| 摘要 |
1. A method of determining a parameter in a composition of an earth formation selected from the electrical conductivity and the volume fraction of a component in a composition comprising a plurality of components of an earth formation, the method comprising: - drilling a borehole in an earth formation to obtain a core sample to be tested; - measuring the electrical conductivity of the composition by a logging instrument; - selecting a relationship between the electrical conductivity of the composition and a plurality of composition parameters including, for each component, physical parameters representing the electrical conductivity and the volume fraction of the component, the components being substantially equally represented in said relationship by means of said physical parameters; and - determining said selected parameter from said relationship and the measured conductivity of the composition, characterized in that an auxiliary parameter is introduced in said relationship, depending on the conductivity of one of said components and a mixing coefficient, whereby the mixing coefficients depend on the geometrical configuration of the components in the composition and determine the amount of percolation of the individual components. 2. The method of claim 1, wherein said plurality of composition parameters includes at least one fitting parameter, and wherein each fitting parameter is determined by applying said relationship to a data set obtained by measuring the electrical conductivity of at least one sample representative for said composition for various magnitudes of at least one of said parameters. 3. The method of claim 1 or 2, wherein said relationship is selected to be (σeff-σ0) (Lσeff + (1-L) σ0)<-1> = Σφk(σk-σ0) (Lσk+ (1-L) σ0)<-1> wherein σ0 represents the auxiliary parameter in the form of a conductivity tensor, k = 1 ... N, N being the number components, σeff represents the conductivity tensor of the sample, σk represents the conductivity tensor of component k, φk represents the volume fraction of component k, L represents a depolarisation tensor. 4. The method of any of claims 1-3, wherein said auxiliary parameter is selected to be σ0 = Σ hk.σk; wherein σ0 represents the auxiliary parameter in the form of a conductivity tensor representative for the conductivity in the three principal directions, k = 1 ... N, N being the number of components, σk represents the conductivity tensor of component k, hk represents the mixing coefficient tensor pertaining to component k. 5. The method of any one of claims 1-4, wherein said mixing coefficients are selected so that the sum of the mixing coefficients substantially equals unity. 6. The method of any of claims 1-5, wherein said mixing coefficients are non-negative. 7. The method of any of claims 1-6, wherein each mixing coefficient is selected to be a function of at least the volume fraction of the component pertaining to said mixing coefficient. 8. The method of claim 7, wherein said function is a monotonous increasing function in the volume fraction of the component pertaining to the mixing coefficient. 9. The method of claim 7 or 8, wherein said function is selected so that the mixing coefficient vanishes for vanishing volume fraction of the component pertaining to the mixing coefficient. 10. The method of any of claims 1-9, wherein each mixing coefficient is selected as hk = &lamda;k φ kvk (Σ&lamda;n φn vn)<-1> wherein k,n = 1... N, N being the number components in said plurality of components, &lamda;k represents a percolation rate tensor pertaining to component k, φk represents the volume fraction of component k, vk,n represents a percolation exponent pertaining to component k, n. 11. The method of claim 10, wherein at least one of hk &lamda;k and v forms a fitting parameter. 12. The method of any of claims 3-11, wherein the depolarisation tensor is positive. 13. The method of any of claims 3-12, wherein the depolarisation tensor has unit trace. 14. The method of any of claims 3-13, wherein the depolarisation tensor equals 1/3 times the unit tensor. 15. The method of any of claims 1-14, wherein the step of determining each fitting parameter by applying said relationship to the data set is carried out through an iterative process. 16. The method of claim 15, wherein the iterative process includes repeatedly applying said relationship in a minimisation scheme. 17. The method of claim 16, wherein the minimisation scheme is applied to a mismatch between the measured electrical conductivities of said components and the electrical conductivities of the components as determined through said relationship. 18. The method of any of claims 1-17, wherein said composition includes an earth formation. 19. The method of claim 18, wherein said earth formation includes at least one of rock, brine, hydrocarbon fluid and clay. 20. The method of claim 19, wherein said parameter which is determined forms the volume fraction of one of the hydrocarbon fluid and the brine. |
