No abstract

The presence of swelling clays, namely, montmorillonite and illite-smectite mixed layer clays alike, significantly affects well stimulation processes, such as hydraulic fracturing. In this study, the inhibition potentials of three natural amino acids, namely, glycine, lysine monohydrochloride (lysine MHCl), and methionine, on the swelling properties of swelling clays were evaluated using laboratory and theoretical simulation techniques. Linear swelling tests, rheological analysis, zeta potential measurements, FTIR, and FESEM analyses were employed in this experimental work. COSMO-RS was then utilized theoretically to describe the physics by which the proposed amino acids inhibit the swelling of the clay minerals. The obtained results confirmed the clay stabilizing abilities of the studied amino acids. Glycine reduced the imbibition of water into the clay mineral twice better than KCl (a commonly used clay stabilizer), while methionine and lysine MHCl trailed behind glycine and KCl, respectively. Their clay swelling inhibition potentials were then compared to the base fluid: glycine (35%), KCl (18%), methionine (11%), and lysine MHCl (5%). The COSMO-RS simulation analysis confirmed that the inhibition performance of amino acids is mainly controlled by the following: (1) the activity coefficient (γ) between amino acids with water, (2) the hydrogen bonding energy (E HB ) between the amino acids and water, and (3) the side-chain length (p s ) or surface area of the amino acids. A multiple regression model was also developed using the predicted COSMO-RS properties (γ, E HB , and p s ). The model predictions strongly agreed with the experimental results with percentage errors of less than 0.2%. This study reveals that the unique inhibition potentials of amino acids are mostly dependent on their ability to form strong hydrogen bonds with water and clay minerals and their suitable activity coefficients with the base fluid. However, these unique inhibitive mechanisms vary for each natural amino acid due to their varying side chains. The consideration of amino acids as effective clay stabilizers for hydraulic fracturing activities is, therefore, a step in the right direction for replacing toxic fracturing fluid additives and path-charting the application of greener and cleaner processes for shale gas production.

A benchtop humidity and temperature chamber was used to assess water vapor sorption in four US shale samples at 90 °C. Water sorption isotherms were measured at relative humidity ranging from 10 to 99% and temperature of 90 °C. Shale fractal properties were then evaluated, and capillary pressure (ranging from 1.70 to 386 MPa) was obtained using Kelvin relationship. The results show that Mancos shale, from the US, adsorbed more absorbed water due to its high clay concentration and low TOC. However, Wolfcamp shale, from the US, has the lowest TOC and clay concentration, adsorbing the lowest amount of water. There is little hysteresis between adsorption and desorption isotherms explaining water retention phenomenon in some shales. The obtained fractal dimension values ranged between 2.45 and 2.76 and average of 2.56 indicating irregular pore surface and complex pore structure. All shale sample's capillary curves were fitted to Brooks & Corey and van Genuchten models with nonlinear regression. The fitting coefficient, R2, which represents the proportion of variance for Brooks & Corey fits ranged from 0.90 to 0.97 for imbibition and 0.85 to 0.98 for drainage, while R2 for the van Genuchten model ranged from 0.94 to 0.99 for both imbibition and drainage. Thus, the proposed method can be used to measure capillary pressure–saturation relationships in gas shales.