Conventional drilling methods initially utilized to drill an east Texas HPHT well, presented in this case history, ultimately failed after six attempts were made by an independent operator to drill a "straightforward" horizontal wellbore. The subject HPHT well proved extremely challenging with reservoir BHT of 334°F and approximate 13,900 – 14,500 psi reservoir pressure. The well was plagued by several drilling problems including multiple well-control incidents, a casing failure, surge-swab issues, stuck pipe incidents, trip problems, directional control issues, and finally a blowout.
Utilizing a combination of MPD and UBO techniques, Sidetrack Number 7 successfully met all project and geologic objectives. A Wide variation of pore pressure and fracture pressure equivalent mud densities made accomplishing a primary goal of MPD, ("to precisely control the annular pressure profile throughout the wellbore") difficult but possible, requiring the combination of methods. Neither MPD nor UBO could be consistently utilized while drilling. When precise wellbore pressure management proved difficult due to the pressure regime variations, modification of the MPD technique and application of UBO accompanied by reconfiguration of the BOPE ultimately facilitated optimum control during several subsequent incidents.
Key elements to success were: a) proper understanding of the physics supporting each variation of MPD and UBO used, b) thorough engineering of all problems and preparation of multiple contingency procedures, c) extensive training of all personnel related to drilling and completing the well, including rig crews, engineers, managers, vendors and support crews, and d) involvement of a highly experienced MPD/UBO team.