PETROPHYSICAL ANALYSIS AND PETROGRAPHIC STUDIES OF TOBRA FORMATION, POTWAR SUB BASIN, PAKISTAN

Abstract

The early Permian sedimentary sequence of the eastern Salt Range belongs to the glacio-fluvial origin of the Late Paleozoic Ice-age. Present research work is aimed to understand the petrographic studies of early Permian Tobra Formation in eastern Salt Range and Petrophysical properties of Tobra Formation in Balkassar OXY_01 and Joya Mair_04 well. The field studies measure the Tobra formation in eastern Salt Range and the collection of outcrop samples from Pidh and Tobra sections. The present research work determined four litho-facies of Tobra Formation: Clast-Supported Conglomerate Facies, Massive Sandstone Facies, and Pebbly-Sandstone Matrix-Supported Conglomerates Facies. These Facies expresses glacial influenced debris flow deposits. The petro-graphical studies revealed that the sandstone of Tobra Formation is quartz arenite to lithic arenite and immature to sub mature. For provenance studies ternary plot is used, Tobra Sandstone samples are situated in recycled orogeny field. The grains observed during petrography, are angular to sub rounded monocrystalline and polycrystalline quartz, alkali feldspar and number of lithic fragments from distinct origins. The petrophysical properties of Tobra Formation in Balkassar OXY_01 show the shale volume is 25.1%. The total porosity is 15.9%and effective porosity is 11%. The permeability value is 7.3mD. The water saturation is 31% and hydrocarbon saturation is 68.9%. The petrophysical properties of Tobra Formation in Joya Mair_04 well show the shale volume is 24.5%. The total Porosity is 11.5% and effective porosity is 4.8%. The permeability in Tobra Formation is 1.4mD, the maximum value is 37.4 mD, and minimum value is about 0 mD. The water saturation is 53% and hydrocarbon saturation is 46.9%. The cross plot of Shear Modulus (µ), Bulk modulus (BM) and Young modulus (YM) against density and porosity are used for lithology discriminators, and indicating the zones in Tobra Formation. The correlation of petrographic and petrophysical properties showed that lithology is sandstone and porosity is high.