Abstract

In the last decade, slickwater fracturing has become a popular method of proppant injection for unconventional reservoirs. Advantages for using slickwater fracturing include creating adequate conductivity in low-permeability reservoirs and complex fractures with large fracture surface areas. As the use of slickwater becomes more versatile in oilfield stimulation, different parameters need different solutions for successful jobs in the field. Friction reducers (typically PAM, polyacrylamide) are always used in slickwater treatments to reduce the tremendous friction pressure resulting from extremely high pumping rates. Recent developments demonstrated the necessity of using breakers to mitigate potential formation damage from these friction reducers.

Conventional oxidizer breakers work effectively for well temperatures above 200°F, but breaking synthetic polymer friction reducers at temperatures lower than 150°F is significantly more challenging, even with more reactive persulfate salts. A study was conducted to completely break synthetic polymer under low-temperature field conditions of 110 to 125°F. At these lower temperatures, a catalyst was identified to be added to the conventional breaking package. The catalyst allows viscosity breakdown of the fluid to almost that of water, as confirmed by viscosity measurement using tube viscometers. The working mechanism is believed to be that the breaker catalyst reduces the activation energy of the breaking reaction, enabling the reaction at much lower temperature.

This paper will present the breaking tests at various temperatures with the new breaker package and with conventional breakers. The rheology testing was carried out with rheometer and tube viscometers. Also, low temperature cored flood testing was done to calculate regain permeability of oil after cleanup of the polymer system. It demonstrates that the new breaker package is highly effective on synthetic PAM polymers even at very low temperature.

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