Monitoring pressure and assessing injectivity during fluid injection into a porous medium

Monitoring fluid flow and pollutant transport is important in many geophysical, environmental and industrial processes, such as geological $\textrm {CO}_2$ sequestration, waste water disposal, oil and gas recovery and sea water invasion. But it can also be challenging. Recent studies revealed a series of self-similar solutions to describe the interface shape evolution between the injecting and the ambient fluids during fluid injection into a confined porous layer. The present work focuses further on the pressure evolution. In particular, we present self-similar solutions for the pressure evolution at both the early and late times. Two dimensionless parameters are recognised, including the viscosity ratio $M$ and the rescaled buoyancy $G$ , and their specific role on the pressure evolution is clarified. Laboratory experiments are also performed to measure the pressure evolution at two specific locations during the propagation of a viscous gravity current within a vertically placed Hele-Shaw cell, with a favourable comparison with the model prediction in the unconfined regime. The obtained pressure solutions are also used to explain the field data of bottom-hole-pressure (BHP) evolution from a geological $\textrm {CO}_2$ sequestration project, considering both fluid injection and shut-in operations. The model and solutions might also be of use to assess reservoir injectivity and develop pressure-based monitoring technologies at well bores.