Application of the SGP 1-D Linear Heat Sweep Model

Abstract

A 1-D linear heat sweep model, developed to evaluate the experimental data from the SGP Physical Reservoir Nodel, is based on the equations for heat transfer from irregular-shaped rock blocks as a distribution of spheres having a single effective thermal center. A major parameter of the model is the number of heat transfer units, given by the ratio of the mean residence time of the fluid in one-dimensional flow and the rock mass time consrant. The mean residence time is estimated from reservoir parameters and flowrates, and the rock mass time constant is estimated from thermal properties of the rock type. The model has been adapted to evaluate cold-water recharge behavior in geothermal reservoirs where reservoir temperature cooldown has been observed from Na-K-Ca and Si07 geothermometers. The first : application was a study of the western boundary of the original Cerro Prieto field, where the observed cooldown could be matched by mixing of sweep water from the west, percolating water from above, and hot water from the east, each at its respective temperature. Additional study of the Cerro Prieto field is underway to observe the cooldown history of the reservoir in relation to the observed piezometric level drawdown. A second application is underway at the Los Azufres geothermal field as a series of four heat sweep analyses in both the northern (2-phase) and southern (mostly steam) zones.