CO2-C2H6吞吐提高致密油藏采收率实验研究

注CO₂已经成为致密油藏提高采收率的重要手段之一，相较于纯CO₂，部分烃类气体对原油的降黏及混相能力更强。为此，通过高温高压PVT实验研究了CO₂及复合气体（CO₂-C₂H₆）-原油的饱和压力及黏度的变化特征，并利用高温高压岩心吞吐实验揭示了不同气体介质、吞吐压力及吞吐轮次下原油动用程度。研究结果表明：复合气体中C₂H₆增强了气液两相混相能力，提高了CO₂降黏及溶解能力，原油流动性显著增加。复合气体中随着C₂H₆摩尔分数的增加，原油饱和压力由14.24 MPa 增至18.02 MPa，提高了26.54%；原油黏度由23.68 mPa·s 降至8.76 mPa·s。不同吞吐压力下复合气体（CO₂-C₂H₆）的采收率提高效果均强于纯CO2的，且吞吐压力在最小混相压力附近采收率提高程度高于其他吞吐压力。复合气体（CO₂-C₂H₆）对孔隙半径为0.000 1～0.001 和0.01～1 μm孔隙中的原油动用程度强于纯CO₂的。

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

CO₂injection 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 CO₂and composite gas （CO₂and 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 C₂H₆mole 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.