Reservoir modeling

Screenshot of a structure map generated by Contour map software for an 8500ft deep gas & Oil reservoir in the Erath field, Vermilion Parish, Erath, Louisiana. The left-to-right gap, near the top of the contour map indicates a Fault line. This fault line is between the blue/green contour lines and the purple/red/yellow contour lines. The thin red circular contour line in the middle of the map indicates the top of the oil reservoir. Because gas floats above oil, the thin red contour line marks the gas/oil contact zone.

File:Reservoir modeling software screen snapshot of isopach map for 8500ft deep oil reservoir 28ft thick located in the Erath field, Vermilion Parish, Erath, Louisiana.png

Screenshot of an Isopach map generated by reservoir modeling software for an 8500ft deep oil reservoir 28ft thick located in the Erath field, Vermilion Parish, Erath, Louisiana. The contour interval is 2 ft between successive contour lines. Because oil floats above water, the outer red color indicates the elevation of the water/oil contact zone, which is at the bottom of the Petroleum reservoir. Inside the dark blue color is a thin red contour line which indicates the top of the oil reservoir, 22 feet above the water/oil zone. Because gas floats above oil, the thin red contour line marks the gas/oil contact zone. The five smallest circles inside the image indicate slight depressions along the roof, or oil/gas zone, of the reservoir. Oil drilling to this petroleum reservoir could use Directional drilling to accurately target the 28 ft thick space, 8,500ft underground.

In the oil and gas industry, reservoir modeling involves the construction of a computer model of a petroleum reservoir, for the purposes of improving estimation of reserves and making decisions regarding the development of the field.

A reservoir model represents the physical space of the reservoir by an array of discrete cells, delineated by a grid which may be regular or irregular. The array of cells is usually three dimensional, although 1D and 2D models are sometimes used. Values for attributes such as porosity, permeability and water saturation are associated with each cell. The value of each attribute is implicitly deemed to apply uniformly throughout the volume of the reservoir represented by the cell.

Types of reservoir model

Reservoir models typically fall into two categories:

• Geological models are created by geologists and geophysicists and aim to provide a static description of the reservoir, prior to production.
• Reservoir simulation models are created by reservoir engineers and use finite difference methods to simulate the flow of fluids within the reservoir, over its production lifetime.

Sometimes a single "shared earth model" is used for both purposes. More commonly, a geological model is constructed at a relatively high (fine) resolution. A coarser grid for the reservoir simulation model is constructed, with perhaps two orders of magnitude fewer cells. Effective values of attributes for the simulation model are then derived from the geological model by a process of "upscaling". Alternatively, if no geological model exists, the attribute values for a simulation model may be determined by a process of sampling geological maps.

Uncertainty in the true values of the reservoir properties is sometimes investigated by constructing several different realizations of the sets of attribute values. The behaviour of the resulting simulation models can then indicate the associated level of economic uncertainty.

The phrase "reservoir characterization" is sometimes used to refer to reservoir modeling activities up to the point when a simulation model is ready to simulate the flow of fluids.

Commercially available software is used in the construction, simulation and analysis of the reservoir models.

See also

• Extraction of petroleum
• Petroleum engineering
• Computer simulation
• Seismic to simulation
• Reservoir Simulator

References

• Stephen Tyson. An Introduction to Reservoir Modeling (2007), ISBN 978-1-906928-07-0.