HYDRAULIC FRACTURE PROPAGATION IN ANISOTROPIC FORMATION AND PROPPANT TRANSPORT.

Abstract

Recent advancements in hydraulic fracturing technology have significantly improved the extraction of hydrocarbons and geothermal energy from unconventional reservoirs. The efficiency of hydraulic fracturing in unconventional reservoirs is greatly influenced by proppant transport, fracture geometry, and in-situ stress conditions. Rock anisotropy is known to affect fracture aperture, size, and propagation trajectory and should be considered in modeling and design. We present results of a novel approach to considering proppant transport in multiple hydraulic fractures in anisotropic rock. We employ a DD-based numerical approach to simulate multi-cluster hydraulic fracture propagation under both symmetric and asymmetric stress barriers. The analysis includes the effects of fracture spacing and stress barriers in anisotropic formations, as well as the variation of propagation regime (viscous and toughness).The study explores the critical role of proppant in maintaining fracture conductivity and controlling fracture closure. The effects of proppant size, density, concentration, and slurry injection rate on fracture network efficiency are investigated to optimize proppant distribution across clusters. Comparative analyses of fracture closure following injection, both with and without proppant, highlight the critical role of proppants in maintaining fracture openness. The findings highlight that well-designed proppant schedules can significantly improve fracture connectivity and enhance long-term reservoir performance, offering valuable insights for optimizing hydraulic fracturing operations in unconventional reservoirs. Additionally, this study evaluates the performance of various proppant materials, including petroleum coke-based proppants (PC), high-transported ultra-low-density ceramic proppants (LDC), and resin-coated ceramic proppants (RC), focusing on their crush resistance and packing strength under simulated downhole conditions. Using the Standard procedure outlined in API ISO 13503-2, we assessed both dry proppants across two mesh sizes (10/35 and 35/60) and wet proppants that were exposed to high temperatures (300 °C) for 7, 14, and 30 days to simulate geothermal environments. The proppants were subjected to heat in the presence of water. The dry test results indicate that petroleum coke-based proppants, despite their cost-effectiveness, exhibit significantly lower strength compared to ceramic proppants, with resin-coated ceramics showing exceptional stress tolerance exceeding 15,000 psi. Additionally, the study reveals that the crush resistance and packing strength of proppants generally diminish over time when exposed to high temperatures, with variations depending on the type and size of the proppant. Specifically, petroleum coke-based proppants demonstrated minimal reduction in strength after heat exposure, while ceramic-based proppants exhibited a more pronounced decrease in mechanical performance. Moreover, dry crush tests conducted on mixtures of PC with LDC and PC with RC at various proportions (at a stress level of 5,000 psi) shown that a mix of PC with LDC or RC substantially decreases the generation of fines, lowers compaction, and improves the overall mechanical properties of PC proppants. The findings emphasize the significance of taking temperature effects into account when selecting proppants for geothermal applications, particularly those that are ceramic-based, given the critical impact of prolonged high-temperature exposure on their mechanical integrity.