Towards a road map for mitigating the rates and occurrences of long-term wellbore leakage /

The objectives of this report are to (1) identify persistent problems that have led to the development of leakage problems, (2) discuss methods that have the potential to reduce the rates and occurrences of wellbore leakage, (3) describe methods to improve monitoring and detection of wellbore leakage, and (4) discuss methods to improve the efficiency of remedial workovers. [...] A hollow pipe (referred to as a ‘kelly’) connected to the drilling fluid pumps is screwed into the uppermost joint of the drill pipe and is inserted into the kelly bushing on the floor of the drilling rig, which is used as the benchmark to measure borehole depths. [...] These leakage 20 pathways may form either during the initial drilling and completion of the wellbore (short-term mechanisms) or later during the active life of the wellbore (i.e., after completion and before abandonment), or even in the decades following plugging and abandonment of the wellbore (long-term mechanisms). [...] If the viscosity of the drilling fluid is insufficient, cuttings may not be properly cleaned, and if the density is too low, the hydrostatic pressure (the force exerted by the setting cement) within the borehole may be insufficient to prevent the influx of formation fluids and gases, i.e., the fluid column of the wellbore is less than the fluid pressure in a pore volume (Baker, 2001). [...] A difference in annular space thickness on the two sides of the casing makes displacing the drilling mud and placing the cement slurry more difficult, especially when the interior casing is in direct contact with the exterior casing or the rock wall over a considerable distance.