JST successfully got the authorization of invention patent on a wellhead secondary pack off seal structure in USA by United States Patent and Trademark Office in July, 2021.

During the drilling operation and oil and gas testing, the casing head slip hanger is the basic part of wellhead equipment, which is installed at the upper end of casing string to hang casing strings of each layer and seal the annular space between casings of each layer. As the main seal of slip type casing head, the performance of pack off seal directly affects the application range and normal use of casing head.

At present, most pack off seals used are of annular rubber ring structure, which are basically used under the working conditions of 5000PSI low pressure and temperature range of -18℃~110℃, which can not meet the requirements of slip casing head for higher pressure and wider temperature range. The reasons are as follows:

1. The application temperature range of rubber is relatively narrow, generally in the environment beyond the temperature range of -18℃~110℃

2. Rubber is prone to gas explosion during high pressure relief, resulting in damage to rubber products;

3. Rubber will soften at high temperature, and it is easy to squeeze out from the gap under the action of high pressure, resulting in deformation of slip seal;

4. Rubber will harden and lose its elasticity at low temperature, which will reduce its sealing performance.

The above factors determine that the rubber pack off seals used at present cannot meet the requirements of slip casing head under the working conditions of 15000PSI high pressure and PU temperature grade (-29℃~121℃).

Summary of the invention:

In order to overcome the defects in the prior design, this invention provides a pack off seal structure, which can meet the requirements of using slip casing heads under the working conditions of 15000PSI high pressure and PU temperature grade (-29℃~121℃).

Compared with the prior design, the pack off seal structure of the invention has obvious advantages:

1. the compression resistance is good, and the service pressure can be as high as 15000PSI；

2. The application temperature range is wide and the applicable temperature range can reach PU (-29℃ ~ 121℃);

3. Strong gas explosion resistance. Under the working conditions of 15000PSI and PU(-29℃~121℃), no gas explosion damage occurred after use, and there was no damage at all;

4. Pass the PU temperature grade test of casing head and obtain certification.

Therefore, the pack off seal structure of the present invention will have a very excellent application prospect.