Geochemical modelling of processes in near-wellbore zone under CO2 injection conditions

Abstract

In the conditions of sequestration of acid gases to the rock formation between rocks, reservoir fluids, injected gases, wellbore cement and the casing, the complex geochemical changes occur. Although these processes have been the subject of some research in recent decades, their mechanisms are still not sufficiently recognized, and especially the impact of these processes on the preservation of leak-tightness of boreholes, which is a key element for the success of the sequestration process.The computer simulation accurately reflects the direction of changes taking place during real experiments, additionally providing detailed information on the mineral phases involved in the mineral transformation process within rock and wellbore cement. In the acidic environment created in the analyzed system, the dissolution of portlandite and C-S-H phases, as well as the crystallization of calcite, vaterite and silica, takes place. During the time taken into account in the simulation, the volume of minerals crystallizing in the cement is greater than the volume of dissolved components, but on the other hand, micro-voids may appear in the contact zone. In the case of penetration of pore waters, coming from rocks into the cement, the most intense transformations occur in the cement to a depth of 3 cm from the contact zone with the rock.