井筒屏障完整性及其优化设计——以CO2吞吐井为例

Wellbore barrier integrity and design optimization: A case study on CO2 huff and puff well

随着我国各大油田进入开发中后期,老井“二次采油”甚至“三次采油”所引发的井筒完整性问题频发。现场老井完整性建设不足,增产措施带来的苛刻工况造成井筒管柱腐蚀严重,威胁管柱服役寿命以及井筒完整性,给油田造成极大的经济损失的同时也给油气田安全运行带来隐患。为此,结合我国油气田开发现状,分析了现有井筒完整性标准的不足和重点研究方向。介绍了腐蚀完整性管理概念,并在此基础上,以CO2吞吐井为例提出了基于井筒腐蚀风险与载荷风险双重作用的井筒屏障优化方法,确定了吞吐井的失效敏感区域和服役寿命。结果显示:实例井极限吞吐轮次为7轮;油管失效敏感区域为800~1 500 m,套管失效敏感区域为1 700~2 000 m,建议在失效敏感区域进行重点防护。该研究为各油田依据自身实际情况,本着“全局把控,重点防护,经济有效”的思想开展井筒屏障设计,延长老井免修期,建立科学性、适用性、效益性的完整性管理体系具有重要意义。

As the major oil fields in China step into the middle and late stages of development, the wellbore integrity accidents caused by the “ secondary oil recovery” of old wells and even the “ enhanced oil recovery” happen frequently. The on-site integrity construction of old wells is insufficient, and the harsh working conditions brought by the stimulation measures leads to serious corrosion of pipe strings and threatens the service life of pipe strings and the wellbore integrity, so as to bring about great economic loss to the oilfields while resulting in the hidden troubles to the safe operation of oil fields. The deficiencies of existing wellbore integrity standards and the important research directions were analyzed based on the development status of domestic oil and gas fields. Then, the concept of corrosion integrity management was introduced, and the wellbore barrier optimization method based on the dual action of wellbore corrosion risk and load risk was proposed with CO2 huff and puff well as the example. Finally, the failure sensitive region and service life of huff and puff well were determined. It is indicated that limit huff and puff cycles of the case well is 7, the tubing failure sensitive region is 800-1 500 m and the casing failure sensitive region is 1 700-2 000 m. It is suggested to carry out important protection in the failure sensitive regions. The research results are of great significance to design the wellbore barrier, prolong the workover interval of old wells and establish the scientific, applicable and beneficial integrity management system according to the idea of “global control, key protection and economy and efficiency” based on the actual situations of each oilfield.