Integration of Viscosity/Density Measurements into an Untethered Logging Tool for Rapid Downhole Polymer Degradation Monitoring of EOR Fluids

Abstract Enhanced Oil Recovery (EOR) relies on polymer fluids that are injected to improve oil mobility and reservoir sweep efficiency, enabling improved recovery rates. Polymer degradation, however, can pose serious challenges to the operation if not properly addressed during the injection process. Here we propose using an untethered logging device with an on-board viscometer for direct downhole assessment of polymer degradation and show preliminary tests of the integrated system in a water well. This tool would enable cost-effective and on-demand measurements not currently available to operators. The tool consists of a compact, untethered, and buoyancy-controlled logging tool hosting an onboard viscosity/density sensor. The tool is a handheld device featuring a magnetically attached weight used to make the tool negatively buoyant. The weight pulls the tool down to the bottom of the well. When a target depth is reached, the magnetically attached weight is released, allowing the tool to float back up to the surface. During the descent/ascent period, density and viscosity are logged by use of a custom quartz tuning fork resonator, acquiring continuous measurements. Pressure and temperature data are also obtained with other onboard sensors. Tests of the tool were done in a 1450 ft water well. A series of tests spanning across three different depths were performed. In one of the tests, the logging tool was programed to remain downhole for about 20 minutes. Logs of viscosity and density were obtained by a calibrated quartz tuning fork sensor at a rate of one sample every ten seconds. The sensor was calibrated using Newtonian fluids before the test. In prior studies, the sensor was also tested using Xanthan Gum and other polymer solutions at different concentrations to calibrate the sensor for use in non-Newtonian fluids [1,2]. Full logs of the viscosity/density of the fluids along the water well were obtained. While the density and viscosity held relatively constant, as expected, since the well also hosts other contaminant fluids from prior operations, changes in fluid properties were seen to vary. This was verified by out-of-well tests of the system in a pressurized vessel, where only minimal changes in fluid properties were observed. The viscosity/density sensor was then demonstrated to be quite sensitive, making it promising to detect small changes in fluid properties if properly packaged to avoid contamination.