Research on Damage Characteristics of Clean Fracturing Fluid in Deep Coal Seam

This study focuses on investigating the damage characteristics and mechanisms of Slickwo clean fracturing fluid to the reservoir by using the deep coal seam in the Yan’an gas field as the research subject. During the experiment, fracturing fluids with varying A content were employed to displace coal and rock cores. The impact of these fluids on the permeability and pore structure of coal and rock was analyzed using a combination of nuclear magnetic resonance and high-pressure mercury injection technology. The findings indicate that the permeability damage rates of cores Y-1 and Y-2 post-displacement are 48.4% and 53.6% correspondingly, with the damage worsening as the agent A content increases. NMR data reveals that the fracturing fluid exhibits the highest retention in small pores, followed by medium-sized pores, and the least in large pores. The rise in agent A content enhanced the retention degree in individual pore throats and overall, increasing from 62.24% to 68.74%. The escalation in agent A content results in higher macromolecular residues, causing seepage channel blockages and enhancing the adsorption properties between fracturing fluid and coal rock. This phenomenon leads to inadequate backflow, primarily in smaller apertures. Simultaneously, the interaction between the gel breaker and clay minerals triggers particle migration, blockage, and expansion, consequently diminishing the permeability of coal and rock and inducing specific damages.