Heat flow determination of Archean strata under the karst thermal reservoir of D01 well in Xiong'an New Area

The paper is the result of geothermal geology survey engineering.

Objective The heat flow values in Xiong'an New Area are mostly measured from the Neogene sedimentary cap and dolomite strata. The previous geothermal exploration and utilization horizons are mainly karst thermal reservoirs shallower than 1800m in the Jixian System and the boreholes exposing the Archean are scarce in Xiong'an New Area. Heat flow determinations and analyses from Archean under the karst thermal reservoir are rarely reported by previous researchers. Since 2018, D 01 deep geothermal parameter well with a depth of 3403.67m has been implemented in Niutuozhen geothermal field in Xiong'an New Area. The karst thermal reservoir of the whole Gaoyuzhaung Formation was exposed and the Archean of 1723.67m was drilled by D01 well. The D01 well provides the conditions for the heat flow study from Archean under the karst thermal reservoir in this area.

Methods Based on borehole temperature measurement and thermal conductivity tests, the study on the heat flow from the Archean of D01 well was carried out.

Results The results showed that the Archean of D01 well has significant geothermal characteristics of conduction type, and the geothermal gradient is 18.3℃/km, which is lower than the Neogene geothermal gradient of 48.6℃/km. The thermal conductivity values of 25 Archean gneiss core samples of D01 well were measured with an average value of (2.41±0.40) W/(K·m). Based on the temperature measurement curve and thermal conductivity data of 2300-2700m section of D01 well, the Archean heat flow of D01 well was calculated to be (44.1±7.0) mW/m². The heat flow of the Neogene sedimentary cap of D01 well was estimated to be 84.6 mW/m².

Conclusions The higher part 40.5 mW/m² than Archean of D01 well was considered to be mainly contributed by the lateral convection heat transfer of groundwater in high pore-permeable karst dolomite and the vertical convection heat transfer of groundwater in the Niudong fault. The research results can provide the basic data for the previous heat accumulation mechanism of the groundwater transport and the heat conduction fault. And the results are of great significance to the genetic mechanism of deep geothermal resources and the geothermal field of Archean in Xiong'an New Area.