New Well Intervention Technology That Will Enable Increase In Recovery Rate
Authors: Lindland Hans Jørgen , Inderberg Olav , Braut Arnfinn 
Published: October 2008

This paper describes development of new subsea well intervention technologies that will support increased reservoir recovery. Subsea lubricator for seven inch and 10.000psi applications operated from dynamically positioned vessels has been developed and are now ready for use in the North Sea. Composite materials for wireline cables with high electrical current transfer capabilities and composite risers and coil tubing are also described in the paper. The working process using systems approach and Hazop/Hazids etc are focused upon.

Introduction

When an oil field has produced oil and gas for many years and finally is closed down, there is still much oil left in the ground. Generally for oil fields between 60-70% of the original reserves in a reservoir remains permanently in the ground. The last years advancements in seismic,-reservoir,-and well technology have lead to a tremendous increase in reservoir recovery rates. For the offshore industry especially fields with platform based (dry wells) have seen this effect. Subsea completed wells are currently lagging somewhat behind in this development trend.

This paper describes new intervention equipment that will enable increase in reservoir recovery rate.

Earlier Subsea well intervention

Subea wells are mainly maintained/ intervened due to reservoir reasons. These vary from field to field due to the different reservoir conditions, the nature of the produced or injected fluid(s), the configuration and status on the equipment installed, etc. One of the main categories being to gain information of the production condition down hole or stimulate the well production.

The wells are normally maintained so that optimal well performance is met. This also includes any modifications of the well/ completion to enable proper drainage of the reservoir(s). Data acquisition is required to diagnose the well in case of unexpected performance, verification of the composition and rates from the different zones open to production, etc. This is especially important in order to enable best possible reservoir production management, and in some cases preparation for heavier intervention operations.

Traditionally the well maintenance or workover operations have been divided into 2 categories, "heavy" and "light" interventions.

Typical categorising of well intervention work as being discussed in connection with the Norwegian Continental Shelf(NCS) is shown in figure 1 where:are mainly wireline operationsare work over riser operationsare operations including using marine riser & BOP Fig. 1 Intervention Classification(AVAILABLE IN FULL PAPER) Recent initiatives have been launched to enable more cost effective intervention methods. The use of monohull vessels that are available in the market at a substantial lower rate is the key to more cost effective solutions.

-"Heavy" interventions usually mean operations requiring the use of a heavy (18 3/4") drilling Blow Out Preventer (BOP) for pressure control.

Removal of Christmas Trees, tubing replacement, sidetracking (are typical examples of "heavy" intervention operations" today. This will change over time as capabilitiesof lighter systems are further developed. Several semi submersible drilling rigs are operating in the North Sea, able to perform this type of operation.