Characterization of rock properties. We obtained rock samples from the Bowland formation in the UK, from other EU formations, and from North America. We demonstrated that understanding the mineral-scale control on permeability in these rocks is essential to calculate realistic estimates of the extent of recoverable gas reserves of many European countries. We undertook novel 3D imaging of the microstructure of the shale samples at multiple scales from micro- to nano-metres. We imaged the pores (where gas would be held), the connection between the pores (which control flow of gas) and the natural fractures present (that enhance gas production). In one innovative experiment, we monitored fracturing and healing of rock samples using the synchrotron. We analysed the geomechanical properties of some European shales: Bowland shales, which are clay—poor, deform in a relatively brittle manner. Other European shales are more ductile. The results suggest a low fracture healing rate of Bowland shale and a good potential for hydraulic fracturing.
Rock-fluid interactions. We quantified the amount of hydrocarbons that can be adsorbed at down-hole temperature and pressure conditions in shale rocks. We calculated transport properties of shale gas in mature kerogen and of a variety of fracturing fluid models in clays. Several important data related to the relative strength of interactions of important compounds such as naturally occurring radioactive materials with clay basal and edge surfaces, and their relative mobility. To validate our understanding, we produced engineered materials that contain micro- and mesoscale pores and we used them to address the pore size effect on fluid behaviour. By studying carbon dioxide and light hydrocarbons we obtained results that support the prospective use of CO2 for enhanced desorption of gas from shales.
Hydraulic fracturing fluids. We developed and characterized ‘green’ formulations, based on polysaccharides and viscoelastic surfactants. All formulations exhibited suitable mechanical and rheological properties as well as good thermal resistance. Rhamnolipids, saponins and sodium citrate were found to significantly modify the rheological properties, even in small amounts; carbon black induces electro-responsiveness, increases viscosity and improves thermal resistance; azorubine, a food dye approved by FDA, imparts light-responsiveness. Moreover, the implementation of magnetic field revealed to be an effective strategy in order to further reduce the scale formation and precipitation.
Fluid transport modelling. We developed a molecular-level understanding of the mechanisms by which fluids transport within rock formations. We integrated this understanding in stochastic models to predict the permeability of shale formations when pore distribution, chemical composition, and fluid content are known. We developed software to describe fluid transport in a rock with existing fractures, and we demonstrated that this software can describe the propagation of a fracture network upon hydraulic fracturing stimulation. The software can also describe the alteration of the stress in the sub-surface, which could be used to reduce the likelihood of induced seismicity.
Risk assessment. We developed modelling tools for assessing the safety hazards of shale gas wells. Models for predicting explosion and jet fire consequences of a well blowout, with a computational flow model simulating transient discharge from a well, have been developed. Computational methodologies to assess the risk of induced seismicity during reservoir stimulations have also been developed. The effectiveness of the well-blowout model in a case study based on realistic design of a shale gas exploration site has been demonstrated. The induced seismicity model was successfully applied to a case study at an Enhanced Geothermal System in Basel, Switzerland.
Reduction of the environmental impact. We applied optimization methods to minimize the amount of energy required for purifying flow-back and produced water. The correct coordination of fracking scheduling with water reuse allows reducing freshwater consumption. We also developed software to quantify the environmental impact of shale gas within the lifecycle of a well. Life cycle inventory data has been collated. Then, a parametric excel tool has been built for easy implementation. Our comparative analysis demonstrated that shale gas as a source of electricity has lower environmental impacts than, e.g. coal, and the sensitivity analysis revealed that the ultimate recovery of a shale gas well has strong effect on the environmental impact quantified per unit of produced natural gas.
Conclusions and dissemination. While shale gas exploration and production is in its infancy in the European Union, the present study provides cutting edge tools that can be used to assess the environmental impact of the technology. It is argued that the regulatory framework is for the most part adequate, and that transparent dialogue with all stakeholders is a necessity for obtaining the social license to operate. Consistent with this finding, the ShaleXenvironmenT consortium has offered a number of public dissemination events, has published numerous peer-reviewed Open Access journal articles, and maintain a website rich of information.
