ABSTRACT:

This paper presents the results of the evaluation and development of improved cement formulations for well abandonment. The developed cement formulations showed lower shrinkage under bulk conditions, expansion under influx conditions, better mechanical strength, higher bonding strength, and lower permeability. With many maturing fields in the North Sea, Mediterranean and Africa, field abandonment will become an issue in the near future. To reduce cost and liability, there is a need to increase the success ratio of well abandonment. The industry indicates that pressure on the annulus is a problem, which implies that traditional cementing techniques do not always provide an effective seal. Although there are many causes of cement sheet failure, cement properties are believed to be the most significant. Therefore, an investigation was initiated to select cement formulations that can be used as an effective barrier in well abandonment. The selection was performed in three phases. · Placement properties like the thickening time, rheology, fluid loss compressive strength development were evaluated to optimise the slurry design. · The effect of expansion and mechanical properties of the set cement were evaluated to improve the formulation of well abandonment cements. · The optimised slurry formulations were tested on long term stability in a U tube test. The cured cement was subjected to a gas pressure differential and monitored on gas break through for several months. The presented material will help to select a suitable cement material to abandon a well with less risk of leakage through the cement plug.

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