Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2000-12-22
2003-06-03
McElheny, Donald (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
Reexamination Certificate
active
06574566
ABSTRACT:
This invention relates to processing data, and more particularly it relates to a method and apparatus for creating displays, preferably tomographic displays, of three-dimensional (3D) data to aid in visualization of aggregate attribute information. More particularly, it relates to creating tomographic displays to aid in the visualization of aggregate seismic attribute information, which information identifies changes in geology, lithology, and pore fluid content within the earth's subsurface formations.
BACKGROUND OF THE INVENTION
Numerous techniques for exploring the earth to acquire geophysical data are well known. Seismic surveys, however, are the most reliable and most definitive geophysical means of structural representation currently in use. For many years seismic exploration for oil and gas reservoirs has involved the use of a source of seismic energy and its reception by an array of seismic detectors, generally referred to as geophones. When used on land, the source of seismic energy can be a high explosive charge electrically detonated in a borehole located at a selected point on the terrain, or another energy source having capacity for delivering a series of impacts or mechanical vibrations to the earth's surface. The acoustic waves generated in the earth by these sources are partially transmitted back from strata boundaries and reach the surface of the earth at varying time intervals, depending on the distance and the characteristics of the subsurface traversed. These returning waves are detected by the geophones, which function to transduce such acoustic waves into representative electrical analog signals. In use, an array of geophones is generally laid out along a line to form a series of observations stations within a desired locality, the source injects acoustic signals into the earth, and the detected signals are recorded for later processing using digital computers, where the analog signals are generally quantized as digital sample points, e.g., one sample every two milliseconds, such that each sample point may be operated on individually. Accordingly, seismic field records are reduced to vertical and/or horizontal cross sections which approximate subsurface features. The acoustic source and the geophone array are then moved along the line to a new position and the process repeated to provide a complete seismic survey. Three-dimensional (3D) seismic surveys involve geophones and sources laid out in generally rectangular grids covering an area of interest so as to expand area coverage and enable construction of 3D views of reflector positions over wide areas.
After exploration of an area is completed, data relating to energy detected at the plurality of geophones will have been recorded, where the geophones are located at varying distances from the shotpoints. The data is then reorganized to collect traces from data transmitted at various shotpoints and recorded at various geophone locations, where the traces are grouped such that the reflections of the group can be assumed to have been reflected from a particular depth point within the earth, i.e., a common midpoint (CMP). The individual traces are then corrected for the differing distance the seismic energy travels through the earth from the corresponding shotpoints, to the common midpoint, and upwardly to the various geophones. This step includes correction for the varying velocities through the rock layers of different types. The correction for the varying spacing of shotpoint/geophone pairs is referred to as “normal move out.” After this is done the group of signals from the various midpoints are summed. Because the seismic signals are of a sinusoidal nature, the summation process serves to reduce noise in the seismic record, and thus increasing its signal-to-noise ratio. This process is referred to as the “stacking” of common midpoints data. As is well known to those skilled in the art, processing of seismic data may vary, but normally includes normal move out, stacking, migration and deconvolution.
Originally, seismic traces were used simply for ascertaining subterranean formation structure. However, exploration geophysicists have developed a plurality of time-series transformations to obtain a variety of characteristics that describe the seismic traces, and such characteristics have been termed “instantaneous attributes” because values for the attributes are generally obtained for each time sample point in the seismic data, or within a small time window of data points. These attributes provide quantitative measures of the wavelike nature of the seismic signal traces, and may characterize changes in properties of the earths subsurface formations. Examples of instantaneous attributes include, but are not limited to, amplitude, frequency, phase, dip, dip azimuth, power, pseudo porosity, etc. Attributes may be displayed as measured values of the seismic data, or may be calculated based on the seismic data. By mapping displays of such instantaneous attributes on displays of seismic section or volume data, geophysicists have characterized and identified changes in lithology, geology, pseudo porosity and pore fluid content associated with individual reflection events in the seismic trace data. Seismic attributes are not limited to instantaneous attributes, and as used herein an attribute includes any way of characterizing a seismic trace. For example, “interval” attributes, which are the attributes of seismic traces calculated within a seismic interval, are often analyzed.
The sole purpose of the above described and other data processing and measurement efforts, which are known to those skilled in the art, is to facilitate the final and most critical phase of the seismic exploration method, namely, data interpretation. This interpretation includes reduction of the data to a realistic model of the subsurface strata, and illustration of both structural configurations and geologic characteristics of subsurface volumes.
Accordingly, there is a need for seismic displays that aid in understanding and characterizing various attributes by displaying aggregate seismic attribute information in an intuitive and meaningful manner.
In addition to seismic data interpretations, other areas of data interpretation can benefit from improved methods and apparatus which aid in understanding and characterizing various attributes. One such area is medical imaging, such as the imaging of brain scans. Current imaging systems are scale dependent and, hence, it is difficult to compare different brain scan attributes because the subject of one brain scan may be larger or smaller than the subject of a comparison brain scan, such as comparing a child's brain scan to an adult's brain scan.
Accordingly, there is a need for imaging displays that aid in understanding and characterizing various attributes and that are scale independent.
It is an object of this invention to accumulate and display values for attributes in an intuitive and meaningful manner.
It is another object of this invention to display values for attributes in a way that allows better comparison because it is scale independent.
It is another object of this invention to accumulate and display aggregate tomographic values for seismic attributes such as: amplitude, acoustic impedance, continuity factors, pseudo porosity, etc.
It is a more specific object of this invention to accumulate attribute values along a tomographic path within a subvolume of data corresponding to a 3D figure, and to map the aggregate value of the attribute for display on the surface of the 3D figure.
It is another object to compare similar subvolume displays based on their tomographic attribute maps.
Yet another object is to identify geological and stratigraphic features based on the tomographic attribute maps of subterranean volumes.
Still another object of this invention is to characterize subvolumes by combining all values of the tomographic attribute into a single number and assigning the combined value to the center point of the subvolume.
Another object is to automate geologica
Grismore John R.
Lucas William A.
Neff Dennis B.
Conocophillips Company
Cross Ryan N.
McElheny Donald
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