鄂尔多斯盆地中东部奥陶系盐下层系白云岩储层沉积特征及发育演化机理

Sedimentary characteristics and evolution mechanism of Ordovician pre-salt dolomite reservoirs in the central and eastern Ordos Basin

鄂尔多斯盆地马家沟组盐下的碳酸盐岩—蒸发岩层系是未来油气勘探的重要接替层系。由于碳酸盐岩—蒸发岩的特殊沉积组合强烈影响后续差异化成岩流体溶蚀—充填作用,进一步增大了盐下碳酸盐岩储层的复杂性,也给优质储层的分布预测增加了难度。本文以鄂尔多斯盆地马家沟组中下组合为研究对象,基于岩心、薄片、物性资料等开展储层地质学研究,识别出15种岩石类型和10类相序组合,明确了盐下储层类型包括:膏模孔泥晶云岩储层、颗粒白云岩储层、斑状白云岩储层、晶粒白云岩储层和微生物白云岩储层。在孔隙成因和演化分析基础上,建立了“优势沉积相+早期成孔+膏盐岩封盖保存孔隙”的盐下白云岩储层发育地质模式。研究结果深化了对盐下碳酸盐岩层系孔隙形成和保存机理的认识,同时对鄂尔多斯盆地的油气资源勘探开发具有重要的现实意义。

The carbonate-evaporite system of the Majiagou Formation under salt beds in the Ordos Basin is an important strata for future oil and gas exploration.The special pattern of carbonate-evaporite will cause subsequent differential dissolution and filling of diagenetic fluids,further increasing the complexity of pre-salt carbonate reservoirs and making it more difficult to predict the distribution of high-quality reservoirs.Therefore,this study took the pre-salt of the Majiagou Formation in the Ordos Basin as the research object,and conducted reservoir geology research based on cores,thin sections,physical property data,etc.,and identified 15 rock types and 10 types of facies association.It clarifies that pre-salt reservoir types include gypsum-pore dolomite reservoirs,grained dolomite reservoirs,leopard dolomite reservoirs,crystal dolomite reservoirs and microbial dolomite reservoirs.Based on the analysis of pore origin and evolution,the geological model of dolomite reservoir under salt beds development is established,which is“favorable sedimentary facies+pore formation in the early diagenetic stage+stable preservation of pores in carbonate-evaporite systems”.The research results can deepen the understanding of the origin and preservation mechanism of pores in carbonate reservoir under salt beds,and have important practical significance for the development of oil and gas resources in the Ordos Basin.