Abstract: Methods and systems for logging a wellbore having a casing using ultrasonic logging are described. Traditional ultrasonic logging involves using a piezoelectric transducer that is spaced from the inner surface of the casing by a least a distance referred to as the “far-field” distance. Logging in the “far-field,” as traditionally done, avoids destructive interference. The methods and systems described herein allow logging in the “near-field.” Logging in the near-field using the described methods and systems overcomes several difficulties associated with acoustic logging, particularly in attenuative, dispersive, and deviated environments.

Abstract: A centralizer assembly replaces an existing centralizer of a wireline tool so the tool can be used with smaller casing, such as casing smaller than 6-in. The assembly includes first and second centralizer units that replace the existing centralizer on a mandrel. Each unit has a sleeve that fits in a recess of the mandrel, and each unit has slider blocks disposed together in the recess on opposing sides of a divider on the sleeve. Arms hingedly connected to the blocks on each unit connect together at a joint having a roller for engaging in the casing. On each unit, a common pin is disposed through the slider blocks, and biasing elements on the common pin bias the blocks toward one another with different amounts of bias.

Abstract: A centralizer assembly replaces an existing centralizer of a wireline tool so the tool can be used with smaller casing, such as casing smaller than 6-in. The assembly includes first and second centralizer units that replace the existing centralizer on a mandrel. Each unit has a sleeve that fits in a recess of the mandrel, and each unit has slider blocks disposed together in the recess on opposing sides of a divider on the sleeve. Arms hingedly connected to the blocks on each unit connect together at a joint having a roller for engaging in the casing. On each unit, a common pin is disposed through the slider blocks, and biasing elements on the common pin bias the blocks toward one another with different amounts of bias.

Abstract: Methods and systems are described for estimating the level of contamination of downhole fluid and underlying composition using physical property measurements, and mathematical modeling of contamination functions and fluid property mixing laws. The proposed approaches enable computation of estimates of the pumping time needed to achieve a certain contamination threshold level and the determination of whether or not sampling is appropriate at the current point in time based on the predicted compositional properties of the formation fluid.

Abstract: Analysis evaluates formation fluid with a downhole tool disposed in a borehole. A plurality of possible constituents is defined for the formation fluid, and constraints are defined for the possible constituents. The constraints can include boundary constraints and constraints on the system's dynamics. The formation fluid is obtained from the borehole with the downhole tool over a plurality of time intervals, and density of the obtained formation fluid is obtained at the time intervals. To evaluate the fluid composition, a state probability distribution of the possible constituents of the obtained formation fluid at the current time interval is computed recursively from that at the previous time interval and by assimilating the current measured density of the obtained formation fluid in addition to the defined boundary/dynamic constraints.

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: Methods and systems are described for estimating the level of contamination of downhole fluid and underlying composition using physical property measurements, and mathematical modeling of contamination functions and fluid property mixing laws. The proposed approaches enable computation of estimates of the pumping time needed to achieve a certain contamination threshold level and the determination of whether or not sampling is appropriate at the current point in time based on the predicted compositional properties of the formation fluid.

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: Analysis evaluates formation fluid with a downhole tool disposed in a borehole. A plurality of possible constituents is defined for the formation fluid, and constraints are defined for the possible constituents. The constraints can include boundary constraints and constraints on the system's dynamics. The formation fluid is obtained from the borehole with the downhole tool over a plurality of time intervals, and density of the obtained formation fluid is obtained at the time intervals. To evaluate the fluid composition, a state probability distribution of the possible constituents of the obtained formation fluid at the current time interval is computed recursively from that at the previous time interval and by assimilating the current measured density of the obtained formation fluid in addition to the defined boundary/dynamic constraints.

Abstract: A multi-channel detector assembly for downhole spectroscopy has a reference detector unit optically coupled to a reference channel of a source and has a measurement detector unit optically coupled to a measurement channel of the source. The reference and measurement detectors detect spectral signals across a spectral range of wavelengths from the reference and measurement channels. Conversion circuitry converts the detected spectral signals into reference signals and measurement signals, and control circuitry processes the reference and measurements signals based on a form of encoding used by the source. Then, the control circuitry can control the output of spectral signals from the source based on the processed signals or scale the measurement signal to correct for source fluctuations or changes in environmental conditions.

Abstract: A refractive index sensor having one or more sources, an adaptive optical element or scanner, imaging optics, a sensing optic, and one or more detectors. The scanner impinges a signal from the source into the sensing optic and onto a sensor-sample interface at sequential angles of incidence. The detector response increases dramatically to signals reflected from the interface at corresponding sequential angles of reflection equal to or greater than a critical angle. The refractive index sensor also uses an input lens between the scanner and the sensing optic and uses an output lens between the sensing optic and the detector. A processor controls the sensor and can determine index of refraction of the fluid sample based on the detector response and scan rate. The sensor can be used in several operational environments from a laboratory to a downhole tool, such as a formation tester to determine properties in a borehole environment.

Abstract: A multi-channel source assembly for downhole spectroscopy has individual sources that generate optical signals across a spectral range of wavelengths. A combining assembly optically combines the generated signals into a combined signal and a routing assembly that splits the combined signal into a reference channel and a measurement channel. Control circuitry electrically coupled to the sources modulates each of the sources at unique or independent frequencies during operation.

Abstract: Detector assembly for downhole spectroscopy includes a near-infra-red quaternary photodiode that can operate at high temperatures without cooling it to the standard operation temperature range of the photodiode. High temperature operation of the photodiode right shifts the detector assembly's responsivity curve to include wavelengths of up to 2400-nm. The photodiode has manageable dark current at temperatures even at 200° C., and it can be packaged using high temperature construction. The photodiode is operated in photovoltaic mode at high temperatures but can be operated at photoconductive mode at lower temperatures. At least partial cooling can be provided above a predetermined temperature.

Abstract: A downhole fluid analysis tool has a tool housing and a fluid analysis device. The tool housing is deployable downhole and has at least one flow passage for a fluid sample. The fluid analysis device is disposed in the tool housing relative to the flow passage. Inside the device, one or more sources generate a combined input electromagnetic signal across a spectrum of wavelengths, and a routing assembly routes generated signals into the reference and measurement signals. At least one wheel having a plurality of filters is rotated to selectively interpose one or more of the filters in the paths of the reference and measurement signals.

Abstract: A downhole fluid analysis tool has a housing and a flow passage for downhole fluid. A device disposed in the tool housing relative to the flow passage has a one or more sources, one or more sensing optics, one or more detectors, and control circuitry. The source generates an input signal. The sensing optic has a refractive index (RI) higher than crude oil and other expected constituents. A sensing surface of the optic optically coupled to the source interfaces with a downhole fluid. When the variable RI of the downhole fluid reaches a defined relationship to the optic's RI, the input signal interacting with the sensing surface experiences total internal reflection, and the reflected signal from the sensing surface remains in the sensing optic and reflects to a detector. The control circuitry monitors the detector's response and indicates gas break out if the response is above a threshold.

Abstract: A multi-channel source assembly for downhole spectroscopy has individual sources that generate optical signals across a spectral range of wavelengths. A combining assembly optically combines the generated signals into a combined signal and a routing assembly that splits the combined signal into a reference channel and a measurement channel. Control circuitry electrically coupled to the sources modulates each of the sources at unique or independent frequencies during operation.

Abstract: Detector assembly for downhole spectroscopy includes a near-infra-red quaternary photodiode that can operate at high temperatures without cooling it to the standard operation temperature range of the photodiode. High temperature operation of the photodiode right shifts the detector assembly's responsivity curve to include wavelengths of up to 2400-nm. The photodiode has manageable dark current at temperatures even at 200° C., and it can be packaged using high temperature construction. The photodiode is operated in photovoltaic mode at high temperatures but can be operated at photoconductive mode at lower temperatures. At least partial cooling can be provided above a predetermined temperature.

Abstract: A multi-channel source assembly for downhole spectroscopy has individual sources that generate optical signals across a spectral range of wavelengths. A combining assembly optically combines the generated signals into a combined signal and a routing assembly that splits the combined signal into a reference channel and a measurement channel. Control circuitry electrically coupled to the sources modulates each of the sources at unique or independent frequencies during operation.

Abstract: A refractive index sensor having one or more sources, an adaptive optical element or scanner, imaging optics, a sensing optic, and one or more detectors. The scanner impinges a signal from the source into the sensing optic and onto a sensor-sample interface at sequential angles of incidence. The detector response increases dramatically to signals reflected from the interface at corresponding sequential angles of reflection equal to or greater than a critical angle. The refractive index sensor also uses an input lens between the scanner and the sensing optic and uses an output lens between the sensing optic and the detector. A processor controls the sensor and can determine index of refraction of the fluid sample based on the detector response and scan rate. The sensor can be used in several operational environments from a laboratory to a downhole tool, such as a formation tester to determine properties in a borehole environment.

Abstract: A downhole fluid analysis tool has a housing and a flow passage for downhole fluid. A device disposed in the tool housing relative to the flow passage has a one or more sources, one or more sensing optics, one or more detectors, and control circuitry. The source generates an input signal. The sensing optic has a refractive index (RI) higher than crude oil and other expected constituents. A sensing surface of the optic optically coupled to the source interfaces with a downhole fluid. When the variable RI of the downhole fluid reaches a defined relationship to the optic's RI, the input signal interacting with the sensing surface experiences total internal reflection, and the reflected signal from the sensing surface remains in the sensing optic and reflects to a detector. The control circuitry monitors the detector's response and indicates gas break out if the response is above a threshold.