Image analysis – Histogram processing – For setting a threshold
Patent
1991-02-28
1992-09-15
Couso, Jose L.
Image analysis
Histogram processing
For setting a threshold
382 16, 382 21, 364421, G06K 900
Patent
active
051484943
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a plotting process which is particularly suitable for images wherein a direction is preferred, such as the image of a seismic cross-section. When applied to seismology, the process according to the invention in particular enables the portions of seismic horizons of the seismic cross-section having given features to be automatically selected and this cross-section to be interpreted structurally and stratigraphically.
In a very general manner, it may be considered that the substratum consists of an arrangement of geological layers having different features and organised in space according to a given geometry.
In order to define the geometry of the substratum, specialists in substratum exploration, in particular petroleum exploration, use a special technique known as "seismic reflection" which includes emitting acoustic signals on the surface of the ground and recording them after the signals have been propagated through the substratum and have been reflected on particular acoustic borders which are formed at the boundaries of (adjacent) geological layers and are known as reflectors.
The recorded signals are processed so as to obtain particular images of the substratum, known as "seismic cross-sections" which may be assimilated with vertical cross-sectional plans of the substratum and on which the reflectors appear as lineations superimposed over one another, relatively distinguishable, relatively continuous, and are subhorizontal or deformed, with respect to the image of the substratum layers and referred to by specialists as "seismic horizons".
A seismic cross-section consists of a succession, from left to right or from right to left of vertical recordings known as "seismic traces" consisting of signals which have an amplitude which is relatively high and include positive and negative arches, each of these signals being the image of a point of a reflector. The image signals of a given reflector correlate from one trace to another, thus rendering lineations visible.
Certain of these lineations may be very short but, nevertheless, have importance: this is the case with "doublets" for example. It is said that doublets are present on a seismic cross-section when an arch of a frequency signal which is higher and of the same sign as the arches constituting the major lineations is intercalated between two clearly distinguished major lineations which are associated with amplitude arches of the same sign and separated over a great length by a single signal arch having an opposite sign.
Seismic cross-sections prepared by geophysicists are subsequently transmitted to specialists--geophysicists or geologists--who interpret them in order to detect for example reservoirs therein. The interpretation process includes plotting a given number of determined seismic horizons over a plurality of seismic cross-sections describing a given geographical area which may intersect one another, and producing a map therefrom. The plotting operation is conventionally performed by hand. The plotting includes connecting the signals which are considered to belong to a given seismic horizon by optical correlation therebetween, using a coloured crayon. Usually different horizons will be plotted with different colours in order to differentiate them. The image signals of a given reflector will have features--shape, frequency content, number of arches, amplitude, etc.--which are generally similar.
Undoubtedly, a plotting system of this type is a long, tedious and hence costly process. It is not uncommon for one interpretation operation to occupy several interpreters for a number of weeks when a large number of horizons must be plotted over a large number of cross-sections.
This is the case, for example, when reconnaissance exploration is carried out over a very wide geographical area or when "deposit seismology" is performed over a limited area but with very close cross-sections. This manual work may, moreover and consequently, lead to plotting errors which are all the easier to make when the horizons to be plott
REFERENCES:
patent: 4633400 (1986-12-01), Chittineni
patent: 4782446 (1988-11-01), Ehler et al.
patent: 4841444 (1989-06-01), Chittineni
patent: 4992995 (1991-02-01), Favret
Couso Jose L.
Societe Nationale Elf Aquitaine
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