Electrohydraulic Fracturing of Rocks

This book presents a new fracturing technique that should be considered as a potential alternative, or a companion technique, to hydraulic fracturing of tight gas reservoirs and low permeability rock masses. As opposed to hydraulic fracturing which generates a few numbers of large cracks, electro-hydraulic fracturing induces diffuse micro-cracking and fragmentation of rocks. Laboratory tests demonstrate that increases of permeability by two orders of magnitude can be reached, without major cracking in tested specimens. This book discusses the principles of this new technique, reports experiments which have been developed is order to prove the concept and finally describes the numerical model from which the potentialities of this technique in representative reservoir conditions can be assessed.

Preface vii Introduction xi Chapter 1 Experiments in a Representative Environment 1 1.1 Mechanical set-up 1 1.2 Pulsed arc electric generator 4 1.3 Material properties 6 1.4 Measurements of radical permeability 7 1.5 X-ray tomography 9 1.6 Results on model materials 10 1.7 Summary of the results on sandstone 17 1.8 Discussion 18 Chapter 2 Computational Modeling of the Process: Principles 21 2.1 Pressure generated by the pulsed arc electrical discharge 22 2.2 Mechanical modeling of rocks under dynamic loads 29 2.3 Coupled effects between damage and permeability 41 2.4 Summary and conclusions 44 Chapter 3 Validation of the Computational Model 47 3.1 Simulation of the experiments in uniaxial compression 47 3.2 Confined tests on hollow cylinders 52 3.3 Isotropic versus anisotropic permeability 67 3.4 Conclusions 68 Chapter 4 Computations on Representative Reservoir Geometries 71 4.1 Effect of repeated shocks 72 4.2 Simulation on a typical reservoir geometry 75 4.3 Optimization of the process 79 Concluding Remarks and Future Outlook 91 Bibliography 97 Index 103