Mechanics of Hydraulic Fracturing

Fluid-driven fracture growth, called hydraulic fracturing, refers to the process where a pressurized fluid flows into and propagates fractures in the rocks. It is a commonly used technique for well stimulation to extract oil and gas in the petroleum industry and geothermal resources from deep granite and is also widely used in the mining industry to precondition rock for extraction by caving and to reduce seismic risk in deep high stress mines. In addition, fluid-driven fractures are important in several geological processes, for example, associated with the formation of veins and joints and in growth of dikes leading to volcanic eruption. The mechanics of hydraulic fractures involves multiple physical processes including the flow of viscous fluids in fractures, diffusion of fluid into porous matrix material, creation of new fracture surfaces, proppant transport and multiphase flow, and friction slip on natural fractures and faults. In particular, hydraulic fracturing is further complicated by its interaction with geological structures, the tectonic stresses, pore pressure, and rock temperature. Hydraulic fracturing typically occurs as a quasi-static process, but potentially induces seismic events if pore pressure and stress changes are not well controlled and monitored.

Mechanics of Hydraulic Fracturing: Experiment, Model, and Monitoring provides a summary of the continuing research in mechanics of hydraulic fractures for more than two decades along with new research trends, which are of interest to both researchers and industrial operators. At the science level, fracture growth in rocks occurs at a large range of scales. The rock itself as a natural material is heterogenous, consisting of minerals grains including clays, and grain sand cementing minerals. The rock mass is also structurally heterogeneous, containing microcracks, bedding planes, joints and faults. The rock material and structural heterogeneity makes the prediction of fracture growth difficult and careful experimental design and model development are required to advance our understanding. A collection of recent work thus can provide an important summary of current understanding of the multi-scale mechanics of hydraulic fractures.

Volume highlights include:

- Covers the contributions from theory, modeling and experiment including the applications of models to reservoir stimulation, mining preconditioning and the formation of geological structures
- Formation of fracture networks, the primary focus of many early models, plays a secondary role compared to the fracture growth of individual foundations and applications of the process
- Prediction of fracture shapes, sizes, and distributions in sedimentary basins and its importance in petroleum industry
- Predictive models consist of mechanics of this coupling process with results verified by testing against laboratory and field measurements
- Developing a better predicative model, many experimental studies have recently been performed to verify the comprehensive models
- Real-time monitoring methods such as micro-seismicity and trace tracking are widely adopted in petroleum industry to provide the measured fracture shapes for benchmarking the models
- Outcrop mapping provides useful data to which the model predictions can be compared
- Comparisons prove useful in uncovering geometries of fractures like dikes and veins and in studying the process of their formation