Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2002-01-14
2004-06-22
Hoff, Marc S. (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C702S016000
Reexamination Certificate
active
06754587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for processing a seismic 3-D measurement data set comprised of a multitude of seismic traces each having a sequence of data points provided with amplitude values.
2. The Prior Art
Seismic exploration methods are employed worldwide for the purpose of obtaining, in addition to information gained from drilled wells, additional knowledge about geological structures in the subsurface. Owing to the information obtained based on seismic data it is often possible to dispense with further cost-intensive exploration wells, or to limit their number to a minimum.
For seismic surveying of the subsurface, sensors (geophones/hydrophones) are employed, which are lined up successively (2-D seismology), and receive sound waves. Such waves are generated by a seismic source, for example by an explosive charge, by vibrator sources, or by airguns, and partly reflected back to the surface of the earth by the layers of the earth. The waves are registered on the surface by the sensors and recorded in the form of a time series. Such a time series represents the incoming seismic energy by amplitude variations. The time series is stored digitally and consists of uniformly arranged data points (samples), which are characterized by the time and the associated amplitude value. Such a time series is referred to also as a seismic trace. The measurement sequence migrates across the region to be explored, so that a 2-D seismic profile is recorded with such a system.
The goal of the subsequent processing operation is the suppression of noise, for example by stacking or filtering. The results so obtained are vertical profiles in which amplitudes and traveltimes as well as attributes derived from the amplitudes are represented. Such profiles serve as the basis for the further geological interpretation. The geological layers can be observed on a profile by the lateral line-up of the amplitudes.
A three-dimensional data volume is obtained if the data are recorded not along a line but in an areal grid. In the case of the 3-D volume, an amplitude value is assigned to any desired point in the subsurface, the point being described, for example by Cartesian coordinates. The vertical direction is measured in time (sound traveltime).
The measured data are corrected, filtered and, if need be, converted in the course of the data processing. The result is a seismic volume in the form of a 3-D data set that represents the physical properties of the explored subsurface in a seismic image.
It is possible to extract from such a data set any desired sections such as, for example, vertical profiles, and horizontal maps of various subsurface depths, which are then interpreted by geophysicists and geologists in the further course of the exploratory operation. Since such an interpretation of the obtained seismic images substantially comprises a visual correlation, attempts have been made to automate such a subjective interpretation that is depending upon one or more interpreters.
A method for seismic data processing is known from WO 96/18915. In this method, a seismic 3-D volume is divided in a multitude of horizontal slices, which are vertically disposed one on top of the other and spaced from each other, whereby at least one slice is divided in a multitude of cells. In this connection, each cell comprises at least 3 portions of traces whereby the first and the second trace portions are arranged in a vertical plane in the direction of the profiling (=inline), and the third trace portion and the first trace portion are arranged in a vertical plane substantially perpendicular to the direction of the profiling (=crossline). A cross correlation is then carried out between each two trace portions in the two vertical planes. Such a cross correlation supplies inline and crossline values that are dependent on layer dip. Combination of these values in a cell yields a coherency value for the cell that is assigned to a data point of the cell. The final results in turn is a 3-D data volume from which any desired sections can be extracted and displayed.
A method and a device for seismic data processing by means of the coherency characteristics are known from EP 0 832 442 A1, whereby in a manner similar to the method of the patent cited above, a seismic volume is divided in horizontal slices and the latter in turn are divided in cells. The cells have the shape of cubes in the simplest case. Based on the trace portions present in the cells, which amount to at least two in each cell, a correlation matrix is formed as the sum of the differences between inner and outer products of the sets of values from the trace portions. The quotient formed by the highest Eigen value of the matrix and the sum of all Eigen values is then calculated as the measure for the coherency. The result is again a 3-D volume comprised of coherency values.
Furthermore, EP 0 796 442 A1 relates to a method and a device for seismic data processing in connection with which a coherency method based on a semblance analysis is carried out. Similar to the procedure of two methods described above, a seismic data volume is divided in at least one horizontal time slice and the latter is then divided in a multitude of three-dimensional analysis cells, whereby each cell comprises two predetermined lateral directions that are perpendicular to each other, and at least five seismic trace portions that are arranged in the cell next to one another. A semblance value of the trace portions present in the cell is assigned in th respective cell to the corresponding data point. The semblance is in this context a known measure for the conformity between seismic trace portions. The dip and dip direction are determined in this context by scanning different layer dips and dip directions of the analyzed reflector for the best coherency. In addition to the semblance value, the calculated dip data are then displayed for each cell as well.
Furthermore, a method for determining physical properties of the subsurface is known from EP 626 594 A1. In this process, a comparison is carried out between a seismic reference trace recorded at a well location and a reference trace obtained synthetically from log data of a well. Modified synthetic seismograms are subsequently generated that are compared with the other seismic traces. However, only two trace segments are compared to each other, namely one trace segment of a seismic trace and one trace segment of a synthetically generated seismic trace. Lateral environments are consequently not taken into account.
Furthermore, an image processing method is known from the published DGMK (Deutsche Gesellschaft für Mineralölwissenschaft und Kohlechemie=German Society for Petroleum and Coal Chemistry) Conference Report [1996] “Image Processing of Seismic Attributes and Geostatistics in the Upper carbon” by C. HELLMICH, H. TRAPPE and J. FERTIG. This method permits a quantitative characterization of seismic representations and thus further interpretations of the lithology. Different image processing filters are employed to amplitude maps in this process, and the variations, or the continuity, respectively, of the amplitude values of the closer environment are quantified. The filters represent 2-D multi-trace filters, which are used for taking the local environment around a data point into account. Operators employed for this purpose are the entropy and the dispersion, among others. Maps for the interpretation can be generated for the interpretation with all attributes. The quantities “entropy” or “dispersion” are in this respect measures that quantify the variations or continuities of the amplitude in the local environment.
It has to be emphasized in this context that only relative comparisons in the local environment of a data point are considered in the methods described above. Laterally continuous and gradually changing conditions of the surroundings, for example, are consequently not conspicuous in connection with these processing methods. Even in connectio
Föll Marc
Hellmich Carsten
Trappe Henning
Collard & Roe P.C.
Henning Trappe
Hoff Marc S.
Le Toan M.
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