Driving Mechanism And Migration,Accumulation Mechanism Of Oil And Gas In Depression-uplift Composite Structure Of Petroliferous Basin

In the process of oil and gas exploration,a large number of high-yielding mud shale reservoirs have been discovered,and the distribution of these high-yielding mud shale oil and gas reservoirs is closely related to "depression-uplift combination structure".At present,the existence of oil and gas in mud shale is mainly believed to be the result of internal retention or adsorption,which cannot explain the oil and gas accumulation in high-yield mud shale oil and gas reservoirs.In view of this problem,this paper preliminarily studied the driving,migration and accumulation mechanism of oil and gas in the depression-uplift composite structure,by means of simulation experiment,geological data analysis,core observation,microscopic thin section observation,providing a basis for the study of oil and gas accumulation in high-yield mud shale oil and gas reservoirs.Main achievements:(1)The depression-uplift composite structure of source rock series has a uniform or relative differential pressure to drive oil and gas migration.In the depression-uplift composite structure,compared with the high part of the structure,the buried depth of the low part is larger,and the degree of pore compaction and pressure generation is higher,so there is a unified or related differential pressure from the low part of the structure to the surface and the high part of the structure.When oil,gas and water coexist,oil and gas are affected by buoyancy in water,and the direction of buoyancy is mainly upward.(2)In depression-uplift composite structure,the matching of differential pressure and migration medium determines the main migration direction of oil and gas.Generally speaking,the transport performance of fine-grained hydrocarbon source rocks in the direction of parallel planes is better than that in the direction of vertical planes.Therefore,driven by the differential pressure,oil and gas will migrate in a large scale along the direction of parallel planes of fine-grained hydrocarbon source rocks.Although buoyancy is ubiquitous,oil and gas are mainly transported along fractures or pores with higher flatness under the driving of buoyancy.(3)In the depression-uplift composite structure,driven by differential pressure,oil and gas will accumulate in the process of migration.The main reason for this is that the permeability of water phase is higher than that of oil phase and gas phase in the water-wet rock formation,and the migration resistance of water is lower.Therefore,under the the same differential pressure,water will migrate ahead of oil and gas,resulting in the increase of oil and gas saturation.When oil and gas move along the strata in a large scale in fine-grained source rocks,if there is a good reservoir condition in the source rocks,oil and gas accumulation will be formed.