As main oil/gas bearing zones,both Triassic Feixianguan Formation of Puguang gas field and Cretaceous Mishrif Formation in B oilfield of Missan oilfields,Iraq are reef-bank carbonate sediments;however,they are quite different in reservoir physical property.Feixianguan Formation reservoir rocks are mainly dolomite,where mainly oolitic pores,intragranular dissolved pores and intergranular dissolved pores developed with medium porosity and superlow permeability.The Mishrif Formation reservoir rocks are mainly lime stone,where mainly oolitic pores,intragranular dissolved pores and moldic pores developed with medium porosity and medium-low permeability;and local medium porosity and high permeability in vertical direction.The comprehensive study implemented reveals that pene-contemporaneous dissolution played a critical role for the formation of high-quality reservoirs in Feixianguan and Mishrif formations,while the dolomitization made limited contribution to the porosity of Feixianguan Formation reservoirs,but generated important influence on reservoir diagenesis and pore evolution;additionally,the depositional environment is not the fundamental reason to cause the difference in reservoir physical properties between Feixianguan Formation and Mishrif Formation,but it affects the diagenesis in later stage.Instead,differential compaction and cementation are major controlling factors of reservoir difference.Further analysis indicates that burial evolution is the major cause for diagenetic differentiation.Puguang area experienced active tectonic movement,and both open diagenetic system and strong water-rock reaction could provide foundation for the formation of a large amount of cements in Feixianguan Formation reservoirs,which influenced reservoir physical properties.In Missan oilfields,both confined diagenetic system and weak water-rock system were not conducive to cement formation,while they are favorable for pore preservation in reservoirs.The study results could provide a reference for the study on marine carbonate reservoirs and hydrocarbon exploration.%普光气田三叠系飞仙关组和伊拉克米桑油田群B油田白垩系Mishrif组主力产层均为礁滩相碳酸盐岩沉积,但两者储层物性差异较大.飞仙关组储层以白云岩为主,主要发育鲕模孔、粒内溶孔和粒间溶孔,为中孔低—特低渗;而Mishrif组储层以灰岩为主,主要发育粒间溶孔、粒内溶孔和铸模孔,以中孔中—低渗为主,纵向局部发育中孔高渗.综合研究发现:准同生期溶蚀作用是飞仙关组和Mishrif组优质储层形成的主要原因,白云石化作用对飞仙关组储层孔隙度贡献有限,但对储层进一步成岩作用和孔隙演化有重要影响;沉积环境不是造成两者储层物性差异的根本原因,但影响着后期成岩作用;差异压实和胶结作用是储层差异的主控因素.进一步分析表明,埋藏演化是导致成岩差异的主要原因,普光地区构造运动更为活跃,开放的成岩系统与强烈水-岩反应为飞仙关组储层大量胶结物的形成提供了基础,影响了储层的物性;米桑油田群封闭的成岩系统和较弱的水-岩作用不利于胶结物的形成,从而有利于储层孔隙的保存.研究结果可为海相碳酸盐岩储层和油气勘探研究提供参考.
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