伊拉克M油田白垩系Mishrif组潟湖环境碳酸盐岩储集层成因机理

Genesis of Reservoirs of Lagoon in the Mishrif Formation , M Oilfield, Iraq

为深化潟湖相碳酸盐岩储集层非均质性认识,以伊拉克M油田白垩系Mishrif组为例,基于岩心观察、物性分析数据、铸体薄片及压汞实验,对潟湖相储集层特征及成因机理开展研究.结果显示:研究区潟湖环境岩石类型复杂,生物碎屑具有多样性,储集层以低渗、特低渗为主,孔隙度分布范围宽,发育大量的基质微孔、铸模孔和晶间孔.储集层强非均质性是复杂沉积作用和差异成岩作用的结果.潟湖沉积物泥质含量高,发育大量基质微孔,与生物扰动作用相伴生的埋藏白云化作用可形成晶间孔,易溶型生物碎屑被选择性溶蚀形成大量的铸模孔.研究认为:潟湖沉积物原始物性较低,后期成岩作用可改善储集层物性.生物扰动期次、扰动强度、充填物类型、环境的封闭性及外来流体性质等因素控制了潜穴中充填物的改造趋势;生屑类型、成岩序列和成岩环境等影响了沉积物中铸模孔的发育和保存.综合潜穴充填物类型、生屑类型、成岩环境和成岩作用等因素,建立了生物扰动成因孔隙模式和铸模孔发育模式.

In order to understand the genesis of reservoir heterogeneity in lagoon,based on core,reservoir physical property data,cast thin section and mercury injection experiment,the characteristics and genetic mechanism of reservoir of lagoon facies in the Mishrif Formation in M oilfield were studied.The results showed that the reservoirs of lagoon facies were diversified in rock types and bioclastic.The reservoir with low or extra⁃low permeability and wide porosity mainly developed matrix⁃host micropores,intercrystal line pore and moldic pore.The correlation of porosity and permeability were poor.The different diagenesis and complex sedimentation led to serious heterogeneity.The sediments in lagoon had high micrites matrix which was the fundamental of matrix-host micropores.The intercrystalline pore results from the dolomitization after bioturbation.Bioclastic which were easy to dissolve were selective dissolved to form large amount of moldic pore.It concluded that the sediment had poor physical property and the transform by diagenesis were the main reservoir genesis.The factors such as bioturbation period,extent,infill materials,environment closed or open,fluid property controlled the transform tendency to reservoir and the development and preservation of moldic pore was controlled by the bioclastic type,diagenesis sequence and environment.Based on the factors such as infill materials,bioclastic,diagenetic environment and diagenesis,the pore mode associated bioturbation and selective dissolution was established.