Plugging of a Downhole Control Line
Authors: Iversen Morten , Ege Jan Arild 
Published: October 2008

During any operations in a well, two independent barriers must be available. In a well completed with a more advanced completion, the elements that make up each of these two elements become more complex and the probability of failure increases as the number of possible leak-paths increases.

For a completion with an Adjustable Downhole Control Valve (ADCV), the control for this valve penetrates one element of the primary barrier namely the production packer.

Well P-18A on the Saga Petroleum SNORRE field was equipped with an ADCV from PES, the SCRAMS system, and after a relative short operational period, communication and operation of the ADCV was not longer possible.

The failure also resulted in communication from the reservoir through the control line. A rapid pressure increase was observed on the manifold in the wellhead area on the platform. This represented a situation that required remedial action.

This paper describes the process involved with plugging of a leaking downhole control line for an ADCV.

Introduction

The failure of the installed DIACS (Downhole Instrumentation Accusation Control System) on the Saga Petroleum SNORRE field resulted in communication from the reservoir through the control line.

The DIACS system supplied by PES (SCRAMS) is operated by two (2) electrical and two (2) hydraulic control lines. These lines are routed from the surface through the production packer to ADCV and hence, leakage through the control lines jeopardises one of the barriers in the well.

Pressure build-up of both lines was observed in the subject installation and subsequent bleed-off resulted in a rapid pressure build-up, indicating full communication with the reservoir. A risk assessment concluded that the well could continue to be produced as long as compensating measures were in place prior to re-establish the required barriers in the well.

Two options were evaluated, pulling the completion or plugging the control lines, mechanically or chemically. As pulling and re-running of the completion was not an economically viable solution, the work was concentrated on finding the best solution for plugging the control lines.

Testing Conducted

A mechanical solution was regarded as impractical, a resin-based two-component formula was selected as the best solution for plugging of the control line.

The methodology was developed to assist in plugging of tubing in some offshore oil wells in Norway, but never attempted to plug a small control line.

Laboratory testing on the solution was performed, but it was decided that more realistic testing was required to simulate conditions found when plugging a control line.

The objective of the testing was defined by Saga Petroleum and the testing was designed and performed by Weatherford Completion Systems under Saga supervision to simulate conditions encountered in the control line.

As the control lines in question were still hooked up to the well, the temperature profile in the line would range from ambient on surface, 5 °C to 60 °C at the Xmas tree block and down to 90 °C through the packer. The temperature profile is illustrated in Figure 1.