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The geothermal industry has extensively used clay minerals as indicators for changes in temperature and circulation zones in geothermal systems. The latter includes marking the extent of the reservoir section and permeability within the system. Methylene blue (MeB) stain test value and geophysical resistivity data are often the primary tools to locate the reservoir section, especially in the early geothermal exploration stage. The reservoir section is marked by delineating the encompassing clay cap based on the distribution of smectite clay, indicated by a higher MeB value and the existence of a conductive layer. In this paper, we compare the MeB and magnetotelluric (MT) resistivity values with the clay minerals content of rocks, among others, smectite. Whereas the identification of clay mineral composition has typically relied on X-ray diffraction (XRD), we used three analytical methods (i.e. non-imaging infrared spectroscopy (IRS), infrared imaging spectroscopy (IRIS), and XRD). Our research used extracted clay fraction of ground cuttings and the original cuttings taken from the Rantau Dedap geothermal system in Sumatra (Indonesia). The IRS and XRD analyses were done on the same clay fraction, first on air-dried fraction and then on the ethylene glycol treated fraction, while IRIS was done on the original cuttings. The clay minerals identification from the three analytical methods showed similar results. Then, the comparison with MeB test results showed that smectite has the most effect on this test results, followed by mixtures of smectite-chlorite and smectite-illite. The MT resistivity value is a function of clay mineral types and lithology. Different types of clay are associated with varying resistivity ranges; from lowest to highest are smectite, mixtures between smectite and chlorite/illite, kandites, illite and chlorite. Comparing clay composition and MeB and MT resistivity data has given a better understanding of the reservoir location in Rantau Dedap.

Infrared spectroscopy is a non-destructive mineralogical analysis with minimum sample treatment required. The mineral identification in this method is based on the energy reflected by molecular vibrational processes upon incoming infrared radiation which is a proxy for mineralogy and mineral chemistry. With this method, we can identify minerals that are difficult to distinguish using some other methods (i.e. methylene blue stain test, binocular microscopy, and petrography), particularly clay minerals which are the important temperature indicator minerals in geothermal systems. Therefore, it is a promising mineralogy analytic method to be applied in geothermal subsurface samples. However, the application of the method in geothermal studies is still limited, especially the recently-developed infrared imaging spectroscopy (IRIS), which is the extension of the conventional (non-imaging) infrared spectroscopy. This paper reviews the current use of infrared spectroscopy for geothermal exploration and present preliminary results of our work using infrared imaging spectroscopy. Our preliminary results show that infrared imaging spectroscopy can identify much more minerals compared to non-imaging infrared spectroscopy, including minerals which are present only in a small amount. Spatial relationships between hydrothermal alteration minerals might be visible in bigger cuttings grains. However, the initial mineral map classification using Spectral Angle Mapper (SAM) shows that it is difficult to determine the threshold which will give an accurate assignment of minerals.

The Geothermal Capacity Building program GEOCAP, a bilateral program (6MEURO) between Netherlands and Indonesia, has been running since 2013 and is foreseen to continue until 2022. In this public-private partnership we thus have a decade of experience which we share in this session. The session addresses sustainable solutions for geothermal exploration including environment friendly methods, looks at the synergy between surface and subsurface exploration methods, and how to upscale local geologic information to regional prospectivity. In this risk analysis and mitigation, geology as well as economy and the environment are integral components of a multi-disciplinary workflow developed by GEOCAP. Methods for modern exploration of geothermal resources include those derived from remote sensing and earth observation, 3D subsurface/surface (thermo) GIS and modelling, geophysics, geochemistry and engineering. We explore synergies between exploration methods directed towards derisking operations and increasing drilling success rates. In this session through Q&A and open discussion we intend to identify scientific white spots, leading to a preliminary science and policy agenda for future bilateral collaboration on geothermal exploration and education. By emphasizing the focus on (solving) real-world problems we feel there is broad scope for the private sector participation in the session and in setting the agenda. Our target audience are geoscientists, policy makers and private enterprises. This session emphasizes the use of remote sensing public domain images (SAR and thermal) for geothermal exploration, especially in high enthalpy volcanic geothermal systems which generally have significant surface manifestations and are mostly controlled by geological structures, both primary and secondary structures. Some of the developments in remote sensing techniques and methods that have been carried out and the case study of remote sensing analysis in geothermal exploration will also be presented as learning and discussion materials.

Geothermal Energy (GE) is the natural heat energy stored in the rocks and water in the Earth’s interior. GE is a green renewable energy source as compared to conventional sources such as fossil fuels. It provides long-term energy with lower carbon footprint than other renewable energy. However, corrosion and poor or low permeability in geothermal systems are the pervasive issues. Corrosion affects the major components up- and downstream. Corrosion caused by biotic factors is difficult to forecast compared to abiotic corrosion. For that reason, the influence of microbial metabolites on the electrochemical kinetics of carbon steel –biotic corrosion requires thorough investigation. Also, poor or low permeability in geothermal reservoirs is a perennial concern even in highly convective geothermal systems. Techniques typically used in oil and gas reservoirs to enhance reservoir quality can be used in geothermal reservoirs. For example, increasing permeability helps to create heat convection and allows better heat flow from the subsurface to the surface. Acid stimulation can be used to increase permeability however, acid stimulation sometimes fails due to either poor stability of the acid or undesirable interaction between clay minerals in the cap rock and the acid. In this study, bio-corrosion and acid stimulation are studied under simulated non–volcano geothermal conditions. The influence of Extracellular Polymeric Substrates (EPS)-biofilm, acetic and L-ascorbic acids on bio-corrosion are investigated. The electrochemical techniques (PotentioDynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS)), Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES), X-Ray Diffraction (XRD) and pH measurements are implemented in characterization. Subsequently, the interaction of green chelating agents (BCA-1 and BCA-2) and clay minerals (kaolinite and smectite) under CO2 flooding are studied. The research shows that the simulated EPS–biofilm under anaerobic conditions has no influence on accelerating corrosion which is in contrary to results reported in some literature. In addition, the presence of acetic and L-ascorbic acid accelerates corrosion on test coupons. The increase in corrosion rate with acetic acid is in agreement with the available literature while that with L-ascorbic acid contradicts. On the other hand, results on compatibility of clays with green chelating agents show that both have low precipitate of minerals. This makes both green chelating agents suitable for improving the reservoir quality as they have limited reactions with clays. This is the first time to report these findings on BCA-1 and BCA-2. Understanding the influence of metabolites on corrosion enables the development of better strategies to avoid or decelerate corrosion. Moreover, understanding compatibility of clays and green chelating agents would help to increase porosity and consequently permeability

Geothermal energy (Figure 1) is a green renewable energy source that h as potential to provide long-term energy with lower carbon footprint and maintenance costs than other renewable energy. A large portion of the world’s geothermal reserves is in sandstone reservoirs often characterized by quartz grains cemented with clays. Clays form also often the impervious boundary of the reservoir rock, the so-called caprock. Many geothermal reservoirs tend to lose permeability over time during production, therefore techniques are applied to enhance the reservoir quality in terms of fluid permeability. Partial dissolution of sand grains in the reservoir is a possibility to increase porosity and consequently permeability. However, the fluids used for dissolution should have limited reactions with the cementing clay minerals as this would cause collapse of the sandstone grain skeleton reducing permeability. Biodegradable chelating agents (BCA) compared to conventional chemicals (HF and HCl) have little reaction with clay, but can dissolve the sandstone grains; hence green chemicals could be effective for enhancing reservoir quality. The emission of dissolved CO2 from geothermal water becomes more of an issue recently. Biodegradable chelating agents could reduce CO2 emission since they offer high chelating capacities on a large variety of minerals including calcium-rich minerals. Calcium has the capacity to bond with CO2, proving to be effective for CO2 sequestration.

Spatial solutions play an increasingly important role in meeting many of humankind’s complex challenges, such as climate change, population growth, and related claims for sufficient and secure food, water, energy, health, land and housing provision. Earth observations and geospatial technology are rapidly changing society everywhere − mobile, sensor and internet revolutions are touching Africa and Asia equally forcefully. Entrepreneurship and innovation are new aspects in capacity development activities. Many capacity building efforts focus on individuals while sustainable impact requires focus on organizational change and supranational coordination. Over the past several decades, many regional centers have been established for capacity building in Earth observation in developing countries and emerging economies. ITC of the University of Twente is an international knowledge hub in geospatial sciences, with an emphasis on collaborative educational and research activities in geo-information science and Earth observation and participation of students from around the world. SERVIR is a partnership of NASA, USAID, and leading regional technical organizations that develops innovative geospatial solutions to improve livelihoods and foster self-reliance across a global network in Asia, Africa, and the Americas. In this presentation, ITC and SERVIR will provide examples of and lessons learned from our activities and networks to strengthen the capacity and use of Earth observations in the developing world.

This paper provides an overview of geologic remote sensing applied to geothermal resource characterization in the context of the work ITC is doing.

Active interest by the exploration industry with multi-spectral VNIR-SWIR WorldView-3 (WV-3) imagery has been evident since its launch in August, 2014. Pre-launch simulation studies by Kruse and Perry (2013) and later comparison between resampled AVIRIS and WV-3 by Kruse et al. (2015) demonstrated its mineral mapping potential, using the well published hydrothermal test site at Cuprite, Nevada. Subsequent validation studies by Sun et al. (2017) tested WV-3 for its alteration discriminating within the Pobei area, Xinjiang Uygur, NW China. In this same area, Ye et al. (2017) also undertook a validation WV-3 study using 1:100,000 geological mapping and comparisons with ASTER. Neither study at Pobei undertook field sample spectroscopy. In this current validation study using the Rodalquilar epithermal setting in Spain, WV-3 mineral mapping results were compared with those obtained using resampled HyMap and ASTER imagery. In addition, WV-3 derived spectral signatures were compared with ASD spectrometer field observations of various homogeneous ground sites collected simultaneously with the WV-3 acquisition. Comparison between the WV-3, HyMap, ASTER map products were generated using Cudahy (2012) and Sun et al. (2017) band parameter indices for mineral(group)s including kaolinite, AlOH, MgOH, ferrous iron content in MgOH/carbonate, and jarosite. Compositional results generated with ASTER appeared to be noisy and less intense within the Rodalquilar study area. By comparison, Worldview-3 showed spatially coherent patterns and extents that were more comparable with the lithologies and alteration zonation’s published previously by Arribas et al. (1995). Overall, the results show that the combined WV-3 VNIR- SWIR image spatial resolution of 7.5m showed improved discrimination than those derived from equivalent ASTER’s spatial resolution of 30m. Compositional products derived from band parameters designed by Cudahy (2012) generally also gave better results than those from Sun et al (2017) at Rodalquilar. Comparison of the WV-3 surface reflectance product and the field spectral signatures showed a close resemblance for the exposed homogeneous car park targets when using a series of multiple transect grid like observations. Other field observations of various beaches, limestone outcrop exposures and mine-site spoil piles were also examined. Ongoing postgraduate Masters studies are currently being undertaken studying such target ASD spectral field observations and comparisons with the results from variable atmospheric processing and modelling of the WV-3 radiance imagery.

Element maps from the gamma-ray spectrometer (Boynton et al., 2007) are difficult to interpret because of its low spatial resolution. Here, it is attempted using NIR summary products, at higher spatial to predict the element concentration. Such a model could give new insights which geological processes relate to the distribution iron, potassium, thorium, chlorine, silica and water.

Monitoring of soil aggregate breakdown remains, even at the micro-plot scale, a challenge. Remote sensing has shown its potential to assess many different soil properties and is a fast and non-destructive method to investigate soil susceptibility to water erosion. We designed an outdoor experiment to monitor soil aggregates breakdown under natural rainfall at a micro-plot scale using a regular camera. Five soils susceptible to detachment (silty loam with various organic matter content, loam and sandy loam) were photographed once per day. We collected images and rainfall data from November 2014 until February 2015. Considering that the soil surface roughness causes shadow cast, the blue/red band ratio is used to observe the soil aggregates changes. In addition, a Gray Level Co-occurrence Matrix (GLCM) is used to extract the image texture entropy which reflects the process of soil aggregates breakdown. In our research the entropy calculated at 135 degrees along the direction of shadows gives best results. Our results show that both entropy and shadow index follow the wetting and drying cycles with a decrease due to a rain event. This decrease is small due to low rainfall intensity ( -1 ) for the entire period that the experiment ran. However, the biggest rain event of 20 mmday -1 resulted in a decrease in entropy, meaning that sufficient rainfall energy was present to trigger the soil aggregates break down. This research concludes that both entropy and shadow index obtained with a regular camera enable the monitoring of soil aggregate breakdown at a high spatial resolution.