Saga Petroleum will make extensive use of subsea systems to develop the Snorre Field. Of the planned 46 wells needed for the field's first phase development, 10 will be subsea wells. Another 47 subsea wells may be added during the second phase development, bringing the total to possibly 57 subsea wells.
The Snorre Subsea Production System was previously described in OTC paper 62021. This follow-up paper expands the discussion of the system with emphasis on some of the more innovative aspects of the design. Specific issues addressed are: guideline-less drilling and completion system, the manifold system, control system, TFL well-servicing, and the remotely operated maintenance vehicle which will be used to maintain the manifold and control system components.
The Snorre Subsea template system is shown in Fig. 1, which identifies the various sub-systems that comprise the template system. The 10 + 10 template will develop 20 wells, but only 10 at a given time. As a well is depleted it can be abandoned and replaced with another drilled through the same template.
The template system is 48 metres long, 32 metres wide, and (including the 3 metre skirts) 19 metres tall. As installed, with the manifold sub-system (but not the well bay equipment, which will be installed as the wells are drilled) it weighs approximately 2500 tonnes in air. It will be installed by a heavy lift crane vessel in 335 metres water depth, 6 kilometres NE of the Snorre TLP. The template structure is a truss structure made primarily of large diameter tubulars. It features upright sections that provide separating walls between the well slots. These walls, which give the template the appearance of an English "toast rack," serve to protect the adjacent equipment during drilling and installation operations in the adjoining well slot and also are used for guidance of equipment into the well slot.
Immediately after the template is installed it will be leveled by pressuring or applying suction to the skirted mud-mat compartments. Thirty-inch conductions will then be installed in the four corner well slots to stabilize the template. The remaining 6 conductors will then be drilled, cemented, and locked to the template wellguides to complete the foundation. Conventional drilling and completion equipment and casing programs will be used for the Snorre subsea wells, with the exception that guideline-less techniques will be used to install equipment. As previously mentioned, the "toast-racks" play an important role in the guideline-less system. Figure 2 shows a cut-away view of a well slot. One of the two "toast-rack" members is illustrated with its "bumper," the "well guards," and the two drilling guides, that are in each well slot. The bumper, including the corresponding one on the other "toast rack" that has been cut away, interact with bumper plates mounted on the BOP's alignment structure and the tree's alignment structure to position the equipment for installation on the wellhead.
