Application of Log Interpretation Methods to Evaluate Heterogeneity in Diatomaceous Mudstone at Horonobe Area

Hara, Akio; Tsuji, Takashi*; Hoshi, Kazuyoshi*; Yagi, Masahiko*; Nishimura, Mizue*; Kawada, Koji*; Hou, J.-Y.*

To evaluate heterogeneity of diatomaceous mudstone in Horonobe area, physical properties and lithofacies of sedimentary rocks have been estimated from natural ray log data and electrical micro imaging (EMI) log data. Spatial distribution of heterogeneity of sedimentary rocks has been discussed by comparison of log data acquired from several boreholes. Five sedimentary facies, A to E, have been established. Sedimentary facies A and B, which can decipher bedding planes clearly in EMI image, have been developed horizontally with low ray and high SiOcontents while sedimentary facies D, bedding planes are not clear to decipher, have been developed horizontally with high ray and low SiOcontents. The results of this study support the estimation of Hara (2004) namely the strata which characterized with high ray have been high AlOcontents and rich in terrigenous sediments such as clay minerals, on the other hand, the strata characterized with low ray have high SiOcontents and rich in diatomaceous fossils. Layered sedimentary facies can correlate between boreholes based on natural ray log and EMI log analysis. Sedimentary system and spatial distribution of strata of Horonobe area can estimate from the results of the facies correlation.