Characteristics And Comprehensive Evaluation Of Diagenetic Facies Of Chang 6 Reservoir In Eastern Huaqing Area

The tight sandstone reservoir of Chang 6 formation in Huaqing area of Ordos Basin is one of the main battlefields for the development of tight oil in China.The special micro-pore structure caused by the complex diagenesis of tight sandstone makes it different from conventional reservoirs.Therefore,it is necessary to establish a set of evaluation systems suitable for this type of reservoir.Based on the background of reservoir sedimentary deposition,sand body distribution,and lithologic characteristics,this study used microscopic identification to identify the typical diagenesis of the reservoir.According to the results of the division,the diagenetic facies were divided combined with the pore type of the reservoir,and the conventional and constant-speed mercury intrusion experiments were conducted in different diagenetic facies to finely characterize the reservoir's microscopic pore structure.The reservoir evaluations based on various macro and microscopic experiments were finally conducted,and the responsive capacity for different types of reservoirs were studied simultaneously.The main research results are as follows:(1)The lithology of Chang 6 reservoir in Huaqing area is mainly lithic feldspathic sandstone and feldspathic sandstone.Intergranular pores(1.42%)and feldspar dissolved pores(0.67%)are the main pore types.The flake throat is the main type in the study area.The average porosity of the reservoir in the study area is 10.06%,and the permeability is 0.36 m D,which is a typical tight sandstone reservoir.(2)Based on the size of face rate,pore development,dominance of diagenesis,content and distribution of detrital particles and interstitials,the reservoirs in the study area can be divided into five types of diagenetic facies: chlorite membrane residual intergranular pores,hydromica residual intergranular pores,hydro-mica feldspar,hydrocolloid cementation,and carbonate cementation facies,there face ratio gradually decreases,the physical properties continuously decrease,the proportion of destructive diagenesis gradually increases,the pore diameter gradually decreases,the pore structure is gradually complexed and the connectivity gradually deteriorated.(3)The throat radius is the most important parameter to control the reservoir seepage ability.The better the pore throat configuration,the better the physical properties.The volume of the effective pore/throat volume per unit volume of rock sample is obviously related to the increase of the permeability.The volume larger,the seepage ability stronger.For the pore throat region > 0.1 ?m,the accuracy of characterization using the more advanced constant-pressure capillary mercury pressure curve is higher,and for the reservoir pressure limit of <0.1 ?m,a high-pressure mercury pressure capillary pressure curve is used to characterize the interval pore throat distribution.(4)Comprehensive macro and micro parameters were used to establish a set of evaluation criteria for reservoir classification applicable to the study area.Among them,the chlorite membrane-residual intergranular pore facies is the best reservoir,the hydromica-residual intergranular facies and hydromica-feldspar dissolving pore facies are second and third quality,and the cementation facies quality is the worst.(5)There is a clear correspondence between the production response of different diagenetic facies.The hydrocolloid cementation and the carbonate cementation facies produce minimal oil and the volume.The initial oil and liquid production of hydromica intergranular pore facies is relatively high,the water content is low,and the stable production cycle is long.The initial oil and liquid production of the chlorite membrane residual intergranular pore facies is the highest,but it decreases rapidly and the stable production cycle is short.The hydrolyzed feldspar feldspar facies produces low oil production,liquid production and moisture content,and has a stable production cycle.