低渗透油藏CO2驱试井解释方法

Well testing interpretation method for CO2 flooding in low permeability oil reservoirs

针对低渗透油藏CO2驱试井解释方法不明晰的问题,基于多区复合模型渗流理论,考虑低渗透油藏存在启动压力梯度与压力敏感以及CO2驱替过程中流体性质变化的特点,建立低渗透油藏CO2驱试井解释改进模型,并运用数值差分方法进行求解。同时,综合SPSA优化搜索算法对压力曲线和压力导数曲线同时进行拟合,最终形成一套低渗透油藏CO2驱试井曲线自动拟合与参数解释方法。对矿场实际试井曲线解释参数变化规律进行分析,结果表明:考虑低渗透油藏特性对储层渗透率解释值有较大影响,优化后渗透率解释值比初始解释值增加了37.97%;而导压系数、压缩系数变化指数等相关参数解释值受流体分布非均质性影响程度较强,分别较初始解释值降低了16.94%和21.97%。矿场实际数据的应用效果显示,提出的试井解释方法可操作性强,适用性较好。

This paper focuses on the unknown problems of the well testing interpretation method for CO2 flooding in low permeability oil reservoir. Based on the percolation theory of multi-region composite model,an improved model of well testing interpretation is developed,which is solved by the numerical differential method. In this model,the threshold pressure gradient,pressure sensitivity effect and fluid dynamic property during CO2 flooding in the low permeability oil reservoir are considered. Meanwhile,Simultaneous Perturbation Stochastic Approximation(SPSA)optimum searching algorithm is conducted to fit pressure curve and pressure derivative curve simultaneously. Finally,automatic matching and parameter interpretation method of well testing for CO2 flooding in the low permeability oil reservoir is proposed. The variation of interpretation parameters obtained from practical well testing curves is analyzed. The results show that consideration of low permeability characteristics would have an obvious influence on the interpretation of reservoir permeability,and the interpreted permeability after optimization is increased by 37.97% compared with the initial value. On the contrary,the interpreted pressure transmitting coefficient and compressibility variation index are decreased by 16.94% and 21.97% respectively from the original interpretations,which are considered to be influenced seriously by fluid heterogeneity. The applications reveal that the proposed interpretation method is easier to operate,and has good feasibility.