| Abstract |
With the development of geothermal energy and the enhancement of drilling capacity, supercritical geothermal resource emerges. It refers to the water that exists in the supercritical state under the condition of ultra-high temperature and pressure in the deep part of the crust (22.064 MPa, 373.946oC), which is beneficial for geothermal resource development and utilization. In this work, we developed a numerical program for supercritical geothermal systems based on the structure of the TOUGH2 simulator. The IAPWS-IF97 is employed as the thermodynamic formulation. Compared to the previous codes, significant improvements have been made. The advantages of our code mainly include: 1) primary variables are unified following EOS 1, which is friendly for users to be familiar with. 2) A novel method is proposed to deal with the flow between supercritical and subcritical, which is more accessible and physically reasonable. 3) The effect of P-T condition on relative permeability and capillary pressure is considered, which makes it smooth and continuous within the whole P-T range, even around the critical point. 4) Wellbore flow function is coupled with the reservoir flow simulation. One example is given for verification and capability test, which proves the reliability of the code. In our present study, a wellbore-reservoir coupling model is built, to study the fluid dynamics and possible phase changes along wellbores. It is found that water in supercritical condition behaves more like a gas. Production by the siphon phenomenon is also achievable in a supercritical geothermal system. A higher reservoir temperature brings a higher compressibility, more accessible to achieve production by the siphon phenomenon. In addition, under higher temperature conditions, production fluid may present in the steam single-phase state in the early period. In that circumstance, the wellbore friction could be very significant. |