Abstract: An apparatus for measuring mechanical properties of a downhole material, including first and second fixtures each of the fixtures containing a force application fixture to apply a stress to a specimen of the downhole material. A confining sleeve wraps around portions of the first and second fixtures to form a sealed specimen chamber defined by an inner surface of the confining sleeve and ends of the first and second fixtures nearest the specimen. Wall of a confining chamber contain the first and second fixtures, the confining sleeve and the specimen therein. The confining chamber holds a hydraulic fluid therein such that the hydraulic fluid can exert a confining pressure on the confining sleeve to maintain the seal of the specimen chamber and to maintain contact between the inner surface of the confining sleeve and the specimen when the stress is applied to the specimen.

Abstract: An array of sensors provided on the outside of a tubular string for measuring a property within the tubular string. The array of sensors may include a plurality of connected sensors, wherein at least one of the plurality of connected sensors is at least partially encompassed in a shroud. A snorkel line may extend from the shroud, the snorkel line capable of coupling with a sensor port in a tubular of the tubular string. The snorkel line may establish fluid communication between one of the sensors at least partially encompassed in the shroud and a corresponding sensor port of a tubular in the tubular string.

Abstract: A magneto-quasistatic field may be used to align hydrogen of materials within a structure and/or to disrupt the alignment of hydrogen of materials within the structure. Realignment of the hydrogen after the disruption may cause emission of energy from the hydrogen. The characteristic(s) of the energy may be detected and used to generate image(s) of interior portion(s) of the structure.

Abstract: A combination downhole assembly having a setting tool assembly coupled with a downhole tool. The setting tool assembly has an adapter housing configured to couple with a part of a workstring, and a power charge mandrel coupled with the adapter housing. There is a barrel piston releasably coupled with the power charge mandrel. During run-in, the barrel piston is in a first position. Upon activation of a setting sequence, the barrel piston moves to a second position. The setting sequence results in the barrel piston engaging a tension mandrel configured with a deceleration feature.

Abstract: An anchoring assembly for securing a cable having both an optical fiber and an electrical conductor in order to provide a conductive pathway to a downhole tool. The anchoring assembly has a head and tail each having a throughbore with anchor receiving portions. An anchor with a deformable portion maybe inserted into the anchor receiving portions and the head and tail drawn together about the anchor. The anchor receiving portions have a narrowing diameter, which, upon abutment with the anchor causes the deformable portion of the anchor to deflect inward and secure a cable inserted therein. A conductive body is provided in the head or tail for coupling with the cable and providing a conductive pathway to a downhole tool.

Abstract: A system for detection of real time gas expansion within a wellbore using an oil based mud. The system includes one or more ball valve cartridges located in a drill string, where the one or more ball valves are arranged serially along a length in the drill string. Each of the one or more ball valve cartridges include a corresponding gas detection electrode. The system also includes a control system for receiving an output signal from the gas detection electrode. Each of the one or more ball valve cartridges is configured to have a higher pressure rating than a preceding ball valve cartridge, and the gas detection electrode is configured to react with a dissolved gas in the oil based mud, causing an oxidation reaction, and thereby generating the output signal.

Abstract: Systems and methods for extracting and analyzing formation fluids from solids circulated out of a subterranean formation are provided. In one embodiment, the methods comprise: providing a sample of formation solids that have been separated from a fluid circulated in at least a portion of a well bore penetrating a portion of a subterranean formation at a well site; performing a solvent extraction on the sample of formation solids using one or more solvents at an elevated pressure at the well site, wherein at least a portion of one or more formation fluids residing in the formation solids is extracted into the one or more solvents to produce an extracted fluid; and analyzing the extracted fluid at the well site to determine the composition of the extracted fluid.

Abstract: A method includes obtaining a sample of a fluid from a subterranean zone while the fluid is being extracted from the zone. A chemical composition of the sample is measured. A temperature and a pressure of the subterranean zone are measured. The measured properties are associated with a time point. The measured properties are incorporated into a set of historical data. A chemical composition of a fluid to be extracted from the subterranean zone at a future time point is determined based on the set of historical data. A presence of a liquid phase in the fluid to be extracted from the subterranean zone at the future time point is determined. A flow rate of the fluid being extracted from the subterranean zone is adjusted in response to determining the presence of the liquid phase in the fluid to be extracted from the subterranean zone at the future time point.

Abstract: A method includes obtaining a sample of a fluid from a subterranean zone while the fluid is being extracted from the zone. A chemical composition of the sample is measured. A temperature and a pressure of the subterranean zone are measured. The measured properties are associated with a time point. The measured properties are incorporated into a set of historical data. A chemical composition of a fluid to be extracted from the subterranean zone at a future time point is determined based on the set of historical data. A presence of a liquid phase in the fluid to be extracted from the subterranean zone at the future time point is determined. A flow rate of the fluid being extracted from the subterranean zone is adjusted in response to determining the presence of the liquid phase in the fluid to be extracted from the subterranean zone at the future time point.

Abstract: A method includes obtaining a sample of a fluid from a subterranean zone while the fluid is being extracted from the zone. A chemical composition of the sample is measured. A temperature and a pressure of the subterranean zone are measured. The measured properties are associated with a time point. The measured properties are incorporated into a set of historical data. A chemical composition of a fluid to be extracted from the subterranean zone at a future time point is determined based on the set of historical data. A presence of a liquid phase in the fluid to be extracted from the subterranean zone at the future time point is determined. A flow rate of the fluid being extracted from the subterranean zone is adjusted in response to determining the presence of the liquid phase in the fluid to be extracted from the subterranean zone at the future time point.

Abstract: A sampling system for taking fuel samples from an external fuel tank includes a mobile platform, a sample tank carried by the mobile platform, and a supply line connected to the sample tank and configured to conduct the fuel from the external fuel tank into the sample tank. A mixing device is disposed in the sample tank and configured to mix fuel in the sample tank. A discharge line connected to the sample tank and configured to discharge the fuel from the sample tank. A sampling device is configured for removing a partial quantity of the fuel from the sample tank. A method for operating the sampling system is also described.

Abstract: A method includes receiving first fluid property data from a first location in a hydrocarbon reservoir and receiving second fluid property data from a second location in the hydrocarbon reservoir. The method includes performing a plurality of realizations of models of the hydrocarbon reservoir according to a respective plurality of one or more plausible dynamic processes to generate one or more respective modeled fluid properties. The method includes selecting the one or more plausible dynamic processes based at least in part on a relationship between the first fluid property data, the second fluid property data, and the modeled fluid properties obtained from the realizations to identify potential disequilibrium in the hydrocarbon reservoir.

Abstract: A sensor is provided for detecting relative amounts of components within a mixture. The sensor includes a dielectric transducer comprising a first conductive rod and a second conductive rod; an oscillator configured to apply a voltage to the first conductive rod; an amplifier configured receive a voltage from the second conductive rod as input; and a controller configured to periodically sample an output voltage of the amplifier to generate a plurality of sample voltages, compare the sample voltages against distinct voltage values for identifying each of the components to determine the relative amounts of the components.

Abstract: Methods for developing equation-of-states (EOS) composition models for predicting petroleum reservoir fluid behavior and understanding fluid heterogeneity in unconventional shale plays are described. In particular, limited geochemical data from samples taken from the reservoir of interested are utilized to build and tune the EOS model and improve predictions. Real-time applications are also described.

Abstract: Systems and methods for predicting fluid composition in a reservoir formation are disclosed. To accurately and efficiently predict the composition of a sample fluid, an absorption spectrum is obtained over a prefixed set of wavelength channels and a set of basis spectra is received for all constituents of interest in the sample fluid. A set of a-priori constraints on the obtained absorption spectrum and constituent properties to be determined is then obtained, before calculating a joint probability distribution of all constituents of interest based on the obtained spectrum, basis spectra and a-priori constraints. In one embodiment, qualitative states are also computed for all constituents of interest based on the obtained spectrum, basis spectra and a-priori constraints.

Abstract: A method for predicting asphaltene onset pressure in a reservoir is provided. In one embodiment, the method includes performing downhole fluid analysis of formation fluid via a downhole tool at a measurement station at a first depth in a wellbore and determining an asphaltene gradient for the formation fluid at the measurement station. Asphaltene onset pressure for a second depth in the wellbore may then be predicted based on the downhole fluid analysis and the determined asphaltene gradient. Additional methods, systems, and devices are also disclosed.

Abstract: An apparatus for estimating a property of an earth formation includes a carrier configured to be conveyed through a borehole penetrating the formation and a single probe configured to be extended from the carrier and to seal with a wall of the borehole. The apparatus further includes a fluid analysis sensor disposed at the carrier and configured to sense a property of a formation fluid sample extracted from the formation by the probe. A coring device is disposed at the carrier and configured to extend into the probe, to drill into the wall of the borehole, and to extract a core sample. A core sample analysis sensor is disposed at the carrier and configured to sense a property of the core sample. A processor is configured to receive data from the fluid analysis sensor and the core sample analysis sensor and to estimate the property using the data.

Abstract: A method of evaluating a gradient of a composition of materials in a petroleum reservoir, comprising sampling fluids from a well in the petroleum reservoir in a logging operation, measuring an amount of contamination in the sampled fluids, measuring the composition of the sampling fluids using a downhole fluid analysis, measuring an asphaltene content of the sampling fluids at different depths; and fitting the asphaltene content of the sampling fluids at the different depths to a simplified equation of state during the logging operation to determine the gradient of the composition of the materials in the petroleum reservoir.

Abstract: A method for detecting the formation of at least one phase in a mixture, particularly a hydrocarbon mixture. The method may include using a probe to expose a portion of the mixture to electromagnetic radiation to determine the value of a parameter of interest indicative of the formation of a phase. The method may also include using the value of the parameter of interest with a correlation between a known property of the mixture and the value of a parameter of interest to detect the formation of a phase.

Abstract: An arrangement for sampling a fluid, having a sample bottle with an associated piston, wherein the piston separates the sample bottle into an inlet side and a water side, a fluid sample line connected to the sample bottle at the inlet side, the fluid sample line transporting a fluid, a solenoid connected to the sample bottle on the water side of the sample bottle and a check valve connected to the sample bottle on the water side of sample bottle, wherein fluid enters the sample bottle on the inlet side upon actuation of at least one of the solenoid and the check valve on the water side of the sample bottle.

Abstract: Apparatus and method for collecting and preserving in representative condition a fluid sample from a reservoir which comprises: positioning a sample receptacle in the vicinity of a subterranean zone to be sampled, allowing or causing the sample to first flow into the sample receptacle, wherein the movement of the sample into the sample receptacle is restricted by the movement of a sampling piston, and wherein the movement of the sampling piston is further controlled by the rotation of an electrical motor connected to the sample piston such that the rotation of the electric motor translates to lateral movement of the sample piston, the lateral movement of the sample piston in turn allowing sample to enter the sample receptacle, and wherein once an adequate volume of sample has been collected, reversing the direction of the electrical motor will serve to cause the sample piston to exert pressure on the collected sample.

Abstract: A transducer includes a preload adapter having a sleeve portion and an end and a housing including a seating portion and a shaft portion that extends from the seating portion. The transducer also includes a piezoelectric element contained at least partially within a chamber that is at least partially defined by the sleeve portion and shaft portion and a diaphragm coupled to an external side of the end such that motion of the piezoelectric element causes motion of the diaphragm.

Abstract: A device for sampling fluid from an earth formation is disclosed. The device includes: an inlet port disposable in fluid communication with the fluid in a borehole; an injector including an injection chamber in fluid communication with the inlet port, the injector configured to receive a portion of the fluid and direct the fluid toward an analysis unit for analyzing constituent materials in the fluid; and a high pressure valve configured to admit the portion of the fluid at a borehole pressure and release the portion of the fluid into the injector, the portion having a volume that is less than or equal to about one microliter. A system and method for analyzing constituents of fluid in a borehole in an earth formation is also disclosed.

Abstract: A system includes a downhole formation fluid sampling tool and a processor. An optical spectrometer of the downhole formation fluid sampling tool is able to measure an optical characteristic of a formation fluid flowing through the downhole formation fluid sampling tool over a plurality of wavelengths. The optical spectrometer generates optical spectra data indicative of this optical characteristic. The processor is designed to receive the optical spectra data generated by the optical spectrometer and to estimate a formation volume factor of the formation fluid based on the optical spectra data.

Abstract: A gas separation and detection tool for performing in situ analysis of borehole fluid is described. The tool comprises a sampling chamber for a downhole fluid. The sample chamber comprises a detector cell with an opening. The tool also comprises a gas separation module for taking a gas from the downhole fluid. The gas separation module comprises a membrane located in the opening, a support for holding the membrane, and a sealant applied between the housing and the membrane or support. Moreover, the tool comprises a gas detector for sensing the gas.

Abstract: In some embodiments, apparatus and systems, as well as methods, may operate to draw a formation fluid sample into a sampling port included in a down hole tool, to vaporize some part of the fluid sample to substantially fill an injection port with a gas phase, to differentiate gas components in the gas phase to provide differentiated gas components along a concentration gradient, to detect the differentiated gas components, and to determine a fingerprint of the differentiated gas components. Other apparatus, systems, and methods are disclosed.

Abstract: A method and apparatus is provided for off-line concentration determination of components liquid hydrocarbon mixtures such as crude or heavy oil. A sampling unit continuously delivers a sample volume to a fluid flow path while a temperature control module maintains the sample at a predetermined setpoint temperature. A homogenization module helps prevent sample stratification while a flow control module maintain a constant sample flow rate. A spectrometer is communicably coupled to an optical transmission cell to transmit and receive radiation. The transmission cell includes collection optics to capture and aggregate non-collimated radiation emerging from the cell, for transmission to the spectrometer. The spectrometer measures sample spectra at a predetermined rate of flow of the sample volume through the transmission cell. A processor is configured to capture and use the spectra in combination with a model of spectra for the hydrocarbon mixture.

Abstract: Methods and systems to characterize a fluid in a reservoir to determine if the fluid is in one of equilibrium or non-equilibrium in terms of one of gravity, solvency power, entropy effect or some combination thereof. The method includes acquiring tool data at each depth for each fluid sample of at least two fluid samples wherein each fluid sample is at a different depth and communicating the tool data to a processor. Determining formation properties of each fluid sample to obtain formation property data and determining fluid properties for each fluid sample to obtain fluid property data. Selecting a mathematical model based on one of gravity, solvency power or entropy, in view of a fluid property, using one of tool data, formation property data, fluid property data, known fluid reservoir data or some combination thereof, to predict if the fluid is in an equilibrium distribution or a non-equilibrium distribution.

Abstract: A processor accepts sensor data about a geological formation from a sensor. The sensor data is such that processing the sensor data using a processing technique to estimate a parameter of the geological formation without a constraint, whose value is not yet known, produces a plurality of non-unique estimates of the parameter. The processor accepts more than two time-displaced images of fluid sampled from the geological formation. The time displacements between the images are substantially defined by a mathematical series. The processor processes the images to determine the constraint. The processor processes the sensor data using the processing technique constrained by the constraint to estimate the parameter of the geological formation. The processor uses the estimated parameter to affect the drilling of a well through the geological formation.

Abstract: A downhole compressible fluid sampling tool includes a primary fluid flow line deployed between a fluid inlet probe and a fluid outlet line. A fluid analysis module and a fluid pumping module are deployed in the primary fluid flow line. The fluid pumping module includes a pump in parallel with a bypass flow line having a bypass valve. A compressible fluid sampling vessel is deployed in parallel with and in fluid communication with the primary flow line. A method for obtaining a sample of a compressible downhole fluid includes turning off the pump and opening the bypass valve to enable the downhole fluid to flow into the fluid sampling vessel. The pump may then be optionally turned back on to pressurize the sample.

Abstract: An assembly capable of being disposed in a subterranean bore for obtaining a fluid sample is described. The assembly can include an apparatus having a sample chamber and a housing encasing the sample chamber and providing a pressure source. The pressure source can be disposed of in an annulus defined by the sample chamber and the housing. The assembly can be attached to a slick line or wire line and conveyed into a wellbore.

Abstract: Cleanup monitoring and prediction in real time targeting estimation of pumpout volume versus final contamination, including detecting breakthrough of formation fluid to a sampling tool and detecting transition of cleanup regime from a predominantly circumferential cleanup regime to a predominantly vertical cleanup regime. Similar workflow can be employed for estimating contamination at the end of cleanup production for a given pumpout volume.

Abstract: An apparatus for controlling fluid flow that includes a chamber having a first valve and a second valve; a sensor that senses a pressure parameter associated with the chamber; and a controller programmed to operate the first valve and the second valve in response to the sensed pressure parameter may be used to control for flow and to obtain data relating to a formation and/or formation fluid.

Abstract: The invention provides a device and method to quantitatively measure concentrations of volatile organic compound vapors below the ground surface using a preferably “fully” passive device that is placed in a drilled or bored hole for a specified period of time, wherein the sampler constrains the uptake rate to match values that minimize or eliminate the starvation effect and provide acceptable sensitivity for most soil types as calculated via mathematical models.

Abstract: A downhole tool has a housing assembly with an interior and an exterior. A sensor is disposed to the interior of the housing assembly. The sensor is operable to obtain data relative to a fluid parameter of a fluid disposed within the interior of the housing assembly and operable to wirelessly transmit the data to a data acquisition device disposed to the exterior of the housing assembly responsive to interrogation by the data acquisition device.

Abstract: An apparatus and method for estimating a parameter of interest in a downhole fluid using fluid testing module. The fluid testing module may include: a substrate comprising at least one microconduit, and a sensor. The sensor may be disposed within the at least one microconduit or external. The apparatus may include a fluid transporter for moving fluid within the microconduit. The method includes estimating a parameter of interest using the fluid testing module.

Abstract: Apparatus and systems, as well as methods, may operate to draw a formation fluid sample into a sampling port included in a down hole tool or tool body, to vaporize some part of the fluid sample to substantially fill an injection port with a gas phase, to differentiate gas components in the gas phase to provide differentiated gas components along a concentration gradient in a receiving section, to detect the differentiated gas components with a detector, and to determine a fingerprint of the differentiated gas components. A reaction section and a vacuum section may be used for waste consumption and/or absorption.

Abstract: A downhole piston accumulator system is disclosed, such as for a formation tester. The soft piston of the system is designed to withstand high pressure downhole fluids in small volume cylinders, the fluid being collected for optical fluid identification or other analyses. The temperature range of the fluid may vary widely, which can be accommodated by the soft piston. Sealing components on the soft piston include additional materials for sealing the soft piston and otherwise helping to accommodate the wide ranging pressures and temperatures. The piston container or cylinder is designed to properly capture the piston and accommodate piston movement. The piston accumulator system allows an outer or exterior position sensor to detect piston movement, such as by a magnetic sensor.

Abstract: A sensor module for a sensing apparatus configured for operation downhole, within a borehole. The sensor module comprises a sensor array having a plurality of sensors to sense selected formation parameters and a control system for selective and independent operation of each sensor of the sensor array. Each sensor of the sensor array is configured or designed as a discrete sensor unit for individual and independent communication and control. Each sensor of the sensor array may have an associated electronics module that provides standardized electronic connectivity with the control system.

Abstract: For some embodiments, a system includes a moveable structure, moveable in at least a linear direction relative to a supporting structure, a magnetic field sensor assembly including a magnetic field sensor, and a magnet, wherein one of the magnet and the magnetic field sensor is coupled to the moveable structure, and wherein the other of the magnet and the magnetic field sensor assembly is coupled to the supporting structure, and wherein the magnetic field sensor assembly is configured to determine the relative position of the magnet to the magnetic field sensor.

Abstract: A system and method for determining at least one fluid characteristic of a downhole fluid sample using a downhole tool are provided. In one example, the method includes performing a calibration process that correlates optical and density sensor measurements of a fluid sample in a downhole tool at a plurality of pressures. The calibration process is performed while the fluid sample is not being agitated. At least one unknown value of a density calculation is determined based on the correlated optical sensor measurements and density sensor measurements. A second optical sensor measurement of the fluid sample is obtained while the fluid sample is being agitated. A density of the fluid sample is calculated based on the second optical sensor measurement and the at least one unknown value.

Abstract: An apparatus and method for monitoring the water tables in boreholes, such as boreholes used as sampling wells for sampling contaminants in ground water. Fluctuations in one or more ground water levels can be monitored and recorded using transducers, and the changes in the water levels evaluated and considered, particularly in the context of sampling for contaminants where subsurface pollution remediation is contemplated or ongoing. The changes in ground water levels can be tracked in time and correlated, as desired, with the water sampling regime. The transducers used for monitoring pressure changes attributable to water table changes are located advantageously above the surface of the ground, where they are accessible for re-use, replacement, or repair. Apparatus and method for providing an air-coupling between the transducers and subsurface sampling points is disclosed.

Abstract: Apparatus and systems, as well as methods, may operate to draw a formation fluid sample into a sampling port included in a down hole tool or tool body, to vaporize some part of the fluid sample to substantially fill an injection port with a gas phase, to differentiate gas components in the gas phase to provide differentiated gas components along a concentration gradient in a receiving section, to detect the differentiated gas components with a detector, and to determine a fingerprint of the differentiated gas components. The receiving section may comprise a diffusion section. A reaction section and a vacuum section may be used for waste consumption and/or absorption.

Abstract: Methods of and apparatus to estimate one or more volumes of one or more components of a fluid in a sample chamber of a downhole tool are described. An example method includes obtaining a sample chamber volume measurement, a flowline volume measurement and a supplemental volume measurement. The example method includes drawing the fluid into the sample chamber until the sample chamber is substantially full and measuring a characteristic of the fluid in the sample chamber at a first time to obtain a first characteristic measurement. The example method also includes adding a supplemental volume corresponding to the supplemental volume measurement to over-pressurize the sample chamber after measuring the characteristic at the first time and measuring the characteristic of the fluid in the sample chamber at a second time to obtain a second characteristic measurement. The second time is after the sample chamber is over-pressurized.

Abstract: Vibrating wire viscometers are described. Some example vibrating wire viscometer housings include a flowline through the housing to expose a first wire to a downhole fluid, a cavity in the housing to hold a magnet and to conduct one or more additional wires from the flowline to a signal generator, first and second electrically conductive posts mechanically coupled to the housing to hold the first wire in tension within the flowline, and a seal mechanically coupled to the housing to prevent access to the magnet by the downhole fluid.

Abstract: A downhole tool includes a body that includes a sample port through which a sample fluid can be drawn into the downhole tool and a sample channel passing through the body in fluid communication with the sample port and through which the sample fluid travels. The sample channel includes a sample chamber having an inlet and an outlet located along the sample channel, the sample chamber including three cylindrical chambers including a middle resonator cavity surrounded by two outer resonator cavities, one of the two outer resonator cavities including a sensor inlet for receiving a sensor and allowing it to fluidly contact the sample fluid as it travels through the sample channel.

Abstract: The present disclosure is directed to the filtering and collection of downhole fluids. An example system to filter and sample downhole fluids includes a first sampling chamber that includes one or more cone-shaped filters to receive downhole fluid, filter the downhole fluid, and store the downhole fluid, a second sampling chamber, a spool valve to allow the downhole fluid to flow into the first sampling chamber in a first position and to redirect the downhole fluid to the second sampling chamber or a base block in a second position, and a setting line to selectively move the spool valve from the first position to the second position.

Abstract: A methodology that performs downhole fluid analysis of fluid properties of a reservoir and characterizes the reservoir based upon such downhole fluid analysis. The methodology acquires at least one fluid sample at a respective measurement station and performs downhole fluid analysis to measure properties of the fluid sample, including concentration of a plurality of high molecular weight components. For each of a plurality of type classes corresponding to different subsets of a predetermined set of high molecular weight components, a model is used to predict the concentration of the components of the given type class for the plurality of measurement stations. The predicted concentrations of the high molecular weight components for the plurality of type classes are then compared with corresponding concentrations measured by downhole fluid analysis for the plurality of measurement stations to identify the best matching type class.

Abstract: A device for sampling fluid from an earth formation is disclosed. The device includes: an inlet port disposable in fluid communication with the fluid in a borehole; an injector including an injection chamber in fluid communication with the inlet port, the injector configured to receive a portion of the fluid and direct the fluid toward an analysis unit for analyzing constituent materials in the fluid; and a high pressure valve configured to admit the portion of the fluid at a borehole pressure and release the portion of the fluid into the injector, the portion having a volume that is less than or equal to about one microliter. A system and method for analyzing constituents of fluid in a borehole in an earth formation is also disclosed.

Abstract: Vibrating wire viscometers are disclosed. An example apparatus to determine the viscosity of a downhole fluid is described, the apparatus including a wire to be immersed in a downhole fluid, to vibrate when an alternating current is applied to the wire within a magnetic field, and to generate an electromotive force when vibrating within the magnetic field, the wire comprising a first resistance. The apparatus further includes a nulling circuit coupled to the wire, wherein the nulling circuit comprises a second resistance that is selectable to be substantially equal to the first resistance, and an analyzer coupled to the wire and the nulling circuit to determine the first resistance, the second resistance, and a viscosity of the downhole fluid based on the first and second resistances, at least one characteristic of the wire, and the electromotive force.