TECHNOLOGIES
Prestack depth migration
Our series of prestack depth migration algorithms is built to answer imaging requirements of any geological setting. These include two-way wave equation (i.e. Reverse Time Migration), one-way wave equation downward extrapolation, and wave front reconstruction Kirchhoff summation.
The input to our wave equation algorithms are common shot gathers. The wave equation algorithms are implemented in the common shot domain. With high level of optimization, large apertures and wide frequency ranges can be used. The input to our Kirchhoff algorithm are CDP, common shot or common offset gathers. The algorithm is based on a unique implementation of the wavefront reconstruction method resulting with high resolution migrated volumes.
Our prestack depth migrations are highly versatile and are producing accurate depth migrated volumes using narrow azimuth streamer data, multi azimuth streamer data, OBC data or any type of land data.
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Reverse time migration
- Common shot implementation
- Uses a non-smooth velocity model
- Capable of imaging turning waves as well as prism waves
- Based on finite differences solution of the full wave equation
- Includes isotropic as well as anisotropic imaging
Downward extrapolation wave equation
- Common shot implementation
- Uses a non-smooth velocity model
- Best suitable for imaging of low illumination areas such as
subsalt geology and fault shadows - Based on the enhanced phase shift extrapolation algorithm
- Multi arrival and amplitude compensated migration operator
Wavefront reconstruction Kirchhoff summation
- Uses the wavefront reconstruction algorithm for calculation
of traveltime functions - Capable of imaging steep dips by use of turning wave operator
- Capable of using multi arrival traveltimes for areas of complex wave propagation
- Includes isotropic as well as anisotropic imaging
Velocity analysis
Velocity analysis for definition of layer velocity is done by two methods. The first is a prestack depth migration scan. In this method, a series of prestack depth migrations are executed, each with a different trial velocity. The resulting image gathers or full sections are analyzed to select the optimal velocity at each velocity analysis location. The second is grid based reflection tomography. In this method, prestack depth migrated image gathers are analyzed for residual curvature. This is feed to a global inversion process. A combination of scans and tomographic inversion is done as well, and each one of these tools is capable of estimating vertical velocity, delta function and epsilon function.
The two velocity analysis tools are capable of scanning and inverting the interval velocity field in the case of isotropic model building, or alternatively vertical velocity, delta and epsilon fields in the case of anisotropic model building. Anisotropic parameters analysis is done in three steps. First, a vertical velocity field is constructed from the isotropic velocity field by use of local inversion that is built to adjust the velocity boundaries to data supplied from wells. Second, delta tomographic inversion or scans are performed to optimize event moveout in the near to mid offset range. Last, epsilon tomographic inversion or scans are performed to optimize event moveout on the far offset range. The three parameters – vertical velocity, delta and epsilon are each represented by a full volume constructed at each bin and depth sample of the model.
Interpretation and model building
Construction of accurate velocity models is based on repeat iterations of trial models and adjustment of these models based on the trial image. This involves repeat interpretation of the depth migrated volumes. In most cases, the interpretation work requires tools that can handle complex geological settings such as multiple salt bodies or complex overthrust structures. Our interpretation and model representation is based on GoCad technology. The interpreted surfaces are input to GoCad as 3-dimensional curves, linked together to form complex surfaces and then combined to form closed shape geometrical volumes or geological units.
The interpretation work is completed with construction of geological units and then linked with the velocity analysis results supplying the velocity field or anisotropic field of each geological unit. This 3-dimensional model is stored as a volume which can be used by any of our prestack depth migration or simulation algorithms.
With our advanced interpretation tools we are able to assist our clients with the interpretation work required during the model building phase. The final GoCad model is delivered to our clients at the end of the depth imaging project in various formats that can be loaded to any commercial interpretation system.
Simulation
We are offering simulation tools based on a 3-dimensional solution of the full wave equation. This involves construction of a detailed 3-dimensional model, simulation and recording of common shot gathers, and then application of prestack depth migration imaging. The solution of the 3-dimensional wave equation is based on high order finite difference approximation of the acoustic wave equation. Any source wavelet can be input to the scheme, and both recorded sections as well as wave propagation snapshot volumes can be stored and output. Either absorbing surfaces or free surface can be used during simulation, enabling creation of surface related multiples.
The 3-dimensional simulation is used for data analysis and to assist in acquisition design. For data analysis a synthetic dataset is generated and then migrated. Comparing the synthetic preSDM volume to the field data preSDM volume we can differentiate real geological reflections from seismic noise patterns. This can be done only using wave equation simulation where the model is known. Illumination maps and volumes are generated as part of the data analysis. The use of 3-dimensional simulation to assist in acquisition design is a growing use of numerical simulation. Due to the complexity of new wide azimuth acquisition setup and parameters new tools are needed to assist in the design work. Using wave equation simulation we can simulate various acquisition patterns, and as well record simulated data that will help in the selection of processing and imaging techniques. This can greatly help in both reducing the costs of the field data acquisition as well as obtaining higher quality field data.
Computer hardware
Application of prestack depth migration, wave equation simulation and velocity analysis algorithms all require a high-end computational setup. A key part of our technology is a continual upgrade of our hardware technology to the latest technology available. The constant change in prestack depth migration algorithms require constant modification and optimization of our computer environment to support the increase demand in computational speed as well as data transfer and storage. The development of our computer environment is linked to the way our algorithms are implemented, resulting with an optimized hardware/software solution.
In the past two years the industry has moved from imaging by solution of the one-way wave equation to imaging using a solution of the two-way wave equation (i.e. RTM). The hardware setup which is needed for implementation of RTM is much larger than the one needed for implementation of one-way wave equation or ray based imaging using rays or beams. In order to offer a RTM solution to our clients in a timely manner we needed to increase our computing power by a factor of 10. This was achieved by upgrade of our computer setup from CPU based hardware to the newest hybrid GPU/GPU based setup... read more
