PFLOTRAN, a next-generation reactive flow and transport code for modeling subsurface
processes, has been designed from the ground up to run efficiently on machines ranging from
leadership-class supercomputers to laptops. Based on an object-oriented design, the code is easily
extensible to incorporate additional processes. It can interface seamlessly with Fortran 9X, C and C++
codes. Domain decomposition parallelism is employed, with the PETSc parallel framework used to
manage parallel solvers, data structures and communication. Features of the code include a modular
input file, implementation of high-performance I/O using parallel HDF5, ability to perform multiple
realization simulations with multiple processors per realization in a seamless manner, and multiple
modes for multiphase flow and multicomponent geochemical transport. Chemical reactions currently
implemented in the code include homogeneous aqueous complexing reactions and heterogeneous
mineral precipitation/dissolution, ion exchange, surface complexation and a multirate kinetic sorption
model. PFLOTRAN has demonstrated petascale performance using 217 processor cores on problems
composed of over 2 billion degrees of freedom. The code is currently being applied to simulate uranium
transport at the Hanford 300 Area and CO2 sequestration in deep geologic formations.
Keywords: High performance computing, reactive transport, carbon sequestration, multiple realizations,
multiphase flow and transport, Richards equation, domain decomposition.
