偏重偏心防斜钻具的研究与应用

大庆油田海拉尔、延吉、汤原等新探区地层倾角大,井外控制困难,严重影响了钻井速度并增加了钻井成本、研制的偏重偏心防斜钻具,经理论分析和现场试验证明,该钻具在井下旋转过程中所产生的离心力使其偏重段重边的稳定器始终贴向井壁,使钻具产生公转特性,有效地克服钻头自转引起的井斜,其离心力与转速平方成正比,转速越高产生的离心降斜力越大。该钻具能防斜、稳斜和降斜,其结构简单,安装方便,能较好地解决钻定向丛式井直井段的防碰技术难题。该钻具还适应地层倾角大的软到中硬地层,其偏心距的确定、优化组合钻具结构以及合理地选择钻压和转速,对防斜钻井及提高钻速均具有十分重要的作用。在12口井的现场试验中,井斜角均控制在1°以内,满足了钻定向丛式井造斜点井斜角小于1°的要求。

STUDY AND APPLICATION OF UNBALANCED AND ECCENTRIC INCLINING PREVENTION DRILLING TOOL

The existence of high formation dip and difficult deviation control in new exploration area of Daqing oilfield had great effect on drilling speed and increased drilling cost.The unbalanced and eccentric inclining prevention drilling tool can produce centrifugal force when it rotates downhole, the centrifugal force can keep the stabilizer at the heavy side of its unbalanced section close to borehole wall. This causes revolution of drilling tool and overcomes the deviation resulted from self-rotating bit. The centrifugal force is directly proportional to the second power of rotary speed. The higher the rotary speed is, the larger the centrifugal force can be produced. The tool can be used for inclining prevention, angle holding and angle dropping. It is of simple structure and easy installation. And it can solve the technical anticollision problem for straight section of directional cluster well. The tool can also be used in soft to middle-hard formation with high dip. The determination of its eccentriclty, the optimization of drill assembly structure and proper selection of WOB and rotary speed played a key role on inclining prevention drilling and increasing penetration rate. In the field test of 12 wells, deviation angle was controlled within 1°. This met the requirement of the deviation angle less than 1° at the kickoff point in directional cluster wells.