Abstract
The present study details the hydrocarbon source rock geochemistry and organic petrography of the outcrop and subsurface samples of the Middle Jurassic Chiltan Formation and the Lower Cretaceous Sembar Formation from the Sann #1 well Central and Southern Indus Basin, Pakistan. The total organic carbon (TOC), Rock–Eval pyrolysis, vitrinite reflectance (Ro) % and Maceral analysis techniques were used and various geochemical plots were constructed to know the quality of source rock, type of kerogen, level of maturity and migration history of the hydrocarbons. The outcrop and Sann #1 well data on the Sembar Formation reveals poor, fair, good and very good quality of the TOC, type II–III kerogen, immature–mature organic matter and an indigenous hydrocarbon generation potential. The outcrop and Sann #1 well data on the Chiltan Formation show a poor–good quality of TOC, type II–III kerogen, immature–mature source rock quality and having an indigenous hydrocarbon generation potential. The vitrinite reflectance [Ro (%)] values and Maceral types [fluorescent amorphous organic matter, exinite, alginite and inertnite] demonstrate that maturity in both Sembar and the Chiltan formation at surface and subsurface fall in the oil and gas generation zone to cracking of oil to gas condensate zone. Recurrence of organic rich and poor intervals within the Sembar and Chiltan formation are controlled by the Late Jurassic thermal uplift preceding the Indo-Madagascar separation from the Afro-Arabian Plate and Early Cretaceous local transgressive–regressive cycles. From the current study, it is concluded that both Sembar and Chiltan formation can act as a potential hydrocarbon source rock in the study area.
Highlights
The Indus Basin is one of the major sedimentary basins of Pakistan comprising sediments of Precambrian to recent (Fig. 1)
Potential hydrocarbon source rocks occur within the Middle Jurassic Chiltan Formation and the Lower Cretaceous Sembar Formation in the Sulaiman–Kirthar fold belt of Indus Basin
This study area is still underexplored and the advancement of petroleum exploration and production technology provides a hope for the discovery of economically viable hydrocarbon reserves
Summary
The Indus Basin is one of the major sedimentary basins of Pakistan comprising sediments of Precambrian to recent (Fig. 1). Potential hydrocarbon source rocks occur within the Middle Jurassic Chiltan Formation and the Lower Cretaceous Sembar Formation in the Sulaiman–Kirthar fold belt of Indus Basin. Exploration of hydrocarbons in this region faces the challenging complex geology of the area that hinders detailed investigation of the petroleum system of the region. The petroleum generation, migration, and preservation potential of the strata exposed in the study area demands the integration of a detailed geological investigation at the outcrop and subsurface level. The Sembar Formation shows vertical variation in the lithofacies assemblage and very thick organic rich clays are reported in different parts of the Indus Basin. The Chiltan Formation contains organic rich clays in the Indus Basin as reported from different outcrops (Shah 1977) and the Sann #1 well (Robison et al 1995). This study, tries to investigate for the first time the outcrop based hydrocarbon source rock
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