Abstract

Electrical Submersible Pumps (ESPs) reliability is improving considerably therefore the development of a subsea X-mas tree and high voltage connection system that provides and allows well testing directly to the rig was required. It also needs to maintain the ability to perform completion and workover using conventional techniques, in order to make the use of subsea installed ESP's more attractive.

Using existing high voltage wet mateable connection technology operators have to accept several limitations to well testing and barrier philosophy during completion. This adds a factor of unpredictability on the well development which often prohibits its commercial development.

This paper addresses the development of a horizontal high voltage connection which improves / solves these issues. The solution allows well test with the ESP without removing the BOP.

Introduction

Current technology requires the removal of the Blow Out Preventor (BOP) stack to perform "start-up" tests with the ESP, which poses major safety risks, by removing one safety barrier at the well but also adding considerable time to the offshore operations. This paper presents these limitations and a solution to eliminate these, including design details and current qualification status.

The major design problem is the wet mate electrical connections located between the X-mas Tree and Tubing Hanger, due to the large size of the connectors. Traditionally they are mounted vertically with the production bore eccentric to the main body (see figure 1), hence the operational limitations. This also limits the completion tubing sizes that can be used, with maximum 4-1/2" normally installed. Consequently all these restrictions are assessed and an alternative presented.

Existing Technology and Challenges

Mouting a HV of 3.2" (81.3mm) outside diameter vertically dictates a completion tubing of maximum size of 4-1/2". A wet mating mechanism only contributes to an increase in size. The connector disputes for real state inside the completion, more critically at the Christmas Tree level - Side Valve Trees in this case -, with the Tubing Hanger and other downhole penetrations required at the well, hydraulic and electrical.

In order to provide large enough production tubing that can offer the flow rates to make the well economical, the solution was to place the production tubing eccentric, instead of traditionally concentric to the Tubing Hanger, with the required downhole penetrations located around it. Furthermore, the connection mechanism has to be made up vertically, as there is no space to offer a horizontal - perpendicular to the tubing - penetration (as shown on Figure 2).

Therefore, both the Tubing Hanger and the Internal Tree Cap have to be adapted to carry the high voltage connection mechanism. This in turn dictates that the Installation tools be modified to cater for additional alignment and space requirements.

The Tree Cap also makes available space for the incoming power supply from the umbilical to the downhole completion. In order to reduce the number of wet mate connections the tree cap is externally connected to the top of the Christmas tree, with Remotely Operated Vehicle (ROV) assistance.

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