Hydraulic fracturing is a key treatment for economical production from shale formations. High surface pressure is used to fracture the formation, and proppant is pumped to prevent fracture closure after the pressure is removed. The ability of proppant to maintain high fracture width and permeability controls the flow of the hydrocarbon fluids towards the wellbore, and, hence, the behavior of different proppants at in-situ conditions is critical to the success of fracturing operations in shale formations. The objective of this paper is to experimentally evaluate the performance of two widely used proppants in Marcellus shale at elevated stress conditions.

A proppant-crushing test between two samples of Marcellus shale was performed to evaluate the proppant performance at different closure stress values up to 10,000 psia. Two types of proppants were tested: sand and sintered bauxite at different concentrations. This work used a digital microscope to measure the width of the fracture at each closure stress; a series of photographs of the propped fracture were taken, and an image analysis software was used for fracture width measurements. The amount of crushed proppant and induced formation fines due to embedment were also quantified after each test.

The results indicate that with partial monolayer proppant, both proppants experience a significant reduction in the fracture width at elevated closure stresses, reaching as high as 48% at 10,000 psia. Proppant physical properties were found to affect the initial fracture width even though the proppant concentration was the same. The use of multiple layers of bauxite proppant reduced the loss of fracture width to 14% at 10,000 psia closure stress. Results reveal that sand proppant shows a high degree of crushing at 0.05 and 0.25 lb/ft2 proppant concentrations. On the other hand, the use of bauxite results in a higher amount of formation fines due to proppant embedment, which could cause severe damage to the fracture conductivity.

The paper contributes to the understanding of how proppants behave at in-situ conditions of shale hydraulic fractures. Results can be used to optimize proppant and fluid selection, and reduce the sources of damage to fracture conductivity to maximize well productivity.

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