# Introduction¶

This User Manual provides instructions on how to use the PFLOTRAN flow models: Gas-Water for CO2 Storage (GAS_WATER), Black-Oil (BLACK_OIL), Todd-Longstaff (TODD_LONGSTAFF and SOLVENT_TL) and Oil-Water (TOIL). All these models can run both in isothermal and thermal mode

Contents

## Gas-Water for CO_{2} Storage (GAS_WATER)¶

The Gas-water module (GAS_WATER) also describes a two-phase flow model. In this case each phase may contain both components: the aqueous phase may contain dissolved gas, and the gas phase may contains vapourised water. The module solves a molar balance equation for each component and an energy equation to account for thermal effects. For more details see the Mathematical formulation of Gas-Water in the theory guide.

## Black Oil Model (BLACK_OIL)¶

The Black Oil Model is a common fluid treatment in reservoir simulation. In this treatment, gas is allowed to dissolve in the reservoir oil phase. The amount of dissolved gas in the oil is parameterized by the oil saturation pressure, commonly known as the bubble point. Oil properties such as the formation volume factor (volume of oil at reservoir conditions/volume of oil at surface conditions), enthalpy and viscosity will generally be functions of pressure and bubble point. See Mathematical formulation of the Black Oil Model in the theory guide.

## The Todd-Longstaff Model (TODD_LONGSTAFF)¶

The simple Todd-Longstaff model is suitable for cases in which the reservoir is undersaturated with no free gas. In this case the solvent is represented by the gas phase. See Mathematical formulation of the simple Todd-Longstaff Model in the theory guide.

## Solvent Model (SOLVENT_TL)¶

The Solvent model is an extension of black oil model which adds an additional solvent phase, commonly used to represent an injected fluid such as carbon dioxide which is fully or partially miscible with the oil. See Mathematical formulation of the Solvent Model in the theory guide.

## Oil-Water Model (TOIL)¶

The Thermal Oil Immiscible (TOIL_IMS) module describes a two-phase flow model, in which the oil and water phases are considered immiscible.
The module solves a molar balance equation for each phase and an energy equation to account for thermal effects.
Each phase is assumed to contain only one component: the water phase contains 100% H_{2}O, the oil CO_{2} phase contains 100% of a user-defined oil component.
For more details see the Mathematical formulation of toil-ims in the theory guide.

## The Thermal Option¶

In any of the above flow models, if the ISOTHERMAL mode has not been selected, temperature variation will be modeled for each cell. Within a single cell, the fluids and rock are assumed to be in thermal equilibrium, and to share the same cell temperature. In isothermal mode the energy equation is not solved and the temperature is assumed not to vary with time.

## Structure of this Manual¶

This manual gives instructions on how to: (i) build an input file, (ii) monitor the convergence and evolution of a simulation, (iii) view the resulting PFLOTRAN output files.