Modeling of pressure evolution during multiple well injection of CO2 in saline aquifers

Abstract

One of the key aspects of underground carbon dioxide disposal is the injection rate. This defines the amount of CO2 to be injected into a reservoir, and is limited by reservoir fracture pressure. Therefore, it is very important to determine all parameters which contribute to pressure build up to identify optimal injection design. When injection volumes are high, the rate is split between multiple injectors, making the optimization process time consuming for numerical simulations. As such analytical or semi analytical approaches can be very useful.In this paper, a fast semi-analytical approach to evaluate pressure distribution in saline aquifers during multiple well CO2 injection is presented. It is based on general 1-D solutions of the diffusivity equation for three regions (CO2, two-phase and brine) established in aquifers when injection is done using a single well. The boundaries of a two-phase region, where both CO2 and brine coexist in pores, depend on reservoir and fluid properties and assessed using a single numerical simulation, run to match the analytical solution for pressure distribution, and these values are kept constant when extending to multiple well scenarios. Extension to multiple well injection has been conducted using the superposition principle.The results of modeling were compared with the numerical simulations including single well injection and a variety of cases of multiple well injection, with differing numbers of injectors and their placement. Different reservoir properties, such as permeability, formation compressibility as well as vertical size have been considered. Good agreement between modeling and reservoir simulations was observed for all cases.The approach presented here can be used as a pre-screening tool for fast initial evaluation of potential injection sites as well as to suggest injection design ideas and optimization of well placement.