The use of nanoparticles has been demonstrated to enhance the rheological properties of the viscoelastic surfactant (VES) fluid. However, their influence on the rheological properties as a function of temperature is not well known. In this study, a detailed analysis of improved rheological properties and thermal stability of the VES fluid beyond their optimal working temperature was conducted. The effect of nanoparticles was also studied. A base VES fluid was prepared with the required amount of surfactant along with an ionic strength agent dissolved in sea water. The desired type of nanoparticles in required amounts were added to the base VES fluid and homogeneously dispersed. Different types of nanoparticles were added to prepare corresponding nano-VES fluid. Rheological properties of the base VES fluid and different nano-VES fluids were measured against variable shear rate. The fluids were tested at a temperature at which the base fluid shows highest gelling behavior, and at temperatures above and below that value. Results, Observations, Conclusions: The initial thermo-viscosifying effect and eventual thermo-thinning effect with temperature havebeen widely observed for viscoelastic surfactants based fluids. The effectshavebeen attributed to the effect of temperature on the structural changes of wormlike micelles. Nanoparticles being of the dimensions that are comparable with the thickness of these wormlike micelles are readily able to incorporate themselves into these structures and influence their rheological behavior. These interactions change both with respect to temperature and shear rate applied on them. Further, these interactions differ depending on whether the fluid is in the thermo-viscosifying region or the thermo-thinning region with respect to the temperature. Based on the kind of nanoparticle used, significant improvements in rheological behavior from a fracturing fluid perspective have been observed. In addition, shear rates at which a shift from Newtonian to non-Newtonian behavior with respect to shear rate occurs, has also been observed to change. A greater insight into the effect of nanoparticle additives on temperature related rheology of VES fluids has been provided. This understanding is crucial for the optimization of a VES fracturing fluid based on the well-to-well changes in temperatures.
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.
A viscoelastic surfactant (VES) based fluid has been proven to be a cleaner alternative to the conventional polymer based fluid. However, there are still certain technical challenges that need to be overcome to make it as a viable alternative. High fluid loss observed with VES fluids is one such issue that is investigated in this paper. It is known that certain nanoparticles can improve the rheology and fluid loss efficiency of VES fluid when added individually. Lab experiment results demonstrate that in certain conditions adding two different nanoparticles can act synergistically to improve the fluid efficiency more than when adding only one of the nanoparticles.
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