井打在溶洞外的缝洞型油藏数值试井模型

缝洞型碳酸盐岩油藏多发育大尺度的溶洞和裂缝,非均质性极强。这类油藏不能使用常规的连续介质理论描述。根据缝洞型碳酸盐岩油藏的特征,结合地震、地质等资料,建立了井未钻遇溶洞的缝洞型碳酸盐岩油藏数值试井物理数学模型。利用有限元方法对模型进行求解并绘制了试井样版曲线,对影响井底压力动态的主要因素进行了分析。研究表明:当井打在洞外时,由于洞内的渗透性远优于洞外地层,压力导数曲线后期出现明显下掉,溶洞的尺寸主要影响压力导数曲线的下掉幅度。模型解释结果与实测数据对比分析表明,该试井模型具有较高的预测精度,能够为碳酸盐岩油藏的试井分析提供理论指导。

A numerical well test model for wells drilled out of big-size cavity of fractured carbonate reservoirs

Conventional continuous multiple medium theories are not suitable for describing the fractured-cavernous carbonate reservoir with big-size fractures and caves. An interpretation model for well test of naturally fractured vuggy reservoir has been developed with consideration of wells drilled outside a big cavity. The model equations are solved with the finite-element method. The analysis of the affecting factors of dynamic pressure at well bottom indicates that the pressure derivative curve of the late stage will go down and form a concave because of the high permeability of the cave. The scale and permeability of the cave mainly affect the amplitude of the pressure derivative reduction. The predicted model has a good agreement with the field test. This can provide a theoretical basis and guidance for well test interpretation of carbonate reservoir.