Energized fracturing fluids, including foams, CO2, and N2, are widely used for multi-stage fracturing in horizontal wells. However, since density, rheology, and thermal properties are sensitive to temperature and pressure, it is important to understand the flow and thermal behaviors of energized fracturing fluids along the wellbore. In this study, a unified model is developed to simulate the flow and thermal behaviors of different energized fracturing fluids and investigate the changes of fluid properties from the wellhead to the toe of the horizontal wellbore. The velocity and pressure are calculated based on continuity and momentum equations. Temperature profiles of the whole wellbore-formation system are obtained by simultaneously solving energy equations of different thermal regions. Temperature, pressure, and energized fluid properties are coupled in both depth and radial directions using an iteration scheme. This model is verified against field data from energized fluid injection operations. The relative average errors on pressure and temperature are less than 5%. The effects of injection pressure, mass flow rate, annulus fluid type, foam quality, and proppant volumetric concentration on pressure and temperature distributions are analyzed. Influence degrees of these operation parameters on the bottomhole pressure for different energized fracturing fluids are calculated. Required injection parameters at the surface to achieve designed bottomhole treating parameters for different energized fracturing fluids are compared. The results of this study may help field operators to select the most suitable energized fluid and further optimize energized fluid fracturing treatments.
Energized fluids, such as CO2, N2, CO2 foam, N2 foam, and foamed N2 in liquid CO2, have been widely used as fracturing fluids in tight gas, coalbed methane, shale gas, low-pressure formation, depleted reservoir (Gaydos and Harris 1980, Wendorff and Ainley 1981, Freeman et al. 1983, Gottschling and Royce 1985, King 1985, Garbis and Taylor 1986, McDaniel et al. 1997, Gupta and Bobier 1998, Mazza 2001, Gupta 2003, Burke et al. 2011, McAndrew et al. 2014, Wang et al. 2016, Cui et al. 2017, He et al. 2017, Li and Misra 2017, Tang et al. 2018). Energized fracturing fluids have many advantages in comparison to water-based fracturing fluids:
the clean-up speed of energized fracturing fluids is faster due to fluid expansion (Wang et al. 2012, Ribeiro and Sharma 2013).
Less water will be consumed, which is important in some regions where water supply is scarce (Ribeiro and Sharma 2012, McAndrew et al. 2017).
Water damage phenomena, such as water blocking and clay swelling, could be effectively avoided owing to less water and lower leak-off rate (King 1977, Harris 1985, 1987, Ribeiro and Sharma 2012, Kong et al. 2017).
Proppant transport efficiency can be increased due to the extensive interactions of the internal phase in foams (Valko and Economides 1997, Kong et al. 2016, Tong and Mohanty 2017, Tong et al. 2017).