Comparative Study On Chang 2 And Chang 6 Reservoirs Of Triassic Ya Nchang Formation In Panlong Area

The Ordos Basin is an important energy base in China.Oil,gas,coal and other resources are symbiotic in the basin.The Yanchang Formation is a typical low-permeability reservoir.the delta sand body developed in Panlong of eastern basin has always been an important area for oil and gas exploration.The exploration of the Mesozoic in the Panlong area is focused on Chang 2,Chang 45 and Chang 6.In this paper,two sets of reservoirs,Chang2 and Chang6,which are close to buried depth and close to formation time,are selected as the research objects.The petrological characteristics,physical properties,reservoir pore types and pore structure characteristics of the target layer are compared and analyzed to find out their similarities and differences by using a variety of materials such as,cores,cast foils,scanning electron microscope,cathodoluminescence,X-ray diffraction,petrophysical properties and mercury injection.On this basis,the similarities and differences between sedimentary and diagenetic processes are analyzed qualitatively and quantitatively.The main achievements and insights are as follows:1.Two sets of reservoir rock types are mainly feldspathic sandstone,some lithic feldspar sandstone,grain size are mainly fine sand,followed by silt and medium sand,overall Chang2 reservoir rock grain size is larger than Chang 6.Particle sorting,roundness,similar type of support.The heterogeneity is mica and muddy,and the cementation is mainly siliceous,calcite,dolomite and pyrite.The grinding circle is mainly subcircular with grain support,linear contact between grains,pore cementation type,and pressure embedded cementation type.In terms of physical properties,the length of 2 is better than that of Chang 6.2.Sedimentary process is the basis of controlling reservoir physical properties.The development of primary and secondary pores is established by rock composition and structure,and the macroscopic distribution of physical properties is controlled by sedimentary microfacies.There is a good relationship between the high holes in the plane and the distributary channel(underwater distributary channel).The difference of sedimentary environment also leads to the difference of particle size and separation between two sets of reservoirs.The original porosity of the target layer is restored by the quantitative calculation formula of pore and diagenesis evolution.3.Compaction is the main reason for reservoir compaction in this area.The high plastic particle content of the target layer leads to insufficient compaction capacity of reservoir particles,serious loss of original porosity,which is about 60%,and the compaction strength of Chang 6 is slightly greater than that of Chang 2.However,the existence of chlorite film improves the compaction resistance of particles and is beneficial to the preservation of pores.4.Cementation makes the reservoir more dense and destroys the primary pore and its structure,while the dissolution improves the reservoir quality to some extent.The effects of diagenesis stages on the porosity of sandstone in Chang 2 and Chang 6 are calculated quantitatively,and the quantitative evolution relationship between diagenesis and porosity in the study area is established.