finite element code for simulating subsurface multi - phase multi - fluid heat and mass transfer

The Subsurface Flow and Transport Team at the Los Alamos National Laboratory (LANL) has been involved in large scale projects including performance assessment of Yucca Mountain, Environmental Remediation of the Nevada Test Site, the LANL Groundwater Protection Program and geologic CO2 sequestration. Subsurface physics has ranged from single fluid/single phase fluid flow when simulating basin scale groundwater aquifers to multi-fluid/multi-phase fluid flow when simulating the movement of air and water (with boiling and condensing) in the unsaturated zone surrounding a potential nuclear waste storage facility. These and other projects have motivated the development of software to assist in both scientific discovery and technical evaluation. LANL’s FEHM (Finite Element Heat and Mass) computer code simulates complex coupled subsurface processes as well flow in large and geologically complex basins. Its development has spanned several decades; a time over which the art and science of subsurface flow and transport simulation has dramatically evolved. For most early researchers, models were used primarily as tools for understanding subsurface processes. Subsequently, in addition to addressing purely scientific questions, models were used in technical evaluation roles. Advanced model analysis requires a detailed understanding of model errors (numerical dispersion and truncation) as well as those associated with the application (conceptual and calibration) Application errors are evaluated through exploration of model and parameter sensitivities and uncertainties. The development of FEHM has been motivated subsurface physics of applications and also by the requirements of model calibration, uncertainty quantification, and error analysis. FEHM possesses unique features and capabilities that are of general interest to the subsurface flow and transport community and it is well suited to hydrology, geothermal, and petroleum reservoir applications. As the creator and lead developer of FEHM, I will outline the development history of FEHM, describe its general software structure and numerical formulations, and some of its unique features. These features range from novel representations of equations of state to features that allow accurate representation of wellbores and other sub-grid scale phenomena. I will also compare the numerical method used in FEHM, the control volume finite element method (CVFE) with the finite element (FE) method, the finite difference (FD) method, and the integrated finite difference (IFD) method. Finally I compare FEHM with other software of which I am familiar.