This work presents new surface modified nanoparticles (SMN) that act as internal breakers for viscoelastic surfactant (VES) based fluids. Breaking profile is a key performance feature of a fracturing fluid. In addition to providing greater application latitude at high temperatures, the proposed solution is suited for gas wells or where there is less likelihood of encountering formation crude oil, which could also act as breaker for VES fluids.
The SMNs were prepared by organically modifying nanoparticles with specific surface capping agents that have functional groups with the ability to bind on to their surfaces by chemical or physical interactions. The base VES fluid was prepared from a mixture of sea water, ionic strength agents and a viscoelastic surfactant formulation. Varying amounts of SMNs were added to the base fluid and mixed vigorously to form a homogeneously dispersed fluid. The viscosities of the base fluid without SMNs and with varying amount of SMNs were monitored over time at fixed temperature to observe the breaking profile.
The base fluid consisting of VES dispersed in sea water with ionic strength agent exhibits stable viscosity for prolonged times. Compared to base fluid, addition of bare nanoparticles marginally improves the fluid's viscosity, although, the fluid does not break down to very low viscosity within desired time for convenient flowback operations. Slow viscosity drop is ideal from a fracturing fluid point of view that helps in efficiently placing the proppants inside of created fractures and eventual fluid cleanup. However, without the organically modified nanoparticles, the viscosity is too stable causing the post fracturing cleanup to be too slow. With the SMN the viscosity drop could be controlled and achieved in relatively shorter time. Further, with these breaker control over breaking time is also achievable. The SMN internal breakers interact with the worm like micelles and disrupt the gel formed by these elongated micellar structures.
The surface modified nanoparticles with a functional capping agent alters the way the nanoparticles interact with the wormlike micelles from electrostatic interactions to hydrophobic-hydrophobic interactions. This change provides an efficient mechanism for breaking the VES base fluids in absence of any external breaker with high temperature latitude.