川东南页岩气井岩溶浅表层安全高效钻井技术

Safe and Efficient Drilling Technologies for Shallow Karst Strata for Shale Gas Wells in Southeast Sichuan

  • 摘要: 四川盆地川东南构造带东胜背斜北部浅表地层岩溶发育,溶洞层级多,破碎带厚,尤其是嘉陵江组2段以上地层钻井液失返、井壁破碎带掉块严重,井下故障频发,多口井废弃。为了提高页岩气井的钻井效益,采取了优化井身结构、分井段优化钻具组合、分阶段优选钻井液,以及使用“组合法”注水泥固化破碎带井壁等技术措施,形成了川东南页岩气井岩溶浅表层安全高效钻井技术。该技术在东胜背斜北部区块10口井进行了现场应用,降低了浅表层井段发生井下故障的概率,提高了岩溶浅表层的钻井时效,浅表层成井率达到100%,机械钻速提高25.0%,钻井周期缩短63.2%。川东南页岩气井岩溶浅表层安全高效钻井技术为该区块高效开发提供了技术支撑。

     

    Abstract: In the northern part of the Dongsheng Anticline, located in the Southeast Sichuan Tectonic Belt of the Sichuan Basin, karst is developed in shallow strata, here karst caves have many levels, with thick fracture zones. In particular, drilling fluid is often lost during the drilling the strata above the 2nd member of Jialingjiang Formation, fracture zones of the borehole wall fall off seriously, which results in frequent downhole failures and abandonment of wells. In order to improve the drilling efficiency of shale gas wells, technical measures were taken, such as optimizing the casing program, improving the bottom hole assembly(BHA) by well sections, selecting drilling fluids by stages, and cementing the borehole wall with fracture zones by a combination method, which formed the safe and efficient drilling technologies for shallow karst strata for shale gas wells in southeast Sichuan, improving the drilling efficiency of shallow karst strata and shortened the drilling cycle. In addition, the technologies were applied in 10 wells in the northern block of the Dongsheng Anticline. As a result, the probability of downhole complications in well sections with shallow strata was reduced, and the well completion rate in shallow strata reached 100%. The rate of penetration (ROP) was increased by 25.0%, and the drilling cycle was decreased by 63.2%. Having safe and efficient drilling technologies for shallow karst strata for shale gas wells in Southeast Sichuan can provide technical support for efficient development of the block.

     

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