Design of a Drilling Rig for 10,000 ft Water Depth using a Pressured Riser

Abstract

This paper presents the requirements for a drilling rig to drill in up to 10,000 ft of water using a pressured riser. An analysis of deepwater wells drilled was carried out to determine what characteristics (Water depth, drilled depth, number of casing strings etc..) these wells had. A "look forward" portfolio of wells was constructed as the target for the design of the rig. A full QRA was conducted to examine the impact of emerging technologies such as Expandables and Dual Gradient and to determine which choices for rig components were appropriate. The paper includes an outline rig design for deepwater for West Africa and one for GOM operations. An outline specification for the well systems (BOP, riser configuration) is also included. A comparison is made of the impact of drilling deepwater wells with this "new" approach versus using the "conventional subsea BOP" arrangement. The paper also includes details of how the "new" approach may be applied to existing rig types and how it may be applied to a new-build. The cost implications of this step change are examined. Fully risked well cost comparisons ("new" vs "conventional") are provided along with some comment on the risks and consequences of the available choices. The paper concludes that the "new" rig specifications detailed will allow for deepwater drilling in up to 10,000 ft water depth and that in some cases there will be significant overall well cost savings. Conclusions It is possible to configure a surface BOP, slender riser and seabed shut-off device (SSOD) to successfully drill many wells in ultra deepwater. This allows use of a rig smaller than the "conventional" 5th generation rig/ship. The optimum configuration of rig/well equipment will vary depending on water depth, well type etc.. This configuration is best arrived at using a QRA approach to compare the alternatives. Significant cost savings are possible in comparison to well costs that would result from using a conventional marine riser/subsea BOP and the resultant large rig. The savings that result are dependent on the well. The work carried out (and as described in this paper) allows for a totally objective analysis of the deepwater drilling process and (once refined properly) will allow for rational decisions to be taken about rig selection and deployment. The paper sets out a description of the work process rather than detailed results of the process - presentation of detailed results would require back-up that is beyond the scope of a paper. The work that has been carried out shows how operations can be carried out in the most efficient manner possible. This has implications for both exploration and development drilling. Well Characteristics The characteristics of wells that have been drilled or are likely to be drilled were examined in order to identify the requirements for a drilling rig. The major characteristics of these wells are:Water depthMeasured depthFormation/Fracture pressure window (Number of casing strings)Metocean environment

Deploying Dual Gradient Drilling Technology on a Purpose-Built Rig for Drilling Upper Hole Sections

“…6,7 If extending the conductor casing doesn't eliminate enough intermediate strings to start with 16" and drill conventionally below, it may still be possible to complete the well using expandable tubulars and still realize the savings from using the Top Hole DGD rig. For a spud rig, this is particularly a problem when attempting to drill in the marine conductor with a subsea pump kit installed on the 30" wellhead to minimize total running time.…”