Naturally Fractured Reservoirs – Modeling and Simulation Methods

Natural or induced fractures play a crucial role in many petroleum reservoirs. Even though only a small percentage of today’s reservoir models explicitly describe the fractures or the fracture networks, one may claim that practically most petroleum reservoirs are fractured. Due to their complexity, but also due to their commercial significance, naturally fractured reservoirs have been the subject to extensive studies during the past decades.

This paper will try to assess the current situation and methodology for modeling fractured reservoirs. Its main focus will be on recent developments in static and dynamic flow modeling of fractured reservoirs. Especially the latest Evolution in static modeling software capabilities significantly affected past historical workflows and initiated new developments in the reservoir simulation area.

Starting from the historical evolution of dual continuum reservoir simulation models, a review is given on various simulation approaches for fractured hydrocarbon reservoirs. Several methods will be discussed, starting from conventional formulations to the traditional dual porosity model, to discrete fracture network models. All formulations have their own advantages, but have deficiencies in describing some other specifics of fractured reservoirs.

Recently, the petroleum industry tries to integrate information from all possible sources to generate fracture network models and dual continuum simulation models. Most recently, the integration of seismic data into dynamic simulation models has received a great deal of attention. Also, latest developments in the gridding technology raised hopes to be able to cope with full permeability tensors in the near future.

In many naturally fractured reservoirs, the fractures are found in limited zones, so-called “sweet spots” only. Consequently, not all parts of the reservoir models will typically require explicit fracture treatment with dual continuum models.

One of the methods presented in this paper allows automatic generation of dual continuum grid blocks wherever the attributes of the geological model suggest to do so. This approach is called adaptive dual continuum model and it results in simulation models that contain grids that resemble the real geological situation very closely.