哈萨克斯坦里海盆地M区块浅层气井控技术

Well control technology for shallow gas drilling at the M block,Caspian Basin in Kazakhstan

浅层气难于防控的主要原因是气层埋藏浅,一旦打开气层,气体很快窜到井口,还没有来得及采取措施,已经发生井喷或井喷失控,即便是控制了井口,也容易憋破地层,气体窜至地面,造成财产损失、井眼报废和环境污染。哈萨克斯坦里海盆地的M区块,在270～510m井段的不同层位埋藏着十分活跃的浅层气。钻井中为了做好浅层气防控工作和提高固井质量,对M区块前期发生的浅层气井喷情况采取了一系列行之有效的措施:①优化钻井设计;②第1次开钻井段,采用大排量循环固井,水泥浆返至地面,保证324mm套管固井质量;③第2次开钻井段要注重1次井控;④第3次开钻井段采用设计钻井液密度和失水的下限,控制钻时,保证井眼清洁;⑤第4次开钻在碳酸盐岩地层钻进,注重硫化氢防护和防漏。推行上述配套技术,目前在该区块已经完井42口,避免了井喷失控,保障了钻井工程的安全、质量和速度,保护了资源和环境,为同类浅层气井的钻井施工提供了经验。

The shallow burial depth is the main reason for difficult well control of shallow gas drilling.Once the reservoir is opened,gas will migrate to the well head rapidly,far before any precautions will be taken the well already begins to blow out and soon is out of control.Even the wellhead is under control eventually,the formation is easily fractured under pressure,and gas will flee out to the ground,resulting in equipment damage,well abandonment,and environment contamination.At the M block,Caspian Basin in Kazakhstan,active shallow gases exist at beds between 270-510 m.In view of the shallow gas blowouts occurred earlier at the M block,a set of effective precaution measures,for successful well control and better cementing work,were planned as follows:a.the drilling plan and well structure were optimized at first;b.during the first spud-in drilling,a high flow-rate circulation was performed during cementing,and the cement returned to the top,and a good cementing quality was ensured with the 324mm-in-diameter casing string;c.during the second spud-in drilling,the primary well control was emphasized;d.during the third spud-in drilling,the lower limits of drilling fluid density and filtration loss were designed,the drilling time was controlled,and the borehole was always kept clean;e.during the fourth spud-in drilling in carbonate rocks,H2S leakage control and lost circulations were stressed.After being adopted in 42 completed wells,the above-mentioned precaution measures have achieved many goals,including that no blowouts ever occurred,drilling safety,quality and speed are all maintained,and neither damage nor contamination has ever been found to the formation and environment.These will be valuable experiences for the drilling of similar shallow gas wells.