| Based on the observation of cores and thin sections, well log analysis, conventional core analysis and special core analysis，the characteristics of rock types, reservoir spaces, physical properties, pore structure and origins of carbonate reservoir of the Middle Cretaceous Mishrif Formation in the West Qurna Oilfield in Iraq were studied. The main rock types of Mishrif reservoir are micrite bioclastic limestone, bioclastic micrite limestone, rudist rudstone, bioclastic grainstone, sparite bioclastic limestone and residual bioclastic dolostone. The main reservoir spaces are primary interparticle pores, interparticle dissolved pores, primary intraparticle pores, intraparticle dissolved pores, moldic pores, intercrystal pores, micropores and micro-fractures without fillers. The physical properties of reservoir are characterized by medium porosity and medium-low permeability with poor correlation between porosity and permeability, and the rudist rudstone and bioclastic grainstone have the best reservoir physical properties. Among the five types of pore structure which developed in Mishrif reservoir, the two types(medium-high porosity, low permeability, thin throat, and medium-high porosity, medium-low permeability, medium throat), are dominated pore structure, and the heterogeneity is stronger. The main factors which controlled reservoir quality are the overlay of different subfacies and several diagenesises. The high quality reservoirs are controlled by simple coarse bioclastic rock fabric deposited in reef-bank depositional belts with strong water dynamic and serious dissolution. The poor quality reservoir and non-reservoir are controlled by weak water dynamic depositional belts with high micrite content and little bioclastic rock fabric, combined with weak dissolution and strong cementation. Stable tectogenesis results in a little micro-fractures developed in reservoir, which contribute negligible effect to the development of Mishrif carbonate reservoir. |
