Presentation on theme: "João Paulo Pereira Nunes"— Presentation transcript:
1João Paulo Pereira Nunes Pore-scale Simulation of Reactive Transport in Micro-CT ImagesJoão Paulo Pereira NunesSupervisors:Martin J. BluntBranko BijeljicPore-scale consortium meeting, January 2015
2ObjectiveDevelop a pore-scale particle tracking method capable of simulating rock-fluid reactions in carbonates – Predict how petrophysical properties evolve during reactive transportApplications - CO2 injection (EOR or sequestration) and diagenesis modeling
3IntroductionAlready established that acidic fluids flowing through carbonates react with the rock matrix, changing petrophysical and elastic properties of the reservoirPore-scale is the natural scale to study rock-fluid interactions (and then upscale)This work –Lagrangian approach based on a pore-scale streamline method to simulate evolution of petrophysical properties at in situ conditionsQuantify the impact of flow heterogeneity on average reaction ratesValidate the model using 3D dynamic imaging data from a real carbonate
4Reactive transport in four steps Particle Advection – Modified Pollock AlgorithmDiffusion – Random WalkReaction – Flux of particles through solid interfaceVelocity Field update – Finite volume with OpenFoamAll simulations directly on segmented micro-CT images
8Modified Pollock for Streamline tracing at the pore-scale We improve Pollock’s algorithm, to trace streamlines semi-analytically, respecting the no-slip boundary conditions at pore-solid wallsNo need to make the time-step small. More efficient than std. particle tracking methods. Very useful in high Pe flows.In a cubic lattice there are 64 possible types of pores:1 – no solid boundaries6 – one solid boundary15 – two solids20 – three solids15 – four solids6 – five solids1 – six solidsA pore with two solid boundaries:w1u2v2yzxw2
9Example: Pore with one solid boundary zxw1w2u2v1v2Calculate exit times and minimize
10New method captures the complexity of flow in heterogeneous rocks Voxel Time-of-flight distributionsBreakthroughLate arrivalStandard and modified Pollock have very different outcomes. The standard Pollock fails to capture the non-Fickian behavior expected in heterogeneous rocks.
14Reaction rate in the particle approach A solid voxel dissolves when the cumulative flux of particles is > Nhitsk – intrinsic reaction rate Taken from independent experimentsDm – diffusion coefficient∆t – time stepC(r) – particle concentrationNmol – moles of calcite in each solid voxel
15Dynamic imaging experiment – Menke et al. 2014 1733675083100116133149Ketton oolite core flooded with CO2-equilibrated 10MPa / 50CPorosity and permeability increasingPéclet ≈ 2300 Damköhler ≈ 10-5Transport controlled reaction – dissolution limited to regions of significant intake of solute
21Magnitude of the flow field perpendicular to flow direction Dissolution in blackStagnant regions in white (not shown)More dissolution in regions of higher fluxEssentially no dissolution in stagnant regions
22Average dissolution rates ExperimentalSimulationTime (min.)∆ϕkeff[10-4 mol.m-2.s-1]0-170.0290.870.0230.6817-330.760.0270.9033-500.0200.620.0260.84Compare with the batch rate: k = mol.m-2.s-1 (Peng et al., 2014)Average rates 10 times smaller due to transport limitations –no chemical/surface heterogeneity in the model.
23ConclusionsWe have presented a particle tracking method to simulate carbonate dissolution at the pore-scaleThe method was validated using dynamic image data – carbonate dissolution in CO2-rich brine - without any fitting parametersBased on a very efficient streamline tracing method – Modified Pollock algorithmWe predict a decrease of one order of magnitude in the average dissolution rates due to transport limitations onlyEasily modifiable to incorporate deposition and different flow regimes
24Next steps: Impact of the flow rate on the average reaction rates How to define the average rates for face dissolution ?Run simulations on more complex rocksDoes the transition from face to uniform dissolution depends on the degree of heterogeneity?Study different reaction rates PeDa changing