Elsevier

Computers & Geosciences

Volume 108, November 2017, Pages 2-7
Computers & Geosciences

Case study
TOUGH3: A new efficient version of the TOUGH suite of multiphase flow and transport simulators

https://doi.org/10.1016/j.cageo.2016.09.009Get rights and content

Highlights

  • TOUGH3, a new efficient version of TOUGH codes, is introduced.

  • TOUGH3 efficiently simulates multiphase, multicomponent subsurface problem in serial and parallel.

  • PETSc provides solvers that are significantly more efficient than those used by the existing TOUGH codes.

  • High-resolution model that requires parallel execution can provide details not deducible from coarse-resolution model.

Abstract

The TOUGH suite of nonisothermal multiphase flow and transport simulators has been updated by various developers over many years to address a vast range of challenging subsurface problems. The increasing complexity of the simulated processes as well as the growing size of model domains that need to be handled call for an improvement in the simulator's computational robustness and efficiency. Moreover, modifications have been frequently introduced independently, resulting in multiple versions of TOUGH that (1) led to inconsistencies in feature implementation and usage, (2) made code maintenance and development inefficient, and (3) caused confusion to users and developers. TOUGH3—a new base version of TOUGH—addresses these issues. It consolidates both the serial (TOUGH2 V2.1) and parallel (TOUGH2-MP V2.0) implementations, enabling simulations to be performed on desktop computers and supercomputers using a single code. New PETSc parallel linear solvers are added to the existing serial solvers of TOUGH2 and the Aztec solver used in TOUGH2-MP. The PETSc solvers generally perform better than the Aztec solvers in parallel and the internal TOUGH3 linear solver in serial. TOUGH3 also incorporates many new features, addresses bugs, and improves the flexibility of data handling. Due to the improved capabilities and usability, TOUGH3 is more robust and efficient for solving tough and computationally demanding problems in diverse scientific and practical applications related to subsurface flow modeling.

Introduction

TOUGH is a suite of numerical codes for simulating multiphase, multicomponent fluid mixtures and heat flows in multi-dimensional porous and fractured media (Pruess et al., 2012). The simulators have been updated to address a vast range of challenging subsurface problems (Pruess et al., 1997, Pruess, 2004, Finsterle et al., 2008, Finsterle et al., 2012, Finsterle et al., 2014). For instance, new fluid property modules — such as ECO2N (Pruess, 2005) and ECO2M (Pruess, 2011) — were developed specifically for applications to geologic sequestration of CO2 in saline aquifers. A parallel version of the TOUGH2 code — TOUGH2-MP (Zhang et al., 2008) — was developed to enhance the performance for large-scale simulations requiring intensive computations. iTOUGH2 (Finsterle, 2004, Finsterle et al., 2016) provides inverse modeling capabilities as well as sensitivity and uncertainty propagation analyses for TOUGH2 (or any stand-alone simulation program that uses ASCII input and output files), with several enhancements to the simulation capabilities of TOUGH2 (Finsterle, 2016). TOUGHREACT (Xu et al., 2006, Xu et al., 2011) adds transport and reactive geochemistry to the TOUGH2 code. TOUGH+ (Moridis et al., 2008) focuses on advanced applications involving, for example, gas hydrates. Finally, there have been multiple developments to couple geomechanics to the existing suite of codes (for an overview, see Finsterle et al., 2014).

Such extensions of the simulation capabilities were possible due to the open architecture of the TOUGH codes, making the codes applicable to diverse problems involving subsurface fluid and heat flow. However, this diversity has caused several issues: (1) inconsistencies between modules in feature implementation and usage, (2) duplicate efforts in code maintenance and development, and (3) confusion to users and developers. For example, many of the new capabilities available in TOUGH2 V2.1 (an updated version of TOUGH2 V2.0) are not available in TOUGH2-MP V2.0 since additional efforts are required to re-implement these capabilities in a parallel framework. TOUGH2-MP V2.0 does not include all the equation-of-state (EOS) modules available in TOUGH2 V2.1. Similarly, iTOUGH2 V7.1's enhancements in physical process descriptions, thermophysical models and time-stepping procedure are not available in any other TOUGH branches.

TOUGH3 is developed as a new efficient version of TOUGH to address some of the challenges identified above and ultimately to promote the wider use of TOUGH's simulation capabilities. We consolidate relevant capabilities in the following three branches that are most closely related to each other: TOUGH2 V2.1, TOUGH2-MP V2.0 and the simulator component of iTOUGH2 V7.1. We also introduce new linear solver technologies by adding an interface to the PETSc libraries (Balay et al., 2016). In the following sections, we will give an overview of TOUGH3 and highlight its new capabilities. A full list of the capabilities in TOUGH3 is documented in the TOUGH3 User Guide (Jung et al., 2016).

Section snippets

Overview of TOUGH3

TOUGH3 is a general-purpose numerical simulator that solves mass and energy balance equations for fluid and heat flow in multiphase, multicomponent systems, and consolidates serial and parallel implementations of TOUGH into a single code. The code inherits all the existing key processes and features of its predecessors. However, the parallel computing capability and the additional, parallel linear solvers of TOUGH3 remarkably improve the code's computational efficiency. TOUGH3 also implements

PETSc solvers

TOUGH3 includes the interface to PETSc's parallel linear solvers in addition to the existing TOUGH2's serial linear solvers and TOUGH2-MP's Aztec solvers. PETSc provides efficient implementations of linear solvers and interfaces to popular external linear solver packages. The available linear solvers in PETSc are listed on https://www.mcs.anl.gov/petsc/documentation/linearsolvertable.html. Selection of a solver and its options is specified through a configuration file, allowing users to keep

New fluid mixtures

TOUGH3 includes several recently developed EOS modules in addition to the traditional modules in TOUGH2: ECO2N (Pruess, 2005), ECO2M (Pruess, 2011), EOS7C (Oldenburg et al., 2004), EOS7CA (Oldenburg, 2015), T2VOC (Falta et al., 1995), and TMVOC (Pruess and Battistelli, 2002). Many of the recent developments are designed for applications to geologic sequestration of CO2. The field-scale applications using these modules often require solving extremely large or highly nonlinear problems, but can

Conclusions

TOUGH3 is a new efficient version of the TOUGH simulators, which has been developed to improve the capabilities, usability, and efficiency of the codes. We have consolidated serial (TOUGH2 V2.1) and parallel (TOUGH2-MP V2.01) implementations, and process modeling capabilities of TOUGH2 V2.1 and the simulator component of iTOUGH2 V7.1, into a single code. TOUGH3 also includes several new features, specifically the PETSc solver library. We have demonstrated that the PETSc solvers significantly

Acknowledgment

This work was funded by the TOUGH Development Grant through the U.S. Dept. of Energy under Contract No. DE-AC02-05CH11231. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under the Contract No. DE-AC02-05CH11231.

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