四川盆地元坝气田超深水平井井身结构优化与应用技术

四川盆地元坝气田具有超深、高含硫、高压特性,地质环境异常复杂。为此,在充分总结前期探井和开发评价井经验教训的基础上,从完井方式入手,综合考虑地层3个压力剖面、必封点、邻井井下复杂情况、完井方案及钻井成本等因素,采用自中间向两边推导的井身结构设计方法,优化确定出了元坝气田超深水平井的5层套管层序的井身结构。生产套管封隔器坐封位置以上采用高抗硫材质,封隔器坐封位置以下采用国产高镍基抗蚀合金套管,既满足了高含硫气田的长期安全生产,又减少了镍基合金套管的使用量,降低了开发成本。该井身结构在实际生产应用中,有利于气体钻井安全、高效、连续施工,将高压、易塌的陆相地层和海相地层分开,用厚壁套管封固膏盐层,将低压的上二叠统长兴组与其上部的海相高压地层分开,大幅度减少了复杂故障处理时间,有效保护了储层;同时,新完成的超深开发水平井与先期4口开发评价水平井相比,平均钻井周期减少130.3 d,大幅度提高了钻井技术经济指标。

Casing program optimization technology for ultra-deep horizontal wells in the Yuanba Gasfield,Sichuan Basin

The Yuanba Gasfield in the Sichuan Basin is characterized by ultra-depth, high sulphur contents, high pressure, and extremely complex geological setting. Therefore, on the basis of summarizing the experiences and lessons from the previous exploratory wells and development appraisal wells, with the completion mode as a starting point, and with a comprehensive consideration of three pressure profiles, sealing point, downhole complexities of offset wells, well completion plan and drilling cost, a casing program design method deducing from the middle towards the upper and lower ends of the casing was adopted to optimize and determine a 5-layer casing program for ultra-deep horizontal wells in the Yuanba Gasfield. High sulfur-resisting casing above the packer setting location of the production casing and home-made high-nickel base anticorrosion alloy casing below it were suggested, which not only meets the requirement of long-term safe production of high-sulphur gas fields, but also reduces the use of nickel base alloy casing and thus reduces the development cost. In real drilling practices, this casing program is conducive to safe, efficient and continuous gas drilling; it separates the high-pressure and easy-sloughing terrestrial strata from the marine strata, seals the gypsum-salt bed with heavy casing, and separates the low-pressure Changxing Formation from the upper marine high-pressure zone, which can reduce the complexities handling time significantly and effectively protect the reservoir. Compared with the four development evaluation horizontal wells drilled at early stage, the newly drilled ultra-deep development horizontal wells have an average drilling period reduction of 130.3 d, indicating substantial enhancement in technical and economic index of drilling.