PGK Monthly meeting
Met gast spreker Auke Barnhoorn (TU Delft).
18.00-19.00 Presentatie Auke Bernhoorn: “Rock fracturing in the laboratory: Results on fracture propagation in layered media and predicting the onset of fracturing.”
Fractures play an important role in the subsurface because they potentially are preferential pathways for fluid flow in naturally fractured reservoirs, they can compartmentalise reservoirs and they play an important role in seismic events. In addition, fractures can be created during well stimulation. In order to accurately predict the efficiency of flow along fractures the characteristics of the formed fracture networks is required. Characteristics such as fracture apertures and fracture orientations are important, but also the connectivity of the formed network. In Delft we focus in our laboratory research on the evolution of the fracture network to predict how fractures grow and connect through heterogeneous rocks and whether we can use seismic monitoring techniques to determine when and where these fractures start to grow.
In this presentation I will show two aspects of the research we are currently performing at TU Delft on experimental rock fracturing. In the first part of the presentation I will show the results on fracture propagation in layered siliciclastic rocks. We have selected various quartz-rich rock types which exhibit a large range of rock strength. By combining those samples we created layered samples in which a large range of mechanical contrast between the layers is present. We show that fractures formed in the weak layer sometimes propagate into the strong layer even at stress conditions in which fracturing of the strong layer was not expected. At other conditions, fractures remain contained within the weak layer. We can know predict at what depths in layered reservoirs this occurs. This has consequences for increased connectivity between layers in a reservoir or in other circumstances loss of integrity of the sealing layer.
The second part of the presentation shows how we use the analysis of the wave forms of acoustic waves that we send through the rock samples while they are fracturing. By analysing the change in wave amplitude of the wave and the scattering potential of the wave, we show that the technique is sensitive enough to detect the formation of the first microfractures in the samples. These first microfractures precede the formation of the large failure planes which are accompanied by the release of seismic energy. It may thus have the potential to be used as a predicting tool to determine the onset of seismicity in materials and reservoirs.