Reducing Well Costs and Extending Field Life with Intelligently Controlled Trilateral and Quadrilateral TAML Level-5 Multilaterals

Abstract

Abstract Since 1996, more than 260 multilateral junctions have been installed in Norwegian Continental Shelf (NCS) fields; currently, 25 laterals are completed annually. This paper discusses a TAML Level-5 multi-branch multilateral system that was installed in Troll field in 2012. It is now the predominant system, with more than 200 junctions installed in subsea wells. This latest generation of sealed multilateral junctions combined with flow control equipment, including surface-controlled interval control valves (ICVs) and autonomous inflow control devices (AICDs), enables full production control of the main bore and each lateral. The production life of multilateral wells of the Norwegian Troll field is limited by gas breakthrough and/or water cut. Historically, this issue was mitigated by using intelligent completions to control the flow of a maximum of two laterals. If a breakthrough occurred in a lower lateral on wells with three or more laterals, all laterals would have to be choked or shut-in together. This process resulted in lost production and reduced recovery from the other laterals. As trilaterals and quadrilaterals became more common, however, it became necessary to provide flow control for all branches. In October 2012, the Troll team installed the first multibranch multilateral system on Troll N-24. This system is believed to have been the first TAML Level-5, three-branched well with individual branch control installed worldwide. With this new and innovative junction and completion system, the operator could optimize the oil production from new and extended-reach multilateral wells. In addition, the implementation of multilateral technology (MLT) early during the planning stage enables the addition of production intervals at a cost of 20% or less of the initial well cost, which makes many marginal field developments viable projects. Multilateral junctions are typically constructed from the bottom up; the lower main bore is drilled, completed, and prepared for production before milling the window for junctions above. To help mitigate the risk with these operations, several technologies have been implemented, including premilled windows, extended length whipstocks, and lateral screen deployment. On multilateral operations, a dedicated coordinator focus and a proactive engineering team has helped eliminate and/or reduce installation risk to an acceptable level for operators using the technology. Presently, this innovative multilateral solution helps increase oil recovery from Troll and other fields. This increase should help expand the functionality and economic viability of MLT worldwide, particularly in thin reservoirs.