A Sequence Stratigraphic Framework for the Tide Dominated Lower Tarkeshwar Reservoir in the Lakshmi Field (Gulf of Cambay, India) to Enhance Field Understanding and Production Potential

The offshore Lakshmi Field in the southern part of the prolific Cambay Basin, Western India, is an inversion fold structure generated during the Late Miocene. The main reservoirs in the lower Tarkeshwar Formation of the field were deposited during the early Miocene in a global sea-level overall transgressive system following a late Oligocene major low-stand event. The present day satellite images of the Gulf of Cambay provide an effective analogue for the complexities and geometries of a tide-dominated estuarine environment. Flooding surfaces recognized in electro-log motifs from 12 wells in the Lower Tarkeshwar Formation enabled sequence boundaries to be interpreted and facies distribution patterns identified, including forced regressive units and associated complex valley-fill sequences. Analysis of the vertical stacking patterns in the well logs revealed a series of para-sequences through time. Electro-log driven seismic attributes were grouped into four primary geomorphic elements namely, large estuary systems with channels, tidal creeks, muddy tidal flats and migrating tidal bar complexes. These geomorphic elements were analyzed in detail to establish realistic geometrical parameters including shape, size, orientation and thicknesses. Tidal bar geometries were obtained from quantitative data and satellite images of the present day Gulf of Cambay coupled with outcrop analogues of the Sego Sandstones in the Book Cliffs of Utah. Depositional trends were defined and aerial facies distribution maps were generated at key levels. The aerial facies distribution maps and electro-log stacking patterns were integrated to develop a 3D facies model which honored the geometries of the geomorphic elements. Petrophysical property distributions biased to the facies model enabled characterization of the hydrocarbon fluid flow and addressed uncertainties in reservoir connectivity and continuity.

This integrated sequence stratigraphic approach to incorporate electro-facies, quantitative seismic geomorphology and modern day analogues has enabled the Lakshmi asset team to quantify the production potential of these Lower Miocene sands and open up future development opportunities. The result is a success story of transforming a depleting gas field to an economic low-cost oil producing asset.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California