Effects of matrix permeability and fracture on production characteristics and residual oil distribution during flue gas flooding in low permeability/tight reservoirs

Abstract

The effects of matrix permeability and fracture on production characteristics and residual oil distribution of flue gas flooding in low permeability/tight conditions are analyzed systematically by laboratory physical simulation experiments and low-field nuclear magnetic resonance (LFNMR) system. T2 spectra results show that the crude oil is mainly distributed in the corresponding macropores of 100–1000 ms before and after the flue gas injection, and the crude oil in macropores is produced in large quantities after the flue gas injection in both fracture and fracture-free low permeability/tight cores. Additionally, oil production performance indicates that matrix permeability has a remarkable effect in fracture-free low permeability/tight cores. T2 spectra combined with slice scanned images show the migration from the macropores to the medium and fine pores is more obvious in the core with high matrix permeability and the final residual oil distribution is more uniform compared to those of the core with low matrix permeability. Matrix permeability is inversely proportional to the gas channeling point and it has a linear relationships with the gas channeling point in a log-log plot in fracture-free low permeability/tight cores. Besides, fracture can significantly reduce the effect of matrix permeability on oil recovery. The presence of fracture weakens the migration of crude oil in low permeability/tight fracture cores, and the residual oil spreads throughout the core. Fracture plays a dominating role in the gas channeling points for different permeability cores.