水平井分段压裂过程对水泥环完整性影响

水平井分段压裂过程中出现的套管损坏和水泥环完整性问题日益引起关注。目前研究的重点包括地层滑移、套管和水泥环受力等，而对分段压裂过程造成影响的研究较少。为了建立水平井分段压裂水泥环完整性计算模型和方法，首先，利用有限元软件建立有限元模型，得到水平井分段压裂过程中水泥环弹性区和塑性区分布；其次，利用离散元模型分析有限元中得到的塑性变形区域，获取塑性变形区域内水泥环的微裂纹数量；最后，依据水泥环塑性区分布和微裂缝数量得到水泥环的完整性评价。研究表明，除了套管和水泥环刚度比、套管偏心率和水泥环缺陷对水泥环完整性有影响，水平井的压裂段数的影响也较为明显。随着套管和水泥环刚度比增加，水泥环完整性增强；套管偏心率增加和水泥环存在缺陷降低水泥环完整性；水平井压裂段数越多，水泥环完整性降低。

Effect of Horizontal Staged Fracturing on the Integrity of Cement Annulus

Casing damage and the annulus integrity in horizontal multiple-staged fracturing becomes major concerns in the industry. More focus was placed on formation slippage from fracturing fluid leakage into the faults, and stress analysis of casing and annulus, but less on the effect of multiple staged fracturing. In this paper, a model is built up for analyzing the annulus integrity in multiple-staged fracturing, with FEM and DEM. FEM model being setup is employed to obtain the elastic and plastic regions during fracturing, a DEM model acquiring stresses and strains from FEM is carried out to calculate the number of micro-cracks, and both plastic region and micro-cracks of the cement annulus are combined to evaluate annulus integrity. The research shows that besides the effect of stiffness ratio between casing to annulus, casing eccentricity, the multiple stages affect the annulus integrity significantly. The annulus integrity improves as stiffness ratio between casing to annulus increases, and the casing eccentricity and defects deteriorates it. The annulus becomes less integrated as fracturing stage number rises.