Deconvolution well test analysis applied to a long-term data set of the Waiwera geothermal reservoir (New Zealand)

Abstract

The geothermal reservoir at Waiwera has been subject to active exploitation for a long time. It is located below the village on the Northern Island of New Zealand and has been used commercially since 1863. The continuous production of geothermal water, to supply hotels and spas, had a negative impact on the reservoir. So far, the physical relation between abstraction rates and water level change of the hydrogeological system is only fairly understood. The aim of this work was to link the influence of rates to the measured data to derive reservoir properties. For this purpose, the daily abstraction history was investigated by means of a variable production rate well test analysis. For the analysis, a modified deconvolution algorithm was implemented. The algorithm derives the reservoir response function by solving a least square problem with the unique feature of imposing only implicit constraints on the solution space. To further investigate the theoretical performance of the algorithm a simulation with synthetic data was conducted for three possible reservoir scenarios. Results throughout all years indicate radial flow during middle-time behaviour and a leaky flow boundary during late-time behaviour. For middle-time behaviour, the findings agree very well with prior results of a pumping test. For the future, a more extensive investigation of different flow conditions under different parametrisations should be conducted.