Smectite illitization of the Talhar shale, Lower Goru Formation, Southern Indus Basin, Pakistan

Subsurface samples of the Talhar shale, Lower Goru Formation, are analyzed for smectite (montmorillonite) and illite in the Nur-dep#1 (ND‒1), well 2, Southern Lower Indus Basin, Pakistan. The ND‒1, well 2 is an unsuccessful well drilled by the OGDCL, Pakistan, for the shale gas exploration. Illitization and elemental content constrained using XRD qualitative and XRF quantitative analyses, respectively. The illite content increases from 15 to 55% with increasing depth. The fine-grained shale comprises chlorite, kaolinite, halloysite, allophane, muscovite, microcline, illite and montmorillonite. Chlorite was observed at 3450–3452 m, whereas kaolinite is present at depth range of 3450–3482 m. The mix layer expandability decreases from 40 to 20% at depth ranges from 3450 to 3552 m, respectively. The interstratification is random to ordered. Potassium and silicon contents with respect to aluminum and calcium are increasing with depth. Data obtained in this research indicate that the shale gas is immature and the oil is an early–medium stage of maturation.