Evaluation of Long Term Changes of Sulfonated Polymers and the Effect on Propagation in Hths Conditions

Recently, the potential of polymer flooding in high temperature and high salinity (HTHS) fields has been evaluated from lab to pilot scale. The HTHS conditions are beyond performance limits of a standard HPAM. Therefore, there is need for chemistries capable to tolerate these harsh conditions. Incorporation of sulfonated groups in the polymer backbone is known as the best available option to improve salt and temperature tolerance of a polymer. For an effective flooding the loss in polymer viscosity during propagation through reservoir should be limited. This becomes more challenging for HTHS reservoirs as the rate of hydrolysis is significantly higher compared to reservoirs with moderate temperature and salinity. Therefore, for better management of polymer flooding and de-risking a project is of utmost importance to understand polymer characteristics and behavior from injector to producer in early stages of flooding work. Most of the published thermal stability studies have been conducted at reservoir temperature which are lacking long term effect. This challenge may be overcome by using accelerated thermal ageing based on Arrhenius analysis. The method has been previously described in several publications but existing data are still lacking the complete range of degree of sulfonation. In this paper, we indicate that acceleration testing can be applied for degree of sulfonation up to 100 mol%.

The aged polymers may have different hydrolysis degree than injected polymers. Therefore, it is expected that the interaction with reservoir rock may change with time. Most of the existing core flood studies have been carried out with a fresh polymer and the impact of hydrolysis on the propagation deep in reservoir is not widely addressed in literature. The second part of the paper studies the propagation of aged polymer in synthetic cores.

This paper establishes new references for holistic view and understanding changes in polymer behavior and characteristics prior to and during field development.