Abstract
ONGC is working on fast-track development of Malleswaram field in Krishna-Godavari (KG) basin. Proven gas reserves are located in the in the late Cretaceous Nandigama formation which is located at a considerable depth. Exploration wells were drilled and overpressure of up to 1.8g/cc were encountered in Raghavapuram and Nandigama formations. Many drilling challenges related to overpressure were faced, including losses, tight hole, and stuck pipe. Apart from causing non-productive time (NPT), these events also increase the risk associated with drilling and completion of a well. Since, the development phase has just begun and geomechanics study was not incorporated in the exploration phase, there is enough scope to optimize drilling and reduce NPT. This study was conducted with an objective to optimize drilling and completion activities by integrating advanced acoustic and geochemical data for geomechanics based solution. This paper is focused on the new insight developed on the cause of overpressure and characterizing it. A detail analysis on stress direction and its variation with depth and among wells is also presented. In addition, wellbore stability models are also discussed to understand the requirement of appropriate drilling mud weights and casing policy in order to improve wellbore integrity, mitigate drilling risks, and ensure future drilling success. Minimum horizontal stress, breakdown gradient and rock elastic properties generated under the study are also used to generate completion quality flags to aid in identification of stress barriers within reservoir sand units of Nandigama formation.
