Research On Fluid Character And Gas Migration In The Upper Paleozoic Of Daniudi Gas Field

Daniudi gas field is one of the six abundant natural gas fields of Upper Paleozoic in Ordos Basin which belongs to lithostratigraphic gas reservoirs and it shows the characteristics of low porosity, low permeability , subnormal formation pressure, complex reservoir heterogeneity. Along with the increasing degree of the exploration and exploitation, especially the increasing of exploration and exploitation data and cognition for gas accumulation and reservoir diagenesis of Gas Field, it is very important for accelerating gas exploration and exploitation to enough research on pressure character, fluid geochemistry character and gas migration.Base on summarizing research production of former scholar on gas accumulation and reservoir diagenesis, by calculating fluid pressure, gas diffusivity and establishing liquid pressure equation of the gas-water phase in the closed porosity system, researches disequilibrium compaction effect, hydrocarbon generation effect, gas diffusivity effect and the effects of uplift unload, temperature drop and rock rebounding during the formation of low pressure and normal pressure in Daniudi gas field, and illuminates the mechanisms of generating abnormal pressure. By analyzing the enrichment and deficit of ion in the formation water, explains the mechanisms of generating formation water. By analyzing the gas geochemistry character, illuminates gas migration character. Based on the researches, by establishing the condition of gas migration mode, analyses hydrocarbon generation effect, the petrophysical properties of the reservoir and fracture during gas migration, and combines the gas-water distribution character, farther knows gas migration rule, and establishes gas migration mode.Though this research, the conclusion are gained in this thesis:1.From late Triassic to early Cretaceous, because of disequilibrium compaction effect and hydrocarbon generation effect, the Upper Paleozoic formation of Daniudi gas field generated abnormal overpressure, and the end of early Cretaceous, the effects of Uplift unload, temperature drop and rock rebounding made reservoir generate low pressure and normal pressure, gas diffusivity effect limited the increase of abnormal overpressure.2.During reservoir diagenesis, acidity and alkalescence of formation water related to coal layer environment and thermal evolution characteristics of source rocks, and controlled reservoir diagenesis.3.Geochemistry character of formation water and gas show that formation fliud occurred crossing formation flow.4 . The petrophysical properties of the reservoir, fracture and degree of hydrocarbon generation controlled gas migration. Gas migration was mostly vertical migration by vertical fracture. Gas lateral migration occurred commonly in sandstone with better petrophysical properties. Gas lateral migration of long distance in tai2 formation sandstone was relatively easy, but was feebleness in other formations.5.By analyzing fluid pressure, geochemistry character, gas-water distribution, the condition of gas migration mode and migration control factor, establishes gas migration mode, and consider that gas migration period could be compartmentalized two phases: from middle Jurassic to end of early Cretaceous, because of control of gas generation and sand discharge capability, excess differential pressure was biggish in the area, so gas migrated as piston, but migration distance was short. End of early Cretaceous, stratum uplift and gas generation capacity fall, so fluid pressure transformed from disequilibrium to equilibrium, and gas migration mode transformed from migration of piston to replacement migration, till equilibrium.