The Middle East's hard carbonates and abrasive sandstone cause a multitude of drilling problems. In Oman, penetrating thick conglomerates (12–30kpsi) in 12¼-in hole section is a predominate challenge. In Kuwait, drilling the 16-in hole section through hard Dammam-Ahmadi (5–30kpsi) is problematic. Offshore Qatar, building 12¼-in tangent through Hith-Khail (9–30kpsi) causes PDC cutter damage reducing ROP. The region's operators would benefit from a new approach. Shirking conventional heavy-set PDC design philosophy, engineers explored a new concept that concentrated on removing the inefficient low rotational velocity cutters at the center of a PDC bit.
An R&D initiative produced a conical diamond cutting element (CDE) with twice the diamond thickness of a conventional PDC cutter. CDE is manufactured to provide superior resistance to abrasive wear and impact load damage. In laboratory testing, the element exhibits up to 70% increase in cutting efficiency compared to standard PDC cutters. Design engineers then used an FEA-based modeling system to position the CDE at bit center by selectively abbreviating the blades at bit center. By opening the cutting structure in this manner enables a stress-relieved rock column to develop. The CDE then engages the column to continuously crush and fracture the formation thereby increasing ROP potential. This unique design has also proven to increase stability for improved borehole quality.
An 8¾-in PDC (MDSiZ616) with CDE was run in North Dakota and drilled four hole sections (6209–6477ft) in a single trip. The average ROP of the first three CDE runs was 168ft/hr, 46% faster than the best offset average (115ft/hr) set by standard PDC. On the fourth run, a CDE PDC set a Bakken ROP record of 203ft/hr drilling 6301ft of vertical/curve in one run. In Bakken lateral, a 6-in MDSiZ613 with CDE drilled 9544ft at 97ft/hr in one run, a 49% ROP improvement compared to three bits required on an offset lateral. The bit displaying excellent directional control staying within the narrow reservoir window while setting records for highest 24-hour footage (2903 ft/day) and fastest lateral TD to date. The new type CDE bit is currently being evaluated in Middle East/southern Iraq applications and positive results will be outlined in the paper.