University of Twente Student Theses
Identifying the Mineralogical Influences on Porosity-Permeability Variation in Sandstone, Using Short-Wave Infrared Spectroscopy : Implications for Geothermal Potential in Twente
Kulugammana Rankeththegedara, Palinda Mahasen Wickramasinghe (2024) Identifying the Mineralogical Influences on Porosity-Permeability Variation in Sandstone, Using Short-Wave Infrared Spectroscopy : Implications for Geothermal Potential in Twente.
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| Abstract: | Geothermal energy development requires specific subsurface conditions to realise the resource economically. Geothermal energy is gradually becoming popular and developing as a clean, sustainable power source in the Netherlands. The Twente region in East Netherlands also carries out geothermal explorations focusing on the sandstone reservoirs in the Tubbergen Formation, which has been identified as having geothermal potential. Existing drillhole data from extensive hydrocarbon explorations within the region suggest that the porosity and permeability of the Tubbergen sandstone are highly variable, posing a risk for successful geothermal developments. Publicly available scientific information on the porosity-permeability variation is extremely rare to find. Thus, the current research used infrared spectroscopy techniques to reveal the mineralogical factors affecting the Tubbergen sandstone's porosity-permeability. The study is based on the porosity-permeability data from two drill holes (Fleringen 1/FLN and Reutum 1/REU) located north of the University of Twente. Porosity-permeability data was measured on drill core plugs obtained from the depth levels of Tubbergen sandstone layers. The porosity vs permeability plot of the drillhole data shows two distinct trends. FLN samples create one trend while REU samples show another trend with relatively higher permeability values for the same porosity than FLN. The same core plugs were used to acquire shortwave infrared (SWIR) hyperspectral data and analyse the mineralogy to compare it with porosity-permeability data to identify the relationships between the two petrophysical properties and mineralogy. SWIR data was mainly studied using principal component (PC) analysis. The first 12 PC bands were selected for useful information and to conduct further analysis. Mean PC values from each band for each sample were compared against porosity-permeability value to recognise the PC bands, which shows a trend with petrophysical properties. Identified PC bands were further analysed by comparing the image spectra from PCs' dark and bright pixel locations. Brightness intensity (albedo), kaolinite crystallinity (KC), illite/kaolinite relative proportion, and siderite were identified with SWIR data as the controlling factors of porosity permeability. Since PC bands can consist of multiple spectral information, band math operations were used to clarify the effect of individual factors. Mean values of the band math operations for each sample were compared against the porosity and permeability to identify the relationships. Finally, it is revealed that high KC and siderite cause a reduction in porosity, while high illite to kaolinite relative proportions reduce both porosity and permeability. Albedo variation distinguishes the abundance of feldspar-quartz relative to clay, with high and low albedo values, respectively, and indicates a positive relationship with the porosity. As the next step, mineralogical factors were visualised on the SWIR data with linear spectral unmixing, using spectra of siderite, high KC kaolinite, low KC kaolinite, and illite as endmembers. Spectral unmixed results were visualised as RGB colour composite. Endmember distributions showed that illite content in REU is relatively low compared to FLN, which explains the high permeability values of REU samples. |
| Item Type: | Essay (Master) |
| Faculty: | ITC: Faculty of Geo-information Science and Earth Observation |
| Subject: | 38 earth sciences |
| Programme: | Geoinformation Science and Earth Observation MSc (75014) |
| Link to this item: | https://purl.utwente.nl/essays/103750 |
| Export this item as: | BibTeX EndNote HTML Citation Reference Manager |
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