Modeling of Production/Reinjection Behavior of the Kizildere Geothermal Field by a Two-Layer Geothermal Reservoir Lumped-Parameter Model

Abstract

The main parts of a geothermal system are the reservoir and aquifer recharging and surrounding the reservoir. In this study, the reservoir is assumed to be composed of two parts: the upper (shallow) reservoir and the lower (deeper) reservoir which are hydraulically connected. This system can be viewed as similar to a two-layer reservoir system with crossflow.
This paper investigates the production/reinjection behavior of fields consisting of shallow and deeper zones in hydraulic communication. The fluid and rock properties in these zones can vary and the zones can be characterized by different temperatures. An example of such a geothermal system is the Kizildere geothermal field in Turkey. The shallow reservoir lies between 600-800 m depth and its temperature varies from 195 to 205 oC. A recently drilled well produces from a deeper reservoir about 1400-1500 m deep with a temperature of 240 oC. The water produced from the shallow zone has about 1.5 wt % dissolved CO2 whereas the water produced from the deeper zone has nearly 3.0 wt % CO2. Therefore, the distinctly different production and reservoir properties lead to the consideration of a two-layer model of the geothermal reservoir.
A new lumped-parameter model was used to study the production/reinjection behavior of the two-layer reservoir and to history match the long-term production data obtained from the Kizildere geothermal field. In the model, the reservoirs are assumed to be liquid-dominated and contain single-phase compressed water. The advantage of the two-layer geothermal reservoir model over the conventional one-tank model is that the upper and lower parts of the field can be treated separately. Several production and reinjection scenarios such as 1) production and reinjection for both zones, 2) production from the deeper one and reinjection into the shallow one, or vice versa, are investigated. Results of the modeling study for the Kizildere geothermal field indicate that the scenarios considering higher rate of production from the deeper reservoir result in lower pressure drop and thus increase the life of the reservoir. Modeling results discussed in the paper give important clues about the optimized and sustainable development of this type of field.