高地饱压差油藏通常具有中孔中高渗及储层压力变化幅度大等特点,此类油藏开发过程中往往会出现应力敏感现象。为此,以垦利油田为例,针对高地饱压差油藏应力敏感特征,利用天然岩心覆压气测渗透率实验方法,明确了岩心在单次及多次升压降压过程中所受有效应力与渗透率的变化规律,通过定义新的应力敏感系数,形成了此类油藏的乘幂式应力敏感定量表征方法。研究结果表明:30、100、300 mD岩心单次升压降压过程渗透率最大损失率分别为35%、27%、15%,多次升压降压岩心渗透率变化趋势与单次类似,渗透率损失率随升降压次数增大而增大,当储层渗透率低于100 mD时渗透率损失率最大可达30%以上。应力敏感规律及表征方法等研究内容对于高地饱压差油藏合理工作制度、合理产能以及储层保护方案设计的制订具有指导意义。
Oil reservoirs with high formation saturation pressure difference are usually characterized by medium porosity, mid-to-high permeability and wide variation of reservoir pressure, and stress sensitivity is a common problem in the development of such reservoirs. In view of the stress sensitivity of oil reservoirs with high formation saturation pressure difference, taking Kenli Oilfield as an example, the experiment for gas logging permeability of natural core in net confining stress was conducted to obtain the change rule of effective stress and permeability of the core in single and multiple times of pressure rise and fall, and a new stress sensitivity coefficient was defined to develop a power-based stress sensitivity quantitative characterization method for such oil reservoirs. The results showed that the maximum permeability loss of 30, 100, 300 mD cores during single pressure rise and fall was 35%, 27% and 15%, respectively. The change trend of core permeability of multiple times of pressure rise and fall is similar to that of single time of pressure rise and fall. The permeability loss increases with the increase of pressure rise and fall times. When the reservoir permeability is lower than 100 mD, the maximum permeability loss can be up to more than 30%. The study on change rule and characterization method of stress sensitivity is of great important guidance for the formulation of reasonable working system, reasonable productivity and reservoir protection scheme design for oil reservoir with high formation saturation pressure difference.
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