Synthesis and evaluation of scale inhibitors for squeeze treatment of carbonate reservoir

Abstract

A commonly used scale inhibitor (SI) diethylene triamine penta-(methylene phosphonic acid) (DETPMP) and two series of phosphorous-tagged polymeric SIs (PPSIs) were synthesized to inhibit the formation of calcium-based scale in various brines. Introducing the phosphorus tag facilitates the detection of PPSIs, which is helpful to plan a reasonable operation on squeeze treatment. The two PPSI series are P(DEAP-co-AMPS-co-AA) and P(DEAP-co-SSA-co-AA), including three samples for each copolymer, which were synthesized from diethyl allylphosphonate and various monomers. Generally, DETPMP and the PPSI products exhibited good compatibility in high-salinity water, high efficiency in calcium scale inhibition, and most importantly, the chemical detection at low concentration. One sample from P(DEAP-co-SSA-co-AA) showed the best performance in Ca²⁺ scale inhibition with 50:50 formation water and injection water. The PPSI also demonstrated the highest static adsorption onto carbonate. After injection of the chemical solution at 10 wt% followed by a shut-in period of 20 h, permeability of the carbonate core was significantly reduced by treatment with DETPMP. While the permeability remained almost unchanged after the PPSI injection, indicating a low formation damage to the carbonate reservoir. The PPSI concentration was relatively high after the post-flush of reservoir brine, suggesting an effective scale control during the squeeze lifetime. SEM images showed that the cubic and needle-like morphology of CaCO₃ and CaSO₄ scales were not observed in the presence of the PPSI to avoid further crystal growth. XRD results indicated that the intensity of both CaCO₃ and CaSO₄ crystal structures were decreased upon addition of the PPSI.