Assessment of Non-Equilibrium Phase Behavior Model Parameters for Oiland Gas-Condensate Systems by Laboratory and Field Studies

摘要

Non-equilibrium phase behavior of hydrocarbons has a great influence on the development of gascondensate and oil and gas condensate deposits,as well as oil deposits after evolution of dissolved gas.The key parameter of mathematical models that take into account non-equilibrium phase behavior is thecharacteristic relaxation time.The paper presents examples of assessing its value according to the resultsof laboratory experiments and well tests,which also allow verifying the mathematical model and obtaininginput data for the production forecast taking into account non-equilibrium processes.A model of non-equilibrium phase behavior in a compositional formulation,based on relaxation ofthe chemical potentials difference,was verified on the data of a laboratory experiment in a calorimetercell.The numerical algorithm for calculating the dynamics of phase fractions and compositions in a non-equilibrium process was modified to take into account the isochoric condition,which made it possible todirectly compare the simulation results to the real experiment.A good match of the experimental pressure-temperature hysteresis curves was obtained without additional adjustment of the characteristic relaxationtime as compared with the estimate obtained from processing the measured pressure relaxation curve.Thus,the adequacy of the mathematical model and the possibility of evaluating its parameters directly from theexperimental measurements were confirmed.An example of assessing the characteristic relaxation time from well test data is presented for the pressurebuildup(PBU)curve recorded under the conditions of gas dissolution in oil.A sector blackoil-type modelwas used for the well drainage area.For matching the PBU data,various modeling methods for non-instantgas dissolution were considered,including a model based on relaxation of solution gas-oil ratio(sGOR).The results of simulations with the sector model showed that the traditional options for limiting the sGORincreasing rate do not allow adequate matching of the PBU curve under conditions of gas dissolution.Forthe model that takes into account the sGOR relaxation,an in-situ estimate of the characteristic relaxationtime was obtained which provided a fine match of the PBU data.As expected from theoretical concepts,the characteristic relaxation time for the in-situ process has a much larger order of magnitude than for thelaboratory experiments on centimeter-sized cells.The results of the study show the adequacy of relaxation models for non-equilibrium phase behavior incompositional and black-oil formulations for describing real processes and demonstrate the possibility toestimate the characteristic relaxation time from laboratory experiments and well tests,taking into accountits dependence on the process scale.