4D seismic feasibility study: The importance of anisotropy and hysteresis

Asaka, Michinori; Luo, Min; Yamatani, Takashi; Kato, Akira; Yoshimatsu, Keita; Knapp, Levi J.

doi:10.1190/tle37090688.1

Cited by 3 publications

(7 citation statements)

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“…Asaka et al. (2018) found that the stress sensitivity of velocity is different between loading and unloading measurements and stated that friction between grains is a possible cause. They suggested using velocities measured during loading to assess the effect of pore‐pressure depletion.…”

Section: Measured Velocitiesmentioning

confidence: 99%

“…The ultrasonic velocity measurements of Knapp et al (2017) and Asaka et al (2018) on dry tight sandstone were utilized. Quantitative evaluation of minerals by scanning electron microscopy results reveals that quartz is the dominant mineral (approximately 86%) and that kaolinite is second in abundance (approximately 3.4%).…”

Section: Measured Velocitiesmentioning

confidence: 99%

“…Time‐lapse changes in elastic anisotropy occur because pore‐pressure depletion causes changes in the triaxial stress state (e.g., Fjær et al., 2008; Rudnicki, 1999), and rocks often show stress‐induced anisotropy under nonhydrostatic stress conditions (e.g., Herwanger & Horne, 2009; Nur & Simmons, 1969; Sayers, 2002). This can also be caused by the angle‐dependent stress sensitivity of velocities (Asaka et al., 2018).…”

Section: Introductionmentioning

confidence: 99%

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Anisotropic 4D seismic response inferred from ultrasonic laboratory measurements: A direct comparison with the isotropic response

Asaka

2022

Geophysical Prospecting

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Pore-pressure depletion causes changes in the triaxial stress state. Pore-pressure depletion in a flat reservoir, for example, can be reasonably approximated as uniaxial compaction, in which the horizontal effective stress change is smaller than the vertical effective stress. Furthermore, the stress sensitivity of velocities can be angle-dependent.Therefore, time-lapse changes in reservoir elastic anisotropy are expected as a consequence of production, which can complicate the interpretation of the 4D seismic response. The anisotropic 4D seismic response caused by pore-pressure depletion was investigated using existing core velocity measurements. To make a direct comparison between the anisotropic 4D seismic response and the isotropic response based only on vertical velocities, pseudoisotropic elastic properties were utilized, and the two responses were compared in terms of a dynamic rock physics template. A comparison of the dynamic rock physics templates indicates that time-lapse changes in reservoir elastic anisotropy have a noticeable impact on the interpretation of 4D seismic data. Changes in anisotropy as a result of pore-pressure depletion cause a time-lapse amplitude variation with offset response as if there is a reduction in V P /V S (i.e., pseudoisotropic V P /V S decreases), although the vertical V P /V S increases. The impact of time-lapse changes in anisotropy on the amplitude variation with offset gradient was also investigated, and the time-lapse anisotropy was found to enhance changes in the amplitude variation with offset gradient for a given case.

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Section: Measured Velocitiesmentioning

confidence: 99%

Section: Measured Velocitiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Anisotropic 4D seismic response inferred from ultrasonic laboratory measurements: A direct comparison with the isotropic response

Asaka

2022

Geophysical Prospecting

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“…MacBeth, 2004; Holt et al, 2005;Asaka et al, 2018) commonly assess the sensitivity of elastic properties 2 to pressure and saturation using measurements on dry cores combined with the Gassmann theory. 3…”

Section: Measurements 24mentioning

confidence: 99%

“…Due to strong velocity dispersion in fluid‐saturated rocks, time‐lapse seismic feasibility studies (e.g. MacBeth, 2004; Holt et al ., 2005; Asaka et al ., 2018) commonly assess the sensitivity of elastic properties to pressure and saturation using measurements on dry cores combined with the Gassmann theory. However, the process of drying reservoir samples may potentially modify the property of the rock matrix and introduce additional complications.…”

Section: Introductionmentioning

confidence: 99%

Elastic properties of a reservoir sandstone: a broadband inter‐laboratory benchmarking exercise

Ògúnsàmì

Jackson

Borgomano

et al. 2020

Geophysical Prospecting

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Low-frequency forced-oscillation methods applied to a reservoir sandstone allowed determination of the 15 Young's modulus and Poisson's ratio (from axial loading), bulk modulus (by oscillation of the confining 16 pressure), and shear modulus (from torsional forced-oscillation), for comparison with conventional 17 ultrasonic data. All tests were performed on a common sandstone core sample from an oil reservoir 18 offshore West Africa. The results show a steady increase in ultrasonic velocities and shear modulus of the 19 dry specimen as functions of pressure, which suggests a progressive closure of the inter-granular contacts. 20 An increase of bulk and Young's moduli and Poisson's ratio is observed on decane-saturation of the 21 sample when tested with a sufficiently small dead volume. This observation, consistent with Gassmann's 22 theory, suggests that such measurements probe undrained (saturated isobaric) conditions. Diminution or 23 absence of such fluid-related stiffening for low-frequency measurements with dead volumes comparable 24 with the pore volume of the specimen indicate partially drained conditions and highlight the critical role 25 of experimental boundary conditions. Directly measured bulk and shear moduli are consistent with those 26 derived from Young's modulus and Poisson's ratio. These results of the inter-laboratory testing using 27 different measurement devices are consistent in terms of the effect of frequency and fluid saturation for 28 the reservoir sandstone specimen. Such broad consistency illustrates the validity of forced-oscillation 29 techniques and constitutes an important benchmarking of laboratory testing of the elastic properties of a 30 porous medium. 31 32 1.0 Introduction 33 Time-lapse (4D) seismic technology is an important reservoir monitoring tool for the oil and gas industry 34

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Anisotropic AVO: Implications for reservoir characterization

Asaka

2018

The Leading Edge

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Routinely applied methods in seismic reservoir characterization such as forward modeling, wavelet extraction, amplitude-variation-with-offset (AVO) analysis, AVO inversion, and interpretation of seismic data usually assume that the earth can be modeled by a stack of isotropic layers. This assumption may cause significant problems where there are nonnegligible differences in the anisotropic parameters between the various lithologies that cause vertical profiles of VP/VS and the anisotropy parameters to be dissimilar. In this case, a significant mismatch between the seismic data and the isotropic synthetic seismogram AVO response will occur, making far-angle stack interpretation difficult. In some cases, the mismatch might be misinterpreted as a data quality issue. In an offshore Western Australia field, three lithofacies (volcanic rock, sandstone, and shale) need to be correctly identified for detailed reservoir characterization. Here, the AVO response of the actual seismic data is significantly affected by velocity anisotropy. Originally, it was thought that the far-angle stack could be used to detect volcanic rock in the field; however, after accounting for the velocity anisotropy effect, it was found that the far-angle stack enables us to identify sandstone. A proper understanding of the anisotropy effect allows the interpreter to use seismic data more effectively, which leads to a more robust estimation of the distribution of lithofacies in the target area.

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4D seismic feasibility study: The importance of anisotropy and hysteresis

Cited by 3 publications

References 10 publications

Anisotropic 4D seismic response inferred from ultrasonic laboratory measurements: A direct comparison with the isotropic response

Anisotropic 4D seismic response inferred from ultrasonic laboratory measurements: A direct comparison with the isotropic response

Elastic properties of a reservoir sandstone: a broadband inter‐laboratory benchmarking exercise

Anisotropic AVO: Implications for reservoir characterization

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