致密气藏3D裂缝压裂水平井非稳态渗流分析

Transient seepage analysis of multi-stage fractured horizontal well in tight reservoirs with consideration of 3D fractures

综合考虑压裂后裂缝未完全穿透地层厚度及致密气藏应力敏感性基础上,建立了致密气藏多段压裂水平井非稳态渗流模型,通过Laplace变换和无限傅立叶余弦变换得到了该模型半解析解。计算结果表明,致密气藏流体流动可划分为6个流动阶段,分别为早期线性流、早期拟径向流、过渡阶段线性流、过渡阶段拟径向流、拟稳态窜流和晚期拟径向流;应力敏感性主要影响晚期流动阶段,包括过渡阶段拟径向流、拟稳态窜流和晚期拟径向流;应力敏感系数γ越大,在晚期流动阶段压力和压力导数曲线"上翘"得越高;在早期渗流阶段,2D裂缝与3D裂缝压力导数曲线不重合,3D裂缝具有"球形流"渗流特征;垂向渗透率越小,"球形流"渗流特征表现得越明显;在垂向渗透率相同的情况下,穿透比越小,压力导数曲线上"球形流"特征越明显。

Considering that fracture does not fully penetrate the formation thickness after fracturing,and on the basis of stress sensitivity of tight gas reservoirs,an unsteady state seepage flow model of the multi-stage fracturing horizontal well in tight gas reservoirs was established. By applying Laplace transformation and infinite Fourier cosine transformation,the semi-analytical solution of the model was obtained. The calculation results show that the gas flow can be divided into six flow regimes,including early-time linear flow,early-time pseudo-radial flow,intermediate-time linear flow,intermediate-time pseudo-radial flow,pseudo-steady cross flow and late-time pseudo-radial flow. The stress sensitivity effect mainly affects the flow in the late stage,involving intermediate-time pseudo-radial flow,pseudo-steady cross flow and late-time pseudo-radial flow. The type curves ascend with the increasing of stress sensitivity coefficients. In the early seepage stages,pressure derivative curves of 2D and 3D fractures do not overlap. 3D fractures show the seepage characteristic of the spherical flow. The smaller the vertical permeability is,the more obvious the seepage characteristic of the ＂ spherical flow＂ is. Under the same vertical permeability,the ＂ spherical flow＂ characteristic on the pressure derivative curve is more apparent with the decreasing of penetrating ratio.