Schlumberger Technology Corporation

Services Petroliers Schlumberger

Schlumberger Holdings Limited

Prad Research and Development Limited

Anatoly Dementyev

Nicholas J Heaton

Robert Freedman

Henry N Bachman

Krishnamurthy Ganesan

Shin Utsuzawa

Vivek Anand

Daniel Catina

Payam Tabrizi

Cole Mann

Reza Taherian

Dean M Homan

Mark T Frey

David T Oliver

Gabriela Leu

Timothy Hopper

Henry Bachman

A shield for deployment about an antenna on an electromagnetic logging tool includes an electrically conductive, hollow body configured for coaxial deployment about the antenna. The hollow body includes a plurality of slots that extend through the hollow body. An outer surface of the hollow body includes at least one recess, at least a portion of which extends between and substantially orthogonal to the plurality of slots.

Antenna shield for electromagnetic logging tool

A method can include triggering an assessment of pulse width of an X degree pulse of a downhole NMR tool; responsive to the assessment, determining an optimal pulse width of the X degree pulse; acquiring NMR measurements using the downhole NMR tool and the optimal pulse width; and characterizing a formation using at least a portion of the NMR measurements.

Downhole NMR system

A method for fabricating a magnet on a nuclear magnetic resonance logging tool includes identifying a desired magnetic field strength at a predetermined depth of investigation, receiving a set of magnet segments configured for deployment on the logging tool in a magnet arrangement which make up a magnet array on the logging tool, processing a magnetic strength and an angular offset of selected magnet segments and their unique location in the magnet array to compute corresponding magnetic field strength solutions at the predetermined depth of investigation, selecting one magnet arrangement solution that minimizes a difference between the magnetic field strength solution and the desired magnetic field strength at the predetermined depth of investigation, and deploying the magnet segments on the logging tool according to the selected magnet arrangement solution to fabricate the magnet.

Optimization of magnet arrangement for nuclear magnetic resonance well logging tools

The present disclosure relates to generating multiple depths of investigation (DOI) measurements with a saddle point design nuclear magnetic resonance sensor. In general, an NMR sensor in accordance with the present disclosure includes a first magnet at a first radial distance from a radial center, and a second magnet at a second radial distance from the radial center. The first magnet at least partially cancels out a magnetic field gradient produced by the second magnet. Further, the NMR sensor may include an antenna that generates a first set of NMR data from a first DOI by operating at a first frequency and, generates a second set of NMR data from a second DOI by operating a second frequency. Additional frequencies are possible and envisioned.

Saddle point nuclear magnetic resonance tool for measurements at multiple depths of investigation

A method to produce a magnet arrangement, the method having steps of selecting a depth of investigation to be achieved by a downhole tool, identifying a desired magnetic field strength at the depth of investigation, producing a set of magnets to be incorporated into the downhole tool, sorting the set of magnets based on a quality of each of the magnets and optimizing the set of magnets such that the quality of each of the magnets results, when arranged, in the desired magnetic field strength at the depth of investigation and wherein the optimizing minimizes a cost function of the set of magnets produced.

An arrangement for shielding an NMR tool from electromagnetic noise, having a nuclear magnetic resonance tool configured to send and receive signals, a first shield configured around a nuclear magnetic resonance antenna of the nuclear magnetic resonance tool and a second shield configured to reduce the effects of eddy currents in the first shield.

Composite noise shield for magnetic resonance tools

The Larmor frequency for an in situ nuclear magnetic resonance (NMR) tool is determined and used to acquire NMR data. An NMR tool is provided and placed in situ, for example, in a wellbore. An initial estimate of the Larmor frequency for the in situ NMR tool is made and NMR data are acquired using the in situ NMR tool. A spectral analysis is performed on the NMR data, or optionally, the NMR data are digitized and a discrete Fourier transform (DFT) is performed on the digitized NMR data. The modal frequency of the spectral analysis or DFT is determined, and the Larmor frequency for the in situ NMR tool is determined using the modal frequency. The NMR tool is modified to transmit at the determined Larmor frequency and then used to acquire further NMR data.

Determining the Larmor frequency for NMR tools

Methods and systems are provided that enable logging while drilling NMR measurements to be made with magnets placed outside of the drill collar and magnetically permeable members to control the magnetic field gradient. A set of magnets can be disposed on and/or embedded on a drill collar, with an antenna disposed axially therebetween. Alternatively, a set of magnets and an antenna disposed therebetween can be disposed on a sleeve that is slid onto a recess in a drill collar. Additionally, a permeable member can be axially positioned between the set of magnets for affecting the depth of investigation.

Nuclear magnetic resonance tool with external magnets

An apparatus for NMR properties of subsurface formations includes a magnet, a transmitter antenna and at least one of a receiver section of the transmit antenna or a separate receiver antenna having a length along the longitudinal dimension of the apparatus which is shorter than a length of the transmitter antenna along the longitudinal dimension. The apparatus includes circuitry for applying radio frequency current pulses to the entire transmitter antenna and for receiving signals by the at least one of the receiver section of the transmitter antenna and the separate receiver antenna.

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Sugar Land, TX, United States of America

Anatoly Dementyev