Mechanism Study Of Geothermal Resources In The Nanxiang Basin

Based on the theory of structural geology,sedimentology,geothermal science and hydrogeology,with the materials of seismic,logging,temperature and water chemistry,this paper study the heat source,geothermal reservoir,channels,water source,and the geothermal conceptual model is established in the study area.The results of study show that there is a good geothermal background in Nanxiang Basin,the geothermal gradient is increased from the southern sub-sag to the northern slope and the areas where the geothermal gradient higher than 3.5?/100 m were widely distributed.The geothermal field in the study area is widely controlled by tectonic basement,and is influenced by the hydrological condition in the local area.The heat source of Nanxiang geothermal field is dominated by shell heat source and mantle heat source,the lithospheric thermal structure belongs to the “cold crust and hot mantle” type.In accordance with sandstone and mudstone overlying relationship,5 geothermal reservoirs are divided in Biyang and Nanyang sags.Through contrasting and analyzing,the potential geothermal reservoir mainly develops in Eh2,upper segment of Eh3,lower segment of Eh3 in Biyang sag.In Nanyang sag,the development position of potential geothermal reservoir turns to be in Eh1 and Eh2.There are two types of channel in the study area: the skeleton sand and the boundary fault,and the rain water gathered from the surrounding mountains provides a sufficient water supply for the geothermal fields.Detailed analyzed three geothermal fields in Houzhuang-Chengdian,Pingshi-Zhaowa and Weigang area,consequently,three models which are “slope type”,“steep slope type” and “bulge in sag type” are established.Combining with the regional structure profile,geothermal conceptual model is proposed as follows: The mantle source and shell source heating – The low-thermal conductivity – Slope and bulge trap the heat – Rain water provide the water source – Sandstone thermal reservoir.