二连盆地阿南凹陷白垩系凝灰岩类储层特征及有利区分布

Characteristics and favorable zone distribution of tuff reservoirt of Cretaceous in A’nan sag,Erlian Basin

阿南凹陷白垩系腾一下亚段凝灰岩类储层是近年来二连盆地致密油勘探的重点领域。通过岩心观察、薄片鉴定、储层物性分析及X-衍射分析等,采用高压压汞、氮气吸附、场发射电镜、CT扫描等实验方法,分析了二连盆地阿南凹陷白垩系凝灰岩类储层的岩性、物性、储集空间类型和孔隙结构特征,结合有利储层形成机制预测了有利储层发育区。研究结果表明:①二连盆地阿南凹陷白垩系腾一下亚段发育凝灰岩、沉凝灰岩、凝灰质泥岩、凝灰质(粉)砂岩4种凝灰岩类。②研究区凝灰岩类储层物性变化范围较大,平均孔隙度为4.88%,其中超低孔、特低孔的样品数占比为83.6%,平均渗透率为0.067 mD,整体属于超低孔、超低渗储层。凝灰岩主要发育溶蚀孔和脱玻化孔,呈“立体”网络孔隙结构,以介孔、宏孔为主,储层物性最好;凝灰质(粉)砂岩主要发育溶蚀孔和粒间孔,具有微细孔—微喉孔隙结构,介孔发育,储层物性较好;沉凝灰岩和凝灰质泥岩主要发育溶蚀孔、晶间孔和微裂缝,多发育孤立型孔隙结构,以介孔为主,储层物性较差。③研究区凝灰岩类优质储层受沉积作用、成岩作用和构造作用共同控制,沉积作用为优质储层形成提供了物质基础,控制了储层的形成和分布;压实作用和胶结作用降低了储层物性,白云岩化和脱玻化作用改善了储集性能;溶蚀作用是有效储层形成的关键,对物性改善具有积极作用。④研究区发育Ⅰ,Ⅱ,Ⅲ类凝灰岩类储层,Ⅰ类储层集中分布在洼槽区,Ⅱ类储层沿西部缓坡呈条带状分布,Ⅲ类储层分布范围最广。其中A43东、A27北、H16西和A11西南等区块发育的Ⅰ类储层是下一步凝灰岩类致密油勘探的有利区带。

The tuff reservoir in the lower part of the first member of Cretaceous system in A’nan sag has become one of the key fields for tight oil exploration in Erlian Basin in recent years.Based on core observation,thin sec tion authentication,reservoir physical property analysis and X-ray diffraction analysis,using the experimental methods such as high pressure mercury injection,nitrogen adsorption,field emission scanning electron microscopy and CT scanning,the characteristics of lithology,physical property,reservoir space type and pore structure of tuff reservoir of Cretaceous system in A’nan sag in Erlin basin were analyzed.Favorable tight tuff reservoir zones were predicted according to favorable reservoir formation mechanism.The results show that:(1)The tuff tight reservoirs in the lower part of the first member of Cretaceous Tenggeer Formation of A’nan sag of Erlian Basi,are mainly composed of tuff,tuffite,tuffaceous mud and tuffaceous sandstone.(2)The range of physical properties of tuff reser-voirs in the study area is largely,with average porosity is 4.88%.Among them,the number of samples with ultra-low porosity and extra-low porosity accounted for 83.6%,with the average permeability is 0.067 mD.It is an ultra-low porosity and ultra-low permeability reservoir.The tuff reservoir space include dissolved pores and devitrified pores,and have stereoscopic network pore structures,the tuff is mainly composed of mesopores and macropores,the physical properties are the best.The main reservoir spaces of tuffaceous sandstone include dissolution pore and intergranular pores,have micro-thin pore-micro throat pore structures,and mainly develop mesopores,with good physical characteristics.Tuffite and tuffaceous mud mainly develop dissolved pores,intercrystal pores and microcracks,have isolated pore structures,the pore types are mainly mesopores,with poor physical properties.(3)Sedimentation,diagenesis and tectonism jointly control the formation of high-quality tuff reservoir in the study area,sedimentation provide the material basis for the formation of highquality reservoirs,which control reservoir formation and distribution,compaction and cementation reduces reservoir physical properties,dolo-mitization and devitrification improves reservoir performance,the dissolution is the key factor of effective reservoir forming,which has positive impact on improving the physical properties of reservoir.(4)The tuff reservoir can be classified into three types,classⅠ,classⅡand classⅢ.the reservoir in classⅠis mainly concentrated around trough area,the reservoir in classⅡis distributed in the form of stripes along the western gentle slope zone,the distribution range of reservoir in classⅢis the widest,the areas where develop the reservoir in classⅠsuch as the east blocks of A43 well,the north blocks of A27 well,the west blocks of H16 well and south west blocks of A11well are the next favorable targets for tuff tight oil exploration.