Wettability alteration using benzoxazine resin: A remedy for water blockage in sandstone gas reservoirs

Abstract As a low carbon fuel, natural gas is leading the transition to a cleaner energy system. However, water blockage is seen to reduce gas deliverability significantly in many gas producing wells. We have developed an environmentally friendly and cost-effective non-fluorinated chemical treatment using a new benzoxazine monomer as a wettability modifier to combat water blockage. This chemical would adhere to silicate surfaces through a silane moiety followed by the application of a thermally accelerated ring-opening polymerization of the benzoxazine moiety. The performance of the treatment has been evaluated using contact angle measurements, spontaneous imbibition tests, and core-flooding experiments at 60 °C and 10.35 MPa. After chemical treatment, the contact angle shifts from almost 0° to 90°, implying that the treatment alters the wettability from strongly water-wet to an intermediate gas-wetting state. Spontaneous imbibition measurements show about 65% reduction in the volume of water imbibed into the rock sample after chemical treatment, suggesting a substantial increase in hydrophobicity of rock pore surfaces. Core-flooding experiments indicate that the chemical treatment increases gas relative permeability (by up to 22%) whilst decreasing residual water saturation (by up to 10%). Taken together, we demonstrate that this novel non-fluorinated benzoxazine monomer can successfully shift wettability of sandstone rocks from a strongly water-wet to an intermediate-wet state and thus aid to mitigate water blockage at relatively low cost and in an environmentally friendly manner. Furthermore, this chemical can withstand extra high temperatures encountered in many deep low permeability gas reservoirs where water blockage may be highly pronounced.