伊拉克米桑油田群白垩系Mishrif组储层孔隙演化

Pore Evolution of Reservoirs of Mishrif Formation in Missan Oilfields, Iraq

摘要: 伊拉克米桑油田白垩系Mishrif组储层主要为开阔台地相沉积，岩性主要为生物颗粒灰岩和泥晶灰岩，储层具有中孔、低渗特征。根据取芯井岩心、铸体薄片、扫描电镜及阴极发光等分析化验资料，并结合物性资料，对研究区储层孔隙演化特征进行了研究。研究发现，Mishrif组储层孔隙演化受成岩作用影响明显，其中准同生阶段在海底环境形成的胶结作用使孔隙度降低了8%左右，但生屑滩受海平面频繁振荡的影响，暴露在大气淡水环境中遭受大气淡水溶蚀，增加了次生溶孔约15%；早成岩阶段发生的压实作用对储层先存孔隙的影响不大，而胶结充填作用对储层先存孔隙破坏力度大，可使孔隙降低70%~90%；中成岩阶段的重结晶作用没有增加储层孔隙，但为后期的溶蚀作用提供了良好的流体通道和大量水岩接触界面。孔隙演化表明，对优质储层形成贡献最大的成岩作用是准同生阶段溶蚀作用。

Abstract: The reservoirs of Mishrif Formation in Missan Oilfields in Iraq mainly consist of sediments of open platform, with principle rocks of bioclastic grainstone and micrite limestone. The reservoir has the characteristics of medium porosity and low permeability. The core observation, casting thin section, scanning electron microscope and cathode luminescence, combining with reservoir properties, are used to study the evolution of reservoirs of Mishrif Formation. The result shows that the reservoir pore evolution of Mishrif Formation was obviously affected by the diagenesis. The cementation occurred in the penecontemporaneous stage leads the porosity to reduce about 8%, however, due to the atmosphere fresh water dissolution in the penecontemporaneous stage, which relates to subaerial exposure and several relative sea-level falling, some secondary solutional voids are developed, and it increases the porosity about 15%. Mechanical compaction occurred in the early diagenetic stage has little contribution to the reservoir porosity, but the second phase of cementation has been greatly destructive to the early pores, which can decrease the porosity about 70%~90%. Recrystallization did not increase the reservoir porosity, but provide a good fluid channel and a large number of water-rock contact interfaces for the later dissolution. In terms of pore evolution, the favorable diagenesis for formation of good reservoirs is mainly in the early dissolution occurred in the penecontemporaneous stage.