Is there Value in using ATBS Type Polymers in Lower Temperature and Salinity Reservoirs?

Polymer flooding is a mature enhanced oil recovery (EOR) technology that has been in use for >60 years. In recent years, the screening criteria has widened to include much heavier oils as the understanding of the mechanisms of polymer flooding has improved. Similarly, advancements in the range of polymer products have resulted in a wider range of applicable reservoir conditions. Specifically, the incorporation of ATBS (2-Acrylamido-tertiary-butyl sulfonic acid) into polyacrylamide-based polymers (HPAM) has significantly increased the polymer’s tolerance to high temperatures and salinities. This inclusion comes at an increased cost per mass of polymer, however without this inclusion the typical HPAM polymers are not sufficiently viscous and quickly degrade at these more extreme conditions.

This work looks to understand if there is value in using polymers with ATBS inclusion in a case taken from the literature with a low temperature of 31 °C and a moderate salinity of 15k TDS. 6 polymer chemistries of equivalent molecular weight are examined: co-polymers of acrylic acid (AA) and acrylamide (AM) - i.e. HPAM; co-polymers of ATBS and AM; and, ter-polymers of AA, ATBS, and AM. The polymers are evaluated in terms of viscosification per mass of polymer and dynamic adsorption via core flooding. The laboratory data is then used as input for simulation of a conceptual field model with an adverse viscosity ratio of-100 and significant water slumping. The numerical model is evaluated in terms of total recovery and net present value (NPV).

The laboratory data shows that the inclusion of ATBS as a ter-polymer results in a significantly higher viscosity yield and lower adsorption than the basic HP AM. When taken into the numerical model, this polymer - despite an increased cost per mass - results in a higher NPV, reduced water production and quicker production of the oil bank. The optimum dosage is found to be ∼20 cP, above this there is little further improvement in recovery or NPV.

This work presents a detailed argument for use of advanced ATBS polymers for lower temperature and salinity reservoirs. These polymers can result in a lower adsorption and higher viscosity yield than the equivalent HPAM. Using a simple economic model, it is shown that these factors give an improved NPV over HPAM in the specific scenario examined, despite the higher polymer cost. In short, these polymers can be advantageous and economic for cases beyond “high temperature / high salinity”.