The Role of Micro-Proppants in Conductive Fracture Network Development

Micro-proppants use in hydraulic fracturing has had a significant impact on production and has led to a reduction of treating pressure and thus enhancement of the overall hydraulic fracturing treatment. A number of mechanisms have been proposed to explain the success of micro-proppants. However, the role of these proppants on increasing the conductivity of secondary natural fractures and fracture network development has not been well demonstrated. The objective of this paper is to explore and clarify the potential mechanisms involved in the success of micro-proppants. We study the transport and deposition of micro-proppants in propagating facture networks using an advanced simulator "GeoFrac-3D" that can consider irregular fracture geometries and intersection angles not limited to 90 degrees, thereby capturing realistic flow and proppant transport pathways and deposition sites. The method is 3D and fully couples fluid pressure to stresses and allows for dynamic modeling of 3D fracture propagation. Robust multiple 3D fracture propagation is considered using the displacement discontinuity method for the rock deformation and the finite element method for the fracture fluid flow. The pressure dependent leak-off of the fracturing fluid into the rock matrix/natural fracture system is considered. The proppant transport and deposition within the fracture is modeled by treating the mixture of fluid and proppant particles as slurry. The simulation results show that proppant transport into secondary fractures, and relatively less settling are the major factors in micro-proppant effectiveness. Proppant settling velocities and thus proppant distribution is affected by fluid velocity, micro-proppant size, fluid rheology, fracture aperture, hydraulic and natural fracture interaction and near wellbore tortuosity. The results demonstrates that the micro-proppants being smaller size particles have strong potential for the effective uniform proppant placement into the complex fractured unconventional reservoirs; hence, to increase their conductivity for the oil and gas in-flow. Additionally, as the micro-proppant can enter into the tight natural or secondary fractures, it will reduce pressure dependent leak-off of the fracturing fluid into the surrounding formation, which will result in reduction in treating pressure.