CO2驱沥青质沉积对致密储层的伤害机理——以鄂尔多斯盆地延长组长8储层为例

为了揭示CO2驱替过程中沥青质沉积对致密储层的伤害机理,文中基于岩心核磁共振T2谱测试原理,开展了CO2注入压力下的岩心驱替实验,研究了沥青质在岩心中的沉积特征,评价了沥青质沉积对储层的伤害程度。实验结果表明:沥青质沉积量和渗透率伤害率随着CO2注入压力的升高呈现先快速上升后趋于平缓的趋势;在CO2注入过程中,沥青质主要沉积在弛豫时间大于10 ms的大、中孔隙,导致大、中孔隙占比下降,微细、小孔隙占比增加,且随着CO2注入压力的升高,大、中孔隙占比下降幅度增大,微细、小孔隙占比上升幅度增大;此外,沥青质沉积会引起润湿性发生反转,随着沥青质沉积量的增加,润湿反转指数增大,岩心润湿性不断向强油湿方向转变。

Damage mechanism of asphaltene deposition to tight reservoir during CO2 flooding:taking Chang 8 reservoir of Yanchang Formation in Ordos Basin as an example

In order to reveal the damage mechanism of asphaltene deposition to tight reservoir during CO2 flooding,the core displacement experiments under different CO2 injection pressures were carried out according to core nuclear magnetic resonance T2 spectrum testing.The sedimentary characteristics of asphaltene in core were studied,and the damage degree of asphaltene deposition under different injection pressures was evaluated.The results show that with the increase of CO2 injection pressure,the amount of asphaltene deposition and permeability damage rate increase quickly at first and flatten at later.In the process of CO2 injection,asphaltene is mainly deposited in the large and medium pores that relaxation time was larger than 10 ms,which led to the gradual decrease of the proportion of large and medium pores,and the increase of the proportion of micro and small pores with the increase of CO2 injection pressure.Moreover,asphaltene deposition will cause the wettability reversal.With the increase of asphaltene deposition,the wetting inversion index will increase,and the wettability will transport to strong oil-wet.