Distribution Characteristics And Resource Evaluation Of Cenozoic Geothermal Reservoirs In Jiyang Depression

Geothermal energy,as a real green and clean energy source,has the characteristics of renewable and great resource potential.Exploiting and utilizing geothermal resources according to local conditions is of great significance for China to successfully achieve"Carbon Peak"and"Carbon Neutral".In this paper,the medium and low-temperature thermal storages of the Guantao Formation and Dongying Formation of the Cenozoic are selected as the target section and evaluate the geothermal resources,providing the basis for the overall development of geothermal resources in the Jiyang depression and expanding the scale of the geothermal industry.In this paper,we have investigated comprehensive geothermal data for the Jiyang depression.The ichnography of the geothermal gradient,terrestrial heat flow,and geothermal distribution of this depression are presented.The geothermal gradient in the study area ranges from 32.0℃/km to 42.5℃/km,with an average of 35.5℃/km,which is 30.0℃/km higher than the global average and close to the general average of 35.8℃/km in the Bohai Basin.The current terrestrial heat flow value is distributed in the range of 52.8～81.6mW/m² with an average of 65.7±5.5mW/m².The temperature in the Jiyang depression varies from 43℃to 60℃in the depth range of 1000m,and from 74℃to 96℃in the depth range of 2000m.Most areas in the Jiyang depression have anomaly geothermal features,which reflects that the whole Jiyang depression has a high geothermal temperature and belongs to a typical"hot basin",as consistent with the previous understanding.Compare to different ichnography of geothermal,the distribution of the temperature in the upper3km coincides with the high and low distribution of geothermal gradient,and the distribution characteristics are matched with the tectonic pattern of the basin with concave-convex alternating,that is,the sedimentary area is low and the uplift area is high.Combined with the analysis of geothermal geology,it is considered that the shallow buried depth of Moho is the fundamental reason for the higher geothermal background in Jiyang depression,and the combination of tectonic framework and lithologic factors in the basin jointly determines the distribution of geothermal field in the study area.The reservoirs of the Guantao and Dongying Formations are widely distributed in the Jiyang depression basin,which is controlled by regional tectonic and basement fluctuation.The general distribution rule is that the buried depth of roof and floor changes from shallow to deep and the thickness become thick from south to north.At the raised area,the burial is shallow and the thickness is thin,while in the depression area,the burial is deep and the thickness is large.The heat storage temperature is mainly determined by the buried depth of the interface or the thickness of the formation but is less affected by the geothermal gradient.According to the geothermal geological conditions of the hot reservoir,the study area is divided into a large number of small units to calculate the geothermal resources.The geothermal resources of the Guantao Formation are 721.8×10¹⁸J,equivalent to 246.6×10⁸t of standard coal,and the amount of recoverable geothermal resources is 180.5×10¹⁸J,equivalent to 61.7×10⁸t of standard coal;while the geothermal resources in the Dongying Formation are 321.8×10¹⁸J,equivalent to 109.9×10⁸t of standard coal,and the amount of recoverable geothermal resources is 80.5×10¹⁸J,equivalent to27.5×10⁸t of standard coal.The above evidences suggest that the Jiyang depression contains abundant geothermal resources.