Boots – shoes – and leggings
Patent
1995-11-13
1998-06-09
Cosimano, Edward R.
Boots, shoes, and leggings
364400, 364421, 367 38, 367 53, 367 73, G01V 128
Patent
active
057645140
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a method of modelling kinematic seismic data and, more particularly, a method of producing a three-dimensional model of kinematic seismic data; that has been processed by at least one migration operator.
2. Related Art
The expression "migration operators" refers to processes that reposition the seismic energy. These processes are well known to those skilled in the art and some forms of them are mentioned later in the description.
To determine the geometrical subsurface structure of the earth it is standard practice, in oil prospecting, to study the subsurface propagation of elastic or acoustic waves emitted by sources on the surface of the earth at points known as "shot points". The subsurface waves are reflected by reflectors existing in the various boundaries between layers and therefore return to the surface where they cause time-varying vibrations which may be by receivers of a data acquisition device at points called "receiving points". Each of these recordings is associated with the position of a mid-point at the middle of a straight line segment joining the shot point and the receiving point associated with the record. The data acquisition device is adapted such that a plurality of different records can be associated with the same mid-point or with the same area on the surface (or "bin") and the various mid-points, which are usually equidistant from each other, are aligned on a line called the seismic profile or lie on a grid which is usually a regular grid ("3D grid").
Each record in the collection of records associated with the same mid-point is known as the common-mid-point (CMP) gather. These records are processed to correct for the effects of the oblique path followed by the acoustic wave as a function of the distance between the shot point and the receiving point. Thus the record is referred to as the theoretical time corresponding to shot and receiving points coincident at their initial mid-point, i.e. to a zero source-receiver offset. The dynamic corrections known as NMO (Normal Move Out) corrections that correct for the effects of the oblique acoustic paths are dependent on speeds known as "stacking speeds" and in theory allow simulation of the record that would have been obtained if the shot point and the receiving point had been at the mid-point. Stacking of the corrected records of each gather provides a stack records called "stack-traces", the juxtaposition of which (according to the coordinates of the mid-point or the center of the bin) constitute the "3D stack seismic block". The 3D stack seismic block may be regarded as a distorted three-dimensional image of the subsurface structure, with time along the vertical axis and two distances along the horizontal axes.
However, the NMO corrections are based on a number of limiting hypotheses. A form of processing called DMO (Dip Move Out) was therefore developed and is now in extremely widespread use. It is usually applied to the seismic data before stacking (pre-stack), but after NMO correction, in order to eliminate as much as possible of the effect of reflector dip on the stack speeds as possible. A detailed description of the DMO operator is given in an article entitled "What Is DMO?" by S. M. DEREGOWSKI, FIRST BREAK, Vol. 4, No. 7, pp.7-24 July 1986, and in other publications, for example, U.S. Pat. No. 4,878,204.
However, the DMO operator is based on a relatively simple hypotheses. More complex operators are therefore applied to the seismic data, including the "pre-stack time migration" operator.
Having obtained a satisfactory 3D stack seismic block and the corresponding set of stack speeds, the "3D time migration" step is usually executed. The object of migration is to provide the interpreter with an acoustic image of the subsurface structure that resembles (as closely as possible) a geological image. However, the processing by the time migration operator is based on a simplified version of the wave equation and does not take into account the finer d
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Raynaud Bernard
Robein Etienne
Cosimano Edward R.
Elf Aquitaine Production
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