Integration of Core, Log and Well-Test Data to Understand a Complex Volcanic Reservoir, Barmer Basin, Rajasthan, North West India
Timothy O’Sullivan1, Vr Sunder1, Yatindra Bhushan1, Sumit Mishra1, Paul M. Compton1, Brian Bell1, and V.V. Subba Rao2
1Reservoir Development, Cairn India, Gurgaon, India
2ONGC, Dehradun, India
The Raageshwari Deep gas reservoir consists of volcanogenic sediments overlying basic and siliceous volcanics. The volcanic complex probably belongs to the Deccan igneous province which was formed at about the Cretaceous - Tertiary boundary. The overlying volcanogenic sediments are assigned to the Fatehgarh Formation, and are probably Early Tertiary in age. The volcanics and sediments now occur in a tilted fault block in the Barmer Rift Basin.
The volcanogenic sequence is complex both in terms of mineralogy and fabric. Many volcanic fabrics are simply not present in typical sedimentary rocks and this complexity makes porosity and permeability prediction very challenging at all geological scales.
The core, log and well-test data sets each individually add to the understanding of the porosity and permeability distribution, but it is through their detailed and careful integration which provides sufficient confidence in reservoir understanding to enable well-founded commercial decisions.
This study has challenged conventional thinking in two areas. Firstly, the utility of NMR data is often doubted in iron-rich rocks. However, this study has shown that NMR data can be used with great success provided there is adequate rock calibration. Secondly, for these volcanic rich rocks, a more accurate calculation of effective porosity was possible after permeability had been estimated from the NMR data (conditioned to both core and well-test data). This workflow is the reverse of the typical petrophysical procedure which calculates porosity first and then permeability.
This paper also demonstrates that it is possible for volcanogenic sequences to contain large volumes of producible hydrocarbons and encourages operators to look more closely at volcanic sections in other basins that until now have been relegated as “too difficult” to investigate.
Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery