CHALLENGES WITH JOINTED-PIPE UNDERBALANCED OPERATIONS

Successful underbalanced operations demand a systematic approach with integration of engineering, operations, production, reservoir, and geo logy. There are significant advantages to underbalanced drilling (UD). Formation damage can be minimized if proper circulating fluids and op erating parameters are chosen; there is an opportunity for reservoir e valuation and characterization while drilling; lost circulation and di fferential sticking can be avoided, combined with improvements in dril ling rate of penetration (ROP); and it also provides an alternative me thod of well control. This paper discusses engineering challenges and considerations for underbalanced operations using multiphase flow as w ell as advances made during UD with rotary jointed pipe. Excluding air , mist, and foam, underbalanced techniques with multiphase fluids are reviewed. Much of the discussion and concepts also apply to coiled-tub ing underbalanced operations.