An Investigation into Proppant Transport in a Tortuous Fracture During Supercritical CO2 Fracturing

Abstract

ABSTRACT: In this paper, laser topography scanning technology is used to extract the fracture morphology after supercritical CO2 fracturing to generate a tortuous fracture model. Then a supercritical CO2 slurry flow model is established based on CFD-DEM coupling method, and the proppant transport in the tortuous fracture is simulated. The flow and proppant transport characteristics of supercritical CO2 slurry in tortuous fractures were analyzed, and the effects of injection velocity, injection temperature and injection pressure on proppant transport and distribution in tortuous fractures were investigated. The results show that the flow of supercritical CO2 slurry in tortuous fractures forms curved dominant channels compared to planar fractures, and the formed proppant dune is not uniformly distributed within the fractures. Low injection velocity in tortuous fractures is more likely to cause sand plugging, and increasing the injection velocity can weaken the effect of fracture structure on proppant transport. Low injection temperature and high injection pressure facilitates the transport and distribution of proppant in tortuous fractures. The results of the study contribute to an in-depth understanding of the flow behavior of supercritical CO2 slurry in tortuous fractures. 1. INTRODUCTION Unconventional oil and gas reservoirs are characterized by low reservoir porosity, poor fluid permeability and low natural production capacity, making it difficult to develop them on a large scale by conventional extraction methods. Thanks to the emergence and development of hydraulic fracturing technology, the process of commercial development of unconventional oil and gas, such as shale gas, has been greatly accelerated (Denney, 2010). However, with the wide application of hydraulic fracturing technology, it also faces a series of challenges such as water consumption, reservoir clay expansion, and groundwater contamination (Hyman et al., 2016; Liu, Jiang, Huang, and Sugimoto, 2018). CO2 plays an important role in enhanced oil recovery (EOR) because of its good solubility and strong extraction ability in crude oil, which can significantly reduce crude oil viscosity, swell and increase capacity, and reduce interfacial tension by mixing phase with crude oil in multiple contacts(Hill, Li, and Wei, 2020; Li et al., 2017). When CO2 is injected into the reservoir, it changes to a supercritical state at the temperature and pressure conditions of the reservoir. Supercritical CO2 has shown great advantages as a fracturing fluid in eliminating reservoir damage, improving shale gas recovery and storing CO2 in the underground, and is a new waterless fracturing technology with broad application prospects(Middleton et al., 2015; Yang et al., 2021).