Experimental Study Of CO₂ Flooding In Extra-low Permeability Reservoirs

With the increase of energy demand,unconventional reservoir becomes the focus of oilfield development due to the conventional cannot meet the social needs.Though we have rich reserves of low permeability reservoirs,routine methods are inadequacy for exploiting,except gas flooding.Considering the characteristics,such as enable to achieve miscible phase with oil,efficiently reduce oil viscosity,magnify formation volume factor and improve the oil water mobility,and the advantages including small investment,low risk and quick returns of CO₂,it is widely applied in-situ.Whereas,there is a significant impact on the PVT parameters and flow laws after CO₂ injected.Therefore,many experiments are performed based on the characteristic of formation oil dissolved CO₂,of which mainly contains the experimental studies on the flow law,displacement effects and the optimization of injection manners with different permeable long cores from Shengli Oilfield G89 block.The results demonstrate that there is some change of the flow laws as the increase of CO₂injection.The more CO₂ injection,the less value of minimum start-up pressure gradient of formation oi and the shorter non-linear segment.Besides,CO₂ has a remarkable influence on the PVT parameters.The more dissolved CO₂ volume in the formation oil,the bigger formation volume factor and the less density and oil viscosity.And the minimum miscible pressure is 29.8 MPa.The characteristic of non-newton fluids measured at miscible condition is more apparent as the core permeability decreases.And the relationship between the characteristic parameters of velocity-pressure drop curve and mobility is also established.To optimize the CO₂ injection manner,a comparison of displacement effects between CO₂flooding after water flooding and WAG was conducted,of which results suggests the latter one is the optimum.