Study on an All-in-One Solid-Free Suspension as Flow-Back Fluid for Deep Coal-Bed Methane Development

The flowback fluid of a fracturing fluid for fracturing formations containing deep buried coalbed methane (CBM) has high salinity and complex components, and is therefore hard to be reused. The suspension based fracturing fluids widely used in present have high solids contents which can cause serious damage to tight coal beds. To deal with these problems, a solids-free integrated suspension has been developed with an oil-soluble polymer ZL-1 as the stabilizer, white oil as the solvent, and into the solvent add the following additives one by one: a polyacrylamide drag-reducer AE, an isopropanol initiator and OPE-10 as the phase change material (PCM). The single-factor control variable method is used in determining the type of each of the components for the reaction; using the orthogonal experiment method, the optimum composition of the suspension is determined as: 65% white oil, 1.3% stabilizer, 3.25% PCM, 0.455%initiator, 30% drag reducer. Results of the evaluation of the general performance of the suspension show that at a salinity of 200 g/L, the apparent viscosity of a fracturing fluid made from the solids-free suspension is 40% higher than the apparent viscosity of a fracturing fluid made from the conventional suspensions containing bentonite stabilizers. SEM analysis, Zeta potential measurement and nanometer particle size analysis prove that the dense layered structure formed in the solids-free suspension fracturing fluid has better salt-resistant shielding effect. Moreover, after gel breaking, the solids-free suspension fracturing fluid has no residue remained, the average permeability damage of the solids-free suspension fracturing fluid to the coal samples is less than 15%, and is therefore reusable in deep coalbed methane fracturing.