海上油田开发井钻井优化设计和应用实践

Optimal design and application of development well drilling in offshore oilfields

摘要:

LF7-2油田位于我国南海珠江口盆地LF区块，是一个小规模油田，根据前期探井揭示，上部地层以厚层泥岩为主，极易水化、分散，使钻井液性能变差；起下钻过程中钻具遇卡、遇阻等复杂情况频繁发生；钻头选型不尽合理，易泥包；下部地层以砂泥岩互层为主，岩石致密、可钻性变差，钻具扭矩、摩阻增加，定向钻进时滑动困难，井眼轨迹控制难度大，给钻井提速增效带来诸多困难。根据探井地质情况和岩石力学剖面，利用钻井软件优选平台位置，对开发井井身结构、井眼轨迹、钻柱力学、钻井液、固井等方面进行钻井仿真模拟，制定出科学的钻井设计方案，在直井段采用“牙轮钻头+直螺杆+MWD”钻具开展防斜打直，造斜段使用“PDC钻头+弯螺杆+MWD/LWD”开展复合钻井，水平段采用“PDC钻头+PowerDriver+MWD/LWD”开展旋转导向钻井，实现精准化钻井，顺利完成6口开发井施工。现场应用单井平均机械钻速29.43 m/h，钻井工期191.59 d，工期比设计提前28.41 d，钻井提速增效显著，降低开发成本。通过PowerDriver的近钻头井斜、自然伽马实时测量和传输，减少地质误判，实现对储层顶界面的实时探测，使储层钻遇率达100%，收到较好的经济效益和投资回报，实现小油田的效益开发。

Abstract:

The LF7-2 Oilfield is a small-scale oilfield located in the LF block of the Pearl River Mouth Basin in the South China Sea. According to previous exploration wells， the upper stratum is dominated by thick mudstone which is easily hydrated and dispersed， leading to poor performance of the drilling fluid， frequent drilling string sticking and resistance during tripping， and bit balling due to improper bit selection. The lower stratum is dominated by alternate sand and mudstone which is dense， and of poor drillability. As a result， the drilling torque/drag increased with difficulty in slide drilling and control of the well trajectory during directional drilling， which brough many difficulties to the drilling speed and efficiency. According to the geological conditions and rock mechanics profiles from exploratory wells， drilling software was used to optimise the platform location and simulate development well drilling in terms of the wellbore structure， wellbore trajectory， drill string mechanics， drilling fluid， cementing and other aspects， so as to formulate proper drilling design. For the vertical well section， the “rock bit+mudmotor+MWD” drill assembly was used for vertical drilling； for build-up sections， the “PDC bit+mudmotor+MWD/LWD” was used for compound drilling； and for horizontal sections， the “PDC bit+PowerDriver+MWD/LWD” was used for rotary steering drilling to achieve precision drilling. In such a way， 6 development wells were successfully completed. Field use indicated the average ROP was 29.43m/h with the total drilling period per well of 191.59 days， 28.41 days ahead of the design， which improved drilling efficiency， and reduced development costs. Near-bit inclination and gamma real-time measurement and transmission of PowerDriver reduced geological misdiagnosis， and can provide real-time detection of the roof of the reservoir with the reservoir intersection rate reaching 100%， resulting in good economic benefits and investment return to achieve profitable development of small oilfields.