High-viscosity friction reducers (HVFR) have been actively studied and implemented recently in fracturing as a proppant carrier fluid in unconventional reservoirs due to advantages over crosslinked fluids and linear gels. The vast majority of the known studies are performed in unconventional jobs, where pumping rates are significantly higher than in conventional fracturing treatments. A study was designed to answer the question how an HVFR can be used effectively in conventional treatments deep wells.
The analysis was based on a propped fracturing case study in a deep live annulus well completed with relatively small inside diameter (ID) fracturing string. High friction, significant depth, low reservoir permeability, and abnormal pressure indicate that HVFR can be a replacement for the conventional heavy crosslinked gel under certain conditions. Thorough laboratory testing was performed to optimize the recipe of the HVFR for the given conditions. After analysis of the injection and calibration tests, the obtained HVFR efficiency, friction, and downhole behavior were used to optimize the main treatment. The fracturing was performed successfully, placing 26 tons of proppant into the fracture.
Analysis of the treatment was performed in an advanced fracturing simulator with multi-physics model that is capable of modeling the complex proppant transport and redistribution processes within the fracture. Simulation results revealed that towards the end of the treatment, the increased concentration of the proppant resulted in accelerated proppant settling at the fracture bottom, leading to the step-like pressure-out. Treatment results and post-treatment simulations revealed that at given rates (15 to 17 bbl/min) and HVFR efficiency (∼21%), the carrying capacity of the HVFR is enough to place 26 tons of proppant at maximum concentration of 3.5 to 4.0 PPA with 28 to 30% pad percentage. The calibrated model showed that the created fracture has an effective half-length of about 75 m, fracture height of 50 m, and dimensionless fracture conductivity approximately equal to 4.5. A new fracture flowback optimization software was used to estimate the set the limits for drawdown during cleanup; the amount of the predicted proppant flowback (<100 kg) was proved by the top-of-proppant tag.