Understanding the Depositional Environment in Early Cretaceous Reservoirs: Application of Oil Based Borehole Imaging in Krishna-Godavari Basin, Eastern Offshore India

Zuber A. Khan¹, Sanchita Ganguly², and Chandramani Shrivastva^2
1Geology, Gujarat State Petroleum Corporation Ltd., Gandhinagar, India
²DCS, Schlumberger, Mumbai, India

A proper understanding of the sedimentology, micro structural controls and heterogeneities in the reservoir properties is imperative to establish the sedimentary environment of deposition. With the increasing usage of oil-based muds worldwide, latest borehole imaging tools are being extensively used for a comprehensive understanding of geological architecture of reservoirs since they aid in interpretation due to the high resolution data. Numerous borehole image examples from Krishna-Godavari (KG) Basin, Eastern Offshore India present a spectrum of processes that give rise to different architectural elements of shallow marine reservoir systems of Early Cretaceous.

The KG sedimentary basins poses a lot of challenges in understanding the palaeo transport direction of sediments due to many structural complexities introduced by the rifting of Indian plate from Antarctica. With the help of borehole image logs and dipmeter interpretations, understanding of various depositional facies and the sediment dispersal directions have improved.

The Early Cretaceous reservoirs of tidal channels and tidal bars are interpreted with the facies associations identified on the borehole image logs and associated dip azimuth variations. The major lithofacies identified are sandstone (massive, laminated and cross-bedded), shale (thin laminated and slumped), siltstone (laminated) and heterolithics (thin alternation of sand/silt and shale). These associations of sedimentary features and facies help in understanding the different architectural elements of the system with the relative shallowing and deepening of the basin.

Integration of the conceptual model with available wireline logs, mud logs and core data and modern day analogues provide key guidelines in static modeling of reservoir to prepare for petrophysical facies model in pursuit of better prospects.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery