Synthesis and performance evaluation of water-absorbing resin coated with polymethyl methacrylate as a lost circulation material

Lost circulation will cause huge economic losses every year. In order to effectively reduce the harm of lost circulation to drilling, it is particularly important to use reasonable and efficient lost circulation materials (LCM). As a kind of water-absorbing, expandable and deformable LCM, water-absorbing resin can adapt to holes and cracks of different sizes. In this study, a kind of encapsulated water-absorbing resin LCM (PMMA/PNAD) was proposed. The water-absorbing resin is synthesized by acrylamide (AM), 2-acrylamide-2-methyl-propane sulfonic acid (APMS) and diallyl dimethyl ammonium chloride (DMDAAC) as reaction monomers through aqueous solution polymerization. The shell material is polymethylmethacrylate (PMMA), which is coated on the surface of the water-absorbing resin by oil phase separation method. The results of the experimental evaluation indicate that the water-absorbing resin possesses robust water-absorbing and swelling properties, which significantly affect the rheological properties of the drilling fluid. However, the coated shell can effectively mitigate the impact of the absorbent resin on the drilling fluid. Under the formation environment of 100°C or 2 Mpa, the shell can soften or break to release the absorbent resin. The lost circulation control performance test results show that PMMA/PNAD has good pressure bearing capacity, and can still maintain good lost circulation control at 6.9 Mpa.