Assessment of the Urban Dezhou sandstone geothermal reservoir in North China

Abstract

Sedimentary geothermal reservoirs are one of the two main types of low-temperature reservoirs in China, with productive wells. The reservoirs are characterized by infinite extent, homogeneous aquifers and are heated by heat conduction. This report presents the results of reservoir assessment of the Urban Dezhou Guantao formation sandstone geothermal reservoir in Shandong Province of North China. As a consequence of large-scale production, water level decline problems have occurred in the Urban Dezhou reservoir. Therefore, reinjection tests were undertaken and the results show that 100% of the production water can be reinjected during a space heating period (120 days) without significant cooling in the reservoir. A tracer test model was set up to predict the geothermal temperature changes, they predict the temperature to remain stable for 50 years. Thermal breakthrough is calculated by another simple model to give an idea of the safe distance between reinjection wells and production wells. Monte Carlo volumetric assessment is undertaken to estimate the total recoverable energy in the Urban Dezhou reservoir.

The lifetime of the Urban Dezhou reservoir is estimated based on the current production rate and the recoverable energy. Using the long-term monitoring water level depth data, the sustainable yield of the Urban Dezhou reservoir is estimated based on a two-tank closed lumped parameter model. The prerequisite is a maximum allowable water level depth of 150 m in 50 years’ time. The estimated sustainable yield without reinjection is 25% of the current production rate, which cannot meet the demands of the city. To keep the current production rate, the reinjection rate should be more than 75% of the production rate. By keeping the maximum reinjection rate, which is 80% of the production, the sustainable yield becomes 25% more than the current production rate. Therefore, the sustainable yield with reinjection cannot only meet the demands of the city but also gives potential for more development of the reservoir. Further study of temperature and chemistry changes in the Urban Dezhou reservoir should be undertaken to complete the reservoir assessment.