Reservoir Characteristic Study Of The Chang-8₁Oil Group Of Yanchang Formation In Huaqing Area, Ordos Basin

The Huaqing area is located in the Ordos Basin, China Iraq Shaanxi slopeconstructed, that the region’s Chang-8₁reservoir group is important oil and gasproducing formation. With the further expansion of the scale of oil and gasexploration and development, clearer understanding of the characteristics of thisimportant oil and gas production layer reservoir is particularly important. Because ofthe middle layer is a new exploration layer, lack of the research of its sedimentarycharacteristics, diagenesis and reservoir physical properties, has seriously affected thepost-oil and gas exploration and development. Therefore, this thesis for the the basinHuaqing Chang-8₁reservoir exploration and development of the group status quo,sedimentology and petroleum geology in the field of advanced theoretical methodsand techniques as a guide, the use of drilling cores in the observed data, thin section,scanning electron microscopy, carbonmeans of test and analysis of oxygen isotopes,electron microprobe, vitrinite reflectance and clay mineral X-ray diffraction, thedeposition of the area-sand body characteristics, diagenesis, reservoir structure,reservoir properties such as in-depth analysis, has made aseries of awareness results.China Huaqing regional sedimentary facies analysis shows that the Chang-8₁sandstone reservoirs in the river the context of the leading edge of the river deltas ofthe main development of deposition. Sand body development of favorable facies aremainly underwater delta front distributary channel and mouth bar, crevasse channel isnot very developed. The head of Chang-8₁reservoir group deposition controlled bythe different systems of the northeast, northwest and southwest rivers, forming thenortheast, northwest and southwest of the three major river deltas, but mainly in theNortheast river deltas. Analysis of research on the distribution characteristics of thesand body thickness plane and planar distribution of sedimentary microfacies characteristics show that the deposition thickness of the sand body by the control ofsedimentary facies, delta front, subaqueous distributary channel sand bodydevelopment, the thickness of the sand body than thelarge, thick sand bodiessuperimposed distribution.Reservoir rock characteristics analysis showed that the lithic arkose andfeldspathic lithic sandstone is the main rock types of the head of Chang-8₁reservoirgroup. Quartz content is between21%-70%, with an average of about37%; feldsparcontent between10%-62%, with an average of about35%; debris content of between7%-45%, an average of27%or so. Sandstone granularity to fine sandstone, and thesorting better, skewness is partial and very positively skewed mainly. Primaryintergranular holes for the main pore types, followed by feldspar dissolution porosity.The research of District diagenesis analysis shows that the region there are fourtypes of diagenesis, ie, compaction （pressure solution） the role of cementation,dissolution, and metasomatism. Quantitative analysis of porosity evolution of the areathat the main reason for deterioration of reservoir properties in the region, compactionand carbonate cementation. The dissolution of the sandstone porosity has increasedand enhanced porosity and permeability of sandstone, but the range is limited,because the role is only to produce a small amount of secondary porosity. The divisionof diagenetic stages of the study area that is in diagenetic stage A, the local hasdiagenetic stage B of the area as a whole. The study area is the most favorablediagenetic facies type is dissolution+chlorite rims diagenetic facies class Ⅰdiagenetic facies, but the distribution is small in size, compaction+weak dissolutiondiagenetic phase of Class Ⅱ diagenetic phase was more favorable diagenetic facies,wide distribution,calcite diagenetic reservoir properties is the worst.Porosity and permeability data and mercury injection data, combined with theanalysis of sedimentary facies and diagenesis, to carry out reservoir characteristicsanalysis showed that the low porosity and permeability reservoir is a typical feature ofthe Chinese Qing Chang-8₁reservoir group. Chang-8₁reservoir group porositybetween4.7%-16.5%, an average of10.5%, permeability between the mD0.04-10the mD with an average of1.1the mD. Pore throat connectivity is poor, porecombination of the main types of small pores-micro-jets/fine roar and large pores-micro jets/micro-roar type. The reservoir pore structure is more complex, changesgreater curve analysis showed that the calculated and mercury through the porestructure parameters. By deposition, diagenesis, Huaqing region of clastic materialcomposition, rock type and particle size control of reservoir properties with congenital, late sedimentary facies and diagenesis on the distribution of reservoir propertieshavean impact on the role of dissolution has greatly improved the local reservoirproperties.The above analysis of the study area, the actual needs for exploration anddevelopment in the area, the area of reservoir evaluation comprehensive study showedthat the reservoir in the area is Class Ⅱ and Class Ⅲ reservoir into massivedistribution, localdevelopment class Ⅰ reservoir. On this basis, combined withsedimentary facies of the study area, the thickness of the sand body distribution anddiagenetic facies and reservoir conditions, such as relation of the head of Chang-8₁reservoir group reservoir to predict the distribution of favorable areas, can be used asthe areaNext favorable oil and gas exploration and development goals.