The commonly drilled 16-inch surface borehole section in U.A.E crosses several interbedded formations comprised of limestone, shale, clay and sands, and it is associated to several frequent hole problems experienced in offset wells such as Hole collapse with high abnormal formation pressures, casing not reaching bottom etc. In order to isolate the weak formations from the surface and the reservoir, the 133/8-inchsurface casing should be set in a competent rock (limestone) formation that will not fracture at the casing shoe. The operator is required to drill a long 16-inch directional hole section with dogleg severity (DLS) upto from 1.5°/100 feet. This study presents a novel directional drilling strategy utilized in a deep offshore oil well with high inclination for achieving the challenge imposed by setting the casing shoe in limestone formation, deepest in the region (~8000 feet).
The drilling engineering team conducted an extensive technical and engineering evaluation of the trajectory and problems associated with drilling this section based on previous offset wells, including severe bit/stabilizer/motor bearings wear, loss of signals from MWD, tight hole/stuck pipe incidents, wellbore stability. After a detailed risk assessment, the selected well was planned and executed with this strategy to achieve our target. The paper outlines the process carried out during the drilling and casing running phase in order to successfully complete this well along with establishing several records in U.A.E.
The planned strategy was implemented after successfully drilling the 36-inch surface hole followed by running and cementing the 30-inch Conductor pipe. Then the planned trajectory was drilled with 16-inch Bottom Hole Assembly (BHA) by building in the first 3000 feet reaching an inclination of 40° with DLS upto 1.5°/100 feet and then continuing to drill tangent section upto 8088 feet. The well was drilled with one run by sustaining an average ROP of 37 feet per hour for a total of 10 days. The 133/8-inch casing was successfully run without any major obstructions or tight spots to 8083 feet as there was efficient hole cleaning due to a Friction factor of 0.40 in Open Hole. Nevertheless, this strategy allow us to save approximately 3-4 days per well due to minimizing the drilling time, while achieving the longest surface hole section with one BHA in U.A.E.