Eco-friendly utilization of oilfield fracturing flow-back fluid and coal pitch for preparing slurry: Experiments and extended DLVO study

The fracturing flow-back fluid (FF), as the primary pollutant in oilfield exploitation, is challenging to handle because of the large output and complex components. In addition, large amounts of coal pitch (CP) are insufficiently utilized. In this study, based on the principle of clean production, three dispersants were employed to prepare CP-water slurry (CPWS) and CP-FF slurry (CPFS), which had the characteristics of high efficiency and low pollution. The feasibility of CPWS and CPFS and the influences of dispersants on their performance were systematically studied by measuring the viscosity, rheology and stability. Furthermore, the dispersion mechanisms of dispersants were investigated via adsorption, Zeta potential, and extended DLVO (EDLVO) theory. Results showed that replacing water with FF reduced the slurryability, while the stability was improved. The CPFS exhibited the shear-thinning characteristics, and the components in FF strengthened the pseudoplastic of slurry. Among the three dispersants, the adsorption capacity of AC-1215 was higher than that of PS and MF. And the inorganic salts in FF promoted the adsorption of dispersants. The calculation of interaction energies demonstrated that for CPFS without dispersant, the polar interaction energy played a dominant role, resulting in the aggregation of CP particles. The addition of AC-1215 maximized the total interaction energies (greater than zero) by introducing the steric hindrance energy, which was 1-4 orders of magnitude higher than other interaction energies.