Youli Quan - Academia.edu (original) (raw)

Papers by Youli Quan

All Days, Feb 13, 2008

Water hammer effects resulting from the shutting in of water injection wells are an often ignored... more Water hammer effects resulting from the shutting in of water injection wells are an often ignored issue in petroleum production operations but they have considerable impact on injection well performance and longevity. Mismanaged, they can result in substantial and perhaps irreparable damage. This paper presents a study on the creation and propagation of water hammer due to rapid shut-in of water injectors. Water hammer 1-4 or pressure surge, is a pressure transient phenomenon which has long been known to occur as a result of a sudden change in fluid flow velocity. In water injectors, rapid shut-in creates a water hammer. Over time, injectors that undergo repeated rapid shut-ins often have significantly reduced injectivity and show evidence of sanding and even failure of the down-hole completion 5. It is therefore critical to understand the nature of water hammer including the magnitude, frequency, and energy dissipation. To study the water hammer in water injectors, a field trial was conducted to record pressure pulses generated from rapid shutins, at different well depths, in a soft formation, cased and perforated (C&P) water injector. Modeling work was conducted to understand the data. The results of the field trial and model work demonstrated that: • The magnitude of the first pressure pulse due to abrupt shut-in can be estimated by using the equation: Δp = V×ρ×c, where V is the flow velocity, ρ is the fluid density, and c is the speed of propagation of a pressure signal along the well. • High rate sampling (up to 100 samples/second) is required to capture subtle details of the water hammer signal. • Water hammer can be modeled as a low-frequency pressure wave similar to the higher frequency Stoneley waves produced during VSP's and by acoustic logging tools. • Models of water hammer propagation in a synthetic analog of the test well reproduced most of the details of the signals recorded during the tests.

Proceedings of SPIE, Mar 8, 2007

Sound-speed tomography images can be used for cancer detection and diagnosis. Tumors have general... more Sound-speed tomography images can be used for cancer detection and diagnosis. Tumors have generally higher sound speeds than the surrounding tissue. Quality and resolution of tomography images are primarily determined by the insonification/illumination aperture of ultrasound and the capability of the tomography method for accurately handling heterogeneous nature of the breast. We investigate the capability of an efficient time-of-flight tomography method using transmission ultrasound from a ring array for reconstructing sound-speed images of the breast. The method uses firstarrival times of transmitted ultrasonic signals emerging from non-beamforming ultrasound transducers located around a ring. It properly accounts for ray bending within the breast by solving the eikonal equation using a finite-difference scheme. We test and validate the time-of-flight transmission tomography method using synthetic data for numerical breast phantoms containing various objects. In our simulation, the objects are immersed in water within a ring array. Two-dimensional synthetic data are generated using a finite-difference scheme to solve acoustic-wave equation in heterogeneous media. We study the reconstruction accuracy of the tomography method for objects with different sizes and shapes as well as different perturbations from the surrounding medium. In addition, we also address some specific data processing issues related to the tomography. Our tomography results demonstrate that the first-arrival transmission tomography method can accurately reconstruct objects larger than approximately five wavelengths of the incident ultrasound using a ring array.

Proceedings of SPIE, Mar 8, 2007

Ultrasonic reflection imaging has the potential to produce higher image resolution than transmiss... more Ultrasonic reflection imaging has the potential to produce higher image resolution than transmission tomography, but imaging resolution and quality still need to be further improved for early cancer detection and diagnosis. We present an ultrasound reflection image reconstruction method using the split-step Fourier propagator. It is based on recursive inward continuation of ultrasonic wavefields in the frequency-space and frequency-wavenumber domains. The inward continuation within each extrapolation interval consists of two steps. In the first step, a phase-shift term is applied to the data in the frequency-wavenumber domain for propagation in a reference medium. The second step consists of applying another phase-shift term to data in the frequency-space domain to approximately compensate for ultrasonic scattering effects of heterogeneities within the breast. We use synthetic ultrasound pulse-echo data recorded around a ring for heterogeneous, computer-generated, numerical breast phantoms to study the imaging capability of the method. The phantoms are derived from an experimental breast phantom and a sound-speed tomography image of an in-vivo ultrasound breast data collected using a ring array. The heterogeneous sound-speed models used for pulse-echo imaging are obtained using a computationally efficient, first-arrival-time (time-of-flight) transmission tomography method. Our studies demonstrate that reflection image reconstruction using the split-step Fourier propagator with heterogeneous sound-speed models significantly improves image quality and resolution. We also numerically verify the spatial sampling criterion of wavefields for a ring transducer array.

Proceedings of SPIE, May 13, 2011

We present results of an ongoing project to assess the applicability in reflection seismology of ... more We present results of an ongoing project to assess the applicability in reflection seismology of emerging super resolution techniques pioneered in digital photography. Our approach involves: (1) construction of a forward model connecting low resolution seismic images to high resolution ones, and (2) solution of a Tikhonov-regularized ill conditioned optimization problem to construct a high resolution image from several lower resolution counterparts; the high and low resolution images derived, respectively, from dense and sparse seismic surveys.

Journal of the Acoustical Society of America, Nov 1, 2006

Sound speeds and densities of breast tissue vary in space, and those of tumors are different from... more Sound speeds and densities of breast tissue vary in space, and those of tumors are different from the surrounding tissues. These differences in mechanical properties cause scattering of ultrasonic waves, particularly in dense breasts. An ultrasonic reflection imaging method using a heterogeneous background is presented to properly account for scattering off heterogeneities within the breast. The method is based on downward continuation of ultrasonic wave fields in the frequency-space and frequency-wave-number domains. Synthetic ultrasonic data for scatterers within a heterogeneous breast model were used to investigate the imaging resolution of the method. Imaging examples using ultrasonic data acquired using a clinical prototype, consisting of an ultrasound scanner with a ring transducer array, are presented. The heterogeneous background sound-speed models were obtained using transmission tomography. The imaging results are compared with those obtained using a homogeneous background. The study demonstrates that imaging with heterogeneous backgrounds significantly improves image quality and resolution. [This work was supported through the DOE Laboratory-Directed Research and Development program at Los Alamos National Laboratory.]

Journal of the Acoustical Society of America, 2008

Crosswell reverse time migration (RTM) with up and downgoing wave separation can greatly reduce a... more Crosswell reverse time migration (RTM) with up and downgoing wave separation can greatly reduce artifacts usually seen in the conventional RTM without wave separation. However, the up and downgoing wave separation cannot be efficiently conducted in space-time domain algorithms because the upper/lower half space images are indistinguishable. In order to tackle this problem, we propose a frequency-domain algorithm with up and downgoing wave decomposition for the crosswell RTM. The numerical experiments and field data example demonstrate that the proposed method can greatly attenuate migration artifacts while still keep reasonable efficiency.

Chinese Journal of Geophysics, 1988

Gaussian beam (GB) method is a high-frequency asymptotic method of computing wave-fields in inhom... more Gaussian beam (GB) method is a high-frequency asymptotic method of computing wave-fields in inhomogenous media. Three variant methods, the spectral method, the convolutory method and the wave-packet method, to computing synthetic seismograms by Gaussian beam summation, are discussed in detail. A combined method which may be used in Lroader range is suggested. A convolutory equation which may be convenient for numerical calculation is, given. When GB synthetic sesmograms are computed by the combined method, both convqlu-tory method and wave-packet method may be used, in order to get fairly hign calculative accuracy and speed. Numerical examples for 2-D structure by the convolutory method, the wave-packet method and the combined method are presented.

Poor repeatability caused by near-surface variations is one of the main difficulties limiting the... more Poor repeatability caused by near-surface variations is one of the main difficulties limiting the application of seismic monitoring on land. We developed the Double Time Difference (DTD) method to address this problem. DTD utilizes self-calibration to mitigate the impact of nearsurface variations, making onshore seismic monitoring more practical. Based on the repeatability test of field data, we expect to detect the reservoir changes in our upcoming CO2 injection project.

Medical Physics, 2007

Purpose: To investigate the use of operator independent ultrasoundtomography for breast imaging w... more Purpose: To investigate the use of operator independent ultrasoundtomography for breast imaging with the goal of differentiating breast masses. Method and Materials: A series of in‐vitro and in‐vivo experiments were carried out using a recently developed prototype based on the principles of ultrasoundtomography. To characterize the performance of the prototype, an anthropomorphic breast tissue phantom with embedded inclusions was imaged to yield reflection and transmission (i.e. sound speed and attenuation) tomograms. The in‐vivo performance of the prototype was assessed by imaging 125 patients with suspicious mammograms. Each data set yielded ∼45 to ∼75 tomograms covering the whole breast volume. Masses were identified by biopsy and their locations inferred from conventional mammography and ultrasound exams. These data were compared with the ultrasound tomograms to evaluate the in vivo detection capabilities of the prototype. Results: Our techniques successfully demonstrated tomographic imaging of breast architecture in both reflection and transmission imaging. Furthermore, phantom studies indicated that masses as small as 6 mm in size were detected in all imaging tomograms. In addition, statistically significant differences were observed between the sound speed and attenuationmeasurements of the benign inclusions and cancerous masses. The in vivo data suggested that ∼90% of masses >15mm in size were routinely detected including cancers as small as 8 mm in size. Overall, reflection, sound speed, and attenuationimaging of breast masses were demonstrated both in vitro and in vivo. Conclusion: Operator‐independent whole‐breast imaging and the detection of breast masses are feasible using ultrasoundtomography techniques. Our approach has the potential to provide a cost‐effective, non‐invasive, and non‐ionizing means of evaluating breast masses, leading to more routine analysis and evaluation of treatment response.

Borehole related seismic measurements, such as acoustic logging, vertical seismic profiling, cros... more Borehole related seismic measurements, such as acoustic logging, vertical seismic profiling, crosswell profiling, and single borehole profiling, provide high resolution data which are useful for reservoir characterization and locating new well sites. Study of elastic waves in boreholes is important for understanding and interpreting these borehole seismic data. Real boreholes are usually embedded in a layered formation, and may also have near borehole alterations, e.g., casing, cement, and invaded zones. In this thesis, two new semi-analytical approaches using the generalized reflection/transmission matrices method are developed to simulate these complicated boreholes. The first method simulates boreholes with radial layers; the second method deals with more realistic boreholes which have radial multi-layers with vertical variations in each layer. Because of their efficiency, stability, and accuracy, these new approaches have many applications to borehole seismic problems. In this thesis, I apply them to the estimation of seismic attenuation from borehole data. Attenuation is important for the characterization of rock properties, e.g., porosity, permeability, saturation, and pore fluid viscosity. Measurements of both velocity and attenuation provide complementary information about rock properties. I propose a new method for estimating seismic attenuation based on frequency shift data. In comparison to many other methods of estimating attenuation, the frequency shift method is relatively insensitive to reflection and transmission effects, source and receiver coupling and radiation patterns, and instrument responses. In the frequency shift method, wave dispersion is used as the observed signal for the attenuation estimation. If we use purely numerical methods of simulation, grid dispersion could cause errors. The semi-analytical approaches developed in this thesis do not have grid dispersion, and are appropriate for this attenuation study. To show the validity and applicability, the modeling approaches are used to create synthetic data for a variety of complicated borehole models. The frequency shift method is applied to the synthetic data for attenuation tomography and attenuation logging. The synthetic study reveals the geometrical spreading property of waves in complicated boreholes. Field data examples are also presented. The results show that the estimated attenuation distribution has good correlation with the lithology. ACKNOWLEDGMENTS First, I wish to express my sincere gratitude to my advisor, Jerry Harris. His support, inspiration and stimulating advice are major factors for the successful completion of this dissertation. Jerry is always available for discussions. His physical insight and numerous interesting ideas makes the discussions fruitful and enjoyable. Jerry not only emphasizes theoretical research, but also encourages us make efforts to applied research. I also wish to express my appreciation to Kiyoshi Yomogida. It was his help that made my study at Stanford University possible. Even after Kiyoshi left Stanford, he still gave me many useful suggestions on my work. Special thanks to Xiaofei Chen of University of Southern California, my friend and college classmate. During last a few years, close cooperation between us led to several papers published regarding to the borehole wave simulation. Xiaofei provided extremely valuable help on the development of the wave propagation theory. Nick Smalley was my office-mate. Daily conversation between us gave the office life much pleasure. Nick edited many papers of mine. My attenuation tomography program was modified from a velocity tomography code originally written by Feng Yin. Feng gave me many help on the attenuation work. Thanks to Mark Van Schaack for the work he did on the computer system management and field data editing. Dan Moos gave me many suggestions on sonic logging and wave modeling. Dan very carefully reviewed my dissertation and explained all comments to me in person. I also would like to thank Norm Sleep and Greg Beroza for reading this thesis. I had many discussions with Gary Mavko when I started to work on the attenuation project. He gave many stimulating suggestions. Finally, I would like to thank my wife, Li, my daughter, Cindy, and my parents for their support. Without their support and encouragement, it

There is considerable activity worldwide to investigate storage of carbon dioxide (CO2) in subsur... more There is considerable activity worldwide to investigate storage of carbon dioxide (CO2) in subsurface porous formations [44,7]. Three primary storage settings are being considered: oil and gas reservoirs, deep saline aquifers, and coal beds. In each setting, implementation of a storage project will require understanding of the geomechanics of storage and its impact on long-term retention of CO2, prediction of the movement of the CO2 during the period in which it is injected and beyond, and monitoring of the emplacement and migration of the CO2 at appropriate intervals. In this report, we describe research activities that aim to reduce the uncertainties that present significant barriers to widespread application of geologic storage in coal beds and that will create new options for use of deep storage resources.

SEG Technical Program Expanded Abstracts 2017, 2017

Journal of Applied Geophysics, 1998

A method for tomographically estimating electromagnetic EM wave attenuation based on analysis of ... more A method for tomographically estimating electromagnetic EM wave attenuation based on analysis of centroid frequency Ž. downshift CFDS of impulse radar signals is described and applied to cross-hole radar data. The method is based on a constant-Q model, which assumes a linear frequency dependence of attenuation for EM wave propagation above the transition frequency. The method uses the CFDS to construct the projection function. In comparison with other methods for estimating attenuation, the CFDS method is relatively insensitive to the effects of geometric spreading, instrument response, and antenna coupling and radiation pattern, but requires the data to be broadband so that the frequency shift and variance can be easily measured. The method is well-suited for difference tomography experiments using electrically conductive tracers. The CFDS method was tested using cross-hole radar data collected at the U.S. Geological Survey Fractured Rock Research Ž. Site at Mirror Lake, New Hampshire NH during a saline-tracer injection experiment. The attenuation-difference tomogram created with the CFDS method outlines the spatial distribution of saline tracer within the tomography plane.

Medical Physics, 2007

Purpose: To improve resolution and reduce speckle in ultrasound breast images by accounting for u... more Purpose: To improve resolution and reduce speckle in ultrasound breast images by accounting for ultrasound scattering from breast heterogeneities during reflectivityimage reconstruction.Method and Materials: X‐ray mammography often fails to detect cancers in dense breasts, while breast ultrasound has the potential to detect them. Breast heterogeneities, particularly in dense breasts, generate significant ultrasound scattering. Properly handling ultrasound scattering is critical for reliable cancer detection and diagnosis in dense breasts. Ultrasoundwave propagation in the breast is governed by the acoustic‐wave equation in heterogeneous media, which can be decomposed into two one‐way wave equations describing wave propagation in opposite directions. A split‐step Fourier solution of a one‐way wave equation is used for backpropagation of reflected ultrasoundwaves. The backpropagation consists of two steps: one phase‐shift step in the frequency‐wavenumber domain, and another phaseshift step in the frequency‐space domain. During the backpropagation of ultrasound wavefields, heterogeneous breast sound‐speed models obtained from transmission ultrasound tomography are used to approximately account for ultrasoundwavescattering. The reflectivityimaging method based on the split‐step Fourier propagator is applied to computer‐generated ultrasound data and in‐vivo ultrasound breast data acquired using a ring transducer array. The ultrasoundimages are compared with those obtained using a uniform sound‐speed model.Results: Comparison of ultrasoundreflectivityimages obtained using heterogeneous breast sound‐speed models with those obtained with a uniform model shows that ultrasound scattering of breast heterogeneities needs to be taken into account to obtain high‐resolution and high‐quality breast images.Conclusion: Using heterogeneous sound‐speed models for ultrasoundwave backpropagation during reflectivityimage reconstruction significantly improves image resolution and reduces speckle. The resolution and quality of ultrasoundreflectivityimages are further enhanced with increasing accuracy and resolution of transmission ultrasound tomography.

Borehole related seismic measurements, such as acoustic logging, vertical seismic profiling, cros... more Borehole related seismic measurements, such as acoustic logging, vertical seismic profiling, crosswell profiling, and single borehole profiling, provide high resolution data which are useful for reservoir characterization and locating new well sites. Study of elastic waves in boreholes is important for understanding and interpreting these borehole seismic data. Real boreholes are usually embedded in a layered formation, and may also have near borehole alterations, e.g., casing, cement, and invaded zones. In this thesis, two new semi-analytical approaches using the generalized reflection/transmission matrices method are developed to simulate these complicated boreholes. The first method simulates boreholes with radial layers; the second method deals with more realistic boreholes which have radial multi-layers with vertical variations in each layer. Because of their efficiency, stability, and accuracy, these new approaches have many applications to borehole seismic problems. In this t...

Background In the last two annual reports on CO2 storage monitoring, we discussed the feasibility... more Background In the last two annual reports on CO2 storage monitoring, we discussed the feasibility of using different geophysical options for subsurface CO2 monitoring, and described an innovative approach for near-continuous subsurface monitoring. We also discussed special challenges and requirements with continuous and leak detection of CO2. We chose seismic methods for subsurface monitoring primarily because they are broadly applicable in a variety of geological settings and sensitive to changes in CO2 saturation. To further develop seismic methods, for this particular application, we have proposed adaptive sparse data acquisition to address the problem of cost-effective time-lapse monitoring. We focused our work on leak detection and have proposed data gathering and processing concepts for dynamic imaging and model-based inversion. Developments reported in previous reports included a suite of seismic modeling tools to simulate monitoring and a small-scale field example on seismic...

Proquest Dissertations and Theses Thesis Stanford University 1997 Publication Number Aai9714179 Isbn 9780591219289 Source Dissertation Abstracts International Volume 57 11 Section B Page 6822 149 P, 1997

Seg Technical Program Expanded Abstracts, 1999

All Days, Feb 13, 2008

Water hammer effects resulting from the shutting in of water injection wells are an often ignored... more Water hammer effects resulting from the shutting in of water injection wells are an often ignored issue in petroleum production operations but they have considerable impact on injection well performance and longevity. Mismanaged, they can result in substantial and perhaps irreparable damage. This paper presents a study on the creation and propagation of water hammer due to rapid shut-in of water injectors. Water hammer 1-4 or pressure surge, is a pressure transient phenomenon which has long been known to occur as a result of a sudden change in fluid flow velocity. In water injectors, rapid shut-in creates a water hammer. Over time, injectors that undergo repeated rapid shut-ins often have significantly reduced injectivity and show evidence of sanding and even failure of the down-hole completion 5. It is therefore critical to understand the nature of water hammer including the magnitude, frequency, and energy dissipation. To study the water hammer in water injectors, a field trial was conducted to record pressure pulses generated from rapid shutins, at different well depths, in a soft formation, cased and perforated (C&P) water injector. Modeling work was conducted to understand the data. The results of the field trial and model work demonstrated that: • The magnitude of the first pressure pulse due to abrupt shut-in can be estimated by using the equation: Δp = V×ρ×c, where V is the flow velocity, ρ is the fluid density, and c is the speed of propagation of a pressure signal along the well. • High rate sampling (up to 100 samples/second) is required to capture subtle details of the water hammer signal. • Water hammer can be modeled as a low-frequency pressure wave similar to the higher frequency Stoneley waves produced during VSP's and by acoustic logging tools. • Models of water hammer propagation in a synthetic analog of the test well reproduced most of the details of the signals recorded during the tests.

Proceedings of SPIE, Mar 8, 2007

Sound-speed tomography images can be used for cancer detection and diagnosis. Tumors have general... more Sound-speed tomography images can be used for cancer detection and diagnosis. Tumors have generally higher sound speeds than the surrounding tissue. Quality and resolution of tomography images are primarily determined by the insonification/illumination aperture of ultrasound and the capability of the tomography method for accurately handling heterogeneous nature of the breast. We investigate the capability of an efficient time-of-flight tomography method using transmission ultrasound from a ring array for reconstructing sound-speed images of the breast. The method uses firstarrival times of transmitted ultrasonic signals emerging from non-beamforming ultrasound transducers located around a ring. It properly accounts for ray bending within the breast by solving the eikonal equation using a finite-difference scheme. We test and validate the time-of-flight transmission tomography method using synthetic data for numerical breast phantoms containing various objects. In our simulation, the objects are immersed in water within a ring array. Two-dimensional synthetic data are generated using a finite-difference scheme to solve acoustic-wave equation in heterogeneous media. We study the reconstruction accuracy of the tomography method for objects with different sizes and shapes as well as different perturbations from the surrounding medium. In addition, we also address some specific data processing issues related to the tomography. Our tomography results demonstrate that the first-arrival transmission tomography method can accurately reconstruct objects larger than approximately five wavelengths of the incident ultrasound using a ring array.

Proceedings of SPIE, Mar 8, 2007

Ultrasonic reflection imaging has the potential to produce higher image resolution than transmiss... more Ultrasonic reflection imaging has the potential to produce higher image resolution than transmission tomography, but imaging resolution and quality still need to be further improved for early cancer detection and diagnosis. We present an ultrasound reflection image reconstruction method using the split-step Fourier propagator. It is based on recursive inward continuation of ultrasonic wavefields in the frequency-space and frequency-wavenumber domains. The inward continuation within each extrapolation interval consists of two steps. In the first step, a phase-shift term is applied to the data in the frequency-wavenumber domain for propagation in a reference medium. The second step consists of applying another phase-shift term to data in the frequency-space domain to approximately compensate for ultrasonic scattering effects of heterogeneities within the breast. We use synthetic ultrasound pulse-echo data recorded around a ring for heterogeneous, computer-generated, numerical breast phantoms to study the imaging capability of the method. The phantoms are derived from an experimental breast phantom and a sound-speed tomography image of an in-vivo ultrasound breast data collected using a ring array. The heterogeneous sound-speed models used for pulse-echo imaging are obtained using a computationally efficient, first-arrival-time (time-of-flight) transmission tomography method. Our studies demonstrate that reflection image reconstruction using the split-step Fourier propagator with heterogeneous sound-speed models significantly improves image quality and resolution. We also numerically verify the spatial sampling criterion of wavefields for a ring transducer array.

Proceedings of SPIE, May 13, 2011

We present results of an ongoing project to assess the applicability in reflection seismology of ... more We present results of an ongoing project to assess the applicability in reflection seismology of emerging super resolution techniques pioneered in digital photography. Our approach involves: (1) construction of a forward model connecting low resolution seismic images to high resolution ones, and (2) solution of a Tikhonov-regularized ill conditioned optimization problem to construct a high resolution image from several lower resolution counterparts; the high and low resolution images derived, respectively, from dense and sparse seismic surveys.

Journal of the Acoustical Society of America, Nov 1, 2006

Sound speeds and densities of breast tissue vary in space, and those of tumors are different from... more Sound speeds and densities of breast tissue vary in space, and those of tumors are different from the surrounding tissues. These differences in mechanical properties cause scattering of ultrasonic waves, particularly in dense breasts. An ultrasonic reflection imaging method using a heterogeneous background is presented to properly account for scattering off heterogeneities within the breast. The method is based on downward continuation of ultrasonic wave fields in the frequency-space and frequency-wave-number domains. Synthetic ultrasonic data for scatterers within a heterogeneous breast model were used to investigate the imaging resolution of the method. Imaging examples using ultrasonic data acquired using a clinical prototype, consisting of an ultrasound scanner with a ring transducer array, are presented. The heterogeneous background sound-speed models were obtained using transmission tomography. The imaging results are compared with those obtained using a homogeneous background. The study demonstrates that imaging with heterogeneous backgrounds significantly improves image quality and resolution. [This work was supported through the DOE Laboratory-Directed Research and Development program at Los Alamos National Laboratory.]

Journal of the Acoustical Society of America, 2008

Crosswell reverse time migration (RTM) with up and downgoing wave separation can greatly reduce a... more Crosswell reverse time migration (RTM) with up and downgoing wave separation can greatly reduce artifacts usually seen in the conventional RTM without wave separation. However, the up and downgoing wave separation cannot be efficiently conducted in space-time domain algorithms because the upper/lower half space images are indistinguishable. In order to tackle this problem, we propose a frequency-domain algorithm with up and downgoing wave decomposition for the crosswell RTM. The numerical experiments and field data example demonstrate that the proposed method can greatly attenuate migration artifacts while still keep reasonable efficiency.

Chinese Journal of Geophysics, 1988

Gaussian beam (GB) method is a high-frequency asymptotic method of computing wave-fields in inhom... more Gaussian beam (GB) method is a high-frequency asymptotic method of computing wave-fields in inhomogenous media. Three variant methods, the spectral method, the convolutory method and the wave-packet method, to computing synthetic seismograms by Gaussian beam summation, are discussed in detail. A combined method which may be used in Lroader range is suggested. A convolutory equation which may be convenient for numerical calculation is, given. When GB synthetic sesmograms are computed by the combined method, both convqlu-tory method and wave-packet method may be used, in order to get fairly hign calculative accuracy and speed. Numerical examples for 2-D structure by the convolutory method, the wave-packet method and the combined method are presented.

Poor repeatability caused by near-surface variations is one of the main difficulties limiting the... more Poor repeatability caused by near-surface variations is one of the main difficulties limiting the application of seismic monitoring on land. We developed the Double Time Difference (DTD) method to address this problem. DTD utilizes self-calibration to mitigate the impact of nearsurface variations, making onshore seismic monitoring more practical. Based on the repeatability test of field data, we expect to detect the reservoir changes in our upcoming CO2 injection project.

Medical Physics, 2007

Purpose: To investigate the use of operator independent ultrasoundtomography for breast imaging w... more Purpose: To investigate the use of operator independent ultrasoundtomography for breast imaging with the goal of differentiating breast masses. Method and Materials: A series of in‐vitro and in‐vivo experiments were carried out using a recently developed prototype based on the principles of ultrasoundtomography. To characterize the performance of the prototype, an anthropomorphic breast tissue phantom with embedded inclusions was imaged to yield reflection and transmission (i.e. sound speed and attenuation) tomograms. The in‐vivo performance of the prototype was assessed by imaging 125 patients with suspicious mammograms. Each data set yielded ∼45 to ∼75 tomograms covering the whole breast volume. Masses were identified by biopsy and their locations inferred from conventional mammography and ultrasound exams. These data were compared with the ultrasound tomograms to evaluate the in vivo detection capabilities of the prototype. Results: Our techniques successfully demonstrated tomographic imaging of breast architecture in both reflection and transmission imaging. Furthermore, phantom studies indicated that masses as small as 6 mm in size were detected in all imaging tomograms. In addition, statistically significant differences were observed between the sound speed and attenuationmeasurements of the benign inclusions and cancerous masses. The in vivo data suggested that ∼90% of masses >15mm in size were routinely detected including cancers as small as 8 mm in size. Overall, reflection, sound speed, and attenuationimaging of breast masses were demonstrated both in vitro and in vivo. Conclusion: Operator‐independent whole‐breast imaging and the detection of breast masses are feasible using ultrasoundtomography techniques. Our approach has the potential to provide a cost‐effective, non‐invasive, and non‐ionizing means of evaluating breast masses, leading to more routine analysis and evaluation of treatment response.

Borehole related seismic measurements, such as acoustic logging, vertical seismic profiling, cros... more Borehole related seismic measurements, such as acoustic logging, vertical seismic profiling, crosswell profiling, and single borehole profiling, provide high resolution data which are useful for reservoir characterization and locating new well sites. Study of elastic waves in boreholes is important for understanding and interpreting these borehole seismic data. Real boreholes are usually embedded in a layered formation, and may also have near borehole alterations, e.g., casing, cement, and invaded zones. In this thesis, two new semi-analytical approaches using the generalized reflection/transmission matrices method are developed to simulate these complicated boreholes. The first method simulates boreholes with radial layers; the second method deals with more realistic boreholes which have radial multi-layers with vertical variations in each layer. Because of their efficiency, stability, and accuracy, these new approaches have many applications to borehole seismic problems. In this thesis, I apply them to the estimation of seismic attenuation from borehole data. Attenuation is important for the characterization of rock properties, e.g., porosity, permeability, saturation, and pore fluid viscosity. Measurements of both velocity and attenuation provide complementary information about rock properties. I propose a new method for estimating seismic attenuation based on frequency shift data. In comparison to many other methods of estimating attenuation, the frequency shift method is relatively insensitive to reflection and transmission effects, source and receiver coupling and radiation patterns, and instrument responses. In the frequency shift method, wave dispersion is used as the observed signal for the attenuation estimation. If we use purely numerical methods of simulation, grid dispersion could cause errors. The semi-analytical approaches developed in this thesis do not have grid dispersion, and are appropriate for this attenuation study. To show the validity and applicability, the modeling approaches are used to create synthetic data for a variety of complicated borehole models. The frequency shift method is applied to the synthetic data for attenuation tomography and attenuation logging. The synthetic study reveals the geometrical spreading property of waves in complicated boreholes. Field data examples are also presented. The results show that the estimated attenuation distribution has good correlation with the lithology. ACKNOWLEDGMENTS First, I wish to express my sincere gratitude to my advisor, Jerry Harris. His support, inspiration and stimulating advice are major factors for the successful completion of this dissertation. Jerry is always available for discussions. His physical insight and numerous interesting ideas makes the discussions fruitful and enjoyable. Jerry not only emphasizes theoretical research, but also encourages us make efforts to applied research. I also wish to express my appreciation to Kiyoshi Yomogida. It was his help that made my study at Stanford University possible. Even after Kiyoshi left Stanford, he still gave me many useful suggestions on my work. Special thanks to Xiaofei Chen of University of Southern California, my friend and college classmate. During last a few years, close cooperation between us led to several papers published regarding to the borehole wave simulation. Xiaofei provided extremely valuable help on the development of the wave propagation theory. Nick Smalley was my office-mate. Daily conversation between us gave the office life much pleasure. Nick edited many papers of mine. My attenuation tomography program was modified from a velocity tomography code originally written by Feng Yin. Feng gave me many help on the attenuation work. Thanks to Mark Van Schaack for the work he did on the computer system management and field data editing. Dan Moos gave me many suggestions on sonic logging and wave modeling. Dan very carefully reviewed my dissertation and explained all comments to me in person. I also would like to thank Norm Sleep and Greg Beroza for reading this thesis. I had many discussions with Gary Mavko when I started to work on the attenuation project. He gave many stimulating suggestions. Finally, I would like to thank my wife, Li, my daughter, Cindy, and my parents for their support. Without their support and encouragement, it

There is considerable activity worldwide to investigate storage of carbon dioxide (CO2) in subsur... more There is considerable activity worldwide to investigate storage of carbon dioxide (CO2) in subsurface porous formations [44,7]. Three primary storage settings are being considered: oil and gas reservoirs, deep saline aquifers, and coal beds. In each setting, implementation of a storage project will require understanding of the geomechanics of storage and its impact on long-term retention of CO2, prediction of the movement of the CO2 during the period in which it is injected and beyond, and monitoring of the emplacement and migration of the CO2 at appropriate intervals. In this report, we describe research activities that aim to reduce the uncertainties that present significant barriers to widespread application of geologic storage in coal beds and that will create new options for use of deep storage resources.

SEG Technical Program Expanded Abstracts 2017, 2017

Journal of Applied Geophysics, 1998

A method for tomographically estimating electromagnetic EM wave attenuation based on analysis of ... more A method for tomographically estimating electromagnetic EM wave attenuation based on analysis of centroid frequency Ž. downshift CFDS of impulse radar signals is described and applied to cross-hole radar data. The method is based on a constant-Q model, which assumes a linear frequency dependence of attenuation for EM wave propagation above the transition frequency. The method uses the CFDS to construct the projection function. In comparison with other methods for estimating attenuation, the CFDS method is relatively insensitive to the effects of geometric spreading, instrument response, and antenna coupling and radiation pattern, but requires the data to be broadband so that the frequency shift and variance can be easily measured. The method is well-suited for difference tomography experiments using electrically conductive tracers. The CFDS method was tested using cross-hole radar data collected at the U.S. Geological Survey Fractured Rock Research Ž. Site at Mirror Lake, New Hampshire NH during a saline-tracer injection experiment. The attenuation-difference tomogram created with the CFDS method outlines the spatial distribution of saline tracer within the tomography plane.

Medical Physics, 2007

Purpose: To improve resolution and reduce speckle in ultrasound breast images by accounting for u... more Purpose: To improve resolution and reduce speckle in ultrasound breast images by accounting for ultrasound scattering from breast heterogeneities during reflectivityimage reconstruction.Method and Materials: X‐ray mammography often fails to detect cancers in dense breasts, while breast ultrasound has the potential to detect them. Breast heterogeneities, particularly in dense breasts, generate significant ultrasound scattering. Properly handling ultrasound scattering is critical for reliable cancer detection and diagnosis in dense breasts. Ultrasoundwave propagation in the breast is governed by the acoustic‐wave equation in heterogeneous media, which can be decomposed into two one‐way wave equations describing wave propagation in opposite directions. A split‐step Fourier solution of a one‐way wave equation is used for backpropagation of reflected ultrasoundwaves. The backpropagation consists of two steps: one phase‐shift step in the frequency‐wavenumber domain, and another phaseshift step in the frequency‐space domain. During the backpropagation of ultrasound wavefields, heterogeneous breast sound‐speed models obtained from transmission ultrasound tomography are used to approximately account for ultrasoundwavescattering. The reflectivityimaging method based on the split‐step Fourier propagator is applied to computer‐generated ultrasound data and in‐vivo ultrasound breast data acquired using a ring transducer array. The ultrasoundimages are compared with those obtained using a uniform sound‐speed model.Results: Comparison of ultrasoundreflectivityimages obtained using heterogeneous breast sound‐speed models with those obtained with a uniform model shows that ultrasound scattering of breast heterogeneities needs to be taken into account to obtain high‐resolution and high‐quality breast images.Conclusion: Using heterogeneous sound‐speed models for ultrasoundwave backpropagation during reflectivityimage reconstruction significantly improves image resolution and reduces speckle. The resolution and quality of ultrasoundreflectivityimages are further enhanced with increasing accuracy and resolution of transmission ultrasound tomography.

Borehole related seismic measurements, such as acoustic logging, vertical seismic profiling, cros... more Borehole related seismic measurements, such as acoustic logging, vertical seismic profiling, crosswell profiling, and single borehole profiling, provide high resolution data which are useful for reservoir characterization and locating new well sites. Study of elastic waves in boreholes is important for understanding and interpreting these borehole seismic data. Real boreholes are usually embedded in a layered formation, and may also have near borehole alterations, e.g., casing, cement, and invaded zones. In this thesis, two new semi-analytical approaches using the generalized reflection/transmission matrices method are developed to simulate these complicated boreholes. The first method simulates boreholes with radial layers; the second method deals with more realistic boreholes which have radial multi-layers with vertical variations in each layer. Because of their efficiency, stability, and accuracy, these new approaches have many applications to borehole seismic problems. In this t...

Background In the last two annual reports on CO2 storage monitoring, we discussed the feasibility... more Background In the last two annual reports on CO2 storage monitoring, we discussed the feasibility of using different geophysical options for subsurface CO2 monitoring, and described an innovative approach for near-continuous subsurface monitoring. We also discussed special challenges and requirements with continuous and leak detection of CO2. We chose seismic methods for subsurface monitoring primarily because they are broadly applicable in a variety of geological settings and sensitive to changes in CO2 saturation. To further develop seismic methods, for this particular application, we have proposed adaptive sparse data acquisition to address the problem of cost-effective time-lapse monitoring. We focused our work on leak detection and have proposed data gathering and processing concepts for dynamic imaging and model-based inversion. Developments reported in previous reports included a suite of seismic modeling tools to simulate monitoring and a small-scale field example on seismic...

Proquest Dissertations and Theses Thesis Stanford University 1997 Publication Number Aai9714179 Isbn 9780591219289 Source Dissertation Abstracts International Volume 57 11 Section B Page 6822 149 P, 1997

Seg Technical Program Expanded Abstracts, 1999