The Souedih (also spelled Suwaidiyah) Oilfeld is located in the extreme
northeast of Syria in part of the Mesopotamian Basin. The principal reservoir
of most felds in this region is the Upper Cretaceous, carbonate-rich Massive
Formation. Using data from 25 wells and 36 samples/thin sections, this
study focuses on the nature and distribution of porosity in the main Souedih
reservoir. The Massive A reservoir is 100–120 m thick and represented
by uniform, bioturbated bioclastic packstone and bioclastic packstone
grainstone, deposited in a well-oxygenated, moderate to high-energy,
shallow-marine environment. It is generally well cemented by microsparite
and micrite, and more rarely by sparite. Porosity is highly variable, ranging
from < 1% to 20%. Mouldic porosity is the most common type, with rare
channel and fracture porosity. Average porosity values tend to decrease
eastward across the reservoir, which can also be divided vertically into fve
zones. The uppermost of these shows the highest average porosity > 15%.
The dominance of mouldic porosity throughout the study area indicates that
secondary dissolution was the primary cause and that pre-existing bioclasts
were the principal targets for this dissolution. The source of these diagenetic
fluids is still unclear, although our data do lend some support to the
karstifcation theory. These characteristics are important for understanding
and managing reservoir production, not only for Souedih but for the region
in general.