The first ever multi-hole “fishbone” well involving multiple horizontal branches has been drilled and commissioned at the Prirazlomnaya offshore rig — the only project on the Russian Arctic shelf at which commercial oil production is currently ongoing. The trajectory chosen for the wells allows significantly greater coverage of oil-bearing sections of the strata. The new well represents the fourth injection well at Prirazlomnaya — the platform having 11 wells currently in operation: six production wells, four injection wells, and one absorption well.
A multi-hole well with a fishbone trajectory does not require the construction of separate wells for each horizontal shaft, thereby reducing the extent of works required, and subsequent drilling costs. Each horizontal section, directed at a specific oil-bearing section of the strata, increases the injection capacity of the well, as well as the drainage area.
The horizontal branches having been created through open-hole cutting and shearing, TAML (Technology Advancement for Multi-Laterals) criteria categorise this new well on the Russian Arctic shelf as among the most complex multi-barrel wells in its construction. The process of drilling multi-hole fishbone wells is more labour-intensive than drilling traditional horizontal wells, since the main offshoots and the motherbore have a higher drilling difficulty index (DDI).
Andrey Patrushev, Deputy CEO for Offshore Development, Gazprom Neft, commented: “As a result of the seamless work of the Gazprom Neft Shelf team, the additional horizontal shafts were drilled all in one go, five days ahead of schedule. The most cutting-edge technologies — which are both effective and safe — have been used in developing what is a unique project on the Russian Arctic shelf.”
The Prirazlomnoye field is the only field on the Russian Arctic Shelf at which oil production is being undertaken (commercial production having begun in December 2013). The first consignments of a new Russian “Arctic Oil (ARCO)” were despatched from the platform in April 2014. The licence to develop this field is held by Gazpromneft-Shelf LLC, a subsidiary of Gazprom Neft.
Initially discovered in 1989, the Prirazlomnoye oilfield is located in the Pechora Sea, 60 kilometres from the shore. Recoverable reserves are in the order of 70 million tonnes. The “Prirazlomnaya” ice-resistant offshore rig was designed specifically for development of this field, and is designed for use in the most extreme environmental and climatic conditions, as well as meeting the most stringent safety requirements and withstanding maximum ice loads.
All wells at the Prirazlomnoye field are located within the platform, the base of which then acts as a buffer between the well and the open sea — which can reach depths of up to 20 metres around the field. In addition to which, all wells are specially equipped to prevent the possibility of any uncontrolled emission of oil or gas. Oil storage at the platform involves “wet sump” methodology, preventing the ingress of oxygen into storage tanks, preventing the ingress of oxygen and the creation of potentially explosive conditions.
The offloading line for the pumping of oil to tankers is equipped with an emergency shut-down system, which is activated instantaneously. Emergency icebreaking vessels will be on permanent emergency standby around the platform, equipped with the latest oil-spill recovery equipment.
A “zero-emissions” system is in operation at the Prirazlomnaya rig, with drilling fluid, bit cuttings (“drilling sludge”) and other production waste all pumped into a special re-injection well.