AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Jurassic Petroleum Systems in Kuwait
(1) Middle East Geological Establishment, Al-Ain, United Arab Emirates.
(2) Kuwait University, Kuwait, Kuwait.
The Jurassic succession in Kuwait reached up to 4,750 ft. thick are generally assigned to the Marrat, Dhruma, Sargelu and Najmah formations (mainly carbonates and calcareous shales) and the overlying Hith and Gotnia formations which are composed of anhydrites and evaporites. The oolitic grainstones and packstones of the Marrat Formation is considered to be one of the most important reservoir units in the Jurassic. The Sargelu Formation composed of wackestones, packstones and mudstons with bitumen-bearing horizons form an important reservoir unit. The Najmah Formation is composed of packstones and argillaceous and bituminous limestone has been identified as an important source-rock unit, and where fractured it also constitutes an important reservoir. This oil might be related to generation from the in- situ kerogen or it might be migrated from deeper source rocks.
The nature of the reservoirs in the Jurassic section in Kuwait has porosities that are a mixture of primary and secondary nature. The secondary porosity is related to fracturing system that is believed to be related to the tectonic system in the region. The dolomitization has played its role in connecting the fractures and enhance the quality of these reservoirs.
The Sargelu and Najmah formations are possible and probably source rocks, respectively. These formations characterized by the presence of marine kerogen between Types II and III, and the formations show amorphous rich sapropelic organic matter. The TOC is abnormally high with an average value of 7% wt. and sometimes reach as high as 29% wt. In general the formation is mature especially in its deepest part in the northern oil fields.
Thermal burial history indicates that oil migration from Jurassic source rock, Najmah, started since Tertiary time. During this time the structural traps have already existed. Thus, the oil has been accumulated in the Jurassic reservoirs and capped by the thick evaporite and anhydrite of the Gotnia and Hith Formations. The Jurassic is new and potential exploration target in Kuwait especially after few and recent discoveries from the Marrat and Sargelu formations in deeper major fields.