低渗透应力敏感性油藏的合理开发

Rational exploitation in low permeability oil reservoir with stress sensitivity

针对低渗透油藏开发效果难以达到预期的现象，通过采用变流体压力应力敏感实验方法，保持围压不变对某低渗透油藏的岩心在不同流体压力下的渗透率进行测试。研究结果表明：随着流体压力的减小，岩心渗透率逐渐降低，但减小幅度趋于平缓；岩石渗透率越低，应力敏感性越强，流体压力恢复后，岩心渗透率并不能恢复到原来水平，其原因是低渗透岩石应力敏感性是不可逆的。利用径向渗流理论，结合应力敏感性对渗透率的影响，建立新的油井产能方程，计算出地层压力变化对单井产能的影响。在保持生产压差为4MPa不变的前提下，地层压力下降5MPa，单井的产能降低10%~30%，储层渗透率越低，降幅越大。为使低渗透应力敏感性油藏得到合理高效的开发，储层在进行压裂、射孔和作业过程中需注意油层保护；在开采过程中需观察井底流压的变化，维持合理的生产压差；当油井产油量明显下降后，适时对近井地带储层进行酸化，增大近井地带的渗透率。

It is difficult to achieve a desired development effect in low permeability oil reservoir.Experiment of stress sensitivity at various fluid pressures was made to test the permeability of the cores in a certain low permeability oil reservoir under the condition of constant confining pressure.The results show that the core permeability decreases gradually with the decrease of the fluid pressure,and then tends to be gently.The lower the permeability of the rock,the stronger the stress sensitivity,and the core permeability cannot recover to the former after the fluid pressure recovers.Its reason is that the stress sensitivity of the low permeability rock is irreversible.Based on radial flow theory,a new productivity equation for oil well was derived considering the effect of stress sensitive on the permeability.The effect of formation pressure on single well productivity was calculated.Under the constant producing differential pressure of4MPa,the single well productivity is reduced by10%to30%when the formation pressure drops by5MPa.The lower the reservoir permeability,the larger the fall.In order to develop the low permeability reservoir with stress sensitivity reasonably and efficiently,reservoir protection should be made in the process of fracturing,perforation and operation.In the process of production,the change of bottomhole pressure should be observed and reasonable producing differential pressure should be maintained in the production.After the oil well production declines obviously,real-time aciding should be made to increase the permeability of the near wellbore area.