What Is Seismic Processing?

Use small computers and field-specific seismic processing software to perform timely and simple processing of seismic data in the field. It is a seismic data processing method that mainly examines the quality of seismic data collection. ^[1]

Basic data The data to be tested for on-site seismic processing mainly include all seismic acquisition data such as original seismic data, observation systems or SPS files, measurement data and static correction data. The details are: monthly inspection records of seismic instruments without self-inspection capabilities; analysis and analysis of noise levels of collected raw data; accuracy of shot points and detection points; excitation conditions (including TB conditions) and reception conditions (dead or abnormal) , Reverse polarity, leakage, etc.); the effect of static correction; the recording quality of the collected data and the imaging quality of the target layer on the superimposed section.

The main workflows for on-site processing include:

(1) Accept field original data, including original tapes, instrument shift reports (SPS files), field static correction data, and relevant observation system data. The focus is to check whether each original data meets the requirements, is complete, and can be read correctly. ;

(2) Correctly decode the field record format tape data into a format acceptable to the data processing system, and display some single shot records at the same time to further check the correctness of the data decompilation;

(3) Define the observation system, including defining the actual field locations of shots and inspections and their correlations, and draw and analyze the plan positions of shots and detection points, the coverage times of CMP bins, and the minimum and maximum shot inspections. Distance distribution map, used to check whether it is consistent with the actual situation in the field;

(4) Eliminate abnormal track records, shot records, and outliers through prestack denoising to eliminate strong surface waves and other regular interference, so that the signal-to-noise ratio of the profile after denoising should be significantly improved, and the wave group characteristics are clear;

(5) Through amplitude compensation and deconvolution (optional) processing, the shallow, medium, and deep reflected energy on the seismic record is basically balanced, and there is no obvious energy difference between adjacent shots, and the resolution of the seismic record Significantly improved

(6) Carefully check the elevation data of the shot point and the detection point, draw a plan view of the static correction amount, analyze the rationality of the static correction amount change, perform static correction on this basis, and optionally perform residual static correction if necessary (the time window should be selected (At seismic horizons with better reflection quality), the residual static correction section should not have obvious artifacts, and the section quality should not be lower than the section before the residual static correction;

(7) The density of velocity analysis points should be reasonably selected according to the geological structure. Generally, one point is selected per kilometer. In three-dimensional cases, four velocity analysis points are required per square kilometer. The number should be reasonable, and try to include all kinds of different offsets. The cutting parameters should be correct. The speed scan range should be larger than the actual data range.) The speed picking must be reliable and the spatial changes must be reasonable.

(8) The velocity analysis of inclination time difference correction should be selected. In addition to the principles of velocity analysis, the gather used for velocity analysis should also use the CMP surface element gathers after inclination difference correction. The offset aperture used should be less than the maximum. The inclination of 2/3 of the offset of the gun should be greater than the maximum inclination of the actual data. The cross-section and diffraction waves of the superimposed profile after correction of the inclination time difference should be more abundant, and the oblique reflection is clearer;

(9) The single guns after dynamic correction are superimposed according to coplanar elements to obtain superimposed sections;

(10) Select the post-stack de-noise treatment, pay attention to the selection of appropriate de-noise methods and appropriate parameters;

(11) The post-stack time offset (optional) process is used to return the in-phase axis to a clear position (the offset algorithm and speed field test must be done before the offset);

(12) Carry out some modification processing (optional), such as filtering and gain processing, and try to make the wave group characteristics of the effective reflection in-phase axis clear.

In the field processing work, in order to select the best processing flow and parameters, representative data should be selected for trial processing before performing each important processing step. The items to be processed generally include the following parts: amplitude compensation, deconvolution, residual static correction, resection, correction of tilt time difference, offset velocity field, filtering and gain, denoising, etc. During the on-site processing work, every step of the operation should be completed, the operating documents, quality control drawings and intermediate results should be carefully checked to ensure that the processing methods and parameters used are correct, the operation runs normally and meets various technical requirements. In addition, according to the work Et, the collection quality problems found in the on-site processing should be reflected to the construction quality supervision; each section (each beam line) must also fill in a quality information (feedback) report in duplicate, including the preliminary evaluation of construction effects, problems .

On-site processing is a product of the early 1970s, and it is an iconic event in the history of seismic data acquisition. China also began to develop on-site seismic processing software in the mid-1970s. The self-developed on-site commercial processing software GRISYS appeared in the early 1990s. In 2000, KLSeis, a new generation of seismic data acquisition engineering software independently developed by Oriental Geophysics, was successfully developed. It has strongly promoted the improvement of the quality of data collection in seismic survey sites in China. Nowadays, on-site processing has become the main method for quality control of on-site acquisition by oil companies or seismic contractors. As the seismic geological conditions in the exploration area become more and more complicated, the requirements for the quality of seismic data collection are becoming stricter, and the requirements for on-site processing are becoming higher and higher, resulting in a smaller and smaller difference between on-site and indoor processing. On-site processing tends to replace the pre-processing part of indoor processing, and thus becomes an indispensable part of indoor final processing. ^[2]