页岩气藏部分压开压裂井压力动态分析

 压裂井因为能够提高单井产量和降低成本在页岩气藏的开发过程中得到了广泛应用,然而在实际生产过程中由于页岩储层普遍厚度较大,难以被完全压开。为此,综合考虑页岩气的解吸、扩散和渗流特征,建立了页岩气藏部分压开压裂井的渗流模型,应用Laplace变换、Fourier变换和Duhamel原理,结合Stehfest数值反演对模型进行求解,绘制了相应的压力特征曲线并对其进行了流动阶段的划分,讨论了相关参数对压力动态的影响。研究表明,页岩气藏部分压开压裂井的压力特征曲线存在7个主要流动阶段;裂缝的压开程度主要影响球形流阶段表现的明显程度及压力导数曲线前期位置的高低,解吸系数主要影响压力导数曲线下凹的深度,无因次储容系数主要影响压力导数曲线下凹的宽度和深度,无因次窜流系数主要影响解吸扩散阶段出现的早晚。所获得的结果可为利用压裂井合理高效地开发页岩气藏提供理论支持。

Transient Pressure Analysis of Partial Open Fractured Wells in Shale Gas Reservoirs

Fractured wells find widespread applications in the development process of shale gas reservoirs because of the enhancement of the per well production and the reduction of the cost. However, the reservoir is difficult to be completely opened in practice because of the large thickness of the shale gas reservoir. In this paper, according to the characteristics of desorption, diffusion and seepage, a seepage model of partial open fractured wells in shale gas reservoirs is established. The Laplace transform, the Fourier transform and the principle of Duhamel in combination with the Stehfest numerical inversion algorithm are used to obtain solutions based on the model. The pressure characteristic curves are obtained. The flowing phases are divided in the pressure characteristic curves. The influence of the relevant parameters on the pressure dynamic characteristics is analyzed. It is shown that there are seven main flow stages in the pressure characteristic curves for partial open fractured wells in shale gas reservoirs. The open degree has a main effect on the appearance of the spherical flow period and the position of the pressure derivative curve in the early time. The desorption coefficient has a primary effect on the depth of the dip in the pressure derivative curve. The dimensionless storativity ratio has a major effect on the depth and width of the dip in the pressure derivative curve. The dimensionless transmissivity ratio has a primary effect on the starting time of the desorption and the diffusion in shale reservoirs. The results can provide a theoretical support for the high-efficiency development of shale gas reservoirs using fractured wells.