Investigation of Thermal Degradation Kinetics of Synthetic Polymers in High-Performance Water-Based Muds for Designing Drilling Automation Processes for Viscosity and Fluid-Loss Control
Authors: Balaga Dileep Kumar , Kulkarni Sandeep D 
Published: March 2023

For the purpose of engineering the drilling automation processes, it is necessary to explore the effects of thermal-degradation kinetics of synthetic polymers on the performance in different brine-based drilling muds in terms of time-dependent viscosity and fluid-loss control response. In this regard, three different synthetic acrylamide polymers with molecular weights between 2.8 to 3 million DU and sulfonation range between 15 to 40% are studied in sodium bromide (NaBr) brine based drilling mud systems.

To achieve the substitution during the polymerization process, the sodium salt of 2-acrylamido-2-methyl-1-propane-sulfonic acid was utilized as a sulfonated monomer. The substitutions were verified by NMR testings. The time dynamics of these synthetic polymers were quantitatively investigated using a simple and reliable titration technique in order to comprehend the degradation kinetics at various temperatures. Viscosity and fluid loss testings in drilling muds were contrasted with the polymer degradation which were hot rolled at 250°F and 350°F for various time durations. Viscosity and fluid loss were calculated for variously aged fluids with a conventional viscometer and API & HTHP filter presses.

The titration studies quantified the conversion of acrylamide molecules present in the polymer-chain into acrylic acid; the conversion represents the decay in polymer and was governed by the aging temperature and aging duration. The rate of polymer degradation decreased as the degree of sulfonation i.e., DoS in the polymer-chain increased, which was evident by a rise in Arrhenius activation energy. The drilling fluids which were hot rolled at 250°F showed a reasonable apparent viscosity in a range of 85 - 100 cp at room temperature and minimal HTHP fluid loss of 10 - 18 ml. Similarly, at 350°F hot rolling, all these fluids provided an apparent viscosity between 20 – 30 cp at room temperature with a HTHP fluid loss ranging from 36 – 42 ml. At both the temperature conditions, polymer with highest sulfonation provided a better control than other two polymers in terms of fluid loss and filter cake formation. These viscosity and fluid loss results were explained contradictorily with the effect of activation energy as sulfonation increased. In sodium bromide drilling muds, these results signified that higher sulfonation provides more thermal stability, but the polymer may be customized accordingly as per industry needs.

In order to maintain viscosity and fluid loss management, this research discusses how the polymer degradation kinetics affect the time-dependent performance of synthetic acrylamide polymers in brine-based drilling fluids at high temperatures. Usage of sodium bromide salt provided sustained increase in the base-brine density and also provided conductive environment for sulfonated acrylamide polymers. This is essential for creating drilling automation in terms of polymer replenishment for specific downhole temperature conditions.