Monitoring of prodction decline and pressure drawdown in geothermal reservoirs using decline curves analysis method

Abstract

The application of the decline curves analysis method on the monitoring of production decline and pressure drawdown in geothermal reservoirs was studied. Two geothermal production fields were selected, the Bacon-Manito I in the Philippines and Krafla in Iceland. It was not possible to pursue the analysis for Bac-Man I at this point in time, primarily because there was no substantial and crucial pressure drawdown manifested in the pressure profiles of the five chosen production wells of the field. However, conclusions were drawn that proper resource management is being implemented in the field by the developer and that currently there are no signs of over-exploitation of the resource. In Krafla, it was concluded that the nonlinear second order exponential decay function predominantly defines the trend in production decline observed in Krafla field, based on the result of comparison between the average values of 2 (Chi-Square) obtained from the exponential decay and linear (harmonic) functions. With the simulator program HOLA and the assumed depletion trend in the reservoir pressure of well KJ-18, it was established that KJ-18 pressure drawdown can explain the observed production decline in wells KJ-14, KJ-17 and KJ-19. Estimates of future descent in production of these wells can, therefore, be predicted, assuming KJ-18 pressure depletion trend and with the employment of the second order exponential decay function. In conclusion, the decline curves analysis method can be one efficient tool for the DOE in the performance of its monitoring and regulating function. The technique can enable the Department of Energy (DOE) in the Philippines to analyze ...