【摘要】 热液白云石化可形成优质白云岩储层。通过岩石矿物学观察、地球化学分析以及地震资料解释,四川盆地西南地区中二叠统栖霞组—茅口组广泛发育的砂糖状白云岩为热液白云石化成因,具有如下特征:①白云岩出现频率较高,单层厚度较大,宿主灰岩主要为生屑灰岩和生屑泥晶灰岩;②中—粗晶白云岩发育残余生屑结构,生屑溶蚀后部分被自生石英和鞍形白云石充填,孔隙类型主要为晶间孔和溶蚀孔,平均孔隙度为6%～10%;③基质白云岩包裹体均一温度明显高于白云石化作用时的地层温度,具有偏负的δ18 O值、高的87Sr/86Sr比值以及明显的正Eu异常;④白云岩产出井附近发育基底断裂,且在对应的地震剖面上见"下凹"反射特征。在紧邻基底断裂带,热液白云石化作用强,白云岩储层厚度大,横向连续性好,适合构造圈闭勘探;在远离基底断裂带,热液白云石化作用弱,白云岩储层厚度较小,横向连续性较差,适合岩性-构造圈闭勘探。更多还原

【Abstract】 Hydrothermal dolomitation can form high-quality dolomite reservoirs.Through mineralogic observations,geochemical analyses and comprehensive interpretations of seismic profiles,the Middle Permian saccharoidal dolomite in Qixia and Maokou formations which are related with hydrothermal dolomitization have following characteristics:(1) higher occurrence frequency,greater thickness in a single layer(5～40m),host limestone dominated by bioclasitc limestone or bioclasitc micrite;(2) residual bioclasitc textures developed in mesocrystalline-macrocrystallinpore dolomites and bioclast-dissolved pores partly filled with authigenic quartz and saddle dolostone mostly with intergranular and corroded pores,which porosity averages between 6%and 10%;(3) an obviously higher homogenization temperature of dolomite matrix(125～178℃) than the stratum temperature during dolomitization,which is indicated by more negative oxygen isotopes(-10.1‰～-11.42‰),higher 87Sr/86Sr(0.709 194～0.710 174)and positive Eu anomaly;(4) well-developed basement faults adjacent to dolomite-producing wells and a "sunken" reflection in corresponding seismic profiles.Generally speaking,close to basement fault zones,hydrothermal fluid dolomitization is intensive and dolomite reservoirs are thick and in good lateral continuity,where structure traps are exploration target.On the contrary,far from basement fault zones,hydrothermal fluid dolomitization is weak and dolomite reservoirs are thin and in poor lateral continuity,where hydrocarbon exploration should focus on litho-structure traps.更多还原