Abstract: Field seismograms are gathered into sets having reflections from asymmetrical common reflection points where there is a conversion between longitudinal waves and shear waves. The gathered seismograms are stacked to produce a seismic section which emphasizes the reflections from particular types of formations. In particular, reflections from formations having a significant difference in longitudinal to shear wave velocity, such as oil and gas saturated formations, are emphasized in the stacked section.

Abstract: A logging sonde has directivity control of multiple sources and receivers in linear arrays. Each of the sources produces acoustic pulses which are delayed by a time delay between the sources to direct acoustic energy at an angle such that the resulting acoustic wave strikes a vertical formation orthogonally. The reflections of the acoustic pulses are detected with a linear array of receivers. The acoustic pulse detected by each receiver is delayed by an amount such that the total differential moveout for a reflected directional wave is zero.

Abstract: In seismic exploration, an improved synthetic acoustic log is produced from seismograms by combining band limited reflectivity and velocity functions, both of which are obtained from the seismograms. The reflectivity function is obtained by deconvolving the field seismograms, transforming the reflectivity function so obtained into the frequency domain, and filtering the frequency domain representation to suppress frequencies below the seismic band. The velocity functions is obtained by applying a velocity spectra technique to the field seismograms to produce an acoustic log, transforming the acoustic log into the frequency domain, filtering to suppress all frequencies in the seismic pass band and converting back into the time domain.

Abstract: Pressure and velocity detectors produce outputs which are combined to substantially cancel ghost reflections. The pressure detector produces a positive output in response to upwardly travelling compressional waves and a negative output in response to downwardly travelling rarefaction waves. The velocity detector for this is a positive output in response to upwardly travelling compressional waves and a positive output in response to downwardly travelling rarefaction waves. These outputs are filtered so that the impulse response of the rarefaction waves cancels. The filtered outputs are combined to produce an output in which the ghost reflection is substantially suppressed.

Abstract: In seismic exploration a method for improving seismogram displays is disclosed wherein seismograms having an offset which produces poor signal power are muted and seismograms having offsets with high signal power are stacked. The signal power in a CDP set is determined as a function of different values of assumed acoustic velocity of the earth. This signal detection is repeated for successive values of travel time and offset. The maximum signal power is plotted for values of velocity as a function of travel time and for different ranges of offset to form contours of the maximum signal power as a function of time and offset.

Abstract: The present invention provides a method for determining the spacing and size of air guns in a tuned air gun array. Volume ratios are calculated based upon a predetermined maximum volume for any individual air gun. The volumes are cross-referenced to spacings for optimum air gun interaction. The resulting air gun array operates as a broadband high-energy point source.

Abstract: Multiple reflections are filtered from seismograms by transforming them into an f-k array representing amplitude as a function of frequency and wave number. The inverse of the f-k transform of the multiple reflections is generated. The f-k array of the seismograms is filtered by weighting all samples with the inverse of the f-k transform of the multiple reflections.

Abstract: This specification discloses a method of seismic exploration and in particular a method of generating and gathering field seismic data. Paths or seismic lines are traversed across the earth or water layers overlying the earth and over subsurface earth formations thereunder, and seismic energy is generated and transmitted into the earth and a portion thereof is reflected from the subsurface formations back toward the surface of the earth where the reflected seismic energy is detected and recorded. In conducting the seismic survey, a long linear array of seismic sources is simultaneously activated to produce a seismic pulse that is focused essentially vertically into the earth, and seismic energy is reflected from subsurface formations thereof and is detected by a long array of seismic detectors and is recorded.

Abstract: In marine seismic exploration, the distortion introduced by an anomalous surface layer is removed from seismograms. The surface layer travel time, obtained for example from fathometer readings, is converted to a model depth section of the anomalous surface layer. Another model depth section includes an assigned control layer without the anomaly. From these two depth sections, time corrections are obtained. These time corrections are applied to the seismograms at the time of reflection from each of the subsurface interfaces.

Abstract: The specification describes methods of and apparatus for converting seismic data to migrated seismic depth sections. The apparatus includes a curve follower for following lines of continuity on seismic time sections which represent reflections from particular subsurface interfaces. The curve follower generates signals representing occurrence times and horizontal distances at successive increments along the lines of continuity. These signals are applied to a digital computer which performs a migration operation and generates signals representing the attitude, actual depth and horizontal displacement of successive points on the interfaces. An automatic plotter plots reflection segments at the correct attitude, actual depth and horizontal displacement to produce the migrated seismic depth section.

Abstract: In seismic exploration, refracted seismic energy is detected by seismic receivers to produce seismograms of subsurface formations. The seismograms are produced by directing seismic energy from an array of sources at an angle to be refracted by the subsurface formations and detected by the receivers. The directivity of the array is obtained by delaying the seismic pulses produced by each source in the source array.

Abstract: Common depth point seismic signals from a plurality of seismic receivers are recorded on a field recorder. A first time shifter corrects the seismic signals for multiple normal moveout. A linear dip filter rejects unwanted multiple reflection signals. A second time shifter reverses the multiple normal moveout correction of the first time shifter. A third time shifter corrects the primary reflection signals for normal moveout. The primary reflection signal are then stacked and recorded as a composite common depth point seismic signal.

Abstract: In common depth point seismic exploration, seismic traces are corrected for normal moveout and stacked to form a composite trace. The composite trace is successively time shifted to provide a plurality of reference traces characterized by the normal moveout of the seismic traces. The reference traces are crosscorrelated with the seismic traces, and the resulting correlation functions are utilized to enhance the primary reflection signals of the seismic traces.

Abstract: In common depth point (CDP) seismic exploration, a pilot trace is produced from the stacked trace for each CDP set of traces. The pilot trace is crosscorrelated with each trace of the CDP set during selected time windows. The crosscorrelation time shifts are applied to each trace of the CDP set. The time shifted traces of each CDP set are stacked to form a static corrected seismic record section.

Abstract: In marine seismic exploration, seismograms recording reflected energy generated from the firing of a seismic source are used to measure the characteristics of the medium through which the energy passes. These measurements are converted into control parameters for an array of seismic sources. When the array is fired under control of these parameters, seismograms having enhanced reflections are produced. As an example, at least one seismic source is fired to produce seismograms which are used in the measurement of water bottom reflectivity and water depth. The measured reflectivity and water depth are converted into a time domain operator representative of the inverse of the reverberation distortion in the water layer. An array of sources is then fired in a sequence which produces an acoustic pressure wave having the inverse time domain characteristics.

Abstract: In seismic exploration, reflected seismic energy is detected by hydrophones to produce seismograms to emphasize a dipping formation which is of interest. The seismograms are produced by directing seismic energy from an array of sources at an angle such that it will reflect vertically from the dipping formation and intersect the hydrophones orthogonally. Directivity of the array is obtained by delaying the seismic pulses produced by each source.

Abstract: In marine seismic exploration, a long array of sources efficiently transfers energy along the reflection path. Multiple reflection rejection is achieved by normal move-out discrimination at selected trace distances for each reflection. The length of the source array is changed in accordance with the geological characteristics of the sub-surface formations being explored and the reflection time of reflections from formations of interest. A split source array allows one section of the array to be moved with respect to the other to change the overall length of the array without changing the number of sources which are fired. Primary to multiple reflection enhancement is obtained by selecting only traces having source to detector offset distances with a primary to multiple amplitude response ratio greater than one.

Abstract: A detector spread for marine seismic exploration has arrays with lengths which are dependent upon the acoustic velocity and dip of the subsurface formations being explored, upon the offset distance from the seismic source to the array and upon the reflection time of reflections from formations of interest. Hydrophones are positioned at approximately equally spaced intervals on a towing cable. The outputs of these hydrophones are combined to form arrays having lengths which are multiples of the intervals. Each array has the longest length possible, such that reflection amplitude response will remain in the band 0 .ltoreq. .DELTA.T/.tau. .ltoreq. 1.

Abstract: A system for marine seismic exploration has arrays of sources and receivers which discriminate against horizontal traveling source-generated noise. Directive arrays of sources or receivers have a length which is longer than the wavelength of the lowest frequency of the seismic pulse. The spacing between the elements in the array is less than the wavelength of the highest characteristic frequency in the seismic pulse.