(640a) Modeling Linear Rheology of Nanoparticle-Enhanced Viscoelastic Fracturing Fluids for Unconventional Reservoirs

The recovery of hydrocarbon from ultra-low permeability unconventional reservoirs requires hydraulic fracturing, which creates highly conductive pathways for oil and gas to flow from the reservoir to the wellbore [1]. In hydraulic fracturing, cross-linked polymer-based fluids are applied to fracture sandstone and siltstone formations, because of their high viscosity and thermal stability [2]. However, these fluids have several drawbacks such as poor flowback, significant fracture-face damage, and formation damage [3]. In recent years, to mitigate such prevailing drawbacks of these fracturing fluids, viscoelastic surfactant (VES) based fracturing fluids have been used in field operations [4]. These viscoelastic fluids are composed of long wormlike micelles (WLMs), which behave like pseudopolymers and undergo continuous scission and union that contribute to the complex rheological properties of these fracturing fluids [8]. Specifically, these fluids are excellent drag-reducing agents, as they reversibly form micelles under the removal of high shear stress [4]. These properties make VES-based fracturing fluids ideal candidates for hydraulic fracturing in tight unconventional reservoirs. However, the application of these fluids is restricted because of their poor thermal stability and low viscosity that often lead to the degradation of the WLMs and huge water leak-off from the fracture into the reservoir during field operations [5].
Hitherto, extensive theoretical and experimental works have been carried out to enhance the thermophysical properties of VES fluids, such as viscosity and thermal stability [6]. The previous studies have reported that the addition of nanoparticles to the VES-based fluids can easily enhance the viscosity and thermal stability. Although a good theoretical understanding of the mechanisms involved in the interactions between WLMs and nanoparticles is present in the existing literature, no mathematical model has been developed to predict the rheology of the final product obtained after the addition of these nanoparticles to the surfactant solutions. Motivated by this consideration, a mathematical model to capture the rheology of the micelles in response to the addition of nanoparticles is developed.
In this work, a slip-spring model [8] was adopted to describe the linear rheology of entangled micellar solutions. Specifically, the kinetic Monte Carlo algorithm [9] was implemented to capture the different relaxation mechanisms in the WLM solutions, such as reptation, constraint release, dynamic union-scission, and contour-length fluctuations [10]. Furthermore, the slip-spring model was coupled with an adsorption model to consider the interactions between the WLMs and nanoparticles [21]. This coupled model was validated with experimental results and utilized to predict the linear rheology of VES solutions under different nanoparticle concentrations. Subsequently, it is highlighted that the proposed model is also sensitive to crucial process variables like the surfactant concentration and temperature. Finally, owing to this particular sensitivity, the developed framework was employed to observe the impact of surfactant concentration, temperature, and nanoparticle concentration on the solution rheology.

References
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