Mineralogical And Reservoir Characteristics Of Well Cutting Samples Of Sandstone Of The Permian Tobra Formation From Adhi Field, Potwar Basin, Pakistan

  • Naveed Anjum
  • Adeel Nazeer Pakistan Petroleum Limited (PPL), Pakistan
  • Gohar Rehman Department of Geology University of Peshawar


Adhi Oil and Gas Field represents a NE – SW trending salt cored pop up structure which hosts three reservoirs i.e. Sakesar Limestone (Eocene), Tobra Formation (Permian) and Khewra Sandstone (Cambrian). This study is aimed at examining the depositional texture and diagenetic features of the well cuttings from the sandstone unit of the Tobra Formation and their influence on its reservoir characters using a combination of petrographic, XRD, SEM-EDX and grain size analysis techniques. On the basis of framework grains (Quartz80.81 Feldspar12.35 Lithic fragments6.6), the Tobra Sandstone samples are classified into sub-feldspathic arenites, sublithic arenites, and feldspathic wackes as the most abundant varieties while quartz arenite and subfeldspathic-sublithic arenite are encountered in few intervals. Grain size analysis of Tobra Sandstone samples shows sub-angular to sub-rounded and poor to moderate sorting as indicated by the polymodal nature of majority of the samples (~1.22 -≤5.2 Ф) with few being moderate to well sorted.

The matrix is dominantly consisting of ferruginous clays which shows variable concentration in the studied samples and ranges from 6 to 17% with a mean value of 6.6%. XRD and SEM-EDX analysis of the fine fraction shows illite as the principle clay constituent while kaolinite and montmorillonite occur as the minor mineral phases. Along with sandstone fragments, individual shale cuttings are also encountered in the studies Tobra samples which may occur as interlaminations with the sandstone layers. These shale fragments are also consisting dominantly of Illite, a clay mineral. Mineralogical and textural characteristics exhibit that the Tobra Sandstone bears poor to moderate reservoir potential with few being better ones. Several features such as the abundance of Illite, occurrence of planer to concavo-convex grain boundaries and the rarity of growth structures propose an intermediate burial compaction model for the studied sandstone unit of the Tobra Formation. Mineralogical results indicate that the detritus for the sandstone was derived from the craton interior of the Indian Plate as well as recycled orogen located to the south and southeast of the present-day Potwar Basin and Salt Ranges.


Adams, S.S., 1991. Evolution of genetic concepts for

principal types of sandstone uranium deposits in the United States.

Dickinson, W. R., Bead, L. S., Brakenridge, G. R., Erjavec, J. L., Ferguson, R. C., Inman, K. F., Knepp, R. A., Lindberg, F. A., and Ryberg, P. T., 1983. Provenance of North American Phanerozoic sandstones in relation to tectonic setting: Geological Society of America Bulletin, 94, pp. 222–235.

Reid, D. L., Ransome, I. G. D., Onstott, T. C., and Adams, C. J., 1991. Time of emplacement and metamorphism of Late Precambrian mafic dykes associated with the Pan-African Gariep orogeny, Southern Africa: implications for the age of the Nama Group: Journal of African Earth Sciences, 13(3-4), pp. 531-541.

Dott, R. H., 1964. Wacke, greywacke and matrix-what approach to immature sandstone classification? Journal of Sedimentary Petrology, 34, pp. 625-632.

Dutta, P. K., 2007. First- cycle sandstone composition and colour of associated fine-grained rocks as an aid to resolve Gondwana stratigraphy in peninsular, India. In: Arribas, J., Critelli, S., and Johnson, M. J., (eds.), Sedimentary provenance and petrogenesis: perspectives from petrography and geochemistry. Geological Society of America Special Paper, 420, pp. 241-252.

Franzinelli, E, Porter P. E., 1983. Petrology, chemistry and texture of modern river sands, Amazon River system. The Journal of Geology, 91, pp. 23– 39.

Kazmi, A. H., and Jan, M. Q., 1997. Geology and tectonics of Pakistan. Graphic publishers.

Kazmi, A. H., and Rana, R. A., 1982. Tectonic map of Pakistan 1: 2 000 000: Map showing structural features and tectonic stages in Pakistan. Geological survey of Pakistan.

Khan, M. A., Ahmed, R., Raza, H. A., and Kemal, A., 1986. Geology of petroleum in Kohat-Potwar Depression, Pakistan: American Association of Petroleum Geologists Bulletin, 70(4), pp. 396– 414.

Lillie, R. J., Johnson, G. H, Yousaf, M, Zamin A. S. H, and Yeats, R. S., 1987. Structural development within the Himalayan foreland foldthrust belt of Pakistan. In Sedimentary Basins and Basin forming Mechanism. Canadian Society of Petroleum Geologists Memoir, 12, 379-392

MacKenzie, W. S., and Guildford, C., 1984. Atlas of sedimentary rocks under the microscope. Longman.

Millot, G., 1970. Geology of clays. New York, Springer-Verlag. 29 p.

Nusrat, K. S, Badar, M. H., and Haneef, M., 2003. Geology of the Adhi oil and gas-condensate field and the application of 3D multi-attributes geovolume visualization interpretation techniques to enhance the structural and reservoir information. ATC, Islamabad.

Pascoe, E. H., 1959. Manual of Geol. India and Burma Vol. II India Govt, press Calcutta. 484-1338 pp.

Pettijohn, F. J., 1975. Sedimentary Rocks 3rd Edn. Springer-Verlag, New York.

Pettijohn, F. J, Potter, P. E., and Siever, R., 1987. Sand and sandstone. Springer, NY, pp 1–559,

Pettijohn, F. J., Potter, P. E., and Siever, R., 1987. Introduction and source materials. In Sand and sandstone. Springer, New York, NY, pp. 1-21.

Ramm, M., 2000. Reservoir quality and its relationship to facies and provenance in Middle to Upper Jurassic sequences, northeastern North Sea: Clay Minerals, 35, pp. 77-94

Rossi, C., Kalin, O., Arribas, J., and Tortosa, A., 2002. Diagenesis, provenance and reservoir quality of triassic tagi sandstones from ourhoud field, berkine (Ghadames) basin, Algeria: Marine and Petroleum Geology, 19, pp. 117-142.

Teichert, C., 1967. Nature of Permian glacial record. Salt Range and Khisor Range, West Pakistan.

Ncucs Johrb, Geol. Palacont., Abh., 129(2), pp. 167-184.

Virdi, N. S., 1998. Coexisting Late Proterozoic glacigene sediments and evaporites in the Lesser Himalaya and western Indian Shield-Expression of contemporaneity of low latitude glaciation and tropical desiccation. In Paliwal, B. S., (Eds.), The Indian Precambrian: Science Publication India. Jodhpur, pp. 502–511.

Weaver, C. E., and Pollard, L. D., 1973. The chemistry of clay minerals, Developments in sedimentology, 15. Elsevier, Amsterdam.