Study On Reservoir Microscopic Characteristics And Residual Oil Distribution Of Xi 2 Formation In Niujuanhu Area,Santanghu Basin

This dissertation takes sandstone reservoir in Niujuanhu area in Santanghu Basin as research subject and the target reservoir is low in porosity and ultra-low in permeability.Some further studies on rock and physical characteristics has been carried out in this thesis with various experiments such as casting thin sections,particle size analysis,XRD and so on.Quantitative researches of Xi 2 reservoir on micro-fabric structure and features of seepage are also be conducted by combining analysis from previous research with data acquired from further experiments including high pressure mercury injection,constant-speed mercury injection,oil-water relative permeability and nuclear magnetic resonance.Based on research above,some simulation experiments are conducted in order to acquire a better understanding on formation and distribution of micro residual oil in the study area.Several achievements which have been obtained during study are presented as follows:(1)The rock type of Xi 2 reservoir of Xishanyao formation,Niujuanhu area is medium-fine grained arkose lithic sandstone.The content of interstitial material is relatively high(12.23%).The particle of sandstone in target reservoir contacts in type of point-line and has roundness from medium to good.The average porosity of aiming formation is 12.39%and the average permeability is 3.31×10-3?m.Based on the data analysis above,target reservoir has a poor property.(2)The main pore types of the reservoir are intergranular,tuffaceous dissolution and feldspar dissolution pores.The main types of throat are flaky and curved-flaky throats.Point throats are also been found in some area.The capillary pressure curve of this formation is mainly resides in class ? and ?.The radius of pore is relatively uniform(121.17?m-156.73?m)and has an average value of 144.82?m.However,the throat radiuses are different in a large scale(0.52?m-4.91?m)and have an average value of 1.508?m.The development of throat is more important than pore in controlling the petrophysics characteristics and the ability of seepage in target reservoir.(3)The reservoir permeability curve could be divided into three types as I,II,III and seepage capacity of permeability in the reservoir changed from strong to poor as type various from I to III.The average value of saturation of mobile fluid is 48.42%and it is mainly resides in good-medium level.(4)Based on the data acquired from real sandstone water-oil displacement experiments of different pore types,the displacement in interparticle pores is always netted.The waterflood swept area is medium-small and swept efficiency is medium.Micro residue oil is mainly caused by flowing around effect in small area.The displacement in dissolved pore and intergranular pore processed evenly and the efficiency of swept is high.The microscopic residual oil in these pores is mainly distributed as droplets which have been cut off and the residual oil left in corner.The displacement in micro pores processed finger-like and the displacement efficiency is low.Micro residual oil of this type of pores is mainly caused by flowing around effect and distributes in large area.(5)With comprehensive classification of target reservoir,the grade I reservoir always contains the best property,seepage ability and the highest water flooding efficiency.However,this type of reservoir is less distributed in the study area and most of it has been flooded which lead to a low potential in residual oil exploration.Although the grade ? and ?reservoir has the moderate-inferior seepage ability and medium water flooding efficiency,their widely distribution in the target area have made them the key of next step of exploration.The reservoir of grade IV has the worst property and seepage ability which makes this type of reservoir the least valuable in further exploration and development.