Characteristics of Tidal Sand Bars in the Gulf of Khambhat using Satellite Images and Field Mapping, Western India

Saha, Sourav¹, Anupam Ghosh¹, Stuart Burley², Santanu Banerjee¹, Pratul Kumar Saraswati¹ (1) Indian Institute of Tehnology, Bombay, Mumbai, India (2) BG Exploration and Production India Ltd, BG House, Hiranandani Business Park,Mumbai, India, Mumbai, India

The modern day Gulf of Khambhat is identical in depositional setting to the underlying hydrocarbon-bearing Oligo-Miocene sedimentary succession of the Tapti Fields. Although many wells have been drilled on these fields, only limited core is available through the reservoir interval and seismic imaging of reservoir bodies is poor. The modern day tidal sand bodies have been mapped and their length, height and width measured from satellite images as well as at outcrop.

Tidal bars in the outer gulf are linear with curved crests and are spaced 3-5 km apart, forming narrow, high relief (~20 m) ridges 60 to 100 km long and 3-5 km wide oriented 170-290 to the main tidal current (N-S). In contrast, estuarine tidal sandbars are more equant shaped with lower relief, spaced 50m to 1 km apart and oriented at small, oblique angles of 50-80 counterclockwise to the main flow (E-W). In these shallow-water settings, sandbars spread laterally, amalgamate, and are dissected by flood- and ebb-tide channels. As a result bars in the inner estuary are typically 5 to10 km long and 4 to 6 km wide, flat-topped with large widths and are oriented parallel to one another and the estuarine valley walls.

Cumulative-probability curves (CPC) of tidal bar dimensional data from the Gulf of Khambhat are used to assess chance of success (COS) of sand bodies of specific reservoir area, thickness, and spacing are being developed. A CPC plot of tidal bar dimensional data indicate 50% probability (P50) of finding sand bars of 1229 m length, 470 m width, 321 m spacing and 1.1 m thick. This can be used to predict probability of tidal sand occurrence in analogous Oligo-Miocene reservoirs. *project sponsored at IIT Bombay by the Tapti Concession JV Partnership which includes ONGC, Reliance Industries Ltd and BG India.