Untethered Downhole Viscometer for Polymer Degradation Monitoring During Enhanced Oil Recovery Operations

M. Gonzalez, H. Seren, T. Thiel, T. Davis, T. Hillman, C. Powell, S. Ayirala, L. Maskeen, A. Sofi, M. Deffenbaugh
Aramco Services Company: Aramco Research Center—Houston,
United States

Keywords: rheology, process monitoring, fluid property sensors, viscosity, density, oil and gas


During tertiary oil recovery, or enhanced oil recovery (EOR), polymers are added to the injected water in order to increase its viscosity and have a more favorable oil displacement for enhanced production. However, these polymers can suffer from degradation due to physical or chemical processes taking place during the injection process. During degradation, polymer scission occurs due to stretching and breaking of the polymer chains, ultimately reducing the molecular weight of the polymers and thus the viscosity of the fluid. Due to the large impact that a failed polymer flooding project may have on the economic development of a field, monitoring the quality of the injected polymer is of utmost importance. The ability to monitor viscosity changes in the fluid while downhole may provide valuable information to substantially reduce risks that may incur in high costs from fluid losses and operational inefficiencies. However, there are currently no means to obtain viscosity measurements downhole on a regular basis during EOR operations. Here, we describe a downhole viscometer integrated into a compact untethered well logging tool that can be deployed downhole with minimal logistics. The logging tool is buoyantly driven: it is pulled downhole by magnetically detachable weight which is released at a programmed well depth to allow the tool to float back up to the surface. The tool hosts sensors to create logs at different depths for temperature, pressure, and viscosity. The platform is powered and controlled by a carefully optimized low-power electronics system. The integrated viscometer is based on a miniature piezoelectric tuning fork sensor able to perform simultaneous viscosity and density measurements through its resonant properties while immersed in the test fluid. The device was fully calibrated in the lab using synthetic polymer samples at different concentrations in order to provide equivalent information as a standalone laboratory rheometer at 6.1 s-1. The viscosity calibration procedure was validated against field-collected samples. We show here details about the development of the tool and its different components as well as preliminary tests for each of the components and the integrated system.