水力锚锚爪结构对套管变形及挤压应力的影响

为优化水力锚爪结构参数,减小水力锚爪结构对套管的损伤,针对普通螺纹齿形锚爪和镶硬质合金锚爪结构,利用材料力学理论建立了镶硬质合金锚爪接触处套管所受的挤压应力公式,采用有限元法分析了普通螺纹齿形锚爪接触处套管的变形及挤压应力。分析表明,普通螺纹齿形锚爪和镶硬质合金锚爪均会对套管产生不同程度的损伤;在相同油管内外压差作用下,与镶硬质合金锚爪相比,普通螺纹齿形锚爪接触处套管所受挤压应力和径向变形较小,对套管损伤最小。研究结果表明,试油压裂用水力锚结构应采用螺纹齿形设计;在相同油管内外压差作用下,镶硬质合金锚爪接触处套管所受挤压应力随牙齿楔角增大呈幂律指数降低,随牙柱直径增大呈幂律指数下降,随锚爪直径增大呈多项式增大,随牙齿后角呈指数增大,但增大幅度较为平缓,随轴向载荷增大呈多项式增大,但增大幅度较小;建议牙齿楔角取10°,锚爪牙柱直径取10~12 mm,锚爪直径取40~50 mm。研究结果为水力锚锚爪结构设计提供了理论依据。 

The Effect of Hydraulic Anchor Structure on Casing Deformation and Extrusion Stress

In this paper, an analysis is conducted on the structural characteristics of ordinary and carbide hydraulic anchor so as to optimizeits structure to reduce its damage on casings. A formula for the extrusion stress on the casing at the biting position of carbide hydraulic anchors is derived based on material mechanics theory, and the casing deformation and extrusion stress at the biting position of ordinary hydraulic anchors is analyzed by using finite element method. It was demonstrated that casings are damaged at different degrees by ordinary and carbide hydraulic anchors. Ordinary hydraulic anchors will cause less radial deformation and extrusion stress on the casing than carbide hydraulic anchors under the same tubing pressure differential.Based on the analysis results, screw tooth design should be adopted in hydraulic anchors.When the tubing pressure difference is the same,extrusion stress exerted on the casings at the biting position of carbide hydraulic anchors decreases by power-law index with wedge angles and tooth diameters, but increases polynomially with anchor diameters and axial loads (in smaller amplitude), and increases exponentially with anchor tooth back angles gently. Results indicate setting the wedge angle at 10°, the anchor tooth diameter 10-12 mm and the anchor diameter 40-50 mm.Research provides a theoretical basis for the structure design of hydraulic anchors.