The geological evolution of the northern region of Colombia has resulted in lateral/oblique compressional stresses leading to the development of tilted faulted blocks and associated subsidence, followed by intense folding/uplift that has impacted the stress regime and the pore pressure evolution. Previous pore pressure prediction approaches often considered a shallow overpressure associated with a high fracture gradient (FG), and thereby allowing an assumption for a wide operational mud window. Drilling experiences however, indicated a contrasting scenario and thereby a better understanding and a more accurate estimation of overpressure and FG became necessary.

With the aim of optimizing drilling operations, a geomechanics analysis was conducted, based on existing information incorporating local geological inputs and production well data, in order to better predict wellbore stability, pore pressure, fracture gradient and to identify related drilling risks for the planned wells.

The resultant geomechanical model confirmed the presence of shallow overpressure development, the occurrence of which, along with its distribution and magnitude, is mainly controlled by the geological events (especially uplifting) that shaped the basin. Subsequent updates of the model managed to explain the frequent occurrences of water inflows, gas kicks, high volume of losses (a gain-loss situation) and instability recorded in previous wells. It also predicted a feasible but conservative mud weight window for the wells in this field. Understanding the geological evolution allowed for a better comprehension of the stress regime changes over time. Through an enhanced understanding of the geological and geomechanical influences, a risk mitigation strategy was developed to proactively reduce pore pressure and wellbore instability related drilling effects encountered in the earlier wells.

So far, well schematics and mud weight windows have been optimized in five wells through utilizing this geomechanics approach to deal with the challenges imposed by a narrow mud window. The planned wells have been successfully drilled in record time with no major drilling problems by using the recommended mud pressures and optimized drilling practices.

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