多期溶蚀胶结作用对生物碎屑灰岩物性的影响:以伊拉克A油田白垩系Mishrif组Mi4段为例

Effect of Multi-stage Dissolution and Cementation on Physical Properties of Cretaceous Bioclastic Limestone in the A Oilfield,Iraq

伊拉克A油田Mishrif组Mi4段生物碎屑灰岩经历了不同期次的溶蚀和胶结作用,为了探究多期溶蚀胶结作用对生物碎屑灰岩物性的影响,以及分析同生—早成岩期溶蚀和胶结作用的主控因素。基于岩心观察、薄片鉴定和图像分析等定性—半定量分析方法,结合胶结物的岩相学特征、碳氧同位素、阴极发光以及流体包裹体均一温度等数据,划分了Mi4段生物碎屑灰岩的溶蚀和胶结期次。结果表明:Mi4段存在同生—早成岩和中成岩改造,共发育同生期组构选择性溶蚀、同生—早成岩期暴露溶蚀、同生—早成岩期胶结、中成岩期溶蚀以及同生—早成岩期叠加中成岩期胶结5种溶蚀胶结期次。同生—早成岩期溶蚀胶结相对储层物性改造明显,该阶段形成的成岩相中溶蚀相的物性最好,渗透率范围为6.96×10^(-3)~27.73×10^(-3)μm^(2)。同生—早成岩期的溶蚀作用受生物碎屑类型控制,富藻屑泥粒灰岩为主的Mi4-2层溶蚀程度最高,其次为藻屑含量稍低的Mi4-3和Mi4-4层;同生—早成岩期的胶结作用受古地貌和储层到层序界面距离的影响,在四级层序界面之下的Mi4-1层胶结程度最高。

The bioclastic limestone of the Mi4 section of the Mishrif Formation has undergone multiple phases of dissolution and cementation in oilfield A in Iraq.To investigate the impact of multiphase dissolution and cementation on the physical properties of bioclastic limestone and analyze the primary controlling factors during the dissolution and cementation of the early stages of the process.Based on qualitative and semi-quantitative analysis methods,including core observation,thin-section identification,image analysis,petrographic characteristics,carbon and oxygen isotopes,cathodoluminescence,and fluid inclusion homogenization temperature data,the dissolution and cementation periods of Mi4 bioclastic limestone were divided.These results indicate that the bioclastic limestone in the Mi4 section underwent diagenetic transformation during the eogenetic-early and mesodiagenetic stages,resulting in five phases of dissolution cementation.Eogenetic fabric selective dissolution,eogenetic-early diagenetic karstification,mesogenetic dissolution,eogenetic-early diagenetic cementation,and eogenetic-early diagenesis superimposed with mesodiagenetic cementation.The physical properties significantly evolve during eogenetic-early diagenetic due to solution-cementation processes with permeability ranging from 6.96~27.73×10^(-3)μm^(2).Dissolution was found to be controlled by bioclastic types during both the eogenetic-early stages,with algae-rich pelitic limestone exhibiting the highest degree,followed by the Mi4-3 and Mi4-4 layers with low algae-debris content.Furthermore,it was observed that the paleo-geomorphology and distance between reservoirs influenced the cementation process during the eogenetic-early stage,with the Mi4-1 layer showing the highest degree under the quaternary sequence interface.