Multivariate and spatial statistical analysis of Callovo-Oxfordian physical properties from lab and borehole logs data: Towards a characterization of lateral and vertical spatial trends in the Meuse/Haute-Marne Transposition Zone

The geological exploration of the Meuse/Haute-Marne area began in 1994. Several boreholes were drilled, and the Callovo-Oxfordian argillites, thought to become a potential storage formation, were cored and logged. A 250 km2-wide Transposition Zone was delimited, which was subject to further investigations in 2007 and 2008, including another series of coring and logging in four additional boreholes. The main objective of this study is to improve the knowledge of the spatial variability of geological and physical properties of the Callovo-Oxfordian formation. First, using multivariate statistical analysis methods, relations and correlations were sought between well-log parameters and lab properties to identify log attributes that were likely to provide relevant information about the spatial continuity of rock properties as measured on cores in laboratory. They show that well-log compressive velocity is well correlated to static Young modulus and compressive strength measured on cores, and that downhole bulk density and porosity are well correlated to dynamic Young modulus, dynamic shear modulus and compressive velocity on cores. Second, a combination of Principal component analysis and Fuzzy clustering was used on well-log data to identify equivalent homogeneous log-units on the boreholes. The analysis of the spatial continuity and trends of properties in argillaceous units across the Transposition Zone was first conducted on the well-log properties that proved to be well correlated to properties measured on cores, lab properties remaining the reference physical properties. Lateral and vertical spatial trends were observed and interpreted on the selected well-log properties. In order to confirm that these spatial trends were effective and could apply to physical properties measured on cores, the spatial continuity of some correlated lab properties was studied. Similar trends were found that validated the approach of using log properties for characterizing the spatial continuity of core physical properties.

► We recognize homogeneous and transition log-units in the Callovo-Oxfordian.
► We analyse the spatial variability and trends of log and core properties.
► Relevant correlations are found between well-logs and mechanical cores properties.
► Two main directions of lateral spatial trends are identified from the available data.
► The vertical variability consists in two superimposed periodic and linear phenomena.