Experimental study on enhancing oil recovery of tight reservoirs through CO2-C2H6 huff and puff

Abstract

CO2 injection has become one of the most important methods of enhanced oil recovery in tight reservoirs， but some hydrocarbon gases have more viscosity-reducing and miscibility on oil compared to pure CO2. Therefore， this article studied the saturation pressure and viscosity changes of oil with CO2 and composite gas （CO2 and C2H6） by PVT experiments at high-temperature and high-pressure and revealed the percentage of producing oil with different gases， huff and puff pressures， and rounds by core huff and puff experiments at high-temperature and high-pressure. The results show that the C2H6 in the composite gas enhances the gas and liquid miscibility， improves the CO2 viscosity reduction and dissolution ability， and significantly increases the fluidity of oil. With the increase of C2H6 mole fraction in the composite gas， the saturation pressure of oil increases by 26.54% from 14.24 MPa to 18.02 MPa， and the viscosity of crude oil decreases from 23.68 mPa·s to 8.76 mPa·s. Under different huff and puff pressures， the oil recoveries of composite gas （CO2 and C2H6） are better than that of pure CO2， and the increase of recovery near the minimum miscibility pressure is higher than under other huff and puff pressures. The percentage of producing oil by composite gases is higher than that of pure CO2 in the pores of 0.0001-0.001 μm and 0.01-1 μm.

Keywords

• tight reservoir
• saturation pressure
• viscosity
• core experiment
• nuclear magnetic resonance （nmr）