Graph theory and DFN analysis: a case example of the impact of network behaviour analysis on well location assessment

Naturally fractured reservoirs account for an increasing proportion of operator’s portfolios, (McKeown, 2001, submitted) and techniques for objectively assessing the properties of Discrete Fracture Networks (DFNs) are therefore of great interest. This paper presents some of the latest techniques available for the analysis of DFN behaviour. Of particular importance to the hydrocarbon industry are those factors affecting the ability of the network to transmit fluid and the likely patterns of transmission across the network. These patterns of behaviour will significant impact the risk assessment of well placements and productions strategies. The first section of this paper presents the theory and technique of connectivity mapping using graph theory. The utility of this technique is clearly shown by the case study presented in the second section. The example is from a complex thrust trap in Argentina and clearly illustrates both the need to understand the evolution of an area (in order to produce realistic DFNs) and also the need for rapid, interactive assessment of the impact of significant variables (fracture length, dilatancy state, etc) on the DFN behaviour. The evolution of the study area was modelled and the strain imposed on the reservoir was modelled. Elements of the strain history were used as a guide in developing the DFN. The impact of changing stress regimes on connectivity behaviour is demonstrated.