This paper describes the results obtained as well as the equipment and techniques used on the Glenelg field in the UK central North Sea (CNS) to perforate and complete a new high-pressure high-temperature (HPHT) production well.
This paper begins by discussing the types of equipment required for HPHT coiled-tubing (CT) intervention. This includes the front-end engineering for the hottest, deepest, highest pressure, and most deviated well produced from, to date, in the UK CNS. This paper discusses the CT string design, as well as the selection of downhole tools, for temperatures above 400°F. The CT intervention, wireless casing collar locator (WCCL), depth correlation, and perforating operations are presented. This is the hottest environment in which WCCL technology has been successfully applied worldwide.
The lessons learned during this project, together with the results from this case history, are presented. Conclusions are drawn about moving forward with both the WCCL technology and conducting similar operations.
The operating company's Elgin, Franklin, and Glenelg fields are located in the central North Sea Graben area, east of Aberdeen, Scotland. The Elgin/Franklin/Glenelg development is the world's largest HPHT development. The three fields are serviced by wellhead platforms over Elgin and Franklin and a production/utilities/quarters (PUQ) platform attached to the Elgin wellhead platform. The combined capability of these two fields is 770 MM BOE and a design rate of 170,000 bbl/day (14.6 MM m3) condensate. To date, the Glenelg field has been developed with a single production well, 7300 m in length, drilled from the Elgin platform. The Glenelg reservoir is located 4 km west-south-west of the Elgin platform and is some 5600 m below sea level. A map of central North Sea HPHT fields is shown in Fig. 1. The reservoir temperature approaches 400°F (200°C) and reservoir pressure is over 16,300 psi (1124 bar). The Glenelg well has a production potential of 30,000 BOPD.
The heavy-duty jackup drilling rig, Rowan Gorilla V (RGV), is on contract to the operating company and was on location over the Elgin wellhead platform throughout this project.
The ultimate objective of this project was to safely and effectively perforate the long interval of the Glenelg HPHT well through CT-conveyed guns. To do this, it was necessary to develop a suitable methodology to address the following key issues:
Conduct all operations safely and show due care and attention to environmental concerns.
Maintain accurate perforation depth. Develop a WCCL to accurately locate depth in HPHT conditions, avoiding the use and complication of an e-line through the CT.
Develop a design for a CT string capable of being run and retrieved under extreme well-control situations. Perform engineering calculations to help ensure that the selected CT design would be capable of running without buckling or collapsing at expected conditions.
Retrieval of the guns as required after perforating because the well had insufficient rat-hole for the gun string length.
Qualification of the CT spread. Onshore qualification of all the equipment, simulating the offshore work environment as closely as possible before mobilizing the equipment spread.