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.