TECHNOLOGIES

SeismicCity’s technology includes a series of unique proprietary prestack depth migration 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. SeismicCity’s prestack depth migration algorithms are implemented using hybrid CPU / GPU computer clusters.

Our series of prestack depth migration algorithms are 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. The main wave equation algorithm which we used in production is Reverse Time Migration (RTM). We are offering isotropic RTM as well as VTI and TTI anisotropic RTM. The input to our Kirchhoff summation 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, wide 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
• Includes isotropic as well as anisotropic imaging
• TTI anisotropic RTM
• VTI anisotropic RTM

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
• TTI anisotropic algorithm
• VTI anisotropic algorithm

We are using two methods for velocity analysis and construction of the layers velocity fields. The first tool is reflection tomography. Reflection tomography is a grid based, global inversion technique. It is based on iterations of full volume prestack depth migration, where at each iteration residual curvature is analyzed on image gathers and is input to a global inversion process. The tomographic inversion and update tool which we are using is built to optimize the vertical velocity field, as well as anisotropic delta and epsilon fields. A fully TTI model can be optimized for use in TTI prestack depth migration when dip and azimuth fields are input.

The second velocity analysis and update tool which we offer is a prestack depth migration scan. In this method, a series of prestack depth migrations are executed, each with a different trial velocity or anisotripic parameters. The resulting image gathers or full sections are analyzed for selecting the optimal velocity and anisotropic field.

For generation of dip and azimuth volumes we use a unique tool that inputs the main geological surfaces and construct dip and azimuth volumes at the spacing needed for application of prestack depth migration. The dip and azimuth volumes together with delta, epsilon anisotropic volumes and the vertical velocity field are the five parameter volumes input to TTI prestack depth migration algorithms.

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 and anisotropic field of each geological unit. The 3-dimensional models are stored as volumes 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.

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. This is done for isotropic media as well as VTI and TTI anisotropic media. At each case, a different set of wave equations is used for the numerical simulation. Any source wavelet can be input to the simulation, and both recorded sections as well as wave propagation snapshot volumes can be stored and output. Based on the objective of the work, either absorbing surface 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.

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 several 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 RTM solution to our clients in a timely manner we needed to increase our computing power. We achieved this task by upgrading our computer setup from CPU based hardware to the newest hybrid GPU/GPU based setup... read more