With the increased use of regional sand in hydraulic fracturing operations, a noticeable reduction in friction reducer performance has been identified with some sources when compared directly to northern white sand. In practice, when switching from regional to northern white sands, a change in observed treating pressure is consistently seen. The objective of this paper is to discuss and understand the mechanism responsible for the reduction in friction reducer performance when using regional sand types.
After observing the change in friction reduction associated with the regional sands, it was clear that a more in depth look at the mechanisms involved was needed. By testing the friction reducer performance before and after interaction with both regional and northern white sands, it was observed that the regional sands reduced the performance in both viscosity generation and friction reduction. Further SEM images showed the regional sand to be both more jagged and porous than northern white examples leading to the theory that the regional sand had a positive charge associated with it where the northern white did not.
From field trials with different friction reducers and different regional sands, pressure drops up to 1200 psi have been observed at various rates, sand concentrations, and friction reducer loadings. The SEM imagery depicted stark differences between the two sands, where northern white is relatively round and spherical, the regional sand is more jagged and has porous features on the surface. The regional sand was also speculated to have a positive charge. The combination of the porous features and the positive charge are likely interacting with the anionic friction reducers and removing some of it from solution. This leads to the observed reduction in friction reducer performance. To further validate this theory, a sample with an increased pH showed that both the loss in viscosity and friction reduction were reversed when using regional sands.
As the market share of regional sands continues to grow, this paper will become increasingly relevant to operators and services companies using these sands. Implementing a solution to the reduction in friction reducer performance will help the regional sand sources to become more economical by reducing the use of unnecessary friction reducer.