页岩气体积压裂过程中套管失效机理研究

Study on failure mechanism of casing in stimulated reservoir volume fracturing of shale gas

为了研究体积压裂过程中套管失效问题,基于页岩气水平井X-1h钻完井资料,提出了微地震数据反演方法,并结合岩石断裂力学和岩石损伤力学,建立了X-1h体积压裂地层-多簇射孔-套管有限元模型。有限元结果表明:体积压裂范围内的地应力场发生明显变化,甚至出现"张应力"区和"零应力"区的应力反转现象,该特征将不同程度地使套管在地层中出现"悬空"状态,导致套管沿其径向产生一定程度的挠度变形,沿轴向套管呈现"S"型变形。适当增加压裂段与段之间的间距,缩短多簇射孔压裂段的有效长度,可以有效地降低或控制水平段套管的"S"型变形量。该研究方法和研究成果为体积压裂技术的套管变形失效控制以及页岩气安全生产提供了理论依据。

Aiming at the problem of casing failure in the process of stimulated reservoir volume fracturing,an inversion method of microseismic data was put forward based on the drilling and well completion data of X- 1 h shale gas horizontal well. A finite element model of the stimulated reservoir volume fracturing formation,multi- clustering perforation and casing was established for X- 1 h well by combining with rock fracture mechanics and rock damage mechanics. The results showed that the in- situ stress field in the range of stimulated reservoir volume fracturing changes obviously,even the stress reversal phenomena of tension stress area and zero stress area occur. This characteristic causes the ＂ overhang＂ status of casing in the formation with different degree,which results in a certain extent deflection deformation of casing in the radial direction and a S-shape deformation of casing in the axial direction. The S- shape deformation of casing in horizontal section can be effectively decreased or controlled by appropriately increasing the interval of fracturing segments and shortening the effective length of multi- clustering perforation fracturing segments. The method and achievements provide the theoretical basis for the control of casing deformation failure with stimulated reservoir volume fracturing technology and the work safety of shale gas.