Seismic method and system of improved resolution and discrimination

A method for processing seismic data, comprising the steps of:

• collecting the time-varying seismic detector output signals from a plurality of seismic sensors positioned in a cable;
• selecting a series of signal values from each sensor at fixed time intervals apart during a predetermined time window;
• storing the series in a two dimensional matrix memory, one dimension representing the sensor position and the other dimension representing the time intervals;
• calculating the desired relative time delay relationship among the sensors that are selected to form a desired array to substantially eliminate moveout between the sensors of that array;
• determining the time-dimension address for each said selected sensor that corresponds to the relative desired time delay relationship;
• forming the array by selecting the output signal value for each sensor according to the determined time-dimension address, and;
• summing the selected output signal values to form a composite signal so that the composite signal has the signal to noise ratio benefits of an array of sensors and the high frequency response of a single sensor.

An improved method for producing seismic records of the type in which the outputs from a plurality of sensors are selected in groups to form group array signals, wherein the improvement comprises the steps of:

• (a) receiving and storing the instantaneous values of the outputs from each sensor in a group at fixed time intervals;
• (b) calculating a desired amount of time displacement for each sensor in the group relative to the other sensors in that group as a function of reflection time and sensor position;
• (c) determining the multiple of the time interval most closely corresponding to each time interval most closely corresponding to each said time displacement for each sensor;
• (d) selecting the sensor outputs stored at the determined time-interval multiples;
• (e) summing the selected outputs to form the group array signals;
• (f) recording said outputs on an archival storage medium;
• (g) utilizing said group array signals to produce displays of seismic data depicting the characteristics of subsurface geologic formations.

An improved seismic exploration system of the type having an elongate seismic cable including a plurality of seismic sensors at intervals therealong for receiving reflected seismic signals, wherein the improvement comprises:

• (a) means for selecting a subset of the sensors from which a group signal is to be formed;
• (b) means for establishing a time window having a predetermined width;
• (c) matrix storage means for receiving signals from the subset during the time window;
• (d) means for storing the signals in a first dimension of the matrix as a function of sensor location and in a second dimension as a function of time;
• (e) means for extracting signals from the matrix storage associated with different sensor locations and displaced in time with respect to each other by delays selected to substantially eliminate the effects of moveout between the sensors within the subset;
• and
• (f) means for combining the extracted signals to form the group signal.

An improved seismic exploration system of the type having an elongate seismic cable including a plurality of sensors therealong for receiving reflected seismic signals, wherein the improvement comprises:

• (a) means for selecting a subset of sensors from which a group signal is to be formed;
• (b) means for determining the relative time delays required between the signals of the sensor in the subset as a function of reflection time to substantially eliminate the effects of moveout therebetween;
• and
• (c) means for combining the signals in accordance with the determined delays to form a seismic trace.

A method for processing seismic data to provide the improved signal-to-noise ratio characteristics of an elongated array whilst retaining the high frequency resolution of a single sensor, including collecting time-distributed seismic signals, sampled at fixed sample intervals, generated by a plurality of spatially-distributed seismic sensors in response to impinging seismic waves, comprising the steps of:

• (a) ordering the signal samples, collected during a time window having a predetermined width, into a desired format in accordance with the spatial distribution of the seismic sensors and the time distribution of the sampled seismic signals;
• (b) designating subpluralities of seismic sensors as members of desired seismic sensor arrays;
• (c) determining, as an integral multiple of said sample interval, a time correction for time misalignments of the generated signals due to travel-path angularity of said seismic waves impinging upon the respective designated sensors of each said array;
• (d) for each seismic sensor designated as a member of an array, identified according to its spatial distribution, selecting a seismic signal sample according to its time distribution as determined by said time correction;
• and
• (e) for each said array, combining said selected signal samples to form composite array signals.

A method for producing improved recordings of seismic signals collected from a plurality of spatially-distributed seismic sensors that are selectably subdivided into sensor groups, each of which includes a desired number of members, the method comprising the steps of:

• (a) sampling the seismic signals collected from said seismic sensors at fixed sample intervals during a time frame having a fixed length equal to a predetermined multiple of said sample interval;
• (b) storing said samples as a function of the spatial distribution of said seismic sensors and the sample-interval multiple of each said sample;
• (c) calculating the differential time displacements for each member of the selected sensor groups relative to the other members of those groups as a function of reflection travel time, the spatial distribution of the sensors, and an arbitrary velocity function;
• (d) determining the multiple of the sample interval that most closely approximates the calculated time displacements;
• (e) for each selected sensor group, extracting the samples stored at the determined sample-interval multiples corresponding to the members of each group;
• (f) combining the extracted samples from the members of each sensor group to form a group signal;
• (g) recording said group signals as a visual seismogram;
• and
• (h) substantially concurrently, archivally recording the seismic signal samples collected from said plurality of seismic sensors.