TECHNOLOGIES

SeismicCity’s technology includes a series of unique proprietary algorithms developed with the objective of constructing accurate and reliable depth migrated seismic data. These are combined with commercial software used for interpretation and model building.

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 downward extrapolation wave equation, and wave front reconstruction Kirchhoff summation.

The input to our wave equation algorithms are common shot or CDP gathers. The wave equation algorithms are implemented in the common shot domain. With high level of optimization, large apertures and wide frequency range 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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Technical specifications:

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
  
  

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 travetimes for areas of complex wave propagation
• Includes isotropic as well as anisotropic imaging
  
  

Velocity analysis for definition of layer velocity is done by one or by the combination of 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 base reflection tomography. In this method, prestack depth migrated image gathers are analyzed for residual curvature. This is feed to a global inversion process.

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 inversion or scans are performed to optimize event moveout in the near to mid offset range. Last, epsilon 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 using the depth imaging grid dimensions.

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 work is based on GoCad technology. The interpreted surfaces are input to GoCad as 3-dimensional, 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, and these results are delivered to our clients at the end of the depth imaging project.    

Prestack depth migration, velocity analysis and wave equation simulation algorithms all require high end computational setup. A key part of our technology is development and implementation of the latest computer technology as well as software upgrade to take advantage of new hardware technology. Our computer setup is all based on 64 bit AMD dual core opteron hardware.  This includes a series of computer clusters equipped with large scale disk storage, multiple nodes and fast data connection.

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.   

Our simulation tools are based on a 3-dimensional solution of the full wave equation. This involves construction of a detailed model, common shot simulation and prestack depth migration imaging. The wave equation algorithm is a 4^th order finite difference approximation of the acoustic wave equation. The solution of the wave equation is done in the space domain. Any source wavelet can be input to the scheme, and both recorded sections as well as wave propagation snapshots can be stored and output.

The 3-dimensional simulation is used for acquisition design, creation of prestack data for testing of prestack depth migration algorithms and seismic data analysis. Either absorbing surfaces or free surface can be used during simulation, enabling creation of surface related multiples.

The wave equation simulation is done in one of the following cases: as part of acquisition design, during depth imaging to assist with interpretation of complex seismic images, or post depth imaging to assist with illumination and amplitude analysis of seismic data.