Porosity enhancement potential through dolomitization of carbonate reservoirs, a case of study from the Euphrates Graben fields, East Syria

The dolostones and dolomitic limestones of the lower Cretaceous Judea formation are a key target ofhydrocarbons in most of the Euphrates Graben fields. Core materials investigation, thin sections petrographicallyexaminations, and petrophysical evaluations were obtained to determine enhancement ofthe porosity through dolomitization. Results showed that the lagoon-shallow marine carbonates of theJudea formation are subdivided into two main zones;the upper “limestone zone” is micritic limestonesdominated with no reservoir potential, and the lower “dolomite zone” is dolomitic limestones anddolostones dominated with good to very good reservoir potential. Dolomitization of the mudstones andwackestones of the micritic limestones resulted in formation of microcrystalline dolomicrite and earlyfabric destructive dolomites. Conversely, dolomitization of the packstones and grainstones resulted information of the fabric destructive and saddle dolomites. Based on petrography data, dolomitization ofthe “limestone zone” is interpreted by the seawater dolomitization mechanism at low-temperatures,while dolomitization of the “dolomite zone” is interpreted by the burial dolomitization mechanismunder high temperature and pressure conditions. The “limestone zone” is characterized by the poorestreservoir quality, while the “dolomite zone” is characterized by the best reservoir quality. The seawaterdolomitization did not significantly enhance the porosity, while the burial dolomitization contributes toenhancing the preserved secondary porosity. Stylolites microfractures and dissolution seams associatedwith dolomitization played as major factors in porosity enhancement of the dolostones and dolomiticlimestones and serving as pathways for hydrocarbon migration. Dissolution processes increased theporosity and more permeability unless they are filled with the precipitated dolomite and/or calcite.Calcification had significant effects on the porosity by blocking the cavities and channels and decreasedthe effective pore volume.