The interpretation of the controlling action of Cretaceous to Tertiary tectonic compression on the reservoir in the southern margin of Junggar Basin: vitrinite reflectance and grain packing density

Abstract：Vitrinite reflectance is one of the important reflections of the controlling action of tectonic compression on the reservoir in the southern margin of Junggar Basin. Grain packing density is a direct result of tectonic compression that controls the reservoir. An analysis of the measured vitrinite reflectance of the Cretaceous-Neogene source rocks from the wells and outcrops and a study of the Cretaceous-Upper Tertiary micro-reservoir and grain packing density in 14 wells reveal the evolution of tectonic compression controlling the reservoir in the southern margin of Junggar Basin from Cretaceous to Tertiary. The high Ro values were in the eastern Hutubi area in the southern margin of Junggar Basin, and the low Ro values were in the western area in Cretaceous. And the distribution of grain packing density is the same as the distribution of Ro values, as shown by the map. Because of the uplifting of the Bogeda Mountain in the Late Jurassic to early Cretaceous period, the tectonic compression in Hutubi area was stronger than that in Xihu-Dushanzi area in the southern margin of Junggar Basin. The distribution of vitrinite reflectance in Palaeogene was different from that in Cretaceous. The values of Ro and grain packing density in Anjihai-Manasi-Tugulu anticline area of the middle-distal thrust belt decreased in two directions, i.e., the foot of the thrust belt and the foredeep. So the main reservoir-controlling factor was the buried thermal effect instead of the tectonic compression. Because of the re-uplifting of the Tianshan Mountains in Upper Tertiary, the tectonic compression changed the main reservoir-controlling factor through the distribution of grain packing density. An analysis of the micro-reservoir shows that the relationship between porosity and Ro was in negative correlation, so were the things at the diagenetic stage in Cretaceous; nevertheless, in Lower-Tertiary, the relationship between porosity and Ro was in positive correlation.