| Title | Calculation of Geothermal Stored Heat from a Numerical Model for Reserve Estimation |
|---|---|
| Authors | Peter FRANZ, Mathew NEVILLE-LAMB, Lutfhie AZWAR, Jaime QUINAO |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | stored heat numerical model |
| Abstract | The assessment of stored heat in a geothermal reservoir is one of the recommended methods by the AGRCC Geothermal Lexicon for the estimation of a geothermal reserve. Prior to development, when very little information about the reservoir properties is known, the reservoir stored heat is usually estimated using probabilistic methods to find a first guess and an uncertainty range. Once development of a geothermal reservoir has begun it is quite common to generate a numerical model and calibrate it vs. observed field data. This means that the reservoir properties needed for the calculation of stored heat are more constrained once the model is calibrated. By running a simulation through the calibration time and through a future development scenario one can calculate stored heat at each time step and thus get detailed information about the recovery factor, which is a key uncertainty in the initial stored heat estimation. A drawback in using stored heat for the estimation of a geothermal reserve is that it only calculates heat in place at a given time. If applied over the complete numerical model domain it can overestimate the reserve by an order of magnitude since it would include hot but impermeable reservoir areas. A method is required to determine additional thresholds to exclude the model domain in which fluid extraction would not succeed. In this study we present a stored heat calculation on a numerical model and the application of thresholds which we believe should be taken into account. In particular we applied a permeability threshold and used wellbore simulation to exclude all areas of the model domain which could not be used for producing fluid. The results of this study could be used in the discussion for defining a standard procedure for the estimation of geothermal reserves from numerical models. |