关键词: 钙质隔层, 识别标准, 成因机制, 有效盖层, 勘探成效, 沙湾组, 准噶尔盆地

Abstract: The degree of exploration in the1st sand group of the Shawan-1 member of the Neogene (N1s1 1) in the Chepaizi bulge of the Junggar Basin has been generally high, and it is consequently becoming increasingly difficult to tap the potential of the area. A change in the research approach is therefore urgently required to provide support for re-understanding of reservoirs and to promote the search for new exploration targets. Based on comprehensive analysis of cores, thin sections, well logging and seismic data, research into identification standard, formation mechanisms, and seal performance of calcareous barriers inside sand bodies has been carried out, and the petroleum geological significance of the calcareous barriers were analyzed. The results show that calcareous barriers are distributed in the middle and upper parts of sand bodies in the 1st sand group, and that the lithology is mainly fine sandstones with calcite cementation. According to well loggings it is characterized as high Rt, low AC, high DEN, decreasing GR, and SP with feature of a certain return range. The calcareous barriers have a ‘ternary composite’ genesis. The formation of the calcareous barriers is controlled by 3 factors: transition surface of progradation-retrogradation in a short-term cycle; a sedimentary system of shallow braided river delta in an arid environment, and strong calcareous cementation in sedimentary to shallow burial stages. According to analysis of caprock breakthrough pressure, the calcareous barriers can be served as effective caprocks. Guided by these factors, re-understanding of reservoir characteristics based on barrier distribution has been carried out. Several new, and favorable, exploration blocks have been discovered around the reserve area, multiple wells have been successfully drilled, and large-scale reserves have been identified. The exploration performance that has been achieved is promising.