Marine riser insert sleeves

A method of operation in a body of water using an offshore floating drilling structure and a subsea well in which drilling mud is used and which comprises:

• connecting a riser pipe between said floating drilling structure and said subsea well;
• drilling a hole by operations through said riser pipe while applying tension thereto;
• running a first string of casing through said riser pipe and setting it in said hole;
• running a sleeve insert, of less length than that of said riser pipe and having a density greater than that of said water but less than that of said mud, in said riser pipe with the lower end of said sleeve insert above said subsea well to effectively reduce the volume in said riser pipe and to effectively reduce the required tension applied to said riser pipe, the lower end of said sleeve insert not being in sealing contact with said wellhead, and said sleeve insert having an outside diameter over substantially its entire length which is only slightly less than the inside diameter of said riser pipe;
• and
• continue drilling through said sleeve insert and said first string of casing.

An apparatus for use with a drilling structure floating on a body of water, in a rotary drilling operation in which a drilling mud is circulated which comprises:

• a riser pipe connected between said drilling structure and a subsea wellhead;
• means to apply tension to said riser pipe;
• and
• a sleeve insert in said riser pipe having a cross-sectional size to substantially fill the annulus between the bore of the sleeve insert and said riser pipe along substantially the full length of the sleeve, the density of said sleeve insert being greater than that of the sea water but less than that of said mud to effectively reduce the tension required on said riser pipe, said sleeve being of less length than said riser pipe and the lower end of said sleeve insert not being in sealing contact with said wellhead.

A method of operation in a body of water using an offshore floating drilling structure and a subsea well in which drilling mud is used and which comprises:

• connecting a riser pipe between said floating drilling structure and said well;
• drilling a hole by operations conducted through said riser pipe;
• running a first string of casing through said riser pipe and setting it in said hole;
• running a sleeve insert having a density only slightly greater than that of said water in said riser with its lower end above said subsea well to effectively reduce the volume of space in said riser pipe;
• continue drilling operations through said sleeve insert and said first string of casing;
• running a second string of casing through the interior of said first sleeve insert and setting same in place;
• and
• thereafter running a second sleeve insert inside said first sleeve insert, the interior diameter of said second sleeve insert being not greater than the internal diameter of said second string of casing.