Hierarchical Organization of Flow Network in Fractured Carbonate Reservoirs: Identification and Characterization of Key Parameters

摘要

From field data, outcrop observations, and ground-water flow studies, this paper illustrates that if the assessment of the fracture network organization is effectively an important stage of the reservoir characterization, it cannot be dissociated from the evaluation of the scale relationships, the relation with stratigraphy, and the distribution of fracture hydraulic properties. In Lacq Field, a giant gas field in a fractured carbonate reservoir, the flow network is assessed through the use of dynamic data. Vertical distribution of producing zones shows a very clear control of effective open fractures by stratigraphy, and therefore carbonate lithology. In the same time, producing zones are not located in the areas in which fracture density is the highest. Same results are obtained from the observations of in-situ fracture networks and water incomes in a tunnel and a subsurface quarry. It clearly demonstrates that fracture density is the not the driving parameter for flows, and could be anti-correlated with fracture effective aperture. The computation of equivalent permeability on fracture models shows that fracture aperture distribution (and therefore hydraulic properties distribution) is a more prevalent parameter for uncertainty assessment than fracture distribution. Lastly, the spacing between open producing fractures along vertical or horizontal profiles show either exponential or power-law experimental distributions, regarding the spatial correlation between geological features. This proves the hierarchical organization of the flows, together with the needs for an evolution of the simplistic representation of a constant matrix block size within each cell of the dual porosity reservoir model. These studies enable to up-date the typology of fractured reservoirs we previously published.