低渗透砂岩油藏隔夹层注气突破压力及注气开发策略——以柴达木盆地尕斯库勒油田E_(3)^(1)油藏为例

Breakthrough pressure and development strategy for gas injection in interlayers in low-permeability sandstone reservoirs:a case study of the Gasikule E reservoir,Qaidam Basin

隔夹层发育的陆相低渗透砂岩油藏在水驱后面临亟需采用提高采收率接替技术的难题,综合运用岩心观察、薄片分析、扫描电镜、压汞及突破压力实验等方法,研究了柴达木盆地尕斯库勒油田E31油藏隔夹层类型及特征,明确了注气突破压力规律,分析了隔夹层发育油藏注气提高采收率策略。研究结果表明,尕斯库勒油田E31油藏主要发育泥质和钙质两类隔夹层,以泥质隔夹层为主,钙质隔夹层分布相对较少。隔夹层渗透率以小于0.01 mD为主,与储层相比其物性及孔隙结构极差,呈纳米级孔喉,渗流能力低。在同种饱和介质条件下,突破压力梯度与渗透率呈幂指数关系。隔夹层纵向封隔能力强,泥质隔夹层平均突破压力梯度为储层的103~491倍。气体易选择性驱替原油,同种岩心条件下饱和水后突破压力梯度最大,为饱和油后岩心突破压力梯度的2~4倍。隔夹层将储层分为多个流动单元,有效抑制气体超覆,扩大气体波及体积,有利于陆相低渗透砂岩油藏水驱后注气提高采收率。

Aiming at the urgent need for EOR replacement technology after water flooding in continental low-permeability sandstone reservoirs with interlayers,comprehensively using the methods such as core observation,thin section analysis,scanning electron microscopy,mercury injection,breakthrough pressure experiments,this paper studies the types and characteristics of interlayers in the Gasikule E31 reservoir,clarifies the law of breakthrough pressure during gas injection,and analyzes the enhanced oil recovery strategy for gas injection in reservoirs with interlayer development.Studies have shown that argillaceous and calcareous interlayers mainly develop in Gasikule E31 reservoir,dominated by the argillaceous interlayers.There are few calcareous interlayers.The permeability of the interlayer is mostly less than 0.01 mD.Compared with the reservoir,the interlayer has extremely poor physical properties and pore structure,as well as nanometer-scale pore throats and low percolation capacity.Under the same condition of saturated medium,the breakthrough pressure gradient has a power exponential relationship with the permeability.The interlayer has strong longitudinal isolation ability,and the average breakthrough pressure gradient of the argillaceous interlayer is 103 to 491 times that of the reservoir.Gas is easy to selectively displace crude oil.Under the same core condition,the breakthrough pressure gradient is the largest after water saturation,which is 2 to 4 times that after oil saturation.The interlayer divides the reservoir into multiple flow units,effectively suppressing gas overlap and expanding the swept volume of gas,which is conducive to enhanced oil recovery through gas flooding after water flooding in continental low-permeability sandstone reservoirs.