Shell Oil Comapny

Richard Gerrit Hakvoort

Johannes Maria Koelman

Melis Van Der Horst

A method of providing a computed induction log of an induction logging tool run through an interval of a wellbore that extends through a layered formation invaded by wellbore fluid. The method comprises computing a first response of the induction logging tool by solving for each formation layer the Maxwell equations for the electromagnetic field using a one-dimensional concentric cylinder model not taking into account the effects of formation layering and of the orientation of the logging tool with respect to the formation layering, and determining for each formation layer an equivalent resistivity that gives for a homogeneous environment a response of the induction logging tool that equals the first response; and solving for a number of logging points the Maxwell equations using a one-dimensional layered model using the equivalent resistivities as computed in step wherein the effects of the formation layering and of the orientation of the logging tool with respect to the formation layering are taken into account, to provide the computed induction log of the induction logging tool.

Induction logging

A method of determining electric resistivity of an earth formation (1) surrounding a wellbore filled with a wellbore fluid, is provided, which method comprises: operating a resistivity logging tool (2) in the wellbore so as to provide a plurality of resistivity logs (FLG.sub.1, . . . , n) (3) of the earth formation (1) for different radial intervals (1, . . . , n) relative to the wellbore; for each radial interval (k), selecting a modelled resistivity profile (Rmod.sub.k) (4); inputting the modelled resistivity profiles (Rmod.sub.1, . . . , n) (4) to a logging tool simulator (6) so as to provide for each radial interval (k) a modelled resistivity log (MLG.sub.k) (7) having a depth of investigation corresponding to the radial interval (k); for each radial interval (k) updating the modelled resistivity profile (Rmod.sub.k) (7) in dependence of an observed deviation of the resistivity log (FLG.sub.k) (3) from the modelled resistivity log (MLG.sub.k) (7); and repeating steps c)-d) until for each radial interval (k) the difference between the resistivity log (FLG.sub.k) (3) and the corresponding modelled resistivity log (MLG.sub.k) (7) is below a selected threshold value (8).

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Rijswijk, Netherlands

Richard Gerrit Hakvoort