prediction model (Yoshioka et al. 2005a), we calculated temperature profiles for a wide range of water-inflow conditions. In these calculations, we assumed that one section of the well produced water or gas, while the rest of the open section of the well produced oil. From sensitivity studies, we showed the predictions of the relative water-andgas production rates that create detectable temperature anomalies in the temperature profile along the well. By using the model to match an actual temperature log from a horizontal well, we demonstrate how this model can be used to identify water-inflow locations.