Greetings everyone.

As others have said, this is not a number you can readily guess or calculate. We often deal with onshore wells that have vertical design growth of 300mm or more, I think the largest wellhead displacement I have been asked to consider in my designs has been 500mm (20").

When I have had to design piping from wellheads where I am unsure of the actual wellhead vertical growth (usually the clients provide this information) I usually end up making a conservative estimate, and then state clearly on the drawing that the piping has been designed assuming a well head growth of Xmm, and that if the actual well head growth is larger than this to contact the engineer for a design check. In the end you are limited as to what you can do if you are not given the information required.