Evaluation of the Performance of Chemical Breakers on Various Types of High Viscosity Friction Reducers

Abstract

Abstract The use of synthetic high viscosity friction reducers (HVFRs) has become common practice in hydraulic fracturing as a reliable method for delivering proppant into target formations. HVFRs address many of the challenges that are present when using cross-linked or linear gels and provide reliable performance across a wide range of water qualities. Despite these advantages, HVFRs present their own difficulties that must be addressed. The use of oxidizing or enzymatic breakers is essential when cross-linked gels are used for proppant transport to reduce the fluid's viscosity to a point where formation pressure is sufficient to allow the well to produce, and to minimize formation damage. While HVFRs are not nearly as viscous as cross-linked gels, they have sufficient molecular weight and are viscous enough, and persistent enough, to negatively impact flowback when a well is brought online. Moreover, it has been found that synthetic polymers can also cause serious formation damage similar to or worse than gel-based systems resulting in negative effects on the well's production. As a result, breakers are also commonly used in conjunction with HVFRs to maximize production of the well after stimulation is complete. It is difficult to know if these treatments are effective, however, and are largely guided by prior experience. Such reliance can be dangerous, however, given that HVFRs can comprise a wide range of chemical compositions, molecular weights, and physical forms. We believe a more systematic study of breaker effects on HVFRs is warranted to develop a better understanding of how combinations of breakers and HVFRs should be applied in field operations. Here we will discuss a series of laboratory investigations conducted to understand how different types of HVFRs respond to treatment with various breakers. The breakers selected are chemically distinct and may operate via different mechanisms (e.g., oxidative, non-oxidative), or on different timescales (e.g., instantaneous, slow release). Likewise, the HVFRs are comprised of distinct polymer backbones, and thus we anticipate will behave differently when exposed to the breakers. Indeed, significant differences in viscosity reduction behavior are observed depending on the HVFR-breaker pairing, concentrations of the two components, and test temperature. Some findings were unsurprising, such as the broad applicability and rapid response of instantaneous oxidative breakers, while others were not, such as the relatively selective and temperature-dependent response of non-oxidative breakers. Such a diversity of breaker chemistries and response behavior may initially seem overwhelming for completion engineers designing a stimulation pump schedule. However, we believe that this diversity may, in fact, present an opportunity for more nuanced treatments (i.e., break profiles) through judicious selection and application of breaker and HVFR combinations, all within the context of a well's characteristic temperature and water chemistry.