Pore pressure is one of the most critical variables on the geomechanical model design, and upon this variable depends largely the successful drilling of oil wells. This pressure is calculated conventionally considering the mechanical stresses, essentially the disequilibrium for compaction, using empirical correlations developed from information taken mainly from the Gulf of Mexico. The use of these equations, does not reflect real situations most of the time, giving pore pressure values inferior to the formation pressures, which may complicate the drilling operations, especially on exploratory wells, increasing the nonproductive times (NPT). The main objective of this investigation is to implement a mathematical model which includes the most common overpressure causes documented in literature, and which allow to quantify the effects of: the under compaction and the thermal stresses due to the water expansion, the kerogen cracking and the oil in shale formations. In order to include the effect of the water expansion, the geothermal gradient and a sedimentation history of a Colombian basin were taken into account. For the hydrocarbons generation, an organic material maturation model was applied, to determine the oil and gas fraction generated. This model was applied to a Colombian basin and providing as a result, a pressure profile quantifying the effect of each mechanism mentioned above. The results obtained with the model shows coherence with the events reported on the study area wells. Similarly, it could be evidenced that, despite the compaction is the main cause of overpressure in depths no deeper than 3000 meters, at greater depths, the thermal stresses contribution may be up to 14% of the total overpressure. For this reason, the proposed model allows to decrease the uncertainty on the pore pressure model. Additionally, the pressure model was simulated with the software PetroMod with the objective of including the boundary conditions, along with the horizontal and vertical flow conditions across the permeable layer, increasing the representativeness of the pore pressure model.

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