Geocellular modeling
Posted by D Nathan Meehan September 30, 2010

Oil and gas operators are faced with a difficult task in extracting their product from geological formations deep beneath the earth’s surface. One of the most difficult issues is of course identifying where such formations exist and contain all the properties needed to be productive. Geological formations are rock layers. Oil and gas is usually found in sandstones, limestones or dolomites. Many current plays have shales as reservoirs (see http://blogs.bakerhughes.com/reservoir/2010/06/04/what-is-a-shale-anyway); however, most oil and gas reservoirs use shale layers either as sources of hydrocarbons or seals to prevent hydrocarbons from escaping.

The geological formation that may contain hydrocarbons has to have sufficient porosity and permeability to be productive. Porosity is simply the fraction of the bulk volume of rock that is not rock (imagine the spaces in between sand grains) and ranges from a few percent to more than 30%. Most hydrocarbon formations also contain water in the pore spaces which may or may not flow along with the oil or gas. Permeability is a measure of how easily fluids flow through a porous rock and varies dramatically by layer and areally. Geological models capture the spatial variability in porosity, permeability and water and hydrocarbon saturations.

Geological layers and formations exhibit even more complexity in the subsurface than they do at the surface and may include meandering river channels and streams, carbonate reefs, beaches, dunes and the jumbled mix of sands and shales that characterize turbidites . Complex faults, salt domes and other features further complicate the subterranean environment.

Operators use seismic surveys, well logs, cores, etc. for ways to map subsurface formations. Previous generations of mapping technology yielded 2-D maps of the complex 3-D environment. Three-dimensional models have improved radically in the last few decades and modern tools like JOA’s JewelSuite™ provide enormous leverage for oil and gas operators. Geocellular models use grids to construct a static model of the reservoir containing all of the petrophysical, geological, geophysical, fluid and rock data as spatially distributed throughout the reservoir. This can serve as input to a dynamic model incorporating reservoir simulations. In a reservoir simulator fluid flow and material balance equations are solved for each of the grids to predict reservoir behavior under various alternatives. JOA’s model has unique features that result in state-of-the-art performance for both static and dynamic models.

The 3-D gridding technology in JewelSuite™ is the basis for a new method of integrated reservoir modeling. The Jewel grid—with its orthogonal, vertically stacked cells—is particularly powerful for fields with complex geology. JewelSuite models also can communicate reservoir complexity to reservoir simulators, giving clients unparalleled connectivity and accuracy in simulation results when compared to other industry packages. JOA is cooperating with other industry leading firms to form the centerpiece of a seismic-to-simulation interpretation approach and to solve complex geomechanical problems.

More information about complex reservoir modeling can be found at http://www.jewelsuite.com/; more information about reservoir development services at Baker Hughes can be found at http://www.bakerhughes.com/products-and-services/reservoir-development-services.

Figure 1: Typical reservoir model

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D Nathan Meehan
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