Experimental Determination of the Phase Transition Point in Gas Condensates using a Cost-Effective Semiautomated Isochoric Apparatus

摘要

A robust high precision experimental approach to determine dew point pressure of gas condensates in the laboratory is proposed in this study. Gas condensate reservoirs have been the center of attention for numerous numerical and experimental studies for decades. Their perplexing fluid flow and phase behavior results in various production challenges including condensate banking and compositional changes due to retrograde condensation accompanying production from these reservoirs. Therefore, accurate prediction of dew point pressure (DPP) is crucial in developing long-term production plans for these reservoirs. Isochoric method, an indirect high precision way of DPP and phase transition condition determination, is commonly used in other disciplines where a clear non-visual determination of phase transition of a fixed volume of fluid is needed. This study provides an insight into this approach in determining DPP for a binary mixture of hydrocarbons. A semi-automated apparatus for measuring and monitoring equilibrium conditions along with fluid properties is designed based on the isochoric method. The apparatus provides constant volume, variable pressure (0 to 1500 psi), and variable temperature (290 to 410 K) experimental conditions. Pressure and temperature measurements are used to detect the phase transition point along the constant mole-constant volume line based on the change in the slope of this line at the transition point. Results are plotted on the phase envelope (P-T diagram) of the same mixture using different equations of state and the accuracy of each of these equations of state in providing the most reliable prediction of DPP is analyzed. Reproducibility of the data is examined and error estimation for the entire experiment is provided. This experimental method is inexpensive, less time consuming, and more accurate compared to other PVT experiments and is applicable for multicomponent systems. It does not require gas expulsion or sample recombination throughout the procedure and could be identified as the only reliable way of quantifying the effect of porous media on phase behavior.