Evaluation of wire-line well logs from the borehole Kyrkheddinge-4 by comparison to measured core data

Abstract: This study is an evaluation of formation characteristics, as derived from wire-line well logs, of the Lund Member in the borehole Kyrkheddinge-4, 3 km east of Staffanstorp, Skåne, Sweden, through the comparison to measured core data. The purpose is to assess the feasibility of using some of the porosity and permeability equations and cross-plots derived for the investigated section and applying them to deeper aquifer formations in Kyrkheddinge- 4, where no core data exist. Shale corrected porosities are calculated from the Density, Neutron and Sonic logs for 41 levels from the borehole, including additional porosities from the compaction corrected Sonic log. These porosities were derived using standard equations and cross-plots. These data were compared to porosity values obtained directly from core samples from the same investigated levels. The results suggested that the shale corrected Density log values have the strongest linear relationships to the measured core data, although the R2 value is extremely low at 0.29. However, the R2 value increases to 0.74 for sandstone samples, although this is based on 4 data points, which compares to an R2 value of 0.12 for the 26 marlstone samples. The results suggest it is not possible to fully rely upon the porosity values obtained from the wireline log equations. The main reason is due to the complex lithologies and the high amount of shale/clay present in the formations. Together with shale data, lithological characteristics such as compaction of the sandstones are important, to obtain accurate corrected porosity values on which the equations and cross-plots are based. Permeabilities were unable to be calculated and therefore, unable to be compared to the measured core permeabilities. This was due to the lack of data of the irreducible water saturation (Swirr) parameter, which cannot be obtained in Kyrkheddinge-4, as the permeable horizons are 100% water saturated and the equations required to calculate Swirr principally rely upon the presence of hydrocarbons.