Apparatus, systems, and methods may operate to correct measured voltage data for selected weak differential measurements to provide corrected voltage data. Additional activity may include adjusting the corrected voltage data to remove level shifts in the measured voltage data caused by downhole tool impedance to provide adjusted voltage data, converting the adjusted voltage data into apparent resistivity data, inverting the apparent resistivity data to determine true resistivity values for a geological formation, and operating a controlled device according to the true resistivity values for the geological formation. Additional apparatus, systems, and methods are disclosed.

A system to obtain information about a subsurface formation, in some embodiments, comprises an array of acoustic transmitters in a first well; a distributed acoustic sensing (DAS) fiber in a second well; and processing logic, in communication with the array of acoustic transmitters and the DAS fiber, that activates the array of acoustic transmitters and the DAS fiber so as to use the Doppler effect to obtain information about the subsurface formation.

Methods for determining oil-water contact positions and water zone resistivities are provided. In one example, the method may involve performing a 1D inversion on data collected by a resistivity logging tool. Further, the method may involve scanning a resistivity profile of a reservoir generated by the 1D inversion for a boundary position below the resistivity logging tool. Furthermore, the method may involve applying a local residual weighted average on the boundary position to generate an initial estimation of an oil-water contact position and inverting the initial estimation of the oil-water contact to generate water zone resistivity and a modified oil-water contact position. Additionally, the method may involve miming a smoothing local post-processing operation to generate a layered model and performing a 2D inversion on the layered model.

Methods for determining oil-water contact positions and water zone resistivities are provided. In one example, the method may involve performing a 1D inversion on data collected by a resistivity logging tool. Further, the method may involve scanning a resistivity profile of a reservoir generated by the 1D inversion for a boundary position below the resistivity logging tool. Furthermore, the method may involve applying a local residual weighted average on the boundary position to generate an initial estimation of an oil-water contact position and inverting the initial estimation of the oil-water contact to generate water zone resistivity and a modified oil-water contact position. Additionally, the method may involve miming a smoothing local post-processing operation to generate a layered model and performing a 2D inversion on the layered model.

The disclosed embodiments include systems and methods to evaluate formation resistivity. In one embodiment, a method to evaluate formation resistivity proximate a wellbore is provided. The methods includes receiving data indicative of resistivity measurements of a formation proximate a wellbore at different distances within a range of distances from the wellbore. The method also includes analyzing the data to determine approximate formation resistivity of the formation at different distances from the wellbore. The method further includes generating at least one curve, each indicative of an approximate formation resistivity of the formation at the different distances from the wellbore, overlaying the at least one curve on a graph indicative of the formation resistivity of the formation within the range of distances from the wellbore, and providing the at least one curve overlaid on the graph for display on a device.

The disclosed embodiments include systems and methods to evaluate formation resistivity. In one embodiment, a method to evaluate formation resistivity proximate a wellbore is provided. The methods includes receiving data indicative of resistivity measurements of a formation proximate a wellbore at different distances within a range of distances from the wellbore. The method also includes analyzing the data to determine approximate formation resistivity of the formation at different distances from the wellbore. The method further includes generating at least one curve, each indicative of an approximate formation resistivity of the formation at the different distances from the wellbore, overlaying the at least one curve on a graph indicative of the formation resistivity of the formation within the range of distances from the wellbore, and providing the at least one curve overlaid on the graph for display on a device.

Logging-while-drilling (LWD) tools may include multiple instruments interleaved into a compact configuration in a single drill string section that may be capable of nuclear magnetic resonance, resistivity, porosity, gamma density measurements, or any combination thereof. For example, a LWD tool may include a drill collar section containing: a nuclear magnetic resonance (NMR) electronics module and an NMR sensor module interleaved with a nuclear source and at least one nuclear detector.

Logging-while-drilling (LWD) tools may include multiple instruments interleaved into a compact configuration in a single drill string section that may be capable of nuclear magnetic resonance, resistivity, porosity, gamma density measurements, or any combination thereof. For example, a LWD tool may include a drill collar section containing: a nuclear magnetic resonance (NMR) electronics module and an NMR sensor module interleaved with a nuclear source and at least one nuclear detector.

An estimated value for invasion depth of an invasion zone in a subsurface measurement zone is calculated in a one-dimensional optimization procedure based on multi-array laterolog measurement data. A one-dimensional optimization problem is defined as having the invasion depth as a sole variable measurement zone parameter. The one-dimensional optimization problem is then solved by automated, iterative modification of the invasion depth value. The one-dimensional optimization problem can be a function to minimize a misfit error between (a) multi-array measurement values for resistivity of the subsurface measurement zone, and (b) predicted measurement values calculated in accordance with a simulated measurement zone model based at least in part on the invasion depth. In one embodiment, the optimization function defines a misfit error between (1) normalized differences between respective measurements of neighboring measurement arrays of the multi-array laterolog tool, and (2) normalized differences between respective predicted measurement values for neighboring measurement arrays.

Apparatus and methods operable to determine a resistivity of a subterranean formation surrounding a wellbore. One such method includes using an apparent impedance function depending on a frequency variable and a plurality of unknown parameters, at least one of the unknown parameters depending on a formation impedance of the subterranean formation. The method also includes applying a voltage, at each of a plurality of frequency values, between electrodes of a resistivity tool that is disposed in the wellbore. The method also includes measuring, across the electrodes, a plurality of apparent impedance values, each corresponding to a different one of the frequency values. The method still further includes determining the unknown parameters based on the frequency values and the apparent impedance values, and estimating the formation resistivity based on an expression that includes at least one of the unknown parameters.