提拉-释放法套管下入机理

Mechanism analysis of pull-up and quick release technique during casing running process

关键词:  套管下入  提拉-释放法  摩阻  应力波  影响因素

Key words:  casing running  pull-up and then release method  friction  stress wave  influence factors

摘要:

提拉-释放法是钻井现场下套管遇阻时最常用且易用的增加套管下入能力的方法,但其应用主要是凭经验操作,缺乏机理分析和必要的理论指导。根据提拉-释放后一段水平井眼中套管柱的运动机理和实际井眼中套管柱的运动机理本质上相同这一认识,建立提拉-释放法套管下入机理分析模型,阐明该方法的套管下入机理,以此为基础研究套管长度、摩阻系数、轴向压力、无因次提拉力和管柱释放方式等因素对套管下入能力的影响。结果表明:提拉-释放法进行套管下入是利用提拉-释放过程产生的应力波减小摩阻,即使在原始轴向压力小于总摩阻的情况下仍然可以推动套管柱前进;套管长度、摩阻系数与提拉-释放法套管下入的单次轴向位移呈负相关,轴向压力、无因次提拉力与提拉-释放法套管下入的单次轴向位移呈正相关,快速释放管柱时的单次轴向位移明显更大。

Abstract:

In order to solve a suck-up problem during casing running process in well completion, the most frequently used and accessible method is the pull-up and then quick release technique. However, its application is mainly based on experience, and lack of mechanism analysis and theoretical guidance. In essence, the motion of the casing string in a section of horizontal well after a pull-up and then quick release is similar to that in an actual wellbore, and thus an analysis model for the mechanism of casing running during the pull-up then release process was established, and corresponding programs were coded. The influences of many factors on the trip-in ability of the casing have been analyzed, including the casing length, friction coefficient, axial pressure, dimensionless tensile force and different release ways. The results indicate that casing running during the pull-up and then release can make use of the stress wave produced in the process to reduce friction, which can push the casing to move forward even though the original axial compression force is less than the total friction. The length of the casing and the friction coefficient are negatively correlated to the axial movement of the casing, while the axial pressure and dimensionless tensile force are positively correlated to the axial displacement during the pull-up and then release process. Meanwhile, the axial movement of the casing in a rapid release process is much larger than that in a slow release process.