二连盆地阿南凹陷白垩系腾格尔组致密油储层特征及主控因素

Characteristics and main controlling factors of tight oil reservoirs in Cretaceous Tengger Formation,A’nan Sag,Erlian Basin

二连盆地阿南凹陷白垩系腾格尔组一段下亚段广泛发育一套与火山活动相关的“特殊岩性”致密储层,是致密油勘探的主要目的层。基于岩石薄片观察和储层物性系统分析,结合扫描电镜、压汞、CT扫描和核磁共振等分析,对该层段不同岩性致密储层特征和“甜点”发育主控因素进行综合研究。结果表明:腾一下亚段主要发育凝灰质岩、砂岩、白云岩和泥岩四大岩类,凝灰质岩和砂岩是致密油储层发育的有利岩性。储层中主要发育溶蚀孔、晶间微孔、残余粒间孔、泄水孔和微裂缝等5类储集空间,其中凝灰岩中以脱玻化晶间孔和溶蚀孔占主导,砂岩中以残余粒间孔和溶蚀孔最有利。储层孔隙结构可划分为3类4亚类,薄层凝灰岩和溶孔发育的细砂岩储层孔隙结构较好,沉凝灰岩与白云岩孔隙结构较差。不同类型储层含油非均质性强,含油量受储层岩性、孔渗条件和孔隙结构控制。凝灰质岩致密储层“甜点”发育主要受火山碎屑沉积方式、脱玻化作用和溶蚀作用控制,砂岩类储层“甜点”发育主要受沉积微相、岩石结构和溶蚀作用共同控制。

A set of“special lithology”tight reservoirs related to volcanic activity developed widely in the lower submember of the first member of Cretaceous Tengger Formation(K1 bt1x)in the A’nan Sag,Erlian Basin,which is the main target for tight oil exploration.Based on section observation,physical property analysis,scanning electron microscopy(SEM),mercury intrusion porosimetry,CT scanning and nuclear magnetic resonance(NMR),the characteristics and main controlling factors of“sweet spots”of tight oil reservoirs with different lithologies in the K1bt1x were studied.Tuffaceous rocks,sandstones,dolomites and mudstones developed in the K1bt1x,and tuffaceous rocks and sandstones are the favorable lithologies for the development of tight oil reservoirs.The reservoir space consists of dissolved pores,intercrystalline micropores,residual intergranular pores,drainage pores and microfractures.The main reservoir space of tuff includes devitrified intercrystalline pores and dissolution pores,whereas that of sandstone includes residual intergranular pores and dissolution pores.The reservoir pore structures can be divided into 3 types and 4 subtypes.The thinlayered tuff and fine sandstone with solution pores have better pore structures,but the sedimentary tuff and dolomite have poor pore structures.The reservoir has a strong oil content heterogeneity controlled by reservoir lithology,porosity and permeability.The development of“sweet spots”in tuffaceous tight reservoirs is mainly controlled by the volcaniclastic deposition,devitrification and dissolution,while the development of“sweet spots”in sandstone reservoirs is mainly controlled by sedimentary microfacies,rock structure and dissolution.