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基于离散裂缝的多段压裂水平井数值试井模型及应用

A NUMERICAL WELL TEST MODEL FOR MULTI-FRACTURED HORIZONTAL WELLS BASED ON DISCRETE-FRACTURE MODEL AND ITS APPLICATION

  • 摘要: 水平井压裂技术已经成为开发低渗透油气藏、页岩气藏和致密气场等非常规油气藏的关键技术。基于离散裂缝模型,对裂缝进行简化,建立了二维多段压裂水平井有限导流数值试井模型,利用有限元方法求解模型,获得多段压裂水平井试井理论曲线和压力场特征。分析表明:多段压裂水平井的试井理论曲线一共分为七个阶段:井筒储存段、裂缝线性流段、裂缝-地层双线性流段、裂缝干扰段、地层线性流段、系统径向流段和边界作用段,其中裂缝-地层双线性流段和裂缝干扰是其典型特征。分析了裂缝数量、裂缝间距、裂缝不对称、裂缝不等长和裂缝部分缺失等因素对试井理论曲线的影响,结果表明:裂缝数量和裂缝间距对试井理论曲线的影响最大。较多的裂缝、较大裂缝间距、对称的裂缝和等长的裂缝有利于降低压裂水平井井底的流动阻力,提高产能。将建立的数值试井模型应用于四川盆地一口多段压裂水平井的压力恢复测试的数值试井解释,结果表明:本文建立的模型可以较好的拟合压力恢复测试数据,可以获得裂缝的导流能力和裂缝长度,为压裂效果评价和压裂设计提供指导。

     

    Abstract: Horizontal well fracturing technology has become a key technology in the development of low permeability oil and gas reservoir, shale gas and tight gas and other unconventional reservoirs. This paper developed a numerical well test model for multi-fractured horizontal wells based on discrete-fracture model which simplifies the fractures as lines. The finite element method was applied to solve the mathematical model and get the type curves and pressure profiles. The log-log type curve of bottom hole pressure can be divided into seven stages: wellbore storage, fractures linear flow, fractures-formation bilinear flow, fractures interacting flow, formation linear flow, radial flow, and boundary domain flow. Among them, the fractures-formation bilinear flow and fractures interacting flow are the two typical features. The effect of fractures’ numbers, distance of fractures, asymmetry of fractures, fractures with unequal length, and some fracturing failure on the transient pressure and derivative responses were also studied. The analysis results showed that the number of fractures and the spacing between fractures have the greatest influence on the type curves. More fractures, fractures with larger distance, symmetrical fractures with equal length were propitious to reduce the flow resistance of bottom hole and increase production capacity. The multi-fractured well test model proposed in this paper was applied in the interpretation of build-up tests of multi-fractured horizontal wells. The results of a field case in Sichuan Basin shown that the model matched with the tested data very well. The developed numerical well test model can be used to obtain the parameters of reservoirs and fractures, and to provide technical support for the design and evaluation of hydraulic fracturing.

     

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