Insights into unique in-situ self-adaptive sealing property of pressure-activated sealant in leaks: Experimental and numerical investigations on mechanism of liquid-to-solid transformation triggered by differential pressure

Abstract

Pressure activated sealant (PAS) has been proven safety and efficiency for quick leak repairs in oil & gas production, due to the unique in-situ self-adaptive sealing property. However, its sealing mechanim of the liquid-to-solid transformation under leak pressures remains poorly understood to date. Elucidating the sealing mechanism of PAS is critical for designing and developing a new generation of wellbore sealing repair technology. In the present work, we conducted a pioneering investigtion that integrated experimental techniques with numerical simulations, to systematically explore the in-situ self-adaptive sealing performance of PAS in leaks. Firstly, latex deposition experiments were carried out to fabricate PAS from carboxylated acrylonitrile butadiene rubber latex (XNBRL), and then the physicochemical features of the XNBRL-based PAS, including chemical composition and microsctructure, were typically characterized using FTIR and SEM techniques. Subsequently, the micro-leak sealing capability of XNBRL-based PAS was evaluated under 20 MPa. The results showed that the fabriacted PAS is a type of multiphase fluid, wherein disperse phase are of regular spherical shape with an average size of 239.75 μm. The disperse phase are essentially compound droplets with material interfaces, exhibiting unique interfacial mechnical and chemical properties in the surrounding flow. PAS demonstrated excellent pressure-activated sealing performance towards crack and screw leaks, and solid barriers can be rapidly formed to fill micro-leaks in 500s under 16 MPa. Considering the microstructural and dynamic features of compound droplets, a mechanical-chemical coupling model was proposed to explain the activation and agglomeration process of liquid sealant at leak. In the jet flow field caused by differential pressures, the self-adaptive sealing process of PAS consists of four stages: (1) the impact deformation of compound droplets in jet flow, (2) compound droplets activated by breakup of hydrated membrane, (3) adhesion and agglomeration of activated compound droplets, and (4) self-adaptive solidification of deformed drolpets to fill and block leakages. Finally, three-dimensional (3D) numerical simulations were empolyed to investigate dynamic deformation of compound droplet in the pressure differential flow, to rationalize liquid-to-solid transformation of PAS. The numerical results showed that dynamic motion of compound droplet in jet flow field includes deformation of compound droplet, breakup of outer hydrated membrane, and collision of inner polymer core with wall. The hydrated membrane completely breaks up into ligaments in 0.8 ms, facilitating exposure of activated inner core and enables further chemical agglomeration, which agrees generally well with the experimental and model analyses.