鄂尔多斯盆地马家沟组白云岩储层特征及成因机理

Discussion on characteristics and origin of Majiagou Formation dolomite reservoir in Ordos Basin,China

以鄂尔多斯盆地下奥陶统马家沟组白云岩为研究对象,对不同类型白云岩的岩石矿物学属性、地球化学特征、孔隙结构特征、发育层位及分布规律进行对比研究,并结合成因,将白云岩分为3类:(1)泥粉晶白云岩,以岩盐矿物溶蚀型孔隙为主,在含膏云坪相带呈带状分布,横向分布稳定,形成于准同生白云岩化作用;(2)粉-细晶白云岩,以白云石晶间孔为主,主要发育于蒸发岩层系的短期海侵沉积期,受控于浅埋藏期渗透回流白云岩化作用;(3)中-粗晶白云岩,以残余原始粒间孔及格架孔为主,主要发育于台地边缘礁滩及古隆起周边高能颗粒滩相带,并经历了埋藏白云岩化作用。奥陶系白云岩分布具有"层控性"和"相控性",形成了现今白云岩储层多层叠合发育的特点,为奥陶系多套含气组合的发育创造了有利条件。

Mineralogical properties, geochemical characteristics, pore structure characteristics, development and distribution of different types of dolomites from the Majiagou Formation of Lower Ordovician are studied. It reveals that the dolomite can be divided into three types in terms of their genesis. The first type is micritic to powder crystallized dolomite with evaporite mineral dissolved pores and develops in dolomitic tidal flat facies, with penecontemporaneous dolomitization. The second type is powder to fine crystallized dolomite with intercrystalline pores and develops in platform inner shoal facies, with penetration reflux dolomitization. The third type is fine to medium crystallized dolomite with residual primary intergranular pore and framework pores, and develops in high energy bank facies, with burial dolomitization. The strata-bound and facies-bound features of dolomite are the main controlling factor of superimposed development of different types of dolomite reservoir in Ordovician, which provided favorable conditions for the development of multiple sets of gas combination in Ordovician.