Conductor Supported Pulltube Bundle - An Alternative Approach to Supporting Pipelines on a Fixed Plafform
Authors: Dorgant Paul L. , Hansen Mark C. , Gallaher Dale M. 
Published: October 2008

The Enchilada platform was designed as a central Hub for numerous pipelines in the Garden Banks area of the Gulf of Mexico. A new approach was developed to bring these pipelines up to the platform deck. The Enchilada platform was designed for 17 pipeline connections and as many as 23 pipelines were considered during the design. This large number of pipelines required either a new approach for the pipeline connections or the use of a jacket structure with more main legs. The four main legs of the Enchilada jacket did not have sufficient space for conventional individual or bundled pulltubes. The approach developed for Enchilada was to bring all pipelines up to the deck within the conductor guide framing through vertical pipeline bundles nicknamed CONSPUB's (Conductor Supported Pulltube Bundle). The CONSPUB's are vertically supported near the base of the jacket and require only lateral support at each guide elevation. The vertical portions of the CONSPUB's are field installed, which defers costs for future pipelines. This paper describes the designdetails used for the Enchilada design and discusses alterative details that may also be used. Benefits of this approach are discussed including cost savings and future pipeline flexibility, The CONSPUB approach described in the paper will provide designers with an alternative to conventional leg supported pulltubes and risers.

Introduction

The overall field development strategy in Garden Sanks Blocks 128 and 172 is described in Reference I. The Enchilada platform was designed as part of this field development and was planned as a central Hub for numerous pipelines. Prior to the decision to design the Enchilada structure as a Hub, the Enchilada platform was planned as a minimal stand-alone facility for drilling and production. The original jacket design concept consisted of a four-leg jacket to be installed in two lifted pieces and joined in-place offshore. The two-piece lifted jacket concept offered significant cost and schedule advantages2 and it was preferred to utilize the same concept even with the higher functional requirements of a hub, specifically a large number of pipelines. The final platform was designed for 17 pipeline connections and as many as 23 pipelines were considered during the early design. Conventional pulltubes are supported along the main legs of the jacket. Incorporating 17 pulltubes would have caused significant congestion of the four main legs of the planned Enchilada jacket. The design team concluded that the four-leg jacket structure did not have sufficient space for conventional individual or bundled pulltubes. A new approach was developed to bring these pipelines up to the platform deck. This approach was to bring all pipelines up to the deck within the conductor guide framing through vertical pipeline bundles nicknamed CONSPUB's (Conductor Supported Pulltube Bundle). The vertical portions of the CONSPUB's can be field installed, which defers costs and eliminates lift weights of the future pipelines. The deferred weight was an important factor for the Enchilada jacket, since the lift weight of the jacket sections were near the capacity of the offshore construction vessel cranes. Deferring costs improves the profitability of the project and avoids pre-installing components that may never be used.