Research and Development of a Novel Internal Rigid External Soft Plugging Agent

Rigid plugging agents have high strength and are difficult to adapt themselves to the sizes and shapes of the formation pores; Soft plugging agents, on the other hand, have strong self-adaptive capacity, but their compressive strength is low. Effective and efficient plugging cannot be obtained by the rigid or the soft plugging agent only. By combining the advantages of the soft and the rigid plugging agents, a new “soft outside rigid inside” plugging agent was developed through solution polymerization. This new plugging agent was made with calcium carbonate as the rigid core material, acrylamide and 2-acrylamido-2-methylpropane sulfonic acid as the main polymerization monomers, N,N-Methylene-bisacrylamide as the crosslinking agent, and ammonium persulfate-sodium bisulfite redox system as the initiator. The new plugging agent has small expansion ratio when water is absorbed, high compressive strength, good thermal stability and little impact on the rheology of the drilling fluid. Compared with soft plugging agents, this new plugging agent has better filtration control capacity and plugging performance in sand-bed test.