吉林油田页岩油水平井二开钻井关键技术及应用

Key second-spud horizontal-well technologies for shale oil in Jilin oilfield and their application

吉林油田页岩油主要位于松辽盆地南部长岭凹陷,已经完钻5口纯页岩水平井。由于目的层层理和裂缝发育,造成井壁稳定性差,在施工过程中,存在返砂效率低、井壁易坍塌、水平段延伸困难、摩阻扭矩大等技术难题。针对这些问题,通过井身结构优化、强封堵钻井液应用、高效PDC钻头及提速工具优选、井筒清洁参数优化及压力精确控制等技术攻关,形成页岩油二开长水平段水平井钻井关键技术。应用结果表明:①采用强抑制强封堵高性能油基钻井液能有效封堵裂缝,大幅降低钻井液侵入量,并有效防止页岩膨胀,提高井壁的化学稳定性;②钻井液排量大于38 L/s、顶驱转速大于80 r/min能够保持水平井井筒清洁,节约短起下钻及下套管前通井的时间3 d以上;③个性化PDC钻头配合旋导施工能大幅度提高机械钻速,使井壁浸泡时间缩短30%以上。优化起钻速度使井底压力波动降低52%,进一步提高井壁稳定性;④吉林油田页岩油水平井由三开井身结构简化为二开井身结构,水平段长度提高82.75%,机械钻速提高53.73%,钻井成本降低33%。

Shale oil in Jilin oilfield is mainly discovered in Changling sag,southern Songliao Basin where five pure shale horizontal wells have been drilled.However,both well-developed bedding and fractures bring about poor wellbore stability.Especially,there exist some drilling problems,such as low sand return rate,wellbore collapse,difficult horizontal extension,and large torque and drag.So,key second-spud horizontal-well technologies were created for shale oil by optimization of casing program,adoption of strong sealing drilling fluid,selection of efficient PDC bit or rate of penetration(ROP)enhancement tools,optimization of wellbore cleaning parameters,and precise control of pressure.After their application,it is shown that(i)the high-inhibition,high-plugging and high-performance oil-based drilling fluid can be used for plugging fractures with effect,reducing fluid influx greatly,avoiding shale expansion,and increasing chemical stability of wellbore;(ii)horizontal wellbore cleaning can be kept at the fluid discharge and top drive speed all greater than 38 L/s and 80 r/min,respectively,thus cutting down the drifting time before short trip or casing more than 3 d;(iii)individual PDC bit in conjunction with rotary steering can substantially raise the ROP and further shorten the wellbore soaking duration by more than 30%.Optimization of drilling speed can lowered the fluctuation of bottomhole pressure by 52%,further improving the wellbore stability;and(iv)the casing program is simplified to second spud from third spud,which enables horizontal intervals to be 82.75% longer,ROP to be 53.73% higher,and drilling costs to be 33% lower,respectively.