Numerical simulation of fluid flow, proppant transport and fracture propagation in hydraulic fractures for unconventional reservoirs.

The distribution of proppant injected in hydraulic fractures significantly affects fracture-conductivity and well-performance. The proppant transport and suspension in thin fracturing fluid used in unconventional reservoirs are considerably different from those of fracturing fluids in conventional reservoirs, due to the very low viscosity of fracturing fluids used in the unconventional reservoirs, poor ability to suspend proppants and hence quick deposition of the proppants. This research presents the development of a three-dimensional computational fluid dynamics (CFD) modelling technique for the prediction of proppant-fluid multiphase flow in hydraulic fractures for unconventional reservoirs. The Eulerian-Lagrangian multiphase modelling approach has been applied to model the fluid flow and proppant transport, and the kinetic theory of granular flow is used to model the inter-proppant, fluid-proppant and proppantwall interactions. The existing proppant transport models ignore the fluid leak-off effect from the fracture side wall and the effect of fracture roughness. Thus, at the interface between the fracture and surrounding porous medium, the mass flow rate from the fracture to porous rock is calculated based on the permeability and porosity of the rock. The leakage mass flow rate is then used to define the mass and momentum source term at the fracture wall as a user-defined function, to investigate the proppant transport in hydraulic fractures with fluid leak-off effect. Furthermore, the hydrodynamic and mechanical behaviour of proppant transport on fracture roughness was studied in detail using different rough fracture profiles, and a relationship between the fracture roughness and proppant transport velocity is proposed. Lastly, an integrated model is developed, which simulates the proppant transport in dynamically propagating hydraulic fractures. The existing models either model the proppant transport physics in static predefined fracture geometry or account for the analytical models for defining the fracture propagation using linear elastic fracture mechanics. This limits the fracture propagation model to brittle rocks and neglect plastic deformations. Thus, in the present study, the fracture propagation was modelled using the extended finite element method (XFEM) and cohesive zone model (CZM), which can model the plastic deformations in the ductile rock. The fracture propagation was coupled with the CFD based proppant transport model, to model the fluid flow and proppant transport. The parametric study was then performed to investigate the effect of variation in proppant properties, fracturing fluid properties and geomechanical properties on the proppant transport. This study has enhanced the understanding of the flow and interaction phenomenon between proppant and fracturing fluid, and provides a technique with potential application in fracturing design for increasing well-productivity. The model can accurately simulate the proppant transport dynamics in hydraulic fracture and the present study proposes a solution to a frequent fracture tip screen out challenge faced in the petroleum industry. Thus, the developed modelling techniques provide petroleum engineers with a more suitable option for designing hydraulic fracturing operations, simultaneously modelling fracture propagation and fluid flow with proppant transport, and improves confidence by accurately tracking the distribution of proppants inside the fracture

Numerical modelling of proppant transport in hydraulic fractures.

The distribution of proppant injected in hydraulic fractures significantly affects the fracture conductivity and well performance. The proppant transport in thin fracturing fluid used during hydraulic fracturing in the unconventional reservoirs is considerably different from fracturing fluids in the conventional reservoir due to the very low viscosity and quick deposition of the proppants. This paper presents the development of a three-dimensional Computational Fluid Dynamics (CFD) modelling technique for the prediction of proppant-fluid multiphase flow in hydraulic fractures. The proposed model also simulates the fluid leak-off behaviour from the fracture wall. The Euler-Granular and CFD-Discrete Element Method (CFD-DEM) multiphase modelling approach has been applied, and the equations defining the fluid-proppant and inter-proppant interaction have been solved using the finite volume technique. The proppant transport in hydraulic fractures has been studied comprehensively, and the computational modelling results of proppant distribution and other flow properties are in good agreement with the published experimental study. The parametric study is performed to investigate the effect of variation in proppant size, fluid viscosity and fracture width on the proppant transport. Smaller proppants can be injected early, followed by larger proppants to maintain high propping efficiency. This study has enhanced the understanding of the complex flow phenomenon between proppant and fracturing fluid and can play a vital role in hydraulic fracturing design

Effect of fracture roughness on the hydrodynamics of proppant transport in hydraulic fractures.

The effect of fracture roughness is investigated on proppant transport in hydraulic fractures using Joint Roughness Coefficient and a three-dimensional multiphase modelling approach. The equations governing the proppant transport physics in the fracturing fluid is solved using the hybrid computational fluid dynamics model. The reported proppant transport models in the literature are limited to the assumption of a smooth fracture domain with no fluid leak-off or fluid flow from fracture to rock matrix interface. In this paper, a proppant transport model is proposed that accounts for the proppant distribution in rough fracture geometry with fluid leak-off effect to surrounding porous rock. The hydrodynamic and mechanical behaviour of proppant transport was found directly related to the fracture roughness and flow regime especially under the influence of low viscosity fracturing fluid typically used in shale gas reservoirs. For the proppant transport in smooth fractures, the fracture walls employ mechanical retardation effects and reduce the proppant horizontal velocity resulting in more significant proppant deposition. On the contrary, for the proppant transport in rough fractures, the inter-proppant and proppant wall interactions become dominant that adds turbulence to the flow. It results in mechanical interaction flow effects becoming dominant and consequently higher proppants suspended in the slurry and greater horizontal transport velocity. Furthermore, the mechanical interaction flow effects were found to be principally dependant on the proppant transport regime and become significant at higher proppant Reynolds number

Proppant transport in dynamically propagating hydraulic fractures using CFD-XFEM approach.

Numerically modelling the fluid flow with proppant transport and fracture propagation together are one of the significant technical challenges in hydraulic fracturing of unconventional hydrocarbon reservoirs. The existing models either model the proppant transport physics in static predefined fracture geometry or account for the analytical models for defining the fracture propagation. Furthermore, the fluid leak-off effects are usually neglected in the hydrodynamics of proppant transport in the existing models. In the present paper, a dynamic and integrated numerical model is determined that uses computational fluid dynamics (CFD) technique to model the fluid flow with proppant transport and Extended finite element method (XFEM) to model the fracture propagation. The results of fracture propagation were validated with the real field results and analytical models, and the results of proppant transport are validated with the experimental results. The integrated model is then used to comprehensively investigate the hydrodynamical properties that directly affect the near-wellbore stress and proppant distribution inside the fracture. The model can accurately model the proppant physics and also propose a solution to a frequent challenge faced in the petroleum industry of fracture tip screen out. Thus, using the current model allows the petroleum engineers to design the hydraulic fracturing operation successfully, model simultaneously fracture propagation and fluid flow with proppant transport and gain confidence by tracking the distribution of proppants inside the fracture accurately

A new CFD approach for proppant transport in unconventional hydraulic fractures.

For hydraulic fracturing design in unconventional reservoirs, the existing proppant transport models ignore the fluid leak-off effect from the fracture side wall and the effect of fracture roughness. In this paper, a model is proposed using three-dimensional computational fluid dynamics approach with fluid leak-off rate defined along the fracture length and considering the effect of fracture roughness on proppant distribution. Based on the simulation results, it is recommended that neglecting the fracture roughness in the proppant transport model can result in over predicting the proppant bed length and underpredicting the proppant suspension layer by 10–15%. Furthermore, neglecting the fluid leak-off effect can result in under predicting the proppant bed height by 10–50% and over predicting the proppant suspension layer by 10–50%. This study has enhanced the understanding of the proppant-fracturing fluid interaction phenomenon by accounting detailed physics to optimise the hydraulic fracturing design

Computational Fluid Dynamics Modelling to design and optimise Power Kites for Renewable Power Generation

Power kites provide the potential rewards of obtaining the disused energy supply from high altitude wind. This paper aims to provide a design of Power kite and optimise the potential for renewable power generation. The Power kite was modelled using Computational Fluid Dynamics (CFD) to study its characteristics. The numerical modelling results were compared against the wind tunnel experimental study and two 3D printed Power kites. The design was optimised using several variables, including aerofoil choice, surface roughness, wind speed and operating parameters. Attempts at optimising the kite design were implemented. The results suggest that operating the kites at minimum 15 m horizontal separation is favourable, with the trailing kite operating below the leading, removing the potential for this kite to operate in the wake turbulence of the first. As the wind speed is generally very low at low altitudes, it is recommended to use a symmetrical aerofoil for the kite design, as these tend to produce greater lift with low Reynolds airflow. This paper presents relevant, applicable data which can be used for predicting the performance, and potentially optimising further Power kite designs

Computational fluid dynamics modelling to design and optimise power kites for renewable power generation.

Power kites provide the potential rewards of obtaining the disused energy supply from high altitude wind. This paper aims to provide a design of power kite and optimise the potential for renewable power generation. The power kite was modelled using computational fluid dynamics to study its characteristics. The numerical modelling results were compared against the wind tunnel experimental study and two 3D printed power kites. The design was optimised using several variables, of which include aerofoil choice, surface roughness, wind speed and operating parameters. The results suggest that operating the kites at minimum 15 m horizontal separation is favourable, with the trailing kite operating below the leading, removing the potential for this kite to operate in the wake turbulence of the first. This paper presents relevant, applicable data which can be used for predicting the performance, and potentially optimising further power kite design

Numerical fluid flow modelling in multiple fractured porous reservoirs.

This paper compares the fluid flow phenomena occurring within a fractured reservoir for three different fracture models using computational fluid dynamics. The effect of the fracture-matrix interface condition is studied on the pressure and velocity distribution. The fracture models were compared based on the variation in pressure and permeability conditions. The model was developed for isotropic and anisotropic permeability conditions. The results suggest that the fracture aperture can have a drastic effect on fluid flow. The porous fracture-matrix interface condition produces more realistic transport of fluids. By increasing the permeability in the isotropic porous matrix, the pressure drop was significantly higher in both the fracture and reservoir region. Under anisotropic conditions in the 3D fractured reservoir, the effect of the higher longitudinal permeability was found to lower the pressure in the fractured reservoir. Depending on the properties of the fractured reservoir, this study can enhance the understanding of fracture-matrix fluid interaction and provide a method for production optimisation