Conference Agenda

If you look at the media, you come across new horror stories about water almost every day. Experts warn of a life-threatening global water crisis. Reports of droughts, wars for water, poisoned water and the end of our water resources are fuelling fears to die of thirst or of running out of water. How realistic is this news? Is this the truth or is this information the typical hype of the media where "only bad news is good news"?

The presentation answers the question and gives an analysis of the global water scarcity. It describes the current water situation and makes a prediction up to the year 2050. In the first part the current water demand and water supply are presented with focus on the global water balance and today’s water scarcity. In the second part, the future water scarcity in terms of population boom, economic development, increase of living standards (urbanization, industrialization and change of diet), climate change, and non-sustainable water use is discussed. It is shown that our future water demand will increase dramatically until 2050, while our water supply will stay more or less constant. To close this gap, possible options are rather in an improvement of the water demand management than water supply management. That means that the water saving potential is much higher than the possible increase of the water supply. A key role plays the agricultural water consumption for irrigation which makes up the largest part of our water demand. Despite all the optimizations our water demand will increase until 2050. Therefore, it is very likely that in the future water and land resources for natural ecosystems will further decrease mainly due to the worldwide increase of agriculture. Additionally, adaption to climate change requires adaption to climate variability, stronger weather extremes, seasonal changes, and higher temperatures.

The solution of the water problem requires the application of a wide spectrum of methods whereby the socio-economic obstacles are at least as critical as the technical challenges. The main question for the future still remains: How to share the world’s water resources in a fair way among its inhabitants?

Shallow aquifers in Holocene flood basins around the world are loci for the pollution of arsenic, which poses a severe health threat to millions of people. Groundwater is the prime source of water for consumption and irrigation in densely-populated areas of developing countries. Arsenic concentrations are conditioned by the meandering-river geomorphology of the Holocene flood basins, and show a high spatial variability. The combination of high organic carbon deposition rates and the presence of solid-state arsenic constitutes a potential locus for pollution in clay-filled clay plugs. After the reductive dissolution in anoxic conditions, the mobilized arsenic migrates to adjacent sandy point-bar aquifers, and accumulates in high concentrations by stratigraphic entrapment. In this paper the pollution threat is quantified through the calculation and analysis of solid-state arsenic in clay plug sediment. To assess the arsenic volume in clay-plug sediment, the bulk sediment volume of twenty clay plugs on the Middle Ganges Plain of Bihar (India) was calculated by combining surface area analysis of Sentinel-2 satellite data with side-scan sonar depth profiling of oxbow lakes, and with sedimentological data from four cored shallow wells. Arsenic concentrations in the clay-plug sediment, obtained elemental analysis (ICP-MS based) of 18 core sub-samples and complemented with published concentration data, yielded an average arsenic content of 28.75 mg/kg sediment in the 12 m thick clay plugs, and a total arsenic weight of 0.07 – 3.13 ^. 10⁶ kg per clay plug. Arsenic and iron concentrations in the sediment decrease with depth, and this testifies to the increased dissolution.

In this study, we carry out an evaluation of the potential for induced seismicity arising from hydraulic stimulation of low to intermediate enthalpy porous reservoirs, by taking the geothermal reservoir of Groß Schönebeck (northern Germany) as study case. The aim is to evaluate the spatial and temporal distribution of 26 events, which were triggered by hydraulic stimulations in the volcanic section of the reservoir. The results from the THM simulations of this hydraulic stimulation are in agreement with the calculated overpressure and indicate that an increase in the reservoir fluid pressure is most likely responsible for the recorded micro-seismicity. Our current evaluation shows an increase of slip and dilation during the treatment on the seismic plane, of magnitudes close to the failure level as based on Mohr-Coulomb friction concept which would have led to a reactivation of the fault plane and related seismic activity.

We conclude this contribution by presenting a thermodynamically consistent framework to describe the deformation dynamics at the semi-brittle semi-ductile transition, thereby extending the classical mechanical analysis to faulting processes. We will focus on (i) the role of damage weakening and its impact on the evolution of localized deformation and (ii) the role of porosity evolution as precursor to dilatant brittle deformation. We will demonstrate how such a framework can bridge the gap between the microstructural evolution, expressed in terms of a damage intensity variable, and the macroscopic response of porous rocks subject to differential loading and in the presence of fluids.

Modelling dynamic rupture is essential to correctly describe the process of induced seismicity. Defmod, an open-source finite-element code featuring quasi-static loading, co-seismic volumetric strain, and dynamic rupture, is used to simulate the entire chain of induced seismicity, from pressure evolution due to fluid injection and extraction, building up of stress, and nucleation of dynamic faulting, to wavefield propagation towards the surface. To study induced earthquakes caused by fluid extraction, we modelled the behaviour of a 2-D poroelastic medium including a predefined fault by assigning a fluid source, either constant or varying, in a homogeneous reservoir layer to induce a pressure-field change. For each quasi-static step, the pressure field difference generates a displacement field that in turn affects the pressure through a coupling matrix, depending on Biot's coefficient. The rate of pressure variation is subject to the fluid source as well as the material properties, e.g., porosity and fluid mobility, which affect the speed and distribution of the stress build-up on the fault and thus the pattern of rupture nucleation. In addition, we implemented a predefined pressure profile to simulate the induced rupture in case of a uniform depletion of the reservoir to allow for a comparison with other studies. The results provide useful insights on the causality between reservoir-pressure behaviour and the induced seismicity.

Fluid extraction from subsurface reservoir sandstones frequently results in surface subsidence and induced seismicity, such as observed in the Groningen Gas field (the Netherlands). The cause lies in reservoir compaction driven by the increase in effective overburden stress. Deformation mechanisms in sandstone include instantaneous elastic deformation, inelastic, time-independent processes, such as critical grain breakage and/or compaction of intergranular clay rims, and/or creep due to stress corrosion and pressure solution. However, no physics-based models exist to predict inelastic reservoir compaction under in-situ conditions, limiting the ability to evaluate the impact of reservoir exploitation.

Deformation is driven by stresses transmitted across grain-to-grain contacts. Therefore, it is key to relate the grain-scale deformation mechanisms to grain-scale stress distribution, grain strength and deformation rate. These stress-strain relationships cannot be obtained experimentally. As a first step to obtaining such relationships, we performed 2D high-resolution (i.e. sub-micron) linear elastic Finite Element Method simulations on aggregates consisting of quartz, feldspar and/or intergranular clay, with porosities in the range 12-26%. We systematically investigated the effect of porosity and mineralogy, as well as aggregate texture (i.e. grain contact roughness, pre-existing flaws, large pores (i.e. voids) and grain packing), under boundary conditions relevant for the Groningen gas field (i.e. macroscopic vertical strain up to 0.2%, no lateral displacement).

Our fixed-displacement simulations (200 µm diameter grains, flattened contacts, cubic packing), showed compressive stress concentrations (σ₁ and σ₃) at contact edges, which increased in magnitude with increasing porosity, as opposed to the tensile stress concentrations expected for point contacts following Hertzian contact theory. Locally replacing quartz grains by feldspar showed no significant change in grain-contact or -volume stress. By contrast, the presence of intergranular clay rims, with a thickness of up to 10 µm, reduced the compressive stress concentrations at contact edges between quartz grains by a factor of three, while also reducing Bulk Modulus by up to 20%. In addition, our simulations particularly illustrated the effect of aggregate texture on local stress. As expected, grain contact roughness substantially increased the normal stress acting on contact asperities, while tensile stresses up to 60 MPa developed at the grain-contact ‘channels’. These stresses increased with increasing asperity amplitude and/or contact area. Locally enhanced tensile stresses were also observed at surface flaw tips and around larger voids in the aggregate. However, compared to a cubic-packed aggregate, the largest effect was observed for a hexagonal-packed aggregate, with tensile stress concentrations at inclined contact edges, which intensify with increasing porosity, and/or other textural changes. Our results suggest that rock microstructure and texture play an important role in controlling the grain-contact and -volume stress-strain behavior, which could lead to over/underestimation of the magnitude of local stress, hence the driving force for grain-scale deformation, if not adequately accounted for.

The Netherlands is subject to anthropogenic and natural subsidence with rates which are an order of magnitude higher than sea-level rise. Because one-third of the Netherlands lies below mean sea level, subsidence may threaten the country’s subsistence with major socio-economic consequences. Subsidence is a normal natural process but is overprinted and accelerated by anthropogenic activities which causes deep or shallow processes. Deep processes are caused by the extraction of hydrocarbons and salt, whereas shallow processes are primarily caused by lowering of phreatic groundwater levels. At present, the relative contribution of each process to total subsidence (i.e. natural plus anthropogenic) is unclear. Such information is important for stakeholders to support decision making on subsidence mitigation and it should be substantiated with independent scientific studies.

We present the outline of a hybrid Artificial Intelligence (AI) big data and model workflow to disentangle different subsidence forcing and we report on preliminary results for an area covering a gas field in the Friesland coastal plain and an area in the peat-rich central Rhine-Meuse delta plain. The proposed workflow is a hybrid approach between a knowledge-based physical model and machine-learning techniques. The big input data comprises a suite of static (structural model) and time-dependent subsurface data (phreatic groundwater level, reservoir pressure), and geodetic measurements. Geomechanical models provide the connection between the drivers (groundwater levels and reservoir pressures) and the surface movement.

In parallel, a Bayesian approach is developed solely coupling physics-based models for both deep and shallow processes and data assimilation techniques. Performances of both approaches, the hybrid AI and physics-based, are compared in the aim to achieve more accurate and more reliable spatiotemporal subsidence predictions for each subsidence forcing.

The issue of subsidence is one of the serious problems in the plains of Iran. Rafsanjan plain is also prone to this danger due to the high level of groundwater abstraction. In this study, an attempt has been made to study the extent and process of subsidence expansion over a period of time. For this purpose, ASAR and SENTINEL 1 radar images related to 3 four-year periods were prepared from Anar plain and PS-InSAR method was used to determine the amount of subsidence and its monitoring. The results show that between 2008 to 2012, the southern parts of the plain had an average subsidence of 10 cm per year, and between 2012 to 2016, the subsidence rate increased to 11.7 cm per year while between 2016 to 2020, the subsidence rate has increased more sharply and has reached 18.2 cm per year. Also, during these years, the area of subsidence has increased from 5,000 to 15,000 hectares and the subsidence trend has expanded to the northern parts of the plain. By preparing a map of groundwater level drop related to the last decade of the studied plain, it is determined that the areas that have subsided are completely consistent with the areas with more water table drop. Therefore, due to the increase in the cultivation of pistachio orchards in recent years and as a result of more use of groundwater, the rate of subsidence has increased.

With increasing energy and communication demands, and recent advances in technology, seafloor infrastructure becomes more abundant. For instance, a global network of seafloor cables transfers >99% of digital data traffic and breakage of those cables can disrupt financial trading, communications and internet connections. Cables that cross submarine channels are particularly vulnerable to breaks by powerful avalanches of sediment, called turbidity currents.

Assessing geohazards in these systems is difficult due to limited mapping or monitoring. Submarine canyons and channels cannot be monitored using satellites, hence we rely on offshore expeditions to these often-remote systems and use acoustic instruments like multibeam echosounders to map them. The resolution of such mapping is often much lower compared to their on-land counterparts. These resolution issues, coupled with a paucity of repeated surveys, limit our understanding of how these systems evolve over time.

Here we present the most detailed time-lapse imagery of a deep-sea submarine channel yet. We use these data to demonstrate the power of high resolution time-lapse mapping of the seafloor, and show how a new process controls how submarine channels evolve. The upstream-migration of steep steps in the channels, called knickpoints, can fundamentally reshape the channel. This process bears similarities with waterfalls and their migration in rivers, but the rate and scale of migration is much greater. These new insights have important implications for understanding how other deep-sea channels evolve and for assessing hazards posed to critical seafloor infrastructure that support our day to day lives.