Scientific questions and environmental impacts addressed. Transport of fluids within rock mass, which is solid rock matter plus discontinuities such as fractures or faults, is a scale-dependent phenomenon. On the small scale (micro-scale), which is within intact rock, transport is through pores and micro-fractures. Above a certain scale (on the meso-scale), which is in general in the decimetre range, persistent discontinuities are evident; these discontinuities may be layering in sedimentary rocks, such as shale, and fractures. The fractures are typically evident in distinct orientations, which is the result of geological processes at geological time scales (millions of years). Commonly, the fractures are connected and make up the so-called distinct fracture network (dfn). Transport is governed by these fractures on the meso-scale. At larger scale, decametre and above, faults are evident. Faults are large scale discontinuities, that show high fracture densities. These faults may be conductive in certain cases but may also be smeared and impermeable due to diagenetic processes or large deformation. Non-conductive faults confine oil- and gas-bearing compartments. These general statements are valid for shale formations also. Pores contribute to fluid transport on the sub-centimetre scale, at larger rock volumes fractures increasingly become the dominant fluid transport pathway. Faults may be hydraulically confining reservoirs and act as fluid transport barriers. For a broader introduction to the matter, the reader is referred to Xxxxxxxxxx and Xxxxxx (2017). WP6 was tasked with establishing a connection between atomistic, molecular-scale calculations and predictions for large-scale transport of fluids within shale rock formations. With this it is possible to use laboratory measurements of rock and predict (upscale) permeability for large scale applications. With this, it is possible to analyse the environmental impact of any shale gas exploration or production much better. Examples are the simulation of fluid migration in fracture networks and faults, or the assessment of the risk for induced seismicity. The work summarised focusses on using micro-scale modelling and permeability measurements to study the influence of fractures on the transport of fluid in shale rock mass. Modelling of a typical shale play fracture network has been conducted and simulation of fluid transport with increasing model size has been conducted to identify a so-called representative elementary volume for bulk permeability. This bulk permeab...
Scientific questions and environmental impacts addressed. In this work package, methodologies to assess the risk of induced seismicity during reservoir stimulations are developed and applied to case studies. These methodologies are computational, and hence mathematical modelling techniques are used to simulate fluid injection into a reservoir and quantify the seismic response based on the reservoir’s characteristics. The methodologies are applicable to hydraulic fracturing of shale gas reservoirs during the fluid injection stage and also during the “shut-in” period afterwards when the flow into the reservoir is stopped. Possible causes of induced seismicity in hydraulic fracturing of low permeability rock formations are illustrated in Figure 25. Firstly, levels of micro-seismicity that are too weak to be felt at the surface are generated during the creation of fractures in the rocks themselves. These events are part of the hydraulic fracturing process, which induces the formation of fracture networks to enhance fluid transport in the sub-surface. For the triggering of events that are strong enough to be felt at the surface, several scenarios are possible, which could generate a permeable pathway between the fluid injection point and a pre-existing fault. Direct fault activation may occur when a hydraulic fracture directly intersects a pre-existing fault. Indirect activation could be triggered by diffusion of pore pressure away from the injection zone along local faults and fractures. Additionally, faults may be activated if injection xxxxx are drilled directly into them, via fluid flow through existing fractures, through more permeable rock strata above or below shale formations, or through bedding planes that interface the rock strata (Xxxxxx et al., 2013). Even in the circumstances when stimulated fractures and the fracturing fluids may be hydraulically isolated from any pre-existing faults. The fault may in fact be activated through perturbations in the stress field brought about by changes in volume or mass loading transmitted to the fault poroelastically (right, Figure 25).The developed robust predictive methodologies can be used as preliminary assessment of the risk of induced seismicity for given geological conditions and injection parameters such as volumetric rates and pressures. They could also be coupled to seismic monitoring techniques during the fluid injection operations for the adaptive adjustment of seismic safety margins in relation to the seismic response of a reservoir. These methodologies can ...
Scientific questions and environmental impacts addressed. This Work Package aims to provide careful experimental characterisation of the shale rock samples extracted from formations throughout Europe, studying experimental fracture formation and propagation, as well as fluid behaviour in core samples. The team members have developed new technologies to push the existing limits. The improved understanding of microstructure, pore network and mechanical properties in shales from this project will allow assessment of more efficient gas extraction processes. The imaging and quantification of fracture initiation and propagation will enhance the gas shale recovery and also improve the prediction of the environmental impact on earthquakes and leakage in ground water.
Scientific questions and environmental impacts addressed. The main task of WP5 is the formulation of hydraulic fracturing fluids specific for the shale formations found in Europe. Since every shale formation is unique, fracturing fluids effective in North American shale formations might not be effective in European ones. In this framework the study of formulations with physico-chemical properties that are appropriate with the pressure-temperature conditions and the composition of shale gas formations is fundamental for the potential exploitation of European shale basins. At the same time, environmental concerns about shale gas extraction cast doubts on the toxicity of the chemicals which are present in fracturing fluids. To minimize the environmental impact of hydraulic fracturing and reduce the amount of pollutants in flowback and produced water, all the substances which are potentially dangerous are replaced by greener alternatives. On this basis, the four primary objectives of WP5 are:
Scientific questions and environmental impacts addressed. WP7 focused on the synthesis, characterization and understanding the properties of novel porous materials, in particular zeolites, with regard to the adsorption of methane and carbon dioxide. Porous materials, zeolites as typical representatives of natural microporous materials, are common in the nature and understanding of their behavior as for the adsorption and transport of methane and carbon dioxide are directly related to this topic of the ShaleXenvironmenT project (SXT). More specifically, to get a better insight into the behavior of shale gas in reality to make some model, in optimum case, having predictable value, it is important to prepare well- defined materials. For that purpose we have synthesized series of zeolite, which are microporous crystalline materials with precisely defined sizes of their micropores. These were not only those already known in the literature but also we have applied our own new procedure called ADOR (for details see below). To understand the behavior of fluids in the well-defined pores, we have investigated two approaches, i) combined adsorption and diffusion study of light alkanes using computer simulations, and ii) adsorption of carbon dioxide in the series of isoreticular zeolites.
Scientific questions and environmental impacts addressed. Safety and environmental risks associated with exploration and exploitation of the shale gas resources can be related to induced seismicity caused by hydraulic fracturing, and also to well failures and blowouts at the exploration stage during drilling into shale formationsiii. Fluids lost from a well during a blowout can also result in environmental damages, with in some cases significant remediation costs. In this part of the project, we have focused on evaluation of safety hazards of shale gas xxxxx, aiming to provide modelling tools for use at the design stage to ensure best protection of near-by population and people working on the site. To ensure accurate evaluation of safety hazards we have focused on coupling of models predicting explosion and jet fire consequences of a well blowout, with a transient computational flow model simulating transient discharge from the well during uncontrolled release.
