鄂尔多斯盆地古隆起东北侧马五_4~1储层膏模孔类型及充填过程分析

Analysis on the Types and the Filling Process of the Anhydrite-model Pore of Ma5_4~1 in Northeast of the Palaeohigh,Ordos Basin

利用岩芯和薄片资料,通过薄片孔隙描述、铸体薄片图像分析等方法,在对研究区马五14储层孔隙类型划分的基础上,详细划分了膏模孔充填类型,并对其充填过程进行了阐述。研究结果表明,研究区马五14储层主要发育溶蚀孔(膏模孔和其他溶孔)、晶间孔、晶间溶孔、微裂缝4种类型的孔隙,且以膏模孔为主。通过镜下薄片对膏模孔内不同充填物观察发现,充填物主要为白云石、方解石、硬石膏,其中半充填的膏模孔中主要充填物为白云岩粉砂、白云岩粉砂+石英、白云岩粉砂+铁白云石3种类型,而全充填的膏模孔中主要充填物为白云岩粉砂+方解石、白云岩粉砂+石英+方解石、白云岩粉砂+硬石膏3种类型。综合分析认为膏模孔是含膏云岩中石膏等易溶晶体溶蚀后,晶体轮廓保留而形成的,首先裸露风化壳期先充填白云岩粉砂和深灰色方解石,其次深埋藏期充填自生石英、白色亮晶方解石、铁白云石及硬石膏。

Using the data of cores and thin sections,based on the classification of Ma514 reservoir pore types in the study area and through the pore description of thin sections,the image analysis of casting thin sections and other methods,this paper gives a detailed classification of gypsum-model pore filling types and makes an elaboration of filling process. The study shows that Ma514 reservoir developed the following 4 pore types as dissolved pore（anhydrite-model pore and other solution pores）,intercrystalline pore,intercrystalline solution pores and microcrack in the study area.According to the analysis to the carbon-oxygen isotopic characteristics of different fillings in the anhydrite-model pore,the fillings are mainly composed of dolomite,calcite and anhydrite,the fillings of partial filling anhydrite-model pore are mainly composed of dolomite silts,dolomite silts ＋ quartz,dolomite silts ＋ ankerite and the fillings of all filling anhydrite-model pore are mainly composed of dolomite silts ＋ calcite,dolomite silts ＋ quartz ＋ calcite and dolomite silts ＋ anhydrite. The comprehensive analysis reveals that the anhydrite-model pore is formed by the preservation of crystal outline after the dissolution of gypsum and other easily soluble crystals. Filling process in the anhydrite-model pore can be divided into the following several stages. Firstly,the anhydrite-model pore is filled with dolomite silts and dark-gray calcite in the naked weathering period. Then,the anhydrite-model pore is filled with authigenic quartz,white sparry calcite,ankerite and anhydrite.