Effect of Geologic Parameters on CO2 Storage in Deep Saline Aquifers

摘要

The results of modeling injection into and long-term storage ofrnCO2 in a deep saline aquifer with a commercial black-oilrnreservoir simulator are presented. Realistic CO2/water pVTrnproperties covering all pressure, temperature andrncompositional conditions accounted for during the simulationsrnhave been used. The pressure and temperature in the aquifer isrnabove the CO2 critical pressure and temperature giving rise tornthe existence of a two-phase fluid system of CO2 as a fluid andrnan aqueous phase containing dissolved CO2. The impact ofrnCO2 injection rate, reservoir layering, capillary pressure andrnresidual CO2 saturation for water re-entering CO2 filledrnvolumes (hysteresis in fluid saturations) on CO2 distributionrnand storage in the deposit have been studied. The re-distributionrnof water occurs after stop of CO2 injection due torngravity segregation of denser CO2 saturated water and CO2-freernwater.rnFor upscaling studies a small section of the reservoirrnmodel (typically a reservoir grid block) was finely gridded andrnstudied separately for various reservoir parameters andrninjection rates. The fine model showed that the sweeprnefficiency of CO2 displacing saline water and both positionrnand quantity of CO2 in each grid block of the reservoir modelrnare sensitive to the CO2 injection rate and the effective verticalrnpermeability. By increasing the viscous to gravity force ratio,rnthe sweep efficiency increases resulting in more CO2 trappedrnas residual gas. More CO2 is also trapped in the case ofrnincreasing CO2-water capillary pressure. Estimating thernamount of trapped CO2 from the average CO2 saturation isrnpossible when the sweep efficiency is good (evenly distributedrnCO2) but may give bad estimates when CO2 only enters part ofrneach large grid block. This shows that to get reliable estimatesrnof the amount of trapped CO2 the distribution of CO2 in eachrngrid block is important and the traditional upscaling methodsrnhave to be extended to incorporate the effect of CO2rndistribution on trapped gas. Especially the effect of fine-scalernlayering must be upscaled properly.