Extensive job planning aids in rig-assist HPHT cleanout

The operation used a hydraulic workover unit in three wells in the UK North Sea.

Alan Lamont and Paul Radcliffe, Shell; Mark Klinck, John Brumfield and Gavin Bell, Halliburton

In a High-Pressure, High-Temperature (HPHT) cleanout operation, a Hydraulic Workover Unit (HWU) was used to clean out the production tubing to allow isolation barriers to be installed. The wells had been shut in for some time following production of reservoir solids.

In rig-assist mode, the HWU deploys pipe against surface pressure with the jackup drilling rig providing pipe-handling support. Detailed planning and risk assessment were required during operations because well conditions changed. Some equipment problems required a review of planned operations, and onshore tests were carried out before mobilization for the intervention project’s second phase.

Modifications were required to the HWU to withstand the high buckling loads associated with snubbing against high pressure. Additionally, special downhole tooling was required to accommodate extreme well conditions. This article discusses the development work involved and the subsequent performance of the equipment. Operating performance statistics and lessons learned are presented.

INTRODUCTION

Shearwater Field is located in the central North Sea in Block 22/30b, 138 mi east of Aberdeen. The field was discovered in 1988 and developed with dual platforms installed in 297 ft of water. The development consisted of a Process, Utilities and Quarters (PUQ) platform linked to a WellHead Platform (WHP) by a 262-ft bridge, Fig. 1.

The main producing reservoir is located about 15,000 ft below the surface and is characterized as HPHT. Well SW-08 is an S-shaped well with a BottomHole Pressure (BHP) of 15,400 psi and BottomHole Temperature (BHT) of 365°F.