Temperature prediction model for a producing horizontal well
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Distributed temperature sensors (DTS) are increasingly used for monitoring producing sections of horizontal wells. The temperature data from DTS are reliable, accurate and continuous in time (readings every few minutes) and space (readings every meter). One of the potential uses of DTS is to infer the amount and types of fluid entering horizontal sections. To perform such an inference requires a temperature model. A new analytical model was developed here for predicting the inflow temperature of a fluid entering a horizontal wellbore during production. The distinguishing aspect of the model is that it accounts for subtle thermal energy effects including fluid expansion, viscous dissipative heating, and thermal conduction. Reservoir inflow and wellbore flow are coupled by modeling the reservoir as multi-segmented reservoirs in which the direction of flow in the reservoir is perpendicular (not parallel) to the wellbore. The coupled model is then used to simulate several examples to illustrate how temperature changes with flow rate and type of fluid entering a wellbore. vii We further develop a numerical temperature model of a bottom water drive reservoir to demonstrate the uses of temperature profiles in detecting water entries. Water in this numerical model is initially located in a deeper and warmer zone below a horizontal well. Results show that oil or water can enter the wellbore 2-3 oF higher, while gas can enter with 5-6 oF lower, than the geothermal temperature. Inflow temperature causes the slope of the wellbore temperature profile to change notably, depending on the flow rates and types of fluid entering. The temperature profile can locate a zone that is producing excessive water or gas if the rate is large. The size of the temperature changes on the profiles is obviously detectable by DTS, which has a resolution as fine as 0.0045 oF for the time and spatial average of 1 hour and 50 feet if the cable range is less than 3,000 feet. This study has confirmed the uses of DTS in reservoir monitoring of a horizontal production well.