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Triassic Petroleum System of Kuwait

Husain, Riyasat 1; Sajer, Abdulaziz 1; Al-Khamiss, Awatif 1; Iqbal, Mohammed K.1; Al-Zeabout, Nadia 1
1 Kuwait Oil Company, Ahmadi, Kuwait.

Triassic section of Kuwait is under explored due to its occurrence at greater depths, poor seismic imaging and hostile drilling and testing environment. Consequently exploration data is scarce. However, recent exploration wells in the West Kuwait have shed new light on Triassic Stratigraphy, established the flow of hydrocarbons from Triassic reservoirs and provided valuable leads for working out the elements of Triassic Petroleum System in Kuwait.

Triassic stratigraphy of Arabian Gulf is represented by Upper Khuff, Sudair, Jilh and Minjur formations. In western part of Kuwait, an additional stratigraphic entity named as Kra Al-Maru unit is found preserved between underlying Sudair and overlying Jilh formations. The unit flowed measured quantities of gas and condensates in Mutriba and Kra Al-Maru areas and is interpreted to be self sourced. A hypothetical petroleum system namely Kra Al Maru (.) Petroleum System is envisaged based on available exploration data. Lower clayey carbonate part of the unit has source potential with original Total Organic Carbon and Hydrogen Index in the range of 3-4% and 300-500, respectively. Triassic section entered oil window during Middle Cretaceous and wet gas window during Late Cretaceous. Overlying unit consisting of cyclical packages of dolomudstones, laminated to bedded anhydrites and dolomitic shales forms the reservoir rocks for the system. Conventional reservoir rock quality is poor as porosity is reduced by replacive and pore-filling anhydrite. Matrix permeability values typically are <0.01 mD. Fracture analysis shows that the fractures are confined within the dolomudstones and do not extend through the bedded anhydrites. Fracture-related permeability values range up to 3.3 mD and flow is attributed to the fracture network preferentially developed within the more brittle dolomudstones. The intraformational halite and anhydrite can act as local seals for this system while a major salt unit in the middle part of the Jilh Formation is expected to be the regional seal. Structures are predominantly late Jurassic to mid Cretaceous in age, and pre-date peak Triassic source rock maturation. The stratigraphic limit of the system lies below Jilh Salt down to Top of Khuff Formation. Geographically it covers onland part of Kuwait west of NNE trending Kuwait Arch.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009