To be able to lubricate long perforating assemblies (guns) in horizontal wells, and to retrieve them without killing the well has always been attractive for many reasons, both from an operational point of view and to minimise formation damage.
This paper describes a case study from the Siri Field where lubricating long gun assemblies against a tubing-retrievable downhole lubricator ball valve (DHLV) enabled running up to 1000 m of 3.5" perforation guns in two runs in a live well. This was performed without the use of a surface deployment system, and without exposing the tubing-retrievable surface controlled subsurface safety valve (TRSCSSV) to potential damage in the event of inadvertently dropping the perforation guns during completion.
Use of this equipment gives also the added benefit of considerably reducing the equipment rigup heights for Siri in the future life of the field, after he jackup drilling rig has moved off location.
The Siri Field, discovered in 1995, is located in the Danish Sector of the North Sea (Fig. 1). Production started in March 1999. The field is developed with five oil producers and two SWAG (Simultaneous Water And Gas) injectors, drilled using a jackup rig located over a wellhead tower. Well interventions will typically be rigless, requiring standalone equipment mounted on the wellhead tower. The horizontal producers have up to 1000 m perforations and it was desirable to perforate the entire interval underbalanced.
Siri is expected to produce at relatively high water cuts for most of the field's life, and it is water-related problems which most likely will be the main reasons for future well interventions. Scale inhibition treatments at the rate of 1/well/year, reperforation and plugback of watered-out or gassed-out zones form the bulk of the anticipated workover program throughout field life. Coiled tubing would be the most likely intervention method. It is obviously desirable to perform these well interventions without killing the well.
Siri is developed with a wellhead tower containing 12 well slots, at a centre-centre spacing of roughly 1,1m, connected to a jackup production platform. Headroom from the Xmas trees to the weather deck is only 2–2.5m.
With future workovers in mind, ample deck space was included in the platform design, also workover fluid tanks and extra living accommodation to allow wireline, coiled tubing, pumping, snubbing and possibly coiled tubing drilling operations to be carried out at short notice from the platform, and without rig mobilisation.
The wellhead tower weather deck itself measures roughly 12m×15m and is open to the sea on three sides. All rigup for well operations is above the deck. For coiled tubing operations with a deployment system, this could involve a 10–15m riser in addition to pressure control equipment. During completion operations with the drilling rig on location, support is available, but standalone operations could pose safety and logistical problems, requiring use of scaffolding or a workover derrick arrangement, and being highly weather-dependent. Use of long production logging tools would also lead to high rigups (Fig. 2).