Impact of pressure dissipation on fluid injection into layered aquifers

Abstract

Carbon dioxide (CO 2 ) capture and subsurface storage is one method for reducing anthropogenic CO 2 emissions to mitigate climate change. It is well known that large-scale fluid injection into the subsurface leads to a buildup in pressure that gradually spreads and dissipates through lateral and vertical migration of water. This dissipation can have an important feedback on the shape of the CO 2 plume during injection, but the impact of vertical pressure dissipation, in particular, remains poorly understood. Here, we investigate the impact of lateral and vertical pressure dissipation on the injection of CO 2 into a layered aquifer system.We develop a compressible, two-phase model that couples pressure dissipation to the propagation of a CO 2 gravity current. We show that our vertically integrated, sharp-interface model is capable of efficiently and accurately capturing water migration in a layered aquifer system with an arbitrary number of aquifers. We identify two limiting cases -'no leakage' and 'strong leakage' -in which we derive analytical expressions for the water pressure field for the corresponding single-phase injection problem. We demonstrate that pressure dissipation acts to suppress the formation of an advancing CO 2 tongue during injection, reducing the lateral extent of the plume. The properties of the seals and the number of aquifers determine the strength of pressure dissipation and subsequent coupling with the CO 2 plume. The impact of pressure dissipation on the shape of the CO 2 plume is likely to be important for storage efficiency and security. * christopher.macminn@eng.ox.ac.uk 1 arXiv:1901.03623v2 [physics.flu-dyn]

Gas injection and leakage in layered aquifers

“…Our geological setting is the same as in Jenkins et al [25]. We consider a layered system comprising an alternating stack of N z aquifers and N z +1 seals (Figure 1).…”

“…In a confined layer, distributed leakage is complicated by the fact that both fluids can cross the seals at any point, leading to a rich flow problem that has not previously been explored. Jenkins et al [25] recently studied distributed leakage of the ambient fluid (brine) during gas injection into a layered system of horizontal aquifers separated by thin seals, but assuming that the gas cannot leak (i.e., that the entry pressure is never exceeded). Distributed brine leakage is interesting and important in its own right, because it enables strong vertical pressure dissipation and therefore plays an important role in mitigating pressure buildup during gas injection [26][27][28].…”

“…Distributed brine leakage is interesting and important in its own right, because it enables strong vertical pressure dissipation and therefore plays an important role in mitigating pressure buildup during gas injection [26][27][28]. Jenkins et al [25] showed that vertical pressure dissipation is also coupled to the motion of the gas plume, leading to a more compact plume shape by suppressing the formation of the advancing gas tongue.…”

“…A key aspect of the present study is that, as in Jenkins et al [25], we focus on a layered system. This enables a strong coupling between injection, migration, leakage, and pressure dissipation across layers.…”

“…We show here that this coupling becomes even more complex when gas leakage is introduced. In §II, we review the model of Jenkins et al [25] and extend it to include gas leakage. In §III, we outline our numerical scheme and then explore the different factors that control the buildup of capillary pressure along the underside of the seal.…”