Study On The Formation Characteristics Of The Weathered Ma5 Layer Of Ordovician System In Daniude Gas Field

Northeastern ordos basin,the ordovician majiagou group daniudi area Ma55 section for new horizon of gas exploration in lower palaeozoic era,has attracted many attentions of the experts and scholars in recent years,but the Ma55 period of dolomite reservoir formation and distribution of has not been very good to solve.Based on the experts on the basis of predecessors research to sedimentary petrology,carbonate reservoir geology,oil and gas geochemistry for theoretical guidance,based on the drilling,core analysis,well logging and testing data,the ordovician weathering crust in the region,ancient karst geomorphology,sedimentary facies,reservoir petrology,reservoir physical properties and the causes of dolomite and dolomite reservoir distribution and main controlling factors to do the system research.(1)regional geological data,the results showed that the study area majiagou ma five period for the regressive period tidal flat sedimentary environment,the carbonate tidal flat facies sedimentation.Through study of core data,slices,analysts say the Ma55 on the section of the lithology is given priority to with dark gray,colored clay micrite,horizontal grain layer development,subtidal zone static water environment,the development of tidal flat microfacies under ashes.(2)this paper,by using core,logging and laboratory analysis data,such as the ordovician weathering crust karst in daniudi area symbols,type,vertical zoning,puberty is studied,think the supergene period of ancient karst region is the main development,there are three periods of karst cycle,and the Ma55 main purpose layer vertical vadose zone is located in the ancient karst phase 3 times.(3)in this paper,weathering crust thickness in the overlying strata is used to determine the tectonic setting in geomorphology,degree of residual determine the denudation thickness or karst weathering crust,and the organic combination of the two research palaeogeomorphic form.Will ultimately be the ancient landform is divided into two secondary geomorphic unit karst highland and oblique,karst karst slope is divided into high,slope area,groove three three geomorphic units.(4)the Ma55 period of development in the study area powder-fine crystal dolomite reservoir,the main pore types of intergranular pore and intergranular dissolved pore,the average porosity of 5.56%,the average permeability 0.48 x 10-3?m2.By lithology types,structure,morphology,degree of order,carbon and oxygen isotopes and the Ma5(1+2)period of dolomite reservoir comparison and analysis,combining with the characteristics of dolomite distribution,determine the Ma55 dolomite into mixed water baiyun paraphrase because supergene period.(5)through to the ancient karst in the study area,the ancient landform,purpose the cloud formation and distribution of comprehensive study,preliminarily determines the Ma55 period of dolomite reservoir distribution laws:?karst highland,groove of dolomite reservoir from development,interface of photoelectric absorption index of karst groove dolomite reservoir is low,show that a higher degree of dolomite Bai Yunhua;?karst hills,slope area dolomite reservoir development is less,only small pit development position in the local development of dolomite reservoir.