Modelling geochemical effects of geothermal reinjection in the Tanggu low-temperature field, China

Abstract

As a strategy for geothermal production and a method to deal with the problem of pressure decline due to reservoir depletion, geothermal reinjection is going to be carried out in the Tanggu geothermal field, China. In the early stages of the project, it is necessary to obtain information about the reservoir response to the operation. Because of limited data at this stage, geochemical modelling is the only approach that can be used to understand the effects of reinjection on reservoir properties. Two different geochemical modelling approaches have been employed to simulate the geochemical effects of reinjection. In one, water-rock interaction is considered while in the other, account is taken of the migration of silica in the reservoir during reinjection. The results show that reinjection has a positive effect on the reservoir porosity on account of the volumetric balance of dissolution of rock and precipitation of secondary minerals. The effect is important at the beginning of reinjection in an area of about 50 m radius around the reinjection well. As a result of water-rock interaction, the secondary mineral assemblage is composed of quartz (chalcedony), calcite, muscovite, kaolinite and clinochlore. The composition of the reinjected water is the same as that of the geothermal water in the reservoir.