This work was carried out as part of the GeoCquest project. The authors gratefullyacknowledge the funding of the GeoCquest project provided by BHP.

• Krause, M., Krevor, S. & Benson, S.M., 2013 A Procedure for the Accurate Determination of Sub-Core Scale Permeability Distributions with Error Quantification. Transp Porous Med. 98: 565.

• Reynolds, C., Krevor, S., 2015. Characterizing flow behaviour for gas injection: Relativepermeability of CO2-brine and N2-water in heterogeneous rocks. Water Resources Research 51(12), 9464–9489.

• Pini, R., and S. M. Benson (2013), Characterization and scaling of mesoscale heterogeneities insandstones, Geophys. Res. Lett., 40, 3903–3908, doi: 10.1002/grl.50756.

Effect of capillary induced flow on CO2 residual trappingMaartje Boon , Hailun Ni, Charlotte Garing, Sally M. Benson

Department of Energy Resources Engineering, Stanford University

INTRODUCTION

Residual trapping is one of the main mechanisms for immobilizing CO2 after theinjection phase of a geological sequestration project. Residual trapping results fromcapillary forces at the pore scale which lead to snap-off and bypass of CO2. Forheterogeneous systems, there is, in addition to the capillary potential at the porescale, a capillary potential at the scale of the heterogeneity which will result incapillary induced flows and trapping. We investigate the impact of capillary inducedflow on multiphase flow behavior and its implications for residual trapping of CO2

by performing experimental and numerical core-flood tests.

EXPERIMENTAL AND NUMERICAL METHODS

We will measure:• Absolute permeability• Porosity• Capillary pressure (MICP)

The subcore scale permeability field of the core and itscharacteristic relative permeability curve are obtainedusing the method by Krause et. al, 2013.

The Stanford University general purpose research simulator(GPRS) is used to model drainage experiments for realisticand synthetic rock samples.

DOES LAMINATION DIRECTION IMPACT RESIDUAL TRAPPING ?

CONCLUSIONS

• The direction of the heterogeneity and the scale of the heterogeneity impact thecapillary induced flow forces and, therefore, impact the capillary pressure andsaturation distribution.

• For systems with a larger scale of heterogeneity, capillary disequilibrium can existeven in the capillary dominated regime resulting in capillary induced flow whenthe system relaxes. Due to the countercurrent nature of these flow it will likely toincrease the extent of residual gas trapping.

• This work shows that for layered rock with small variations in permeability,laminations direction has minimal impact on the local capillary forces and doesnot effect the residual trapping potential.

CAPILLARY PRESSURE GRADIENTS CAN LEAD TO CAPILLARY INDUCED FLOW

RESULTS AND DISCUSSION

REFERENCES

ACKNOWLEDGEMENT

In heterogeneous rocks, the capillary pressure function (black curves in left figure) variesthroughout the rock: capillary heterogeneity.

• Capillary limit (very low flow rates): relatively strong capillary forces move the systemtowards capillary equilibrium (blue line).

• Viscous limit (high flow rates): relatively strong viscous forces push the system out ofcapillary equilibrium (red line) creating capillary pressure gradients which can lead tocapillary induced flow.

NUMERICAL CORE-FLOOD TESTMETHOD TO CREATE MODEL OF ROCK CORE

In horizontally layered cores the system becomes closer toequilibrium with distance because the fluid phasesredistribute over the different layers.

The magnitude and propagation of the impact on thecapillary strength number depends on flow rate anddirection of flow.

WHAT HAPPENS WHEN THE INJECTION PHASE ENDS?

Laminations with a small difference in permeability between layers do not impact the residual trapping ability of the rock.

EVEN IN THE CAPILLARY DOMINATED REGIME CAPILLARY DISEQUILIBRIUM EXISTS:

CAPILLARY STRENGTH NUMBER

The capillary strength number (Ncs)quantifies the capillary induced flowpotential at the voxel scale.

EXPERIMENTAL CORE-FLOOD TEST

• Irreducible gas saturation (trapping)• Relative permeability

Gradients in capillary pressure can result in capillary induced flow when the system relaxes.

CROSS-FLOW IS OBSERVED IN HORIZONTALLY LAYERED SYSTEMS

IN VERTICALLY LAYERED CORES THE SYSTEM IS PUSHED AWAY FROM CAPILLARY EQUILIBRIUM AT EACH INTERFACE

Reynolds & Krevor, 2015

Nc= 10-8

Nc= 10-7