A SHORT GEOLOGICAL HISTORY

AND THE NATURE OF OIL FIELDS

       The producing oil fields and other discovered structures of  N.O.C. extend over almost two-thirds of northerly  Iraqi land, from the northern borders with Turkey down to the 32.5 parallel in the south of of the country . The majority of these fields are  anticline and dome shaped structures which were formed by alternating tectonic movements throughout the geologic times. Most of the structures were formed within a broad basin at the edges of the Arabian Plate of which Iraq represents the northern and north eastern flank.

Geologic and stratigraphic column of the oil basin in Iraq comprises all types of rock formations including source, reservoir and cap rocks. Sedimentary rock thicknesses of the basin increase toward an east and north east shelf, termed  ( Unstable Shelf ), and decrease toward western desert called(stable shelf)

      The sedimentary rock cover in Iraq responded to various types of  compress ional forces that occurred late in geological times and brought about the diverse physiographic( topographic ) features of Iraq, the N.O.C. fields being a part of this morphology. The relief of structures increase from west to east and north east .    

 Most of   N.O.C. oil and gas  reservoirs are of carbonate rocks which have high effective and secondary porosities ( including vugs and fractures ) responsible for the prolific oil fields as well as very high production rates of oil from individual wells.

     Original hydrocarbon ( oil and gas ) accumulation in the source ( mother ) rocks  migrated vertically and/or horizontally from source rocks, such as massive shale formations to be eventually trapped in relatively porous and permeable  reservoirs rocks capped by impervious solid formations.       The existence of wide-spread fractures in most oil reservoirs, such as Kirkuk Main Limestone Reservoir, creates excellent conduits of fluid( oil, gas and water)movement along and across the reservoir thereby imparting high productivity to most of the oil wells. One of the wells in Kirkuk field, for example, had produced more than (100000) barrels per day which is commensurate to an average most of oil field production rates the world over.

       The geological nature of the oil basin in Iraq, and, hitherto, the relatively immature status of exploration operations for most potential areas, entail the prospect of finding further large oil fields and/or extensions of the known ones. This means that the outlook for North Oil Company’s future oil reserves, and, hence, production rates, is very prosperous in deed.