A New Method for Shale Oil Injecting-Stewing-Producing Physical Modeling Experiments Based on Nuclear Magnetic Resonance

Abstract

Enhancing oil recovery in shale is a critical technology for improving shale oil extraction efficiency. It is essential to develop a comprehensive set of physical simulation methods that are coherent and aligned with practical field operations. This paper establishes an integrated experimental approach, encompassing the entire Injecting-Stewing-Producing cycle, to simulate the actual Huff-n-Puff process accurately. Initially, the fracturing and flowback states are simulated by injecting an imbibition fluid, followed by a 48 h well-soaking process using CO2. The extraction is then carried out under various pressures. The microtransportation of crude oil across different pore sizes and the extent of extraction during shale oil Huff-n-Puff are investigated using Nuclear Magnetic Resonance technology. The results suggest that there was an initial increase in crude oil within pores smaller than 20 nm at the beginning of the Huff-n-Puff process. In Contrast, crude oil in pores larger than 200 nm was preferentially extracted, with oil in smaller pores (<200 nm) migrating to larger pores before extraction. After the initial Huff-n-Puff cycle, the extraction efficiency of the shale oil core reaches 29.55%, constituting 63.3% of the total extraction achieved over three Huff-n-Puff cycles. This study also identifies a critical pressure drop to 60% of the initial pressure as the optimal point for injection in subsequent Huff-n-Puff cycles. These experimental insights provide valuable guidance for the practical implementation of enhanced oil recovery techniques in shale formations.

Keywords

• shale oil
• Huff-n-Puff
• nuclear magnetic resonance
• microscopic transport
• enhanced recovery