Producible fluid oil saturations of the Upper Cretaceous unconventional carbonate plays, northern Arabian plate

Abstract

The Upper Cretaceous Karababa and Karabogaz Formations of the northern Arabian Plate include units of organic-rich and organic-lean carbonates. The Karababa A Member and Karabogaz Formation are represented by organic-rich mudstones and wackestones. The Karababa B and C Members consist of organic-lean dolomitic wackestones, wackestones, and packstones. These formations are composed of between 35% to 100% calcite, and 14% to 28% dolomite. Measured total organic carbon (TOC) contents of organic-rich source rocks of the formations range from 1.03 to 7.82 wt. %, and calculated vitrinite reflection maturity values range from 0.48% to 0.91%. The maturity data demonstrate that organic-rich levels of these formations occur in the immature, early mature, and mature oil generation windows. Oil saturation index (OSI) threshold has been optimized as 100 oil/g TOC to early mature levels and 60 mg oil/g TOC to mature levels since the sorption coefficient varies widely as a function of thermal stress. Both OSI values and corrected OSI (OSIc) values of the immature and early mature organic-rich (source rocks) and organic-lean (tight reservoirs) of the Karababa and Karabogaz Formations are below the 100 mg oil/g TOC, which indicates that unconventional commercial fluid phase oil production is not probable. Many OSI values and nearly all OSIc values of the mature source rocks and tight reservoirs exceed the 60 mg oil/g TOC, indicating potential presence of producible fluid phase oil. The maximum OSIc values of the organic-rich (the Karabogaz Formation and Karababa A Member) and organic-lean carbonates (Karababa B and C Members) have been calculated as 231.7 and 368.6 mg oil/g TOC, respectively. However, modeled fluid oil saturations exhibit lower values.