The Study On Storage Layers Migration Mechanism Of Meshwork-carpet Type Oil And Gas Pool-forming System In Zhanghua Depression

In meshwork-carpet type oil and gas pool-forming system, storage layers play important roles in hydrocarbon migration and accumulation. Based on the study of storage layers basic characteristics, quantitative evaluation on storage layers is achieved by studying the mechanism of hydrocarbon migration.On basis of sequence stratigraphy analysis, the sedimentary characteristics of storage layers is studied by summarizing sedimentary facies types and distribution law. Based on this, the storage layers of Zhanghua depression are divided into two sets, which are described both in ichnography and section to reflect their structures. Physical properties such as porosity and permeability are studied and analyzed. .According to the distribution characteristics of oil-migrating faults and the relationship between fault movement period and oil-gas infusing period, dynamic study of storage layers in episodic expelling hydrocarbon period is carried out from two aspects: Oil vertical migration mechanism along faults from source rocks to storage layers and oil lateral migration mechanism in storage layers. First establishing mathematical model of oil pressure gradient in faults on the basis of geological model, the pressure gradient formula is deduced according to energy conservation principle.The remaining pressure of oil can be calculated accordingly. This can provide initial values for the study of oil vertical migration law in storage layers. And according to distribution characteristics of remaining pressure, oil migration direction in storage layers can be determined.Then building pressure gradient model of oil lateral migration and pressure relief model based on different geological models of storage layers, the pressure gradient formula of oil lateral migration in storage layers and pressure relief formula are also deduced. By the above formulas, migration resultant force formula is obtained considering different dynamics and resistances. The condition and range of oil migration, carpet-forming or pool-forming in storage layers can be judged according to distribution law of migration resultant forces, so as to reveal oil migration law in storage layers..According to the study results of migration resultant forces in episodic expelling hydrocarbon period, combined with distribution characteristics of sands thickness, porosity and permeability, storage layers of Zhanghua depression are divided into transported type and accumulated type by analyzing main controlling factors of storage layers quality. The study results are analyzed in typical blocks and comprehensive evaluation map is ultimately made up. This way, comprehensive evaluation on storage layers is achieved, which combines static with dynamic. According to reservoir forming location, oil source and the characteristics of hydrocarbon migration and accumulation, reservoir forming patterns of meshwork-carpet type are induced based on the study of reservoir types. And favorable exploration direction is pointed out clearly.