Application Of Integrated Geophysical Prospecting In Shallow Geothermal Exploration

Geophysical exploration is particularly important in geological exploration,which has the advantages of wide exploration area,large depth and low cost,and can provide fast and effective basis and guidance for solving geological problems.Geothermal exploration in recent years gradually rise,the single geophysical prospecting methods widely used in the process of exploration,and geophysical interpretation has multiple solutions,in interpretation state there is a certain depth,breadth,and the precision is insufficient,cannot effectively discriminant geothermal geological conditions of exploration,the exploration hole layout guidance is not strong,and funds utilization rate is not high,also delay the construction period.Zhangye Basin,located between Qilian And Beishan mountains,has the value of geothermal exploration and development due to its large sedimentary thickness and certain thermal storage conditions.Linze county urban area and southern area in alkaline saline basin in the west,so this article in linze county urban area and southern geothermal resource exploration project,collecting exploration area in the past such as geology,hydrology,geophysics,drilling data,on the basis of comprehensive analysis,choose the gravity measurement,controlled source audio-frequency magnetotelluric sounding,and vertical electrical sounding of three kinds of geophysical exploration method,respectively,find out formation sedimentary rhythm,basin boundary and structural distribution and acid distribution characteristics of rock mass,the deep fault location and stratigraphic lithology structure,shallow strata structure in the basin,provide powerful basis for exploration hole layout.Through the comprehensive application of the three methods,the following cognition can be obtained:(1)Gravity profile measurement is effective for the analysis of basin sedimentary rules,in linze county urban area and the south,from south to north of bouguer gravity anomaly and residual gravity anomaly increase gradually,local gravity anomaly curve changes,show strata exploration zone from south to north,from coarse to fine is gradually increasing,formation density,have good instruction effects for basal and thickening;(2)Vertical electrical sounding method for shallow geologic structure in the discrimination and the division of strata structure has obvious advantages,the results show that the exploration area of quaternary strata thickness thinning from south to north,the apparent resistivity,generally between 100-400?·m,stratigraphic lithology mainly shaly sand,and gravel stone,gravel,etc.,lower part of quaternary formation of neogene,apparent resistivity between 20-60?·m,stratigraphic lithology mainly mudstone,argillaceous sandstone,electric sounding curve tail lifted up,and the granite weathering crust corresponding;(3)Although the resolution of the controlled source audio-frequency magnetotelluric sounding method is low,for the recognition of the shallow strata ability is weak,but its detection depth is big,deep in the discriminant of deep structure,division of stratigraphic lithology,identification of basement rock interface has advantages of exploration area 1000 m below the apparent resistivity is greater than 100?·m,and the granite weathering crust corresponding;It is inferred that the thermal cap rocks in the exploration area are upper strata of quaternary and neogene,and the geothermal reservoirs are mainly mudstone and sandy mudstone of the Neogene Baiyanghe Formation,and granite is the main heat source.Through drilling and logging verification,the inferred interpretation results of geophysical exploration are basically consistent with the actual stratigraphic structure of the exploration area.The logging shows that the granite stratum has strong radioactivity,and the radioactive decay provides abundant heat source for the stratum to heat up.Prove the geothermal exploration use gravity profile measurement of controlled source audio-frequency magnetotelluric sounding-vertical electrical sounding,the basin boundary delimitation,discrimination,stratigraphic lithology classification,basal identification has a good effect,the exploration area geothermal field of reservoir and cap,and source condition analysis and the exploration hole's location,construction has good guidance meaning.