Accueil > EGW 2018 : 6th European Geothermal Workshop > Abstracts > Session 1 : Assessment of Geothermal Resources > Session 1 : Oral Presentations

Session 1 : Oral Presentations

KEYNOTE Geothermal assessment : a regional approach, available tools and research frontiers

Eugenio Trumpy, Adele Manzella

PDF - 360.9 ko
Trumpy and Manzella

Geothermal energy is seldom considered in energy planning at national and regional levels in Europe and worldwide. Principal reasons are the relative lack of specific incentives and the rather difficult and lengthy regulation, which add to the risk related to the development of a project. A fundamental aspect of any energy policy and investment is the certainty around assessment of the energy resources, including geothermal. Therefore, a key requirement for further exploiting geothermal energy by increasing the number of projects as well as the variety of uses is to clearly identify and rank resources and opportunities.

To minimize the exploration risk and the cost for reservoir development on one hand, and to maximize the profitability and the reservoir sustainability on the other hand are key objectives of the Sub program “Assessment of Geothermal Resources” in European Energy Research Alliance – Joint Program on Geothermal Energy (EERA-JPGE).

The assessment of geothermal resource is a recursive and scale-based process. The integration of existing data allows to identify the most perspective areas, on which exploration activities have to be consequently carried out to obtain new and more detailed data. Therefore, a new and refined resource evaluations guarantee a higher accuracy level of the geothermal resource knowledge. The same recursive approach can be applied from the continental scale up to the local (lease area) scale of investigation. Naturally, different scales imply different data typology and detail.

The investigation and assessment of geothermal resources rely not only on direct underground geological data, mainly from wells, but also require their integration, with indirect sources, from geological, geochemical and geophysical surveys and remote sensing data. The integrated analysis and visualization of multiple types of datasets, also in a tri-dimension way, improve and constrain the exploration.

Historically, maps of terrestrial heat flow and of temperature distribution at different depths were used to pinpoint areas potentially important for geothermal development. Recently a more accurate resource mapping is required not only by stakeholders for the preparation of feasibility study and the documentation for research and permit leases or to compare technical reports but also by administrations and associations for preparing regulations and dissemination of information and opportunities.

Mainly at continental and regional scale, Geographical Information Systems (GIS) software provide tools for the spatial analysis of multiple parameters to assist selection of prospective sites, based on pre-defined criteria. The concept of favourability is currently widely used in literature as a fully integrated analysis able to classify the most interesting prospecting areas. In applying GIS tools, the conceptual model plays a crucial role in the choice of layers (parameters) that will be involved in the favourability map computation. The layers are usually ranked and weighted using statistical criteria or estimated on the basis of expert opinion, referred to as “data-driven” or “knowledge-driven” models respectively. Favourability maps should be not confused with the geothermal potential maps, which provide a quantitative assessment of the geothermal resources.

Various approaches, taking into account data from deep regional reservoirs (e.g., temperature, petrophysical parameters and flow properties) based mainly on hydrocarbon industry data, have been used to calculate the geothermal potential and to provide a major resource base of geothermal energy for direct heat and power production. Currently, the geothermal community is working on defining a common protocol to estimate performance by using coded parameters and to reduce mining risk.

Data access is an important step to help scientists, stakeholders, investors and geothermal developers, and the basis for a more accurate resource assessment and feasibility studies. Although many initiatives in Europe collect and organize geothermal data for different purpose and at different scale, usually this information is not easily accessible for different reasons (i.e., authorizations and licences, format and data type, …). For example, scientists, operators or consultants organize and use geothermal databases, which contain underground data and provide maps (e.g. temperature and heat flow distributions), which are seldom accessible to the public. Regional, national and European administrations produce, collect and organize regulations, documents, reports, descriptions and maps of geothermal leases and authorizations, together with energy production values. Promote the access to geothermal information at the European level via the development of an Information Platform, creation of standard and common data model at EU level and harmonization of national data to speed up data discovery and mining is considered a priority for the next future.

Towards a porosity-independent permeability update model for large-scale reactive transport simulations

Joan Delort Ylla, Allan M.M. Leal, M.O. Saar

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Delort Ylla et al.

We present a new permeability update model when mineral dissolution and precipitation reactions are considered in continuum reactive transport simulations in porous media. The model is independent of porosity and formulated such that permeability changes occur across the faces of the discretized cell elements, rather than on their center nodes as is usual in the literature. Each face in the mesh is assumed to have a connecting channel along which the fluid flows from one cell to the other and reacts with the surrounding minerals. Initial aperture values for these channels are assigned in a way that consistently reproduces the desired initial permeability field. As the fluid flows and reacts along these channels, these apertures change and so does their intrinsic permeability. The proposed permeability update method has been tested in a 1D reactive transport problem in which CO2-saturated brine flows through a column of porous rock composed of 90% quartz and 10% calcite (volume composition). As expected, calcite is dissolved at the entrance and re-precipitates in the middle of the core, where a temperature step is empirically imposed. Our novel permeability update model behaves in a similar fashion to Kozeny-Carman-like models when permeability decrease is caused by mineral precipitation. This result shows the difficulty of implementing a permeability update model truly independent from the size of the discretized cell elements. We found however promising ideas that might be worth investigating in the future.

Geothermal potential of Anticosti sedimentary basin, Canada

Violaine Gascuel, Karine Bédard, Félix-Antoine Comeau, Jasmin Raymond, Michel Malo

PDF - 392.9 ko
Gascuel et al.

The Anticosti Island, like most remote regions of Canada, relies entirely on fossil fuels for energy consumption. As an effort to diversify energy sources and reduce greenhouse gas emissions, a first estimate of the geothermal potential of the Anticosti sedimentary basin was done, considering both electricity production and direct heat use. Geothermal resource quantification was achieved through a numerical heat transfer model based on a 3D geological model, simulating heat conduction in the Earth’s crust (Bédard, Comeau et al. 2014).

The Anticosti sedimentary basin consists of an upper Ordovician to lower Silurian carbonate platform, which unconformably overlies the Precambrian basement. A 3D geological model of the basin, integrating data from 24 oil and gas exploration wells and public seismic lines, was initially built with eight distinct geological units : Romaine, lower Mingan, upper Mingan, Macasty, lower Vauréal, Upper Vauréal-Ellis Bay-Becscie , Merrimack and Gun River-Jupiter-Chicotte. These units are manly composed of limestone and shale, with dololstone at the base of the sequence, and sandstone in the eastern part.

Thermal conductivity of the geological units as well as internal heat generation rate were derived from geological and well logs, with a theoretical value for each weighted lithology composing the units.

The undisturbed ground temperature near surface, used as a first type boundary condition for the 3D numerical model, was calculated from meteorological data using (Ouzzane, Eslami-Nejad et al. 2015) global correlation. A constant heat flow of 15mW/m2 was established at the base of the model at 40.5km (Moho depth) as a second type boundary condition. Available bottom-hole temperature data were corrected for drilling disturbances, considering time since circulation stopped according to the method of Waples and Ramly (2001), and for paleoclimatic effects. Terrestrial heat flow and a heat generation of the Precambrian basement were calculated analytically at the location of the 24 wells, according to 1D temperature modeling and assuming the same heat flow at Moho depth. Basement heat generation values were interpolated in 2D and included in the model for the corresponding layers. Vertical side boundaries were considered adiabatic and heat convection was neglected due to a lack of reliable data to constrain flow properties and boundary conditions.

The 3D heat conduction model was solved in steady state with the finite element method using Feflow.

Results show that a temperature of 120 °C, which is considered the lower value needed for an efficient binary geothermal power plant, can be reached between 4 to 5.4 km depth in the Precambrian basement. The most promising temperature anomaly is located in the southeastern part of the island, reaching 120 °C at 4 km depth. However, it is a barely populated area, so the potential for the development of a geothermal plant in the near future is inexistent. The most populated area of the island is the locality of Port-Menier in the northwestern part of Anticosti. A temperature of 120°C is reached at a depth of about 5 km below this locality. Direct geothermal energy use to heat building appears more feasible, with a temperature of 57°C reached at a depth of 2.1 km at the base of the sedimentary basin, which corresponds to the dolostone of the Romaine Formation having a relatively high permeability, reaching more than 10 mD according to Glover (2003).

Future work perspectives include laboratory analysis to measure thermal and hydraulic properties of rock samples from all lithologies. These values could be up-scaled using knowledge of the stratigraphy to improve the numerical model defining geothermal resources.

Interdependencies between physical, design and operational parameters in a two doublet configuration for direct use geothermal heat

Alexandros Daniilidis, Hamid Nick, David Bruhn

PDF - 562.6 ko
Daniilidis et al.

The increase of renewable energy supply is a main objective at several levels of governance. Geothermal energy has a substantial potential for supplying renewable heat for direct-uses. Nonetheless, high upfront costs and marginal profits can hamper the development of deep, direct-use geothermal energy projects (Daniilidis et al., 2017). Therefore, the necessity arises to improve energy extraction and economic output. Understanding the options for this improvement requires a systematic analysis of this complex system.

The interference between doublets was found to be beneficial when injector and producer wells of adjacent doublets are alternating and the Net Present Value (NPV) is improved when doublet spacing equals well spacing(Cees J.L. Willems et al., 2017). Moreover, reducing well spacing allows for more doublets to be installed within the same license area (C. J.L. Willems et al., 2017).

In this work we present a synthetic Hydraulic-Thermal (HT) model using the Finite Element Method (FEM). The model includes two doublets separated by a fault. The reservoir part has a thickness of 150m and comprises of three layers with equal thickness and different flow properties. Basement and overburden impermeable layers with a minimum thickness of 250m provide conductive recharge to the reservoir. A range of well spacing and placement, layered reservoir and fault flow properties, as well as fault throw parameters are considered in the analysis. The parameter space is selected to be representative of direct use geothermal systems in conduction dominated geological settings (Moeck, 2014). All parameter combinations are simulated for 50 years.

The cold front breakthrough is monitored separately for each doublet, while different thresholds for the cold front definition are also considered. Additionally the total produced energy and the NPV are evaluated for each doublet and the system overall. The insights from this analysis improve the understanding of interdependencies between physical and operational parameters with respect to produced energy and economic output. Results from the synthetic models can serve as guidelines to reducing the considered options in full scale field models.

3 octobre 2018