Rheological correlations for oil based drilling foams
Abstract This paper summarizes results of experimental investigation conducted on rheology of oil based foams. Flow loop experiments were conducted varying base liquid viscosity (3.4, 8.3, and 12.3 cP) flow rate (1 52 L/min) and foam quality (34 68 percent) High quality oil based foams (greater than 68% were not stable to perform rheology tests. The base liquids were mixtures of mineral oil, diesel oil, and fluorosurfactant. A flow loop has designed and built to generate and circulate foam fluids to study their rheological behavior. Experiments were conducted at 690 kPa and ambient temperature (26 2 degC) To identify the existence of wall slip, tests were conducted using different diameter (13.4, 19.6 and 31.8 mm ID) pipe viscometers. Fully transparent PVC pipes were used as viscometers to visualize homogeneity of the foam. Foam degradation during the test was minimized by regenerating the fluid at the maximum flow rate for each flow measurement. Experimental results indicate expected foam viscosity trend that shows substantial viscosity increase with foam quality and base liquid viscosity. The foams displayed non Newtonian (i.e. shear thinning) behavior, which improves with foam quality. For most field applicable shear rate range (10 1000 1/s) power law model best fits rheology of the foams. Like aqueous foams, consistency index increased with foam quality while fluid behavior index demonstrated moderate reduction. Slight right shifting of flow curve was observed in the small diameter viscometer. Since the shifting was not observed in other pipes, it can be attributed to wall slip or experimental artifacts that can mimic a similar effect. Applying nonlinear regression analysis, an empirical model is formulated to compute power law parameters (n and K) of the foams. The data from small diameter pipe is not considered in the regression analysis due to the shifting of flow curves. Currently, existing models developed for aqueous and polymer based foams are often used for estimating flow behavior of oil based foams. However, discrepancies of the models can be very high when they are used for unintended applications. Hence, predictions of the new and existing models are rigorously compared. Results indicate that the new model has better accuracy than the existing ones.