川西地区深井非常规井身结构设计与实践--以九龙山构造龙004-X1井为例

Design and application of unconventional casing program in deep wells,western Sichuan Basin:A case study of Well Long-004-X1 in the Jiulongshan Structure

位于四川盆地西北部的九龙山构造属于多产层超高压气藏,地质条件复杂,深井钻进过程中,三叠系雷口坡组—嘉陵江组地层缩径卡钻、嘉二段盐水侵、飞仙关组—吴家坪组漏喷同存等故障频发,严重影响了深部井段的钻井安全、加长了钻井周期。为此,通过总结九龙山构造深井钻井施工的特点与难点,以及已钻井常规井身结构不足的原因,结合建立的地层三压力剖面上存在的必封点位置,进而提出了一套深井非常规井身结构优化设计方案,即在深部井段提供3层套管层次,以满足分隔深部窄密度窗口井段地层的要求且可灵活调整,同时下部井段的固井环空间隙能够保证注水泥的基本要求。该设计方案在龙004-X1井实践获得成功,平均机械钻速达到了1.89 m/h,钻井周期缩短至418 d,同比邻井事故复杂损失时间降低了2 589 h,满足了该区深井安全快速钻井的需要,为该区开发二叠系超高压气藏积累了宝贵的经验。

With complex geological conditions, the Jiulongshan Structure in the northwestern Sichuan Basin can be classified as a gas reservoir with multiple pay zones and super high pressures. During the drilling of deep wells, some incidents occurred frequently, such as bit sticking in the Triassic Leikoupo and Jialingjiang Formations, saltwater invasion in Jia-2 Interval and coexistence of lost circulation and blowout in the Feixianguan and Wujiaping Formations. Consequently, drilling safety and drilling periods for intervals in deeper formations were affected significantly. Based on an analysis of the specific features of and difficulties in drilling operations for deep wells in the Jiulongshan Structure and the deficiency in the existing conventional casing program design, and combined with the positions to be sealed on pressure profiles of formations, an optimized design for deep wells were proposed for an unconventional casing program. Namely, a casing program with three easing layers were proposed for intervals in deeper formations to separate in- tervals with narrow-density window. The program can be adjusted flexibly. Moreover, annular clearances for cementation in lower intervals can satisfy the basic requirements for cement injection. With an average ROP up to 1.89 m/h and drilling time reduced to 418 days, the designed program were applied successfully in Well Long-004-X1. Compared with neighboring wells, this well had a reduced accident complex loss time of 2 589 hours. The new program can meet the demands of fast and safe drilling of deep wells in the Jiulongshan Region. Successful application of this program may provide precious experiences for the development of Permian gas reservoirs with super high pressures within the concerned area.