导流能力不均匀的部分压开垂直裂缝试井分析方法

考虑水力压裂不能完全压开厚层,压裂后支撑剂无法到达裂缝尖端,缝内导流能力分布不均匀,采用两段导流系数定量表征裂缝内不均匀的导流能力,建立了导流能力不均匀的部分压开垂直裂缝试井模型。运用Laplace变换求解渗流方程,获得考虑井筒储集效应与表皮效应的井底压力解,绘制典型曲线图版,模型参数敏感性分析表明:裂缝内不均匀分布的导流系数会影响井底压力响应特征,差异程度取决于裂缝两端导流系数比。压力与压力导数在双对数曲线上会出现斜率介于0.25～0.5的特征直线段。用本文提出的模型对新疆油田某油井试井解释表明实际储层厚度大于压裂厚度,为进一步改善压裂效果和提高解释精度提供了依据。

A Semi-Analytical Solution for a Partially Penetrating Well intercepting with a Two Segments Vertical Fracture

Hydraulic fracturing cannot completely open thick layers. The proppant delivery is usually restricted near fracture tip during the process of hydraulic fracturing, resulting in huge difference of fracture conductivity distribution. This paper introduces a concept of unequal conductivity to characterize the unpropped fracture. We then formulate the flow model for a partially penetrating well in vertical anisotropy formation. And we employed Laplace integral transformation to find the solution with consideration of wellbore storage and skin effects. We graphed the pressure and its derivative on a log-log plot, and investigated the effects of major model parameters on pressure responses. The results indicate that lower fracture conductivity at the tip does affect the BHP response. The degree of pressure change depends on the degree of fracture conductivity reduction. We observed a characteristic line with a slope between 0.25 and 0.5 on the pressure derivative curve. Finally, our model was applied to interpret field transient pressure data from the Xinjiang oil field, which was examined to be an effective tool to estimate the fracturing thickness and the effect after hydraulic fracturing. Moreover, it can effectively improve the accuracy of well test interpretation.