Retaining apparatus use in a wellhead assembly and method for using the same

A method for retaining an apparatus within the central bore of a wellhead assembly, the method comprising:

• providing a first retaining means within the bore of the wellhead assembly;
• providing a second retaining means within the bore of the wellhead assembly;
• providing the apparatus with an engagement assembly for engaging with the second retaining means within the bore of the wellhead assembly;
• positioning the apparatus within the bore of the wellhead assembly so as to be retained by the first retaining means;
• engaging the engagement assembly with the second retaining means;
• applying a preload to the apparatus against the second retaining means to urge the apparatus toward the first retaining means.

An internal tree cap for installation in the central bore of a wellhead assembly, the wellhead assembly comprising first and second retaining means within the bore of the wellhead, the internal tree cap comprising:

• a cap housing for location within the bore of the wellhead;
• a first engagement assembly for engaging with the first retaining means in the bore of the wellhead to thereby retain the cap housing within the bore of the wellhead;
• a second engagement assembly for engaging with the second retaining means in the bore of the wellhead;
• a preload assembly operable when the cap housing is located within the bore of the wellhead, the preload assembly when operated bearing against the second retaining means to urge the cap housing towards the first retaining means, the preload assembly thereby applying a preload to the cap housing between the first and second retaining means.

A wellhead assembly comprising:

• first and second retaining means within the bore of the wellhead;
• an internal tree cap retained in the bore of the wellhead, the internal tree cap comprising:
• a cap housing for location within the bore of the wellhead;
• a first engagement assembly for engaging with the first retaining means in the bore of the wellhead to thereby retain the cap housing within the bore of the wellhead;
• a second engagement assembly for engaging with the second retaining means in the bore of the wellhead;
• a preload assembly operable when the cap housing is located within the bore of the wellhead, the preload assembly when operated bearing against the second retaining means to urge the cap housing towards the first retaining means, the preload assembly thereby applying a preload to the cap housing between the first and second retaining means.