Fluid Loss
In formations with permeability that exceeds 20 md, the fluid-loss behavior of linear HEC gel systems is completely governed by the invasion of the whole gel into the formation. A filter cake does not build up on the faces of the fracture, and the leakoff rate is controlled by the rheological behavior of the gel in the porous medium.
HEC gels have been observed to behave as power-law fluids in high-permeability formations.
The non-Newtonian power-law nature of fluid leak-off in high-permeability formations has led to some interesting insights into its fluid leak-off behavior. One consequence of using non-Newtonian fluids is that their leak-off can decrease faster over time than that of a Newtonian fluid.
As a non-Newtonian fluid invades the formation rock, the shear rate inside the porous media is very high, typically about 10,000/sec. As the depth of fluid invasion increases, the filtrate rate decreases as does the shear rate within the rock. The fluid’s apparent viscosity increases with the decreasing shear rate due to the fluid’s shear-thinning nature. The increase in apparent viscosity aids in controlling fluid leakoff. This fluid behavior also implies that high-permeability treatments with linear gels shouldhave higher fluid efficiencies than predicted with a single value of CVC and that using fluids that are highly non- Newtonian in nature (lower values of n ?) may provide lower fluid efficiency.
