Wettability Alteration Using Silane to Improve Water-Alternating-Gas Injectivity

Abstract

Wettability is a main component that determines multiphase flow characteristics in a porous medium. Altering the wettability of a rock has a wide range of applications in the field of geosystems engineering, such as enhanced oil recovery, improving gas well deliverability, and geological CO2 sequestration. Considering how injectivity in many field water-alternating-gas (WAG) processes is lower than expected, wettability alteration is especially suitable to address the reduction in relative permeability encountered during water injection. Several methods for injectivity improvement exist, including the use of surfactants, nanoparticles, salts, and alkalis. Using silanes to modify wettability has been a prominent technique in surface chemistry for decades but has very rarely been applied to porous mineral rocks, especially carbonates. This work explores the use of silanes to render sandstone and limestone surfaces more hydrophobic, thereby reducing gas blockage that causes injectivity loss. Contact angle measurements were taken and showed good wettability alteration away from water wet, exhibiting contact angles well above 90°, regardless of treatment conditions. Centrifuge tests were carried out, and the resulting residual fluid saturations and capillary pressure curves proved that the treatment is also effective on the pore scale. Corefloods conducted in sandstone and limestone cores showed a 45 and 65% increase in water relative permeability after WAG cycles after treatment, respectively. This translates directly to improvements in injectivity based on this treatment method.