Abstract

Kuwait has proven oil reserves and production from supergiant and giant fields that include the Greater Burgan (Burgan, Ahmadi, and Maqwa), Raudhatain, Sabriya, and Minagish fields. These fields are associated with very gentle oval anticlines interpreted as drape structures over deep-seated fault scarps or as growth structures related to halokinesis. These structures are generally very simple, consisting of a series of roughly parallel, anticlinal uplifts trending NNW-SSE, with a few having a more N-S to NNE-SSW trend.

Reservoir rocks are found in the Jurassic Marrat, Sargelu, and Najmah Formations (carbonates), the Lower Cretaceous Ratawi and Minagish Formations (sandstones and carbonates), and the Middle Cretaceous Burgan and Wara Formations (sandstones), as well as the Mauddud and Mishrif Formations (carbonates). Depth of reservoirs range from 3680 m (12,073 ft) in the Middle Jurassic to 2000–3650 m (6561–11,975 ft) in the Lower Cretaceous and 1000–2570 m (3281–8432 ft) in the Middle Cretaceous.

The most important reservoirs are the Lower and Middle Cretaceous sandstones, which are sealed by interbedded and overlying shales. Several Jurassic and Cretaceous limestone units form additional, but subordinate, reservoirs that are generally sealed by shales. Only the Upper Jurassic Gotnia salt and the overlaying Hith Anhydrite seem to act as a regional seal for Middle Jurassic limestone reservoirs.

Proven and potential source rocks with high TOC values, characterized by a mixture of marine and terrestrial sapropelic organic matter, are present in the upper-Lower and Middle Jurassic and the Lower and Middle Cretaceous. Kerogens from these rocks fall between Type II and II–III. The maturity level and quality of the kerogen in the Makhul (Sulaiy) Formation suggests that they are the most likely source rocks for the Cretaceous reservoirs, and responsible for generating part of the oil which has accumulated in present structures.

Source rock characteristics for the Jurassic succession vary and range from moderate to excellent TOC values in the Sargelu and Najmah Formations. Similarly, the Middle Jurassic succession potentially represents mature oil generation. Oil generation from Jurassic source rocks began in the Late Cretaceous at the time when structural traps had already started to form. The Makhul (Sulaiy) source rock entered the oil window during the Early Tertiary, whereas oil expulsion occurred throughout Tertiary time.