The Application Of The Geogas Field In Buried Fracture

Fracture structure has been an important content in resource exploration and engineering geology measurement and assessment. Currently, conventional geophysical and geochemical methods such as seismic prospecting, and electrical prospecting have mainly been applied to detect fracture structure. However, in river bed area composed by rivers and floodplain large gravel layer, these methods have some limitations(For seismic method, gravel layer inside riverbed have different from outside in attenuation by absorption and velocity pickup of seismic wave, the former will add much difficulties to seismic data acquisition and processing. The flow of underground diving and large earth surface humidity will cause interference for electrical, magnetic signals).Geogas measurement technology can solve detection problem of buried fracture structure in these areas; the technology is easy to carry and handle.Fracture structure has helped to geogas migration; high value abnormal of geogas can be formed above. From the formation and migration mechanisms of geogas: A vertical rising gas flow is prevalent exist in earth interior, under the migration to earth surface, these gas flow can carry solid particle exist in the form of nanoparticle; multiple elements gas flow can be shaped. Pressure difference exist between fracture structure and Surrounding formation, the pressure difference increase up flow velocity, besides flow rate, the number of nanoparticle migrate increased, thus rock-forming elements formed in near-surface and some trace elements abnormal appeared. Therefore, above the fracture structure, the number of geogas will be greater than other regions; the content of many elements in geogas will be significantly higher than the background value. Based on detecting near-surface rock-forming elements and some trace elements abnormal, geogas survey is a method to seek buried fault zone.Yarra River, Kangding County in Sichuan province, has rich reserves of water resources. Along the river from major groove to Long cloth have various locations can be as favorable areas for water conservancy site. Kangding locate in Chuanxi earthquake belt, according to geological data suggested, there may be buried fracture growth.If buried fracture through water conservancy favorable areas will bring huge risks for engineering construction. Therefore, developing buried fracture detection along the Yarra River is an important part of engineering geological assessment, and has a significant meaning for the safety of local water conservancy project site testing.This paper supported by NNSF of China"Geogas Research of buried geological bodies and fracture"and Huaneng company kangding area the hydropower planning project "Yarra River buried fracture geophysical and geochemical exploration". The projects through developing geogas survey in Yarra River, according to abnormal characteristics of geogas, combining workspace geological conditions, and through the analysis to determine buried fracture location. In order to guarantee the reliability of the buried fracture confirmation, at the same time, developing the measurement of Soil radon (Rn) concentration with line total points geogas survey. to contrast.Firstly, geogas migration mechanism and the information reflected from geogas measurement were anlnysed, merits of geogas survey to the traditional geophysical and geochemical measurement techniques were discussed. Secondly, the application of geogas survey (a kind of nuclear detection techniques) in Yarra River to develop buried fracture detection confirms the existence of buried fracture and gains a good application effect. The significant meaning about geogas survey techniques in detection buried fracture practical application confirmed. In addition, the difficulty of geogas survey and technical improvements corresponding by practical projects are discussed.Finally, according to integrated information of geophysical and geochemical exploration to quickly determine the activity of faults were discussed (Publicly reports about this issue have not yet seen at home and abroad;To this end, carrying out research in this area, not only has scientific theory meaning , no doubt of great engineering significance).The followings are the main research results and basic conclusions:1,Rare earth elements (La,Ce,Nd,Sm) and heavy metallic elements (Y,Cu,Pb,Zn,Sr) in geogas above buried fracture both have obvious heighten abnormalities, anomaly contrast usually greater than 3, sometimes can achieve 10 or more. These heighten abnormalities usually indicate the location of fracture, and the size of anomaly contrast can reflect the size of the fracture activity (the greater anomaly contrast, the fracture activity more strongly). 2,According to the results of this geogas survey, the existence of buried fracture from major groove to Long clot (along the Yarra River channels) confirmed, the best application results achieved. The relationship between the location,size of geogas anomalies and the location,activity of buried fracture confirmed. The significant meaning about geogas survey techniques in detection buried fracture practical application proved.3,Comprehensive analysis of Information obtained by geogas survey,emanation survey and soil alpha measurement, presume the region does have a buried fracture growth, and composed by at least two branch fracture, fault width in 40 ~ about 80m. Fracture and rivers in close proximity and in some areas there may be overlap or intersect. Taking into account the existence of buried fracture and potential activity will bring huge risks to the construction of water conservancy project, proposals not to build large-scale water conservancy projects in the region's are given.4,Preliminary study confirms that the possibility to evaluate fault activity by the fisher discrimination, fuzzy comprehensive evaluation and fuzzy diagnosis. Particularly those based on the overall model evaluation. Preliminary studies suggest that this confirmation of Yarra River fracture for active fracture. In view of the problem of fault activity is more complex, the current compared region limited, the use of mathematical method for evaluating fault activity issues remain to be researched and further improved through the evaluation practice in more regional. However, the scientificalness and effectiveness of such method is certain.