Laboratory Results of Proppant Transport in Complex Fracture Systems

Abstract

With a global paradigm shift towards exploring shale reservoirs, the industry focus has moved towards optimizing hydraulic fracturing in these reservoir types. Low-viscosity slickwater fracture treatments are commonly used as a completion technique in these ultra-low permeability reservoirs. Each shale reservoir is different due to the presence of in situ natural fractures and other geologic complexities, and thus the resultant hydraulic fracture network is distinct and the proppant transport in these "created" complex fracture networks is not clearly understood. Much speculation exists in the industry as to how efficiently the proppant is transported from the primary fracture into subsidiary fractures, if it is at all. A better awareness of proppant movement in complex fracture networks can possibly help with better hydraulic fracture treatment designs by focusing on parameters that enhance transport in the subsidiary fractures and understanding what impacts this transport may have on the resulting production. This paper discusses a series of tests carried out in a low-pressure laboratory setting to evaluate proppant transport in complex fracture networks. Different slickwater treatment scenarios were simulated by pumping sand slurry through a series of complex slot configurations while varying the slot complexity, pump rate, proppant concentration, and proppant size. Results from twenty-seven tests carried out provide some interesting insights into the nature of proppant transport and settling in complex fracture networks. In the case of a primary slot system, the proppant transport was observed to occur via traction carpet after the creation of a proppant dune. However, in the case of secondary slots, the proppant transport was found to be dependent on the dune buildup in the primary slot. Two mechanisms were observed to be transporting the proppant into the secondary slots: 1) proppant flowing around the corner at pump rates higher than the threshold pump rate (related to the threshold velocity in the primary slot), and 2) proppant falling from the primary slot due to the effects of gravity, regardless of the pump rate.

Quantifying Proppant Transport in Thin Fluids - Theory and Experiments

“…Several other authors have presented slot experiments, including Patankar et al (2002), Brannon et al (2006), Woodworth and Miskimins (2007), and Sahai et al (2014). Most of this work has been directed at determining equilibrium bank heights and critical fluid velocities.…”

“…Three different Advanced Ceramic Proppants (30/40, 40/50 and 50/60) were pumped though the slot described by Sahai et al (2014). Although the slot configuration included secondary slots, the main purpose of the work was to measure transport in the primary slot.…”

“…Until recently (Sahai et al, 2014), it had not been determined whether proppant will enter the side fractures in complex networks or preferentially flow in the main fracture. Many of the fractures in complex fracture networks are assumed to be unpropped because it has been assumed that proppant cannot "turn the corner" and flow out of the main fracture into other branches.…”

Numerical study of supercritical CO2 and proppant transport in different geometrical fractures

“…Sahai et al fabricated lab-scale experimental apparatus to evaluate proppant flow in secondary fractures and concluded that proppant was able to flow in secondary fractures by drag force of the fluid or rolling into them as a result of the effect of gravity. 11 Alotaibi et al extended this work and highlighted the mechanism of proppant transport during proppant bed development; they further included friction loss and proposed a scalable correlation for 30/70 brown sands to estimate the equilibrium sand bed height for different flow rates and sand concentrations. 12 Tong and Mohanty studied the proppant transport in fractures with different types of bypass angle, considering the effects of shear rate and proppant size.…”

“…Sahai et al . fabricated lab‐scale experimental apparatus to evaluate proppant flow in secondary fractures and concluded that proppant was able to flow in secondary fractures by drag force of the fluid or rolling into them as a result of the effect of gravity . Alotaibi et al .…”