Transforming Local Sands into a Reliable, Alternative Proppant Source

摘要

An abundant supply of low-cost local sands and their associated logistical advantages have incentivized operators over the last couple of years to use them in hydraulic fracturing treatments of unconventional reservoirs. Local sands are known for their low crush strength and high angularity and can contain other mineral particulates, besides quartz, compared to high-quality sands. This paper describes laboratory tests to demonstrate that low-quality sands, when treated with a binder, can generate stable, highly conductive channels within a simulated propped fracture, which could help maximize and also maintain production of hydrocarbons from the reservoir. Laboratory experiments were conducted to evaluate the performance of local sands when used in aggregate structures, simulating proppant ridges or partial packs formed in a propped fracture. These aggregates were formed by coating sand grains with a binder and placing them in molds to be cured before testing. The sand aggregates were then placed in API conductivity cells to determine the effect of closure stresses on aggregate height, size expansion, binding agent concentrations, and conductivity measurements. Cyclic stress testing was also performed to evaluate the stability of the aggregate structure and conductivity retention of flow channels as the aggregate was subjected to varying stress loads. The results obtained during this study indicate that the flow capacity of conductive channels prepared from proppant aggregates using local sands is comparable to those prepared using high-quality sand or high-strength manufactured proppant. Fines migration from proppant crushing within the aggregate was observed not to be a concern because sand grains connected and encapsulated by the binder helped lock the crushed sand together. Despite having diminishing permeability within the aggregates, flow capacity of solids-free channels between aggregate masses dominates flow through the propped fracture, making formation of proppant aggregates with high-quality sand or high-strength proppant (HSP) unnecessary. This suggests that using local sands, despite their low crush resistance, during fracturing treatments can effectively enable well production by forming highly conductive voids or channels on top of the settled sand packs in the propped fractures in a shale reservoir.