Processing

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Processing is a very broad topic.

In the Seismic industry there are 3 main phases

1) Acquisition

2) Processing

3) Interpretation

Seismic Data Processing is a profession that requires specific education, knowledge, training and tools for execution.

Processing reduces the originally recorded data from the acquisition step (pre-stack data) into the data volumes (post-stack data) that are used for interpretation to locate hydrocarbon reservoirs in the subsurface of the earth. There are many steps involved that can be categorized into different classes.

1) Geometry and Header assignment - to assign each trace to its common surface and subsurface location as well as shot to receiver distance and azimuth for example.

2) Time adjustments - to compensate for travel time differences due to variations in surface topography and near surface geologic variations and source to receiver distance variations. These processes are commonly referred to as "statics" and "nmo or normal moveout".

3) Wavelet compression - to collapse reflection events into a very short duration event instead of the original recorded signature. This is typically referred to as "Deconvolution" which has a variety of different technical implementations.

4) Noise Attenuation and signal to noise ratio improvements. - to remove as much noise as possible and retain and enhance as much primary signal as possible.

5) Adding (or stacking) traces that have a common subsurface reflection point.

6) Pre and / or post stack imaging to relocate all of the recorded samples and build an image where the events on the image are at their proper positions in time (or depth) and space. Imaging, or migration, is one of the most complex and compute intensive steps in the processing sequence.

7) There are other steps that can be performed such as Inversion and Attribute Extraction that can be used to extract more geologic information from the recorded seismic data to add more information to the interpretation step.

This outline is extremely simplified. It is not uncommon to apply 100's of individual processes to the seismic data through a complete processing sequence. It is the job of the seismic data processing professional to know which processes to apply in which order and with what specific parameters.

A typical processing sequence for a Land project may look something like this:

1) Assign Geometry and remove bad/noisy traces

2) Apply Datum Statics

3) First Arrival Picking

4) Refraction Statics estimation and application

5) First Arrival noise removal

6) Deconvolution

7) FK Filter

8) Velocity Analysis

9) Reflection Residual Statics estimation and application

10) Velocity Analysis

11) CDP stack

12) Post Stack noise attenuation - FK dip filter

13) Post Stack Migration

14) Pre Stack Migration - Kirchhoff with velocity model update tomography for 10 iterations

15) Stack of pre-stack migration output in depth