A Secret of Two Tremendous Oil and Gas Machinery in Kuwait

Andriany, Rita; Akbar, Hussain; Al-Khamiss, Awatif; Al-Fares, Abdulaziz
Exploration Studies, Kuwait Oil Company, Ahmadi, Kuwait.

Oil-oil and oil-source correlation proven there are two main important petroleum systems in Kuwait includes 1) Najmah-Najmah (!) petroleum system of Jurassic age, and 2) Makhul-Burgan (!) petroleum system of Cretaceous age. The organic-rich Najmah shale and mudstone of Makhul are believed as tremendous oil/gas-producing machinery for mostly the hydrocarbon reserves in Kuwait. The significant different characteristic of two mentioned petroleum systems can be clearly distinguished.

Najmah Formation lying over Sargelu Formation and unconformably overlain by high-pressured anhydrite beds of the Gotnia Formation. Source rocks assessment have performed on 659 samples from exploration wells. The deepest section in the northern part of Kuwait is dominated by shale sequence (kerogen type II); while the shallower section in western and south-eastern parts dominated by the carbonate sequence categorized as the kerogen type III. Oils generated from Najmah reservoir are 95% similar to the Najmah shale in the active pod kitchen. The limestone units that sandwiched between three oil-producing machinery units in the Najmah Formation (Oxfordian) serve as conventional reserves, while the source rock itself is projected as the unconventional reserves.

Potential source rocks assessment of Makhul formation implies lower TOC values compare to source rocks from Najmah formation, however the hydrocarbon richness in range good to very good. Geochemical screening analysis of cuttings obtained from three old-exploration wells indicate that source rock from Bubiyan and Jlyah areas perform as potential charge to generate gas (type III gas prone). Meanwhile, Medina contained mixed type II/III (oil/gas prone) and established as active pod kitchen for Cretaceous System due to their genetic relationship to oils trapped in Burgan reservoir.

Najmah Formation covered by the extremely thick (high pressurized) of the anhydrite that acts as natural sealing for conventional and unconventional reserves. The similarity geochemical character between oils trapped in Burgan reservoir and other reservoir in the Cretaceous System is accurate evidence that hydrocarbon reserves (oil/gas) accumulated within Cretaceous system have been charged from Makhul source rock (Cretaceous age). However, hydrocarbon generated from shallower reservoir system indicates there is a mixing source (Jurassic and Cretaceous).

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012