The geochemical characterization of crude oils reservoired in Cretaceous sequences, Lower Indus Basin, Pakistan.

Geochemical analyses of the 10 crude oils from Cretaceous sequences, Lower Indus Basin, Pakistan, are performed to characterize source, depositional environment, biodegradation, and thermal maturity to establish genetic relationship. Low sulfur, high pristane/phytane (Pr/Ph) ratios, and high American Petroleum Institute gravity indicate oxic depositional environment and terreginous input of organic matter (OM). Full suite ofn-alkanes, low isoprenoid/n-alkane ratios, elevated saturates/aromatics ratios, and the absence of unresolved complex mixture indicate typical non-biodegraded light crude oils. The carbon preference index, odd even predominance, Pr/n-C17, and Ph/n-C18ratios reveal that source rocks generating Lower Indus Basin crude oils are thermally mature. Based on geochemical analyses, the source OM input is probably terreginous mixed with marine, deposited under suboxic to oxic depositional environments. [ABSTRACT FROM PUBLISHER]