A Simple and Reliable Approach for the Estimation of the Joule-Thomson Coefficient of Reservoir Gas at Bottomhole Conditions

摘要

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. The 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 (T) of a fluid for a given change in pressure (P) at constant enthalpy. The JTC also serves as an input for the interpretation of temperaturelog 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 with the JTC is also presented. The methodology has been validated at three levels with 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 with laboratory-scale data, and comparison of experimentally observed vs. predicted temperature drop for a given drawdown with actual reservoir data. A good match with experimental data was obtained within all three areas, demonstrating the reliability of the methodology.