Potential Proterozoic Petroleum System: Northwest Himalayan Thrust Belt, Jammu (India)

Hakhoo, Naveen ¹; Bhat, Ghulam M.¹; Koul, Sumita ¹; Craig, Jonathan ²; Thusu, Bindra ³
(1) Institute of Energy Research and Training (IERT), University of Jammu, Jammu, India. (2) Eni Exploration and Production Division, Eni, Milan, Italy. (3) MPRG, Deptt. of Earth Sciences, University College London, London, United Kingdom.

The Sirban Limestone of Proterozoic age occurs in detached inliers of Jammu region in India and extends westwards to the oil producing Potwar Basin in Northeast Pakistan. The Reasi Inlier, 40 km long and 12 km wide, is the largest inlier in Jammu region. This sequence comprises of reservoir quality, dark-grey dolomite, limestone with seal horizons of chert and argillites and organic rich shale intervals. The limestones possess vuggy, inter- and intragranular, fracture, inter- and intralayer porosities. The shales with organic matter content of 10% have oil/gas generating potential. Some of these carbonate and shale horizons yield Neoproterozoic microflora, comparable with those reported in North African Neoproterozoic sandstones and Late Proterozoic carbonates of the giant oil and gas fields of the Baikit Anticline of the Siberian Platform.

The sequence is juxtaposed against the Tertiary sedimentary sequence in the north of the Reasi Inlier and the contact between the two has conventionally been considered as a major regional unconformity but recent study reveals this contact as a back thrust. The inlier along with the Tertiary sedimentary sequence is also involved in the north directed re-entrant and furthermore, within the Reasi Inlier a “Triangle Zone” occurs in the Anji valley east of the Reasi town. These rocks also exhibit multiple generation folds in the area. North of the Reasi Inlier, Chenab River veers its course from west to south, forming a loop - a drainage anomaly. This drainage anomaly seems to be an expression of a subsurface structure and considered potential target for hydrocarbon exploration.

Along the back thrust at Kanthan village, gas seep samples from the Chenab River bed, analysed for bulk chemical and isotopic composition reveal the presence of dry gas rich in CH4 & N2 and having δ13C < - 60‰, indicating possible shallow source of biogenic origin.

The association of reservoir quality limestones with seal horizons and organic rich shales, together with the presence of gas seeps and the observed “Triangle Zones” and drainage anomaly supports the existence of a potential petroleum play in the Sirban Limestone.

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