Phase Behavior Analysis of a Gas Condensate Reservoir

Abstract

Retrograde condensation is the term used to describe certain unusual features that result from condensate production in gas reservoirs. Unlike traditional gas reservoirs, this kind of reservoir experiences phase behaviour changes that affect the flow characteristics. This study's primary goal is to examine the nature of a specific gas condensate reservoir and create a model to track changes in fluid flow under specified circumstances. In this case, the Kailashtila gas field of Bangladesh has been taken into consideration. Both laboratory tests and simulations are performed to analyse the fluid composition, phase behaviour. Results are then summarized using simulation software (PVTSIM) to develop the phase diagram and other property curves of the fluid. The simulated and lab results implicate the reservoir to be a lean gas reservoir which is retrograde in nature. In the second part, a mathematical model is developed to represent the changes in flow pattern due to condensate banking near well-bore region. The condensate banking surrounding the wellbore has a significant impact on the deliverability of gas wells producing below the dew-point pressure. The pressure transient test analysis is further complicated by condensate banking because of the multiphase flow and mixture composition shift. Analytical approach has been employed to find a solution of the model and then the sensitivity analysis of the model has been performed by incorporating real field test data. According to the model, the reservoir is the total of three flow zones. The three flow areas are as follows: outer region 3 contains just gas; middle region 2 contains both gas and condensate but only gas is mobile; and inner region 1, which contains both gas and condensate flowing simultaneously. The pressure squared approach has been selected to determine the flow rate considering real field production and pressure transient test data under specified condition. The response obtained from the analysis matches with the trend of typical flow curve but showed deviation in the calculated and observed results.The condensate utilized as a feedstock in oil refineries is the subject of the study's third section. To produce assay data both laboratory tests and computer-aided analysis has been performed. The goal of this work is to develop a method to a comprehensive and organized characterization of gas condensate as a refining feedstock. The study also focuses on a critical examination of the assay data from samples of gas condensate that were taken from Kailashtila (KTL) gas fields. The study initially carried out laboratory tests to establish the boiling point. Empirical correlations are used to determine the necessary physical parameters for calculations involving the refining process. Utilizing Peng Robinson's thermodynamic model, a simulation software (DWSIM) helps in creating pseudo-components and their associated attributes using the generated true boiling point data. Thus, the study investigated the fluid's overall phase behaviour in both subsurface and surface conditions. The study's findings showed that by adjusting the number of trays or equilibrium stages in the distillation column, one can modify the amount and quality of product obtained as well as lower the energy consumption of a specific distillation process. Although condensates are usually defined through compositional analysis, this study took a slightly different approach than it would with crude oil. Oil refineries that are thinking about using condensate as an alternate of crude oil, may find the study helpful in constructing and simulating the refining process, assessing feedstocks, and determining economic worth.