Analysis Of Oil And Gas Distribution And Control Factors In Niger Delta

Niger delta is rich in oil and natural gas resources in the basin,has proven oil and gas reserves in the world ranking twelfth.By means of data inquiry,statistics of oil and gas reservoir and reserve data,and dissection of typical reservoirs,the structural,stratigraphic,sedimentary and petroleum geological characteristics and reservoir-forming modes of the study area are defined,and the distribution characteristics of oil and gas and its main geological controlling factors are analyzed.The tectonic divisions are divided into gravity detachment extensional tectonic area,gravity detachment diapir tectonic area and gravity detachment thrust tectonic area.The strata are divided into three groups from bottom to top,namely,Akata Formation,Agbada Formation and Benin Formation,which belong to the diachronic stratigraphic unit.The Akata Formation in the Niger Delta Basin is shallow-sea and pre-delta deposits,while the Agbada Formation is progradational nearshore-front deposits.The main sedimentary microfacies sandstone reservoirs are delta distributary channel,underwater distributary channel and estuary bar.The organic source of the Niger Delta is characterized by the duality of ocean itself and land source,and the contribution of land source organic matter input is particularly important.Source rocks are mainly developed in three sets of strata: the first is Cretaceous;the second is Upper Cretaceous-Paleocene;and the third is Paleogene-Eocene-NeogeneMiocene.The main types of kerogen are type II and type III.The Acata Formation began hydrocarbon expulsion in Miocene.The Agbada Formation sandstone is the reservoir development section in the study area,which has a wide distribution range.The main caprock in the Niger Delta is the interbedded shale of the Agbada Formation.The Akata shale is also sealed in the lower part of the Agabada sandstone.The main types of traps are diapir structure,fault nose and fault block,rolling anticline and collapse structure,followed by stratigraphic traps.Oil and gas accumulation includes two modes.Sourcefault-reservoir mode is the most important reservoir formation mode in the basin.Growth faults connect the source rocks of the Akata Formation with the reservoirs of the Agbada Formation and form vertical migration channels.Source-reservoir models are mostly developed in the transitional zone and frontal compression zone of the study area,and hydrocarbon expulsion from source rocks directly enters the sandstone joined by faults.Oil and gas distribution is mainly controlled by structural(mainly fault)and organic matter source,distribution,oxidation degree,maturity and other geological factors:(1)Oil and gas fields in the whole area are roughly parallel to the extension direction of the fault,because of the continuous activity of the fault,oil and gas migrate to the shallow part.(2)The organic matter preservation in the low-value area of HHI is poor,located in the southwest direction of the study area,and the number of oil and gas reservoirs is small.The high-value area of HHI has good preservation conditions and is located in the northeast direction of the Niger Delta,enriching most of the reservoirs in the region.(3)Terrestrial plants contributed more to natural gas production in the areas with higher contribution of terrestrial plants,while lower contribution of terrestrial plants contributed less to the continental margin organic matter and more to oil production in the areas affected by the ocean.(4)In the offshore Delta area,the thickness of Akata Formation and Tertiary mudstone increased,resulting in a higher geothermal gradient.All areas overlying the Akata Formation,the main hydrocarbon-producing strata,had reached a mature-high evolution stage long ago,and gas was dominant.Especially in the eastern side of the delta center,the Agbada Formation has the thickest sedimentary facies zone,the lowest geothermal gradient,low thermal maturity of source rocks and short hydrocarbon generation time.The maturity of organic matter is relatively low and oil production is the main factor.