... However, most of the reservoirs discovered to date have been relatively thin. ... point with ... more ... However, most of the reservoirs discovered to date have been relatively thin. ... point with changing frequency (Figure 6). Typical applications of the spectral decomposition data include (1) direct detection of hydrocarbons through a distinctive spectral response or ...
Seismic imaging in foothills areas is challenging because of the complexity of the near-surface a... more Seismic imaging in foothills areas is challenging because of the complexity of the near-surface and subsurface structures. Single seismic surveys often are not adequate in a foothill-exploration area, and multiple phases with different acquisition designs within the same block are required over time to get desired sampling in space and azimuths for optimizing noise attenuation, velocity estimation, and migration. This is partly because of economic concerns, and it is partly because technology is progressing over time, creating the need for unified criteria in processing workflows and parameters at different blocks in a study area. Each block is defined as a function of not only location but also the acquisition and processing phase. An innovative idea for complex foothills seismic imaging is presented to solve a matrix of blocks and tasks. For each task, such as near-surface velocity estimation and static corrections, signal processing, prestack time migration, velocity-model building, and prestack depth migration, one or two best service companies are selected to work on all blocks. We have implemented streamlined processing efficiently so that Task-1 to Task-n progressed with good coordination. Application of this innovative approach to a mega-project containing 16 3D surveys covering more than 9000 km 2 in the Kelasu foothills, northwestern China, has demonstrated that this innovative approach is a current best practice in complex foothills imaging. To date, this is the largest foothills imaging project in the world. The case study in Kelasu successfully has delivered near-surface velocity models using first arrivals picked up to 3500 m offset for static corrections and 9000 m offset for prestack depth migration from topography. Most importantly, the present megaproject is a merge of several 3D surveys, with the merge performed in a coordinated, systematic fashion in contrast to most land megaprojects. The benefits of this approach and the strategies used in processing data from the various subsurveys are significant. The main achievement from the case study is that the depth images, after the application of the near-surface velocity model estimated from the megasurveys, are more continuous and geologically plausible, leading to more accurate seismic interpretation.
For developing a high-fidelity, high-resolution seismic denoising method, we use the two-dimensio... more For developing a high-fidelity, high-resolution seismic denoising method, we use the two-dimensional complex wavelet transform (2D CWT) to analyze noise and signals. By investigating a surface wave's features and evaluating factors affecting the fidelity of the method, the best practice for the wavelet transform-based denoising has been established. First, static and normal moveout correction are applied on shot gathers. Then, 2D CWT is used to attenuate linear noises. The results demonstrate that the proposed method and practice significantly attenuate noises and preserve the signal's amplitudes and frequency band. In addition to denoising, we also apply the 2D CWT to decompose a seismic image into multiscale images with different resolutions. Multiscale decomposed images derive more detailed information for subsurface structures and fault networks. The decomposed images depict sharper structures and reveal detailed features of faults more significantly than the original im...
Second International Meeting for Applied Geoscience & Energy
To image complex subsurface structures, the wavefield recording layout is more suitable than the ... more To image complex subsurface structures, the wavefield recording layout is more suitable than the conventional method of seismic data acquisition layout since it is better to attenuate noise and to record more energy that impacts subtle aspects of the geologic objective. However the wavefield recording layout increases acquisition costs significantly and also leads to challenges for subsequent data processing. Although the costs for receivers have been reduced remarkably as the acquisition technology has been improved for land seismic exploration, but the costs for sources haven't changed much. We propose a cost effective wavefield recording acquisition layout: staggered sources for 3D land seismic data acquisition to improve complex subsurface structures image without increasing acquisition cost. The layout of staggered sources divides one shot line in conventional layout into multi-sub-shot lines. The subshot lines are equally staggered along the shooting direction within rolling interval between two adjacent templates which leads to smaller distance between shot lines with same total number of shots for a survey. The proposed layout has been applied on a synthetic 3D model derived from a field 3D survey. In this case study, one shot line with 6-shots in the conventional layout is divided into 3 staggered sub-shot lines with 2 shots for each sub-shot line. To examine the effectiveness of this layout, the forward modeling is used to generate 3D synthetic seismic shot gathers for both conventional and staggered source layouts. Illumination analysis, prestack reverse time migration, and turning ray tomography are performed respectively. The results show that the staggered sources acquisition layout provides stronger illumination, higher fidelity subsurface image, and more reliable near surface models than the conventional source acquisition layout without increasing the acquisition cost.
Turning-ray tomography and tomostatics have been applied to areas with rugged topography and stro... more Turning-ray tomography and tomostatics have been applied to areas with rugged topography and strongly variant nearsurface geology. A short review of the methodology of turning-ray tomography and tomostatics will be outlined and its application to real field data examples will be demonstrated. Questions frequently asked will be highlighted to show 1) when and where tomostatics will work better than conventional refraction statics; 2) limitations of tomostatics; and 3) key steps to run tomostatics. Quality controls will be illustrated to ensure the robustness of turning-ray tomography and tomostatics. In addition to tomographic evaluation of long wavelength statics, refraction statics continue to play an important role into the near surface modeling evaluation. In fact, refraction statics has been the preferred choice to estimate large and long wavelength statics on P wave data. Does the same methodology apply to pure shear wave data? A new methodology of analyzing and FB picking on m...
Seismic imaging for the Eldfisk SOA requires a good understanding of overburden geology and detai... more Seismic imaging for the Eldfisk SOA requires a good understanding of overburden geology and detailed reservoir structure. In Eldfisk, we found that, based on well logs and seismic amplitude attributes, gas zones represented as pancake-shaped geobodies in the overburden, produce significant time sags in modeled seismic sections that are similar to sags observed on field datasets. Amplitude decays observed on the acquired seismic data also suggest that the pancake-shaped geobodies are heterogeneous, causing scattering and energy loss. The main contribution of this paper is to develop a workflow to convert geologic modeling property (e.g. porosity) to seismic velocity for 3D seismic modeling and RTM imaging. High-resolution seismic modeling and imaging are important for well planning and field development at Eldfisk. The integrated velocity model contain both geobodies constructed from the overburden and detailed geologic features such as small faults in the reservoirs. Results from the full 3D RTM and decimation studies have illustrated that receiver spacing greater than 300x300 m would produce significant artifacts in the reservoirs. Target-oriented visibility studies based on the integrated velocity model suggested that dominant energy around ~5-10km may provide imaging uplift to reservoir structures in the Eldfisk SOA.
London 2013, 75th eage conference en exhibition incorporating SPE Europec, 2013
We developed a workflow for advanced seismic acquisition design. Visibility analyses, wave-equati... more We developed a workflow for advanced seismic acquisition design. Visibility analyses, wave-equation modeling, RTM imaging and critical reflection illuminations are used to understand the causes of poorer images beneath the salt in the deepwater of Gulf of Mexico. Results indicate that the poorly imaged subsalt target horizons are partly because of the limited maximum offset (4 to 7 km) in acquisition and processing, and partly because of the critical angle reflections at the base of the salt. For the former, one can increase the cable length in acquisition. However, if critical reflection becomes a problem, it is impossible to improve imaging using surface seismic, no matter how long the cable is used. The advanced modeling and imaging can be used not only for seismic acquisition design, but also for subsalt structural interpretation.
In January of 1985, a densely-recorded, wide-aperture seismic experiment was performed by the Uni... more In January of 1985, a densely-recorded, wide-aperture seismic experiment was performed by the University of Texas at El Paso and at Dallas, across the southwestern Oklahoma aulacogen. A two-dimensional P-wave velocity distribution is estimated for the Wichita uplift, the Anadarko basin, and the interface between them, by iterative tomographic imaging of travel-time picks from seven shots located near the 100-km-long recording line. The region that is imaged is roughly triangular in shape, with depth = 0 km at the ends of line and ≈ 15 km near its center. The main features that are revealed are a high-velocity (>6.8 km/sec) central core in the Wichita uplift and an asymmetrical Anadarko basin with decreasing velocities toward the basin axis. There are indications, within the uplift, of local high-velocity sills and a local low-velocity region that may be a remnant of normal crustal material.
Seismic imaging in foothills areas is challenging because of the complexity of both near-surface ... more Seismic imaging in foothills areas is challenging because of the complexity of both near-surface and subsurface structures. Single seismic surveys are often not adequate in a foothill- exploration area, and multiple phases with different acquisition designs within the same block are required over time to get desired sampling in space and azimuths for optimizing noise attenuation, velocity estimation and migration. This is partly because of economic concerns, and partly because technology is progressing over time, and it creates the need for unified criteria in processing workflows and parameters at different blocks in a study area. An innovative idea for complex foothills seismic imaging is presented to solve a matrix of blocks and tasks. For each task, such as near-surface velocity estimation and static corrections, one or two best service companies are selected to work on all blocks. We then implement streamlined processing efficiently so that Task-1 to Task-n progressed with good...
One of the challenges for land seismic exploration in foothills is estimating velocities. This is... more One of the challenges for land seismic exploration in foothills is estimating velocities. This is because of the complexity in both near-surface and subsurface structures. This paper illustrates a robust approach of velocity-model building for both shallow and deep sections, using joint turning-ray and reflection tomography. First, turning-ray tomography is performed to derive a near-surface velocitydepth model. Second, we combine the near-surface model with an initial subsurface model as the starting model for reflection tomography. During reflection tomography, both near-surface and subsurface velocity-depth models are jointly updated. This method is practical and efficient for velocity model building and prestack depth imaging in foothill regions.
A special challenge for land seismic exploration is estimating velocities, in part due to complex... more A special challenge for land seismic exploration is estimating velocities, in part due to complex near-surface structures, and in some instances because of rugose topography over foothills. We have developed an integrated turning-ray and reflection-tomographic method to face this challenge. First, turning-ray tomography is performed to derive a near-surface velocity-depth model. Then, we combine the near-surface model with the initial-subsurface model. Taking the combined model as starting model, we go through a reflection tomographic process to build the model for imaging. During reflection tomography, the near-surface model and subsurface models are jointly updated. Our method has been successfully applied to a 2D complex synthetic data example and a 3D field data example. The results demonstrate that our method derives a very decent model even when there is no reflection information available in a few hundred meters underneath the surface. Joint tomography can lead to geologic pl...
... However, most of the reservoirs discovered to date have been relatively thin. ... point with ... more ... However, most of the reservoirs discovered to date have been relatively thin. ... point with changing frequency (Figure 6). Typical applications of the spectral decomposition data include (1) direct detection of hydrocarbons through a distinctive spectral response or ...
Seismic imaging in foothills areas is challenging because of the complexity of the near-surface a... more Seismic imaging in foothills areas is challenging because of the complexity of the near-surface and subsurface structures. Single seismic surveys often are not adequate in a foothill-exploration area, and multiple phases with different acquisition designs within the same block are required over time to get desired sampling in space and azimuths for optimizing noise attenuation, velocity estimation, and migration. This is partly because of economic concerns, and it is partly because technology is progressing over time, creating the need for unified criteria in processing workflows and parameters at different blocks in a study area. Each block is defined as a function of not only location but also the acquisition and processing phase. An innovative idea for complex foothills seismic imaging is presented to solve a matrix of blocks and tasks. For each task, such as near-surface velocity estimation and static corrections, signal processing, prestack time migration, velocity-model building, and prestack depth migration, one or two best service companies are selected to work on all blocks. We have implemented streamlined processing efficiently so that Task-1 to Task-n progressed with good coordination. Application of this innovative approach to a mega-project containing 16 3D surveys covering more than 9000 km 2 in the Kelasu foothills, northwestern China, has demonstrated that this innovative approach is a current best practice in complex foothills imaging. To date, this is the largest foothills imaging project in the world. The case study in Kelasu successfully has delivered near-surface velocity models using first arrivals picked up to 3500 m offset for static corrections and 9000 m offset for prestack depth migration from topography. Most importantly, the present megaproject is a merge of several 3D surveys, with the merge performed in a coordinated, systematic fashion in contrast to most land megaprojects. The benefits of this approach and the strategies used in processing data from the various subsurveys are significant. The main achievement from the case study is that the depth images, after the application of the near-surface velocity model estimated from the megasurveys, are more continuous and geologically plausible, leading to more accurate seismic interpretation.
For developing a high-fidelity, high-resolution seismic denoising method, we use the two-dimensio... more For developing a high-fidelity, high-resolution seismic denoising method, we use the two-dimensional complex wavelet transform (2D CWT) to analyze noise and signals. By investigating a surface wave's features and evaluating factors affecting the fidelity of the method, the best practice for the wavelet transform-based denoising has been established. First, static and normal moveout correction are applied on shot gathers. Then, 2D CWT is used to attenuate linear noises. The results demonstrate that the proposed method and practice significantly attenuate noises and preserve the signal's amplitudes and frequency band. In addition to denoising, we also apply the 2D CWT to decompose a seismic image into multiscale images with different resolutions. Multiscale decomposed images derive more detailed information for subsurface structures and fault networks. The decomposed images depict sharper structures and reveal detailed features of faults more significantly than the original im...
Second International Meeting for Applied Geoscience & Energy
To image complex subsurface structures, the wavefield recording layout is more suitable than the ... more To image complex subsurface structures, the wavefield recording layout is more suitable than the conventional method of seismic data acquisition layout since it is better to attenuate noise and to record more energy that impacts subtle aspects of the geologic objective. However the wavefield recording layout increases acquisition costs significantly and also leads to challenges for subsequent data processing. Although the costs for receivers have been reduced remarkably as the acquisition technology has been improved for land seismic exploration, but the costs for sources haven't changed much. We propose a cost effective wavefield recording acquisition layout: staggered sources for 3D land seismic data acquisition to improve complex subsurface structures image without increasing acquisition cost. The layout of staggered sources divides one shot line in conventional layout into multi-sub-shot lines. The subshot lines are equally staggered along the shooting direction within rolling interval between two adjacent templates which leads to smaller distance between shot lines with same total number of shots for a survey. The proposed layout has been applied on a synthetic 3D model derived from a field 3D survey. In this case study, one shot line with 6-shots in the conventional layout is divided into 3 staggered sub-shot lines with 2 shots for each sub-shot line. To examine the effectiveness of this layout, the forward modeling is used to generate 3D synthetic seismic shot gathers for both conventional and staggered source layouts. Illumination analysis, prestack reverse time migration, and turning ray tomography are performed respectively. The results show that the staggered sources acquisition layout provides stronger illumination, higher fidelity subsurface image, and more reliable near surface models than the conventional source acquisition layout without increasing the acquisition cost.
Turning-ray tomography and tomostatics have been applied to areas with rugged topography and stro... more Turning-ray tomography and tomostatics have been applied to areas with rugged topography and strongly variant nearsurface geology. A short review of the methodology of turning-ray tomography and tomostatics will be outlined and its application to real field data examples will be demonstrated. Questions frequently asked will be highlighted to show 1) when and where tomostatics will work better than conventional refraction statics; 2) limitations of tomostatics; and 3) key steps to run tomostatics. Quality controls will be illustrated to ensure the robustness of turning-ray tomography and tomostatics. In addition to tomographic evaluation of long wavelength statics, refraction statics continue to play an important role into the near surface modeling evaluation. In fact, refraction statics has been the preferred choice to estimate large and long wavelength statics on P wave data. Does the same methodology apply to pure shear wave data? A new methodology of analyzing and FB picking on m...
Seismic imaging for the Eldfisk SOA requires a good understanding of overburden geology and detai... more Seismic imaging for the Eldfisk SOA requires a good understanding of overburden geology and detailed reservoir structure. In Eldfisk, we found that, based on well logs and seismic amplitude attributes, gas zones represented as pancake-shaped geobodies in the overburden, produce significant time sags in modeled seismic sections that are similar to sags observed on field datasets. Amplitude decays observed on the acquired seismic data also suggest that the pancake-shaped geobodies are heterogeneous, causing scattering and energy loss. The main contribution of this paper is to develop a workflow to convert geologic modeling property (e.g. porosity) to seismic velocity for 3D seismic modeling and RTM imaging. High-resolution seismic modeling and imaging are important for well planning and field development at Eldfisk. The integrated velocity model contain both geobodies constructed from the overburden and detailed geologic features such as small faults in the reservoirs. Results from the full 3D RTM and decimation studies have illustrated that receiver spacing greater than 300x300 m would produce significant artifacts in the reservoirs. Target-oriented visibility studies based on the integrated velocity model suggested that dominant energy around ~5-10km may provide imaging uplift to reservoir structures in the Eldfisk SOA.
London 2013, 75th eage conference en exhibition incorporating SPE Europec, 2013
We developed a workflow for advanced seismic acquisition design. Visibility analyses, wave-equati... more We developed a workflow for advanced seismic acquisition design. Visibility analyses, wave-equation modeling, RTM imaging and critical reflection illuminations are used to understand the causes of poorer images beneath the salt in the deepwater of Gulf of Mexico. Results indicate that the poorly imaged subsalt target horizons are partly because of the limited maximum offset (4 to 7 km) in acquisition and processing, and partly because of the critical angle reflections at the base of the salt. For the former, one can increase the cable length in acquisition. However, if critical reflection becomes a problem, it is impossible to improve imaging using surface seismic, no matter how long the cable is used. The advanced modeling and imaging can be used not only for seismic acquisition design, but also for subsalt structural interpretation.
In January of 1985, a densely-recorded, wide-aperture seismic experiment was performed by the Uni... more In January of 1985, a densely-recorded, wide-aperture seismic experiment was performed by the University of Texas at El Paso and at Dallas, across the southwestern Oklahoma aulacogen. A two-dimensional P-wave velocity distribution is estimated for the Wichita uplift, the Anadarko basin, and the interface between them, by iterative tomographic imaging of travel-time picks from seven shots located near the 100-km-long recording line. The region that is imaged is roughly triangular in shape, with depth = 0 km at the ends of line and ≈ 15 km near its center. The main features that are revealed are a high-velocity (>6.8 km/sec) central core in the Wichita uplift and an asymmetrical Anadarko basin with decreasing velocities toward the basin axis. There are indications, within the uplift, of local high-velocity sills and a local low-velocity region that may be a remnant of normal crustal material.
Seismic imaging in foothills areas is challenging because of the complexity of both near-surface ... more Seismic imaging in foothills areas is challenging because of the complexity of both near-surface and subsurface structures. Single seismic surveys are often not adequate in a foothill- exploration area, and multiple phases with different acquisition designs within the same block are required over time to get desired sampling in space and azimuths for optimizing noise attenuation, velocity estimation and migration. This is partly because of economic concerns, and partly because technology is progressing over time, and it creates the need for unified criteria in processing workflows and parameters at different blocks in a study area. An innovative idea for complex foothills seismic imaging is presented to solve a matrix of blocks and tasks. For each task, such as near-surface velocity estimation and static corrections, one or two best service companies are selected to work on all blocks. We then implement streamlined processing efficiently so that Task-1 to Task-n progressed with good...
One of the challenges for land seismic exploration in foothills is estimating velocities. This is... more One of the challenges for land seismic exploration in foothills is estimating velocities. This is because of the complexity in both near-surface and subsurface structures. This paper illustrates a robust approach of velocity-model building for both shallow and deep sections, using joint turning-ray and reflection tomography. First, turning-ray tomography is performed to derive a near-surface velocitydepth model. Second, we combine the near-surface model with an initial subsurface model as the starting model for reflection tomography. During reflection tomography, both near-surface and subsurface velocity-depth models are jointly updated. This method is practical and efficient for velocity model building and prestack depth imaging in foothill regions.
A special challenge for land seismic exploration is estimating velocities, in part due to complex... more A special challenge for land seismic exploration is estimating velocities, in part due to complex near-surface structures, and in some instances because of rugose topography over foothills. We have developed an integrated turning-ray and reflection-tomographic method to face this challenge. First, turning-ray tomography is performed to derive a near-surface velocity-depth model. Then, we combine the near-surface model with the initial-subsurface model. Taking the combined model as starting model, we go through a reflection tomographic process to build the model for imaging. During reflection tomography, the near-surface model and subsurface models are jointly updated. Our method has been successfully applied to a 2D complex synthetic data example and a 3D field data example. The results demonstrate that our method derives a very decent model even when there is no reflection information available in a few hundred meters underneath the surface. Joint tomography can lead to geologic pl...
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