Controlling factors of fracture aperture reduction based on experimental study using proppant pack apparent Young's modulus

Abstract

The hydraulic fracture aperture packed by proppants determines the fracture conductivity and is pivotal to oil and gas production. After hydraulic fracturing, the fracture width decreases owing to proppant embedment, deformation, and crushing. However, the analysis of fracture width reduction based on the mechanical properties of the proppant pack is limited. In this study, an experiment is designed to obtain the apparent Young's modulus, which represents the rigidity of the entire pack, and steel sheets are used to replace rock samples to eliminate heterogeneity and weaken the effect of proppant embedment. Subsequently, the effects of proppant type, concentration, and size on the apparent Young's modulus are discussed. Finally, the controlling factors and mechanisms of fracture width reduction are determined. The results indicate that the fracture width decreases linearly with increasing closure pressure for the ceramsite pack, and that the apparent Young's modulus is associated with the fracture aperture variation, which is governed by proppant embedment and deformation. The apparent Young's modulus increases as the proppant concentration increases or the proppant size decreases, whereas the proppant size imposes a more prominent effect. However, the mixed-size ceramsite pack shows only slight improvements in terms of propping ability. This study provides new insights into factors governing proppant pack deformation. • The apparent Young's modulus is defined through experimental results to quantitatively characterize mechanical properties of the whole proppant pack. • The proppant pack will experience at least 1 rigid-to-plastic deformation cycle under closure pressure. • The apparent Young's modulus for ceramiste can be inserted into fracture width calculation correlation, of which the fracture width decrease is mainly dominant by proppant embedment and deformation. • Proppant concentration and size both have influence on apparent Young's modulus, but the latter is more profound . The finer the particles are, the higher the modulus of the proppant pack is.