巴音都兰凹陷南洼槽云质岩成藏研究及有利目标优选

Study on hydrocarbon accumulation of dolomite rocks in south subsag of Bayindulan sag and optimization of favorable targets

通过采用岩心观察、薄片鉴定、X衍射、扫描电镜、测井相、地震相、沉积相等方法,分析了二连盆地巴音都兰凹陷南洼槽下白垩统阿尔善组云质岩成藏机理。结果表明:阿尔善组云质岩储集层岩石类型以云质砂岩为主,白云岩次之,储集空间类型为裂缝-孔隙型,主要为受构造活动(断裂)形成的裂缝型空间和差异压实作用下形成的原生粒间、晶间孔隙以及溶蚀作用下形成的粒间、粒内溶孔、晶间溶孔,云质岩成藏主要控制因素为源储运配置关系、物性临界值以及溶蚀作用有效降低油气充注毛管压力等,进而以云质岩储集层有效孔隙度≥12.2%、渗透率≥0.3 mD、厚度≥40 m为划分标准,对南洼槽云质岩有效储集层分布进行预测:平面主要分布在南洼槽巴Ⅰ构造带北部、西南斜坡中内带、巴Ⅱ构造带中部,优选井位目标为B 36南圈闭。

Through core observation,thin section identification,X-ray diffraction,scanning electron microscope,log facies,seismic facies and sedimentary facies,the mechanism of hydrocarbon accumulation of dolomite rocks in Lower Cretaceous A′ershan group of south subsag in Bayindulan sag,Erlian Basin was analyzed.The results show that the rock types of dolomite reservoir in A′ershan group are mainly dolomite sandstones,followed by dolomite rock.The reservoir space type is fracture-pore type,which is mainly composed of fractured space formed by tectonic activity(fault),primary intergranular and intercrystal pores formed under differential compaction and intergranular,intragranular and intercrystal dissolved pores formed by dissolution.The main controlling factors for oil and gas reservoir forming of dolomite rocks are configuration relationship of source,storage and migration,physical property critical value and dissolution effectively reducing capillary pressure of oil and gas filling,etc.The effective reservoir distribution of dolomite rocks in south subsag was predicted based on the dividing critera of dolomite reservoirs with effective porosity(≥12.2%),permeability(≥0.3 mD)and the thickness(≥40 m).The plane is mainly distributed in the northern part of BaⅠstructural belt,the middle and inner zones of southwest slope,and the middle of BaⅡstructural belt in south subsag.The preferred well position target is B36 south trap.