Subsurface Transport Over Multiple Phases

STOMP is a suite of numerical simulators for solving problems involving coupled flow and transport processes in the subsurface. STOMP is based on mathematical equations that describe our understanding of hydrologic, thermal, thermodynamic, geochemical, and geomechanical processes. STOMP solves these equations by parsing a subsurface volume into computational blocks and then solving algebraic forms of the equations collectively for the blocks. The suite of STOMP simulators is distinguished by application areas and solved mathematical equations.

Stomp logo

PNNL’s Subsurface Transport Over Multiple Phases Simulator (STOMP) is an analytical tool for investigating coupled processes involving multifluid flow, heat transport, geochemistry, and geomechanics> in the subsurface. The simulator was initially developed to assess nuclear waste repository performance but greatly expanded its application domains over its nearly three-decade development life. The simulator is now being applied to support laboratory and field investigations in a number of domains, such as environmental remediation/stewardship, geothermal resources, production of natural gas hydrates, subsurface permanent storage of carbon dioxide, and oil and gas recovery using conventional and unconventional technologies.

Some of the unique applications and features of the simulator for environmental work are the ability to model vegetated surface barriers, flow and transport in deep vadose zones under thermally altered states, and innovative technologies such as soil desiccation, soil vapor extraction, reactive barriers, and freeze walls.

For geothermal resource modeling, the simulator is fully capable of modeling hydrothermal systems, including geochemical reactions, such as those occurring through mineral dissolution or carbonate precipitation with carbon dioxide re-injection. It can also be applied to model enhanced/engineered geothermal systems (EGS) in hot dry rock, where fracturing is necessary to achieve permeability. For EGS, STOMP models fracture and borehole flow and transport via an embedded modeling approach.

STOMP is unique in the natural gas hydrate domain with its capabilities for modeling ternary gas systems, allowing for the investigation of production technologies involving depressurization, thermal stimulation, inhibitor injection, and hydrate forming gas injection.

Its fully coupled well models, geochemical module ECKEChem, and geomechanical model GeoMech, give the simulator fully coupled THMC capabilities for investigations of carbon sequestration in deep saline formations or utilization in enhanced oil recovery.

Beyond those capabilities of STOMP that are described here, PNNL has additionally developed capabilities for modeling unusual subsurface systems, such as the pyrolysis of oil shales using down-hole fuel cells. Whereas STOMP is routinely used for environmental assessments at U.S. DOE sites, its code structure and active development team allow it to be extended to new research and application domains.

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Modular Design



  • variably saturated flow and transport in water systems
  • aqueous geochemistry
  • environmental restoration and stewardship
  • vadose zone and groundwater interactions


  • multifluid gas-brine systems with heat transport and geochemistry
  • sequentially coupled poro-thermo-elastic geomechanics
  • hydrothermal and enhanced geothermal systems
  • embedded fractures and boreholes
  • vegetated surface barriers


  • multifluid CO2-brine systems with heat transport and geochemistry
  • sequentially coupled poro-thermo-elastic geomechanics
  • carbon sequestration in deep saline formations
  • carbonate mineralization in on- and off-shore basalts


  • three-phase compositional systems with heat transport and geochemistry
  • sequentially coupled poro-thermo-elastic geomechanics
  • embedded faults
  • oil and gas reservoirs
  • enhanced oil production
  • black-oil module


  • ternary gas hydrate systems
  • sequentially coupled poro-thermo-elastic geomechanics
  • natural gas hydrate reservoirs
  • depressurization, thermal stimulation, inhibitor injection technologies
  • guest molecule swapping


  • nonvolatile and volatile single component NAPL
  • multifluid wells
  • organic surface spills and disposals
  • vadose zone residual NAPL formation
  • soil-vapor extraction