Method of determining subterranean formation parameters
A method for assigning a wettability or related parameter to a subvolume of formation located between two or more boreholes is described. The method includes the steps of obtaining measurements of resistivity at a subvolume, obtaining further parameters determining a relation between resistivity and saturation from logging measurements along the two or more boreholes, obtaining geological measurements defining geological or rock-type boundaries within the formation between the two or more boreholes, selecting the subvolume such that it is intersected by the geological or rock-type boundaries; transforming the resistivity measurements into the saturation at the subvolume; and using the saturation and/or the further parameters to determine the wettability or related parameter for the subvolume.
1. A computer-implemented method for assigning a saturation and wettability or related parameter to a subvolume of formation located between two or more boreholes, said method comprising the steps of:
using an EM survey to obtain measurements of resistivity at said subvolume;
obtaining further parameters determining a relation between resistivity and saturation from logging measurements from a logging tool along said two or more boreholes;
obtaining a geological measurement defining geological or rock-type boundaries within said formation between said two or more boreholes;
selecting said subvolume such that it is intersected by said geological or rock-type boundaries;
transforming said resistivity measurements into said saturation at said subvolume wherein the step of transforming the resistivity measurements into the saturation at the subvolume includes extra- or intrapolating parameters measured at one or more wellbores to the location of said subvolume using knowledge of the layer boundaries in the formation; and
using said saturation and/or said further parameters to determine said wettability or related parameter for said subvolume.
2. The method of claim 1 , wherein the measurements of the resistivity include cross-well electro-magnetic or surface-wellbore electro-magnetic measurements.
3. The method of claim 1 , wherein the further parameters are selected from a group consisting of a parameter related to porosity of the formation, a resistivity associated with the water in the subvolume, an exponent of said parameter related to porosity in the relation and/or an exponent of the saturation in said relation.
4. The method of claim 3 , wherein in the determination of the saturation and the wettability the dependence of a saturation exponent on wettability is used.
5. The method of claim 1 , wherein in the determination of the saturation and the wettability the dependence of a resistance ratio on said saturation is used.
6. The method of claim 1 , wherein the further parameters include a parameter related to porosity of the formation and/or at least one of the Archie exponents.
7. The method of claim 1 , wherein the geological measurement defining geological or rock-type boundaries are seismic measurements.
8. The method of claim 1 , wherein the geological measurement defining geological or rock-type boundaries are sonic and ultrasonic, resistivity, nuclear, dielectric, optical or other logging measurements capable of identifying layer boundaries or other discontinuities along the wall of a wellbore.
9. The method of claim 1 , wherein the step of transforming the resistivity measurements into the saturation at the subvolume includes extra- or intrapolating parameters measured at one or more wellbores to the location of said subvolume using knowledge of the layer boundaries in the formation and a distribution of said parameters at a scale smaller than a resolution of the resistivity measurement to determine the saturation and/or wettability related parameters at a resolution exceeding said resolution of said resistivity measurement.