Formation mechanism of high-temperature geothermal resources in the Songliao Basin

The Songliao Basin, situated in Northeast China, boasts a significant geothermal background evident in numerous boreholes, indicating a rich geothermal resource potential with temperatures exceeding 150℃ at depths of 5km. This study aims to elucidate the formation mechanism of high-temperature geothermal resources in the Songliao Basin, analyzing various aspects such as the thermal properties of rocks, temperature fields, terrestrial heat flow, heat source contributions, Meso-Cenozoic thermal history, deep thermal structures, and factors influencing geothermal resource formation. The research offers valuable theoretical support for the exploration and evaluation of high-temperature geothermal resources in the Songliao Basin. The research involves testing the rock thermal conductivity of 263 core samples and 99 outcrop samples, as well as the rock heat generation rate of 80 core samples and 56 outcrop samples from the Songliao Basin and its periphery. The measured thermal conductivity ranges from 0.58 to 3.94W/(m·K), with an average value of 1.96 W/(m·K). Heat generation rates vary between 0.31 and 4.98μW/m³, averaging 1.72μW/m³. A comprehensive thermal conductivity and heat generation column for the Songliao Basin was established by integrating current testing data with previous records. Based on data from over 3000 oil test temperatures collected in this study and previous temperature data compilations, the temperature distribution characteristics of the Songliao Basin were clarified. The overall geothermal gradient averages 40-50℃/km, with terrestrial heat flow ranging between 50-100 mW/m² and exceeding 80 mW/m² in most areas. The heat generation contribution from different lithologies in each stratum was calculated based on the heat generation rate. The sedimentary layer's heat generation contribution is primarily between 5-10 mW/m². The mantle heat flow surpasses crustal heat flow, constituting approximately 60% of the total heat flow. A partial melt in the crust of the Songliao Basin contributes about 10% to heat generation contribution, with a notable impact on mantle heat flow. The Songliao Basin underwent testing for apatite fission track and (U-Th)/He age, coupled with a Meso-Cenozoic thermal history simulation. The outcomes reveal a substantial cooling trend in the basin starting at the end of the Cretaceous period, persisting to the present day. This analysis contributes to a more comprehensive understanding of the formation history of the current geotemperature field within the study area. The study analyzes the influence of the deep thermal background on high-temperature geothermal accumulation by scrutinizing the distribution characteristics of thermal lithospheric thickness, the Moho surface, and the Curie isotherm, along with exploring the correlations among these factors. A comprehensive analysis, considering reservoirs, channels, caps, and fluid origin, establishes the formation conditions of high-temperature geothermal resources. Factors controlling and high-temperature geothermal accumulation are clearly defined, culminating in the establishment of a high-temperature geothermal accumulation model for the Songliao Basin.