Rheology and hydraulics of polymer-based foams at elevated temperatures
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2019 Elsevier B.V. Foam has been successfully used for different operations like well stimulation, drilling, enhanced oil recovery (EOR), cleanout, and acidizing operations in the oil and gas industry. Additionally, the low liquid content of foam provides a distinct advantage in terms of lesser material requirements. However, accurate prediction of rheology is necessary for the success of field operations, which requires a rheological model that incorporates the effect of temperature on foam properties as it circulates downhole. In the present investigation, polyanionic cellulose (PAC)based foam was generated using nitrogen as the gas phase and its rheology was determined using a recirculating flow loop that has three pipe viscometers (3.05, 6.22, and 12.7 mm ID)and a fully-eccentric annular section (9.53 mm OD 12.57 mm ID). Experiments were conducted within the temperature range of 24 to 149 C and at various foam qualities (gas phase volume fraction). The foam was circulated at different flow rates and the differential pressure across each pipe section was recorded. All tests were conducted at 6.89 MPa. The foams displayed power-law fluid behavior in the shear rate range tested (1005000 s1), which is often experienced in the wellbore. Like its base liquid, polymer foam exhibited thermal thinning and a significant rheology change with temperature. Only high-quality foam (75%)at ambient temperature (24 C)showed yielding behavior, which was measured in a pipe viscometer under static condition. The disappearance of yield stress at elevated temperature could be attributed to thermal thinning of the liquid phase that weakens the strength of bubble structure. Experimental data is used to develop new correlations to predict power-law fluid parameters as a function of temperature, base fluid properties, and foam quality. Moreover, the measurements are compared with the predictions of existing models, and discrepancies are observed, which could be attributed to the variation in foam generation technique, the nature and concentration of polymer, and the concentration of surfactant used in the experiments in which data was obtained to develop the models. Furthermore, annular pressure loss measurements obtained at low temperatures (24 and 79 C)show predominantly good agreement with predictions of a hydraulic model that uses the new correlations. Discrepancies increased with temperature as the foam becomes unstable due to thermal thinning of the liquid film and subsequent weakening of bubble structure.
