Architectures and Technology Gaps for TLPs and DDCVs in Ultradeep Water
Authors: Bhat S.U. , Kelly P.J. , McBee H. , Wybro P.G. 
Published: October 2008

TLPs and DDCVs, both mini and hub class, have limitations as their use is extended to ultradeep water. Using a consistent set of base case design basis, ultradeep TLP/Mini-TLP and DDCV systems were configured. A consistent and logical system engineering process was then used to identify technology gaps and possible enabling or enhancing technologies. This paper reviews the scenarios evaluated and the findings.

Introduction

Deep Draft Caisson Vessels (DDCVs) or Spars have been used in the Gulf of Mexico in water depths up to 4,800 ft. Similarly, Tension Leg Platforms (TLPs) have been used in G.O.M. in up to 4,000 ft water depth. Both of these systems have limitations for applications in ultradeep water (5,000 to 10,000 ft water depth). For example, it is generally considered that the conventional TLP is no longer competitive beyond 4,500 ft water depth. At the same time, it is recognized that new technologies such as alternative hull designs and carbon fiber tendons can potentially extend the applicability of TLPs to ultra-deep waters. The offshore industry has a need to identify the current limitations of dry tree platform technology for application in ultra deep water, and to assess potential enhancing and enabling new technology opportunities on a consistent basis. DeepStar has addressed this need in the recently concluded phase II of Systems Engineering studies on ultra deepwater floating systems. The scope of the DeepStar study included both dry tree and wet tree floating systems.

Brown and Root Energy Services (BRES) led a team of contractors to execute the floating systems part of the Deep-Star project. SBM-Imodco, Sea Engineering, Inc. and Stress Engineering Services joined BRES in this phase. Additionally, Ocean Production Technology, LLC was retained by DeepStar to perform the drilling system portion of the work. Mentor Subsea provided the subsea system costs. A Value Engineering Team consisting of Energy Valley and Project Associates, Inc performed required lifetime economic analyses.

The study developed a consistent and logical process using the Functional Analysis System Techniques (FAST) method to identify the functional relationships of deepwater development systems and their components. This process used in the DeepStar project has been described by Morrison and others [1]. An introductory overview can also be found in [2]. Base case scenarios were used to "test" the FAST map information to identify any technology gaps. The base cases included DDCV, TLP, Semi-submersible and FPSO based field architectures. The process used was presented to the industry in two workshops. Base case FAST maps, field architectures, platform configurations, and costs were presented to the industry in these workshops and participants' input on potential technology gaps and enhancing technologies was obtained. A number of promising technology enhancers which improve existing practices were identified along with enablers, technologies that are not currently available. Once the "enabling" and "enhancing" opportunities were identified, an evaluation process was used to determine a "prize value," considering CAPEX, OPEX and risk implications.