Analysis and Modeling of Proppant Transport in Inclined Hydraulic Fractures
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AbstractThe understanding of proppant transport in fractures plays a critical role in estimating propped fracture dimensions and performance. Modeling of such processes is challenging because of the complex interactions between fluid, proppant particles and fracture geometry. Existing models generally assume vertical planar fracture geometry, whereas the reality in the subsurface maybe much more complex. In this study we use discrete element method and computational fluid dynamics simulations to demonstrate that interactions between proppant particles and fracture side walls play an important role in proppant transport efficiency.To calibrate our numerical model, we conducted two validation simulations that describe particle settling tests and laboratory proppant transport experiments. Through scoping calculations, we determined the correct drag force model and matched both analytical solutions and experimental data for a wide range of flow regimes. We then constructed two hydraulic fracture simulation domains, one with a vertical planar fracture (as a base case), and the other with an inclined planar hydraulic fracture. In the main component of our study, we conducted proppant transport simulations using our benchmarked models in both domains and compared the proppant distribution results.By analyzing the velocity and trajectory of proppant particles during transport, we identified two different stages of the proppant transport process - a "suspension" stage and a "settling" stage. During the suspension stage, fluid drag and gravitational forces dominate, driving proppants further into the fracture. When the proppants collide with existing proppants dunes, the proppant particles lose momentum and become "settled." Our results show that settled proppant are more difficult to be mobilized by fluid drag force, for the reason that kinetic energy is easily dissipated inside proppant dunes. Finally, we observed that proppant settles slower in inclined planar fractures, due to the supporting force from fracture side walls cancelling part of the gravitational force which act on the particle. This leads to a better proppant placement efficiency in inclined fractures.ObjectivesThe objective of this work is to provide a better understanding of proppant transport behavior in inclined planar fractures by means of numerical simulation. A significant difference from prior (laboratory) experiments is the capability of our model to simulate proppant transport at field-scale flowrates. Such acapability is critical in understanding proppant transport and appropriately designing it by ensuring that the correct Reynolds number and flow regime are used in the design calculations.
