KOC has been drilling deep HPHT wells from the mid 1980's, and during this time the Kuwait deep well prospects have become deeper and more challenging. The rigs utilized to drill these wells have evolved over the years to meet these challenges, with new technologies being used to improve both operational and safety aspects.
Five years ago an enhanced rig type upgrade was introduced with the application of Top Drive, additional third 1700 HP mud pump and larger 5 1/2" O.D. drill pipe. This resulted in a step-change improvement in drilling performance.
In 2003 KOC began a project to look into the radical re-design of the deep rig specifications. Hamad Al Hamad and Partners was awarded the contract to complete the detailed design, procure and operate the rig, and National Oilwell Varco was assigned as the main rig construction contractor.
For the rig design certain new concepts were to be developed in readiness for a future campaign of deep HPHT exploration wells. These included the following; the rig should be safer and more automated, the capacity of the main equipment items and the mud system should be state of the art both in capacity and equipment specifications, the 15M BOP stacks should be re-designed to minimize handling, and the rig should be adapted for operation in the harsh summer conditions in Kuwait.
This paper will discuss the evolution of Deep Drilling Rig design in Kuwait, the design and specification of the new HAH-124 rig plus the construction/rig-up of the unit. The case study will also focus on lessons learned during this process and conclude with recommendations for future new rig builds.
Drilling of deep HPHT wells in Kuwait requires both the local and international drilling contractors to adhere strictly to overall required capacities of equipment for safely and efficiently drilling Jurassic and deeper exploratory prospects from depths of 15,000 ft to over 22,000 ft TVD. As Figure 1 of a sample North Kuwait Khuff well indicates, power to operate requires the utilization of 3000 HP rigs due to heavy casing hookloads for the 24" and 18–5/8" casings, high mud weights at relatively deep depths in 16" and 12–1/4" hole sections, and fairly high torques throughout the well. Likewise, mud volumes in these wells require adequate capacities and processing capabilities for the larger hole sections, especially when dealing with 19.5 ppg mud systems with a solids content of around 45% corrected in the 12–1/4" hole section at 14,000 ft.