| Abstract |
In order to understand the geothermal background for the formation of geopressured geothermal resources in the Yinggehai Basin, we simulated the thermal history during the Cenozoic by using 2D finite-element model. Yinggehai basin had experienced three phases of extension in the Cenozoic with phase I: 50-45Ma, phase II: 28-22Ma and phase III: 5.2- 1.9Ma. Since the time interval of each extension is quite short, much shorter than the thermal relax time (65Ma) of the lithosphere, the inheritance of extension is considered in the model. Extension rate mode may affect evolution process for young basins like Yinggehai greatly, where extension duration could not be neglected compared with the whole evolution time. Therefore, we chose uniformly retarded rate mode in the model to reconstruct the thermo-mechanical evolution history of the basin. In addition, the effect of lateral non-uniform extension is also considered in the model provided the width of the basin is very small and the lateral heat transfer is quite large. In expectation of well understanding the basin thermal history, we selected a seismological cross-section as calculated model. Model results show that, the degree of three phases of extension is much similar with the largest extension coefficient of 1.681. In the evolution period of Cenozoic, the basement heat flow maintained 50-70mW/m2 all the time. The highest heat flow value appearing on the subsidence center of the cross-section is 58 mW/m2 for the first stage, 60mW/m2 for the second stage and 68 mW/m2 for the third stage. It is obvious that the basin is getting hotter and hotter after each extension. The paleo-temperature reached its highest value at about 1.9Ma and the present basement heat flow is about 60-70 mW/m2. Considering the radiogenic heat in the sediments, the surface heat flow ranges from 70 to 90 mW/m2, consistent with the observed value of 84 mW/m2. |