Troika- Experience with Super Duplex Tubing for HydraulicIChemical Umbilical
Authors: Brown N. , Stevenson M. , Nossen P. , Holen P. 
Published: October 2008

A 14 mile hydraulic control/chemical injection umbilical links the Troika subsea development manifold to the Bullwinkle platform. This paper discusses the experiences gained through the complete process starting with contractor selection, looking at design standards, manufacturing facilities, inspection requirements and the level of client involvement to ensure technical integrity and a quality product.

Introduction

The Troika development is an oil field located 150 miles offshore Louisiana in the Green Canyon area of the Gulf of Mexico. Designated as the Green Canyon 244 Unit, the development includes block 200,201,244-and 245. Troika is jointly owned by BP Exploration Inc. (BPX), Marathon Oil Company (MOC) and Shell Offshore Inc. (SOI), with BPX serving as the operator. Fig. 1 shows the Troika field location.

Troika is located in 2700 ft of water and features an eight well subsea manifold with five well initially installed in a cluster arrangement. Production from Troika is transported via two 10 inch flowlines for processing on the Shell Bullwinkle platform 14 miles away located on Green Canyon block 65 in 1350 ft of water.

The Troika development is control by a multiplexed electro-hydraulic control system operated from the Bullwinkle platform. The control system is linked to the manifold by an electrical and hydraulic/chemical umbilical. The function of the hydraulic/chemical umbilical is to provide high and low pressure hydraulic fluid for all the actuated valves on the manifold and subsea trees, methanol to all the subsea trees and both flowlines and chemicals (paraffin & corrosion inhibitors) to both flowlines. In addition it includes a bleed line for the well annulus fluids. An overview of the Troika field development is given in OTC 8845' and the layout is shown in Fig. 2.

This paper takes an overview of the Hydraulic/chemical umbilical and outline some problems experienced with emphasis on the use of super duplex tubing meeting the requirements of ASTM specifications. It looks at what quality program were in place during the manufacture of the tubing, how the problem was discovered, what steps were taken to identify the extent of the problem and how it was overcome.

Design Requirements

The initial design requirements were established in the conceptual design study completed by Intec Engineering included the line function, fluids, inside diameter, required flow rate and pressure rating. The material selection was based on Shell Offshore material recommendation of either 2507 super duplex or zinc coated steel tubing. The functional and fluid requirements are summarized in Table 1.

Contractor Selection

The contractor selection process was typical for any major equipment purchase for an offshore project. An inquiry document was prepared with a technical functional specification for the hydraulic/chemical umbilical only defining the inside diameter of each line, pressure rating, material and service/design life. This allowed each bidder to choose what they consider the appropriate design criteria for the wall thickness calculations of the tubing and the configuration of the actual tubes inside the umbilical.