CO2 Sequestration [Viscous Fingering; Capillary Fingering]

1. Are we critically deciding the resultant phase (gas/liquid/super-critical) of injected CO2 into the formations (deep saline aquifers; depleted oil/gas reservoirs; unminable coal seems) – ‘solely’ as functions of aquifer/reservoir temperature and pressure?

Or

‘CO2 storage capacity’ will be also taken into account?

2. Following the injection of CO2 into saturated subsurface formations, CO2 would try to displace the existing pore fluids that remain to be more viscous than the injected CO2. If so, then, to what extent, Capillary Number and Viscosity Ratio would try to define the resulting displacement pattern of the immiscible fluids, if

(a) Velocity of the invading fluid keeps changing with space and time?

(b) IFT between invading (CO2) and defending (brine) fluids keep fluctuating significantly?

(c) Contact angle of defending fluid (brine) on a substrate associated with a drainage condition remains varying?

(d) Viscosity values of CO2 and brine keep varying significantly with time and space?

How easy would it remain to measure IFT and contact angle of brine on rock surface – surrounded by gaseous/liquid/super-critical CO2 - @ field conditions – towards obtaining Capillary number and Viscosity ratio?

3. How do we have a control over - capturing the combination of viscous and capillary forces @ field-scale that would essentially dictate the resulting displacement pattern (viscous-fingering/capillary-fingering/stable displacement)? How exactly to delineate the phase-boundaries for the respective displacement pattern – with varying pore-size distribution and aquifer geometry?

With evolving aquifer/reservoir pore-geometry, whether, Capillary fingering would only occur under a relatively lower CO2 injection rates, irrespective of Viscosity ratio?

4. As the viscosity of CO2 being lesser than brine (viscous fingering develops during CO2 injection as the viscosity values of gaseous, liquid and super-critical CO2 generally remain to be orders of magnitude smaller than brine viscosity @ field pressure/temperature conditions), following viscous fingering, whether CO2 – by default – would flow through the least resistive pathways – in the absence of sweeping the most of the brine, which remains located out of the least resistive or preferential pathways?

In such cases, how easy would it remain to deduce the resultant displacement efficiency (as a function of Capillary number and viscosity ratio)?

Feasible to control CO2 flow pattern in order to obtain maximum displacement efficiency?

Or

CO2-water foams be used to attain stable-displacement and to enhance brine sweeping?

How exactly to deduce the displacement ratio (which involves CO2 saturation after breakthrough) – in transition zones (the crossover zone between capillary-fingering and viscous-fingering; or, between viscous-fingering and stable-displacement) @ field-scale?

Suresh Kumar Govindarajan

https://home.iitm.ac.in/gskumar/

https://iitm.irins.org/profile/61643