Research on Synergistic Permeability Enhancement Technology of Staged Fracturing Acidification in Low-Permeability Coal Reservoirs

In order to solve the problem of low permeability in carbonate-rich coal reservoirs, a novel method of staged fracturing acidification treatment combined with physical-chemical synergistic permeability enhancement was proposed based on hydraulic fracturing theories and acid dissolution mechanisms. Systematic acidizing experiments identified an optimized multicomponent acid formulation specifically for the Sanyuan Coal Mine reservoirs. Mercury intrusion porosimetry and X-ray Fluorescence spectroscopy were systematically employed to characterize the acid-induced alterations in both mineral composition and pore-structure characteristics within the coal reservoirs. Permeability measurements under various methods were conducted using a multiphase and multifield true triaxial test system, elucidating the influence of stimulation treatments on the permeability evolution of coal reservoirs. Field implementation demonstrated that the staged fracturing acidification enhanced coalbed methane extraction concentration by factors of 1.62 and 4.32, achieving factors of 1.58 and 5.09 increases in pure quantity compared to hydraulic fracturing and conventional boreholes, respectively. The staged fracturing acidification synergistic permeability enhancement measure outperformed individual hydraulic fracturing or acidizing by promoting fracture-pore network development, improving structural connectivity, and optimizing methane transport pathways through dual physical-chemical mechanisms.