PGS: Ultima transforms seismic processing
PGS Ultima addresses the long-standing challenge of building full-bandwidth terrestrial models and in a recent First Break article, the PGS authors present sample data from the Gulf of Mexico and Brazil to illustrate the effectiveness of this. new tool.
PGS Ultima is equivalent to performing full waveform inversion (FWI) and least squares migration (LSM) simultaneously, using raw seismic data and modeling the full acoustic wave field.
The main advantage of PGS Ultima is that an accurate model and reflectivity can be derived faster, because simultaneous inversion solves both using the same raw seismic data. PGS can bypass most of the processing steps of a seismic sequence because we are using raw seismic data and the evolution of the products is mutually reinforcing. In addition, there is no leakage between the parameters, so that the two products of the simultaneous inversion are not contaminated with each other, unlike many current industrial approaches.
Yang explains in the First Break article “With a single modeling engine, parameterized in terms of speed and vector reflectivity, the two properties of the Earth are iteratively updated using their appropriate sensitivity kernels based on the theory of reverse diffusion. Vector reflectivity is estimated as the least squares migration of the data domain and is the key to updating the velocity model beyond the maximum penetration depth of refracted and plunging wave energy. ‘
He adds, âWith examples from the field, we demonstrate how the new vector reflectivity modeling solution combined with appropriate inversion kernels enables us to meet the long-standing challenge of building full-bandwidth terrestrial models. ”
Synthetic tests validate the simultaneous reversal approach
A modified version of the SEG / EAGE overlap model is used to validate the simultaneous inversion, PGS Ultima. The actual speed, density and reflectivity are shown in A, B and D below. The initial velocity model is given in C and the output of PGS Ultima is given in E and F. PGS Ultima has correctly solved the velocity model and correctly positioned the reflectors and estimated the reflectivity and the output compares very well with the real ones examples in A and D.
Example of synthetic test of the model of overlap SEG / EAGE. Models of actual speed (A) and density (B). Model of initial velocity (C) and true vertical reflectivity (D). Inverted vertical reflectivity (E) and simultaneous inversion speed (F).
The performance of the new simultaneous reversal is shown in two sample field data below. In both examples, a simple muzzle velocity model is used and zero reflectivity. There is minimal pre-processing.
Gulf of Mexico Case Study | Provide accurate speed models and reliable amplitudes
The first example comes from the deep waters of the Gulf of Mexico, in the De Soto Canyon region. GeoStreamer data was acquired with a maximum offset of 12 km. All of the recorded data, i.e. the entire wave field, was used for the inversion.
In the example below, A shows the initial velocity model and C shows the reflectivity of the first iteration of the inversion, which is equivalent to an RTM image using the starting velocity model. Because the data contained multiples, crosstalk artifacts are seen in the RTM image and are indicated by the yellow oval.
The results after several simultaneous inversion iterations are shown in B and D. The PGS Ultima models clearly show higher resolution and reduced crosstalk in the final reflectivity model.
Example of De Soto Canyon terrain data. Initial (A) and reverse (B) speed models. Vertical reflectivity of the first iteration (C) and final reverse vertical reflectivity (D). Note the reduction in crosstalk as indicated by the yellow oval.
Campos Case Study | PGS Ultima resolves sharp drops and accurately images the target area
The second field example comes from a deep water environment in the Campos basin, off Brazil. Although the maximum online offset in the survey is 10 km, the water column of more than 3 km makes it difficult to update deep targets using the refracted energy. Simultaneous reversal was applied to the total pressure data using full records (i.e. without event selection). The slider images below show the vertical reflectivity patterns corresponding to the first and last iteration of the inversion. Speed ââupdates extend beyond the maximum penetrating depth of diving waves.
It’s important to remember that minimal pre-processing is applied before reversing, which greatly improves the time it takes to achieve this result compared to traditional workflows.
Amplitudes are much better balanced over the entire section on the PGS Ultima image. This is not only due to an improved speed model, but also the reverse reflectivity which compensates for any incomplete data missing from the acquisition pattern and geometric lens effects causing variable lighting in the basement.
There is an improvement in the resolution of the Shallow Rift system and an improvement in the consistency of the deep reflectors in the mini-basin and steep salt flanks. The top arrow indicates a finely bedded sedimentary unit truncated by faults. The middle arrows on the far left and far right highlight steeply sloping salt flanks and the lower arrows are located closer to the target range where carbonates are present above and below salt.
Comparison of images of the Campos basin. Vertical reflectivity of the first iteration (left) compared to the final reverse vertical reflectivity of PGS Ultima. The top arrow indicates a finely bedded sedimentary unit truncated by faults. The middle arrows on the far left and far right highlight the steeply sloping salt flanks. The lower arrows are located closer to the target range where carbonates are present above and below the salt.
The last example below is a 3.4 km depth slice through the Campos dataset. On the left side, the initial migration is covered by the starting speed model. This model is relatively invariant laterally, with the exception of the salt responses, represented by the color red. On the right side, the reverse reflectivity is covered by the reverse velocity model of PGS Ultima. Looking at the results from PGS Ultima on the right, it is evident that the reverse velocity model contains much more resolution and conforms well to reflectivity without reflectivity being imposed.
The geometry of the saline bodies in the center and to the right has been updated from the original model and the underlying reverse reflectivity is both higher resolution and better spatially balanced in terms of amplitude.
The PGS Ultima Velocity model appears consistent with reflectivity.
Position targets with precision with PGS Ultima
PGS believes that it is possible to reduce the project turnaround time by at least 50% by using PGS Ultima.
The results demonstrate that while the velocity model is iteratively updated, an accurate estimate of the earth’s reflectivity is generated simultaneously. FWI and LSM can be run together as a single inversion workflow using minimally processed data. Simultaneous reversal reduces turnaround time for model building and imaging projects and eliminates the need for tedious manual interpretation, especially in complex geological settings. PGS Ultima solves these challenges by transforming traditional processing and imaging workflows into a data-driven approach that provides precise velocity patterns and reflectivity using simultaneous inversion.