Patent Application
20190063169
The field of the invention is tieback connections to a wellhead requiring specific space out in applications where metal to metal seals for high pressure applications are needed.
In assembling subsea wells there is often a distance that needs to be spanned between an upper end of a tubing string or an isolation packer and the wellhead. Frequently, in deep wells this distance could be 1524 meters or more. The spacing between the lower support location and a hanger in the wellhead needs to be closely approximated by the length of the assembled string in between. Stretch of the tubulars under their own weight complicates this space out. In the past this required what was called a dummy run where the string was landed on the lower support and assembled to the wellhead hanger location. The offset from the desired dimension was marked by closing BOP rams on painted DP joints. The string was then pulled so that sections could be replaced with different lengths and another trip in the hole was made to get the optimum spacing between the tubing or packer support in the wellbore and the wellhead hanger. On offshore applications this could be very costly in view of the additional rig time needed to make the additional trip and rig up and rig down casing equipment again.
Metal to metal tieback seals were developed by Baker Hughes, a GE company but they required continuous weight to hold a sealing connection. Due to thermal expansion or contraction concerns it was not certain in the past that such a connection would have the requisite weight on the connection, which forced the joint to be cemented to hold the connection together. The need to cement also added logistical complexities and cost particularly in offshore applications.
Telescoping joints have been developed to address the space out issue by allowing as much as 7 meters leeway to connect to the wellhead hanger and avoid making a dummy run. Telescoping joints for subsea use are described in U.S. Pat. No. 9,664,000; 2015/0129240; U.S. Pat. No. 5,090,737 and U.S. Pat. No. 3,667,547.
What has not been available and is addressed by the present invention is a way to provide metal to metal tieback seal and keep it operative without a need to cement as in the past in a tieback string that saves a dummy run but at the same time allows for high pressure connections using metal to metal sealing optionally including the seals in a telescoping space out joint. The joint is located in the string at a depth where the weight of string connected to the lower end of the telescoping joint provides the weight to keep a metal to metal seal weighted so that it will function without a need for a cementing job, although cementing can still be optionally done. These and other aspects of the present invention can be more readily understood from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention can be determined from the appended claims.
A tieback string assembly features a metal to metal nose seal weighted down with casing extending between a lower end of a telescoping joint also optionally having metal to metal seals for spacing out to a wellhead casing hanger. The telescoping joint is located so that the hanging weight off the telescoping joint lower end is sufficient to energize the metal to metal nose seal engaged to a sleeve or a liner top packer. The tieback string is smaller in outside diameter than the parent casing through which it is run. The assembly retains high pressure by avoiding lower pressure rated elastomers in the nose seal or the telescoping joint.
For operators with needs to contain high pressure in deep wells the combination of a telescoping joint placed in a string at a precise location so that hanging weight off the joint 18 satisfies the need to keep a predetermined weight on the metal to metal seal 14 when used in combination with a joint 18 that features metal seals as well, the assembly described provides the solution.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
