世界碳酸盐岩油气田的储层特征及其成藏的主要控制因素

世界碳酸盐岩储层的类型可识别为6种类型:不整合面之下的储层、白云岩储层、鲕粒和团粒浅滩储层、生物礁储层、微孔隙储层以及微裂缝储层。尚有深埋溶解型储层,但此类较少。上述各类储层,如出露水面,遭受雨水淋滤,必将增加其孔隙度,成为重要的油气储层。中东地区碳酸盐岩之所以能形成世界级的大油气田,其基本要素为油气的生储盖层组合的密切配置、有台地内继承性发育的生油盆地、含油气层的年代较新,且石油进入构造圈闭的时间也较晚、构造圈闭规模巨大、有十分理想的区域性的盖层。正是这些要素的有机配合,从而形成世界上无可匹敌的大油田。对中国碳酸盐岩油气田的储层研究,应寻找上述这些原生储层,又经历次生溶蚀和白云石化作用,这样才能成为有效的油气储层。

Characteristics of carbonate reservoirs for oil and gas fields in the world and essential controlling factors for their formation

The types of carbonate reservoir for oil and gas fields in the world can be divided into the following six categories:(l) reservoirs developed beneath a regional unconformity through leaching and dolomitization;(2) dolomite reservoirs formed in subtidal to supratidal environments,and in cyclic sequences;(3) oolitic and peloidal shoals;(4) organic reefs;(5) microporosity within the micrites and chalks;(6) microfractures within the micrites.In addition,some rare types,such as the burial-diagenetic dissolution type are also considered here.All of these reservoir types are greatly enhanced for their hydrocarbon potential if they are exposed above sea level and were subjected to intensive fresh water leaching(solution).Thus they became important reservoirs for oil and gas.The main,essential factors for the formation of the giant oi1 and gas fields in the Middle East are discussed briefly here as a typical example.These factors are as follows:(1) source rocks,reservoirs and cap rocks are closely linked together;(2) presence of relatively deep,stagnant source basins which acted as the main sources for hydrocarbons in Jurassic-Tertiary reservoirs;(3) main reservoirs occurred in rocks of relatively younger ages(Mesozoic and Cenozoic);(4) the entry of oil into reservoirs occurred geologically very late,even later than the formation of the traps that resulted from Miocene-Holocene orogeny;(5) presence of huge anticlinal structures;(6) presence of regional,widespread cap rocks.These factors are so intimately associated in the Middle East that its incomparable,giant oil and gas fields were formed.As for the study of carbonate reservoirs in China,we should pay great attention in looking for the primary carbonate reservoir types mentioned above,which were subjected to leaching and dolomitization during later diagenesis.Under such conditions,efficient carbonate reservoirs would have been formed.