Experimental investigation of long-term fracture conductivity filled with quartz sand: Mixing proppants and closing pressure

With the rapid technological advances in hydraulic fracturing, the economic development of ultra-tight gas/oil reservoirs becomes feasible, altering current energy image between demand and supply. The key parameter evaluating the artificial hydraulic fracture is the long-term conductivity, manifesting the transport capacity for reservoir fluids. The majority of previous contributions focused on the impacts of inherent proppant properties on long-term fracture conductivity, while the influence induced by mixture proppants with a wide range of particle size has not received due attention. In particular, as for the realistic field case, multiple types of proppants with diverse particle sizes are utilized to reach desirable conductivity. At the same time, the stress conditions inevitably change within the depressurization development process, leading to the evident enhancement of closing pressure towards artificial fracture, acting as the detrimental role for long-term fracture conductivity. As a result, it is dramatically necessary and urgent to reveal the mutual influence arising from mixture proppants as well as closing pressure. In order to address this issue, series of laboratory experiments are implemented, and comprehensive theoretical analysis in terms of experimental data is performed. Results show that (a) reduction of particle size is observed with increasing closing pressure, the average decreasing rate approaches 19.3%; (b) Closing pressure acts as a detrimental role impairing conductivity, the amplitude is able to reach 42.1% as for the mixture case with a relatively high proportion of mesh-20/40 particles; (c) Mixing proppants uniformly fails to enhance fracture conductivity effectively, and the forward segmentation is demonstrated as the suitable strategy and beneficial for fluid transport capacity. The contribution expects to advance current understanding regarding the impact of mixture proppants on long-term fracture conductivity.