Diagenesis modelling as a tool to prevent drilling tight geothermal sandstone reservoirs

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Abstract

The Danish subsurface holds a vast geothermal resource residing in porous sandstones that are widely distributed geographically and stratigraphically, and therefore have the potential to supply heat to the district heating networks located in many Danish cities. The reservoir depths vary greatly due to differential effect of burial and uplift episodes resulting in varying degree of compaction and cementation of the sandstones, since some of them have been exposed to high temperature and pressure. Therefore, it can be challenging to predict the reservoir quality (and thus the economic profitability) of the sandstones in the subsurface as the reservoir properties may have been deteriorated or damaged by diagenetic alterations during deeper burial in the past. To investigate this geological risk, diagenesis modelling is used to map out and evaluate the degree of cementation and thereby prevent the costly drilling of tight geothermal sandstone reservoirs henceforward.

The diagenesis modelling is built on rigorous knowledge of the processes that cause alteration of the composition and reservoir properties of sandstones during burial. Input parameters to the model comprise mineralogical data, petrographic measurements, core analysis data, provenance information, and burial histories to calibrate the model to the reservoir-specific characteristics. The burial histories provide the estimated depth, temperature, and pressure development of the sandstones through geological time, which is calculated by basin modelling calibrated using mineralogical and organic temperature constraints. The present-day reservoir depth, thickness, and distribution are known from seismic interpretation and wireline logs. Sedimentological investigations of drill cores combined with sequence stratigraphic correlations are used to determine the range in depositional environments as well as the regional facies distribution.

The forward diagenesis model results are applied to create regional reservoir property maps based on the paleogeographical reconstructions at selected Late Triassic – Early Jurassic time-slices representative for the depositional setting of the Gassum Formation, being the main reservoir. The resulting simulated geographical distribution of porosities and permeabilities can be used to optimize the placement of new wells. The results show that the sandstones are appropriate for geothermal exploitation in many areas, though with a large variation in reservoir properties that must be considered when determining the feasibility of each new geothermal project.
Original languageEnglish
Publication statusPublished - 2022
EventEuropean Geothermal Congress 2022 - Berlin Congress Center, Berlin, Germany
Duration: 17 Oct 202221 Oct 2022

Conference

ConferenceEuropean Geothermal Congress 2022
Abbreviated titleEGC
Country/TerritoryGermany
CityBerlin
Period17/10/2221/10/22

Programme Area

  • Programme Area 3: Energy Resources

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