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Fracture Characterisation from Basement Reservoir: A Study from Mumbai High

Satyanarayana Pratha1, P. K. Sinha2, A. V. Sathe2, G. C. Katiyar1, and G. C. Agarwal3
1MH Asset, ONGC,Mumbai, Mumbai-400051, India
2KDMIPE, ONGC, Dehradun, India
3Consultant, Independent, Bhopal, India

Mumbai High structure, in the western offshore basin of India, established the presence of Hydrocarbon accumulations in the fractured Basement rocks by exploratory drilling. The basin floor is represented by Deccan trap and granitic, and metamorphic rocks. The thick sedimentary section of Paleocene to Holocene age lies unconformably over the basement and hosts the most prolific hydrocarbon bearing carbonate sequences.

Since basement is unique in terms of reservoir nature, conventional methods of interpretation are not enough to characterize the basement fractures as basically the porosity and permeability are generated by a network of interconnected fractures which are the possible accumulation pockets of hydrocarbons. It is also difficult in the absence of shear wave data to convincingly identify the fractures.

However, the seismic data analysis might suggest the fractures are associated with anomalies in amplitude or impedance, which may not be directly attributed to only fractures as non-fracture heterogeneities in the sub-surface could also be the source of such anomalies. Hence, data analysis in combination with the geometric surface attributes can lead to logical conclusions to infer the effects of faults and associated fractured corridors.

An attempt has been made on PSDM seismic data to map detailed fault framework as faults are one of the fracture drivers. Geometric attributes viz., dip, azimuth and coherency are generated for the identification and establishing the fault pattern. The clear basement event has been correlated and various surface attributes were generated to qualitatively demarcate the fractured areas and thereby exploratory targets

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