Drilling damage mechanisms

Review of the drilling history (drilling reports) can reveal damage caused early in the life of a well. This includes an understanding of fluids used and their properties (oil based or water based, pH, solids used, etc.). There are two primary drilling damage mechanisms to consider ... 

Damage mechanics principles have been applied extensively for well stability problems, especially for hard, brittle and fractured shale rocks. Constitutive models using damage concept, coupled with hydro-chemical swelling models, have been developed based on experimental results, and applied for design of drilling fluid density, combined with FEM methods (Liu, 1995). 

Delamination is one of the most common damage forms associated with drilling of polymer composites. The most common types of drilling-induced damage mechanisms are peel-up delamination at entrance and push-down delamination at exit side of the drilled hole. The various other types of drilling-induced damage found are fibre... 

Microvias that are created by laser drilhng can be located at a reduced pitch for CAF studies because one does not expect drill damage from a laser-ablated hole and it will not be subjected to the drill wander of a mechanically drilled hole. Thus, laser drill tolerances are below 0.025 mm (0.001 in.). 

Productivity damage attributable to drilling or completion fluids results from three mechanisms ... 

This type of damage is dealt with comprehensively in Section 8.8. It can be particularly severe in seawater giving rise to cavitation corrosion or cavitation erosion mechanisms, and hence can be a considerable problem in marine and offshore engineering. Components that may suffer in this way include the suction faces of propellers, the suction areas of pump impellers and casings, diffusers, shaft brackets, rudders and diesel-engine cylinder liners. There is also evidence that cavitation conditions can develop in seawater, drilling mud and produced oil/gas waterlines with turbulent high rates of flow. 

Meyer, T., Drum, P. G. (1996). Fragmentation and Rock mass Damage Assessment - Sunburst Excavator and Drill and Blast. In Proceedings of the HARMS 1996 - Rock Mechanics Tools and Techniques (pp. 609-617). 

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