Abstract

This paper describes the hierarchical approach used to characterize the regional state of stress in tectonically active settings. The example featured here is the Cusiana field where wellbore instability was a serious problem. The Cusiana field is located in the foothill of the Colombian Andes, South America. A key to solving the instability the was to identify what stress information was needed to improve drilling performance. Using drilling records, caliper logs, cavings samples, cores from the reservoir and a few meters of borehole image, an internally consistent working hypothesis of the state of stress was formulated, tested and refined. Simple calculations based on elastic-brittle model, confirmed also b, y drilling data, showed that the minimum principle stress is horizontal and the overburden was the intermediate stress. Elastoplastic modeling of borehole deformation in sands and shales based on core testing and finite element analysis placed tighter constraints on the relative principal stress magnitudes and the magnitude of the maximum horizontal stress.

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