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Elastic wave propagation and scattering in prestressed porous rocks

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Science China Earth Sciences 2020年第9期63卷 1309-1329页

作者： li-yun fu Bo-Ye fu Weijia SUN Tongcheng HAN Jianlin liU Key Laboratory of Deep Oil and Gas China University of Petroleum(East China)Qingdao 266580China Laboratory for Marine Mineral Resources Qingdao National Laboratory for Marine Science and TechnologyQingdao 266071China Key Laboratory of Earth and Planetary Physics Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China Institutions of Earth Science Chinese Academy of SciencesBeijing 100029China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing 100049China

Poro-acoustoelastic theory has made a great progress in both theoretical and experimental aspects,but with no publications on the joint research from theoretical analyses,experimental measurements,and numerical *** key issues challenge the joint research with comparisons of experimental and numerical results,such as digital imaging of heterogeneous poroelastic properties,estimation of acoustoelastic constants,numerical dispersion at high frequencies and strong heterogeneities,elastic nonlinearity due to compliant pores,and contamination by boundary *** poroacoustoelastic theory,valid for the linear elastic deformation of rock grains and stiff pores,is modified by incorporating a dualporosity model to account for elastic nonlinearity due to compliant pores subject to high-magnitude loading stresses.A modified finite-element method is employed to simulate the subtle effect of microstructures on wave propagation in prestressed digital *** measure the heterogeneity of samples by extracting the autocorrelation length of digital cores for a rough estimation of scattering *** conductexperimental measurements with a fluid-saturated sandstone sample under a constant confining pressure of 65 MPa and increasing pore pressures from 5 to 60 *** simulations for ultrasound propagation in the prestressed fluid-saturated digital core of the sample are followed based on the proposed poro-acoustoelastic model with compliant *** results demonstrate a general agreement between experimental and numerical waveforms for different stresses,validating the performance of the presented modeling *** excellent agreement between experimental and numerical coda quality factors demonstrates the applicability for the numerical investigation of the stress-associated scattering attenuation in prestressed porous rocks.

关键词： Poro-acoustoelasticity with compliant pores Elastic waves Prestressed porous rocks Numerical modeling Stressinduced scattering attenuation

Elastic Characteristics of Digital Cores from Longmaxi Shale Using Lattice Spring Models

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Communications in Computational Physics 2020年第6期28卷 518-538页

作者： Ning liu li-yun fu Key Laboratory of Earth and Planetary Physics Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China School of Geosciences China University of Petroleum(East China)Qingdao 266580ShandongChina

Effective medium methods for the attribution of micro-structures to macro elastic properties of shales are important for the prediction of sweet spots in the shale-gas *** X-ray micro-computed tomography(XMCT),the micro-structures of shale core samples from Longmaxi Formation are visualized and characterized by 3D digital *** an efficient alternative to conventional effective medium methods for estimating elastic properties,we propose a consistent workflow of lattice spring modeling(LSM)to emulate the digital cores using three types of *** attention is paid to investigate the effective Young’s moduli,Poisson’s ratios,and preferred orientations,by uniaxial compression tests along two *** elastic deformation,the impact of lattice arrangements on the anisotropy is even more than those of stress disturbances and micro-structural *** with analytical approximations and theoretical predictions,the LSM numerical scheme shows general applicability for heterogeneous porous rocks.

关键词： Elastic characteristics lattice spring model(LSM) X-ray micro-computed tomogra-phy(XMCT) digital cores

Laboratory insights into the effects of methane hydrate on the anisotropic joint elastic-electrical properties in fractured sandstones

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Petroleum Science 2023年第2期20卷 803-814页

作者： Sheng-Biao liu Tong-Cheng Han li-yun fu Shandong Provincial Key Laboratory of Deep Oil and Gas China University of Petroleum(East China)QingdaoShandong266580China Laboratory for Marine Mineral Resources Pilot National Laboratory for Marine Science and TechnologyQingdaoShandong266071China

Fractured hydrate-bearing reservoirs show significantly anisotropic geophysical properties. The joint application of seismic and electromagnetic explorations is expected to accurately assess hydrate resources in the fractured reservoirs. However, the anisotropic joint elastic-electrical properties in such reservoirs that are the key to the successful application of the joint explorations, remain poorly understood. To obtain such knowledge, we designed and implemented dedicated laboratory experiments to study the anisotropic joint elastic-electrical properties in fractured artificial silica sandstones (with fracture density of about 6.2%, porosity of approximately 25.7%, and mean grainsize of 0.089 mm) with evolving methane hydrate. The experimental results showed that the anisotropic compressional wave velocities respectively increased and decreased with the forming and dissociating hydrate, and the variation in the increasing trend and the decreasing extent of the velocity perpendicular to the fractures were more significant than that parallel to the fractures, respectively. The experimental results also showed that the overall decreasing trend of the electrical conductivity parallel to the fractures was steeper than that perpendicular to the fractures during hydrate formation, and the general variations of the two conductivities with complex trend were similar during hydrate dissociation. The variations in the elastic and electrical anisotropic parameters with forming and dissociating hydrate were also found to be distinct. Interpretation of the experimental results suggested that the hydrate binding to the grains evolved to bridge the surfaces of fractures when saturation exceeded 10% during hydrate formation, and the bridging hydrate gradually evolved to floating in fractures during dissociation. The experimental results further showed that the anisotropic velocities and electrical conductivities were correlated with approximately consistent trends of different

关键词： Fractured hydrate reservoirs Elastic anisotropy Electrical anisotropy Joint elastic-electrical properties Hydrate distribution

A quantitative interpretation of the saturation exponent in Archie’s equations

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Petroleum Science 2021年第2期18卷 444-449页

作者： Tong-Cheng Han Han Yan li-yun fu School of Geosciences China University of Petroleum(East China)Qingdao 266580China Laboratory for Marine Mineral Resources Qingdao National Laboratory for Marine Science and TechnologyQingdao 266071China

Saturation exponent is an important parameter in Archie’s equations;however,there has been no well-accepted physical interpretation for the saturation *** have theoretically derived Archie’s equations from the Maxwell–Wagner theory on the assumption of homogeneous fluid distribution in the pore space of clay-free porous *** theoretical derivations showed that the saturation exponent is in essence the cementation exponent for the water–air mixture and is quantitatively and explicitly related to the aspect ratio of the air bubbles in the *** results have provided a theoretical backup for the empirically obtained Archie’s equations and have offered a more physical and quantitative understanding of the saturation exponent.

关键词： Electrical properties Saturation exponent Archie equation Maxwell-Wagner theory

Seismic attenuation compensation with spectral-shaping regularization

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Earth and Planetary Physics 2022年第3期6卷 259-274页

作者： QiZhen Du WanYu Wang WenHan Sun li-yun fu Shandong Provincial Key Laboratory of Deep Oil&Gas China University of Petroleum(East China)Qingdao 266580China Laboratory for Marine Mineral Resources Qingdao National Laboratory for Marine Science and TechnologyQingdao 266237China Key Laboratory of Geophysical Prospecting China National Petroleum Corporation(CNPC)China University of Petroleum(East China)Qingdao 266580China Department of Physics University of AlbertaEdmontonABT6G 2EICanada

Because of the viscoelasticity of the subsurface medium,seismic waves will inherently attenuate during propagation,which lowers the resolution of the acquired seismic ***-Q filtering,as a typical approach to compensating for seismic attenuation,can efficiently recover high-resolution seismic data from *** most efforts are focused on compensating for highfrequency energy and improving the stability of amplitude compensation by inverse-Q filtering,low-frequency leakage may occur as the high-frequency component is *** this article,we propose a compensation scheme that promotes the preservation of lowfrequency energy in the seismic *** constructed an adaptive shaping operator based on spectral-shaping regularization by tailoring the frequency spectra of the seismic *** then performed inverse-Q filtering in an inversion *** data-driven shaping operator can regularize and balance the spectral-energy distribution for the compensated records and can maintain the low-frequency ratio by constraining the overcompensation for high-frequency *** tests and applications on prestack common-reflectionpoint gathers indicated that the proposed method can preserve the relative energy of low-frequency components while fulfilling stable high-frequency compensation.

关键词： seismic attenuation compensation spectral-shaping regularization data-driven shaping operator offset-related inverse-Q filter

Acoustic viscoelastic modeling by frequency-domain boundary element method

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Earthquake Science 2017年第2期30卷 97-105页

作者： Xizhu Guan li-yun fu Weijia Sun Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China CNOOC Research Center Beijing 100027 China

Earth medium is not completely elastic, with its viscosity resulting in attenuation and dispersion of seismic waves. Most viscoelastic numerical simulations are based on the finite-difference and finite-element methods. Targeted at viscoelastic numerical modeling for multilayered media, the constant-Q acoustic wave equation is transformed into the corresponding wave integral representation with its Green＇s function accounting for viscoelastic coefficients. An efficient alternative for full-waveform solution to the integral equation is proposed in this article by extending conventional frequency-domain boundary element methods to viscoelastic media. The viscoelastic boundary element method enjoys a distinct characteristic of the explicit use of boundary continuity conditions of displacement and traction, leading to a semi-analytical solution with sufficient accuracy for simulating the viscoelastic effect across irregular interfaces. Numerical experiments to study the viscoelastic absorption of different Q values demonstrate the accuracy and applicability of the method.

关键词： Viscoelastic media Viscoelastic boundary element method Frequency-domain implementation Viscoelastic numerical modeling

A Stable Q Compensated Reverse Time Migration Method Based on Excitation Amplitude Imaging Condition

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Communications in Computational Physics 2020年第6期28卷 141-166页

作者： Qingqing li li-yun fu Weijia Sun Wei Wei Wanting Hou School of Geosciences China University of PetroleumShandong 266555China Institute of Geology and Geophysics Chinese Academy of SciencesBeijing 100029China

The stability and efficiency,especially the stability,are generally concerned issues in Q compensated reverse time migration(Q-RTM).The instability occurs because of the exponentially boosted high frequency ambient noise during the forward or backward seismic wavefield *** regularization and low-pass filtering methods are two effective strategies to control the instability of the wave propagation in ***,the regularization parameters are determined experimentally,and the wavefield cannot be recovered *** low-pass filtering method cannot balance the selection of cutoff frequency for varying Q values,and may damage the effective signals,especially when the signal-to-noise ratio(SNR)of the seismic data is low,the Q-RTM will be a highly unstable *** order to achieve the purpose of stability,the selection of cutoff frequency will be small enough,which can cause great damage to the effective high frequency *** this paper,we present a sta-ble Q-RTM algorithm based on the excitation amplitude imaging condition,which can compensate both the amplitude attenuation and phase *** the existing Q-RTM algorithms enlarging the amplitude,the exponentially attenuated seismic wavefield will be used during both the forward and backward wavefield propagation of ***,the new Q-RTM algorithm is relative stable,even for the low SNR seismic *** order to show the accuracy and stability of our stable Q-RTM algorithm clearly,an example based on Graben model will be ***,a realistic BP gas chimney model further demonstrates that the proposed method enjoys good stability and anti-noise performance compared with the traditional Q-RTM with amplitude *** the Q-RTM images of these two models to the reference images obtained by the acoustic RTM with acoustic seismic data,the new Q-RTM results match the reference images quite *** proposed method is also tested using a field seismic data,the res

关键词： Stable reverse time migration attenuation

Born-series approximation to volume-scattering wave for piecewise heterogeneous media

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Earthquake Science 2014年第2期27卷 159-168页

作者： Geng-Xin Yu li-yun fu Beijing Chinese Language and Culture College Key Laboratory of the Earth’s Deep Interior Institute of Geology and GeophysicsChinese Academy of Sciences

An efficient approximate scheme is presented for wave-propagation simulation in piecewise heterogeneous media by applying the Born-series approximation to volume-scattering waves. The numerical scheme is tested for dimensionless frequency responses to a heterogeneous alluvial valley where the velocity is perturbed randomly in the range of 5 %–25 %,compared with the full-waveform numerical solution. Then,the scheme is extended to a heterogeneous multilayered model by calculating synthetic seismograms to evaluate approximation accuracies Numerical experiments indicate that the convergence rate of this method decreases gradually with increasing velocity perturbations. The method has a fast convergence for velocity perturbations less than 15 %. However,the convergence becomes slow drastically when the velocity perturbation increases to 20 %. The method can hardly converge for the velocity perturbation up to 25 %.

关键词： Generalized lippmann–Schwinger equation Piecewise heterogeneous media Born-series approximation Volume-scattering waves

Detection of seismic events on Mars: a lunar perspective

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Earth and Planetary Physics 2019年第4期3卷 290-297页

作者： WeiJia Sun liang Zhao Yong Wei li-yun fu Key Laboratory of Earth and Planetary Physics Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China Institutions of Earth Science Chinese Academy of Sciences Beijing 100029 China State Key Laboratory of lithospheric Evolution Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China College of Earth and Planetary Sciences University of Chinese Academy of Sciences Beijing 100049 China Key Laboratory of Deep Oil and Gas China University of Petroleum (East China) Qingdao 266580 China

The interior structures of planets are attracting more and more detailed attention;these studies could be of great value in improving our understanding of the early evolution of Earth. Seismological investigations of planet interiors rely primarily on seismic waves excited by seismic events. Since tectonic activities are much weaker on other planets, e.g. Mars, the magnitudes of their seismic events are much smaller than those on Earth. It is therefore a challenge to detect seismic events on planets using such conventional techniques as short-time average/long-time average (STA/LTA) triggers. In pursuit of an effective and robust scheme to detect smallmagnitude events on Mars in the near future, we have taken Apollo lunar seismic observations as an example of weak-activity data and developed an event-detection scheme. The scheme reported here is actually a two-step processing approach: the first step involves a despike filter to remove large-amplitude impulses arising from large temperature variations;the second step employs a matched filter to unmask the seismic signals from a weak event hidden in the ambient and scattering noise. The proposed scheme has been used successfully to detect a moonquake that was not in the known moonquake catalogue, demonstrating that the two-step strategy is a feasible method for detecting seismic events on planets. Our scheme will provide a powerful tool for seismic data analysis of the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission, and China’s future lunar missions.

关键词： planetary seismology event detection interior structures despike filter matched filter