The objective of this paper is to showcase the work done to improve proppant placement using high viscous friction reducers in Saudi unconventional reservoirs. Clean-based fluids, mainly water with friction reducer additives, do not exhibit enough viscosity to place the desired proppant volume. Nevertheless, the respective production results made clean-based fluids outperform heavy-based fluids (guar gum-based fluids with cross-link additives).
As the friction reducer is the main chemical to be pumped with water forming the clean-based fluid, as known as slickwater, its optimization is vital in placing the desired proppant volume by using minimal water volume. The optimization comes from two results: friction reducer type and concentration. To determine the best suited type of friction reducer to increase the viscosity of the fracture fluid and reduce drag/friction, lab experiments have been conducted using the available friction reducer types in the industry. Water samples from the field have been collected and was then tested to determine the water quality. Different additives were added and their viscosities were measured using rheometers at surface and downhole temperatures. High-Viscous Friction Reducers (HVFRs) generated the best viscosity at both surface and downhole conditions, when compared to other friction reducers in the market. To determine the optimum concentration of HVFR, different concentrations were used in the high temperature rheometers at surface and bottomhole conditions. The results show exponential relationship between the concentration and the viscosity of HVFR.
The second phase of the project is measuring the resultant conductivity of the HVFR. A lab experiment was conducted using a conductivity cell to measure the conductivity of a proppant pack. A sensitivity analysis was conducted, changing the fluid type inside the proppant pack. Slickwater with HVFR showed better performance than linear gel and crosslink fluids, and showed similar performance to other friction reducers from a conductivity point of view. The third phase of the project is the field test. A well was selected for the trial test where the well lateral was landed in a very challenging zone for proppant placement. The well's average proppant placement percentage was 62%, significantly hindering its expected production results. With the advent of HVFR, the proppant percentage improved significantly to 98%.
The paper highlights the importance of HVFRs in improving proppant placement in challenging unconventional reservoirs, to improve well productivity. This work summarizes the lab tests conducted to ensure placement would be achieved when used in the field, without jeopardizing the production results due to the enhanced viscosity/reduced friction. This work provides a breakthrough in slickwater placements in unconventional reservoirs, as this fracture fluid has become commonplace in Saudi unconventional reservoirs, and in many other unconventional reservoirs around the globe.