Simulation Of Diagenesis History And The Prediction Of The Favorable Exploration Areas Of Chang 7 Tight Reservoirs Of The Yanchang Formation In The Central-southern Part Of The Ordos Basin

The Chang 7 tight reservoirs in the Triassic Yanchang Formation of the Ordos Basin is rich in oil and gas resources and has great exploration potential.In order to make sure the hydrocarbon distribution boundary of the tight reservoirs in the central and southern parts of the Ordos Basin and find the favorable target areas so that predict its favorable zone,this paper restored The diagenetic evolution history of the basin and predicted the diagenetic facies of the research areas based on the analysis of the geothermal field and pressure field by using the software of the numerical simulation of the reservoir diagenesis.Based on the prediction of the diagenetic facies,combined with the characteristics of sedimentary facies of the search areas,we established the relationship model between diagenesis degree and reservoir porosity under the condition of single sedimentary sub-facies and predicted the current porosity of the Chang7 tight reservoir by this model.In addition,we established the order of the reservoir first compaction or accumulation based on the restoration of the history of porosity evolution.Considering the accumulation of oil and gas of tight reservoirs not controlled by structural traps,the favorable exploration target area is determined by sedimentary facies maps and porosity prediction maps.The research results are as follows:The diagenetic facies prediction results show that the Chang 7 tight reservoirs of the Yanchang Formation in the central and southern parts of the Ordos Basin is in the early diagenetic stage at the end of sedimentation of Yan'an Formation,developing the early compaction phase and the early cementation facies;it is in the A₁ and A₂¹ phases of the diagenetic stage at present.Developing early-period dissolution phase and medium-term dissolution phase.Porosity prediction results show that the Chang 7₃ reservoirs has the highest densified degree and the reservoir properties are poor;the Chang 7₁ reservoirs has the lowest densified degree and good physical properties.Under the condition of keeping the diagenetic strength constant,the order of the physical properties of Chang 7 reservoirs from good to bad is:meandering river delta plain>meandering river delta front>braided river delta front>turbidite fan,so we can conclude that the turbidite fan sand is the first to be dense.The results of the restoration of porosity evolution show that the porosity of the Chang 7reservoirs is less than 10%,so the reservoirs is first densifying then the petroleum accumulating and the hydrocarbon accumulation is not controlled by structure.The favorable areas prediction results show that the Chang 7₃ reservoirs has high density,distributing favorable area?B area,porosity is 6%¹0%?and relatively favorable area?C area,porosity is 2%⁶%?;the Chang 7₂ reservoir having the medium density,distributing the most favorable area?A area,porosity is more than 10%?,favorable area and relatively favorable area;the Chang 7₁ reservoir is low in density,distributing the most favorable area and favorable area.