致密油藏体积压裂水平井变窜流系数模型研究

A study on model of volume fracturing horizontal wells with variable interporosity flow coefficient in tight oil reservoirs

水平井结合水力压裂技术已经成为高效开发致密油藏的有效手段。该文针对水平井经过压裂后在主裂缝周围形成的微裂缝密度随着到主裂缝的距离递减变化的特点,基于双重介质模型建立了窜流系数随着到主裂缝距离变化的体积压裂水平井线性流动模型,通过引入Airy函数及Laplace变换求得了模型的解析解,运用Stehfest数值反演技术得到了在实空间中的解,最后对定产量生产时的井底压力动态及定井底流压生产时的产能动态进行了分析。研究结果表明:井底压力及产能动态曲线可分为4个流动阶段,基质形状假设为球形及柱状对结果影响不大;窜流系数最大值越大,总系统线性流就发生得越早,双线性流阶段无因次产能就越大;窜流系数最小值越大,双线性流发生的时间越早,而且持续的时间越长,总系统线性流阶段无因次产能越大。研究结果可为致密油藏压力及产能动态的合理分析提供科学依据。

Horizontal wells with volume fracturing technology have become an efficient way to produce from tight oil reservoirs. Considering the density of microfractures is decreasing from the distance of the main hydraulic-fracture plane. In terms of variable interporosity flow coefficient of the distance from the fracture face and dual porosity oil reservoir model, a linear flow model for volume fracturing horizontal wells in tight oil reservoirs is established. The analytical solution is deduced in Laplace space, based on the Stehfest numerical inversion algorithms and Airy function, and the analytical solution in real space is obtained. Last, the bottom-hole pressure with constant rate and the rate with constant bottom-hole pressure of volume fracturing horizontal wells is analyzed. The results show that the pressure transient and productivity transient curves can be divided into four different flow regimes, and there is almost no difference on the curves, which the geometry of matrix-block is assumed as spherical and cylindrical. The greater the λmax is, the earlier of the total-system linear flow occurs, and the higher the production is during the bilinear flow period. The greater the λmin is, the earlier of the bilinear flow occurs, the longer it lasts, and the higher the production is during the total-system linear flow period. The results obtained can provide scientific basis for reasonable analysis to pressure and productivity behavior of the tight oil reservoirs.