厚层砂岩油藏原油密度影响下的CO_(2)驱重力超覆实验

Experimental study of CO_(2) gravity segregation effected by oil density in thick sandstone reservoirs

厚层砂岩油藏CO_(2)驱时,重力超覆的形成会降低CO_(2)纵向波及效率。为研究原油密度对重力超覆的影响规律和机理,采用长岩心超覆物理模型开展低压(10 MPa)和高压(20 MPa)条件下的CO_(2)驱替实验,以岩心上下部位采收率差异和重力超覆准数表征重力超覆程度。结果表明:随着油气密度差的增大,见气时岩心上部采收率占比增大,重力超覆加剧,导致岩心总体采收率降低;低压时,即使注气速度高于高压条件下,重力超覆准数因油气密度差值较大,也会高于高压条件下,重力超覆对采收率的影响更明显。对于原油密度较大的厚层砂岩油藏CO_(2)驱开发,增加驱替压力、降低油气密度差、增大重力超覆准数,可以提高CO_(2)纵向波及效率。研究结果可为类似油藏注气开发提供借鉴。

For CO_(2)flooding in thick sandstone reservoir,the formation of CO_(2)gravity segregation reduces vertical sweep volume.To study the influence rules and mechanisms of oil density on gravity segregation,long core physical model was used to conduct CO_(2)flooding experiments under low pressure(10 MPa)and high pressure(20 MPa).The degree of gravity segregation is evaluated by the oil recovery difference between the upper and the lower of core and gravity segregation criterion number.The experiment results show that recovery ratio of the upper of the core increases with the increase of the oil density difference,gravity segregation quickens decrease of total oil recovery.The gravity segregation criterion number of low pressure conditions is higher than that of high pressure conditions because of greater oil density difference,even if the gas injection rate is greater.Gravity segregation has a more obvious impact on oil recovery.Therefore,for the development of thick layer reservoir with high oil density,vertical sweep efficiency of CO_(2)flooding will be improved when displacement pressure is increased,oil gas density difference is reduced,and gravity segregation criterion number is increased.The research results can provide reference for gas injection development of similar reservoirs.