Online Journal for E&P Geoscientists

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

With the new discoveries of light oil/condensate in the Jurassic reservoirs in Kuwait, it was needed to employ the advanced geochemical techniques to corroborate the results from conventional correlation techniques to refine the understanding of petroleum systems. The application of biomarkers alone has its own limitation in view of their absence in highly mature oils and condensates and their identical signatures in Jurassic and Cretaceous source rocks. The diamondoids, which are thermally stable compounds occurring naturally both in crude oils and highly mature condensate and natural gas, are found to be reliable in source to oil, oil to oil and gas to gas correlations. The analytical work of diamondoids involved compound specific isotope analysis of biomarker (CSIA-B) and diamondoid (CSIA-D). Diamondoid data was integrated with biomarker and isotope data. The integrated data was successfully interpreted to understand the thermal cracking characteristics of the reservoirs and extent of the secondary cracking area and to distinguish between hydrocarbons generated from the Jurassic and Cretaceous source rocks.

Forty two crude oil and condensate samples from different Jurassic and Cretaceous reservoirs of Kuwait have been analyzed. The methyldiamantanes/admantane in the Cretaceous oils varied from 1.0 to 11.5 ppm. This is indicative of charging from more than one source rock to Cretaceous reservoirs. This mixture is derived from deep cracked oil and oil-window oil. The Compound specific isotope analyses of diamondoids (CSIA-D) also support the same results. The methyldiamantanes/admantane in Jurassic oils is greater than 116 ppm indicating that these oil samples are highly cracked. These oil and condensates were found to be derived from established major source rocks - Najmah argillaceous limestone of Kimmeridgian/Oxfordian age and Makhul argillaceous limestone and shale of Tithonian age.