Identification of Hydrocarbon Bearing Zone in Low Resistiviy Chatral Pay (from Unconventional Shaly Reservoir) in Sanand Field, Ahmedabad Block, Cambay Basin, India

Kameshwar Nath¹, P. Sai Ram Prasad², Louella Shah¹, Roop Chand¹, and Dilip P. Sahasrabudhe^1
1WOB, ONGC, Baroda, India
²WLS, ONGC, Nazira, India

Cambay basin, an aborted rift graben, situated in western part of India, is characterized by five tectonic blocks. The area falling in Ahmedabad block has low resistivity pays in Cambay shale formation. Hydrocarbon bearing zones in Cambay shale were identified/tested mainly based on reported significant activity with oil/gas shows. Identifying hydrocarbon bearing zones becomes an arduous task in cambay shale, a predominantly shale sequence. The recorded electric behavior fails to confirm the hydrocarbon content. The problem is compounded by the fact that the only conventional set of log data is available. These pays are not identifiable by conventional logs. Chhatral member in Younger Cambay Shale of Sanand field in Ahmedabad block, Cambay basin is one such pays. Several studies have been carried out to evolve a definite methodology to identify producible hydrocarbon bearing zones in Cambay shale, which falls outside the ambit of conventional reservoir category. This paper offers an approach towards identifying the producing and non-producing zones in Chhatral pay. Resistivity-Sonic overlay technique has been adopted for this purpose. The section of the pay showing separation between the Deep resistivity and DT curves with Rhob activity gives rise to hydrocarbon bearing zone.

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