The paper summarises the results of a study performed by Kvaerner Oil & Gas Field Development and Smedvig Asia Limited investigating the use of tender assisted drilling (TAD) for floating structures.
The paper further discusses the general benefits and challenges associated with the use of tender assisted drilling for floating structures and how the CAPEX and OPEX of field developments can be significantly reduced. Results from a study investigating the use of tender assisted drilling with a wellhead TLP in a benign environment will be used for quantifying the benefits and to describe how the challenge can be solved for a specific development.
Focus is put on the following :
Overall Tender vessel and TLP configuration.
Reduction in size of the TLP due to reduced payload requirement. A conceptual design of a TLP with conventional drilling and tender assisted drilling are presented.
The challenge related to stationkeeping of two floating structures in proximity and how to connect them ensuring that the distance between them is controlled. Several different configurations are discussed and results from non-linear time domain analyses of the two connected vessels are presented.
Safety and operational aspects related to tender assisted drilling are presented. Typical topics covered are drilling operation, installation of drilling and production
Finally cost and schedule estimates are presented.
For any field development one always faces the question whether to use dry or subsea completed wells. There are many arguments to which dry completion offers the most efficient solution considering total capital and operating expenditure.
easy and economical well intervention
increased recoverable reserves as a result of more frequent well stimulation
simple flow assurance
simple well control systems
The main challenge for dry well completion lies in the geographical extents of the field and the fact that the reservoir must be drained from preferably one central position to avoid investing in several wellhead platform structures facilitating drilling equipment. For deep water development this challenge is even more apparent considering that an increased topside capacity has significant knock-on effects on the entire platform configuration. Therefore, many of today's deep water hydrocarbons reservoirs have been developed with a subsea solution and the associated operational problems and adverse effect on the overall recoverable reserves. A solution to the challenge is tender assisted drilling, which reduces the functional requirement to the wellhead platform and therefore makes the dry completion more competitive from a CAPEX point of view.
Tender assisted drilling with self erecting rig capability is a proven technology which in shallow water areas such as Southeast Asia and West Africa has been in use for more than 25 years. Traditionally, the wellhead platforms for which tender assisted drilling are performed have been jacket structures. The benefits transferred to floating structures are expected to be even more pronounced. In deepwater developments dry completion units such as Tension Leg Wellhead Platforms (TLWP), SPARs or Deep Draft Floaters have been shown to be economically attractive.
