CO2 Sequestration [Capillary Trapping]

1. How exactly to distinguish the three related processes namely

(a)        residual trapping;

(b)       trapping due to hysteresis of the relative permeability; and

(c)        trapping due to hysteresis of the capillary pressure

associated with capillary trapping @ field-scale?

OR

Sufficient to conceptualize the capillary trapping as a process, whereby, the capillary entry pressure within the pore-throats of the reservoir rock remains dominant over the buoyancy of CO2 (which essentially curtails the migration of CO2 into adjacent upper pores, failing which, leads to enhanced CO2 storage @ locations below or outside structural/stratigraphic closures; and which has nothing to do with the integrity of cap-rock/seal)?

If so, then, the degree of capillary trapping would remain significantly affected by intra-aggregate and intra-particle micro-porosity?

2. Can we expect CO2 capillary trapping – resulting from differences in capillary pressure entry points – associated with different solid-grains, and with varying sizes of pore entry throats – both in deep saline aquifers; and in depleted oil/gas reservoirs?

3. Whether, capillary trapping of CO2 depend on any other sensitive/dominant parameter than the following parameters?

(a) capillary pressure

(b) permeability anisotropy

(c)  permeability hysteresis

(d)  spatial distribution of porosity and permeability

(e)  pore geometry and pore aspect ratio

(f)   wettability conditions

(g)  IFT between CO2 and brine

(h)  viscosity of CO2

(i)   the presence of impurities within the CO2 gas stream

(j)   relative permeability of CO2 & brine

(k)  initial saturation of CO2 and brine phases

(l)   residual CO2 saturation

(m) flow rate of injected CO2

(n)  total quantum of injected CO2

(o)  the spatial and temporal distribution of injected CO2

(p)   Capillary, Gravity & Coordination numbers

4. How exactly to investigate the dynamics of a CO2 plume, during and after CO2 injection, given the layered and multi-scale reservoir heterogeneity?

5. With the injection of CO2 into the brine-saturated aquifer (drainage), until reaching the irreducible brine saturation and maximum CO2 saturation, would it remain feasible to capture the beginning of the imbibition cycle, upon reaching the irreducible brine saturation @ field-scale?

At the field-scale, during imbibition, whether, the brine would keep on flowing back into the pores, until the relative permeability of CO2 gets reduced to zero – taking into account the definite presence of an irreducible brine saturation?

6. Assuming the summation of saturations of CO2 and brine equaling unity, to what extent, the saturations of CO2 and brine influence the aquifer’s capillary pressure and relative permeability of CO2 and brine?

Suresh Kumar Govindarajan

Professor (HAG)    IIT-Madras

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

https://iitm.irins.org/profile/61643 17-July-2024