Well-Test Analysis of Hydraulic Fractured Wells in Fracture-Vug Low-Permeability Carbonate Reservoirs
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摘要: 缝洞型碳酸盐岩在我国油气资源储量中占有重要地位,因此,研究缝洞型碳酸盐岩压裂井井底压力变化具有重要意义.基于渗流力学基本原理,建立考虑应力敏感和启动压力梯度影响的碳酸盐岩渗流微分方程,利用点源函数理论、Laplace积分变换和Fourier余弦积分变换等方法求得Laplace空间顶底封闭、侧向无限大外边界点源解,通过对点源积分得到面源解;通过Stehfest数值反演得到实空间井底压力解并绘制试井曲线.通过模型对比分析验证了模型的正确性.结果表明:应力敏感系数越大,压力和压力导数曲线上翘越明显;启动压力梯度越大,压力和压力导数曲线上翘时间越早;压裂井打开程度越小,压力导数球形流特征越明显;窜流系数越大,“凹子”出现的时间越早;弹性储容比越大,“凹子”越宽越深.利用该模型可以有效地对缝洞型低渗透碳酸盐岩油藏压裂井的动态曲线进行分析.Abstract: The naturally vuggy and fractured carbonate rock plays an important role in China's oil and gas resources. Therefore, it is of great significance to study the characteristics of well bottom pressure in fracture-vug carbonate rock for hydraulic fractured wells. According to the basic principle of seepage mechanics, the well test model for carbonate reservoirs in view of the stress sensitivity and the threshold pressure gradient was established. The point source function method, the Laplace integral transform and the Fourier cosine integral transform were used to obtain the point source solution with impermeable top and bottom and lateral infinite boundary in the Laplace space. The surface source solution was obtained with the integral of the point source solution; the real-space well bottom pressure solution was obtained through the Stehfest numerical inversion and the well test curves were drawn. The simplified model solution matches with the related literature calculation results as to the threshold pressure gradient. The larger the stress sensitivity coefficient is, the more obviously the pressure and the pressure derivative curve will go up; the larger the threshold pressure gradient is, the earlier the pressure derivative curve will rise up; the smaller the open degree is, the more obvious the spherical flow characteristics will be; the larger the interporosity flow coefficient is, the earlier the 'concavity' will appear; the larger the elastic storage ratio is, the wider and deeper the 'concavity' will be. The proposed model can be effectively applied to analyze the well test curves of hydraulic fractured wells in naturally vuggy and fractured carbonate reservoirs of low permeability.
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Key words:
- hydraulic fractured well /
- carbonate rock /
- stress sensitivity /
- threshold pressure gradient /
- well test
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