A transmitter located on the earth's surface or elsewhere may transmit signals, such as acoustic waves, compression waves or other energy rays or waves that may travel through subsurface structures. The transmitted signals may become incident signals that are incident to subsurface structures. The incident signals may reflect at various transition zones or geological discontinuities throughout the subsurface structures. The reflected signals may include seismic events. Seismic events including, for example, primary (P) waves and shear (S) waves (e.g., transverse waves in which particle motion may be perpendicular to the direction of propagation of the wave) may be used to image subsurface geological structures, for example, transition surfaces or geological discontinuities. A receiver may collect and record data, for example, reflected seismic events.
Surveys may use large numbers of transmitters and receivers to record signals across large geophysical regions. Seismic surveyed regions may, for example, extend to several hundred square kilometers. In some surveys, the distance between transmitters and receivers may be, for example, about twenty meters, transmitted signals may travel up to about ten kilometers, and frequencies of transmitted signals may be about fifty Hertz. Other values or parameters may be used. Recorded data may be collected over intervals of time, for example, ten second intervals, and may be digitized every 4 milliseconds, although other parameters are also possible. For example, the receiver may collect and/or record several tens or hundreds of terabytes of data. Once collected, the recorded data may be stored and/or transmitted to a storage or data processing device such as a memory, server or computing system.
Some seismic acquisition methods, such as multi-azimuth or wide-azimuth data acquisition methods, may significantly increase the number of transmitted and received signals used in order to enhance the illumination of reservoirs below complex structures and increase the precision of geophysical detection. For such methods, single parameters (e.g., pressure or vertical displacement) or multiple parameters (e.g., pressure and three displacement components) may be recorded. Both P waves and S waves may be recorded. Other types of waves and other data may be recorded. Such methods may increase the amount of data recorded for imaging subsurface regions. To accommodate the increased amount of data, systems that record, process, image, or otherwise use the data may require increased storage size, increased speed for access to input and/or output devices, and/or high performance computation (HPC) hardware or the like. Such systems may provide computationally and/or power intensive services.
Exploration of geophysical regions may include imaging the subsurface earth, using seismic data recorded from surveying regions, in order to locate for example hydrocarbon reservoirs. Seismic imaging methods, which may be referred to as seismic migrations, may be classified for example into two main categories: wave equation migrations and ray-based Kirchhoff migrations. Both types of migrations may be used to generate images of the subsurface of the earth. Wave equation migration mechanisms may use numerical solutions to the wave equation to extrapolate the recorded wavefields into the subsurface of the earth. At each level of depth, imaging conditions may be applied to the incident and reflected wavefields. Ray-based Kirchhoff migrations may be performed in two stages: ray tracing and imaging. Ray tracing may model the propagation of waves (e.g., rays), for example, in a direction from a surface towards an image point in a subsurface region, and/or in a direction from an image point in a subsurface region towards a surface. Ray attributes, such as traveltimes, ray trajectories, slowness vectors, amplitude and phase factors, may be computed along the traced rays. In the imaging stage, the ray attributes may be used to obtain an image of the earth's subsurface from the recorded seismic data.
Both wave equation and ray-based Kirchhoff migrations may generate common image gathers (CIGs). CIGs may include multiple image traces at a given lateral location. Each image trace may be generated using a portion of the recorded data that has a common geometrical attribute. For example, an offset domain common image gather (ODCIG) may include multiple image traces, where each trace may be constructed using seismic data points with the same offset or distance between a source and receiver on the earth's surface. An angle domain common image gather (ADCIG) may include multiple image traces, where each trace may be constructed using seismic data points with the same opening angle between the incident and reflected rays at the reflection point.
CIGs generated using traces that share a single azimuth may image geophysical structures with insufficient accuracy. For example, anisotropy effects show that images obtained from different azimuth angles may be significantly different. Imaging geophysical structures, such as faults, small vertical displacements, and sub-seismic scale fractures (e.g., fractures measuring less than tens of meters, which may be below the resolution for detection of typical receivers or other detection instruments), with desired accuracy, may require imaging along substantially each azimuth angle (which may be referred to for example as full-azimuth imaging). Wide-azimuth seismic data may be especially valuable for imaging, for example, below salt dome or salt laden structures, such as those in the Gulf of Mexico. Imaging geophysical structures using, for example, three-dimensional (multi-azimuth) CIGs, instead of commonly used two-dimensional (e.g., single or narrow azimuth) CIGs, may improve image accuracy and provide additional information about the structures. For example, three-dimensional ODCIGs may include multiple image traces that have substantially different azimuth angles on the earth's surface, in addition to substantially different source-receiver offsets. The offset may be a two-dimensional vector, for example, having values for in-line and cross-line components, or a length and an azimuth. Similarly, three-dimensional ADCIGs may include multiple image traces that have substantially different opening azimuth angles at the reflecting surface, in addition to substantially different opening angles. The opening angle may be, e.g., an angle between the incident and reflected rays, measured at the reflection point corresponding thereto. The opening azimuth angle may be, e.g., the azimuth of the normal to a plane that passes through the incident and the reflected rays. Other angles may alternatively be used. Although three-dimensional CIGs may increase imaging accuracy, they may also increase the computational complexity of imaging, visualization, and/or interpretation systems using such gathers. Operation of three-dimensional CIGs may also require extensive memory and storage capacity.
CIGs may be used, for example, in the kinematic and dynamic analysis of subsurface structures. For example, kinematic analysis may be used to build and update geophysical models using tomography mechanisms. Tomography mechanisms may be used to find a set of model parameters that substantially minimize travel time errors along specular rays (e.g., ray-pairs that obey principles of Snell's law at the reflecting surfaces). The travel time errors may for example be measured from the differences between locations of the reflection events along the CIGs. Substantially each reflection event within a given CIG may be related to a specific depth. If a “true” reflector (e.g., a reflection surface element) is located at a definite depth and the model parameters are “correct”, then the reflector elements are typically at the same depth irrespectively of the reflection angle or the offset indicated by the specific trace. When reflection events are not located at substantially the same depth (e.g., when reflection events along the CIGs are not substantially flat), the measured or picked differences between the reflection depths of different reflection events may be used to estimate the travel time errors along the specular rays associated with each trace. A model may be substantially correct when the seismic reflection events along the CIGs are substantially horizontally flat. In order to obtain an accurate model, for example, using an anisotropy model representation, specular rays and the corresponding travel time errors from varying opening angles (or e.g., offsets) for example, from substantially all azimuths may be used. In some embodiments, such three-dimensional CIGs may provide information about the azimuthal dependent travel time errors.
Dynamic analysis may include determining physical and/or material parameters or properties of target subsurface structures using changes in the amplitude and phase of reflected signals measured, for example, along the CIGs. Multi-azimuth CIGs may make it possible to perform azimuthal analysis of amplitude variations with respect to the opening angle (or e.g., offset), which may result in an accurate reconstruction of anisotropy parameters and small scale fractures.
Imaging other than seismic or subsurface imaging for the exploration and production of oil and gas, such as for example, shallow seismic imaging for environmental studies, archeology and construction engineering, may be performed. These other methods may similarly generate large amounts of data and have large computational needs. Other types of imaging, such as medical imaging, may also use a relatively large number of transmitters and detectors and therefore may also use a relatively large amount of data, which may require large storage and intensive computational efforts.
The prior patent application Ser. No. 11/798,996, describes efficient use, storage, processing, imaging, analysis, visualization and interpretation of the rich azimuth data in reduced dimensional coordinate system. In some other imaging applications, the rich azimuth data are decomposed into few (e.g., up to eight) azimuthal sectors. A need exists for displaying the discrete data, stored for example in reduced dimensional coordinate system, or the azimuthally sectorized data, in a continuous full dimensional coordinate system.
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