Reactive Transport: Experiments and Pore-Network Modelling

Transport in Porous Media, 2010

We apply a multi-component reactive transport lattice Boltzmann model developed in previous studies for modeling the injection of a CO2-saturated brine into various porous media structures at temperatures T = 25 and 80°C. In the various cases considered the porous medium consists initially of calcite with varying grain size and shape. A chemical system consisting of Na+, Ca2+, Mg2+, H+, $${{\rm CO}_2^{\circ}{\rm

Water acidifies in the presence of CO2 and prompts mineral dissolution. A 2-D pore network model scheme is developed to investigate reactive fluid flow in CO2 storage reservoirs during injection when advective transport prevails. Mineral dissolution satisfies kinetic rate laws and continues until thermodynamic equilibrium is reached. In advection-dominant regimes, network simulation results show that species concentration, tube enlargement and flow rate can be summarized in terms of the dimensionless Damköhler number Da which is the ratio between advection time along a pore and the reaction time. Reservoirs will tend to experience localized enlargement near injection wells (before water drying) and compact dissolution in the far-field. The Damköhler number couples with initial pore-size variability to distort the relationship between mean tube diameter and either local or network-average flow rates. Both the Damköhler number and pore-size variability should be considered in field-scale numerical simulators.

Journal of Hydrology, 2018

Dissolution and precipitation of rock matrix are one of the most important processes of geological CO 2 sequestration in reservoirs. They change connections of pore channels and properties of matrix, such as bulk density, microporosity and hydraulic conductivity. This study builds on a recently developed multi-layer model to account for dynamic changes of microporous matrix that can accurately predict variations in hydraulic properties and reaction rates due to dynamic changes in matrix porosity and pore connectivity. We apply the model to simulate the dissolution and precipitation processes of rock matrix in heterogeneous porous media to quantify (1) the effect of the reaction rate on dissolution and matrix porosity, (2) the effect of microporous matrix diffusion on the overall effective diffusion and (3) the effect of heterogeneity on hydraulic conductivity. The results show the CO 2 storage influenced by factors including the matrix porosity change, reaction front movement, velocity and initial properties. We also simulated dissolution-induced permeability enhancement as well as effects of initial porosity heterogeneity. The matrix with very low permeability, which can be unresolved on X-ray CT, do contribute to flow patterns and dispersion. The concentration of reactant H + increases along the main fracture paths where the flow velocity increases. The product Ca ++ shows the inversed distribution pattern against the H + concentration. This demonstrates the capability of this model to investigate the complex CO 2 reactive transport in real 3D heterogeneous porous media.

Transport in Porous Media, 2009

Carbon dioxide (CO 2) injections in geological formations are usually performed for enhanced hydrocarbon recovery in oil and gas reservoirs and storage and sequestration in saline aquifers. Once CO 2 is injected into the formation, it propagates in the porous rock by dispersion and convection. Chemical reactions between brine ions and CO 2 molecules and consequent reactions with mineral grains are also important processes. The dynamics of CO 2 molecules in random porous media are modeled with a set of differential equations corresponding to pore scale and continuum macroscale. On the pore scale, convectivedispersive equation is solved considering reactions on the inner boundaries in a unit cell. A unit cell is the smallest portion of a porous media that can reproduce the porous media by repetition. Inner boundaries in a unit cell are the surfaces of the mineral grains. Dispersion process at the pore scale is transformed into continuum macroscale by adopting periodic boundary conditions for contiguous unit cells and applying Taylor-Aris dispersion theory known as macrotransport theory. Using this theory, the discrete porous system changes into a continuum system within which the propagation and interaction of CO 2 molecules with fluid and solid matrix of the porous media are characterized by three position-independent macroscopic coefficients: the mean velocity vectorŪ * , dispersivity dyadicD * , and mean volumetric CO 2 depletion coefficientK * .

A modular pore-scale model is developed to assess the response of wellbore cement to geological storage of CO2. Numerical formulations for modeling of solute transport are presented and a methodology for coupling with geochemical processes is discussed, which includes: (1) advective and diffusive fluxes of solutes within the pore space, (2) aqueous phase speciation, (3) mineral dissolution–precipitation kinetics, and (4) the subsequent changes in pore space geometry. A Complex Pore Network Model (CPNM) is used to discretize the continuum porous structure as a network of pore bodies and pore throats, both with finite volumes. CPNM allows for a distribution of pore coordination numbers ranging between 1 and 26. This topological property, together with a geometrical distribution of pore sizes, enables the microstructure of porous media to be mimicked. For each pore element, transport of solute is calculated by solving the governing mass balance equations. Chemical reaction of the fluid phase with the main reactive solid components (portlandite and calcite) is incorporated through coupling with a geochemical reactive simulator. Average values and properties are obtained by integration over a large number of pores. Using this approach, we investigate how chemical reaction between water-bearing wellbore cement and supercritical CO2 can create a distribution of porosity in a direction parallel to the CO2 concentration gradient and transport path, at 50 °C. The dynamics of this process involve interaction between diffusion dominated mass transport and the kinetics of dissolution and precipitation of portlandite and/or calcite. Simulation of unconfined chemical degradation, in a fluid of constant composition, shows development of different regions: (1) a zone adjacent to the inlet face, which is characterized by an increase in porosity due to extensive dissolution, (2) a carbonation zone with decreased porosity, (3) the carbonation front which made a thin layer with the lowest porosity due to calcium carbonate precipitation, and (4) dissolution zone. These results are in agreement with laboratory observations under similar conditions. This provides confidence that this pore-scale approach can ultimately be applied to model the progress of coupled CO2 transport and cement degradation at critical points along the length of cemented wellbore sections at CO2 storage sites.

Journal of Petroleum Science and Engineering, 2017

Dissolved CO 2 in the subsurface resulting from geological CO 2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes including hydrodynamics, transport, and reactions at the (sub) pore-scale. In this work pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reactions at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This work is motivated by observations of CO 2 seeps from a natural CO 2 sequestration analog, Crystal Geyser, Utah. Observations along the surface exposure of the Little Grand Wash fault indicate the lateral migration of CO 2 seep sites (i.e., alteration zones) of 10-50 m width with spacing on the order of ~ 100 meters over time. Sandstone permeability in alteration zones is reduced by 3 to 4 orders of magnitude by carbonate cementation compared to unaltered zones. One granular porous medium and one fracture network systems are used to conceptually represent permeable porous media and locations of conduits controlled by fault-segment intersections and/or topography, respectively. Simulation cases accounted for a range of reaction regimes characterized by the Damköhler (Da) and Peclet (Pe) numbers. Pore-scale simulation results demonstrate that combinations of transport (Pe), geochemical conditions (Da), solution chemistry, and pore and fracture configurations contributed to match key patterns observed in the field of how calcite precipitation alters flow paths by pore plugging. This comparison of simulation results with field observations reveals mechanistic explanations of the lateral migration and enhances our understanding of subsurface processes associated with the CO 2 injection. In addition, permeability and porosity relations are constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Da and Pe numbers. The functional relationships obtained from pore-scale simulations can be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO 2 seeps.

Previous model studies indicate that injectivity can be impaired by salt precipitation near the injection well during CO 2 injection (Pruess and Müller, 2009). These results are largely determined by the relationship between permeability and salt precipitation which is developed by Verma and Pruess (1988). Liu et al. (2013) presents a new relationship for permeability change owing to salt precipitation near a CO 2 injection well, which differs from previous relationships in that it considers the fact that the salt precipitation occurs only in pore space occupied by brine during the precipitation process, and in that it is based on well-established relative-permeability relationships for two-phase flow in porous media. This work reviews the conceptual models based on which these porosity–permeability relationships are developed. The Liu et al. (2013) model is implemented in the multi-phase reservoir simulator TOUGH2, and simulation is conducted and compared with results in Pruess and Müller (2009). Results show that the two constitutive relations give opposite conclusions in whether CO 2 dry-out will clog the reservoir. In contrast to the conclusion from Pruess and Müller (2009) that permeability will decrease to essentially zero near the injection well, the new simulation predicts much less reduction in permeability. Discussions are given at the end on the evaluation of each relation and relevant experimental evidences.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2014

The CO_{2} behavior within the reservoirs of carbon capture and storage projects is usually predicted from large-scale simulations of the reservoir. A key parameter in reservoir simulation is relative permeability. However, mineral precipitation alters the pore structure over time, and leads correspondingly to permeability changing with time. In this study, we numerically investigate the influence of carbonate precipitation on relative permeability during CO_{2} storage. The pore spaces in rock samples were extracted by high-resolution microcomputed tomography (CT) scanned images. The fluid velocity field within the three-dimensional pore spaces was calculated by the lattice Boltzmann method, while reactive transport with calcite deposition was modeled by an advection-reaction formulation solved by the finite volume method. To increase the computational efficiency and reduce the processing time, we adopted a graphics processing unit parallel computing technique. The relative permeab...

Computers & Geosciences, 2019

CO 2-enriched brine interaction with reservoir minerals and the subsequent mineral trapping of CO 2 alter the morphology of pore structure. Such changes in the pore space modify the storage capacity of reservoirs and increase the longterm security of CO 2 storage. The extent of pore space modification depends on the relative weight of advection, diffusion and reaction mechanisms. We present a general framework for a direct simulation of reactive transport in digitized reservoir rock samples based on a pore-scale modeling in two-dimensional (2D) and three-dimensional (3D) pore-throat networks. We examine the impact of transport properties such as Péclet (Pe) and Damköhler (Da) numbers, on the petrophysical properties and dissolution of mineral in pore space. We implement marker-based watershed segmentation to extract pore networks of 3D micro-CT (Computerized Tomography) scan images. The extracted network is used to simulate the reactive solute transport and dissolution on real rock samples. This approach enables us to study reaction of CO 2-enriched brine with reservoir rock samples, which is vital in predicting long-term security of CO 2 storage. We implement our approach to study CO 2 injection in samples from the Cranfield site, Mississippi, U.S.A.. We show that for small P eDa numbers, the concentration and dissolution patterns are more uniform.

International Journal of Greenhouse Gas Control, 2012

A modular pore-scale model is developed to assess the response of wellbore cement to geological storage of CO 2 . Numerical formulations for modeling of solute transport are presented and a methodology for coupling with geochemical processes is discussed, which includes: (1) advective and diffusive fluxes of solutes within the pore space, (2) aqueous phase speciation, (3) mineral dissolution-precipitation kinetics, and (4) the subsequent changes in pore space geometry. A Complex Pore Network Model (CPNM) is used to discretize the continuum porous structure as a network of pore bodies and pore throats, both with finite volumes. CPNM allows for a distribution of pore coordination numbers ranging between 1 and 26. This topological property, together with a geometrical distribution of pore sizes, enables the microstructure of porous media to be mimicked. For each pore element, transport of solute is calculated by solving the governing mass balance equations. Chemical reaction of the fluid phase with the main reactive solid components (portlandite and calcite) is incorporated through coupling with a geochemical reactive simulator. Average values and properties are obtained by integration over a large number of pores. Using this approach, we investigate how chemical reaction between water-bearing wellbore cement and supercritical CO 2 can create a distribution of porosity in a direction parallel to the CO 2 concentration gradient and transport path, at 50 • C. The dynamics of this process involve interaction between diffusion dominated mass transport and the kinetics of dissolution and precipitation of portlandite and/or calcite. Simulation of unconfined chemical degradation, in a fluid of constant composition, shows development of different regions: (1) a zone adjacent to the inlet face, which is characterized by an increase in porosity due to extensive dissolution, (2) a carbonation zone with decreased porosity, (3) the carbonation front which made a thin layer with the lowest porosity due to calcium carbonate precipitation, and (4) dissolution zone. These results are in agreement with laboratory observations under similar conditions. This provides confidence that this pore-scale approach can ultimately be applied to model the progress of coupled CO 2 transport and cement degradation at critical points along the length of cemented wellbore sections at CO 2 storage sites.