Synthesis of Ultra-High Temperature Zwitterionic Polymer Fluid Loss Reducer for Water-Based Drilling Fluids

Polymer filter loss reducers presently used in water-based drilling fluids have a problem of insufficient functional group density. To address this problem, a multifunction monomer A with hydroxyl and sulfonic acid group is used to replace the single-functional group monomer AMPS to react with AA, DMDAAC and polyether monomer H. The product of the free-radical copolymerization reaction is a quaterpolymer filter loss reducer. The ultra-high-temperature performance, salt-resistance, filtration control property and compatibility of this filter loss reducer was systematically investigated. The results show that after aging at 240 ℃ for 16 hours, a freshwater mud, a saltwater mud and a saturated saltwater mud, each containing 2% of the synthesized filter loss reducer, have API fluid losses that were reduced by 80%. Among these drilling fluids, the freshwater mud, which contains 2% of the filter loss reducer, still exhibits filtration control capacity even after being aged at 260 ℃. This filter loss reducer is excellently compatible with sulfonated lignite (SMC), and the use of the filter loss reducer with SMC makes the drilling fluid rheology easy to control; a drilling fluid treated with the filter loss reducer and SMC, after being aged at 240 ℃ for 16 hours, has an API filter loss of only 1.8 mL and an HTHP filter loss of only 24 mL. The research shows that the quaterpolymer filter loss reducer exhibits both excellent high-temperature stability and salt contamination resistant capacity, making it suitable for use in complex drilling conditions, such as drilling ultra-high-temperature formations and salt and gypsum formations. It provides a theoretical basis and technical support for the molecular design of ultra-high-temperature polymer filter loss reducer and the formulation of ultra-high-temperature saltwater-based drilling fluid system.