Synthesis and Performance Evaluation of a Modified Acrylate Flocculant SDCD for Waste Oil-Based Drilling Fluid

Oil-based drilling fluid is widely used in deep and ultra-deep well drilling, but long-term use will lead to cutting accumulation and performance degradation and cannot be recycled. In this study, octadecyl acrylate (SA), divinylbenzene (DVB), and cetyl dimethylallyl ammonium chloride (C16-DMAAC) were used as raw materials to synthesize a polymer particle SDCD that can be stably dispersed in the oil–water two-phase in ethanol solution as a waste oil-based drilling fluid flocculant. The structure of SDCD was characterized by FT-IR, 1 HNMR, SEM, XPS, Zeta potential, and particle size distribution, and its flocculation mechanism in waste oil-based drilling fluid was analyzed. The results show that the fine particle size of SDCD makes it easy to disperse in the mud, and the positive potential characteristics make it capable of electrostatic adsorption with kaolin. At the same time, the pore structure can provide a specific surface area to enhance the adsorption. When the dosage of SDCD was 2.5 wt%, the flocculation rate reached 87.66%, the slurry showed good rheology and emulsion stability, and it still met the performance standard after 150°C hot rolling again. In addition, SDCD was successfully applied to waste mud treatment on site, which significantly reduced the solid content and improved the mud performance. This study provides an effective method for the recycling of waste oil-based drilling fluid and helps to reduce drilling costs.