Discoverer Enterprise: World's Most Advanced Drilling Unit
Authors: Cole J.C. , Herrmann R.P. , Scott R.J. , Shaughnessy J.M. 
Published: December 2007

Transocean Offshore has received a contract from Amoco Corporation to build the first new floating drilling rig since the orders placed in the mid 1980's. The Discoverer Enterprise will be the world's most advanced offshore drilling rig. Representing the next generation of ultra-deepwater rig, the Discoverer Enterprise resulted from an innovative approach which addressed the overall well construction process and the equipment required to significantly decrease the time required to drill a deepwater well. The Discoverer Enterprise will be a large, dynamically positioned drillship capable of drilling in up to 10,000' of water. Unique drilling features include hull size, a single tubular derrick equipped with two rotary tables, two drawworks and two topdrives which will result in an increase in well construction efficiency making the Discoverer Enterprise a cost effective rig for deep water. It is the first ultra-deepwater rig designed specifically for handling subsea completions and extended well tests.

Introduction

Improvements in deepwater economics as a result of advanced deepwater production technology, tax and royalty relief, and the establishment of deepwater infrastructure are evidenced by the growth in major field developments in the Gulf of Mexico, Brazil and West of Shetlands. The result has been a significant increase in demand for rigs capable of drilling in deep water, particularly in the Gulf of Mexico where over 700 blocks have been leased in greater than 5,000' of water. To date, only three rigs (two DP drillships and a moored semisubmersible) have drilled in greater than 5,000' of water in the Gulf. Increasing demand for deepwater rigs resulted first in an increase in day rates, and then in an increase in contract term. In response to improving economics, contractors began upgrading existing equipment and also converting non-drilling semisubmersible units to meet operator demand. As the capital cost of conversion increased rapidly, new construction became a viable alternative. The last new floating rig built capable of operations in 5,000' of water was the Transocean Richardson, an anchored semisubmersible, which was delivered in 1988. That vessel was built at a cost of $90 million. Building the same rig today is estimated to cost more than $250 million. This level of capital cost requires a dayrate in excess of $180,000 per day to provide an adequate return to the owner. In the case of a duplicate Richardson, the technology or drilling process would not be significantly improved versus the product delivered by the original; therefore, Transocean believed a more cost effective approach to drilling was needed to justify such a large dayrate.

Transocean formed an in-house team of operations and engineering experts whose goal was to develop a process for reducing well construction cost by 40%. At this level of efficiency, an operator can justify the dayrate required for new construction as faster well construction will offset higher daily costs. The Enterprise development team analyzed the entire well construction process and determined the equipment required to improve drilling efficiency. Rig activity has been centered around a single rotary table; therefore, any activity that requires use of the rotary is in the "critical path" to complete the well. The operator must pay for the cost of that activity through the rig dayrate, as well as through additional spread costs such as ROV, MWD, personnel, boats, helicopters, shore base, rental tools, and communications, etc. By utilizing a dual derrick with two rotaries, two topdrives and two drawworks (the dual activity drilling system), the Enterprise concept will remove many typical tubular handling activities from the critical path. The result is greater flexibility, enhanced efficiency and lower cost to the operator.

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