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Geochemical Inversion: A Breakthrough to Determine Cretaceous Petroleum System in Kuwait

Andriany, Rita *1; Al Khamiss, Awatif 1; Al-Fares, Abdulaziz 1; Akbar, Hussain 1; Al-Ali, Salem 1
(1) Exploration, KOC, Ahmadi, Kuwait.

The availability of reliable integrated data from particular petroleum system in certain basin is employed as standard model or reference for geochemical inversion. This reference requires the availability of a number of the geochemical data sets including extract rocks (core and/or cutting) and reservoirs data (oil and gas). Genetic interrelationship between source rocks as parent rocks to its inherited hydrocarbons trapped in reservoirs can be determined and tracked from geochemical analyses like physical, chemical and molecular properties. The character of molecular compound is the most resistant preserved during geological processes, their signatures in extracts and oils can be used as the genetic tracking tools in the geochemical inversion for determining the genetic relationships (oil-to-source correlation), and vice versa.

The molecular of geochemical analyses including gas chromatogram (GC), gas chromatogram mass spectrometry (GCMS), isotopic compounds, and diamondoids is performed for the Jurassic Petroleum System. Najmah-Najmah (!) Petroleum System as Jurassic Petroleum System in Kuwait worked out from relatively complete sets of reliable geochemical data. Thus, it an effective reference to determine the older or younger petroleum systems.

Most of oils trapped in the Cretaceous System in Kuwait have distinctive signatures are characterized by abundance and decrease of certain molecular compounds like biomarkers, carbon isotopes and diamondoids. Cretaceous oils are characterized by low ratios pristane/phytane (0.48 to 0.66) and pristane/nC17 (0.18 to 0.29), high ratios phytane/nC18 (0.35 to 0.54), increase in gammacerane index, and strong preference of steranes nC29 to nC27. Other typical signatures of the Cretaceous oils are depletion in their carbon isotopes saturated values, and decrease in the ratios of dimethyl diamentane to methyl adamantane (diamondoid analysis).

The distinctive molecular oil characters in Cretaceous Petroleum System are distinct from the Jurassic Petroleum System and potential to be used as parameter for geochemical inversion. Geochemical inversion is an inexpensive and fast method for quick look in exploration appraisal. The method is also effective for determining the reservoir compartmentalization.

 

AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain