Constructing low-cost and high-strength ultra-low-density proppants based on the modification of activated carbon framework with in situ hydrolyzed silane

Ultra-low-density proppants (ULDPs) play a crucial role in pushing the development of slick-water hydraulic fracturing technology to enhance oil and gas production. However, the polymer microspheres reported as ULDPs have certain drawbacks such as high cost and weak resistance to high-temperature and pressure. This paper aims to develop a low-cost type of ULDPs, composed of a hard but low-density framework and reinforcing modifier. To achieve this, activated carbon (ACs) was selected as the framework due to its abundant nano-porous structure and strong adsorption capacity. By combining the liquid–solid phase transition reaction of KH570 and the coating effect of phenolic formaldehyde resin, activated carbon-based composite microspheres, referred to as KP-ACs, were produced as ULDPs. The nano-porous structure of ACs facilitates the penetration of KH570 solution into the pores through capillary action. The subsequent sol–gel reaction of KH570 within the pores significantly improved the compactness of ACs. As a result, the total pore volume and specific surface area of ACs decreased from 4.960 × 10−1 cm3 g−1 and 1020.514 m2 g−1, respectively, to 3.383 × 10−4 cm3 g−1 and 0.624 m2 g−1. Additionally, the average peak pressure of individual particles increased from the original 7.8 N to 44.94 N, and the crush ratio at a closure pressure of 52 MPa decreased by 31.5%. Furthermore, due to the low-density characteristics of the modified material, the KP-ACs exhibit a significant increase in compressive strength while maintaining their ultra-low-density properties of 1.4923 g cm−3. They perform much better than commercial quartz sand proppants in terms of compressive strength and durability.