井打在大尺度溶洞内的缝洞型油藏试井模型

天然缝洞型碳酸盐岩油藏中存在大尺度溶洞。鉴于钻井过程中会出现钻杆放空、泥浆大量漏失等现象,建立了井打在大尺度溶洞内的试井解释物理数学模型。通过格林函数和Laplace变换法求得了拉氏空间井底压力表达式,对影响井底压力动态的主要因素进行了分析。结果表明,当井打在洞内时,由于洞内的渗透性要远好于洞外地层,因此压力导数曲线后期出现明显上翘,溶洞的大小主要影响压力从洞内传播到洞外的时间长短。以缝洞型碳酸盐岩油藏中溶洞内一口井为实例对其进行了试井解释,验证了该数学模型。

A well test model for wells drilled in big-size cavity of naturally fractured vuggy carbonate reservoirs

There are always big-size caverns in the naturally fractured vuggy carbonate reservoirs. In view of the phenomena of drill pipe discharge and slurry leakage during drilling operation, an interpretation model for well test of naturally fractured vuggy reservoir was developed in consideration of the wells drilled inside a big cavity. The equations for expressing the pressure at well bottom were obtained by using the concept of the Green's function and the Laplace transformation technique. The analysis on the affecting factors of dynamic pressure at well bottom indicates that the pressure derivative curve of the late stage will upward when the active well is inside the cavity, because the reservoir permeability in side the cavity is higher than that of outer zone. The size of cavity mainly de-termines the time of pressure transmitting to the boundary of the outer zone. A real testing explanation case of a well proved the in-terpretation model in a big-size cavity of the naturally fractured vuggy carbonate reservoir.