Multilateral wells have been proven over decades and have developed into a reliable and cost effective approach to mature field rejuvenation and extended commercial viability. This paper will discuss case studies demonstrating a number of techniques used to create infill multilateral wells in existing fields with a high level of reliability and repeatability.
Techniques reviewed will cover cutting and pulling production casing to drill and case a new mainbore versus sidetracking and adding laterals to an existing mainbore. Discussion will also cover completion designs that tie new laterals into existing production casing providing significantly greater reservoir contact. Temporary isolation of high water-cut laterals brought into production later in the well's life through bespoke completion designs will also be discussed. Case studies will include discussion of workover operations, isolation methods, and lateral creation systems. Where available, resulting field performance improvements will also be discussed.
In Norway, slot recoveries are commonly performed by cutting and pulling the 10-3/4" casing, redrilling a new mainbore, and running new casing. This enables junction placement closer to unswept zones and easier lateral drilling to targets. It does have drawbacks, however, related to the additional time required to pull the subsea xmas tree and challenges associated with pulling casing. In 2019, Norway successfully completed a 10-3/4" retrofit installation, whereas a sidetrack was made from the 10-3/4" and an 8-5/8" expandable liner was run down into the reservoir pay zone where two new laterals were created. The 8-5/8" liner saved time otherwise spent having to drill the section down to the payzone from the laterals. These wells have a TAML Level 5 isolated junction, Autonomous Inflow Control Devices (AICDs) in each lateral, and an intelligent completion interface across the junction, enabling active flow management and monitoring of both branches.
In Asia, infill laterals were added to existing wellbores by sidetracking 9-5/8" casing and tying production back to the original mainbore. These dual laterals were completed with intelligent completions to enable lateral flow management and monitoring of both laterals.
In Australia, dual laterals were created in a similar fashion; laterals are added to existing wells; however, a novel approach was used to manage water from existing lower mainbore laterals whereby they are shut in at completion and opened later when the new lateral is watered out. The older lateral now produces at lower water cut given the time allowed for water coning in the lateral to relax. Using this practice, production is alternated back and forth between the two laterals.
In the Middle East, an older well has been converted from TAML Level 4 to Level 5 in order to prevent detected gas migrating into the mainbore at the junction. This conversion of a cemented junction well has enabled production to resume on this well. The well was converted to incorporate an intelligent completion to enable flow control of each lateral.
This paper intends to provide insights into the various mature field re-entry methods for multilateral well construction, and a review of the current technology capabilities and well designs through the review of multiple case histories.
