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Petrofacies Analysis for Improved Reservoir Characterization-Studies in Sadra Area, Cambay Basin

Janmejai K. Srivastav, Sanjeev Satyarthi, Sukhpal Singh, and Anil K. Gupta
RGL, ONGC, Vadodara, India

One of the most important existing and emerging challenges of geoscientists and engineers is to improve reservoir description techniques. Accurate determination of pore-body / throat attributes and fluid distribution are central elements in improved reservoir description. The Petrofacies analysis is defined as the characterization and classification of pore types and fluid saturations as revealed by petrophysical measurements of reservoir.

In the present study the characterization of reservoir units in Kalol formation in Sadra field of Ahmedabad area of Cambay basin is attempted. The studies were carried out using the petrophysical tools on core plugs from selected wells of the area. The studies include effective porosity, air permeability, pore size distribution, pore throat sorting, pore geometry and formation resistivity studies.

The studies have characterized the pore geometry of three pay units of Sertha member of Kalol formation namely K-VIII, IX & X. The studies indicate that pore geometry and the reservoir characteristics in general get poorer while moving from north to south in the field as a result of the plugging of pore throats and destruction in permeability. The reservoir is largely dominated by micro pores (pore size<1µm) and finer pore channels and have moderate to high irreducible saturation (Sirw 30 to 96%), the effective porosities are good (Φe 15 to 20%) and the permeability is fair (Ka 1.8 to 36 md). The studies have also identified the flow units with better hydraulic quality within the studied interval. The apparent and intrinsic formation resistivity factor has indicated appreciable shale effects. The studies shall help in identifying, correlating and mapping the flow units in the reservoir and shall be useful for more realistic reserve estimation.

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