Fremgangsmåte for å bestemme elastiske jord-parametere i anisotrope media

摘要

In the exploration for underground hydrocarbon deposits it is helpful to obtain a measure of the elastic parameters of earth strata, for they are directly related to, and useful for characterizing, rock strength, porosity, lithology, and pore fluids. The elastic moduli of earth strata are also directly related to the acoustic propagation characteristics of the earth, and along with density constitute primary parameters of earth strata in seismology. One model for drawing useful information from seismic data involves the Christoffel relation, and so far there has been no known way of directly solving this relation exactly without use of approximations or weak anisotropy assumptions. The invention proposes a method of determining the elastic moduli of anisotropic earth strata using acoustic and density data without making simplifying approximations of the Christoffel relation or the assumption of weak anisotropy. To this end, it suggests that the relation be converted algebraically into a linear system and solved analytically to generate a solution for estimating elastic moduli. In a preferred embodiment of the invention, a set of qP phase points obtained from walkaway VSP data, with multiple vertical angles, plus at least one vertical SV point, are used to derive the elastic moduli A11, A13, A33, A55. In the case of FTIV or other orthothrombic media, the present invention may also be applied to obtain additional elastic moduli. IMAGE