Microencapsulation of 2,2′-Azobis(2-methylpropionamide) dihydrochloride initiator using acrylonitrile butadiene styrene as shell for application in lost-circulation control

Gel sealants are often used to recover lost circulation, a problem that plagues drilling engineers throughout many oil and gas development project. Organic cross-linked polymer gel such as cross-linked polyacrylamide gel is one of the most popular and available gel sealant materials. It is of strong sealing ability, but the gelation time is too short to control and ensure safe drilling operation. Initiator used to supply free radical can prolong polyacrylamide gelation time, but the gelation time will dramatically decline with the increase of temperature. Microencapsulation of initiator can increase the gelation time because the concentration of initiator is controlled effectively by microcapsules. This paper proposes microcapsules of an initiator, 2,2′-Azobis(2-methylpropionamide) dihydrochloride (AIBA) encapsulated by Acrylonitrile Butadiene Styrene, prolonging the gelation time of cross-linked polyacrylamide gel. It was prepared via coacervation induced by polydimethylsiloxane (PDMS). The gelation time was prolonged to be eight times greater than that initiated by free AIBA initiator. Fourier transform infrared spectroscopy, thermogravimetric analysis, Ultraviolet-visible spectroscopy, specific surface area analysis, and scanning electron microscopy were used to observe the properties of microcapsules. The results indicated that AIBA was successfully microencapsulated and there were nano-sized pores in the outer surfaces of the microcapsules which serve to control the release of AIBA, and viscosity of PDMS and core/shell ration affected the content of AIBA loaded in the microcapsules. Moreover, it is microencapsulation that makes the concentration of AIBA in water increase stable as a function of time for prolonging the gelation time of sealant system. Computerized tomography (CT) scans revealed that the cross-linked polymer gel system significantly reduces the number of pores inside the cores and enhances pressure-bearing ability. Cross-linked polyacrylamide gel initiated by encapsulated AIBA shows notable potential for recovering lost circulation.