OLR Cement Testing Part 2
Although the OnLine Rheometer (OLR) has been utilized multiple times to measure the rheological properties of drilling fluids, it has yet to be tested with cement slurry. This month, OFITE is set to begin conducting tests on cement slurry in a modified flow loop using the OLR. By employing the squeeze flow technique, the OLR allows for constant, real-time monitoring of the fluid's flow properties. This technique measures storage and loss moduli by applying small cyclic deformations to a liquid sample at various frequencies. Additionally, complex viscosity can be determined through this method, which is useful for process monitoring and trend analysis. This type of measurement has been employed for many years through various industries outside of our typical oil and gas clients. Our aim is to bring this type of measurement and analysis into our standard suite of rheological measurement devices.
The test described below is the first of many tests we are conducting to better understand how flowing fluids behave and how best to implement this tool in oilfield operations and other industries. As you can see from the graph below, the (complex) viscosity increases as dry cement was incrementally added to the slurry. Conversely, as water is added and the cement hydrates, we see the viscosity decrease. The next graph shows the frequency crossover point for the Loss Modulus (or G” or Viscous Component) and Storage modulus (or G’ or Elastic Component) moves from less than 30 Hz to just under 60 Hz as dry cement is added to the slurry. This shift in the crossover point shows the transition of the slurry as more solids are added, as gels develop, and as cement hydration affects intensify.
The OLR was able to successfully monitor the characteristics of the fluid while being pumped and it handled the addition of solids extremely well. It captured the consistent increase in complex viscosity. Other characteristics that were monitored include the Elastic (G’) modulus increasing from approximately 10 pascals to 35 pascals over the same time frame. And the Viscous (G”) modulus becomes the dominant fluid characteristic at a lower frequency or shear rate (28 Hz) while the slurry contains less solids, but twice that frequency (60 Hz) after adding the cement to the slurry. External rheology data also aligns with the OLR results as seen in the table below.