1 Marc Hesse, Toti Larson, Craig Tenney, Mario Martinez, Tuan Ho, Baole Wen, Kiran Sathaye, Esben Petersen 1 University of Texas at Austin 2 Sandia National Laboratory March 03, 2016

Challenge 1: Sustaining Large Storage Rates Challenge 2: Using pore space with unprecedented efficiency Challenge 3: Controlling undesired or unexpected behavior Theme 2: Multifluid Geochemistry --- Geochemistry at the fluid-fluid interface Reservoir dynamics of Bravo Dome natural CO 2 reservoir Reactions of CO 2 with clay minerals Reservoir Dynamics of Bravo Dome Natural CO 2 Reservoir 2 Senior PersonnelStudents and Post-Docs Marc Hesse: experiments and models of continuum/reservoir scale multifluid transport Toti Larson: multifluid (gas) experiments Mario Martinez: convective dissolution modeling Craig Tenney: molecular dynamics simulations Tuan Ho: molecular dynamics simulations Kiran Sathaye: noble gas fractionation during two-phase transport, Bravo Dome characterization Baole Wen: noble gas fractionation during convective dissolution

Noble gas interpretation based on fractionation & mixing models. Relation between classic models and subsurface processes not clear. Developing a physical basis for noble gas fractionations in subsurface flows. Will provide tools to estimate the efficiency of use of pore-space in geological CO 2 storage Storage Efficiency Improve sweep efficiency Predict mineral trapping Enhance capillary (ganglion) trapping Controlling Emergence Prevent unwanted fracturing Control pathway development Prevent unexpected migration of CO 2 Sustaining Injectivity Control wellbore failure Enhance permeabilty/avoid precipitation during injection Guide injection limits CHALLENGES Predict solubility trapping Activity Objectives

Bravo Dome Location and Size 4

Results from CFSES I Sathaye et al. (2014) PNAS 5

Estimate Dissolution Assuming Rayleigh Fractionation 6 Fraction dissolved: Kneafsey & Pruess (2009)

Dissolution Trapping at Bravo Dome 7 1.Mass of gas dissolved at Bravo Dome: ∆M = 366 ± 122 MtCO 2. (65 years emissions coal plant) 2.Total mass of CO 2 emplaced: M ini = 1.6 ± 0.7 GtCO 2 (~annual volcanic emissions) 3.Mass of CO 2 dissolved: 23 ± 7% (much less than local maximum)

Highly Heterogeneous ⇒ Poor Sweep Efficiency 8 Bravo Dome comprises sand channels in a matrix of silt. CO 2 invades the sands not silts. Only 60% of the pore space. Sweep is improved by gravity stable downward emplacement.

Significant Dissolution into Brine Within Silts 9 Dissolved CO 2 Distribution of diss. CO 2 Half of dissolution during injection into residual brine Other half after injection into underlying aquifer

Guiding Question for CFSES II 10 1)What is the compositional signature of CO 2 dissolution occurs during injection? ⇒ Gas composition dynamics (Toti Larson) 2)Does convective dissolution into underlying aquifer really lead compositional signature of Rayleigh fractionation? ⇒ Bravo Dome reservoir dynamics (Baole Wen) 3)What are the fundamental physical properties? ⇒ Partition and diffusion coefficients (Tuan Ho)

Gas composition dynamics (Toti Larson) Sathaye et al. (2016) in revision for EPSL 11

CO 2 Dissolution During Emplacement/Injection 12 All previous work estimating dissolution in field assumes Rayleigh fractionation. Unlikely if dissolution occurs during CO 2 emplacement. Aim of study: What are compositional patterns that arise? Trying to explain left half!

Laboratory Two-Phase Displacement Experiments m vertical column Const. rate injection ( ml/min ) 5ml sampling vials 2-5min intervals Gas chromatograph Initial composition: water equilibrated with 2atm neon Injected composition: gas at 2atm with Ar/CO 2 = 40/60

Noble Gas Banks in Effluent Composition 14

Bank Formation Mechanisms 15 Argon bank: The co-injected argon is enriched because the more soluble CO 2 has dissolved into residual water. Neon bank: The initially dissolved neon is stripped from the water by the arriving gas and accumulates at the front. ⇒ characteristic co-enrichment seen in field data

Bravo Dome reservoir dynamics (Baole Wen) Martinez and Hesse (2015) WRR Wen et al. (2016) in prep. 16

Convective Dissolution Into Underlying Brine 17 Trying to explain right half! Density driven convection Evolution of gas composition Martinez and Hesse (2016)

Does Convection Lead to Rayleigh Fractionation 18 slow diffusion fast diffusion (2x) Convective solute flux Dimensionless time Ra = advection/diffusion = 50,000 Convective fractionation ≠ Rayleigh fractionation. It depends on partition and diffusion coefficients.

Need New Interpretation of Noble Gas Ratios 19 Our preliminary results suggest that convective dissolution does not fractionate noble gases following a classic Rayleigh fractionation pattern. Currently evaluating if differences are significant in comparison with other uncertainties. Need to develop new simple model that accounts for differences in component diffusivities.

Partition and diffusion coefficients (Tuan Ho) 20

Gibbs Ensemble Monte Carlo (GEMC) simulation Two boxes (e.g., brine and He) at specified temperature and pressure Randomly attempt to exchange particles between boxes Accept exchange (or not) according to rules of statistical mechanics Repeat millions of times Calculate ensemble average concentrations particle exchange brine phase He phase Solubility of Helium and CO 2 in Brine H white O red He green Na + blue Cl - purple

Effect of pressure 0.4mol/L NaCl, T=300K Effect of salinity T=300K, P=3MPa Validation: Henry’s constant y i P = Kx i helium in pure water T=300K and P=1atm Experiment: K=14.6 ± 1.4 GPa (Smith 1985) Simulation: K=16.1 ± 3.4 GPa Effect of temperature 0.4 mol/L NaCl, P = 3MPa Solubility of Helium in Brine

Diffusion is predicted using molecular dynamics (MD) simulations. Diffusion coefficient is calculated from mean square displacement as: H white O red He green Na + blue Cl - purple Dynamics of Helium and CO 2 in Brine

D = 6.33 ±1.01 x10 -9 m 2 /s P=0.1MPaP=3MPa Diffusion of He in 0.4mol/L NaCl at T=300K D = 6.22 ±0.35x10 -9 m 2 /s Validation: Diffusion of He in pure water at T=300K and P=0.1MPa Experiment: D=7.22 ± 0.36 x10 -9 m 2 /s (Jahne,1987) Simulation : D=7.06 ± 0.75 x10 -9 m 2 /s Diffusion of Helium in Brine P=14MPa D = 5.94 ±0.75x10 -9 m 2 /s

Preliminary results: Noble gas fractionation during two- phase flow (injection phase) is chromatographic. Noble gas fractionation during convective dissolution (post injection) not Rayleigh. Future work: Models for compositional evolution during convective CO 2 dissolution. Tools to estimate the efficiency of use of pore-space in geological CO 2 storage Storage Efficiency Improve sweep efficiency Predict mineral trapping Enhance capillary (ganglion) trapping Controlling Emergence Prevent unwanted fracturing Control pathway development Prevent unexpected migration of CO 2 Sustaining Injectivity Control wellbore failure Enhance permeabilty/avoid precipitation during injection Guide injection limits CHALLENGES Predict solubility trapping Summary