Intelligent Pigging of the Ekofisk Subsea Pipeline Network
Authors: Nummedal T.A. 
Published: October 2008

In 1988, Phillips Petroleum Company Norway (PPCON) as the operator of the greater Ekofisk field, embarked upon a four year plan to complete an inspection of the entire Ekofisk pipeline system utilizing a 2nd generation intelligent pig. Although costly to implement such inspections, the information is seen as invaluable to ensure stable long term deliveries to the customers as well as to maintain the integrity of the of the pipelines well into the next century. This paper describes the experiences from conducting an inspection program in an North Sea offshore production environment including the preparatory work, offshore effort, findings and subsequent data base development effort.

INTRODUCTION

The Ekofisk Operation

Phase I of the Ekofisk field has been in operation since 1971 and has gradually developed an infrastructure and pipeline system of some 1150 km. PPCON, as the operator for the Phillips Group Norway, is responsible for twenty subsea (20) carbon steel pipelines of sizes varying from 10" up to 36", transporting oil, gas or multi-phase products. The eighteen (18) infield pipelines transport hydrocarbons from a number of outlying production platforms to the Ekofisk Center where oil and gas are separated, processed and mixed with product from third party shippers. The gas is then transported to Emden, Germany through a 442 km long, 36" pipeline for further distribution to the buyers on the continent while the oil is transported to Teesside, UK through a 350 km long, 34" pipeline.

Both export pipelines are owned by Norpipe, a separate company which in turn is owned 50% by the Phillips Group Norway and 50% by Statoil, the Norwegian State Oil Company. Quantities of oil and gas in excess Of 500,000 BBLS of oil and 2000 MMscf/D of gas respectively are transmitted daily through the 34" and 36" trunk pipelines.

The pipeline network is shown in figure 1 while the location of the Ekofisk field is shown in figure 2.

Regulatory Inspection Requirements

The requirements for the inspection of underwater pipelines have been set forth in a compilation entitled "Acts, Regulations and Provisions for the Petroleum Activity and are administered by the Norwegian Petroleum Directorate (NPD), the authority governing petroleum activities the Norwegian Continental Shelf.

Those regulations require that internal inspections be performed using equipment which provides for the detection of corrosion, cracks and changes in pipe diameter, etc. Such inspections shall be performed following start up and the need for subsequent inspections evaluated annually based on the initial findings and in view of operational conditions and quality of the transported products.

Internal Inspection History

Historically the combination of inspection pigging, ultrasonic scanning and product monitoring have been utilized to monitor the internal conditions of the Ekofisk pipelines.

The 1st generation intelligent pigs utilized prior to 1987 did not provide reliable nor accurate enough data. Although these pigs operate on similar principles as newer pigs, the sensoring system is much less sophisticated and consequently accurate sizing of anomalies is not possible which means that only the most severe corrosion can identified.