In offshore drilling, requires an analysis of buoyancy which is owned by the rig. The magnitude of the platform’s buoyancy was affected by the volume of total column which are submerged below sea level. The more volume columns submerged the more stable the platform rig stands. The buoyant force will hold two loads on the rig, the static load and dynamic load. Static load is the overall load of the rig, while the dynamic load is a load of the drillstring to be used in the drilling process. Maerks discoverers a semi-submersible rig with 4 columns and will conduct offshore drilling in the Gulf of Mexico. The planned target depth is 18,000 ft (True Vertical Depth), with drillpipe length for 12,000 ft and 6,000 ft drillcollar. With the formation pressure gradient of 0,465 psi/ft, the density of the mud is 10.54 ppg. Drilling is done with 4 drilling trajectory. It is also use ORQ mooring chain type with a diameter of 2 ¾ "by 4 units that have a tension load of 880 tons that can hold the submerged part so that a constant column during the drilling process that is as high as 15 m.
Department of Petroleum Engineering, Faculty of Mineral Technology, Univesitas Pembangunan Nasional “Veteran” Yogyakarta, Indonesia
Steel Catenary Riser is the preferred solution for riser system in offshore oil & gas production. They are more structurally reliable, technically simple and cost effective compared to other types of riser. As the offshore oil & gas production move to deep and ultra-deepwater regions, the optimum solution have to be determined to overcome the challenges of steel catenary riser such as its weight and size. Catenary Offset Buoyant Riser Assembly (COBRA) is a concept conceived to address most of the problem of steel catenary riser in deepwater. It combines the advantages of steel catenary and hybrid risers and is made up of two parts. The bottom part consists of a rigid steel pipeline in catenary configuration and connected to a sub-surface buoy. A flexible jumper connects it to the floating structure. The flexible jumper and the buoy effectively absorbed the forces acting on the riser and floating structure essentially making the steel catenary undisturbed by the dynamic motions, thus improving its fatigue performance. Numerical simulation of the COBRA concept in a Malaysia deepwater project is carried out by considering the environmental conditions from the Kikeh Field to analyse its static and dynamic performance. The static and dynamic analyses showed that. at the touch-down point, the tension for COBRA is about 50% smaller that for steel catenary riser maing it suitable for deepwater projects in Malaysia.
Faculty of Mechanical Engineering,Universiti Teknologi Malaysia, 81200 Skudai, Johor Bahru, Malaysia
