Operation and Reliability of a North Sea Floating Production System
Authors: McGuire L.V. , Kearns John 
Published: December 2007

This paper describes the reliability and operating history of the U.K. Continental Shelf (UKCS) Block 30/24 floating production facility. The equipment and techniques in use result from experience gained and technologies developed in more than 12 years of operating floating production systems in the harsh production systems in the harsh North Sea environment. This paper discusses the performance of these systems and presents an uptime analysis to quantify the effect of various components on overall efficiency.

Introduction

UKCS Block 30/24 is located 200 miles [320 km] offshore in the central sector of the North Sea. The Argyll, Duncan, and Innes fields are currently on production from this block. The Argyll field provided the first oil production in the UKCS. The semisubmersible production in the UKCS. The semisubmersible drilling rig Transworld 58 was converted to the industry's first floating production facility, and production was started through subsea wells on June 11, 1975. Crude processed by the Transworld 58 was exported by a catenary-anchor-leg-moored (CALM) buoy and shuttle tankers.

The Duncan field, 4 miles [6.5 km] west of Argyll, was discovered in late 1980. A subsea manifold installed between the Duncan and Argyll fields gathered production from four Duncan field satellite wells for transportation of the combined production stream to the Transworld 58. In Oct. 1984, waterflooding to maintain Duncan reservoir pressure dictated the replacement of the pressure dictated the replacement of the Transworld 58 by the floating production facility Deepsea Pioneer. This unit has a waterflooding plant for Duncan and a gas-lift plant to sustain Argyll production.

In Jan. 1985, the Transworld 58 began production from the Innes field, 8 miles [13 production from the Innes field, 8 miles [13 km] north of Argyll. The crude oil was exported through the Argyll CALM buoy and shuttle tankers. By Dec. 1986, the Innes field proved to be of limited extent and unable to support a stand-alone facility. The two Innes wells were tied back to the Deepsea Pioneer, eliminating the need for the Transworld 58.

Fig. 1 illustrates the current physical arrangement of the Block 30/24 production system. Twelve subsea production wells from three different fields, all with differing fluid characteristics, are routed back to a central manifold by individual flowlines or by remote manifolds and feeder flowlines. The crude is separated on a single floating production facility and stabilized. Crude is exported by a CALM buoy and shuttle tankers.

Production Performance Production Performance (Uptime Analysis)

Production uptime is often stated as simply Production uptime is often stated as simply the percentage of time that production is flowing through the process train with no allowance made for either restricted production rates owing to equipment malfunction production rates owing to equipment malfunction or limited availability of individual wells. Using this approach, operators routinely achieve more than 95% uptime. This simplified approach is not adequate to evaluate the operational performance of a producing system as complex as that in Block 30/24.

The concept of uptime was used to identify areas where the overall efficiency of the system could be improved. We have generated a data base for the system that relates uptime to the individual aspects of the overall production system. All the data used in production system. All the data used in the system are based on a well-hour time analysis. One well-hour is accrued to the data base for every hour that a well is available for production. A well is considered available for production unless closed in for a workover or major flowline repair.

Lost production time is identified according to one of five major categories:Field-specific downtime is lost time that does not result directly from a failure of the offshore production facilities. It reflects production time losses associated with production time losses associated with work-overs, downhole mechanical problems like safety-valve failures, and subsea flowline leakages. This time is a direct result of problems that cannot be rectified by personnel problems that cannot be rectified by personnel on the floating production facility or field diving support vessel (DSV) without the intervention of a drilling rig or the acquisition of replacement items, such as new flowlines.Weather downtime reflects well hours lost to severe weather and seastate.Loading-buoy downtime describes well hours lost to tanker changes and any CALM-buoy-related problems or repairs.Production-plant downtime reflects well hours lost to process plant problems, as well as plant shutdowns associated with emergency shutdowns or other plant problems. problems. 5. Major project downtime includes all large items of work that involve planned shutdowns, such as the installation of gas-lift facilities or the Deepsea Pioneer.

Several constraints affect the percent production uptime that can be achieved with the production uptime that can be achieved with the Block 30/24 system.

JPT

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