Abstract

This paper describes the results obtained, as well as the equipment and techniques used on the Jade Field in the UK Central North Sea to provide the perforation and completion operations of two new high-pressure/high-temperature (HP/HT) production wells.

This paper begins by discussing the types of equipment that are required for HP/HT coiled-tubing (CT) intervention. The completion design and methodology of these two wells will be discussed. The CT interventions and different perforating operations will then be presented for these wells. The paper outlines the specific types of downhole equipment that were needed for these operations. This includes, for example perforating gun hangers and detachable perforating connectors. This paper includes the application of new equipment designs and novel solutions to both surface and downhole constraints.

Lessons learned from each case history will be presented and conclusions will be drawn.

Introduction

Over the last 10 to 15 years a number of HP/HT fields have been discovered and brought into production. This has led to both the extension of existing practices and the development of specific new technology and solutions to enhance reservoir production. One of these developments has been the application of CT as an intervention technique. HP/HT CT intervention can be defined as work in wells with over 10,000 psi bottomhole pressure and over 300ºF bottomhole temperature (BHT) or wells where the pressure gradient is over 0.8 psi/ft and BHT 300ºF. The UK Central North Sea has many fields that meet this definition.1, 2 An example of this is the Jade field, located in the UK, as illustrated in Fig. 1, block 30/2c, in approximately 261 ft of water. The Jade field was discovered in 1996 and confirmed by an appraisal well in early 1997. The field has been developed using a normally unattended installation, connected by a 16-in., multi-phase pipeline to the Judy platform, 12 miles south of Jade.

The field is classified as HP/HT because the pore pressure is in excess of 14,000 psi with a BHT above 300° F. Because the Jade reservoir is at a depth greater than 17,000 ft, the pressure gradient in the field is over 0.8 psi/ft. The expected fluid type was gas condensate, which would provide an expected hot shut-in wellhead pressure just below 11,000 psi. On J9, the well maximum inclination is less than 10 degrees.

To date, a total of nine wells have been drilled in the field. Earlier Jade development wells were perforated in drilling mud to ensure full well control was maintained after perforating, but uncertainties remained about the amount of formation damage caused by the mud after perforation.

This paper details the two most recent Jade wells (J08 and J9), which were drilled with heavy-duty, harsh environment, jackup drilling rigs. These were required to access specific slots of the Jade Platform. These rigs were both fitted with 15,000 psi well control equipment and high-capacity offshore cranes that can lift large CT reels with ease. After the wells were drilled, a series of logging runs confirmed the hydrocarbon zones, fluid types, and formation pressures. High-strength 5-in, 18-ppf completion liners were then cemented into the wells to provide zonal isolation and allow the selected formations to be perforated.

Initial Design Considerations

In preparation for both wells, the primary intervention and perforating requirements were identified. The following constraints had a predominant bearing on the perforating solution chosen:

  • Conduct all operations safely.

  • Requirement to perforate underbalance.

  • Minimise the change out time between slickline and CT.

  • Ideally leave no perforating guns across the reservoir.

  • Anticipated perforating gun length was approx 1000 ft.

  • Accurate depth correlation was required for positioning of the guns.

  • Ideally the CT will be out of the hole during the actual gun detonation.

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