Advanced Logs and Seismic Driven Geomechanics in Complex Sandstone Reservoirs for Drilling Optimization

Abstract

Sandstone reservoirs of the South Caspian basin in Turkmenistan are currently undergoing further development—with the addition of deviated wells. The localized depletion occurring in some of the offshore fields in this area has thus far triggered a host of geomechanics-related challenges—including wellbore instabilities and poor hole quality. In anticipation of further depletion over the remaining fields life, geomechanics effects will become more pronounced and the associated technical and economic challenges facing these fields may increase. To assist in future well planning and field development, and to diagnose the problems already encountered in the existing vertical wells, 3D seismic-driven mechanical earth models (MEMs) were built. These covered the main sandstone reservoirs as well as the shaley formations. This integration of data from drilling operations, open hole logs, core, seismic and formation pressure measurements provided a constrained and consistent description of the prevailing in-situ state of stress, pore pressures and rock mechanical properties. These geomechanical models were further improved by accounting for historical depletion in the fields considered. The depletion modelling was performed numerically using a simulator performing finite difference fluid-flow calculations. The results obtained and understanding gained were then considered in the analyses of wellbore stability for future wells. This paper describes these geomechanical analyses and modelling—including the data integration to assess wellbore stability at the current level of depletion.