A Novel Underbalanced-Perforating Gun Deployment System Using Production Packer Technology Successfully Completes Offshore Horizontal Wells in a Single Trip
Authors: Beveridge Martin , Bruce Alex , Robb Thomas , Herron Steve 
Published: October 2008

Abstract
An innovative completion method was recently used to complete two oil fields in the central and northern areas of the North Sea. The Skua field was a single well development and was borderline high-pressure/high temperature (HP/HT) with a reservoir pressure of 9350 psi and a reservoir temperature of 307°F. The Penguin field was a 4-well development with an average reservoir pressure of 8000 psi and reservoir temperature of 265°F. Each sub-sea well required a long horizontal section to maximize production from the tight, highly compartmentalised reservoirs.
The completion designs for the Skua and Penguin fields had to address a number of challenges:What configuration would allow the completion to be run underbalanced without an isolation device?What method of sand control for the Skua HP/HT well conditions?What completion method would maximise production from the long horizontal section?What completion method would provide contingencies in the event of installation failure? Several completion options were reviewed. A new gun deployment system based on production packer technology was chosen because it appeared to offer the best option for meeting all the well requirements. The polished bore receptacle (PBR) and hydraulic set permanent packer were designed with the guns hung off the seal assembly of the PBR.
The system would also allow the tubing conveyed perforating (TCP) guns to be recovered if they failed to fire or malfunction.
The Skua and Penguin wells were all completed with a fully cemented liner. The completion and TCP guns were run, and the wells were successfully completed and perforated underbalanced in a single trip.

Introduction
This paper will describe the development, testing and implementation of a new TCP permanent packer system used in the Skua and Penguin fields in the North Sea. Initial well conditions are detailed in Table 1.
Traditionally, horizontal wells are completed using either a sandface completion where there is a risk of sand production, or a cemented liner and either "shoot and pull" TCP guns or coil-tubing-deployed guns. This paper outlines a novel gun deployment method that allowed the well to be completed underbalanced using a permanent packer and provided a means of recovering the TCP guns had they failed to fire.
The system is comprised of a 9 5/8-in. hydraulic-set permanent packer, anchor, and 6-in. polished bore receptacle (PBR) as shown in Fig. 1. The TCP guns were hung off the seal assembly of the PBR and the 3Â½-in. tailpipe run through the permanent packer to the guns. An additional seal assembly was packed off in the bottom sub of the packer to facilitate setting the packer. The PBR was designed with a 150,000-lbf shear ring, and this was designed to maintain the seals in the static position during the life of the well. The shear ring was designed to shear during a cold kill or scale squeeze only.

Development and Qualification for Skua
Development and qualification revolved around the Completion Equipment Review Team (CERT) analysis of the completion equipment for its intended use. This analysis includes details of