Vassili Mikhaltsevitch

Modified multipulse technique for the effective detection of pure nuclear quadrupole resonance

Modification of the steady-state free precession (SSFP) multipulse technique for the effective detection of nuclear quadrupole resonance (NQR) signals was studied. This modification is based on the use of the preparatory pulse in the SSFP pulse sequences. It was shown that under certain conditions the total intensity of accumulated NQR signal can be increased. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of sodium nitrite (NaNO2) are presented and convincingly demonstrate the technique’s effectiveness.

Multipulse sequences for explosives detection by NQR under conditions of magnetoacoustic and piezoelectric ringing

A number of methods for cancelling magnetoacoustic and piezoelectric ringing signals in the spectroscopy of the nuclear quadrupole resonance are presented. The suggested methods include using the sequence (ϕ0)ϕ-(τ-ϕx-2τ-ϕy-2τ-ϕ−x-2τ-ϕ−y-τ)n and a multipulse analog of the two-pulse Hahn sequence with the first pulse replaced by a short steady-state sequence. Another method presented is the method of orthogonal effective fields for a fast saturation of the quadrupole spin system which can be used for subtracting the magnetoacoustic and piezoelectric components from the signal. The suggested methods can be used for the practical purposes of detecting explosive substances and narcotics.

A low-frequency laboratory apparatus for measuring elastic and anelastic properties of rocks

In this paper we present a new version of low-frequency laboratory apparatus designed for measurements of complex Young’s moduli and extensional attenuation of rock samples at seismic (1÷400 Hz) and teleseismic (≤1Hz) wave frequencies. The device can operate at confining or uniaxial pressures from 0 to 70 MPa. The preliminary data obtained for sandstone quarried in Donnybrook, Western Australia, are presented.

An Experimental Study of Low-Frequency Wave Dispersion and Attenuation in Water Saturated Sandstones

The elastic and anelastic parameters of dry and distilled water saturated sandstones with low (~7.8 mD) and high (~590 mD) permeabilities were measured at various confining pressures and room temperature (22 0 C). The both sandstones were quarried in Donnybrook, Western Australia. The experiments were performed with a new laboratory apparatus utilizing stress-strain relationship, which was developed to measure the complex Young’s moduli of rocks at seismic (1–100 Hz) and teleseismic (≤1 Hz) frequencies, confining or uniaxial pressures from 0 to 70 MPa, and strain amplitudes 10 -8 –10 -7 . The measurements in water saturated sandstones reveal a prominent peak of attenuation in the sample with low permeability at frequency ~0.8 Hz, whereas the attenuation in the high permeable sample remains similar to the attenuation measured under dry conditions. These results demonstrate that for low-permeability rocks seismic frequencies do not necessarily correspond to the low frequency limit of acoustic wave

Methods for optimizing the detection of HMX by nuclear quadrupole resonance

A study of multipulse sequences that can be used for the detection of HMX (N4(CH2)4(NO2)4) has been undertaken. On the basis of this study, a general method for experimentally optimizing multipulse sequences for the efficient detection of substances is proposed. The relaxation parameters and signal intensities for the nitrogen-14 spectral lines of a polycrystalline HMX sample were measured and the lines that are the most important for practical purposes were chosen.

A Low-frequency Apparatus for Characterizing the Mechanical Properties of Rocks

We present a new version of the low frequency laboratory apparatus operating at seismic frequencies and at either confining or uniaxial pressures from 0 to 70 Mpa. The apparatus utilizes a stress-strain technique and measures the complex Young’s modulus, extensional attenuation and Poisson’s ratio of the rock sample at the range of strain amplitudes between 10-6 and 10-8.

The transient processes in multi-pulse nitrogen-14 NQR

It has been demonstrated that transient processes, observed in a single crystal of NaNO2 acted upon by pulse sequences MW-2 and MW-4 and their modifications with 180 degrees flip angle of the pulses (Solid State Nucl. Magn. Resonance 10 (1997) 63; Sov. Phys.-JETP 88(5) (1999) 1580), which manifest themselves in the oscillating form of the NQR signals envelope, can be explained in the frames of a two-particle model. It has been proved that the nature of echo signals in the effective field of multi-pulse sequences received by the inversion of the phase of the sequence pulses or by introducing an additional 180 degrees pulse is connected with re-focusing of accumulated digressions of the flip angle from the ideal 180 degrees pulse. Experimental results of observing single and multiple echoes in a number of powdered nitrogenated substances in the effective field of various sequences at room temperature have been presented.

An experimental study of acoustic responses on the injection of supercritical CO2 into sandstones from the Otway Basin

Quantitative knowledge of the acoustic response of rock from an injection site on supercritical CO2 (scCO2) saturation is crucial for understanding the feasibility of time-lapse seismic monitoring of CO2 plume migration. A suite of shaley sandstones from the injection interval of the CRC-2 well, Otway Basin, Australia is tested to reveal the effects of supercritical CO2 injection on acoustic responses. CO2 is first injected into dry samples, flushed out with brine and then injected again into brine-saturated samples. Such a suite of experiments allows us to obtain acoustic velocities of the samples for a wide range of CO2/brine saturations from 0% to 100%. On injection of scCO2 into brine-saturated samples, the rocks exhibit a decrease of compressional velocities by about 7% with the increase of CO2 saturation from 0% to a maximum of about 50%. Anisotropy of the shaley sandstones from the Otway Basin must be taken into account as the difference in the velocities normal and parallel to bedding is comparable with the perturbation due to CO2 injection and the samples of different orientations exhibit transition from Gassmann-Hill to Gassmann-Wood bound at different scCO2 saturations. Changes of the dry samples before and after the CO2 injection (if any) are not traceable by acoustic methods.

ASEG Extended Abstracts 2012

Summary A study of the pore fluid effects on the elastic and anelastic properties of sedimentary rocks is important for interpreting seismic data obtained for reservoirs as well as for monitoring the fluid movement during both fluid extraction in producing fields and injection of CO2 for storage purposes. In most sedimentary rocks low intrinsic permeability and, as a consequence, low fluid mobility lead to a situation when relative motion between pore fluid and rock skeleton has significant influence on acoustic wave propagation even at seismic frequencies. Therefore, in many cases the experiments conducted only at seismic frequencies are not sufficient to validate commonly used theoretic models of elastic moduli dispersion and attenuation. We present data obtained with a new version of lowfrequency laboratory apparatus designed for measurements of Young’s moduli and extensional attenuation of rocks at seismic (1-400 Hz) and teleseismic (≤1Hz) wave frequencies. The apparatus can operate at confining pressures from 0 to 70 MPa. Elastic and anelastic parameters of dry and water-saturated sandstone quarried in Donnybrook, Western Australia, were measured at various confining pressures and room temperature (~200 C). A peak of attenuation in a watersaturated sample with 14.8% porosity and 7.8 mD permeability was found at frequency 0.8 Hz.A study of the pore fluid effects on the elastic and anelastic properties of sedimentary rocks is important for interpreting seismic data obtained for reservoirs as well as for monitoring the fluid movement during both fluid extraction in producing fields and injection of CO2 for storage purposes. In most sedimentary rocks low intrinsic permeability and, as a consequence, low fluid mobility lead to a situation when relative motion between pore fluid and rock skeleton has significant influence on acoustic wave propagation even at seismic frequencies. Therefore, in many cases the experiments conducted only at seismic frequencies are not sufficient to validate commonly used theoretic models of elastic moduli dispersion and attenuation. We present data obtained with a new version of low-frequency laboratory apparatus designed for measurements of Young’s moduli and extensional attenuation of rocks at seismic (1-400 Hz) and teleseismic (≤1Hz) wave frequencies. The apparatus can operate at confining pressures from 0 to 70 MPa. Elastic and anelastic parameters of dry and water-saturated sandstone quarried in Donnybrook, Western Australia, were measured at various confining pressures and room temperature (~20° C). A peak of attenuation in a water-saturated sample with 14.8% porosity and 7.8 mD permeability was found at frequency 0.8 Hz.

An Experimental Study of Low-frequency Wave Dispersion and Attenuation in Water Saturated Sandstone

at seismic frequencies. Therefore, in many cases the experiments conducted only at seismic frequencies are not sufficient to validate commonly used theoretic models of elastic moduli dispersion and attenuation. We present data obtained with a new version of low-frequency laboratory apparatus designed for measurements of Young’s moduli and extensional attenuation of rocks at seismic (1-400 Hz) and teleseismic (≤1Hz) wave frequencies. The apparatus can operate at confining pressures from 0 to 70 MPa. Elastic and anelastic parameters of dry and water-saturated sandstone quarried in Donnybrook, Western Australia, were measured at various confining pressures and room temperature (~20 C). A peak of attenuation in a water-saturated sample with 14.8% porosity and 7.8 mD permeability was found at frequency 0.8 Hz.