(217at) Rheological Properties of Thermoviscosifying Polymers in High-Temperature High-Salinity Environment

The number of new significant discoveries of oil fields is decreasing worldwide and most of the existing major oilfields are already at their mature stages. Consequently, it is becoming increasingly necessary to produce from these fields as efficiently as possible in order to meet the increasing global demand for oil. With depletion of oil reservoirs and growing demand of oil, it is extremely important to recover maximum oil by using some enhanced oil recovery (EOR) techniques. One of the promising EOR techniques is chemical EOR (cEOR) that has successfully been implemented in some oil fields. In cEOR ultra low interfacial tension between water and oil and high viscosity of displacing fluid is desired to avoid viscous fingering. High viscosity is achieved by using water soluble polymers. One of the major disadvantages of these polymers is the hydrolysis of amide group at elevated temperatures. In the presence of salts, this thermal instability causes a major reduction in viscosity of polymer from the time it was injected to breakthrough. High-salinity and high-temperature remain a big challenge for cEOR. Thermoviscosifying polymers (TVPs) are novel class of materials for cEOR applications that work on the principle of lower critical solution temperature (LCST). The objective of this work was to evaluate the rheological properties of the TVPs and their interactions with different salts and surfactants. Discovery hybrid rheometer (DHR-3) was used for measuring viscosity and other rheological properties. The critical temperature was found to be strong function of polymer concentration. Rheological results of TVPs were compared with conventional hydrolyzed polyacrylamide (HPAM) and copolymer of acrylamide and acrylamido tertiary butyl sulfonate (ATBS). Unlike HPAM and ATBS-AM copolymer TVPs showed high viscosity at high temperature. Also, viscosifying effect was found more pronounced in the presence of salts, while other conventional polymers suffer huge reduction in viscosity in the presence of salts. Effect of different ions and surfactants on the rheological properties of TVPs will be discussed.