Development and Installation of an Extended Reach Multilateral Junction

Abstract

A multitude of extended reach technologies have been utilized in the West Sak field on the North Slope of Alaska to reduce surface impact in a remote and environmentally sensitive area. Significant to the shallow heavy oil West Sak development is the use of multilateral horizontal wells with a junction providing mechanical support and both through-tubing lateral isolation and re-entry capabilities. However, as extended reach drilling capabilities evolved to routinely reach departure to true vertical depth ratios in excess of five to one, multilateral junction technology did not evolve at the same pace. A new multilateral junction was designed to match current extended reach drilling capabilities and replace existing multilateral equipment which was utilized beyond its intended limit incurring both installation and production risk. The newly designed junction allows lateral liners to overcome drag limitations by rotating the liner and junction to setting depth in one trip and includes several positive indicators to ensure a successful installation. This paper discusses the evolution of multilateral wells in the West Sak development, the limitations of multilateral junctions when utilized in extended reach wells, the development and testing of a new multilateral junction, and several successful field installations. Operation highlights during the completion phase of a multilateral well with a lateral departure to true vertical depth ratio in excess of six to one are included. Existing tools such as oil based mud lubricants and thorough torque and drag prediction were combined with the new junction for a successful completion which progressed the application for multilateral junctions in extended reach wells Multilateral History in the West Sak Development The West Sak field is a heavy oil accumulation within the Kuparuk River Unit on the North Slope of Alaska (Figure 1). It is a Cretaceous, shallow marine sandstone at vertical depths from 2,400 feet on the western edge of the Unit to 3,800 feet on the eastern edge. The field contains 7–9 billion barrels of oil in place with an oil gravity that ranges from 10–22 degrees API. Initial oil production began in the late 1990's from 29 conventionally deviated wells (18 producers and 11 injectors) on a 40-acre water flood pattern with typical production rates of 150–250 barrels oil per day (BOPD). These rates did not support the high cost of the wells and alternative well designs were considered (Targac, et al, 2005). Consequently, operators on the North Slope began experimenting with horizontal and multilateral horizontal production wells which had become an attractive alternative to vertical wells in the multi-layered West Sak reservoir. With multilateral technology, two or more of the West Sak pay sands could be accessed from a single well. In the year 2000, three dual lateral horizontal wells were drilled and completed in the Kuparuk River Unit targeting the upper two West Sak sand intervals. The first of the these wells had an upper lateral length of 3,024 with an ERD ratio of 1.37 while the most difficult of these three wells had an upper lateral length of 3,580 feet with an ERD ratio of 2.04. Note: ERD ratio in this paper is calculated as the (unwrapped surface departure) ÷ (true vertical depth from RKB). The wells were completed with sand exclusion screens in the laterals, TAML (Technical Advancement of Multi-Laterals) Level 4 junctions with both the main bore and lateral cased and cemented at the junction, and artificially lifted with electric submersible pumps (ESP). Upon the economic success of the three first multilateral horizontal West Sak wells in 2000, it became readily apparent that the development would be even more profitable by optimizing well construction. Drilling and well completion costs were by far the largest portion of the capital cost and any reduction in these costs would decrease the cost per barrel produced. Additionally, increased reservoir exposure realized by drilling and completing longer laterals could increase production per well and would further decrease the cost per barrel produced. The West Sak drillsite would evolve to reach subsurface targets exceeding a 15,000 feet radius at depths approaching 3,000 feet TVD (Figure 2).

North Sea World Record Installation–Deepest Sealed Multilateral System

“…This has been an ongoing development in MLT, where ML junctions have been installed in both horizontal and ERD wells (Peterson et al 2009). One of the main drivers for MLT advancement in Norway is undoubtedly Statoil's Troll oil field (Berge et al 2006).…”