| The Fuxian Formation and Yan10-Yan8 oil layers in the Jurassic strata of the Longdong area of the Ordos Basin are the main oil producing layers in the area.Compared with the Yanchang Formation reservoir,the Jurassic reservoir has advantages such as low development cost and good comprehensive benefits.With the further deepening of oil and gas exploration and the update of well seismic data,the current level of refined understanding of the ancient geomorphic morphology in the area is low,too macro,and the internal characteristics of the ancient rivers in the study area are not clear.There are significant differences in the types and scales of oil reservoirs in different ancient geomorphic units,and the reservoir formation laws are complex.In view of this,this article combines rock cores,field outcrops,and the latest seismic interpretation data to finely depict the ancient geomorphology of the study area through impression method,restore the internal characteristics of ancient river channels,and classify the types of ancient geomorphic units.Based on the restoration of ancient landforms,data such as core data,well logging interpretation,cast thin sections,scanning electron microscopy,and quantitative particle fluorescence were used to study the sedimentary evolution process and reservoir characteristics of the Fuxian Formation Yan8 oil layer formation,with a focus on analyzing oil and gas characteristics and summarizing the accumulation patterns of oil reservoirs.The main achievements and understanding achieved are as follows:(1)At the end of the Triassic,the Ordos Basin experienced two tectonic uplift movements,the first being an overall uplift movement and the second being an uneven uplift,with a large uplift amplitude at the southwest edge of the basin.In Longdong region,ancient river valleys,ancient slopes,inter river hills,ancient highlands,and ancient geomorphic units are developed,with ancient river channels filling the Fuxian Formation and Yan10 Formation;(2)The ancient river channel is not straight and symmetrical,but consists of channels and inter river hills of different depths and scales.The ancient river channel of Gan Shan is steep in the north and gentle in the south,and three continuous low convex zones extending in the northeast direction are developed at the bottom boundary of the ancient river;The ancient channel of Qingxi Ancient River is steep in the east and gentle in the west,with less development of inter river hills;(3)In the study area,braided river deposits are developed in the Fuxian Formation,low curvature meandering river deposits are developed in Yan 10,and high curvature meandering river deposits are developed in Yan 9 and Yan 8.From bottom to top,the thickness of the sand body gradually decreases,the continuity decreases,and the fine particle deposition gradually increases;(4)The pore types of the Fuxian Formation Yan8 oil layer formation in the study area are mainly intergranular pores,with a small amount of feldspar dissolved pores,intergranular dissolved pores,rock debris dissolved pores,and intergranular pores developed.Generally,low porosity and low permeability reservoirs are the main types;(5)The enrichment of oil and gas in the study area is influenced by multiple factors:the abnormal pressure of Chang 7 and the buoyancy of Jurassic strata provide the driving force for upward migration of oil;Oil and gas migrate through transport systems such as fractures and leaching zones;The distribution of weathered clay layers controls the location of oil entering the Jurassic reservoir;The favorable traps formed by the thickness of upper hydrocarbon expulsion and paleogeomorphology control oil enrichment;Local reservoirs have undergone short distance adjustment due to the impact of late tectonic movements.According to the law of oil and gas enrichment,there are 22 favorable targets in the study area,with a total area of 283km~2,among which there are 19Ⅰtargets. |
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