SubSea MudLift Drilling: Design and Implementation of a Dual Gradient Drilling System

Abstract

Abstract The SubSea MudLift Drilling Joint Industry Project (SMD JIP) completed Phase II of the design and development of a dual gradient subsea pumping system in June 2000. This paper is the last of a series of three discussing the SMD JIP's evolution of dual gradient drilling (see SPE 71357, "SubSea MudLift Drilling Joint Industry Project: Delivering Dual Gradient Drilling Technology to Industry"; and SPE 71358, "SubSea MudLift Drilling: Planning and Preparation for the First Subsea Field Test of a Full-Scale Dual Gradient Drilling System at Green Canyon 136, Gulf of Mexico").1,2 The mudlift pumps (MLPs) and other SMD system components were thoroughly tested in the flow loop at the Hydril Technology Center (HTC), but the components were not yet integrated into a system which could be deployed on an offshore well. The next step was specifying which rig would be used for drilling a selected test well; the rig's specifications would determine how the SMD system integration design progressed. Modifications to the rig would also be necessary to ensure that the SMD system could be safely installed. The Ocean New Era (Diamond Offshore) was identified as the test rig. This is a 2nd generation 2449 ST VDL rig with 1500ft water depth capability. Once the New Era was selected, both SMD and rig personnel began the parallel tasks of fitting the system to the rig, and modifying the rig to accommodate the additional weight, power requirements and ancillary equipment that the SMD system installation would entail. The dimensions and design of the SMD package were dictated by the size of the rig's moonpool, its BOP handling equipment and the LMRP height. Based on coordination with rig personnel, the SMD system was assembled in its "rig-adapted" form at HTC, including all manifolding, the seawater power system, the MLPs, and the electronic controls. In compliance with the JIP Basis of Design (BOD), a full-scale factory acceptance test (FAT) of the system was initiated on April 30, 2001 and completed on May 16, 2001. Prior to the FAT, separate testing was performed on certain SMD components not specifically associated with pumping, including the solids processing unit (SPU) and the drillstring valve (DSV). The hydraulic power system along with hydraulic lines, control pod, control cabling and connectors, were all tested in a hyperbaric chamber to simulate deep ocean conditions. A final "endurance" test of the system was conducted before transporting it to the rig at dockside in Galveston. This paper will discuss the parallel efforts of the rig and SMD teams to design, test and integrate the SMD system on the rig. In addition, the results of the FAT and component testing carried out in Phase III, and the lessons learned will be examined. Introduction The dual gradient SMD system is ultimately intended for use in 4,000–10,000ft water depths, but the prototype system was installed on a second-generation semi-submersible contracted to drill a test well in 910ft of water. This test venue would allow the SMD teams to evaluate its subsea operation without incurring the high costs of drilling from a larger rig with greater water depth capacity. This test would also confirm that the SMD system could be retrofitted to a smaller rig, thereby extending the rig's water depth capabilities, one potential benefit of dual gradient drilling. The New Era had been used as a training center for two years prior to contracting to drill the world's first SMD well. As a JIP participant, Diamond had a significant investment in the success of the system. Supervisory personnel from Diamond were seconded into the project full-time and the process of integrating the SMD system to the rig began. Several SMD components were independently tested. The solids processing unit (SPU), which is located upstream of the MLPs in the SMD system, was installed on the flowline of an offshore rig and monitored as it processed gumbo, cuttings from water-base and synthetic-base muds, cement and float equipment, and all other solids normally encountered in offshore drilling returns.