消除滑脱效应的致密砂岩储层应力敏感评价

室内评价储层岩石应力敏感程度多采用气体渗透率作为评价参数,而致密砂岩储层岩性致密,孔喉细小,受气体滑脱效应的影响,所测气体渗透率偏高,导致致密砂岩储层应力敏感程度被低估。针对常规方法导致致密砂岩储层应力敏感程度被低估的问题,以鄂尔多斯盆地镇泾油田长8致密砂岩储层为例,采用等价液测渗透率作为评价储层应力敏感的参数,消除了气体滑脱效应对实验结果的影响;并结合平面径向流理论,分析了应力敏感对产能的影响。结果显示,采用气测渗透率低估了致密砂岩储层岩石应力敏感的程度;并且岩心渗透率越低、有效应力越大、低估程度越严重;随有效应力的增加,致密砂岩岩心的气测渗透率、等价液测渗透率均呈先快速降低后缓慢降低的趋势,渗透率变化率与有效应力之间呈幂函数关系;应力敏感现象导致生产井井底附近存在"渗透率漏斗";并且储层渗透率越低、生产井井底压力越低,"渗透率漏斗"越深,延伸的范围越广,应力敏感对产能的影响越大。

Stress Sensitivity Evaluation of Tight Sandstone Reservoir Eliminate the Influence of Gas Slippage

Tight oil as a new hot spot for of the global unconventional oil and gas resources, following shale gas, shows great development potential. But due to the the tight lithology and tiny pore throats, and strong micro heterogeneities, the stress sensitive effect of the production process there is much stronger than conventional oil and gas reservoirs. The stress sensitivity of low permeability reservoir is undervalued by gas permeability because of gas slippage effect. Klinkenberg permeability is used here to eliminate the slippage effect during stress sensitivity evaluation of Chang-8 member in Zhenjing Oilfield , Ordos Basin. Combined the experience formula of stress sensitivity test and planar radial flow theory, the influence of stress sensitivity on oil production is analysied. The results shows that the evaluation of tight sandstone reservoir rock stress sensitivity is underestimated using gas permeability because of the slippage effect. The lower core permeability is and the greater effective stress loaded , the more undervalued. Along with the increase of effective stress , gas permeability and klinkenberg permeability of low permeability sandstone were both dipping initially fast then slowly. The relation between the change of permeability and the effective stress on rocks accords with power function. Stress sensitivity of rock built up a permeability drawdown cone around the wellbore , and the lower the reservoir permeability and bottom hole pressure are , the permeability funnel extended deeper and wider, the lower the oil production.