685results about "Seismic data acquisition" patented technology

There is provided herein a system and method of seismic data collection for land and marine data that utilizes narrowband to monochromatic low-frequency non-impulsive sources designed to optimize the ability of migration/inversion algorithms to image the subsurface of the Earth, in particular, full-waveform inversion.

A method for seismic surveying is disclosed which includes towing a first seismic energy source and at least one seismic sensor system. A second seismic energy source is towed at a selected distance from the first source. The first seismic energy source and the second seismic energy source are actuated in a plurality of firing sequences. Each of the firing sequences includes firing of the first source, waiting a selected time firing the second source and recording signals generated by the seismic sensor system. The selected time between firing the first source and the second source is varied between successive ones of the firing sequences. The firing times of the first and second source are indexed so as to enable separate identification of seismic events originating from the first source and seismic events originating from the second source in detected seismic signals.

This is a method of separating simultaneous sources that uses an inversion-type approach. Each source will preferably activated at a random time with respect to the others. These random delays tend to make the interference between sources incoherent while the reflections create coherent events within a series of shots. The shot separation is performed via a numerical inversion process that utilizes the sweeps for each shot, the start times of each shot, and the coherence of reflection events between nearby shots. This method will allow seismic surveys to be acquired faster and cheaper.

A method of seismic surveying comprising the steps of actuating the or each vibrator in a first vibrator group at time T0, and subsequently actuating the or each vibrator in a second vibrator group at time T1 that satisfies T0<T1<T0+S1+L where S1 is the sweep time of the first vibrator group and L is the listening time. At least one of the first vibrator group and the second vibrator group comprises at least two vibrators. The first group and the second group of vibrators may be the same group, or they may be different groups. This method enables the time required to complete a seismic survey to be reduced compared to the prior art “simultaneous shooting” and “slip-sweep shooting” techniques.

In a case where the first group and the second group of vibrators are different, the method may further comprise actuating the or each vibrator in the first vibrator group at time T2, where T1<T2<T1+S2+L and S2 is the sweep time of the first vibrator group, and then actuating the or each vibrator in the second vibrator group at time T3 where T2<T3<T2+S1+L and where T3−T2≠T1−T0. The varying time delay between a shot of the first vibrator group and the corresponding shot of the second vibrator group means that harmonic noise will occur at different times in the shot records so that the noise may be eliminated by appropriately combining the shot records.

A method for coding and decoding seismic data acquired, based on the concept of multishooting, is disclosed. In this concept, waves generated simultaneously from several locations at the surface of the earth, near the sea surface, at the sea floor, or inside a borehole propagate in the subsurface before being recorded at sensor locations as mixtures of various signals. The coding and decoding method for seismic data described here works with both instantaneous mixtures and convolutive mixtures. Furthermore, the mixtures can be underdetemined [i.e., the number of mixtures (K) is smaller than the number of seismic sources (I) associated with a multishot] or determined [i.e., the number of mixtures is equal to or greater than the number of sources). When mixtures are determined, we can reorganize our seismic data as zero-mean random variables and use the independent component analysis (ICA) or, alternatively, the principal component analysis (PCA) to decode. We can also alternatively take advantage of the sparsity of seismic data in our decoding process. When mixtures are underdetermined and the number of mixtures is at least two, we utilize higher-order statistics to overcome the underdeterminacy. Alternatively, we can use the constraint that seismic data are sparse to overcome the underdeterminacy. When mixtures are underdetermined and limited to single mixtures, we use a priori knowledge about seismic acquisition to computationally generate additional mixtures from the actual recorded mixtures. Then we organize our data as zero-mean random variables and use ICA or PCA to decode the data. The a priori knowledge includes source encoding, seismic acquisition geometries, and reference data collected for the purpose of aiding the decoding processing.

The coding and decoding processes described can be used to acquire and process real seismic data in the field or in laboratories, and to model and process synthetic data.

Seismic prospecting method and device using simultaneous emission of seismic signals obtained by coding a signal by pseudo-random sequences, and notably a periodic signal phase modulated by such sequences.Signals such as, for example, periodic signals phase modulated according to a pseudo-random code (binary for example), produced by a control unit, are for example emitted in the ground by means of vibrators, the seismic signals reflected by the subsoil discontinuities in response to the periodic signals emitted are picked up by receivers coupled with the formation and recorded in an acquisition and recording system. The periodic signals are emitted simultaneously by the vibrators. The control sequences of the coded periodic signals intended for all the vibrators are obtained either from the same random binary sequence with respective time lags evenly distributed over the length of the control sequence according to the number of vibrators used simultaneously (first mode), or from different sequences selected from among a group of sequences of minimum crosscorrelation (second mode), or by combining the two aforementioned modes. The respective contributions of the various vibrators are separated by correlating the signals received and recorded with signals constructed from the various control sequences obtained with time lags. The vibrators can be divided into several groups, the vibrators of each group being controlled by a binary sequence belonging to a minimum crosscorrelating group.Application: seismic prospecting or seismic monitoring of reservoirs for example.

A method for the simultaneous operation of multiple seismic vibrators using unique modified pseudorandom sweeps and recovery of the transmission path response from each vibrator is disclosed. The vibrator sweeps are derived from pseudorandom binary sequences modified to be weakly correlated over a time window of interest, spectrally shaped and amplitude level compressed. Cross-correlation with each pilot signal is used to perform an initial separation of the composite received signal data set. Recordings of the motion of each vibrator are also cross-correlated with each pilot, windowed, and transformed to form a source cross-spectral density matrix in the frequency domain useful for source signature removal and for additional crosstalk-suppression between the separated records. After source signature removal in the frequency domain an inverse transform is applied to produce an estimate of each source-to-receiver earth response in the time domain. The method has application to both land and marine geophysical exploration.

A transmission wave field imaging method, comprising the transmission of an incident wave field into an object, the incident wave field propagating into the object and, at least, partially scattering. Also includes the measuring of a wave field transmitted, at least in part, through an object to obtain a measured wave field, the measured wave field based, in part, on the incident wave field and the object. Additionally, the processing of the measured wave field utilizing a recursive reconstruction algorithm to generate an image data set representing at least one image of the object.

This is a method of separating simultaneous sources that uses an inversion-type approach. Each source will preferably activated at a random time with respect to the others. These random delays tend to make the interference between sources incoherent while the reflections create coherent events within a series of shots. The shot separation is performed via a numerical inversion process that utilizes the sweeps for each shot, the start times of each shot, and the coherence of reflection events between nearby shots. Implementation of this method will allow seismic surveys to be acquired faster and cheaper.

A data set can be corrected for the effects of interface waves by interferometrically measuring an interface wavefield between each of a plurality of planned locations within a survey area; and correcting survey data acquired in the survey area for the interface waves. The interface wavefield may be interferometrically measured by receiving a wavefield including interface waves propagating within a survey area, the survey area including a plurality of planned survey locations therein; generating interface wave data representative of the received interface wavefield; and constructing a Green's function between each of the planned survey positions from the interface wave data. Other aspects include an apparatus by which the interface wavefield may be interferometrically measured and a computer apparatus programmed to correct the seismic data using the interferometrically measured interface wave data.

There is provided a method of seismic acquisition that utilizes a bank of restricted-bandwidth swept-frequency sub-band sources as a seismic source. Each seismic source will cover a restricted sub-band of frequencies, with all the sources taken together covering the full frequency range. Adjacent frequency bands may partially overlap, but non-adjacent frequency bands should not. The sources may be divided into two or more groups, with no sources covering adjacent frequency bands being placed in the same group. The sources within a group can then be separated by bandpass filtering or by conventional simultaneous source-separation techniques. The source groups may be operated simultaneously but separated in space, and the individual sources themselves may each operate independently, on a sweep schedule customized for that particular source.

A system and method monitor a hydrocarbon reservoir for drainage in volumetric three dimensions. Monitoring between wells is imperative for optimum reservoir management and is achieved by mapping the hydrocarbon fluid pathways in a producing reservoir. Unlike conventional 4D or time-lapse reflection seismic imaging systems that use a controlled active seismic source and records reflected seismic energy at receivers, the system and method exploit the minute vibrations, or micro-earthquakes generated in the reservoir layers that are induced by fluid movement. These microseisms are detected as the fluids move in the reservoir.

A method for simultaneously operating multiple seismic vibrators using continuous sweeps (little or no “listening” time between sweeps) for each vibrator, and recovering the separated seismic responses for each vibrator with the earth signature removed. Each vibrator is given a unique, continuous pilot signal. The earth response to the motion of each vibrator is measured or estimated. The vibrator motion records for each vibrator and the combined seismic data record for all the vibrators are parsed into separate shorter records. The shorter records are then used to form a system of simultaneous linear equations in the Fourier transform domain, following the HFVS method of Sallas and Allen. The equations are then solved for the separated earth responses.

This invention discloses a valve that generates a hydraulic negative pressure pulse and a frequency modulator for the creation of a powerful, broadband swept impulse seismic signal at the drill bit during drilling operations. The signal can be received at monitoring points on the surface or underground locations using geophones. The time required for the seismic signal to travel from the source to the receiver directly and via reflections is used to calculate seismic velocity and other formation properties near the source and between the source and receiver. This information can be used for vertical seismic profiling of formations drilled, to check the location of the bit, or to detect the presence of abnormal pore pressure ahead of the bit. The hydraulic negative pressure pulse can also be used to enhance drilling and production of wells.

Apparatus and methods are provided for simultaneously retrieving data from multiple data acquisition units and for recharging such data acquisition units. The data offload and charging unit comprises a frame that defines stations for holding the data acquisition units and a host computer. A combined power and communications port at each such station is adapted to interface with one of the data acquisition units such that power may flow from the data offload and charger unit to that data acquisition unit and data may flow from that data acquisition unit to the host computer substantially simultaneously. Communications links are provided between the host computer and each combined power and communications port.

The transmission method utilizes multiple seismic acquisition units within an array as intermediate short range radio receivers/transmitters to pass collected seismic data in relay fashion back to a control station. Any one seismic unit in the array is capable of transmitting radio signals to several other seismic units positioned within radio range of the transmitting unit, thus allowing the system to select an optimal transmission path. Utilizing an array of seismic units permits transmission routes back to a control station to be varied as needed. In transmissions from the most remote seismic unit to the control station, each unit within a string receives seismic data from other units and transmits the received seismic data along with the receiving unit's locally stored seismic data. Preferably, as a transmission is passed along a chain, it is bounced between seismic units so as to be relayed by each unit in the array.

A method of acquiring seismic data adapted for a land or transition zone environment including placing a location identifier in a particular location, placing a seismic sensor near the location identifier, reading the location identifer using a seismic data cable, recording seismic data acquired by the seismic sensor using the seismic data cable, and assigning sensor position coordinates to the seismic data based on measured position coordinates of the location identifier. The invention also includes an apparatus adapted for seismic data acquisition in a land or transition zone environment including a location identifier, a seismic senor capable of being placed near the location identifier, a seismic data cable, means for reading the location identifier using the seismic data cable, means for recording seismic data acquired by the seismic sensor using the seismic data cable, and means for assigning sensor position coordinates to the seismic data based on measured position coordinates of the location identifier.

The invention discloses a way to recover separated seismograms with reduced interference noise by processing vibroseis data recorded (or computer simulated) with multiple vibrators shaking simultaneously or nearly simultaneously (200). A preliminary estimate of the separated seismograms is used to obtain improved seismograms (201). The preliminary estimate is convolved with the vibrator signature and then used to update the seismogram. Primary criteria for performing the update include fitting the field data and satisfying typical criteria of noise-free seismograms (202). Alternative ways to update are disclosed, including signal extraction, modeled noise extraction, constrained optimization based separation, and penalized least-squares based separation. The method is particularly suited for removing noise caused by separating the combined record into separate records for each vibrator, and is advantageous where the number of sweeps is fewer than the number of vibrators (200).