Geological Evolution of Surat Depression and Development of Hydrocarbon Pools in Contigeous Areas

Dimri, Bandana ¹; Misra, Kiran S.¹
(1) Petroleum Engineering And Earth Sciences, University of Petroleum And Energy Studies, Dehradun, India.

Surat depression is very significant geomorphologic feature, located south of Saurastra in western offshore region of India. The very presence of several hundred meter deep depression in the coastal region suggests continuing active subsidence. This ENE-WSW trending elongated feature is in the lateral continuity of Narmada-Tapti rift zone, which divides Indian peninsula into two distinct geological entities. Interpretation of seismic profiles,by processing the data by Pre-Stacking and Depth Migration (PSDM) techniques have given an insight to better understand the sedimentary sequences, below and above the Cretaceous volcanics, the thickness patterns and geological evolution. Rapid increase in thickness of both Mesozoic and Tertiary sequences within the Surat depression, indicates it’s prolong geological history starting with the beginning of Mesozoic Era. The thickness of Cretaceous volcanics, however, remains unchanged. Seismic profiles also exhibit different patterns of distribution of coral reef complex across this depression. To the north across the Kutch- Saurastra offshore, Paleocene reefs are located on the western side, while successively younger Eocene and Miocene complexes are on the eastern side, while Paleocene reef complexes are overlain by younger Eocene reefs in the south.

Like all other half graben and rift structures of peninsular India, the Surat depression is also marked by the presence of discrete nearly vertical faults, with pronounced subsidence along northern margin, while on the southern side there are innumerable enechelon faults with incremental subsidence. Concentration of organically charged sediments in the floor portion of the Surat depression seems to have been due to various geological and oceanic processes. Rapid burial and thermal maturity seem to have generated hydrocarbons, which moved upward through innumerable nearly vertical faults to get preferentially accumulated in suitable reservoirs rocks, located on the submerged Bombay platform.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.