Traditional Level 4 multilateral technology has focused on high-end applications with the intent of creating a foundation for conversion to Level 5 functionality. The Level 4 junctions are typically evaluated on three core capabilities: connectivity, isolation, and accessibility. As the evaluation criteria focuses on junction performance, little attention has been spent on reducing installation risks, junction hardware, and complexity. Recently, the effort to re-invent the Level 4 multilateral junction as a simple, low cost, low risk installation has been initiated. This new, back-to-basics approach to constructing a cemented junction has been developed by reverting to proven milling & completion techniques.
This paper will introduce this new method for installing a Level 4 junction by detailing the lessons learned from a Venezuelan field trial. The paper will show how standard milling and completion techniques can be used innovatively and reliably to create simple multilateral junctions. In addition, it will explore the extensive testing and simulations needed to ensure consistent mainbore access creation while emphasizing installation simplicity. Lastly, the field trial will be compared to other Level 4 installations in the region.
As multilateral junction equipment and systems began to evolve, there was an increasing need to categorize multilateral systems industry-wide based on levels of functionality at the junction. An elaborate naming convention was developed by the consortium group: Technology Advancement of MultiLaterals (TAML), which identified the functionality level, flow control, lift mechanisms, and re-entry capability. There are essentially six functionality levels that are commonly used to describe all multilateral junctions. Only those levels discussed in this paper are defined below:
Level 3. A junction where an open hole lateral is created from a cased and cemented mainbore. Screen, slotted pipe, or liner is placed in the open hole lateral and is anchored back to the mainbore by some means. This is the lowest level in which mechanical integrity at the junction may occur.
Level 4.A junction in which both the lateral and the mainbore are cased and cemented.
Level 5.A junction where both the lateral and the mainbore are usually cased and cemented, and the junction is hydraulically isolated using completion equipment. This is the lowest level in which pressure integrity at the junction may occur.1
The oil industry strategy has been to provide a wide variety of multilateral systems such as pre-milled windows, manufactured mainbore access windows, and completion based junction solutions. Junction construction technology has been driving the design of multilaterals industry-wide with complex hardware and methodologies. For Level 4 multilateral installations, the emphasis has been to convert the basic Level 4 to a Level 5 to provide completion based flow control and hydraulic isolation at the junction. The challenge is to provide only the functionality that is essential to meeting the minimum well requirements.2
In an effort to focus on simple, low cost, and low risk technology, Weatherford has adopted a "back-to-basics" approach to developing multilateral systems. Leveraging to their strengths as a milling company, Weatherford set out to develop a Level 4 multilateral junction using proven milling techniques and off-the-shelf components while minimizing costly completion hardware.