Amoco Sharjah Oil Company (ASOC) has drilled several dual-lateral horizontal wells in its Sajaa Field since 1996. Two of the wells did not reach their geologic and leg length objectives due to massive, incurable lost circulation and several of the wells were hampered by differential sticking. A recently completed well was drilled using underbalanced techniques in order to mitigate or eliminate these occurrences. Dry sales gas from the Sajaa Gas Plant re-injection system was used to achieve the underbalanced condition. A 7" tieback casing string with perforations in the bottom joint was installed prior to drilling the horizontal legs and the gas was injected down the 7" × 9 5/8" annulus. Conventional mud motors and MWD tools were used in the bottom hole assemblies with the addition of a back pressure valve and a " restrictor" sub. Clean water with periodic high viscosity pills was pumped down the drill string. Surface equipment included a rotating blow out preventer (RBOP), a choke manifold with two bladder type adjustable chokes, sample catchers and a four-phase separator. The project was completed ahead of schedule, under budget, and without an accident or serious incident. The two main benefits were achieved plus some additional ones such as increased penetration rates and more efficient sidetracking. This paper discusses the pre-planning and team building conducted prior to beginning underbalanced operations, the surface and down hole equipment involved, the general procedures followed, plus the operating parameters and results experienced.

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