METHOD FOR CREATING SECONDARY SIDETRACKS IN A WELL SYSTEM

摘要

1. A method for creating a secondary sidetrack in a well system for production of hydrocarbon fluids and gases from a hydrocarbon formation, which well system comprises a main wellbore and a primary sidetrack which debouches into the primary wellbore, the method comprising inserting an unexpanded expandable liner into the primary sidetrack and radially expanding the liner, characterized in that an opening is created in the wall of the expanded liner in the primary sidetrack and that a secondary sidetrack is drilled into the hydrocarbon bearing formation through said opening. 2. The method according to claim 1, wherein the expandable liner is formed by a coiled tubing through which drilling fluid is pumped towards a downhole drilling assembly which is used to drill the primary sidetrack and which coiled tubing is radially expanded after the primary sidetrack has been drilled. 3. The method according to claim 1 or 2, wherein the secondary sidetrack is drilled with a drilling assembly which is connected to a coiled tubing, which tubing is expanded after the secondary sidetrack has been drilled to form a lining in the secondary sidetrack. 4. The method according to claim 1 or 2, wherein the secondary sidetrack is lined along at least part of its length with an expandable slotted liner which is expanded inside the secondary sidetrack such that a series of staggered slots in the liner open up into diamond shaped apertures. 5. The method according to claim 4, wherein an expandable sandscreen is arranged around the expandable slotted liner in the zone where hydrocarbon fluids flow into the well system. 6. The method according to claim 1, wherein an unexpandable liner is inserted into the secondary sidetrack which liner is perforated in the zone where hydrocarbon fluids flow into the well system. 7. The method according to claim 1, wherein the capillary sidetrack is uncased along at least part of its length. 8. The method according to claim 1, wherein a plurality of primary sidetracks debouch into the primary wellbore and wherein a plurality of secondary sidetracks debouch into at least one of the primary sidetracks. 9. A well system comprising at least one primary sidetrack and at least one secondary sidetrack wherein the primary sidetrack comprises an expanded expandable liner which comprises an opening into which a secondary sidetrack debouches. 10. The well system of claim 9, wherein the expanded liner in the primary sidetrack has an internal width which is substantially equal to the internal width of a casing in the primary wellbore. 11. The well system of claim 10, wherein one or more tertiary sidetracks debouch into at least one secondary sidetrack so that a root-like multilateral well system is created.