Authors: Younessi, A; Rasouli, V

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Younessi, A & Rasouli, V 2008, 'Representing a Rock Engineering System to Analyse Wellbore Instability Due to Fracture Reactivation', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium, Australian Centre for Geomechanics, Perth, pp. 381-394.

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Abstract:
In drilling practices, as the wellbore is the only route to transfer the produced hydrocarbon to the surface, the instability of the wellbore during drilling and production is a major concern. Sliding failure along the fractures (especially faults) that intersect the wellbore is one of the wellbore instability mechanisms. Here, in comparison with the slope stability, a well known phenomenon in mining and civil industry, during drilling process the drilling mud can penetrate through the discontinuities, and during production, the reservoir depletion causes changes in the horizontal stress magnitudes. Both of these effects could lead to the fracture reactivation and wellbore instability. The rock engineering systems (RES), initially introduced in mining and civil related geomechanics field, is an approach to analyse the interrelationship between the parameters playing in the wellbore failure mechanisms. In this study, after discussing all the failure mechanisms in a wellbore, and identifying all the effective parameters in wellbore instabilities, an interaction matrix is introduced to study the failure mechanism, particularly the sliding failure mechanism. Thereafter, the interaction intensity and dominance of each principal parameter in the system is established to classify the parameters. The other aspect of the systems approach is establishing when positive feedback within the system can occur, which leads to instabilities. The results indicate the ability of this method to analyse the wellbore instability with regard to fracture reactivation mechanism and help to find a better engineering action to mitigate or eliminate instabilities.

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