Method and apparatus for seismic signal processing and exploration

A method of locating subterranean features, faults, and contours, comprising the steps of:

• (a) accessing 3D seismic data covering a pre-determined volume of the earth;
• (b) dividing said volume into an array of relatively small three-dimensional cells wherein each of said cells is characterized by at least five laterally separated and generally vertical seismic traces located therein;
• (c) determining in each of said cells the semblance/similarity of said traces relative to two pre-determined directions;
• and
• (d) recording said semblance/similarity of said cells in a form for display as a two-dimensional map of subterranean features.

In seismic exploration wherein 3D seismic data comprising reflected seismic energy is recorded as a function of time and wherein a computer is used that is programmed to process such seismic traces and to produce an image therefrom that is representative of subterranean features, an article of manufacture comprising:

• a medium that is readable by a computer and that carries instructions for said computer to perform a process comprising the steps of:
• (a) accessing 3D seismic data over a predetermined volume of the earth, said data comprising seismic traces that are characterized by time, position and amplitude;
• and
• (b) ascertaining the similarity of nearby regions of said 3D seismic data of said volume by:
• (1) dividing at least a portion of said data into an array of relatively small, adjacent, three-dimensional analysis cells, wherein each of said analysis cells contains portions of at least five seismic traces;
• and
• (2) computing a seismic attribute for each cell that is a function of the largest of a plurality of measurements of semblance and the corresponding apparent dip and the corresponding apparent dip azimuth.

In seismic exploration wherein reflected seismic energy is recorded as a function of time to produce a series of seismic traces, a method comprising the steps of:

• (a) accessing a data set of seismic traces distributed over a three-dimensional volume of the earth, said volume of the earth having subterranean features characterized by dip and dip azimuth;
• (b) calculating a plurality of measures of the semblance of said traces within a relatively small three dimensional analysis cell that is located within said volume and at one part of a predetermined time layer, wherein each measure of semblance is at least a function of time, the number of seismic traces within said analysis cell, and the apparent dip and apparent dip azimuth of said traces within said analysis cell;
• (c) computing a seismic attribute for said analysis cell that is at least a function of the largest of said plurality of calculated measures of semblance and the corresponding apparent dip and the corresponding apparent dip azimuth, wherein said corresponding apparent dip and said corresponding apparent dip azimuth are defined to be estimates of the true dip and an estimate of the true dip azimuth of the seismic traces within said analysis cell;
• (d) repeating steps (b) and (c) along other parts of said time layer;
• and
• (e) forming a map of said seismic attributes over said time layer.

A method of seismic exploration, comprising the steps of:

• (a) reading a 3D seismic data set comprising seismic signal traces that are distributed over a volume of the earth;
• (b) selecting at least one horizon slice from said volume and forming therein cells that are arranged into laterally extending rows and columns, each of said cells having at least five seismic traces extending generally therethrough;
• (c) computing for each of said cells:
• (1) a plurality of semblance measurements of said traces, wherein each measurement is at least a function of time, the number of seismic traces within said analysis cell, and the apparent dip and apparent dip azimuth of said traces;
• (2) the largest of said plurality of measurements of semblance;
• and
• (3) an estimate of the true dip and an estimate of the true dip azimuth of the seismic traces within said analysis cell from the apparent dip and apparent dip azimuth corresponding to said largest measurement of semblance;
• and
• (d) displaying, over said at least one horizon slice, of representations of said largest measurements of semblance and said estimated true dips and said estimated true dip azimuths of each of said cells.

In the exploration for gas and oil wherein over a volume of the earth seismic traces are recorded, a method comprising the steps of:

• (a) grouping at least parts of at least five relatively close seismic traces into a plurality of relatively small three-dimensional analysis cells;
• (b) performing in each of said cells a plurality of measurements of the semblance of said parts of said traces as a function of at least time, the number traces therein, the apparent dip of said traces, and the apparent dip azimuth;
• (c) identifying in each of said cells the largest of said plurality of measurements of semblance, the corresponding apparent dip, and the corresponding dip azimuth;
• and
• (d) converting said largest measurements of semblance, said corresponding dip and said corresponding dip azimuth of said cells into color attributes of hue, saturation and lightness, wherein for each cell:
• one of said dip azimuth, said dip, and said largest measurements of semblance is mapped onto one of a lightness scale, hue scale, and a saturation scale;
• another of said dip azimuth, said dip, and said largest measurements of semblance is mapped onto another of said lightness scale, said hue scale, and said saturation scale;
• and
• the remaining one of said dip azimuth, said dip, and said largest measurements of semblance is mapped onto the remaining one of said lightness scale, said hue scale, and said saturation scale.

A device adapted for use by a workstation wherein 3D seismic data is read into memory and processed into a color display of subterranean features, comprising:

• computer readable means carrying instructions for a process comprising the steps of:
• (1) digitally locating said 3D seismic data in an array of relatively small three-dimensional cells, wherein each of said cells contains representations of a part of at least five seismic traces;
• (2) calculating for each of said cells an estimate of the semblance, an estimate of the true dip, and an estimate of the true dip azimuth of said parts;
• and
• (3) converting said estimates of semblance, said estimates of true dip, and said estimates of true dip azimuth into an array of digital values corresponding to the color attributes of hue, saturation, and lightness.

A method of prospecting for hydrocarbon deposits, comprising the steps of:

• (a) obtaining a color seismic attribute display of 3D seismic data for a predetermined three-dimensional volume of the earth, said display being generated by using data obtained by a computer and at least one program for said computer that instructs said computer to perform the following steps:
• (1) convert said volume into an array of relatively small three-dimensional cells, wherein each of said cells has a portion of at least five seismic traces located therein;
• (2) make a plurality of semblance measurements within each of said cells, wherein each measurement is at least a function of time, the number of seismic traces within said cell, the apparent dip of said traces and apparent dip azimuth of said traces;
• (3) select the largest of said plurality of measurements of semblance in each cell;
• (4) use as an estimate of the true dip and an estimate of the true dip azimuth in each cell the apparent dip and apparent dip azimuth that correspond to said largest measurement of semblance in said cell;
• (5) map said estimates of true dip azimuth onto a hue scale;
• (6) map said estimates of true dip onto a saturation scale;
• and
• (7) map said largest calculated measures of semblance onto a lightness scale;
• and
• (b) using said color display to identify subsurface structural and sedimentological features commonly associated with the entrapment and storage of hydrocarbons.