Characteristic Description And Fovorable Area Optimization Of Chang 8 Reservoir In The Both Sides Of Xifeng Ordos

In this paper,the reservoir of Chang 8 layer in Yanchang Formation of Triassic in both sides of Xifeng Ordos is studied.The main belts of Xifeng and the both sides of Xifeng are belong to the southwest sedimentary system and the both sides of Xifeng are the target areas for the next production and construction.The chang 8 layer of the district is a typical low-permeability reservoir.The distribution of sand bodies in reservoirs changes rapidly and the geological conditions are complex,leading to unclear production and construction directions.In response to these problems,based on the data of cores,well logs and others.this paper studied the characteristics of sedimentary microfacies and reservoirs by various methods,and then evaluated and classified the reservoirs.Based on the evaluation of reservoirs,the favorable blocks are forecasted.It provide reliable guidance for the production and construction of the target area in the next step,and at the same time provide a geological basis for stable production in the later period.Concluded as follow:?1?The Chang 8 oil-bearing beds in the study area belongs to a delta front subphase sedimentary deposit.The sedimentary microfacies mainly consist of underwater distributary channels and inter distributary bays.The sedimentary facies and sand bodies are generally distributed in the southwest-north-east direction.?2?The main types of rock in the target layer of the study area are mainly lithic feldspathic sandstone and feldspathic lithic sandstone,and the interstitial fillings are dominated by carbonate minerals and authigenic chlorites.The main pore types are intergranular pores and feldspar dissolved pore.The chang 8 reservoirs in the study area experienced a variety of diagenesis,and is in the mid-diagenetic stage now.There are four diagenetic facies in the study area,which are the facies of chlorite membranes+intergranular pores?quality reservoirs?,the facies of kaolinite cementation+feldspar dissolved pore,the facies of calcite cemented?poor reservoirs?,and the facies of dense diagenetic.The porosity of the reservoir is about 8.64%on average,and the permeability is about 0.48?m×10^-3?m² on average.?3?Based on the characteristics of sedimentary microfacies and sand body distribution in the study area,combined with the characteristics of rock types,the characteristics of pore structure,and the characteristics of diagenesis in the study area,the reservoir evaluation is classified into four types:type ? is called the high-quality reservoirs,type ? is called the higher quality reservoir,type ? is called the general reservoir,and type ? is called the poor reservoir.The quality of the four types of reservoirs deteriorated in turn.The largest distribution of the study area are type ? and type ? reservoirs.?4?The type of oil and gas reservoirs in the study area is mainly lithologic reservoirs.Based on the comprehensive evaluation of reservoirs and combined with the results of test oils,this paper have done the screening work for 6 small layers of chang 8 layer in the study area,and favorable areas is performed.There are 5 type I blocks,39.83km² in total,and 12 type ? blocks,totaling 410.71km².