达县—宣汉地区长兴组礁滩白云岩成岩过程中的孔隙演化

Porosity evolution during the diagenesis of the reef shoal dolostones from the Changxing Formation in the Daxian-Xuanhan region, Sichuan

关键词:  达县—宣汉  上二叠统  长兴组  礁滩白云岩  成岩作用  川东北

Key words:  Daxian-Xuanhan region  Upper Permian  Changxing Formation  reef shoal dolostone  diagenesis  northeastern Sichuan

摘要:

川东北达县—宣汉长兴组礁滩白云岩具有良好的油气储集潜力。作者通过大量岩石常规薄片、铸体薄片观察研究,发现该礁滩白云岩储层储集空间主要为次生成因的晶间孔、晶间溶孔、粒间粒内溶孔、生物体腔内溶孔和生物格架间溶孔。这些孔隙的形成和演化除了受沉积作用、构造作用和有机质热演化史的影响外,还受成岩作用的控制。首先在海底-暴露-浅埋藏环境下,压实及胶结使原生孔隙基本消失;而准同生混合水白云石化及早期暴露溶蚀作用改变了沉积物内部结构,形成众多微小孔隙的网络及溶孔,为后期形成大量孔隙创造了条件。其次在中—深埋藏环境下,强烈的重结晶作用和溶蚀作用使得岩石形成大量的次生孔隙,大大提高了礁滩白云岩的储集性能。

Abstract:

The reef shoal dolostones from the Changxing Formation in the Daxian-Xuanhan region, Sichuan have good potentials for oil and gas reservoirs. On the basis of the observations of routine thin sections and cast sections, the reservoir spaces in the reef shoal dolostones consist mostly of intercrystal pores, intercrystal solution openings, intergranular and intragranular solution openings, visceral solution openings and organic framework solution openings. The formation and evolution of the pores are generally constrained not only by deposition, tectonism and thermal evolution of organic matter but also by diagenesis. The compaction and cementation are responsible for the disappearance of primary pores in the submarine-exposure-shallow burial environments. The penecontemporaneous mixing water dolomitization and early exposure and dissolution result in the modification in the internal structures and textures of the sediments, and formation of extensive micropore networks and solution openings. The intense recrystallization and dissolution permit the generation of abundant secondary pores and improvement of the reservoir capacity of the reef shoal dolostones in the intermediate to deep burial environments.