Development of a new cost-effective polymer gel for water control in oil and gas well

Excessive water production from petroleum reservoirs has been a serious problem. Polymer gel is one of the common successful treatments. In this study, cheap polyacrylamide (PAM) polyethylenimene (PEI) gel system was developed for use at high temperature applications. The effect of salts on PAM degree of hydrolysis was studied by using NaCl and NH4Cl. These salts showed good compatibility with field mixing water whereas, NaCO3 (a high effective retarder) was observed to form a white precipitate with PAM / PEI at high temperatures. 13C NMR and DSC revealed that NH4Cl increased PAM degree of hydrolysis more compared to NaCl. Rheological measurements showed that NH4Cl decrease the viscosity of the hydrolyzed PAM. The cross-linking retardation was concluded to be due to charge shielding effect rather than deceased PAM hydrolysis. The strength of PAM / PEI was examined through dynamic measurements taking into account different parameters like temperature, polymer and cross-linker concentrations, initial pH, salinity, salt (retarder) effect. The gelation kinetics was studied by DSC and modeled using rate-based processes. The developed PAM / PEI gel system was evaluated in sandstone and carbonate cores at high temperature (150°C) and pressure (1000 psi). A reduction in permeability of about 94% was obtained in sandtone core. In the carbonate core, about 99.8% permeability reduction was achieved by PAM / PEI at the same conditions. The proposed PAM/PEI system proved to provide satisfactory gel strength at high temperature using field water.