Hydrocarbon Accumulation Conditions And Major Controlling Factors Of Mesozoic Oil And Gas In F Basin,North Africa

The F basin of North Africa is one of the important oil-producing areas in Egypt.This area is rich in oil and gas resources and complex in structure,characterized by stereoscopic oil and gas accumulation in multilayer system.However,the current understanding of hydrocarbon accumulation pattern and accumulation rule is unclear,resulting in a higher proportion of lost wells in the development process.To solve this problem,this thesis analyzed the regional tectonic setting,tectonic evolution characteristics,stratigraphy,sedimentary evolution characteristics and other basic geological conditions of the F basin in North Africa.Comprehensive evaluation of hydrocarbon accumulation conditions in F basin was carried out,including source rocks,reservoirs,caprocks,traps,dredging systems and their temporal and spatial matching relationships.Besides,this thesis also investigated the types of proven oil and gas reservoirs and the distribution characteristics of oil and gas in the basin.Then the hydrocarbon accumulation rules and main controlling factors were summarized,providing guidance for the future exploration direction.Generally,the main achievements of this thesis are as follows:1.The Mesozoic in the F Basin is a complete petroleum system.The main source rock is the Middle Jurassic Khatabat group,with a thickness of 50?400m,TOC content of 0.5?3%,type II organic matter,and a vitrinite reflectance Ro of 0.7?1.2%.During the mature or high maturity stage,a large number of hydrocarbons are produced.2.The main reservoirs are the Lower Jurassic RQ group,the Middle Jurassic Safa group,the Upper Cretaceous AEB group and the Kharita group.Their lithology is mostly sandstone with a porosity of 7-20% and a permeability of 10?700 m D,which indicates medium or good reservoir.In addition,there are high-quality regional caprock developed over the reservoir,macroscopically controlling the accumulation of oil and gas.The local caprock also plays a role in oil and gas accumulation.3.The F basin experienced a long period of intense tectonic movement.The folds and faults are well developed,and the faults are mostly normal faults.Due to the influence of tectonic movement,the trap is mainly composed of structural traps,including extruded anticline trap,nasal trap and fault block trap under lateral plugging of normal fault.However,a few stratigraphic unconformity occlusion traps and lens traps have been found in F basin.4.A large number of effective traps are formed during the Mesozoic tectonic activities in the F basin.The source rocks of the Khatabat Formation have already entered the oil-producing threshold in the early Cretaceous,and a large amount of oil was generated from the Early Cretaceous to the Neogene.During the Late Cretaceous Tulun period,the basin compressive movement was intense,and the secondary migration of oil and gas reached a peak.Therefore,the Late Cretaceous Toulon period is a critical moment for oil and gas accumulation in the F basin.5.There are two types of hydrocarbonaccumulation model of the F basin.One is“endogenous-sand body dredging-short distance lateral migration” model,and the other is“exogenous–fault channeling-vertical migration” model.The endogenous accumulation model is mainly responsible for the control of the favorable hydrocarbon generation zones and traps,and the exogenous accumulation model is mainly controlled by the drainage system.6.The controlling factors of hydrocarbon accumulation in the F basin were analyzed.Firstly,the favorable hydrocarbon-producing areas of the main source rocks in the basin basically control the plane distribution of oil and gas.Secondly,the faults control the migration and accumulation of oil and gas.The open faults during the oil and gas migration period are the main pathways for vertical gas migration,while the closed fault becomes the sealing condition of the trap.The Upper Cretaceous oil and gas are mostly distributed near the oil source fault.Thirdly,the physical properties and distribution of sandstone reservoirs control the reservoir systems and reserves.Finally,good regional caprocks and partial caprocks allow oil and gas to be preserved for long periods of time.Through the above studies,the distribution rules of oil and gas reservoirs and the main controlling factors of accumulation in F basin have been clarified,which can provide guidance for future oil and gas exploration and development.