摘要
To accelerate the CO_(2) trapping in geological storage sites,several injection strategies have been proposed by researchers so far.However,the question remains unanswered as to which one of these injection strategies is the most efficient in terms of immobilising CO_(2) and more importantly,how these strategies might be improved.In this paper,we attempt to simulate a typical geological CO_(2) storage scheme in an aquifer using the E300 compositional reservoir simulator and subsequently investigate and compare the impact of various injection strategies on CO_(2) immobilising efficiency.Secondly,the impact of adding a short period of post-brine injection on various strategies is newly investigated.Our results reveal that using a relatively short period of post-brine injection can significantly improve total CO_(2) trapping efficiency in all the strategies.In general,by using post injection of brine,more CO_(2) is spread out through the aquifer and,as a consequence,by increasing the interfacial area of the CO_(2) plume,the amount of dissolution as a result of mass transfer increases significantly.Moreover,the effect of convection can become stronger in the case of post-brine injection creating a stronger density instability and thus a more rapid initiation of convection.Furthermore,when brine is injected into the system,CO_(2) is displaced away from the well resulting in a forced imbibition process and thereby enhancing the capillary trapping efficiency.The post-injection of brine has also one more particular effect in strategies of horizontal injection and simultaneous CO_(2)/brine injection in different intervals.In this regard,postbrine injection creates a stronger downward pressure gradient that counters the tendency of the CO_(2) plume to rise and therefore retards the CO_(2) in reaching the top of the aquifer.This increases the time that the CO_(2) can be in contact with the fresh formation brine and so enhances the trapping efficiency.We envisage that the post-brine injection could enhance the total trapping efficiency of CO_(2) from 26%,30.8%,39.8%and 59.1%to 47.7%,44.2%,62%and 63.9%,when it was added into different strategies of CO_(2) continuous injection,simultaneous injection of CO_(2)/brine in the same and different intervals and a horizontal system,respectively.However,our findings show that the effectiveness of post-brine injection may be reduced in high vertical permeability values and in this respect,capillary trapping can be more affected by vertical permeability variation.Furthermore,the results show that selection of the rate and duration of post-brine injection can have considerable effects on total CO_(2) trapping efficiency.
