浅海微孔泥晶碳酸盐岩储层研究进展

微孔泥晶灰岩储层是一种重要的油气储层类型，尤其是对于中东地区白垩系碳酸盐岩储层，这明显不同于典型碳酸盐岩储层—古风化壳型岩溶储层、礁滩相储层及层状白云岩储层等三大类型。泥晶基质具有致密镶嵌结构和白垩质结构两种结构类型。泥晶晶体具有微菱形、圆形和它形三种晶体形态，以圆形泥晶储层物性最好，微菱形泥晶储层其次，它形泥晶为致密储层。微孔（直径小于10 μm）是泥晶基质中孔隙的主体，除此还发育铸模孔、海绵状基质溶孔和溶蚀沟道等。微孔的形成主要受原始矿物组分和成岩条件的共同制约:低镁方解石灰泥是微孔泥晶灰岩形成的先决原始矿物条件，相对矿物学稳定性可促进原始组构包括原生晶间微孔的保存。特殊的成岩环境是微孔泥晶灰岩发育的必要改造条件，泥晶灰岩中孔隙的形成是早期浅层埋藏下大气淡水淋滤及埋藏成岩期间有机酸溶蚀作用等两期溶蚀叠加的结果。在浅埋藏淡水透镜体内，方解石次生加大（奥斯特瓦尔德成熟过程）形成了沉积物早期胶结，防止压实的同时部分保留了原始结构和晶间微孔网络，还通过消除小晶体提高了渗透性；淡水选择性淋滤也形成了较广泛发育的铸模孔。在埋藏成岩过程中，有机酸性流体溶蚀作用形成海绵状基质溶孔及溶蚀沟道，也导致了圆形泥晶晶体的形成。

Research Progress on Shallow-sea Microporous Micritic Carbonate Reservoirs

Microporous micritic limestone forms important hydrocarbon reservoirs in the Middle East， and is clearly different from the three major reservoir types in China， namely， marine paleo-karst reservoirs， reef-shoal reservoirs and stratified dolostone reservoirs. The matrix texture is of two kinds: tight mosaic textures， and chalky textures. The micrites occur in three crystal forms: micro-rhombic， rounded and anhedral. Rounded micrite crystals form the best reservoirs， followed by micro-rhombic micrite reservoirs and anhedral tight reservoirs. Micropores （< 10 μm diameter） are the main pores in the micrites， in addition to spongy matrix dissolution pores， mold holes and dissolution channels. The formation of micropores is mainly restricted by the original mineral components and the diagenetic conditions. Low-magnesium calcites are the essential precursor minerals. Relative mineralogical stability may preserve primitive structures that include intergranular micropores. The formation of pores in micritic limestones is the result of two stages of early atmospheric freshwater leaching during shallow burial and organic acid dissolution during buried diagenesis. In the shallow freshwater burial case， calcite overgrowth （the Ostwald ripening process） leads to early cementation that prevents compaction while partially retaining the original structure and intergranular micropores， and increases permeability by eliminating small crystals. Freshwater selective leaching also forms widely developed mold holes. In deeper burial diagenesis， the dissolution of organic acid fluid forms spongy matrix dissolution pores and dissolution channels， which also leads to the formation of rounded micrite crystals.