关键词: 准噶尔盆地东南部, 石炭系, 煤系烃源岩, 火山作用, 天然气, 勘探潜力

Abstract: The Junggar Basin is rich in natural gas resources but low in discovery level. The discovery of the Carboniferous self-generation and self-accumulation gas reservoir in Well Fu26 in the southeastern part of the basin has revealed a brand-new exploration field of natural gas. A set of coal-measure source rocks are developed in the Upper Carboniferous Batamayineishan Formation in the southeast of Junggar Basin, whose lithologies are mainly carbonaceous mudstone and coal-measure mudstone, with a small amount of coal. In the carbonaceous mudstones and coal, the average hydrogen index is 182 mg/g, and the total content of exinite and sapropelinite in the organic maceral of some samples is more than 20%. The organic matter of type Ⅱ₂-Ⅲ is dominant, mainly producing gas, with certain oil-generating ability, indicating medium to good source rocks as a whole. For the carbonaceous mudstone and coal in Batamayineishan Formation, the average Pr/Ph ratio is 4.14, the C₁₉/C₂₁ and C₂₀/C₂₁ tricyclic terpane ratios, the C₃₀ diahopane/(C₃₀ diahopane+C₂₉trisnorhopane) ratio and the relative content of C₂₉ regular steranes are high, but the gammacerane index is low, indicating that it was formed in a freshwater oxidative sedimentary environment with dominant input of terrestrial higher plants. Coal-measure mudstones were developed in sedimentary water with high salinity and high input of aquatic organisms, and were formed in the transitional environment from oxidation to reduction. Coal-measure mudstone is slightly worse than carbonaceous mudstone in terms of the organic matter type and abundance, dominated by type Ⅲ kerogen, which is mainly due to the strong seasonal changes in the low-energy coast or shallow waters of the gulf. At the end of the Cretaceous, the source rocks of Batamayineishan Formation matured in large areas in the depression and slope areas in the southeast of Junggar Basin, and they have generally entered a high-mature to over-mature stage, while only part of source rocks in the uplifting areas have entered the main oil generation window. Volcanic activity has obvious promotion effect on the formation and evolution of source rocks:some source rocks are rich in tuffaceous components and show good hydrocarbon generation capability. In some areas, the vitrinite reflectance of source rocks is abnormally high due to heating by magma, causing its hydrocarbon generation window to migrate to the shallow part. In the southeast of Junggar Basin, the Carboniferous source rock of Batamayineishan Formation has a thickness of over 100 m, covering an area of 3835.4 km². In the east slope of the Fukang sag and Jimsar sag, there are two gas generation centers with the gas generation intensity greater than 100×10⁸m³/km². On the whole, the southeast of Junggar Basin has the resource potential to form large- and medium-sized gas fields, and it is expected to become an important area for natural gas exploration following the Kalameili gas field.

Key words: southeast of Junggar Basin, Carboniferous, coal-measure source rocks, volcanism, natural gas, exploration potential