Flow Control, Flow Control March 2019
By Bob Eden Rawwater Engineering Company Limited G lobally referred to as plugging and abandonment P A the decommissioning of depleted oil and gas wells involves the insertion of plugs downhole to seal the reservoir The objective is to prevent surface leakage and cross contamination and to return the integrity of the caprock penetrated when the well was first opened to a predrilled state Plugging and abandonment is completed almost exclusively by the application of cement slurry typically with three cement plugs inserted at different depths in the wellbore to achieve a secure seal The process consumes hundreds of feet of cement can cost hundreds of thousands of dollars per well can take several days to complete and offshore requires the use of a rig The three cement plugs in the P A process follows the requirements in the U K Norway and the U S for plugging namely a primary plug above the depleted reservoir a secondary plug that can also form a continuous seal with the primary plug and a surface plug sitting beneath the seabed see Figure 1 The plugging process is designed to create 24 March 2019 Figure 1 Three cement plugs in the P A process Features Oil Gas Developing alloy based alternatives for oil well plugging and abandonment While cement has been the most widely used abandonment medium the development of bismuth alloys offers advantages as an alternative All images courtesy of Rawwater
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