Heat Transfer Engineering, Vol.32, No.1, 69-79, 2011
Rheology and Convective Heat Transfer Properties of Borate Cross-Linked Nitrogen Foam Fracturing Fluid
This article considers the rheology and convective heat transfer characteristics of borate cross-linked guar and borate cross-linked foam fracturing fluid by conducting experiments on a large-scale test loop at 30 MPa. The results show that severe chemical degradation of borate cross-linked guar occurred as temperature increased. When temperature was higher than the threshold value, the cross-linker was almost disabled and the guar was no longer cross-linked. It was also found that the viscosity of borate-cross-linked foam fracturing fluid was proportional to the increment of foam quality, which was inversely proportional to the increase of temperature. The influence of fluid behavior index on the velocity gradient of non-Newtonian fluid at the wall is tremendous, resulting in a negative temperature-dependent convective heat transfer coefficient. Moreover, to calculate the convective heat transfer coefficients of these two fluids and also to match the experimental data, a multiplier should be utilized to account for the shear-dependent thermal conductivity and heat transfer enhancement. The contribution of shear-induced bubble-scale microconvection was significant for the heat transfer enhancement of foam fluid. The correlations between the viscosity and the convective heat transfer coefficient of borate cross-linked guar and borate cross-linked foam fracturing fluid deduced from the experimental data were also obtained.