Characteristics of geothermal reservoirs in the Wumishan Formation and groundwater of the Middle-Upper Proterozoic and the geothermal status in the Beijing–Tianjin–Hebei region: Implications for geothermal resources exploration

Exploration of the geothermal resources in the Beijing–Tianjin–Hebei region has been kept for tens of years, and the recent success of geothermal exploration in the Xiongxian County provides a new model for the utilization of geothermal resources in this area. This research integrates the formation of temperature obtained from hydrocarbon drilling, experiments of reservoirs’ micro-characteristics and physical property, and employs the previous works on the regional geological settings to investigate the geothermal reservoirs and geothermal status. The microphotography indicates that the reservoir space is dominated by supergene karst in the Wumishan Formation which is mainly controlled by the topography when the interval emerged. The groundwater in the Pre-Paleogene has the similar composition of the hydrogen and oxygen isotope with the atmospheric precipitation, and the salinity of the groundwater has an increasing trend from the Taihang Mountain and the Yanshan Mountain to the depocenters, which indicates the groundwater originates from the atmospheric precipitation of the Taihang Mountain and the Yanshan Mountain and transports to the depocenters. The thermal conductivity of the lower carbonate rocks is much higher than the upper clastic intervals. This difference makes the upper clastic intervals of the Paleogene and the Neogene good seals for geothermal reservoirs and leads to the regional anomaly of the terrestrial heat flow: the intrabasin highs have a thicker thickness of the Pre-Paleogene carbonate deposition with high thermal conductivity, which results in high efficient thermal transmission and high terrestrial heat flow. Consequently, this research suggests that the intrabasin highs and slopes are the favourable areas for geothermal exploration with reservoirs of good quality, high terrestrial heat flow and efficient groundwater supply, and several areas were selected to be the potential targets for the Wumishan Formation and the Pre-Paleogene.

Study on Reservoir Fracture Prediction of Wumishan Formation in Renqiu Buried Hill

The third segment of Wumishan formation in Renqiu buried hill was taken as an example, based on crustal stress obtained by acoustic logging information and by use of rock cut fracture criterion and spread fracture criterion, the fracture distribution in the researched area was studied. The results showed that the degree of fracture development is high in the southern fault, northern fault and eastern fault in the researched area, south-central area is the compared developed fracture zone, the central and the central-western areas are the slightly developed fracture zones, while the north and northeast are the less developed fracture zones. At the same time, it is found that the fault has a significant impact on distribution of fractures.

The Mesoproterozoic ‘seismite’ at Laiyuan (Hebei Province, E China) re-interpreted

A 1-million m3 breccia near Laiyuan (Hebei Province, E China) occurs as a block-like lithological unit between dolo-stones of the 1.55-1.45 Ga (Early Mesoproterozoic) Wumishan Formation. It has previously been interpreted as a seismite, but it appears not to fulfil any of the commonly accepted criteria that jointly are considered diagnostic for seis-mites. Its presence in a graben-like structure with almost vertical bounding fault planes rather indicates an origin as a (submarine) valley fill. As the valley originated by tectonic activity in the form of faulting, the breccia can be considered as a secondary effect of seismic activity, but it does not represent a seismite.