伊拉克艾哈代布油田中-下白垩统碳酸盐岩储层孔隙结构及控制因素

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

伊拉克艾哈代布油田中-下白垩统碳酸盐岩储层孔隙结构类型划分及其差异性的受控因素和成因的认识是制约该类储层分类评价的一个关键问题。本文综合运用了常规薄片、铸体薄片、扫描电镜、电子探针、常规物性、压汞分析、阴极发光、稳定同位素分析等手段及统计分析方法对储层的主要孔隙类型、喉道类型、喉道分布类型进行了研究,并在此基础上确定了高孔中渗细喉型、中高孔低渗细喉型、中高孔特低渗微喉型、低孔特低渗极微喉型四种孔隙结构类型及其划分依据和方案,同时指出了在该类储层中好的孔隙结构具有网络状、偏细型、分选较差的孔喉特征。通过分析明确了孔隙结构差异性的主要控制因素为岩石组构和溶蚀作用,认为该套储层的孔喉空间及结构是以沉积形成的原生孔隙受同生期或准同生期的溶蚀改造为基础,并在后期表生岩溶作用下的改造而成;而先期受岩石组构控制下的溶蚀作用控制了储层孔隙结构的差异性。通过本文研究将对中东地区该类储层的形成及分类评价研究具有较好的指导意义。

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.