| The reservoir of Et,in A’er sag of Erlian Basin is a typical low permeability sandstone and conglomerate reservoir,With the exploration and development process,The complex micro-pore structure restricts the exploration and development process of the A’er sag.The use of conventional single test methods in the quantitative characterization of its micro-pore structure encountered a bottleneck.It is difficult to evaluate the microscopic reservoir characteristics of low permeability reservoirs effectively.The application of physical testing,casting thin film,scanning electron microscopy,particle size analysis,conventional pressure mercury,constant pressure mercury,nuclear magnetic resonance,oil-water infiltration experiment,Real sandstone visualization displacement experiment,start pressure gradient experiment and other test methods.The characteristics of micro-pore structure,movable fluid occurrence characteristics,seepage characteristics,starting pressure gradient and its influencing factors were studied in this area.The micro-pore structure difference and seepage difference of low-permeability,ultra-low permeability and ultra-low permeability reservoirs are compared from the microscopic point of view,and the development characteristics and main controlling factors of low permeability reservoirs in the A’er sag depression are studied at the same time.Mainly aware of the following aspects.Mainly aware of the following aspects:(1)The oazian lithology is sandstone and gravel and gravel,The composition of the debris:Cuttings(34.2%),Quartz(25.2%),feldspar(24.2%),The sandstone type is mainly composed of feldspar lithic sandstone and lithic feldspar sandstone.The content of interstitial material is 14.9%,mainly kaolinite and illite.The pore type is dominated by intergranular pores and feldspar pores.Throat type to sheet,curved-based,followed by necking,tube bundle(2)Porosity is mainly distributed 7.9-17.2%,with an average of 14.5%and the porosity is mainly low porosity.The permeability is mainly distributed 0.14～15.6×10-3pμm2,with an average of 6.5×10-3μm2.The reservoirs in the study area are low porosity and low permeability reservoirs.(3)According to the flooding pressure of the mercury intrusion curve<1MPa,between 1-2MPa,more than 2MPa will be divided into three types of reservoir pore structure.Class I for the low drainage pressure-fine throat type,II type in the row of discharge pressure-micro-throat throat type,Ⅲ type for the high and medium displacement pressure-nano-suction throat type.(4)Constant pressure mercury is obtained when the permeability is greater than 1.76×10-3μm2,the correlation between the throat radius and the permeability is weakened and the intersection becomes discrete,The average throat radius is lower than the mainstream throat radius trend is more and more obvious.Especially when the permeability is less than 5× 10-3μm2 and the throat radius is less than 2μm,the reservoir throat radius is more obvious than the control,and the reservoir development is difficult.Reflecting the reservoir heterogeneity by the pore throat ratio of large,easy to produce high permeability of the channel,causing the wells early see the water(5)According to the classification of movable fluid saturation,the T2 cutoff values of the samples are mainly between the second class(better)and the third class(middle)reservoirs,with the average distribution of 22.13%.The main reason for the distribution of cutoff is that the porosity and porosity of the sandstone and conglomerate reservoirs are poor and the heterogeneity is strong.The total porosity and intergranular pore porosity have a great effect on the saturation of the moving fluid,and the content of the dissolved pore has a certain contribution to the movable fluid.The increase of the micropores reduces the effective movable space,Followed by the clay mineral content,pore throat radius ratio.(6)According to the characteristics of the seepage curve,three types are classified:type I aqueous phase concave type,type II water phase linear type,type III water phase concave type.The I type of water on the concave,good reservoir properties(K>10mD),Clay mineral content is relatively small,reservoir sensitivity is poor.II type water phase linear,reservoir physical properties in general(1<K<10mD),Clay minerals are prone to expansion.Ⅲ type water phase concave(K<1mD),Clay mineral content is high and the reservoir has a strong sensitivity.(7)The study area is mainly composed of pore-intergranular pore type,intergranular pore-pore-dissolving type and micro-displacement channel.The main displacement type is homogeneous,mesh-homogeneous,finger-mesh.Residual oil type is mainly around the flow,cluster,film-like oil film,broken,island-like.The heterogeneity of pore structure is the main controlling factor affecting oil displacement efficiency(8)Based on the measurement of the starting pressure gradient,the permeability is greater than 20 × 10-3 μm2.Can be considered as the boundary between nonlinear seepage and linear seepage.The size of the starting pressure gradient parameters is mainly affected by reservoir physical properties,solid-liquid interface,pore structure and fluid properties.According to the actual measured pressure gradient parameters to calculate a reasonable well distance of 148m.(9)In this paper,we study the microscopic pore structure and seepage characteristics of low permeability reservoirs,and determine the main factors such as throat size,distribution range,pore throat ratio,separation coefficient and clay mineral content.Using the analysis of the starting pressure gradient,the boundary between the linear and nonlinear seepage characteristics of the reservoir is determined,The formula is deduced only for reservoirs with permeability less than 20 × 10-3m2.According to the example,it is proved that the formula is reliable... |
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