Exercise 5
In Exercise 2 we saw that the lithostatic stress state does not, by itself, generate fractures. With this in mind, use the Mohr diagrams of the Solution for Exercise 2 (failure envelopes and the Mohr circles that represent the lithostatic stress state for the dolostone and mudstone) to answer the questions below.
a) In the case that fluid pressure (p) is present, what would happen to the Mohr circles?
b) If this fluid pressure is high enough to make the Mohr circles intercept the failure envelopes, what type of fractures would be formed in the dolostone? And in the mudstone? Explain your answers.
c) Is it possible that fractures propagated by the opening mode and by the shear modes be formed in the same rock at a given location, at the same time? Explain.