Polyacrylamides which are used in oil applications i.e. polymer flooding and water based muds, are hydrolysed versus time and temperature. This leads to a lack of tolerance towards electrolyte contamination and to a rapid degradation inducing a loss of their properties. Modifications of polyacrylamide structure have been proposed to postpone their thermal stability to higher temperatures. Monomers such as acrylamido methylpropane sulfonate (AMPS) or sulfonated styrene/maleic anhydride can be used to prevent acrylamide comonomer from hydrolysis. The aim of this work is to study under controlled conditions, i.e. anaerobic atmosphere, neutral pH, the stability of sulfonated polymers in order to distinguish between hydrolysis and radical degradation reactions.
It has been observed that up to 100°C, the AMPS group is stable and protects the acrylamide function from hydrolysis up to 80%. At higher temperature, even the hydrolysis of the AMPS group occurs, giving acrylate and ß, ß dimethyl taurine, with a kinetics that depends on temperature and time. Degradation in terms of molecular weight then occurs indicating that it follows a radical decarboxylation reaction. it can be limited either by the use of free radical scavenger or when the polymer is in the presence of a mineral phase such as bentonite.
These results provide valuable data for the determination of the limits of use of sulfonated copolymers and guidelines for optimizing chemical structure of sulfonated polymers used in water based formulation, in particular to enhance their thermal stability.
Different constraints such as environmental regulations or specific well conditions i.e. shale drilling, high formation temperature require the development of improved water based formulations1,2. Different polymeric additives are used in water based formulations to reduce filtration, limit the cuttings dispersion, increase the carrying capacity of the fluid, stabilize the suspension by dispersing the weighting agent. They are of varying molecular weight, structure, functionality, charge… depending on their role within the formulation. The problem of high temperature fluids is of main concern since deeper formations are now investigated and classical formulation fluids present evolution of their properties with temperature. Thermal degradation of polymeric additives used for water based formulations may badly affect mud characteristics and induce at high temperature different phenomena such as loss of rheological properties, particle sedimentation, clay gelation, bad filtration characteristics that may be detrimental for the formation damage.