In seismic prospecting, an acoustic or seismic wave energy source is positioned either on the surface or in the subsurface of the earth, or is towed a predetermined distance beneath the surface of a body of water. A seismic source signal of some preselected waveshape and energy content is generated by the seismic energy source. The energy generated by the source penetrates through the layers of material comprising the subterranean portion of the earth in the region being prospected. Since the energy propagates at different speeds in each layer of material, refractions, reflections, and diffractions of the seismic energy occur at each layer. These energy reflections, refractions, and diffractions cause secondary seismic energy signals to return toward the surface of the earth. At the surface, the returning seismic signals are detected by a plurality of geophones, hydrophones, or seismic detectors spaced in a geometric array. The detectors generate electrical signals in analog or digital form which are representative of the amplitude of the reflected, refracted, and diffracted seismic energy signals arriving at the detectors.
The seismic signals can then be recorded in the field in analog or digital form and transmitted to a data processing center for further processing or can be further processed directly in the field. The further processing can involve, for example, writing source and receiver location data into each seismic record, filtering to remove undesired noise, gain correction, editing to remove undesirable traces, deconvolution, common depth point (CDP) sorting, corrections for normal moveout, corrections for statics, and the like.
The source-detector configurations for the generation and collection of seismic data include configurations for two-dimensional and for three-dimensional seismic prospecting. A configuration for two-dimensional seismic prospecting typically has the detectors arrayed along a line so that a detector location can be determined by the position of the detector in the line. A configuration for three-dimensional seismic prospecting typically has the detectors arranged in a configuration which would require, to determine the location of each detector, specifying two values, for example, an X and a Y coordinate, or longitude and latitude, etc.
Conventional two-dimensional seismic exploration techniques are relatively insensitive to error in the location of the seismic sources and receivers, hereafter location error. This relative insensitivity to location error results because seismic sources and receivers are, as indicated, typically located along a seismic line so that only locations along the line are required and these locations are relatively easy to determine using, for example, a surveying chain.
In three-dimensional seismic exploration techniques now in use and being developed, an accurate knowledge of the positions of the seismic sources and detectors used during the acquisition of the seismic data is a requirement. These locations are required for processing of the seismic signals, and further, as indicated, both X and Y coordinates (or latitude and longitude, etc.) of the source and detector locations must be known to properly process, for example, to stack and migrate and otherwise process the recorded seismic data. Location errors in the positions of the seismic sources and detectors can seriously degrade the quality of the resulting seismic images of the subsurface.
Location errors can occur or develop in a number of ways. Some possibilities include, for example, (1) surveying errors; (2) incorrect estimation of missing station locations after station flags are destroyed; (3) communication errors between shooter and observer concerning what source point is being initiated; (4) processing errors; and (5) bookkeeping errors anywhere along the surveyor-driller-shooter-observer-processor sequence.
Accordingly an object of the invention is a method for determining relative location errors of a seismic record.
A further object of the invention is a method for determining and correcting relative location errors of a seismic record.
Other objects of the invention are such methods applied to seismic records comprising data obtained from three-dimensional seismic prospecting.
Yet other objects are displays of seismic data in which relative location errors are displayed and/or corrected.
Further objects and advantages of the invention will be apparent to persons in the art from the following disclosure and the drawings.