The Research On Petrophysical Facies Classification Of Low Permeability Sandstone Reservoir And Prediction Of Favorable Areas

Chang 6₁ reservoir of Fanxue Area in Ordos Basin is a typical low-ultra porosity and ultra permeability sandstone reservoir,which is the main production layer of the study area.Based on the phscial property,casting thin slice,the SEM,X-ray,high pressure mercury injection and constant-speed mercury injection,nuclear magnetic resonance,oil-water relative permeability and so on,according to the detailed description made for the different type of diagenetic facies,then the microscopic characteristics of various reservoir are clearly defined.Through the superposition of sedimentary facies and diagenetic facies,combined with experimental characteristic parameters,the favorable area of the Chang 6₁ reservoir is predicted.The main conclusions of this paper are listed as follows:Chang 6₁ of Fanxue Area deposited a set of delta front subfacies from the source of northeast,the major rock types are arkose and lithic feldspar sandstone,clay minerals and carbonate cementation are developed,the particle size is fine,the sorting is from medium to preference and the grinding circle is poor.Chang 6₁ had experienced a complex diagenetic evolution process and most of the reservoir had entered phase A of middle diagenesis,the rest had been in the phase B of middle diagenesis,the compaction and cementation reduced the porosity rate by 55.72%and 32.41,which are the main factor causing the densification of the reservoir,dissolution with increases in the average porosity is 4.36%,the composite pore type formed by the dissolution pore of feldspar and the residual intergranular pore is the most common in the study area.Analyzing the clay mineral content and the surface porosity,the Chang 6₁ reservoir is divided into six types of diagenetic facies,which are characterized by a variety of experimental testing methods.The reservoir quality of the kaolinite and chlorite cementation-integranular pore is optimal,the diagenetic facies belt has high physical property and the development of integranular pore with large pore throat radius,the pore coordination number is high and has the good connectivity;the reservoir has high saturation of movable fluid,the displacement interference of oil and water two is low,the seepage is strong and the oil displacement efficiency is high.The dense phase of carbonate cementation is worst,which has the poor physical property and the pore structure characteristics,the cements are developed and then fill pore,the radius of pore and throt is small and the connectivity is inferior,the reservoir has low saturation of movable fluid,the displacement interference of oil and water is serious,and the oil displacement efficiency is low,they are basically invalid reservoir in research area.Based on the superposition of sedimentary facies and diagenetic facies,optimizing RQI for dividing parameters,the reservoir petrophysical facies is divided into three types?PF1,PF2 and PF3?,and the main favorable zones are PF1 and PF2,combined with the experimental results of typical wells and production dynamic index,complete the favorable prediction,which has a good consistency with the distribution of sedimentary microfacies and diagenetic facies in the study area.