Abstract: A search is made down each trace of a seismic record at the approximate period of the multiple events to find a trace segment which most resembles a selected later segment of the same trace. An autocorrelation procedure is initially employed to determine the approximate period of the multiples and a crosscorrelation procedure is then employed to determine the time alignment of the two segments which produces maximum correspondence between the two segments. The degree of correspondence is determined by a "least-squares-fit" procedure. A portion of the earlier segment is subtracted from the later segment. The amount of the earlier segment to be subtracted is determined by the degree of correspondence. The procedure is incremented along the trace until the entire trace has been processed. Each trace is handled in the described manner until the entire record has been processed.

Abstract: A method of seismic exploration comprises transmitting waves from transmission sources into the medium to be explored and picking up signals in a receiver and recording these as traces, the signals being produced by reflection in the medium, the sequential transmission of the sources taking place at intervals less than the reflection time of the longest transmitted waves, the repeated transmission of any one source taking place at intervals at least equal to the said reflection time and therein being an intercorrelation function of a series of transmission instants of all the sources and a series of transmission instants of any one of the sources to give a relationship between the maximum peak amplitude and the secondary residue amplitude greater than a predetermined value and grouping the recorded traces corresponding to the same reflection point, adjusting the traces in relation to the associated source providing the information relating to the reflection point and adding together the adjusted traces relati

Abstract: The present invention indicates that gas-containing strata of an earth formation have low Poisson's ratios and that the acoustic contrast with the overburden rock has a surprising effect as a function of the angle of incidence on a seismic wave associated with an array of sources and detectors: viz., a significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence occurs. Thus, differentiating between high-intensity amplitude annomalies of nongas- and gas-containing media is simplified: progressive change in amplitude intensity of resulting traces generated by the field array as a function of offset between each source-detector pair, is associated with the last-mentioned medium only.

Abstract: The present invention indicates that gas-containing strata of an earth formation have low Poisson's ratios and that the acoustic contrast with the overburden rock has a surprising effect as a function of the angle of incidence on a seismic wave associated with an array of sources and detectors: viz., a significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence occurs. Thus, differentiating between high-intensity amplitude anomalies of nongas- and gas-containing media is simplified: progressive change in amplitude intensity of resulting traces generated by the field array as a function of offset between each source-detector pair, is associated with the last-mentioned medium only.

Abstract: A method for removing an undesired surface wave from a reflected wave in a method for seismic exploration is accomplished by placing first and second detector arrays at a location on the surface of the earth in the direction of movement of the surface wave. The array has a length less than the length of the shortest wave length of the interfering wave to be eliminated. Signals from both arrays are recorded and processed by first adding the received signals to form a first output, subtracting added signals to form a second output, shifting one of the output signals by 90.degree., adjusting its amplitude and subtracting the phase shifted and adjust signal from the remaining signal thereby removing the surface wave.

Abstract: A seismic prospecting roll along switch incorporating electronically controlled switches in an improved switch arrangement requiring far fewer switches than previous systems. In a simple form, one switch is provided for each geophone input with one contact of each switch connected to one of the inputs and the other contact of each switch connected in pairs, appropriately selected, to the inputs of amplifier and filter channels. A controller is provided for electronically closing the appropriate switches for each roll along position. In most roll along positions geophone inputs are connected out of order to the signal processing channels and the sequence is corrected by a modified multiplexer which connects the processing channels to a system analog to digital converter.

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: A seismic prospecting roll along switching system using a relatively small number of switches to provide roll along prospecting while also providing variable gapping with minimum loss of active channels. In a simple form two sets of switches are provided with each set having one switch provided for each geophone input and with switch outputs connected in pairs, appropriately selected, to the inputs of signal processing channels. The two sets of switches are connected to the processing channels in a skewed or staggered manner with the amount of skew corresponding to a selectable gap. A controller is provided for electronically closing the appropriate switches from each set in accordance with the desired gap. Additional switch sets may be employed to provide additional selectable gaps while maintaining complete utilization of processing channels.

Abstract: Disclosed is a seismic data gathering system for use in well drilling operations. A seismic pulse generator may be placed in the drill string near the drill bit and advanced in the well for generation of seismic pulses at any depth. An array of seismometers, rotationally symmetric about the well, may be arranged at the surface to detect both pulses refracted above the seismic pulse generator and pulses reflected at interfaces below the generator. According to the method of the invention, the refracted and reflected seismic pulse data may be reduced and analyzed to determine the drilling direction of the drill bit, the lithology through which the drill is passing, the position and approximate shape of nearby oil or gas reservoirs otherwise missed, and to look ahead of the drill bit to determine geologic conditions in advance of the drilling.

Abstract: This disclosure deals with measuring either discontinuous or continuous impedance transitions in various media to identify or delineate the properties and nature thereof by transmitting radiant energy waves to such media to produce reflected waves therefrom, deconvoluting the outgoing and returning waves, and integrating the resulting reflection impulse-response function so as to enable appropriate interpretation of the resulting display for identification and related purposes.

Abstract: Seismic signals from detectors forming split spreads are utilized to correct for weathering, elevation, and the like signals from detectors forming an expanded spread. The signals of the seismic section delineated by the expanded spread have applied thereto time changes under the control of a hyperbolic generator. There are generated as a result of the sweeping across the section and lengthwise thereof of the seismic signals the generation of functions utilized to provide normal moveout corrections of greater precision or accuracy than heretofore. With the normal moveout corrections of greater accuracy applied to the signals of the seismic section, additional corrections are made for dip and thereafter for delineation of the velocity characteristics of the earth along the stratigraphic column. There is included provision not only for identification of primary reflections and multiples but also for the elimination of multiples from the signals of the seismic section.