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CACT-OG is a joint operating company consisting of CNOOC, ENI, and Chevron as its Principal Companies. CACT- OG is the operator of Huizhou HZ 25-4 oilfield in South China Sea, which was discovered in December of 2005 as multiple oil bearing zones found in the vertical exploratory well drilled by a semisubmersible rig. HZ 25-4 field is located in block 16/19 in central area of Pearl River mouth basin, located 6 km southwest of the HZ 19-2 platform in a water depth of 102 meters. After discovery, extensive studies were conducted for the development of this field. It was decided to upgrade the existing drilling rig on the nearby HZ 19-2 field platform and drill extended reach (ERD) wells from the platform. Three of five ERD wells were drilled and completed with 6" horizontal laterals and stand alone screens for sand control. A number of challenges appeared while drilling these wells including: ERD drilling experience level, excess torque and drag, hole instability, hole cleaning and resulting pack off, high side force and casing wear, high ECD due to shallow TVD, losses due to high ECD and fault encounter, and shock and vibration. The result of these challenges was long times to complete the wells and excess budget overruns. After the completion of the third well, it was been decided to suspend the operations and perform detailed analysis on the challenges with extensive lessons learned in order to approach the remaining two ERD wells in the Plan of Development with a different strategy. Following the studies and drilling analysis, the revised final plan included a new engineering design, revised operations procedures and monitoring, new approach for team building and training, and implementation of newer technologies such as utilization of Aluminum Drill Pipe and Continuous Circulating Devices. The result of the new plan applied has been a dramatic improvement in performance and consistent savings in budget. It has been observed that this different drilling approach and technology has opened a new window on how to drill challenging ERD, and that is a key to improved drilling performance.

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.