In situ composite of graphene oxide in polyacrylamide to enhance strength of hydrogel with polyethyleneimine as crosslinker

Polymer gel was widely used in the petroleum industry for water shutoffs to enhance oil recovery or for plugging to control lost circulation events. By free radical polymerization of acrylamide monomers in presence of graphene oxide (GO) nano sheets, polyacrylamide graphene oxide composite (PAMGO) was synthesized and used to prepare high strength hydrogel with polyethyleneimine (PEI) as crosslinker. The gelation time of gel was determined with viscosity test and gel strength was evaluated with rheological measurements and sand pack breakthrough pressure test. ATR-FTIR and SEM test was adopted to characterize the structure and morphology of the gel. The results showed that compared to polyacrylamide (PAM) gel, gelation time of composite gel decreased while gel elasticity modulus increased. The breakthrough pressure of composite gel is 21.71 MPa and increased by 20.71%. However, the mixing of graphene oxide in PAM gelling solution causes detrimental effects on gel strength and the breakthrough pressure of the mixture gel is only 3.72 MPa. The ATR-FTIR spectroscopy confirmed that the type of hydrogen bonding in the composite gel was different from that in the PAM GO mixture gel. The hydrogen bonding between N, O in composite and hydrogen atom on GO in the composite gel can enhance gel strength with reducing porosity and more crosslinking density of gel while the hydrogen bonding for H of NH2 in PAM with oxygen atom on GO in the mixture gel can occupy the crosslinking points, resulting in less crosslinking density and gel strength.