从古老碳酸盐岩大油气田形成条件看四川盆地深层震旦系的勘探地位

建设四川大气区亟待寻找天然气资源丰富、勘探潜力大的接替新领域。为此,在系统梳理我国克拉通盆地深层古老海相碳酸盐岩大油气田形成的烃源、储层、成藏组合等条件和大气田分布规律的基础上,分析了四川盆地深层震旦系天然气成藏富集条件,评价了上震旦统灯影组的天然气勘探潜力和有利目标区。研究结果表明:(1)源灶保持的有效性与规模性,储集体的有效性与规模性,储盖组合的有效性、规模性与近源性是深层碳酸盐岩大油气田形成的必要条件,古隆起、古斜坡与古断裂带是寻找深层碳酸盐岩大油气田的有利区;(2)该盆地新元古界—寒武系发育3套优质烃源岩,有机质成熟度仍处于裂解成气的最佳窗口,成气规模大;(3)该盆地灯影组微生物碳酸盐岩经建设性成岩作用改造,形成有效储集层,大范围分布;(4)灯影组源盖一体,台缘、台内均具备近源成藏的有利条件。结论认为,四川盆地深层震旦系油气成藏条件良好,是未来天然气勘探的重点接替领域,其中川中古隆起及其斜坡带长期处于天然气聚集的有利部位,规模勘探应高度关注灯四段台缘带、灯二段台缘带、川中古隆起斜坡带灯影组台内丘滩体和川东地区灯影组丘滩体4个有利领域。

Exploration status of the deep Sinian strata in the Sichuan Basin: Formation conditions of old giant carbonate oil/gas fields

To construct a giant Sichuan gas province, it is in an urgent need of exploring new replacement areas with abundant natural gas resources and great exploration potential. In this paper, the formation conditions (e.g. source rock, reservoir and play) and the distribution laws of the deep-seated old giant marine carbonate oil/gas fields in China's Craton Basins were investigated systematically. Then, the accumulation and enrichment conditions of deep Sinian natural gas in the Sichuan Basin were analyzed. Finally, potential and favorable target zones of natural gas exploration in the Dengying Formation of Upper Sinian were evaluated. And the following research results were obtained. First, the effectiveness and scale of source kitchens, reservoirs and reservoir-caprock assemblages and the proximity are the necessary conditions for the formation of deep-seated giant carbonate oil/gas fields, and paleo-uplifts, paleo-slopes and paleo-fault zones are the favorable areas of searching deep-seated giant carbonate oil/gas fields. Second, in the Sichuan Basin, three sets of high-quality source rocks are developed in the Neoproterozoic-Cambrian System, and their maturity of organic matter is still in the optimal window for cracking gas, so the gas generation scale is large. Third, after the microbial carbonate rocks of Dengying Formation in the Sichuan Basin were reconstructed by constructive diagenesis, effective reservoirs are formed and distributed widely. Fourth, owing to the integrated source rocks and cap rocks of Dengying Formation, the marginal platform and the intra platform have favorable conditions for proximal hydrocarbon accumulation. In conclusion, the deep Sinian in the Sichuan Basin has good conditions of hydrocarbon accumulation and it is an important replacement area of natural gas exploration. Paleo-uplifts and slopes in the central Sichuan Basin have been the favorable locations of natural gas accumulation for a long period. Large-scale exploration shall focus on four favorable areas, including the marginal platform zone in the fourth Member of Dengying Formation, the marginal platform zone in the second Member of Dengying Formation, the bioherm beach body of Dengying Formation intra platform in the paleo-uplifts and slopes of the central Sichuan Basin, and the bioherm beach body of Dengying Formation in the eastern Sichuan Basin.