ABSTRACT

Abnormal pressures are encountered during exploration drilling in different parts of Krishna–Godavari Basin on the east coast of India. The nature and stratigraphic occurrences of the overpressure zones vary across the basin. Three different clusters of wells, covering a large part of the basin encompassing both onshore- and offshore-drilled wells, are analyzed to capture this variation. A wide range of pore-pressure gradients from normal to as high as 18 MPa/km was observed in the present data set. The tops of overpressure zones demonstrate a large range from 2200 to 3000 m (6562 to 9842 ft). These depths generally correspond to either a Miocene deltaic sequence or Cretaceous synrift and postrift sequences. Available well data reveal two main reasons for the development of overpressure. Considerably high pore-pressure regimes in the Cretaceous sequence in the eastern corner of the basin are found to be mainly caused by gas generation, whereas disequilibrium compaction is proposed as the main cause for overpressure in the other parts of the basin. The outcome of this analysis provides a fair idea of the nature, magnitude, and distribution of the overpressure, and this will also help to strategize further exploration activities in the basin.

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