Malleswaram field in Krishna-Godavari (KG) basin has proven gas reserves in the late Cretaceous Nandigama formation. Many drilling challenges were faced, including losses, tight hole, and stuck pipe in the Raghavapuram and Nandigama formations overlying the reservoir interval. This study was conducted to provide a solution for drilling optimization by mitigating drilling-related nonproductive time (NPT). Integration of acoustic and geochemical data for geomechanics study provided a new insight into cause of overpressure and need for revamping of casing policy to significantly improve wellbore stability, mitigate risks, and ensure future drilling success. Generated stress models can be used to optimize hydraulic fracturing in these reservoirs. A completion quality based on stress model indicates the need for multistage fracturing due to the presence of stress barriers inside sand units in Nandigama formation.

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.