内蒙乌兰格尔地区上古生界砂岩的成岩作用

DIAGENESIS OF UPPER PALAEOZOIC SANDSTONE IN THE WULANGAR REGION, INNER MONGOLIA

内蒙乌兰格尔地区的上古生界厚逾400m,大部分砂岩属于致密型低孔渗性的岩体。本文主要论述这些砂岩的成岩作用及其对储层孔渗性的影响。记砂岩具有四个成岩阶段:1.机械压实作用和早期胶结作用;2.碳酸盆的胶结作用和交代作用;3.溶蚀作用;4.晚期自生粘土矿物的形成和早期粘土矿物的重结晶作用。其中强烈的机械压实作用减少砂岩的孔隙,碳酸盆矿物的胶结作用尤其显著地减少了孔隙度和渗透率。但是,胶结物和部分颗粒的后期溶蚀作用是改善某些层段储集性能的有利因素。

The Upper Paleozoic in the Wulangar Region, Inner Mongolia is more than 400m thick. Most of sandstones belongs to the reservoir of compact type with low porosity and poor permeability. This paper deals with the diagenesis of sandstones and their influence on porosity and permeability. Four stages of diagenesis are generalized as follows: 1. Mechanical compaction of grains and early cementation; 2. Cementation and metasomasis by carbonate minerals. 3. Corrosion of Minerals ( mostly carbonate cement or feldspars) . 4. Formation of late authigenic clay minerals and recrystalliz-ation of early clay minerals. The analysis of diagenetic evolution indicate that intense mechanical compaction led to the decrease in the pores in the sandstones, especially cementation of the carbonate minerals obviously reduced the porosity and permeability. Hcwever, late corrosion of the cements and partial grains is a favourable factor, which improved the reservoir property of several segments.