Wellbore Stability Improvement Using Caving Analysis

Abstract

A geomechanical study 1D for wellbore stability was performed in Putumayo Basin where some instability issues were recorded. Cavings analysis was conducted to understand and enhance the wellbore stability while drilling the wells, nonproductive time related to geomechanics and drilling events must be mitigated. A comparison was made between predrill, real time and postdrill model to update, validate and improve the wellbore stability prognosis for future wells. Borehole collapse was predicted by using Mohr-Coulomb failure criterion and uncertainties were reduced with cavings analysis due to lack of caliper readings and sonic well logs while drilling. The windows limits were obtained by building a 1D geomechanical model as a result of using offset well data and calibrated with own wellbore and regional data. Multiple wellbore stability 1D models were built and calibrated. In some zones, the borehole collapse was overestimate and cavings were useful to choose the optimum mud weight to maintain the wellbore stable. Therefore, it was important to monitor the wellbore stability while drilling the well and mitigate borehole collapse.

Real time drilling geomechanics methodology was successfully developed and implemented in some wells for forecasting the wellbore stability, which was enhanced by using cavings analysis. A group of experienced professionals executed a simplified methodology, analyzing cavings morphology, measuring cavings rate and size for time decision; take proper actions while drilling to mitigate drilling events. This paper will show the importance of cavings analysis in real time.