System and method for performing oilfield simulation operations

A method of performing an oilfield operation of an oilfield having at least one wellsite, each wellsite having a wellbore penetrating a subterranean formation for extracting fluid from an underground reservoir therein, the method comprising:

• determining a time-step for simulating the reservoir using a reservoir model, the reservoir being represented as a plurality of gridded cells and being modeled as a multi-phase system using a plurality of partial differential equations, the multi-phase system having a plurality of phases;
• calculating, by a computer processor, a plurality of Courant-Friedrichs-Lewy (CFL) conditions of the reservoir model corresponding to the time-step, the plurality of CFL conditions being calculated for each of the plurality of gridded cells and comprising a temperature CFL condition, a composition CFL condition, and a saturation CFL condition, wherein the temperature CFL condition comprises a convection term dependent on a phase volumetric rate and a conduction term dependent on a heat transmissibility;
• simulating, by the computer processor, a first cell of the plurality of gridded cells using an Implicit Pressure, Explicit Saturations (IMPES) system to obtain a first simulation result, the first cell having no CFL condition of the plurality of CFL conditions with a value greater than one;
• simulating, by the computer processor, a second cell of the plurality of gridded cells using a Fully Implicit Method (FIM) system to obtain a second simulation result, the second cell having at least one CFL condition of the plurality of CFL conditions with a value greater than one;
• and
• performing the oilfield operation based on the first and second simulation results.

A method of optimizing computer usage when performing simulations for a reservoir using a reservoir model wherein the reservoir model is gridded into cells, the method comprising:

• a. determining a preferred percentage of cells to be simulated using an Implicit Pressure, Explicit Saturations (IMPES) system for optimizing computer usage;
• b. determining a time-step for simulating the reservoir;
• c. calculating, by a computer processor, Courant-Friedrichs-Lewy (CFL) conditions according to the time-step for each cell of the reservoir including calculating a temperature CFL condition, a composition CFL condition, and a saturation CFL condition, the temperature CFL condition being calculated based on a thermal simulator;
• d. calculating, by the computer processor, a percentage of cells having no CFL condition greater than one;
• e. determining, using the computer processor, whether the percentage calculated from step d is equal to or greater than the preferred percentage and if not, reducing the time-step and returning to step c;
• and
• f. simulating, by a computer processor, all cells having no CFL value greater than one using the thermal simulator with the IMPES system and simulating all other cells using the thermal simulator with a Fully Implicit Method (FIM) system.

A computer system with optimized computer usage when performing simulations for an oilfield operation of an oilfield having at least one wellsite, each wellsite having a wellbore penetrating a subterranean formation for extracting fluid from an underground reservoir therein, the computer system comprising:

• a processor;
• memory;
• and software instructions stored in memory to execute on the processor to:
• a. determine a preferred percentage of cells to be simulated using an Implicit Pressure, Explicit Saturations (IMPES) system for optimizing computer usage;
• b. determine a time-step for simulating the reservoir;
• c. calculate Courant-Friedrichs-Lewy (CFL) conditions according to the time-step for each cell of the reservoir model including calculating a temperature CFL condition, a composition CFL condition, and a saturation CFL condition, wherein the temperature CFL condition comprises a convection term dependent on a phase volumetric rate and a conduction term dependent on a heat transmissibility;
• d. calculate a percentage of cells having no CFL condition with a value greater than one;
• e. determine whether the percentage calculated from step d is equal to or greater than the preferred percentage and if not reducing the time-step and returning to step c;
• and
• f. simulate all cells having no CFL value greater than one using the IMPES system and simulating all other cells using a Fully Implicit Method (FIM) system.