摘要
Abstract
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-per-formance 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)in-dividual 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.关键词
井筒清洁/页岩油/二开井身结构/提速/井壁稳定Key words
Wellbore cleaning/Shale oil/Second-spud casing program/ROP increase/Wellbore stability
