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Predicting geomechanical properties of rock and other types of porous media is essential to accurate modeling of many important processes, such as wave propagations, seismic events, and underground gas storage, and CO₂sequestration, all of which involve deformation of the pore space. We propose a model to predict the porosity dependence of the Young's and bulk moduli in heterogeneous porous media by combining the universal power law, predicted by percolation theory that describes the behavior of elastic moduli near the percolation threshold of the solid skeletons, and the effective‐medium approximation (EMA) for elastic materials that is accurate away from the threshold. The parameters of the model have unambiguous physical meanings, and can, in principle, be measured. We estimate the parameters ‐ the percolation threshold , crossover point between the EMA and percolation power law, the average particle coordination number , and the elastic moduli of the solid skeleton by using experimental data or numerical simulations for a wide variety of porous media in both two and three dimensions. Whenever data are available, the predictions are consistent with them. We then predict the elastic moduli for another 10 porous media using the proposed model and the estimated parameters without adjusting any new parameter. The predictions are in most cases in agreement with the data, hence indicating the accuracy of the approach. 

Abstract Hydraulic fracturing of oil and gas wells is a water intensive process. Limited availability, cost and increasing government regulations restraining the use and disposal of fresh water have led to the need for alternative fracturing fluids. Using CO2 foam as a fracturing fluid can drastically reduce the need for water in hydraulic fracturing. We address the addition of polyelectrolyte complex nanoparticles (PECNP) to surfactant solutions to improve foam stability, durability and rheological properties at high foam qualities. Polyelectrolyte pH and polyanion/polycation ratios were varied to minimize particle size and maximize absolute zeta potential of the resulting nanoparticles. Rheological tests were conducted on foam systems of varying surfactant/PECNP ratios and different foam quality to understand the effect of shear on viscosity under simulated reservoir conditions of 40°C and 1300 psi. The same foam systems were tested for stability and durability in a view cell at reservoir conditions. Supercritical CO2 foam generated by surfactant alone resulted in short lived, low viscosity foam because of surfactant drainage from foam lamellae. However, addition of PECNP strengthens the foam film by swelling the film due to increased osmotic pressure and electrostatic forces. Electrostatic interactions reduce dynamic movement of surfactant micelles, thereby stabilizing the foam lamellae, which imparts high durability and viscosity to supercritical CO2 foams. From the rheology test results, it was concluded that increasing foam quality and the presence of PECNP resulted in improved viscosity. Also, foam systems with PECNP showed promising results compared with foam generated using surfactant alone in the view cell durability test. The addition of optimized polyelectrolyte nanoparticles to the surfactant can improve viscosity and durability of supercritical CO2 foam during hydraulic fracturing, which can lead to large reductions in water requirements. 

ABSTRACT Precipitate scale formation is a major issue for the oil industry, plugging equipment, and reservoirs and resulting in increased operational costs. Poly(vinyl sulfonate) (PVS) is often used as a scale inhibitor to prevent the formation of barium sulfate scale. However, PVS effectiveness is limited by its short lifetime in reservoir. In this article, PVS has been entrapped in polyelectrolyte complex nanoparticles (PECNPs), altering its charge and thus enabling improved adsorption on the rock surface. As the ionic strength of the surrounding brine increases, the PVS is then released from the PECNPs, making it available to inhibit scale formation gradually. Positively charged PECNPs were made using a combination of poly(ethyleneimine) (PEI) and PVS. After NPs optimization, static adsorption tests were performed, which confirm the nanoparticles' rapid and strong adsorption. An increase in the ionic strength of the displacing fluid was used to decompose the PECNPs structure and release the PVS into solution. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 47225.