The gas hydrate deposits of the Krishna-Godavari (KG) basin in India have a huge potential of fulfilling the energy needs of the country for several years to come. We present a detailed thermodynamic and kinetic study of methane hydrate formation and dissociation in the presence of an actual Krishna-Godavari (KG) basin marine sediment sample at varying concentrations, i.e., 10, 20, and 35 wt %, in an aqueous solution. This study revealed the possibility of dual induction during methane hydrate formation in the presence of pure water and 10 wt % KG basin sediment solution. As the sediment concentration increased, the inhibition effect during the methane hydrate formation became more pronounced. The heat of dissociation values were found to be decreasing with the increase in sediment concentration. The kinetic experiments depicted the stochastic nature during the hydrate formation. The methane gas consumption and the rate of methane hydrate formation were found to be high in the case of pure water, followed by 10, 20, and 35 wt % sediment solutions. However, the initial rate of methane hydrate formation among the sediment solutions was observed to be high in the case of the 20 wt % sediment solution. The water-to- hydrate (W-H) conversion and gas-to-hydrate (G-H) conversion were found to be reducing with an increase in sediment concentration due to the confining effect of the water−gas system. During kinetic dissociation, the stable temperature range before the hydrates actually started dissociating was found to be increasing with sediment concentration, and the maximum temperature up to which the hydrates remained stable was ~6 °C. The rate of hydrate dissociation was high in the case of the pure water system and slightly decreased in the 10 wt % sediment solution; however, it was found to be almost similar in 20 and 35 wt % sediment solutions. This study will certainly add value toward a better understanding of the KG basin reservoir for future exploration of methane gas from the hydrate deposits.

Deep CO2 storage reservoirs show a wide range of heterogeneous structures across different scales. Here, we show how high-resolution heterogeneity in both permeability and capillary entry pressure control dissolution and local capillary trapping of supercritical CO2 (ScCO2). Prior works mainly considered homogeneous reservoirs or simplified heterogeneity with horizontal and fixed capillary transition zones. Most of those studies ignored simultaneous free-phase ScCO2 spreading and solutal fingering. To advance understanding of heterogeneity effects, we have performed two- dimensional numerical simulations for ScCO2 injection into the middle of a storage reservoir. We have computed metrics including the spatial plume moments to compare the dissolution trapping and spreading of ScCO2 during the injection and post-injection period for different variances and correlation lengths of log-normal permeability and capillary entry pressure fields. The results show that the second-order spatial moment of the ScCO2 saturation field in the horizontal direction decreases by 10% as the permeability variance increases from 0.1 to 3.0. But it decreases by 50% as the capillary entry pressure variance becomes 1.1. For higher capillary entry pressure variance, the ratio of dissolved CO2 mass to free-phase ScCO2 mass decreases, showing higher local capillary trapping. The vertical distance between the centers of mass of the ScCO2 and dissolved CO2 plumes (representing the downward flow of dissolved CO2 through solutal fingering) is greater for heterogeneous reservoirs.

Laboratory studies of cavity initiation and propagation in weak or cohesionless materials rely on post-test observations to assess fracture geometry. The experimental setup in this work is a Hele- Shaw cell, which allows for visualization of cavity initiation and propagation within the sand pack, modified to apply differential confinement to a fully 3D specimen. Injection experiments with glycerine at different concentrations and at varying injection rates were conducted with anisotropic boundary conditions on loose sand. The fracture initiation and evolution were observed under various flow rates and viscosities. Infiltration and dislocation of particles were the main mechanisms observed in the tests. Fracture-like channels initially developed in a circular shape due to cavity expansion but then formed rod shapes (shear bands, material fluidization) where an anisotropic stress was applied. This transition from circular to elongated cavity appeared earlier in the tests with higher viscosity fluids, while higher injection rates produced wider openings as the larger volume of fluid was able to displace more particles. Although the cavity showed directionality in all cases, it became less confined to the propagating plane as the flow rate increased. For higher viscosities, the cavities tended to be more circular, whilst for lower viscosities, the cavities showed more directionality.

Cohesion between grains in a geological system is perhaps the simplest and ideal representation of a range of material systems including soft rocks, structured soils, mudstones, cemented sands, powder compacts, and carbonate sands. This presence of inter granular cohesion is known to alter the ensemble mechanical response when subjected to varied boundary conditions. In this study, a hollow cylinder apparatus is used to investigate the mechanical behavior of weakly cemented sand ensembles by mapping the state boundary surfaces including the failure surface (locus of peak stress state) and the state of plastic flow (locus of final stress state). When these materials are sheared, the plastic deformation accumulates due to breakdown of cohesion between the grains, which introduces a lag in occurrence of peak stress ratio and maximum dilatancy, unlike a typical frictional granular material. This breakdown of cementation is affected by changes in the initial mean effective stress, initial reconstitution density, and intermediate principal stress ratio (stress path on the octahedral plane). The final state locus, emergent at large strains, was found to depend on the initial reconstitution density. Further, the parameters are extracted for calibration and prediction exercise using an elastic plastic constitutive model. In this and several other models, the effect of cementation is considered as an additional confinement to the ensemble. Such an approach predicts the stress state precisely but does not predict the volumetric response accurately, especially at large strains.

In this work, we present the application of a fully coupled hydro-mechanical method to investigate the effect of fracture heterogeneity on fluid flow through fractures at the laboratory scale. Experimental and numerical studies of fracture closure behavior in the presence of heterogeneous mechanical and hydraulic properties are presented. We compare the results of two sets of laboratory experiments on granodiorite specimens against numerical simulations in order to investigate the mechanical fracture closure and the hydro-mechanical effects, respectively. The model captures fracture closure behavior and predicts a nonlinear increase in fluid injection pressure with loading. Results from this study indicate that the heterogeneous aperture distributions measured for experiment specimens can be used as model input for a local cubic law model in a heterogeneous fracture to capture fracture closure behavior and corresponding fluid pressure response.

In the present study, the cyclic triaxial tests and resonant column (RC) tests were carried out, to study the effect of frequency on reconstituted marine clay saturated with distilled water and NaCl solutions. Slurry consolidated samples were prepared at 50 kPa vertical stress. Samples were isotropically consolidated at three different effective confining pressures i.e. 80, 150 and 300 kPa. The loading frequencies adopted for the study were 0.1 Hz and 1 Hz with a number of 100 loading cycles. The results show that the effect of frequency could affect the shear modulus of clay soil reconstituted with varying pore fluid chemistry. The shear modulus increases and damping ratio decreases with increase in loading frequency for clay soil reconstituted with concentrated saline solution. Furthermore, the seismic response analysis was conducted to study the effect of frequency on marine clay soil reconstituted with distilled water and electrolyte solutions using one dimensional equivalent linear DEEPSOIL software.

Electrochemical treatment of soil, ECT is the technique of deploying an external electric potential for introducing stabilizing chemicals into the intended zone of soil improvement. The current flow modifies the basic soil-electrolyte chemistry, reflected mostly in the form of soil pH. In view of this, the manuscript reviews the alterations in clay fabric and ionic-species interactions instigated with the modifications in surface charge due to soil pH alterations. The derived consequences of system chemistry changes are discussed concerning its impact on the migration mechanisms during ECT viz. electro-osmosis and electro-migration. Though ECT is familiar to the research fraternity for decades, the attempts made hitherto for compiling the available literature on ECT are limited. Given this, by depicting the pioneering developments over time, the present study also provides a concise review of the research carried out in the area of ECT by highlighting the impact of electrochemical modifications upon the treatment efficiency.