海上钻井表层导管表面摩擦力变化机理研究

表面摩擦力对海上钻井表层导管承载力和井口稳定性具有至关重要的作用,但关于表层导管喷射过程中和喷射完成后的表面摩擦力变化机理尚不清楚。为此,建立了表面摩擦力的计算模型,分析了导管喷射过程中和喷射完成后土体应力状态的变化情况,认为在表层导管喷射下入过程中超孔隙水压力的形成和消散是表面摩擦力变化的主要原因。现场模拟试验结果表明:表层导管底部传感器测得的径向应力较大;各层的有效应力随时间的延长而下降,在达到一定值后又逐渐增大,这与钻井过程中桩的径向应力变化规律吻合;喷射完成后,土体表面摩擦力随时间的延长呈现出非线性增加的趋势,变化率在前12 h逐渐上升,72 h之后表面摩擦力曲线逐渐趋于平缓。研究结果可为表层导管的现场作业和后续研究提供理论依据。

Study on the Variation Mechanism of Skin-friction Force on Surface Conductor in Offshore Drilling

Skin-friction force plays a vital role in the bearing capacity of surface conductor and wellhead stability in offshore drilling,but the variation mechanism of skin-friction force during and after the jetting of surface conductor is not clear.Therefore,in the article,the authors built a calculation model of skin-friction force,analyzed the changes of soil stress state during and after the jetting of surface conductor,and believed that the formation and dissipation of excess pore water pressure during the jetting entry of surface conductor are the main reasons for the change of skin-friction force.Field simulation test results show that the radial stress measured by the sensor at the bottom of the surface conductor is large;the effective stress of each layer decreases with the extension of time,and increases gradually after reaching a certain value,which is consistent with the change law of radial stress of pile during drilling;after jetting,the skin-friction force of soil shows a nonlinear increasing trend with the extension of time,the change rate gradually increases in the first 12 h,and the skin-friction force curve gradually tends to be flat after 72 h.