Tieback assembly for marine underground wellhead

The invention discloses a tieback assembly for a marine underground wellhead. The tieback assembly mainly comprises a riser pipe, a tieback head, a 133/8'' casing pipe, a 133/8'' casing pipe tieback head, a 95/8'' casing pipe, a 95/8'' casing pipe tieback head, a tieback hanger and the like. When the tieback operation is required for the marine underground wellhead, the tieback head is in locking connection with the marine underground wellhead through a locking block and the tieback head is sealed with the marine underground wellhead through a seal V and a seal VI; the 133/8'' casing pipe tieback head is in threaded connection with the tieback hanger and is sealed with the tieback hanger through a seal VII; and the 95/8'' casing pipe tieback head is connected with the tieback hanger through threads on a connecting ring and is annually sealed by metal seal. The tieback assembly disclosed by the invention is compact in structure and convenient in operation and better meets the requirement of a tieback process o