Enhancing overpressure and velocity of methane detonation by adding sodium chlorate with a view to fracturing shale

Abstract

Contamination and inefficiency of combustion improver is an unaddressed issue in emerging in-situ methane explosive fracturing. In this work, a cleaner oxidant with higher oxygen content, NaClO3, was employed as an alternative to KMnO4. Explosion experiments on a series of NaClO3 and CH4-O2-air mixtures were conducted in a 500 L pipeline setup, whereby the influences of NaClO3 intrinsic parameters including particle diameter, specific surface area and loading concentration on the enhanced effects were first explored. It is discovered that there is a critical parameter that maximizes the specific surface area of NaClO3 after adsorption and agglomeration, thereby significantly promoting explosion. Two samples closest to it with a diameter of 22.4 and 11.9 μm, corresponding to concentrations of 0.2 and 0.1 g/L, respectively. Furthermore, the influences of equivalence ratios on the enhanced effects of two NaClO3, and the underlying improved mechanisms, were investigated. Results indicate that NaClO3 can provide sufficient O2 to promote the development of flame fronts and thus boost the wall impact and horizontal propagation of detonation waves; meanwhile, an oxygen-rich atmosphere created by decomposition can cause violent explosions in originally fuel-rich mixtures. In methane with a volume fraction of 16% and an equivalence ratio of 1.25, NaClO3 can generate an explosion overpressure of up to 33.197 MPa with a rise rate of 2.221 GPa/s, and a detonation velocity of 1.359 km/s.