| The Songliao basin in the northeast of China is an important oil-bearing basin in China, in which occurrence of abundant oil and gas as well as perspective geothermal resources is dependent upon tectonic setting and particular thermal structures of the basin. It is thus of practical value to study tectonic evolution of the Songliao basin, geothermal effect and the genesis of geothermal resources, and then make a comprehensive appraisal of the geothermal resources.This paper focuses on geothermal resources of the Songliao basin, particularly in the Dumeng area. A systematic study of geophysics, tectonics, petroleum and geothermal geology, and sedimentology, combined with numerical simulation, was performed for this purpose. The results are shown as below.1) Tectono-thermal evolution: The history of the Songliao basin is divides into four stages, high-temperature doming and extension, high-temperature rifting, low-temperature depression, and low-temperature shrinkage. Numerical simulation of mechanical process shows that the basin appeared in the early- to late- Jurassic as a result of rapid low-angle subduction of the Pacific plate towards the northwest, of movement of the Siberian block towards the southeast, of many other influences such as internal thermal stress in the mantle, gravitational force, stress of phase transition, etc. Both the Pacific plate and the Siberian block slowed down in the early Cretaceous, and almost stopped in the middle Cretaceous with the rapid decrease of abnormal heat in the mantle below. Afterwards, reactivation of the Pacific plate and thermal in the mantle below became the major factors in controlling the evolution of the Songliao basin during the Cenozoic.2) Geothermal structures: The Mohor discontinuity is buried at a depth of 29~33km in the Dumeng area, the least buried depth being less than 29km. In a similar configuration, the Curie surface is buried at a depth of 18~24km in the area. It tends in plan view to increase its depth in a semi-concentric pattern to the east of Du 401 well. This indicates a tendency that the depth of the Curie surface is lower in the northwest than in the southeast. Interestingly, a broad area of Hercynian and Yanshannian granites is found in the basement.3) Present Temperature field: Numerical technique was employed to simulate the present temperature field in the Dumeng area. Calculated temperature ranges from 80-91 ℃ at depth of 2000m,from 63~70℃ at depth of 1500m and from 42~48℃IVat depth of 1000m. Resulting geothermal gradient is 3. 8-4. 4/m and the flux is 62-65 mW/ra2. Geotemperature in the Dumeng area is fairly high, especially in the Xiaolingke and Xingdian. This suggests the presence of favorite conditions for geothermal resources in the area.4) Genesis and tectonic setting: Three sources for geothermal resources in the Dumeng area are recognized as heat derived from the mantle, heat derived from the intruded magma, and radioactive heat. The geothermal resources in distribution took place in rifting environment where high connectivity and high openness between the mantle and the crust provided a favorite condition for upward conduction of heat at depth. Deep faults cutting through the lithosphere were believed as the good tunnel for the conduction. In the study area, the Xiqi fault and the Xiaolinke fault are the two major controlling structures. The fault zones and their vicinities are the most likely perspectives.5) Sedimentary sequence and petrology: Fine sandstones and siltstones dominate in geothermal reservoirs in the Dumeng area. Rock fragments commonly have a large amount in these rocks cemented by mud, calcium and silicon. Calcium cementation is the major factor in controlling properties of the reservoirs. Pores in the rocks consist of primary pore, dissolution pores and cracks. Experiment with electric properties indicates that good reservoirs are those rocks having high time difference, low density, high neutron porosity, intermediate resistance and intermediate negative abnormity of natural electri...
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