鄂尔多斯盆地杭锦旗地区山西组储层成岩作用及孔隙演化

RESERVOIR DIAGENESIS AND PORE EVOLUTION OF SHANXI FORMATION IN HANGJINQI AREA,ORDOS BASIN

山西组致密砂岩是鄂尔多斯盆地上古生界重要的油气产层,其致密化过程对储层质量有重要影响。采用镜下鉴定、阴极发光、扫描电镜、储层物性和包裹体测温等测试分析手段,研究杭锦旗地区山西组储层发育特征、成岩作用和孔隙演化。结果表明:山西组岩石类型主要是岩屑石英砂岩、岩屑砂岩和石英砂岩;储层除有少量原生粒间孔外,还发育大量次生孔隙;主要经历了压实、胶结和溶蚀作用;基于石英包裹体测温数据,山西组均一温度集中分布在80~100℃和120~140℃,表明至少存在晚三叠世-早侏罗世和中侏罗世-早白垩世至今两次烃类充注,确定了山西组成岩演化序列;储层主要经历了压实、多期胶结和多期溶蚀作用后,最终致密化;储层致密的直接原因是压实作用,平均视压实率为68.90%;储层以硅质胶结和碳酸盐胶结为主,平均视胶结率为20.40%;溶蚀作用是最重要的增孔作用,平均视溶蚀率为80.06%。

The Shanxi Formation tight sandstone is the major oil and gas producing layer in the Upper Paleozoic of Ordos Basin, and its densification process has an important effect on reservoir quality. The development characteristics, diagenesis and pore evolution of the Shanxi Formation in Hangjinqi area are studied by means of thin section identification, cathodoluminescence, scanning electron microscopy, reservoir physical property and inclusion temperature measurement. It shows that the rock varieties of Shanxi Formation are mainly lithic quartz sandstone, lithic sandstone and quartz sandstone. In addition to a few primary intergranular pores, the sandstone reservoir mainly develops a large number of secondary pores and the rocks experienced the process of compaction, cementation and dissolution. Quartz inclusion temperature measurement reveals that the homogenization temperature of the Shanxi Formation is concentrated in the range of 80-100 ℃ and 120-140 ℃, implying that there were at least two hydrocarbon charges from the Middle Jurassic to the Early Cretaceous and from the Middle Cretaceous to the present, which accomplished the diagenetic evolution sequence of the Shanxi Formation. It shows that the Shanxi Formation tight sandstone reservoir has experienced compaction, multi-stage cementation and multi-stage dissolution, and the final densification. The direct cause of reservoir densification is compaction, and the average apparent compaction rate is 68.90%. Siliceous cementation and carbonate cementation are the dominant cementation types in the reservoir and the average apparent cementation rate is 20.40%. Dissolution is the most important pore increment and the average apparent dissolution rate is 80.06%.