Numerical modeling of exploitation and reinjection of the Guantao geothermal reservoir in Tanggu District, Tianjin, China

•Models for the Guantao geothermal reservoir in Tanggu, Tianjin city, China were developed by AUTOUGH2.•Reservoir pressure and temperature were simulated for various scenarios.•Well distance influence on well pressure and temperature were analyzed.•Thermal breakthrough occurs at a doublet well distance of 250m.•The suggested minimum well distance is 500m. This paper establishes conceptual and mathematical models for the low-temperature Guantao geothermal reservoir (a study area of 533km2) in the District of Tanggu, Province of Tianjin, China. The models are developed using AUTOUGH2 code for production history. Pressure and temperature histories of 20 production wells were simulated, primarily by adjusting well productivity indices and the permeabilities of the various rock types. Good consistency was obtained between the measured and simulated pressure profiles. Pressure and temperature distributions of the Guantao reservoir were predicted for the production over the next five years, based on history matching simulations. The influence of different reinjection rates on reservoir pressure, temperature, and water level were studied. The results showed the average annual water level drawdown for the entire study area is 3.4m over five years. The average annual water level drawdown is projected to be 1.3m with 60% reinjection rate and 0.2m with 100% reinjection rate. The reinjection is based on the addition of a make-up wells which constitute a doublet with the existing production wells. Based on this observation, reservoir pressures and temperatures were further studied with doublet well distances ranging from 700m to 250m, for the injected separated water rate of (respectively) 60% and 100%. The results indicate that the pressure of production wells increased slightly with decreasing doublet well distances. A sensitivity analysis on the doublet-well distances showed that the distance between the reinjection and production wells should be greater than 500m to avoid thermal breakthrough.