Wells

Subsea well abandonment cost estimation requires the identification of minimum requirements for full and adequate isolation of formation fluids both within the wellbore and from surface. For example in th UK the identification of the scope of work reference would be made to the UKOOA publication “ Guidelines for the Suspension and Abandonment of Wells”, Issue 1,June 1994.

Reference would be made to the following:

• API RP 57, First Edition, Jan 1986.
• Norwegian Petroleum Directorate Guidance for Drilling and Well Activity.
• US MMS regulations.
• CSON 12
• SSM CS 16

These guidelines are therefore considered to be applicable for the UK wells, which are governed by UK safety regulations, due to the Guidelines reference to CSON 12. Well plugging and abandonment in other parts of the world would be governed by local regulations.

A semi-submersible drill rig would be the primary option for plugging and abandoning the subsea wells. An alternative would be the use of a well services vessel.  

To abandon the subsea wells in accordance with the UKOOA Guidelines, the following basic requirements must be met:

• All discrete permeable zones penetrated by the well should be isolated, both from each other and from surface, using permanent barriers.
• Hydrocarbon bearing permeable zones should have at least two permanent barriers from the surface.
• All casing strings will be retrieved a minimum of 10 feet below seabed in accordance with CSON 12. All surface equipment removed and a seabed clearance certificate issued.

Providing the above requirements are met the removal of downhole equipment is not a requirement.
 

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