Relationship Research Between Compressional Velocity And Density In Sedimentsbearing Gas Hydrates

Velocity and density are important parameters to reflect subsurface elastic properties,the intrinsic link between the two information is one of the important content of petrophysical properties research,Relationship Research between Compressional Velocity and Density mainly based on empirical formula.For seismic inversion, in order to compensate for the lack of the limited bandwidth of the seismic data itself, it is necessary to establish an initial low-frequency model,low-frequency components often need to be extracted from the log data and compensation, if the log data without density information, which is calculated according to Gardner empirical formulain most cases.Since the empirical formula is strongly affected of geographical conditions,for the seismic inversion of unconsolidated sediments bearing gas hydrate,the direct use of Gardner empirical formula and other empirical formula are not reasonable.this paper collectedlogging data from East China sea in Dongsha area and Shenhu area and some logging data fromDSDP84, ODP184 and ODP164 expeditions,Analyse the relationship between Compressional Velocity and Densityof drilling strata with or without gas-hydrate respectively,and try to establish the regression equationbetweenCompressionalvelocity and density.It’s showed that in the gas-hydrate layer, especially those containing block hydrate,there is significant negative correlation between P-wavevelocity and density, But in the hydrate-free layer, there is positive correlation between P-wavevelocity and density. In both cases, the characteristic rules between P-wavevelocity and density are quite different. It is mainly reflects in the increasing or decreasing rate of P-wavevelocity changing along with density. Therefore, this paper proceeds to analyse this characteristic rules difference using effective medium theory, particularly from these points:gas-hydrate saturation, porosity, lithology difference,nature difference of pore water and so on. Theoretical results are verified by the part of the actual data, there is good agreement between them.Finally, using well logging data in some area, we taking porosity as a variable, exploringtwo-parameters model among P-wave velocity, density and porosity. It’s found that the generalization ability is not very strong, and each coefficient has a big difference,which also shows that unified two-parameters model should be variable coefficient model with clearer physical meaning, different sea area should take its corresponding coefficient.