With the advent of distributed temperature sensing (DTS), accurate and continuous monitoring of the wellbore temperature profile is possible, which helps identify fluid flow from each reservoir layer. Reliable prediction of fluid flow during large drawdown requires an accurate value of the Joule-Thomson coefficient (JTC), which is a measure of the change in temperature of a fluid for a given change in pressure at constant enthalpy. The JTC also serves as an input for interpretation of temperature log data, which can be used to identify water or gas entry locations. Furthermore, an accurate JTC value is important when modeling the thermal response of the reservoir.

The equation-of-state (EOS) method can be used to predict the JTC of reservoir gas. However, this might not be an easy task because of the complexity involved. In contrast, a simple and reliable method to evaluate the JTC for reservoir gas is presented. Conditions under which this method is applicable are discussed in detail by referring to a typical phase diagram. In addition, a discretized approach to calculate the temperature change during a throttling process using the JTC is also presented.

The methodology has been validated at three levels using experimental data available in the literature—comparison of experimental vs. predicted JTC values of mixtures, comparison of experimentally observed vs. predicted temperature drop for a given pressure drop using lab-scale data, and comparison of experimentally observed vs. predicted temperature drop for a given drawdown using actual reservoir data. A good match with experimental data was obtained within all three areas, demonstrating the reliability of the methodology.

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