Casing mandrel for facilitating well completion, re-completion or workover

A casing mandrel and a tubing head for an independent screwed wellhead, comprising in combination:

• the casing mandrel having a bottom end supported in a casing bowl of the independent screwed wellhead, an annular shoulder engaged by a casing bowl nut of the independent screwed wellhead, and a top end that extends above a top of the lockdown nut and comprises an outer surface with a pin thread and a smooth cylindrical seal surface above the pin thread, and an inner surface with a seal bore in a top of an axial passage through the casing mandrel, the seal bore being adapted to receive a fixed-point packoff of a pressure isolation tool;
• and
• the tubing head comprising a box thread that engages the pin thread and elastomeric seals received in seal grooves above the box thread that engage the seal surface.

A method of completing a cased well with an independent screwed wellhead, comprising mounting a tubing head to a casing mandrel that supports a production casing from the independent screwed wellhead, the casing mandrel comprising an axial passage that has a diameter at least as large as an internal diameter of the production casing and a seal bore at a top of the axial passage adapted to receive a fixed-point packoff connected to a high-pressure mandrel of a pressure isolation tool used to stimulate production zones of the cased well.