Binning of three dimensional seismic data

#The invention involves the acquisition and processing of three dimensional (3D) seismic data, and, in particular, the acquisition and processing of seismic data using a sampling grid.

#Three dimensional seismic exploration of the earth's terrestrial and marine subsurface is used in the exploration, production, and development of hydrocarbons. In seismic exploration, underground geological structures are illuminated and imaged with sound energy. The basic components of a surface seismic exploration system would include a source (e.g., a dynamite explosion or airgun sounding) on the earth's surface and a receiver on the surface. The source generates sound waves to be reflected from a subsurface structure and the receiver receives and records the upwardly reflected sound energy. Data from the seismic experiment are recorded in the form of a seismic trace, i.e., a record of the reflected sound events received at the surface receiver over a period of time. The image of the subsurface is constructed by processing the reflected energy from many of these seismic traces.

#In "prestack imaging," seismic traces from single source-receiver pairs are processed individually. In "poststack imaging," on the other hand, data from many single source-receiver pairs are combined by stacking (summing) before processing to increase the signal-to-noise ratio and to reduce the number of seismic traces that must be processed. The traces are first grouped into "common midpoint gathers" and then operations such as Normal Movement ("NMO") and Dip Moveout ("DMO") are performed. A midpoint is defined as the surface location halfway between a trace's source and receiver.

#FIG. 1A shows a known three dimensional acquisition geometry for land, transition zone, and ocean bottom cable surveys with source lines perpendicular to receiver lines.

#FIG. 1B shows a regular grid superimposed on the regular geometric configuration of sources and receivers in FIG. 1A.

#FIG. 2 shows a computer system in accordance with an embodiment of the invention.

#The invention provides a method and apparatus for acquiring and processing 3D seismic data, for example, data from a 3D seismic survey, using a hexagonal sampling grid. The method and apparatus group seismic traces into hexagonal bins defined by a hexagonal grid instead of into rectangular bins defined by a rectangular grid. The method and apparatus may be described for square and regular hexagonal grids, but are applicable to rectangles and hexagons of any shape. Use of hexagonal bins instead of rectangular bins improves both efficiency and symmetry. Hexagonal grids require 13.4% to 25% fewer grid points than rectangular grids for sampling circularly bandlimited, two-dimensional signals. Hexagonal grids also offer 50% more symmetry than rectangular grids, leading to more accurate digital operators and calculations.

#The cost of a 3D survey is defined by the bin size and, consequently, the receiver and source individual station interval. Because hexagonal binning requires fewer gridpoints than rectangular (square) binning, for practical applications, the source or receiver interval may be increased, which may help reduce the survey cost.

#Before discussing the method further, reference is made to FIG. 2 which shows a computer system 100 configured in accordance with an embodiment of the invention. Computer system 100 comprises a central processor (CPU) 120 coupled to a display 110, a keyboard 130, a memory 140, and input/output (I/O) devices 150. Display 110 may be a computer monitor or equivalent device for displaying information associated with input or output information (e.g., seismic information) to a user. Keyboard 130 may be a computer keyboard for the user to input information to the computer system 100. Memory 140 stores instructions 145 which are used to instruct the CPU 120 to carry out processes in accordance with embodiments of the invention including, for example, instructions related to the steps shown in FIG. 5 below. Memory 140 comprises a computer-readable memory medium which may be volatile or nonvolatile memory, or a combination of both, for example, a hard disk, a floppy disk, a CD-ROM, magnetic storage, optical storage, RAM including DRAM, flash memory, registers, or any other appropriate storage medium. I/O devices 150 represent a communication device or a combination of communication devices (e.g., a modem, ISDN adapter, telephone lines, wireless services) or other information propagating or telecommunications devices or media, used for reception or transmission of sample data or processed data. The I/O devices 150 may also be used for receiving or transmitting instructions in accordance with an embodiment of the invention to be stored or retrieved from the memory 140.