多压力系统中钻井安全作业密度的确定和应用——以四川盆地五探1井?333.38 mm井眼钻井为例

四川盆地东部达州—开江古隆起上的风险探井——五探1井设计?333.38 mm钻头钻经的地层层位多、压力系统复杂,钻井过程中要钻遇气层、易漏层、易坍塌层,如何确保合理的钻井液密度以安全顺利钻达目的层是一个必须要研究并解决的问题。为此,通过分析研究该井工程技术难点及处理技术手段,在总结井控安全密度、垮塌抑制密度、缩径抑制密度、厚泥饼临界密度、漏失密度等5种安全作业密度求取方法的基础上,提出了安全作业密度的解决方案并进行了现场应用。结果表明:(1)在气显示活跃、缩径井段,选择井控安全密度、缩径抑制密度二者中高者为安全作业密度;(2)在井漏、垮塌为主的井段,选择井控安全密度、垮塌抑制密度二者中高者为安全作业密度,再辅以堵漏和其他工程技术措施提高地层承压能力;(3)五探1井顺利完成?333.38 mm井眼段钻井,井身质量全优,?273.05 mm套管顺利下到位。结论认为,利用上述解决方案成功地破解了该井多压力系统安全钻井的技术难题。

Determination of drilling fluid density for safety drilling in multi-pressure system strata and its Application: A case study on Ø333.38 mm hole section of Well Wutan1 in the Sichuan Basin

According to the design of Well Wutan1, the strata drilled by Ø333.38 mm bit is composed of multiple intervals with a complex pressure system, and gas layers and the layers where circulation loss and collapse tend to happen easily will be encountered, so how to keep a rational drilling fluid density so as to reach the target layers smoothly shall be researched and solved. In this paper, the engineering and technical difficulties and treatment technologies of Well Wutan 1 were analyzed. Then, the solution of safety operation density was put forward after 5 calculation methods for safety operation density were summarized, including well control safety density, collapse suppression density, hole shrinkage suppression density, critical density of thick mud cakes and leakage density. Finally, the solution was applied on site. And the following research results were obtained. First, in hole shrinkage sections or the sections with active gas shows, the safety operation density was the higher one between well control safety density and shrinkage suppression density. Second, in the hole sections where circulation loss or collapse was dominant, the safety operation density was the higher one between well control safety density and collapse suppression density. Besides, plugging and other technological measures were adopted to improve the formation-bearing capacity. Third, the Ø333.38 mm hole of Well Wutan 1 was drilled smoothly, and the wellbore was of high quality and Ø273.05 mm casing was run to the designed position smoothly. In conclusion, the safety drilling difficulties of Well Wutan 1 in multi-pressure system strata are solved successfully by using the above mentioned solutions.