Estimation of elastic moduli of mixed porous clay composites

Abstract

We have developed a procedure for estimating the effec­tive elastic properties of various mixtures of smectite and kaolinite over a range of confining pressures, based on the individual effective elastic properties of pure porous smectite and kaolinite. Experimental data for the pure samples are used as input to various rock physics models, and the predictions are compared with experimental data for the mixed samples. We have evaluated three strategies for choosing the initial prop­erties in various rock physics models: (I) input values h ave th e sa me porosit y, (2) input values have the same pressure, and (3) an average of (I) and (2). The best results are obtained when the elastic moduli of the two porous constituents are de­fined at the same pressure and when their volumetric fractions are adjusted based on different compaction rates with pressure. Furthermore, our strategy makes the modeling re­sults less sensitive to the actual rock physics model. The method can help obtain the elastic properties of mixed unconsolidated clays as a function of mechanical compaction. The more common procedure for estimating effective elastic properties requires knowledge about volume fractions, elas­tic properties of individual constituents, and geometric de­tails of the composition. However, these data are often uncer­tain , e.g., large variations in the mineral elastic properties of clays have been reported in the literature, which makes our procedure a viable alternative.