塔里木盆地寒武—奥陶系碳酸盐岩储集特征与白云岩成因探讨*

塔里木盆地油气资源丰富，在寒武—奥陶系碳酸盐岩中发育有优质储集层。在野外地质观察、岩心观察与分析、常规薄片和铸体薄片观察鉴定基础上，详细研究了塔里木盆地寒武—奥陶系碳酸盐岩的储集特征，划分了储集空间类型，并对不同储集空间形成与演化做了初步分析。碳酸盐岩储集层的储集空间可分为孔、洞、缝3大类，进一步又划分为粒内孔、粒间孔、晶间孔、铸模孔、生物格架孔、孔洞、洞穴、构造缝、压实压溶缝和溶蚀缝10小类。溶洞与裂缝为最有效的储集空间。碳酸盐岩的原始储集空间经历了多期成岩作用改造，另外后期构造活动也提供了大量裂隙通道，有效储集空间绝大部分为次生成因，溶蚀作用很大程度上改善了储集性能。碳酸盐岩储集层分为裂缝—孔隙型、裂缝—孔洞型和裂缝型，其中裂缝—孔洞型为最有效的储集层。在寒武系和下奥陶统发育了不同成因的白云岩：寒武系白云岩主要形成于蒸发潮坪/潟湖有关的潮上和潮间带，属于准同生期产物；下奥陶统白云岩主要属于回流渗透/混合水白云岩化产物，另外在下奥陶统礁滩石灰岩部分白云岩化，属于交代白云岩化产物。在盆地深部奥陶系中同时发育有交代成因白云岩，属于晚期埋藏白云岩化产物。

Discussion on characteristics of the Cambrian-Ordovician carbonate rocks reservoirs and origin of dolostones in Tarim Basin

High quality reservoirs occur in the Cambrian-Ordovician carbonate rocks with abundant oil and gas resources in the Tarim Basin.Based on field geological inspection,core observation and analysis,identification of normal thin sections and cast sections,the detailed survey on its storage features and the classification of space type were conducted;and the formation and evolution of different storage spaces were preliminarily analyzed.In conclusion,the storage space of carbonate rocks could be divided into three categories,pores,vugs and fractures;Furthermore,it could be subdivided into intergranular pores,intragranular pores,intercrystal pores,moldic pores,organic framework pores,vugs,caverns,structural fractures,compaction dissolved fractures and dissolved fractures.Caverns and fractures are the most effective space for storage.Carbonate rocks underwent multi-stage reconstruction by diagenesis.In addition,late-stage tectonic activities also provided a large amount of fissures.Most of effective storage space is secondary-genetic,and dissolution enhances reservoir performance to a large degree.The reservoir types are fracture-pore,fracture-cave and fracture ones,and the fracture-cave type is the critical reservoir.Dolostones of different origins occur in the Cambrian and Lower Ordovician.The Cambrian dolostone was predominantly formed in supratidal and intertidal zones,associated with tidal flat and lagoons.It belongs to penecontemporaneous product.The Lower Ordovician dolostone mainly belongs to reflux-see-page/dorag dolomitization product.Part of the Lower Ordovician reef and beach limestone was dolomitized and then belongs to the replacement product that also occurs in deep Ordovician strata and belongs to burial dolomitization product in late stage.