Study of Flow Modulation for Enhancement of Power Generation
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Geothermal energy that can be extracted in the future from Engineered Geothermal System (EGS) will be plentiful, renewable, and a clean source of energy. However, no commercial scale EGS power plant has been built yet. This is mostly due to the costs associated with the exploration, drilling and production of this clean energy. Research will be key in exploring the technology necessary for economic development of this type of power plant. The cost barriers can be avoided by using efficient turbines and pumps which will reduce the cost of getting the hot energy out of the earth. Especially in the case of EGS, which involves creating a fracture network in hot rock in low permeability formation, it is very important to reduce the cost of operation. With advancement in technology for efficient and economical turbines, pumps and drilling operations can make such a system feasible. Along with the technology, it is very important to maintain these reservoirs at certain temperatures for a long period of time for economical energy extraction. The Fenton Hill-1 hot dry rock experiment was successfully simulated and matched with field data by using MULTIFLUX code. First, the reservoir was subjected to a continuous coolant fluid circulation. The pumping power and geothermal energy recovery are evaluated from the model for base case characteristics. Keeping the reservoir properties the same, the EGS reservoir was subjected to various pumping rates and modeled with on-off circulation, which was similar to a huff-puff operation. The variable flow rate and pressure affected the fracture extension both longitudinal and aperture direction. This non-linearity allowed for increasing the active heat transport surface area. For this study, a flow pattern, which is similar to huff-puff, was used; this flow pattern gave recovery time to the reservoir to gain the temperature which it lost during the production phase. This work shows the advantages of using different flow pattern during the operation of EGS reservoir. Temperature decline and the net thermal power generated from the reservoir are compared with the base case of Fenton Hill-1 field study using different injection scenarios. The change in the rate of fluid injection will affect the fracture diameter, fracture aperture and the downhole pressure. These changes are discussed in this study for different cases. The effect of daily flow modulation is discussed for a 75 day's simulation time period and a yearly study for a long thermal drawdown is also included with periodic, weekly on-off flow injection.It was seen from the result that, on-off injection scenario will help the reservoir to recover its temperature which it lost during the production phase. This on-off time can be adjusted according to the rate of thermal drawdown of the reservoir.