2019 AAPG Annual Convention and Exhibition:

Datapages, Inc.Print this page

Present-Day Stress State Prediction of a Tight Gas Reservoir Using Geomechanical Models —A Case Study From the Lower Magdalena Valley Basin, Colombia


A geomechanical modelling workflow was applied to a tight gas sand reservoir of Oligocene to Miocene age, located in the Lower Magdalena Valley Basin, northwestern Colombia. 1D and 3D mechanical earth models (MEM) were used to integrate the existing knowledge about the reservoir structure, mechanical rock properties, pore pressures and information on regional stresses. Modelling results provide a prognosis for the present-day stress state in the model domain which can be used for various applications. The workflow starts with the development of 1D MEM’s for which wells with logs and core data were available. This method targets the derivation of mechanical properties in the vertical direction and provides a first-order prediction of the stress changes with depth, e.g., the magnitudes of the vertical and the two horizontal stresses. For the 3D MEM, the subsurface geometry was derived from seismic interpretation and well data. Additionally, seismic inversion process and rock physics methodologies were considered to obtain a second set of mechanical properties. A comparison between the two population methods and the resulting stress field predictions is made. The final model is a result of the combination of both data sets. Comparison of the two populating approaches the 3D MEM shows that lateral heterogeneities are captured through seismic inversion-derived mechanical properties while log-derived population results in a more homogeneous distribution. The resulting dominant stress regime in the study area is a normal faulting regime with a governing orientation of SHmax in the WNW-ESE direction. Calculated stress magnitudes and orientation results were calibrated against field measurements. Seismic-driven geomechanical models have the advantage that their resolution and coverage allows to include horizontal heterogeneities in rock properties in the geomechanical analysis. On the other hand, wellbore-scale studies serve to take into account the presence of smaller structures that may disturb or enhance the production process. Integrated approaches consider the necessary variables to characterise the present-day stress state in the reservoir and show higher fidelity in the results. These results intend to enhance the currently available information and scale down the uncertainty of the process related to exploration and production of the area.