Automatic quality control of seismic travel time
Seismic data from seismic exploration surveys are mapped into a hypercube of bins or voxels in a four-dimensional space (X, Y, Offset, and Azimuth) according to Common Mid-Point (or CMP) between source and receivers. The mapped data from individual voxels or bins is then analyzed by multimodal statistics. Robust estimates of first break picks are obtained from the analysis. The first break picks are then used to as seed inputs for autopicking iteration, which proceeds to convergence. Estimates of confidence levels in the data are provided for re-picking to reduce computer processing time in successive autopicking iterations. Analysis is provided of different seismic attributes such as azimuthal velocity variations indicative of anisotropy, positioning errors of sources/receivers, geometry errors, and three dimensional distribution of inversion residuals. Analysis is also performed of standard deviation of the travel time data useful for estimating data errors in the inversion covariance matrix.
1. A computer implemented method of forming an estimate of the velocity of travel of seismic energy waves in the rock formations of the earth by forming corrected measures of refracted seismic energy travel times during travel from a seismic source to an array of seismic detector geophones during a seismic survey by removing anomalous travel times from a seismic trace gather detected by the seismic detector geophones during the seismic survey, comprising the steps of:
(a) assembling in the computer the seismic trace gather detected by the array of detector geophones during the survey;
(b) selecting in the computer from the assembled seismic trace gather a first break dataset of initial estimates of the refracted energy travel times at the detector geophones during the survey;
(c) assembling the selected initial estimates of the refracted energy travel times of the seismic gather into bins of a travel time attribute cube with an at least three-dimensional binning according to dimensional spacing in a first horizontal x dimension, a second horizontal y dimension, and a source-receiver offset axis dimension of refracted energy common midpoint for refracted seismic wave travel during the survey;
(d) forming measures of the time distribution of the selected initial estimates of refracted energy travel times in individual bins of the travel time attribute cube;
(e) removing seismic traces in the individual bins with refracted energy travel times which differ from the measures of the time distribution by more than a specified time interval; and
(f) forming an adjusted travel trace gather of the seismic traces remaining in the individual bins after the step of removing;
(g) comparing the travel times of the adjusted travel trace gather in the individual bins with a specified measure of accuracy; and
(h) if the compared travel times of the adjusted travel trace gather are within the specified measure of accuracy,
(i) storing compared travel times of the adjusted travel trace as the corrected measure of the travel times; and
(j) performing a tomographic inversion of the stored corrected measures of the travel times to form an estimate of the velocity of travel of the seismic energy waves in the rock formations of the earth;
and, if not,
(k) performing for the formed adjusted travel trace gather the steps of removing seismic traces in the individual bins with refracted energy travel times which differ from the measures of the time distribution by more than a specified time interval, and comparing the travel times of the adjusted travel trace gather with a specified measure of accuracy.
2. The computer implemented method of claim 1 , wherein the step of assembling further includes assembling the selected initial estimates of the refracted energy travel times of the seismic gather into the travel time attribute cube according to an azimuth axis of refracted energy common midpoints for refracted seismic wave travel during the survey.
3. The computer implemented method of claim 1 , further including the step of forming a confidence indicator measure of the travel times in the individual bins of the travel time attribute cube.
4. The computer implemented method of claim 3 , wherein the step of storing further comprises the step of storing the confidence indicator measure of the travel times of the adjusted travel trace gather.
5. A data processing system forming an estimate of the velocity of travel of seismic energy waves in the rock formations of the earth by forming corrected measures of refracted seismic energy travel times during travel from a seismic source to an array of seismic detector geophones during a seismic survey by removing anomalous travel times from a seismic trace gather detected by the seismic detector geophones during the seismic survey, comprising:
(a) a processor performing the steps of:
(1) assembling in the computer the seismic trace gather detected by the array of detector geophones during the survey;
(2) selecting in the computer from the assembled seismic trace gather a first break dataset of initial estimates of the refracted energy travel times at the detector geophones during the survey;
(3) assembling the selected initial estimates of the refracted energy travel times of the seismic gather into bins of a travel time attribute cube with an at least three-dimensional binning according to dimensional spacing in a first horizontal x dimension, a second horizontal y dimension, and a source-receiver offset axis dimension of refracted energy common midpoints for refracted seismic wave travel during the survey;
(4) forming measures of the time distribution of the selected initial estimates of refracted energy travel times in individual bins of the travel times attribute cube;
(5) removing seismic traces in the individual bins with refracted energy travel times which differ from the measures of the time distribution by more than a specified time interval; and
(6) forming an adjusted travel trace gather of the seismic traces remaining after the step of removing;
(7) comparing the travel times of the adjusted travel trace gather with a specified measure of accuracy,
(8) if the compared travel times of the adjusted travel trace gather are within the specified measure of accuracy,
(9) storing compared travel times of the adjusted travel trace gather as the corrected measure of the travel times;
(10) performing a tomographic inversion of the stored corrected measures of the travel times to form an estimate of the velocity of travel of the seismic energy waves in the rock formations of the earth;
and, if not,
(11) performing for the formed adjusted travel trace gather the steps of removing travel times which differ from the measures of the time distribution by more than a specified time interval, and comparing the travel times of the adjusted arrival trace gather with a specified measure of accuracy; and
(b) a memory receiving for storage the compared travel times of the adjusted arrival trace gather as the corrected measure of the travel times.
6. The data processing system of claim 5 , wherein the processor in performing the step of assembling further assembles the selected initial estimates of the refracted energy travel times of the seismic gather into the travel time attribute cube according to an azimuth axis of refracted energy common midpoints for refracted seismic wave travel during the survey.
7. The data processing system of claim 5 , further including the processor performing the step of forming a confidence indicator measure of the travel times in the individual bins of the travel time attribute cube.
8. The data processing system of claim 7 , wherein processor in performing the step of storing further performs the step of storing the confidence indicator measure of the arrival times of the adjusted travel trace gather.