Modelling reinjection into vapour-dominated two-phase systems: Part 1—Experiments on model design

Abstract

Water injection into vapour dominated geothermal systems has been recognized as a necessary strategy to sustain production of geothermal resources. Computer simulation is an important tool in the planning and management of injection. Because of enhanced techniques and their flexibility, geothermal simulators can make a range of approaches to simulate this process; however different settings of a model may lead to different predictions. In order to progress to a good generic 3D model which can produce a realistic prediction of injection effects in vapour-dominated two-phase reservoirs, we decided to first set up a 2D model which allows numerical experiments to be carried out quickly. This 2D model was used to investigate the effect of different model parameters on the predictions of performance and to assess the importance of various modifications to the model. The aim of these experiments was to determine the best choice of model parameters to obtain a model of a vapour-dominated reservoir suitable for the investigation of reinjection effects.The model is based loosely on the Darajat system but the results should be relevant for other similar reservoirs such as Larderello, Kamojang and The Geysers. Model parameters such as vertical permeability, porosity and relative permeability are investigated. Different injection rates and start-times for injection are tried. Various aspects of model design such as grid refinement, use of an embedded radial grid near the wells, dual porosity and nine-point differencing are investigated.