Development and Application of Enhancements to the iTOUGH2 Simulator for Geothermal Reservoir Management

Abstract

An essential aspect of sustainable operation and management of a modern-day geothermal field is a state-of-the-art numerical reservoir model. A field-wide conceptual model of the reservoir, based on all available and applicable production and geoscience data, is used to construct a numerical model. iTOUGH2 is a simulation-optimization framework widely used in numerous engineering and academic disciplines and is based on the successful TOUGH2 non-isothermal, multiphase flow and transport simulator. In this case, the focus is on applications related to geothermal reservoir engineering and groundwater hydrology. iTOUGH2 is highly flexible, incorporating an ever-increasing arsenal of methods for model parameter estimation, local and global sensitivity analyses, data-worth and error propagation analysis. To meet increasing demands set by the industry for detailed numerical modeling, the iTOUGH2 platform is under continuous development. The ability to incorporate proper physics into the simulator will clearly aid in the model calibration and result in more realistic future production scenarios of interest to the geothermal field operator. This paper discusses the development of several recent enhancements to the iTOUGH2 platform and demonstrates how they can be applied. This includes: (1) A full 2D tensorial anisotropic scheme (supporting irregularly structured, non-rectangular meshes with sloped layers); (2) coupling of the FLOWELL wellbore simulator with iTOUGH2 to enable the direct use of wellhead production data for model calibration and predictions. The FLOWELL simulator can model liquid, two-phase and superheated steam flow and can be applied to directional wells with many feedzones and various well segments with different diameters and friction factors; and (3) a module for two-phase simulation of water and multiple tracers, which allows for simultaneous calibration of multiple tracer returns with other transient data such a pressure decline and temperature/enthalpy changes. Included in the new tracer module is preferential phase partition, tracer adsorption to the rock matrix and time/temperature dependent degradation to daughter species. The enhancements will be described and demonstrated through various examples of modeling geothermal areas in Iceland and others.