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

Suri, Yatin

Abstract

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.

Citation

SURI, Y. 2020. Numerical simulation of fluid flow, proppant transport and fracture propagation in hydraulic fractures for unconventional reservoirs. Robert Gordon University, PhD thesis. Hosted on OpenAIR [online]. Available from: https://openair.rgu.ac.uk

• Thesis Type: Thesis
• Deposit Date: Mar 1, 2021
• Publicly Available Date: Mar 1, 2021
• Keywords: Proppant transport; Hydraulic fractures; Fracture propagation; Fluid dynamics; Fluid flow
• Public URL: https://rgu-repository.worktribe.com/output/1239030
• Award Date: Nov 30, 2020