Abstract
Enzyme breakers have been widely used in water-based fracturing fluids for more than three decades. Enzyme breakers have several significant advantages compared to traditional oxidizer chemical breakers. First, enzymes specifically break long-chain polymers without causing undesirable damage to the wellbore, formation, or fracturing equipment. Second, because of the catalytic nature of the enzyme, they are not consumed, thereby requiring minimal amounts. Third, enzymes are non-toxic compared to oxidant breakers. However, enzymes operate under a narrow pH range and often become inactive at high pH values. In addition, at elevated temperatures, their activity decreases or completely diminishes as a result of denaturing. This paper discusses a new method to extend the breaker activity of a mannanase enzyme to higher pH and temperatures by the addition of lignin-based additives.
Results show that the addition of lignosulfonates stabilizes the enzyme at an elevated temperature and pH, thereby extending enzymes breaker performance beyond what was previously achievable. Another aspect of fracturing fluid breakers that is difficult to control is break time. Generally, varying the amount of breaker provides customizable break times. For example, if a faster break time is required, then a larger amount of breaker is added to the fluid. However, enzymes are highly expensive, and the use of greater amounts to achieve a faster break adds significant cost. On the other hand, if lesser amounts of enzyme are used, extended break times are achievable, but the polymer breakdown becomes incomplete, which could lead to formation or propped fracture permeability damage. In this study, it was possible to modulate the break times of guar-based fluids by varying the amount of lignosulfonate and keeping the enzyme loading constant. The higher loading of the less-expensive lignosulfonate aids in faster breaking of the fluid viscosity. Consequently, this approach is more economical as it requires less enzyme loading. Additionally, the polymer breakdown is complete despite the low amounts of the enzyme used. The effects of different structural types of sulfonated lignins on enzyme activity are also discussed.
To the best of the authors' knowledge, there are no mannanase enzyme stabilizer additives available in the oilfield industry. Introduction of these new additives will aid in improving higher temperature and pH tolerance of mannanase enzyme breakers.
