Selective NMR pulse for downhole measurements
AssigneeHalliburton Energy Services, Inc.
InventorsChang S. Shin, Paul Joseph Ganssle, Shriram Sarvotham, Songhua Chen
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Abstract
Various embodiments include a method for generating a pulse for use in nuclear magnetic resonance (NMR) logging. One such method generates the pulse by adjusting one or more of pulse parameters including a pulse shape, a pulse amplitude, a pulse phase, and/or a pulse frequency. The generated pulse produces a substantially uniform nuclear spin saturation or nuclear spin inversion response from a fluid. A wait time between the pulse transmission and an echo that indicates spin equilibrium has been achieved is substantially equal to a T1 time indicating characteristics of the fluid.
Claims16
A method for shaping a downhole nuclear magnetic resonance (NMR) pulse, the method comprising;
- adjusting one or more of a shape, an amplitude, a phase, or a frequency of an adiabatic pulse to produce a configured adiabatic pulse of saturation or inversion based on:
- total and peak radio frequency (RF);
- power consumption;
- pulse width;
- or
- bandwidth;
- generating the configured adiabatic pulse to transmit the configured adiabatic pulse into a downhole geological formation;
- determining when the adiabatic pulse is configured to produce a saturation or inversion of magnetization from the geological formation by determining a calculated response from Bloch's equations based on an echo response;
- transmitting the configured adiabatic pulse into a fluid in the geological formation;
- waiting a predetermined time;
- transmitting a readout pulse sequence based on the pulse;
- receiving an echo from the fluid;
- determining from Bloch's equations if the echo indicates spin saturation or inversion;
- and
- determining characteristics of the fluid based on the predetermined wait time.
A nuclear magnetic resonance (NMR) device for downhole logging, comprising:
- an NMR unit to transmit and receive NMR signals;
- and
- control circuitry coupled to the NMR unit, the control circuitry configured to generate one or more adiabatic pulses of saturation or inversion based on:
- total and peak radio frequency (RF);
- power consumption;
- pulse width;
- or
- bandwidth,
- wherein the generated pulses produce a nuclear spin saturation or nuclear spin inversion response from a fluid of a downhole geological formation, and
- wherein the control circuitry is further configured to wait a predetermined time prior to controlling transmission of a recovery pulse sequence and receiving an echo indicative of a percentage of nuclear spin saturation or nuclear spin inversion of the fluid.
A system for NMR logging, comprising:
- a downhole logging tool housing including a nuclear magnetic resonance (NMR) tool, the NMR tool comprising:
- an NMR unit comprising a transmitter to transmit NMR signals and a receiver to receive echoes from a formation in response to the transmitted NMR signals;
- and
- control circuitry coupled to the NMR unit, the control circuitry configured to shape an adiabatic pulse of saturation or inversion by adjusting:
- total and peak radio frequency (RF);
- power consumption;
- pulse width;
- or
- bandwidth,
- such that the adiabatic pulse is configured to produce a nuclear spin saturation or nuclear spin inversion response from a fluid of a downhole geological formation using a least amount of RF energy as determined by Bloch's equations,
- wherein the control circuitry is further configured to:
- select an adiabatic pulse and readout sequence from a plurality of adiabatic pulses and read out sequences;
- determine results for Bloch's equations for the selected adiabatic pulse and readout sequence;
- determine a first proportionality between a peak amplitude of the selected readout sequence and a peak amplitude of the selected adiabatic pulse;
- generate activations for T1 and T2 measurements based on the results of the Bloch's equations;
- determine an RF amplitude for a readout pulse of the readout sequence;
- and
- multiply the first proportionality by a second proportionality determined theoretically to generate a resultant RF amplitude for the adiabatic pulse.
Dependencies are inferred from the claim text.