In 2005, Kuwait Oil Company Exploration Group (KOC) began drilling KM-05, a deep directional exploration well in their West Kra Al maru (KM) field. The well was projected to TD at 16,285 feet MD. In order to intersect the reservoir fractures at the appropriate angle to enhance production potential, the well profile required drilling a 16″ directional hole section. The operator considered this a significant challenge to complete the build section with a 16″ PDC as it had never been attempted at a depth below 11,500 ft, but they wanted to explore the possibilities.
Similar vertical wells required both roller cone and PDC bits to complete the section. Because roller cone had unacceptably low ROP, the operator determined PDC would offer the best option to efficiently drill the build section, therefore offering the best chance for success. Contingencies allowed for fallback to roller cone because of the PDC's anticipated high reactive-torque, the ability to meet directional objectives and limited experience drilling deep directional wells in this large hole size.
In the preplanning stage, the operator's drilling team closely examined new technologies which would allow them to achieve their goals, especially drilling the demanding deep directional section. The entire BHA was engineered to ensure the ROP and directional requirements would be met. A team was organized to aggressively seek technology/best practices that would efficiently deliver well objectives. The team identified that poor tool-face control in limestone would be the primary obstacle. BHA and PDC bit technology was a key focuses in optimizing the 16″ directional section. Due to this careful planning and collaboration between the operator and service providers, the directional objective in the 16″ hole section of one PDC bit run was achieved. By applying new technology the section was drilled 13 days faster than the directional offsets constructed with roller cones with an estimated savings of US$258,364.
The typical depth for an exploration well in the KM field (Figure 1) is between 15,500 ft and 16,500 ft with completion being either in 9–1/4" 6" or 6–1/2" size based on the target formation. Because of the depth and anticipated formation pressures of the KM-05 exploratory well, the 18–5/8″ casing had to be set at a greater depth requiring the 16″ hole section to be drilled directionally at depths never attempted before by the operator in this field.
Formation analysis (limestone, anhydrite and mudstone) revealed a large range of unconfined compressive strength (UCS) values (8,000 psi and 20,000 psi) added to the complexity of the challenge. The changes in formation strength and lithology can cause issues with PDC especially when drilling with a motor in a directional application as negative drill breaks can occur causing loss of tool-face or even motor stalling. The operator required new steerable PDC bit technology to efficiently drill the demanding 16″ directional hole section.
PDC bits by nature of their shearing action generate more torque than a roller cone bit (Figure 2). Until recently, PDC technology was often avoided for directional applications when used in conjunction with a positive displacement motor (PDM) because of high reactive torque. The aggressive PDC cutting action often lead to loss of tool-face control or even motor stalling forcing the operator to reduce weight on bit (WOB) to control the tool-face resulting in lower ROP, more time off bottom to orientate and ultimately higher drilling costs.