Abstract

The paper reviews the Rocky Flowline project from preliminary design through detail design, testing, fabrication, and installation, The emphasis of the paper is on the issues involved with deep water insulated flowlines, with special emphasis on fabricating and reeling insulated pipe-in-pipe flowlirres. The paper highlights the design and installation of 21,000 ft of dual insulated 3-inch inside 6-inch flowlines in water depths up to 1785 feet. The paper and project is of significance to those in the industry involved in deep water oil development and the transportation of waxy crudes.

Project Overview

The Rocky Prospect is located in 1785 f=t of water in Green Canyon Block 110 (Figure 1). It is being developed by a single subsea oil well tied back approximately four miles to the Green Canyon 65A (Bullwinkle) platform by two nominal three inchflowlines of pipe-in-pipe construction till-rated for the design shut in tubing pressure of 7200 psig. A strong water chive is expected resulting in production rates of up to 8000 BOPD

The well was drilled, cased and temporarily abandoned in Second Quarter 1995. The flowlines were installed in July 1995 by the reeling method. The flowlines were laid horn GC 65A towards the well where they were terminated on a common sled which was placed a short distance from the wellhead, Completion of the well and the installation of the subsea hardware began in December 1995 and first production occurred in January 1996. Flexible pipe jumpers installed by the completion rig connect the subsea tree to the sled.

The subsea tree is an API 10,000 psi design with a single master valve and a piloted hydraulic control system. A thermoplastic hose umbilical connects the well to a hydraulic control panel located on GC 65A. The umbilical includes conduits for the hydraulic control functions and chemical injection, as well as electrical cables for pressured temperature date transmission back to GC 65A. Facilities are provided to allow paraffin inhibitor to be injected downhole and methanol to be injected at the tree if required for hydrate inhibition.

The dual flowlines allow periodic round trip pigging from the platform via a pigging loop on the Gee. The well can be configured to flow through either one or both of the flowlines, A surface choke at GC 65A is used to control the flow rate. In the event of an extended shutdown, the flowlines are displaced with dead oil to prevent hydrate formation.

Preliminary Design

In order to mitigate paraffin and hydrate concerns it was deem necessary to minimize heat loss in the flowlines keeping the platform arrival temperature above the anticipated crude oil cloud point of 90 degrees Fahrenheit. Preliminary analysis indicated that externally applied insulations could not meet this design criteria. Flowline bundle and pipe-in-pipe designs each were capable of meeting the heat retention criteria and were both investigated further.

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