A method for optimizing and controlling rocking drillstring–assisted slide drilling

Rocking the drillstring at the surface during slide drilling is a common method for reducing drag when drilling horizontal wells. However, the current methods for determining the parameters for rocking are insufficient, limiting the widespread use of this technology. In this study, the influence of rocking parameters on the friction-reduction effect was investigated using an axial–torsional dynamic model of the drillstring and an experimental apparatus for rocking-assisted slide drilling in a simulated horizontal well. The research shows that increasing the rocking speed is beneficial improving the friction-reduction effect, but there is a diminishing marginal effect. A method was proposed to optimize the rocking speed using the equivalent axial drag coefficient–rocking speed curve. Under the influence of rocking, the downhole weight on bit (WOB) exhibits a sinusoidal-like variation, with the predominant frequency being twice the rocking frequency. The fluctuation amplitude of the WOB in the horizontal section has a linear relationship with the rocking-affected depth. Based on this, a method was proposed to estimate the rocking-affected depth using the fluctuation amplitude of the standpipe pressure difference. Application of this method in the drilling field has improved the rate of penetration and toolface stability, demonstrating the reliability and effectiveness of the methods proposed in this paper.