ABSTRACT
Offshore fields are usually developed through several deviated wells drilled from each platform to increase the drainage area. However, drilling deviated boreholes mostly have the potential of wellbore mechanical instabilities which may lead to excessive cost and risk. Herein, we investigated the optimum wellbore trajectory and Safe Mud Weight Window (SMWW) for developing an offshore carbonate gas field in southern part of Iran. This was done through building a Mechanical Earth Model (MEM) followed by carrying out sensitivity analyses on various wellbore deviation and azimuth.
Results showed drilling deviated wellbores in the minimum horizontal stress direction yields wider SMWW in comparison to the direction of maximum horizontal stress. However, full waveform sonic scanner data showed that the horizontal stresses re-orientate as the depth increases. Therefore, a particular well trajectory does not necessarily lead to an optimal stable deviated wellbore for all layers. Different wellbore trajectories were recommended to reduce wellbore instability problems. For a 2D wellbore trajectory, a kickoff point at a depth of 1000 m was suggested with an azimuth towards NE or SW. This would result in mitigating wellbore mechanical instabilities for future deviated wellbores being drilled in this field.
