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Wells Plugged in 2013

DH4

Dh4 is the deepest well drilled during the CO2 project and is situated in the UNIS Well park in Adventdalen. The BQ 
string was installed at 870 m; below this the drill hole was uncased, i.e. open to the formation. During the P&A, the 
sandstone formation at 773 to 799 m, which had never been tested, became available when the BQ string was cut and 
retrieved to the surface. 

According to the original drilling plan from 2009, 30 litres of cement was administered into the well to secure the BQ 
string. The pre-plan for DH4 was to secure/plug the open-hole section of the well, cut and retrieve the BQ string from 
790 m and access the formation through the NQ string. 

Interface casing/cement
(micro-annulus, channel)

Interface casing/cement
(micro-annulus)
(wax, scale, oil, dirt, etc)

Bulk permeability
(connected pore, crack, channel)

Leak in casing (connection)
(connected pores, cracks)

Annulus cement
(connected pores, cracks)

Interface rock/cement
(micro-annulus, channel)
(mudcake, cutting, oil, etc.)

Barrier Failure Model

Figure from: Guidelines on the qualification of materials 

for the suspension and abandonment of wells issue 1 July 

2012

Bullhead Cement is used when the well is open to a permeable formation. The cement can be pumped directly down 
the well to the formation (see figure below)

Balanced Cement plug is used when the well is tight (no perme-
able formation). The cement is pumped and the flow controlled 
/ balanced through a work string that is retrieve from of the 
well after the work is finished. (See figure below).

• During tagging a weight is sent down on top of the plug for verifying the depth and consistency (solid/properly 

set). Alternatively

• Coring the cement plug by drilling will  verify that the cement is hard and of good quality. In all cases

• Pressure testing – used to verify that there is no leakage (solid plug) and that the plug has strength to handle 

certain pressure. (see figure opposite for potential leak paths for a permanent plug).