A Submicron-Scale Plugging Agent for Oil-Based Drilling Fluid Synthesized Using the Inverse Emulsion Polymerization Method.

Due to the increasing difficulty of drilling in the later stages of oil and gas field development, the development of micro-pores and micro-fractures is becoming common. Conventional plugging agents have relatively large particle sizes. So, choosing the appropriate plugging agent can prevent leakages. Using the inverse emulsion polymerization method, acrylamide, 2-acrylamide-2-methylpropane sulfonic acid and acrylic acid were selected to be the main reaction monomers, N,N'-methylenebisacrylamide was used as a crosslinking agent, sorbitan monostearate and polyoxyethylene sorbitan anhydride monostearate were used as emulsifiers, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride was used as the initiator to synthesize a nano-scale plugging agent for oil-based drilling fluid. The plugging agent was characterized using infrared spectroscopy, scanning electron microscopy, and thermogravimetry analysis. The results showed that the plugging agent is spherical and uniform in size, with particles being in the submicron range. Additionally, it exhibited strong temperature resistance. Finally, the performance of the plugging agent was evaluated via experiments conducted under normal temperature and pressure, high-temperature and high-pressure, and core-plugging conditions. After adding the plugging agent to the oil-based drilling fluid, the basic rheological properties of the oil-based drilling fluid were not significantly affected. Furthermore, the filtration loss was significantly reduced under normal temperature and pressure, as well as under high-temperature and high-pressure conditions, after aging. When the plugging agent with 3% concentration was added, the reduction rate of pore core permeability reached 96.04%. Therefore, the plugging agent for the oil-based drilling fluid can effectively improve the wellbore stability and has a promising potential for field applications.