Piedemonte fields (Floreña and Pauto) are located in a tectonically and geologically complex area in the Colombian foothills, characterized by rugged topography, deep reservoirs, highly folded layers, high magnitudes and anisotropy in the stresses, presence of natural fractures and interbedded shale and sand sequences. The aforementioned features result in elevated drilling costs related to severe wellbore stability problems associated with high production of cavings, hard tripping, stuck pipe and sidetracking issues.

Geomechanical and wellbore stability modeling are important tools to reduce drilling costs related with operational problems by setting adequate mud weights, evaluating well trajectories and casing designs and identifying operational risks. In the Piedemonte fields, this kind of modelling represents a big challenge considering that every well needs a specific wellbore stability model due to the geological complexity, additionally, the information required can be limited due to operative or cost constraints of logging, coring or performing leak off tests and the risks associated.

The present work describes a methodology for the construction of confident geomechanical and wellbore stability models despite the lack of relevant information in the overburden formations. This methodology allows the integration of the most relevant information regarding mud weights, wellbore trajectories, attack angles evaluation, drilling parameters, a comprehensive cavings monitoring and detailed drilling event analysis for the building of probabilistic wellbore stability models that incorporate the uncertainty of the geomechanical model. This work has contributed to the improvement of the well planning phases, reduction of the uncertainty in the geomechanical parameters and the identification of root causes of the drilling events while minimizing the likelihood of its occurrence.


Despite tremendous efforts and developments in the analysis of wellbore stability problems, unplanned drilling events and operational problems continue causing considerable extra costs in many drilling projects around the world. Drilling wells in the Pauto and Floreña fields, known as the Piedemonte fields, represents a big challenge due to its geological and geomechanical conditions. First drilling campaign in the Floreña and Pauto fields was between 1994 and 1998. Deterioration of the hole and severe wellbore stability problems led to performing 21 side tracks in eight wells drilled (N. Last et al., 1995). Geomechanics understanding and wellbore stability modelling have helped to decrease hole problems. However, drilling wells is still an expensive activity, mainly due to operational problems related with wellbore instability. In the last drilling campaign 21 wells have been drilled in the Piedemonte fields evidencing several problems related with high cavings production, stuck pipe, hard tripping among others resulting in 17 side tracks and over costs above 80 MM USD.

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