卡点精确计算方法与应用

Accurate free point calculation method and its application

钻井过程中由于地层或操作不当等因素导致偶发的卡钻,不仅延长了钻井周期,而且可能导致次生故障甚至埋钻等事故,造成严重经济损失。目前,现场采用的提拉法计算卡点方法没有考虑井内管柱所受摩擦阻力影响,导致计算出的卡点深度误差随着摩阻增加而增加,难以适用于高摩阻直井及大斜度井。基于卡点深度计算原理,运用胡克定律,利用上提、下放过程中相同钩载条件下管柱在井眼内所受摩擦阻力大小相等、方向相反的特点,推导了可消除套管内管柱摩擦阻力影响的卡点深度计算公式,同时提出了该计算公式配套的操作方法和实施步骤。实践证明,该方法计算卡点深度结果准确,具有较强的实用价值。

In the process of drilling,formation factors or misoperation can lead to incidental pipe sticking,which not only extends the drilling cycle,but also may cause secondary failure and even pipe burying and other accidents,resulting in great economic loss.At present,the pulling method adopted on site to calculate free points doesn’t consider the influence of friction drag applied on downhole pipe strings,which increases the calculation error of free point depth with the increase of the friction drag,so it is hardly applicable to high-friction vertical wells and high-angle deviated wells.In this paper,the free point depth calculation formula which can eliminate the influence of the friction drag applied on the pipe string inside the casing was derived by making use of the performance that the friction drag applied on the downhole pipe string under the same hook load in the process of pulling and lowering is equal in value and opposite in direction,according to the free point depth calculation principle and the Hooke’s Law.What’s more,the operation method and implementation step corresponding to this calculation formula were put forward.The practice proves that this method can calculate the free point depth accurately and has a great practical value.