| Many exploration wells in the southern margin of Junggar Basin have obtained high-production oil and gas
flow from the Lower Cretaceous Qingshuihe Formation in wells, which proves that high-quality reservoirs is developed
in Qingshuihe Formation. Based on the paleo-geomorphologic data, this paper analyzes the differences in sedimentary
facies of the bottom sand body of Qingshuihe Formation, the reasons for the stable distribution of sand bodies, and the
distribution patterns of different rock types, by combining analysis of the sand body structures, petrologic characteristics,
heavy mineral assemblages and paleocurrent characteristics of the reservoir. The study suggests that before the deposition
of Qingshuihe Formation, the paleo-geomorphology of the southern margin in Junggar Basin was characterized by the
development of a steep-slope area in the south and a large gentle-slope area in the north, whereas two slope breaks were
globally developed in the gentle-slope area. During the depositional period of Qingshuihe Formation, the study area was in
the process of lake transgression, and retrogradational braided-river deltas and fan deltas were formed under the control of
paleo-geomorphology. In the southern steep-slope area, fan deltas depositional system was developed, and the thickness
of sandstone and conglomerate reservoirs is at the range of 10-30 m. In the northern gentle-slope area, three stages of
regressive braided-river deltas depositional system were developed under the control of two slope breaks, resulting in the
widely developed sandstone reservoirs in the middle and northeastern parts of the southern margin in Junggar Basin. The
sandstone reservoir formed by northern and northeastern source system with a thickness of 20-50 m and relatively good
physical properties, making it a favorable reservoir development area for the Qingshuihe Formation. |
