Boom Clay: Integrating Data and Upscaling Using Geostatistical Techniques

Belgian agency for radioactive waste and enriched fissile materials BOOM CLAY: INTEGRATING DATA AND UPSCALING USING GEOSTATISTICAL TECHNIQUES. TRANSFERABILITY OF REGIONALIZED VARIABLES N. Jeannée (Geovariances) With a contribution of A. Berckmans NIROND-TR 2012-01 January 2012 ii NIROND–TR 2012-01, January 2012 ONDRAF/NIRAS NIROND-TR report 2012-01 CATEGORY B&C Boom Clay: Integrating data and upscaling using geostatistical techniques. Transferability of regionalized variables N. Jeannée (Geovariances) With a contribution of A. Berckmans January 2012 NIROND–TR 2012-01, January 2012 iii The data, results, conclusions and recommendations contained in this report are the property of ONDRAF/NIRAS. The present report may be quoted provided acknowledgement of the source. It is made available on the basis that it will not be used for commercial purposes. All commercial uses, including copying and re-publication, require prior written authorisation of ONDRAF/NIRAS. This report is a joint report of GEOVARANCES and ONDRAF/NIRAS ADDRESS of GEOVARANCES: 49bis avenue Franklin Roosevelt, BP 91 77212 AVON Cedex, FRANCE Contact person at GEOVARIANCES: [email protected] Contact person at ONDRAF/NIRAS: [email protected] ONDRAF/NIRAS Kunstlaan 14 BE-1210 BRUSSELS www.nirond.be Registration of copyright iv NIROND–TR 2012-01, January 2012 Document Datasheet Title Boom Clay: Integrating data and upscaling using geostatistical techniques. Transferability of regionalized variables Subtitle Project Safety and Feasability Case -I Author(s) of the document Reviewer(s) of the document Nicolas Jeannée (Geovariances) Arne Berckmans (ONDRAF/NIRAS) Laurent Wouters (ONDRAF/NIRAS) Jean-Paul Chilès (MinesParisTech) Jacques Deraisme (Geovariances) Series CATEGORY B&C Publication date 2012-02 Document type NIROND-TR Review status Version 1 Status Open Revision number 1 ONDRAF/NIRAS NIROND-TR 2012-01 Subcontractor NOCA-2006-2427 number of report reference number 251-A41 ISBN NA Total number of 119 pages Approver(s) of the document Maarten Van Geet (ONDRAF/NIRAS) NIROND–TR 2012-01, January 2012 v vi NIROND–TR 2012-01, January 2012 Integration Module The Boom Clay Formation is situated in the North-East of Belgium (Province of Antwerp and Limburg) gently dipping at 2 degrees from the outcrop up to a depth of 400m at the Dutch border. It is considered by the Belgian Agency of Radioactive Waste and Fissile Materials (NIRAS/ONDRAF) as a reference host formation for the construction of a disposal system of high and medium-level and/or long-lived waste (B&C waste according to the Belgian Classification). This waste is characterized by a high initial radionuclide concentration and by decay heat emission. In order to evaluate this reference formation a Safety and Feasability Case study is under development. This study verifies the validity of a set of safety statements that, if demonstrated, assure the safety of man and the environment on the long-term. One of these statements requires that the disposal system provides passive long-term safety if implemented according to design specifications. This can be translated into the requirement that the disposal system delays and attenuates radionuclides and other contaminants to the environment as long as required. The latter implies that one should prove that diffusive transport is by far and mainly the only vector by which radionuclides and other contaminants migrate in the host formation. Diffusive transport implies furthermore that the formation has a fine and homogeneous pore structure which results in a low hydraulic conductivity and a hydraulic gradient that is very low. This diffusive transport condition was demonstrated, in a large section of the Boom Clay package at the data gathering locations, by a large set of data collected over the years through destructive and non-destructive methods (data from boreholes, underground and surface lab- tests as well as geophysical logs). Still some uncertainty exists on whether the diffusive transport conditions are valid in the entire region where the Boom Clay occurs. This leads to the question on whether the values of variables of interest related to the characteristics of the Boom Clay Formation itself measured in detail in the Mol area and at other borehole locations are extendable (transferable) to the wider zone of the Boom Clay basin. The transferability of the knowledge obtained at the borehole data throughout the entire basin or a large zone is an exercise that can be conducted through geostatistical methods. The overall objectives of this geostatistical study are fourfold: . Firstly, give an indication of the transferability of data (with error_uncertainty maps) from the Mol area and other (borehole) locations to the whole extension of the Boom Clay zone . Secondly to apply geostatistical techniques to achieve upscaling of designated variables (additive such as granulometry or non-additive such as permeability) NIROND–TR 2012-01, January 2012 vii . Conduct simulations (1 and 3D) and do a faciesmodelling exercise on the entire Basin. Advise NIRAS on the optimization of future drilling and sampling campaigns The objectives were realised by applying the following methodology: . Data collection & extensive data analysis including a recalibration of all data to a relative depth level as well as comparing data of different campaigns . Spatial analysis & change of support modelling for additive and non-additive variables - upscaling. Estimation of designated regionalised variables (K heterogeneity, diffusion parameters) using the appropriate geostatistical techniques. Conditional simulations using the Turning Bands algorithm with Gaussian anamorphosis on 1D level The 3D conditional simulations and faciesmodelling could not be performed due to a lack of data (only 5 boreholes available for the whole basin). The study resulted in the following conclusions: . The ability of geostatistics to provide a suitable framework for analyzing the transferability of these regionalized variables. The database presents an important heterogeneity level and covers only scarcely the large area of interest. Classical statistics are obtained for hydraulic conductivity and diffusion parameters. Correlation and variogram analysis helped in better understanding the relationship between variables and the vertical variability of target parameters. The use of geostatistical techniques highlighted the areas that show the largest errors on the estimation and thus are target zones for further sampling campaigns. Meaningful vertical estimation of target parameters have been obtained on sampled boreholes by applying classical geostatistical algorithms (kriging/cokriging), together with an estimate of the associated uncertainty. The quality of the estimates is largely improved by the use of auxiliary variables: geophysical logs (Gamma Ray and Resistivity) and grain size data. However, very different spatial variability is present if we address either the entire Boom Clay or just focus on central units (Putte and Terhagen). 3D modeling has been performed to capture regional vertical and lateral trends over the area of interest. Due to the global dipping and thickness increase of the Boom Clay towards the North-East, this 3D modeling required a preliminary horizontalization, in order to laterally correlate consistent data. The Double Band has viii NIROND–TR 2012-01, January 2012 been chosen as a reference as it can be easily identified, even on boreholes that have not been cored. An uncertainty envelope has been derived for K modeling, providing a confidence interval for possible Kv/Kh values throughout the Boom Clay. This 3D modeling has not been performed for migration parameters due to the insufficient number of borehole samples. The study resulted in the following recommendations: . In order to decrease the uncertainty on Kv/Kh, there is a need for an additional cored/sampled borehole in the under-sampled central part of the Boom Clay, around Sint-Lenaarts (not cored); the location of this additional borehole can be supported by using the kriging standard deviation results, which show higher uncertainty values in this area. Also, a cored borehole more towards Mol would allow validating a regional K trend, with decreasing K values when moving towards Mol and increasing variability in Putte and Terhagen when moving towards Weelde; this borehole could be ideally placed at the gravity center of a triangle joining Weelde, Zoersel and Mol. This recommendation is consistent with Yu et al. (2011), where it is stated that “the impacts of compaction (burial depth) and lithology on the lateral variation of hydraulic conductivity need further investigations at the region scale”. The importance of good quality geophysical logs (Gamma Ray and Resistivity) has been reminded: quantitative consistency and repeatability between logging campaigns, similarity of tools. Grain size gives a good indication on K at the location of the core only and does not allow a sound prediction of K values at neighboring locations. There is thus a limited added value of using grain size data in terms of K spatial prediction (extrapolation) throughout the Boom Clay because of the small-scale variability of both K and grain size due to the silty/clayey beds. But because the statistical correlation between specific grain size with K values is so good, precise Kv/Kv estimates can be done using the grain size measurements on other locations where Kv/Kh was not measured. Finally, multiplying the analysis of K samples vertically throughout

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