Our industry may have heard of instantaneous attributes for the first time in 1979 with the publication of Taner et al’s paper on “Complex Trace Analysis”1 in Geophysics. This author first became aware of them when in 1982 a little blue booklet, published by the same authors in 1981 in association with Seiscom Delta, came to my attention. It seemed that the suggested use for these attributes was for structural analysis. As an early seismic stratigrapher specializing in lateral prediction at Shell’s Bellaire Research Center, I acquired the programs to run as PAL jobs on our mainframe computer. Color plots of instantaneous phase, envelope, and instantaneous frequency with my own proprietary colorbars helped to look at the Atlantic Margin in a whole new way.
Often called instantaneous attributes, their fundamental distinction is of having a value at every 4 or 2ms sample which enhances continuity, makes discontinuities more apparent, and need not include the “cloaking” and distortion of amplitude.
The culmination at Shell of my work came with it very effective and most confidential application, in the late 80s earliest 90s, at Mars field to solve a drilling problem, reclassify a regional structure, and, most importantly to rewrite the book on the architecture and extents of multiple key reservoirs. Earlier work (’86-’89) on key applications in Brazil had literally caused a rewrite of the stratigraphic lexicon there and brought attention to the importance of their application.
I continued to use the technology ever since on all sorts of platforms and ,until 1999, when Clemenceau and Colbert of Amoco published one instantaneous phase section over Ram Powell field, had never seen another stratigraphic application.
A second go round with multiple attributes in the period from ’98 -2002, was unsupervised but not neural network. It rather was based on technology that was used to map the human genome and as such was limited to the use of only 4 attributes at a time.
Current Case studies
Up to 16 Instantaneous attributes have been generated in a convenient interpretation software for which it is important to know that the Real Part amplitude data is used as the parent volume. A set of “instantaneous attributes” can also be created in the Paradise software (approx. 16) but these are calculated on the conventional RFC amplitude data. This produces an inherent difference in some of the results, notably the Instantaneous Phase.
The intent of either approach is to deliver inherently smoother and higher frequency simultaneous multiple-attribute data to PCA and subsequently to and from the SOM classifier, a learning machine that organizes the samples into natural clusters that reveal geologic features and anomalies in the data. The use of machine learning tools represent a fundamental and dramatic step change in the science of Seismic interpretation (Tom Smith, pers. comm. April 2016). Using these tools, a relatively small group of instantaneous attributes, regardless of depositional environment, seem to do an excellent job of resolving identifiable system and facies tracts in seismic data here with a sample based resolution of 10-12’ for 2ms data.
From the PCA analysis for the Eagle Ford for example, nine attributes were run in the SOM along with using the base survey data to “prune,” that is, remove null values from the data volume so as to not assign a neuron wastefully. A brief description of the five most commonly occurring and most independent instantaneous attributes in neuron clusters in the Eagle Ford is as follows:
- Instantaneous Phase (10.1%) which is useful for stratigraphic and structural continuity and discontinuity enhancement;
- Normalized Amplitude (13.9%) aka Cosine of Instantaneous Phase which returns the energy distinctly from peaks versus troughs;
- Relative Acoustic Impedance (14.8%) helps to resolve geobodies;
- Envelope or Total energy of the entire reflected waveform includes the Real Part (15.9%) or that which is equivalent to the base survey data that is measurable and the Imaginary Part (12.2%) which is not.
- Trace Envelope (5%) comprises a much smaller part of the data
- In addition to the above, Thin Bed Indicator (3.5%), Instantaneous Frequency (2.5%), and Envelope 2nd Derivative (?), rounded out the nine suggested by the PCA. However, these three were less evident in the area investigated or were possibly in the background.
A check of the total relative and total independence of these attributes in the neuron clusters that characterize the facies of the Eagle Ford Group clastics and carbonates showed the following:
Only 3 neuron clusters (facies) out of 26 have just 3 prominent attributes (IP, NA, Real Part). Two of these are the uppermost facies of a carbonate stack #62 for the carbonate regressive margin and #6 at the top of the EF Marl. Both are high resistivity facies. The lowermost part of Geobody 2, N51, has the same order as the upper marl and is not calibrated.
Only 1 neuron cluster or facies, N57, has 6 prominent attributes and its samples comprise only .3 of 1% of the total samples in the 110ms model. Its 2nd, 4th, and 6th attributes are those that each comprise 5% or less of the data. Of these, Trace Envelope, is nearly completely restricted to three neuron clusters (N57, 58, 59) that form the mid to downdip central core of Geobody 1 and N52 in Geobody 2. The only other occurrence is in N24 at the base of the marl section updip which appears to be 95% carbonate in one XRD sample. All calibrated instances are High resistivity.
1 Taner, M. T., F. Koehler, and R. E. Sheriff, Complex seismic trace analysis, 1979, Geophysics, v.44, no. 6, p. 1041-1063, 16 Figs., 1 Table, June.