Volume 57

Mechanism Study of CO₂ Huff-n-Puff for Enhanced Shale Oil Recovery Based on Core Experiments and Numerical Simulation Lianjie Hou, Junrong Liu, Wenyue Sun

Abstract

Shale oil reservoirs suffer from low recovery (<10%) due to ultra-tight formations. CO₂ huff-n-puff (HnP) is a promising enhanced oil recovery (EOR) technique, but its underlying mechanisms remain unclear. This study integrates nuclear magnetic resonance (NMR) experiments and numerical simulations to investigate and quantify the contributions of different EOR mechanisms.CO₂ was injected into shale cores, followed by soaking and production, while NMR tracked oil mobilization distance. Results showed that increasing soak time from 30 minutes to 24 hours extended mobilization distance from 18 mm to 42 mm and boosted recovery from 6% to 20%. A compositional simulation model, history-matched to experiments, revealed that oil swelling and dissolved gas drive dominated the recovery process. With longer soaking (5 minutes to 48 hours), oil swelling increased its contribution from 0% to 50%, while rock expansion remained below 10%. Higher soaking pressures (5-11 MPa) enhanced extraction and gas drive effects.This study provides new insights into CO₂ HnP in shale oil reservoirs and offers a robust framework for evaluating and optimizing EOR performance in ultra-low-permeability systems.

Keywords CO₂ huff-n-puff; shale oil; numerical simulation; EOR mechanisms