Dominant Controlling Parameters of Multi-Component Thermal Fluid Flooding in Fractured Shale Oil Reservoirs

Abstract

Fractured shale oil reservoirs possess ultra-tight matrix pores and suffer unsatisfactory oil recovery under conventional exploitation, while systematic comparisons among CO2 flooding, CO2/CH4 mixed gas flooding, and multi-component thermal fluid (MTF) flooding remain insufficient for guiding field-parameter design. This work establishes a matrix–fracture coupled dual-porosity compositional model and adopts a single-variable method to quantitatively clarify how injection composition, reservoir permeability, injection pressure, and temperature govern sweep efficiency and the oil recovery factor, as well as the synergistic EOR mechanisms of different displacement fluids. The results show that CH4 acts as a weak active component with limited crude-oil-swelling and displacement capacities; MTF yields the maximum recovery via thermal viscosity reduction, molecular diffusion, and crude oil swelling, whereas pure CO2 is reported to have comprehensive cost advantages according to field-scale practical experience (no quantitative techno-economic calculation is carried out in this work). An injection miscibility threshold of 20–30 MPa is identified, with declining incremental oil yield beyond this range. According to published engineering observations, excessively high injection temperatures may trigger liquid-phase permeability impairment, which is not captured in the present model. The oil recovery factor positively correlates with permeability within 0.02–0.1 mD, and volumetric fracturing is indispensable for ultra-low-permeability matrices to expand seepage pathways. This study delivers quantitative theoretical references for displacing-agent screening and injection–production parameter optimization in fractured shale oil reservoirs.