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This article describes the steps necessary to conduct a detailed reservoir simulation study (also see “[[Reservoir modeling for simulation purposes]]”). A simulation study requires description of the reservoir's rock and fluid properties, validation of completion and production history, and extensive history matching to validate and modify this input data. When history matching is complete, numerous predictions of field and well performance characteristics are calculated for various development scenarios.

This article describes the steps necessary to conduct a detailed reservoir simulation study (also see [[Reservoir modeling for simulation purposes]]). A simulation study requires description of the reservoir's rock and fluid properties, validation of completion and production history, and extensive history matching to validate and modify this input data. When history matching is complete, numerous predictions of field and well performance characteristics are calculated for various development scenarios.

The reservoir characterization required to define [[porosity]] and [[permeability]] for each grid block in a reservoir simulation model is more stringent and at the same time more loosely defined than reservoir characterization required in detailed development geology studies. A simulation engineer can spend countless hours defining the reservoir model. Nevertheless, despite the plausibility of the interpretation used to develop this description, the ultimate test of the simulation model's validity is its reproduction of production data. The smaller relative uncertainty of production data with regard to input data dictates that simulation engineers may take many liberties in matching that data, while rationalizing their choices with a broad degree of latitude. Development geologists are the most likely source of quality control for the reservoir description developed and modified for a reservoir simulation study.

The reservoir characterization required to define [[porosity]] and [[permeability]] for each grid block in a reservoir simulation model is more stringent and at the same time more loosely defined than reservoir characterization required in detailed development geology studies. A simulation engineer can spend countless hours defining the reservoir model. Nevertheless, despite the plausibility of the interpretation used to develop this description, the ultimate test of the simulation model's validity is its reproduction of production data. The smaller relative uncertainty of production data with regard to input data dictates that simulation engineers may take many liberties in matching that data, while rationalizing their choices with a broad degree of latitude. Development geologists are the most likely source of quality control for the reservoir description developed and modified for a reservoir simulation study.

==Preparing fluid properties==

==Preparing fluid properties==

Two types of fluid descriptions are used in reservoir simulation studies: ''black oil'' and ''compositional''. The black oil description expresses the fluid's volumetric (formation volume factor and solution gas-oil ratio) and flow (viscosity) characteristics as a function of pressure for three phases: oil, gas, and water. In complex fluid mixtures, the fluid's volatility often dictates that volumetric and flow characteristics are not only a function of pressure but also of composition. For these fluids, a compositional description uses an equation of state to describe the fluids' volumetric and flow characteristics. An equation of state describes a fluid in terms of the fundamental physical properties of its components: methane, ethane, heptanes-plus, and so on. These fundamental physical properties—critical pressure, critical temperature, critical volume, acentric factor, and interaction coefficients—are unique for each compositional fluid description derived for a simulation study.

Two types of fluid descriptions are used in reservoir simulation studies: ''black oil'' and ''compositional''. The black oil description expresses the fluid's volumetric (formation volume factor and solution gas-oil ratio) and flow ([[viscosity]]) characteristics as a function of pressure for three phases: oil, gas, and water. In complex fluid mixtures, the fluid's volatility often dictates that volumetric and flow characteristics are not only a function of pressure but also of composition. For these fluids, a compositional description uses an equation of state to describe the fluids' volumetric and flow characteristics. An equation of state describes a fluid in terms of the fundamental physical properties of its components: methane, ethane, heptanes-plus, and so on. These fundamental physical properties—critical pressure, critical temperature, critical volume, acentric factor, and interaction coefficients—are unique for each compositional fluid description derived for a simulation study.

Black oil fluid descriptions are used to describe most oil and gas fields. Primary depletion, [[waterflooding]], and gas injection can all be simulated with black oil models. Volatile oil reservoirs or gas condensate reservoirs generally require compositional models. These models may exhibit such complexities as a fluid whose density is linearly proportional to depth or whose phase switches repeatedly between oil and gas. Thermal models, used to simulate steam injection, may use either black oil or compositional fluid descriptions. Black oil thermal models describe fluid properties as a function of temperature as well as pressure. The importance of oil volatilization in thermal recovery often dictates that compositional models are used to simulate thermal recovery processes.

Black oil fluid descriptions are used to describe most oil and gas fields. Primary depletion, [[waterflooding]], and gas injection can all be simulated with black oil models. Volatile oil reservoirs or gas condensate reservoirs generally require compositional models. These models may exhibit such complexities as a fluid whose density is linearly proportional to depth or whose phase switches repeatedly between oil and gas. Thermal models, used to simulate steam injection, may use either black oil or compositional fluid descriptions. Black oil thermal models describe fluid properties as a function of temperature as well as pressure. The importance of oil volatilization in thermal recovery often dictates that compositional models are used to simulate thermal recovery processes.