Epoxy resin microencapsulated by complex coacervation as physical-chemical synergetic lost circulation control material

Lost circulation has always been a costly and difficult issue in oil and gas development. In this paper, gelatin and gum Acacia were used to encapsulate epoxy resin by the method of complex coacervation. The prepared microcapsules and inert particles were used as composite lost circulation materials (LCMs) to achieve physical-chemical synergistic plugging of formation fractures. The structures and properties of microcapsules were characterized and the compatibility with drilling fluid was analyzed. The adhesive properties of microcapsules to inert particles and the control effect on circulation loss of drilling fluid were evaluated. The results showed that the epoxy resin was well encapsulated in the composite shell, and the prepared microcapsules had a good spherical structure, with the median particle size (D50) of about 90 μm. It was proved that microcapsules had good compatibility with drilling fluid and good thermal stability below 200 °C. The addition of microcapsules made the LCMs system form a tighter plugging zone, its maximum plugging pressure increased by more than 22.2%, and drilling fluid loss decreased by more than 50.8%. This research proves the importance of multicomponent synergy in constructing tight plugging zone, and provides a new idea for the construction of novel composite LCMs system.