DRILLING AND COMPLETION SYSTEM FOR MULTILATERAL WELLS

摘要

1. A wellbore system comprising a main wellbore extending into an earth formation; a branch wellbore extending from a selected location of the main wellbore into the earth formation; a casing arranged in the main wellbore, a branching device arranged in the casing and connected to a conduit extending through the casing to a wellbore facility at surface, the branching device having a main bore in fluid communication with the wellbore facility via the conduit; and a branch bore providing fluid communication between the main bore and the branch wellbore via a window opening provided in the casing, wherein a seal is provided between said branching device and the inner surface of the casing so as to prevent fluid communication between the window opening and the interior of the casing. 2. The wellbore system of claim 1, wherein the seal extends around the window opening. 3. The wellbore system of claim 2, wherein the seal is activated by at least one activating member selectively exerting a force to the branching device in the direction of the window opening. 4. The wellbore system of claim 3, wherein each activating member comprises a pair of wedge shaped elements movable between an extended position and a retracted position in which the wedge shaped elements are at shorter mutual distance than in the extended position, and wherein in the extended position the activating member allows movement of the branching device through the casing and in the retracted position exerts said force to the branching device. 5. The wellbore system of claim 4, wherein the activating member comprises a memory metal member interconnecting the wedge shaped elements, which memory metal element is arranged to move the wedge shaped elements from the extended position to the retracted position upon reaching the transition temperature of the memory metal element. 6. The wellbore system of any claim 1 to 5, wherein the wellbore facility is a drilling facility and wherein a drill string extends via the conduit, the main bore and the branch bore into the branch wellbore. 7. The wellbore system of any claim 1 to 5, wherein the wellbore facility is a hydrocarbon fluid production facility and wherein a branch casing extends from the branch bore into the branch wellbore. 8. The wellbore system of claim 7, wherein the branch casing extends into the branch bore, and wherein an annular sealing element is arranged between the branch casing and the branch wellbore. 9. The wellbore system of any claim 1 to 8, wherein the conduit is a primary conduit and the system further comprises a secondary conduit extending through the casing and providing fluid communication between the main bore and a hydrocarbon fluid reservoir of the earth formation. 10. The wellbore system of any claim 1 to 9, further comprising a passage for hydrocarbon fluid flowing through the casing from the interior of the casing below the branching device to the interior of the casing above the branching device. 11. The wellbore system of claim 10, wherein the passage is formed by a clearance between the branching device and the casing.