Pore structure characteristics and control factors of carbonate reservoirs: The Middle-Lower Cretaceous formation,AI Hardy cloth Oilfield,Iraq

Abstract

The recognition of carbonate reservoir pore structure genesis and the differences in pore structure controlled factors are key issues in restricting reservoir classification and evaluation in the Middle-Lower Cretaceous AI Hardy cloth Oilfield in Iraq. The main pore,throat,and throat distribution types within the carbonate reservoirs are determined using conventional thin section,cast thin section,scanning electron microscopy,electron microprobe,routine physical properties,mercury analysis,cathodoluminescence,and stable isotope analysis. According to the experiments,the pore structures are classified as four types:( a) high porosity and medium permeability thin throat;( b) high porosity and low permeability thin throat;( c) high permeability Conte micro throat; and( d) low porosity and low permeability minimal throat. A good reservoir pore structure is one with network-like,partial thin,poorly sorted pore characteristics. The main controlling factors behind pore structure characteristics are the carbonate rock fabric and dissolution. The syngenetic or penecontemporaneous dissolution and alteration of primary deposition porosity and the latter supergene karstification dissolution form the current pore space and structure. The rock fabric controlled dissolution determines the differences in pore structure. This study will provide subsequent classification and evaluation studies of such reservoirs in Middle East with better guidance.