Prospective evaluation of dry-hot rock development and utilization in Bohai Bay Basin — understanding based on numerical simulation

Abstract

As one of the most promising clean and renewable energy sources, hot-dry rock is getting increasing attention in recent years. The Bohai Bay Basin, located in eastern North China, is a Middle-Cenozoic extensional rift basin formed under the background of North China Craton destruction. The measured geothermal heat flow in the basin ranges from 44 to 106 mW·m-2, with an average of 66 mW·m-2, which is higher than the average heat flow in mainland China (61 mW·m-2). The temperature gradient is generally greater than 30°C /km in the whole basin and is as high as 40-50 °C/km in the uplift area. The geothermal temperature ranges in 180-226 °C at a depth of 5000 m.In the basin, sediment thickness ranges 2 to 4 km, and there is a lot of granite, which is a low porosity, low permeability rock in the basement. Thus, there have been the conditions for the formation of hot-dry rock resources. In this study, the actual geothermal data of the hot-dry rock favorable area in the Bohai Bay Basin were adopted to establish a numerical model to estimate the resources development potential. Based on the modeling of different well spacing and injection – production rates, the optimal solution was selected to calculate hot-dry rock resources. The results show that within 50 years , the average production temperature can be 163°C by the way of ‘Double Production-Injection’ with well spacing of 400 m and injection - production rate of 110m3/h. Under this scheme, the computing recoverable resources is 9.96×1014J/a in the reservoir model with 2km×2km, and the recoverable resources of the whole basin is 3.735×1020J/a. According to the heat load index of 60-100W/m2 per square meter of residential buildings, the area demand of hot-dry rock field is approximately 8000km2 to meet the heating requirement of residents in Beijing, which is less than the probable distribution of hot-dry rock around the city. Given this, the development and utilization of hot-dry rock in the study area can enhance the energy supply guarantee ability in North China and create a green low-carbon energy for sustainable development.