There are many challenges in drilling extended reach well (ERW) for weakly consolidated sandstone and mudstone formations in Bohai Offshore Oilfield. For weak consolidated sandstone formations, it is difficult to control well trajectory, keep wellbore stable and decrease mud loss. For mudstone formations, the challenges include friction between wellbore and drilling tools, hydrating and swelling. At the same time, the measured well depth is larger than 3000 m, and the angle hold are larger than 70 degree. Additionally, the faults and the stress anomaly increase mud loss or complicate ERW drilling. Consequently, sticking of drilling tools or casing, and well collapse occur in past well drilling process.

In order to drill ERW successfully and safely in Bohai weakly consolidated sandstone and mudstone formations, integrated drilling technologies are introduced involving well trajectory design, drilling tool assembly, friction prediction and drilling parameters correction, adjustment of drilling mud, and casing floating and lubricating. The practical measures used include: (1) Different drilling technologies are employed in the deflecting section and hold angle section respectively; (2)Rotary steering-LWD tools are used in the second spud and the third spud; (3) Drilling parameters are corrected in-time according the real-time friction prediction result derived from drilling friction prediction; (4) Marine bentonite mud is used for layers over the oil formation to recover well cuttings rapidly and keep high drilling speed, and polymer enhance cation (PEC in short) drilling fluid are used while drill the oil formation to avoid sticking of drilling tools and protect formation; (5)Floating couplings and addition of lubricant are introduced in running protective casing to avoid sticking. Field testing show that above integrated ERW drilling technologies are practical for the sophisticated weakly consolidated sandstone and mudstone formations in Bohai Offshore Oilfield, and the drilling efficiency is significantly increased. The engineering design of the integrated ERW drilling technologies and field drilling cases are presented in this paper.

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