水平井固井滑套结构对起裂压力影响规律分析

在水平井无限级固井滑套分段压裂中,较高的起裂压力增加了压裂现场施工的难度和风险,是压裂施工遇到的主要问题之一。为有效降低起裂压力,以鄂尔多斯盆地无限级固井滑套压裂为工程背景,建立了地层-水泥环-压裂滑套耦合系统非线性有限元模型,分析了固井滑套长方形、斜向型、圆形孔口以及长方形孔口参数对压裂起裂压力的影响规律。结果表明,在地质力学参数相同条件下,3种孔口形状滑套的起裂压力均随孔口面积的增大而减小;而在孔口面积相同的条件下,长方形孔口比圆形和斜向型更能有效降低储层起裂压力。对于长方形孔口滑套,其宽度对降低起裂压力不明显;其孔口长度增加、数量增多、方位角减小对降低起裂压力十分明显;若孔口方位角不为零,会导致起裂位置变化,引起水力压裂起裂更为困难。

Effect Regularity Analysis of the Cementing Sleeve Structure ofHorizontal Wells on the Initiation Pressure

In the staged fracturing of horizontal wells with the infinite stage cementing sliding sleeve,the high fracture initiation pressure increases the difficulty and risk of fracturing treatments,and is also one of the main problems encountered in the fracturing process.In order to reduce the fracuture initiation pressure,based on the practical application of the infinite stage cementing sliding sleeve in fracturing in the Ordos Basin,the nonlinear finite element model of formation?cement sheath?fracturing sleeve coupling system was established.The effects of the rectangular,oblique and circular orifices on the fracture initiation pressure have been analyzed.It shows that with the same geomechanical parameters of formations,for all the three types of orifices,the fracture initiation pressure decreases with growth of the orifice size.With the same orifice size,the fracture initiation pressure is the lowest when the rectangular orifice is used.For the rectangular orifice,its width has no obvious impacts on the fracture initiation pressure,while the pressure reduces significantly with an increase in the orifice length and number of orifices and a decrease in the azimuth angle.With an azimuth angle unequal to zero,the hydraulic fracture will turn around and propagate along the direction perpendicular to the minimum horizontal principal stress.