High- Density Solid- Free Flexible Microgel Fluid Loss Pill in High- Temperature and High- Pressure Reservoirs: Curing Mechanism and Working Performance

The exploration of a multipressure well is often faced with the problem of blowout and loss of circulation coexisting. Using a high- density temporary plugging agent to plug the lower layer is an effective method to ensure the normal circulation of the upper kill fluid and realize the safe and efficient development of the reservoir. In a previous study, we reported a solid- free flexible colloidal completion fluid (SFCCF; Jia et al. 2022b). In this paper, an ultrahigh- temperature (180 degrees C)- resistant, curable solid- free flexible microgel pill (SFMP) with variable density was prepared based on SFCCF. SFMP is mainly composed of flexible microgel absorbent copolymer material (abbreviated as KA01), and the water absorption law follows Flory's elastic gel theory. SFMP breaks through the upper density limit of traditional solid- free brine- weighted polymer gels, and its curing density is up to 1.8 g/cm(3). The strength of SFMP was increased by crosslinking the stabilizer with KA01 through an acylation reaction. In addition, the hydrogen bonding between stabilizer and phosphate and the phosphorylation between phosphate and KA01 jointly promoted the curing of SFMP. The curing of SFMP is the manifestation of a multistage reaction, and the internal reaction rate increased with the increase in heating rate. SFMP has good performance of dynamic temporary plugging and pressure bearing and can be completely degraded by the chemical breaker. The formation pressure coefficients of the multipressure well in the East China Sea range from 1.20 to 1.42. The SFMP with 1.5 g/cm3 was used to plug the lower perforation layer of the Well AX, which achieved a reservoir protection effect. After the flowback of SFMP, the Well AX met production allocation requirements. The developed SMFP provides a new way for downhole operation in high- temperature, high- pressure (HTHP) multipressure wells.