The application of controlled radical polymerization processes on the graft copolymerization of hydrophobic substituents onto guar gum and guar gum derivatives.

摘要

Guar gum is a naturally occurring polysaccharide; guar gum and its derivatives, such as carboxymethyl guar gum (CMG) are widely used in the oil and gas industry. A hydraulic fracturing fluid for rock formations to enhance oil recovery (EOR) is comprised of viscosifier, gelled CMG, and sand particles (proppants). The gel is mixed with proppant (sand) and pumped at high rate and high pressure into an oil/gas well to the hydrocarbon-producing zone. The applied pressure will force the rock formation to fracture allowing entry of the guar gel/sand mixture. The mixture then fills the resultant fracture. The viscosity of the mixture must be sufficient at this point in the process to prevent the settling of the sand particles. The pressure is then released, allowing closure of the fracture onto the guar/sand mixture. Leaving the guar gel in the fracture zone will block the pores, causing formation damage and a resultant decrease in oil or gas production. Thus, to complete the process, guar gum must be degraded chemically and/or thermally, then flushed from the formation back to the surface. If the degradation of the guar gum yielded a surfactant, removal of the guar gum fragments would be facilitated by emulsification. This optimization is achieved by introducing hydrophobic attachment, such as polystyrene and poly-n-butyl acrylate, to the polymer backbone of CMG. The increased hydrophobicity should dramatically improve the fluid loss control and increase viscosities of the fluid.; The free radical graft copolymerization of the hydrophobic monomers onto guar gum in the presence of ceric ammonium nitrate may be moderated using controlled radical polymerization techniques. The synthesis of a hydrophobic modified carboxymethyl guar gum graft through two living free radical techniques: nitroxide x mediated living polymerization and photo induced RAFT polymerization is presented in this paper. CMG grafted materials with an average weight gain of 71.87% and short oligomeric side chains (with a low degree of polymerization) were synthesized. Hydrophobic modified graft copolymers with higher gel viscosities than CMG gels were produced by the described living free radical polymerizations techniques.