The Potential of N2 as Cushion Gas on Dispersion Coefficient ofSuperCritical CO2 in Sandstone Core Plug During Enhanced Gas Recoveryby CO2 Injection

摘要

Despite the several kinds of literature on the dispersion behaviour of supercritical CO2 in CH4 at conditionsrelevant to enhanced gas recovery(EGR),studies have so far limited in keeping this parameter as low aspossible.This study aims to highlight,experimentally,to determine the effect of N2 as cushion gas onthe dispersion coefficient in consolidated sandstones core plug under reservoir conditions applicable toEGR.A laboratory core flooding experiment was carried out to simulate a detailed process of an unsteadystate methane displacement in Bandera gray and Bentheimer core plugs at reservoir conditions of 40oCtemperature,1500 psig of pressure,the optimum injection rate of 0.4ml/min,and at varying N2 cushionvolumes(8-36 cm3).Further experimental runs were carried out to investigate the effect of high CO2injection rates(0.6-1.2 ml/min)on the longitudinal coefficient of dispersion as it plumes transverses intothe core plugs during the EGR process.The coefficient of longitudinal dispersion declines with raises incushion gas volume,hence the higher the amount of N2 cushion volume the less the dispersion of CO2into CH4.This is due to the high shielding barrier inhibited by nitrogen,making it difficult for the CO2to dispersed itself and mixed with the nascent natural gas resulting in delayed breakthrough as it plumestransverses into the CH4 during the displacement process.The inclusion of N2 as cushion gas prior to CO2injection recorded the highest decline at 36cm3 cushion volume,presenting a 48 and 28% reduction inlongitudinal dispersion coefficient for Bandera and Bentheimer core samples respectively,compared to thatof conventional/traditional CO2 injection(with zero cushion volume).Recording lower nascent CO2-CH4mixing resulting in less natural gas contamination and more storage volumes.Also,a reverse phenomenonwas observed when the CO2 injection rate was increased from 0.6-1.2 ml/min due to the high diffusion rateof CO2 at higher interstitial velocities,resulting in a rapid increase in dispersion coeffient and indirectlyhigh widespread contamination of the remaining natural gas.