Hydrocarbon Accumulation Characteristics And Major Controlling Factors In S Sag Of North Africa

S sag is located in the northern depression of the western desert basin in north Africa.With the discovery of several large oil and gas fields in recent years,this sag shows good exploration potential.However,due to the unclear understanding of petroleum geological characteristics in S sag,the lack of systematic research on the main controlling factors of oil and gas accumulation and the accumulation rules of oil and gas reservoirs,the success rate of drilling is low,about 50%.In this context,this thesis carried out a study on the characteristics and main controlling factors of Mesozoic reservoirs in S sag based on logging,seismic and core data,determined the main controlling factors of oil and gas accumulation through a fine anatomy of the reservoirs,and established the oil and gas accumulation model in the study area,all of which provide important guidance for oil and gas exploration and development in the future.The main achievements of this thesis are as follows:There are two sets of hydrocarbon source rocks in S sag,Jurassic Zahra Formation and the Cretaceous AR-F.The source rocks of the Zahra Formation have a TOC of >1%,a Ro value of0.6%-1.6%,and a Tmax value of 438°C-478°C,making it the main source rock in the study area;The quality of hydrocarbon source rocks in AR-F Member is poor,and only a small amount of hydrocarbon supply is found in the northeast of the sag.Oil source correlation shows that the crude oil of the three main reservoirs in Jurassic Safa Formation,lower Cretaceous AEB Formation and upper Cretaceous Bahariya Formation is mainly from source rocks of Zahra Formation.The reservoir sand body of Safa Formation is mainly distributed in the delta front along the direction of provenance,which belongs to the self-generated and self-storage type,and has good reservoir characteristics of "medium porosity and high permeability" and "thick layer and high yield".Cretaceous reservoirs are mainly composed of sandstone and siltstone,which are deposited in the shallow sea environment and belong to the lower-generated and upper-storage type.There are many dissolution holes.AEB Formation is affected by corrosion,and the reservoir has good pore permeability.Bahariya Formation is highly affected by cementation and forms a medium-porosity and low-permeability reservoir.The S sag mainly develops structural oil and gas reservoirs.Based on the analysis of typical oil and gas reservoirs,it is concluded that oil and gas are distributed in belts on plane.Ring deep concave fault zone and structural high zone are the main places for oil and gas accumulation.The longitudinal hydrocarbon-bearing horizon gradually changes from southwest to northeast.Furthermore,it is clear that the main controlling factors of oil and gas accumulation are faults,reservoir quality and source rocks.Among them,the development of faults controls the hydrocarbon accumulation of cretaceous reservoirs,and the distribution of sand bodies in reservoir quality mainly affects the hydrocarbon migration of Jurassic reservoirs,and the differences in the parent material conditions of the source rocks affect the oil and gas distribution.In this paper,the conditions of reservoir formation in the target area were studied systematically for the first time.The tight tracking and feedback of the exploration wells were made,the deployment plan was adjusted in time,and the exploration results were improved.Nine of the 13 exploration wells were guided to obtain commercial oil and gas discoveries,which greatly improved the success rate of drilling.