Troika "Plan B: Implementation of a Temporary Hydraulic/Methanol Supply System From a Deepwater MODU
Authors: Ames T.J. , Sworn A.W. , Prichard R.M. 
Published: October 2008

Faced with deferring first oil by at least 3 months due to late delivery of the 14 mi. hydraulic umbilical, the Troika Project team developed an alternative scheme (Plan B) for providing hydraulic fluid and methanol (MeOH) to the subsea production system. A hydraulic power unit (HPU) and MeOH injection system were installed on the Troika drilling vessel (Glomar Arctic I). Via a remote controlled radio link tied into the master control station (MCS) on the Bullwinkle platform, the fluids were supplied from the GA-I, through a tensioned umbilical to one of 2 hydraulic umbilical termination hubs at the subsea manifold. Since the electrical umbilical was already installed between Bullwinkle and the subsea manifold, communication with the subsea control pods was executed from the MCS in a normal manner, as in the original system design. However, under Plan B, the MCS also sends a radio signal to the HPU and for the MeOH injection system on the GA-I to supply fluids to the tree control pods or MeOH injection port. Operationally, the system has performed well without any shutdown time attributed to the Plan B control system. With the implementation of Plan B, the original first oil date was achieved and the Troika Project realized over 3MM barrels of oil equivalent prior to the eventual installation of the permanent subsea hydraulic umbilical.

Introduction

The Troika Field is located 150 mi. off the coast of Louisiana in the Green Canyon Unit 244 in 2700 ft. of water and is jointly owned by BP, Shell, and Marathon. The development plan is based on a subsea clustered well and manifold arrangement tied back to the Bullwinkle platform, a distance of about 14 miles. With only 5 months left to meet the Troika team goal of first oil by November 1, 1997, it became clear that due to manufacturing problems, the 14 mi. hydraulic umbilical would not be available until early 1998. The flowlines would soon be connected, the manifold and first well were nearing completionand the electrical umbilical would soon be installed. Without a hydraulic fluid supply and MeOH to mitigate potential hydrates, over 3 months of early production would have to be deferred. The Troika Project team responded with a temporary hydraulic fluid and MeOH supply system located on the Troika drilling vessel, the Glomar Arctic-I (Fig. 1). The temporary system referred to as Plan B, consists of the following:Hydraulic supply system consisting of 2 HPU's, 2 fluid transportation tanks, and a shutdown unit.MeOH injection system consisting of 2 diesel driven pumps, 4-25 barrel MeOH transportation tanks, and a shutdown system.Hydraulic and MeOH umbilicalsTensioner moduleLower umbilical connection systemSESD system

The arrangement of the Plan B equipment is shown in Fig. 2. The temporary system provided the hydraulic fluid and MeOH required to operate the Troika subsea facilities until the subsea hydraulic umbilical became available. Since the electrical umbilical was already installed, control of the subsea facilities from the MCS located on the BulIwinkle platform was executed as originally planned. The main difference between Plan B and the original plan was the source of hydraulic fluid and MeOH which was now supplied from the GA-I.