Fracture networks inside the caprock for CO storage reservoirs may serve as leakage pathways. Fluid flow through fractured caprocks and bypass conduits, however, can be restrained or diminished by mineral precipitations. This study investigates precipitation of salt crystals in an artificial fracture network as a function of pressure-temperature conditions and CO phase states. The impact of CO flow rate on salt precipitation was also studied. The primary research objective was to examine whether salt precipitation can block potential CO leakage pathways. In this study, we developed a novel microfluidic high-pressure high-temperature vessel to house geomaterial micromodels. A fracture network was laser-scribed on the organic-rich shales of the Draupne Formation, the primary caprock for the Smeaheia CO storage in Norway. Experimental observations demonstrated that CO phase states influence the magnitude, distribution, and precipitation patterns of salt accumulations. The CO phase states also affect the relationship between injection rate and extent of precipitated salts due to differences in solubility of water in CO and density of different CO phases. Injection of gaseous CO resulted in higher salt precipitation compared to liquid and supercritical CO. It is shown that micrometer-sized halite crystals have the potential to partially or entirely clog fracture apertures.

During the chemical interactions between fluid and minerals in different geological processes, it is of high importance to predict where secondary precipitates form in the porous rocks as it helps correctly predict the hydrodynamic properties of the porous media. The reactive transport models developed for this purpose need to account for the nucleation process which is probabilistic by nature. To our knowledge, the probabilistic nature of nucleation based on the classical nucleation theory has not been accounted for previously in reactive transport models. In this study, we develop a new probabilistic nucleation model and incorporate it into a pore-scale reactive transport solver to simulate the mineral nucleation and growth in the porous media. Simulations are performed for different supersaturations, growth rates, and flow rates using a single-component mineral reaction. Simulations show that initial supersaturations strongly affect the pattern of secondary precipitate formation. Higher initial supersaturations lead to more uniformly dispersed nucleation on all the grains, while the lower initial supersaturations result in more isolated patterns. Decreasing the growth rate favors the formation of uniformly dispersed nuclei, whereas higher growth rates cause more isolated nucleation. Injection of fluid with a higher velocity gives rise to more precipitation. Moreover, comparison of probabilistic and deterministic nucleation showed that the isolated nucleation patterns cannot be modeled using the deterministic approach. The results showed that permeability for the porous media is influenced by the pattern of secondary precipitate growth and it is demonstrated that generally, the permeability has a direct relation with the initial supersaturation and an inverse relation with the growth rate and the flow rate. Finally, the model was applied for simulation of calcite nucleation and growth on quartz grains. The calcite nucleation and growth exhibit similar behavior to those observed for single-species simulations.

Well productivity in gas condensate reservoirs is reduced by condensate banking when the bottom hole flowing pressure drops below the dew point pressure. Among the several methods which have been proposed for condensate removal, wettability alteration of reservoir rock to intermediate gas wetting in the near wellbore region appears to be one of the most promising techniques. In this work, we report use of a nanofluid to change the wettability of the carbonate and sandstone rocks to intermediate gas wetting. Application of nanofluid in the wettability alteration of carbonate and sandstone rocks to gas wetting has not been reported previously and is still an ongoing subject. Static and dynamic contact angle measurements, along with imbibition tests, have been performed to investigate the wettability of carbonate and sandstone rocks in presence of nanofluid. It was found that the nanofluid used in this work can considerably change the wettability of both surfaces to preferentially gas wetting in just one day of ageing time. We also report the effect of initial oil saturation and ageing time on the nanofluid capability for wettability change. Initial oil saturation reduces the impact of the nanofluid on wettability change, and hence, a pre-treatment before using nanofluid is necessary. In addition to these small slab-scale experiments, applicability of nanofluid in wettability alteration of sandstone rocks to gas wetting is also investigated in core scale. The results of core displacement tests confirm the ability of nanofluid to change the rock wettability from liquid wetting to gas wetting in core samples. They also show the effectiveness of chemical treatment in subsurface conditions.

This study aims at indicating the capability of a state-of-the-art computational intelligence approach for predicting pseudosteady flux and pseudosteady fouling at different operating condition (temperature (T), transmembrane pressure (TMP), cross-flow velocity (CFV), and feed pH) as well as for permeate flux decline at the mentioned operational conditions with processing filtration time. To train and test these models, the experimental data collected during the polyacrylonitrile (PAN) UF process to treat the oily wastewater of a Tehran refinery have been used. The proposed method utilizes a least-squares support vector machine (LSSVM) to carry out nonlinear modeling. The genetic algorithm (GA) was employed to tune the optimal model parameters. GA-LSSVM has the competence of describing the nonlinear behavior. The accuracy of the proposed GA-LSSVM models is very satisfactory and quantified by statistical parameters. Finally, the results obtained by implementing various sensitivity analysis techniques portrayed that T and TMP have the most significant influence on pseudosteady flux and pseudosteady fouling, correspondingly, in comparison with other factors involved in the addressed treatment process.

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Fractures are the main flow path in rocks with very low permeability, and their hydrodynamic properties might change due to interaction with the pore fluid or injected fluid. Existence of minerals with different reactivities and along with their spatial distribution can affect the fracture geometry evolution and correspondingly its physical and hydrodynamic properties such as porosity and permeability. In this work, evolution of a fracture with two different initial spatial mineral heterogeneities is studied using a pore-scale reactive transport lattice Boltzmann method- (LBM-) based model. The previously developed LBM transport solver coupled with IPHREEQC in open-source Yantra has been extended for simulating advective-diffusive reactive transport. Results show that in case of initially mixed structures for mineral assemblage, a degraded zone will form after dissolution of fast-dissolving minerals which creates a resistance to flow in this region. This causes the permeability-porosity relationship to deviate from a power-law behavior. Results show that permeability will reach a steady-state condition which also depends on transport and reaction conditions. In case of initially banded structures, a comb-tooth zone will form and the same behavior as above is observed; however, in this case, permeability is usually less than that of mixed structures.

Investigating fracture evolutions triggered by chemical interactions in caprocks of CO2 storage sites is of great importance when caprock integrity is concerned. Mineral heterogeneity is one of the factors affecting fracture evolution. We present results from flow-through experiments deploying a unique high pressure geo-material microfluidic cell to monitor the fracture evolution of four carbonate-rich caprocks: (1) a homogeneous carbonate-rich sample, (2) a heterogeneous carbonate-rich sample, (3) a heterogeneous carbonate-rich shale sample, and (4) a heterogeneous carbonate-rich organic shale sample, representing different levels of mineral heterogeneity. The results show rather smooth fracture wall dissolution for the homogeneous rock sample. For the heterogeneous sample without shale, however, an altered layer is formed around the fracture that leads to an increase in the fracture roughness. Chemical analyses of effluent solutions demonstrate a decrease in the bulk dissolution rate of calcite over time at a constant flow rate. For the two carbonate-rich shale samples, visual observations using optical microscopy showed little changes in fracture dissolution, although analysis of effluent chemistry confirmed calcite dissolution.