Application of Multiphase Metering in Machar and Monan Fields
Authors: Humphrey A.I. , Hargroves D.W. , Svaren J.-A. 
Published: October 2008

Testing of individual production wells is a significant aspect for the design and the operation of subsea satellite fields. Where long tiebacks are involved, the ability to monitor each well's output with a multiphase meter, positioned close to the wellhead, enhances the field's performance and value.

Application of subsea multiphase metering to two U.K. North Sea satellite fields has shown this equipment operates successfully subsea. In-service experience has shown that deposits & debris can affect meter performance, however provisions for Remote Operated Vehicle (ROV) intervention enable these to be mitigated in a cost-effective manner.

Introduction

Until the mid-90's, well testing on a typical subsea development was achieved by manifolding into a dedicated test line or by testing-by-difference methods. Both options incur high CAPEX or availability penalties.

The Eastern Trough Area Project was designed in 1995, when multiphase meters designed for subsea service were emerging as a potential alternative approach. With the long tiebacks needed for the Machar and Monan fields, the utilization of this new option and its maturity were examined in detail and found to offer significant savings with acceptable risks.

The application of this technology is addressed in this paper, through the stages of design, procurement, fabrication, testing and installation. Start-up and in-service experience has added to the knowledge gained and shown that such equipment adds a more flexible solution to the conventional means of testing subsea wells.

Outline of ETAP

The Eastern Trough Area Project (ETAP) was sanctioned by all partners (BP Exploration Operating Company, Shell U.K. Ltd, Esso Exploration & Production UK Ltd., Agip (U.K.) Ltd, BHP (whose interest was subsequently acquired by Total Oil Marine), Murphy Petroleum Ltd and MOC Exploration (U.K.) Ltd. Subsequently, the Department of Trade & Industry (DTI) granted development consent on 20th December 1995. ETAP comprises an integrated development of initially seven oil and gas accumulations in the Central North Sea of the UKCS. The project is unique in terms of the UKCS as companies holding different interests in each field have agreed to design and construct facilities shared from inception, thereby accessing significant reductions in capital and operating costs. In addition, it represents further development of "Alliance" contracting in the UKCS. Construction work commenced in early 1996. First Oil was in August 1998.

Located within the Eastern Trough in the UK Central North Sea, ETAP produces from seven accumulations, Marnock, Mungo, Monan, Machar Heron, Egret and Skua. In aggregate, the fields can be considered to comprise a "pseudo field" of around 650 mmboe, which is geographically located within an area 35 Km across its maximum dimension. All lie between 130 and 145 miles east of Aberdeen, in water depths of around 85 to 95 metres. On this basis ETAP is the largest oil "field" to be developed in the North Sea in the last 10 years.

Drilling commenced in August 1996 and, in total, some thirty wells will be drilled.