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Giant ACG Field, South Caspian Basin, Azerbaijan – Peculiarity of Oil and Gas Content.


Introduction Azeri-Chiraq-Guneshli (ACG) field along with Shah Deniz, Neft Dashlari (Oil Rocks), Balakhani-Sabunchu-Ramani, Bibiheybat fields is one of the largest oil and gas producing fields of the South Caspian basin. Natural reservoirs and their content of oil and gas deposits occur almost in all horizons of the Middle Pliocene aged Productive Series (PS). Complexity of geological structure of hydrocarbon's deposits related, first of all, on tectonic setting uncertainty and lithologic-reservoir nonuniformity of natural objects, conditioned by peculiarities of sedimentation of detrital materials (brought to this region by Paleo-Volga). Along with the study of the reservoir property of rocks, the reservoir's distribution on the area of horizons with different saturation (upper horizons are gas-condensate burring and lower horizons are saturated with oil/gas/condensate), the reasons of irregular oil-and-gas saturation of the field were studied. The formation of hydrocarbon's structural trap of ACG field occurred on the early stage of Late Pliocene with apotheosis in Post Pliocene period. The filling of traps (by hydrocarbons probably of Oligocene – Miocene age) proceeded during short intervals of tectonic activity which caused the peculiarity revealed by oil and gas saturation of the section of deposits. The tectonic activity and lithological factors affect the field's development in the period of structure formation in the earlier and following stages of Middle Pliocene. Conclusion In spite of detailed study of the field, in which in total more than 300 wells have been drilled, we keep facing with surprises of the nature. There are very complex phase states of hydrocarbon mixture observed in some deposits of the field. For example, the presence of gas condensate deposit with gas solved in water in Qala suit of PS in the Guneshli part of the field. A quite powerful oil rim was detected on gas saturated Upper Kirmaky Sandy Suite (QUQ) and Lover Kirmaky Suite (QA) on the north-west limb of the structure (Shallow Water Guneshli). Some intervals (VII and IX horizons) highly saturated within one area of the field are not saturated enough on another part of the field. Thus, the generalized research of ACG field validates the necessity of more detailed and systematic approach to selection of exploitation objects, estimation of the reservoir properties and hydrocarbon potentials of the field.