Pressure transient analysis of geothermal wells: A framework for numerical modelling

Abstract

The need for numerical models for geothermal pressure transient analysis (PTA) is well recognised. Conventional PTA is based on analytical models which usually do not work for geothermal datasets, therefore PTA is under-utilised by the geothermal industry. A framework for numerical modelling is required to promote comparability of results and increase user-friendliness.A framework is developed in this study using the TOUGH2 simulator and automated using PyTOUGH. A full justification of the grid design and model setup is given. A reference model is then created and subjected to a sensitivity analysis. The only parameter to which the model output is sensitive is the layer thickness of the model. The basic framework is equivalent to the analytical infinite uniform porous reservoir model. An equivalent to the analytical linear impermeable boundary model has also been developed.The framework is then demonstrated by investigating the injection of cold water into a hot reservoir, a major issue for geothermal PTA. The tool is further demonstrated in a case study with datasets before and after deflagration of a well, and was found to produce superior results to the equivalent analytical analysis.