Use of Mohr Diagrams to Predict Fracturing in a Potential Geothermal Reservoir

Inferences have to be made about likely structures and their effects on fluid flow in a geothermal reservoir at the pre-drilling stage. Simple mechanical modelling, using reasonable ranges of values for rock properties, stresses and fluid pressures, is used here to predict the range of possible structures that are likely to exist in the sub-surface and that may be generated during stimulation of a potential geothermal reservoir. In particular, Mohr diagrams are used to show under what fluid pressures and stresses different types and orientations of fractures are likely to be reactivated or generated. The approach enables the effects of parameters to be modelled individually, and for the types and orientations of fractures to be considered. This modelling is useful for helping geoscientists consider, model, and predict the ranges of mechanical properties of rock, stresses, fluid pressures, and the resultant fractures that are likely to occur in the sub-surface. Here, the modelling is applied to folded and thrusted greywackes and slates, which are planned to be developed as an Enhanced Geothermal System beneath Gottingen.

Automated summary

In the pre-drilling stage of a geothermal reservoir, inferences about likely structures and their effects on fluid flow are made using simple mechanical modelling. Mohr diagrams are utilized to show the types and orientations of fractures likely to be reactivated or generated under different fluid pressures and stresses. This modelling approach helps geoscientists consider, model, and predict the mechanical properties of rock, stresses, fluid pressures, and resultant fractures in the sub-surface.