1.3 Place of reservoir modeling in a reservoir study
Geomodeling is also called “reservoir modeling” or “static modeling”. This latest expression emphasizes the fact that geomodeling focuses on quantifying the current state (rocks + fluid distribution) of the reservoir, while “dynamic modeling”, run by engineers, focuses on how the fluids (injected/produced) will move and how the rocks will react during production. Dynamic modeling can be thought of as modeling the reservoir “through time”.
Research on reservoir modeling started in the late 70s to the beginning of the 80s and it has continued to grow ever since as computers became more and more popular, powerful and affordable. Reservoir modeling algorithms rely on visualization techniques that are also used in 3D computer games, in 3D animated movies and in CAD (Computer-Aided Design) tools used in the manufacturing industry to model goods (cars, buildings, planes…). Reservoir modeling has one essential difference though: while other industries build their 3D models by drawing (movies, video games…) or thanks to mathematical equations (geometry of the wing of an airplane for example), geomodeling has to define the geometry of complex objects (horizons, geobodies) from a limited amount of data points (well tops, seismic interpretation…). Interpolation and extrapolation techniques are key (see the chapter 2 on geostatistics).
The development of computers lead also to the development of complex 3D models in the domains of geophysics and flow simulation among others (Figure 1). These tools are very complementary to those found in reservoir modeling packages. Many studies involve first a stage of 3D seismic interpretation and seismic inversion, which results are used as input to the reservoir modeling workflow, which itself feeds complex flow simulation computations. The tools from those different domains are also more and more integrated. It started through the definition of standardized file format to transfer data and results from one domain to the next. Nowadays, many software providers are linking if not merging their different proprietary solutions into a single platform to facilitate even further the integration between the different disciplines.
As mentioned in the introduction, the core of any reservoir modeling study is made of five steps, described in the remaining of this paper: gathering the data, structural and stratigraphic modeling, three-dimensional (3D) grid building, facies modeling and petrophysical modeling (Figure 2).