1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods for processing repeated seismic data acquired using the same seismic survey setup and, more particularly, to mechanisms and techniques for separating seismic waves having different behaviors over the time-lapse domain also called calendar time domain referring to repeated seismic acquisition. To separate waves in this particular domain, the convolution between a constant propagation operator (constant over the calendar time, yet unknown) and a time-lapse variable estimated wave is subtracted from the repeated seismic data. The constant propagation operator that is obtained by solving an inverse problem using the repeated seismic data.
2. Discussion of the Background
A widely-used technique for monitoring oil or gas reservoirs is the seismic imaging of subsurface geophysical structures. The term “seismic imaging” refers to acquiring and analyzing data related to reflected seismic waves after generating seismic waves toward the subsurface structure. The time-lapse wave separation is well suited for processing continuous 4D seismic (repeated seismic) data.
As illustrated in
For example, as illustrated in
The sensor 20 is unable to distinguish between waves as differently marked in
In order to monitor an oil and/or gas reservoir evolution during production, seismic measurements are repeated at time intervals that are large relative to the duration of the seismic measurement. Conventionally, seismic measurements are repeated each year or decade. However, to monitor a reservoir during production, a “continuous” 4D data acquisition means that seismic measurements are performed 4 to 6 times a day, allowing an oil and gas company to make rapid decisions and adjust the production plan.
The data acquired during different measurements is gathered in 4D data sets, the four dimensions being (1) amplitude versus (2) time while data is acquired, (3) distance between the source and the sensor, and then, (4) time as to when the measurement was performed. These 4D data sets are known as repeated seismic data. A subset of repeated seismic data is illustrated in
Accordingly, it would be desirable to provide reliable methods (and devices performing these methods), to accurately extract the target wave (i.e., reflected by the monitored reservoir) from the detected signal that also includes unwanted waves, in order to be able to monitor the target based on repeated seismic data.
According to one exemplary embodiment, there is a method for processing seismic data acquired with the same seismic survey setup over long periods of time. The method includes acquiring sets of seismic data using the same seismic survey setup over multiple days, the sets being gathered as repeated seismic data. The method further includes estimating a time-variable wavelet corresponding to unwanted waves, and determining a propagation of the time-variable wavelet, which propagation is assumed to be constant in time, by solving an inverse problem using the repeated seismic data and the estimated time-variable wavelet. The method also includes extracting signal data by subtracting a convolution of the estimated time-variable wavelet and the propagation from the repeated seismic data.
According to another exemplary embodiment, there is a computer-readable storage medium non-transitory storing executable codes which, when executed on a computer, make the computer process repeated seismic data gathered from sets of seismic data acquired using the same seismic survey setup over multiple days. The method includes estimating a time-variable wavelet corresponding to unwanted waves, and determining a propagation of the time-variable wavelet, which propagation is assumed to be constant in time, by solving an inverse problem using the repeated seismic data and the estimated time-variable wavelet. The method further includes extracting signal data by subtracting a convolution of the estimated time-variable wavelet and the propagation from the repeated seismic data.
According to another embodiment there is a seismic data processing device including an interface configured to receive repeated seismic data gathered using the same seismic survey setup over multiple days, and a data processing unit connected to the interface. The data processing unit is configured to process the repeated seismic data by (1) estimating a time-variable wavelet corresponding to unwanted waves, (2) determining a propagation that is constant in time by solving an inverse problem using the gathered repeated seismic data and the estimated time variable wavelet, and (3) extracting signal data by subtracting a convolution of the estimated time-variable wavelet and the propagation from the repeated seismic data.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:
The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of data processing for seismic survey data. However, the embodiments to be discussed next are not limited to this type of data being useable for 4D data acquired using other methods or for processing similar type of data acquired in similar circumstances.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
In order to monitor the evolution of a reservoir (i.e., the target), signal data representing seismic waves reflected from the target need to be extracted from the recorded seismic data.
Thus, in an exemplary embodiment illustrated in
The seismic survey setup may include one or more sources and plural sensors buried below a weathering layer of a surveyed formation. The seismic survey setup may be placed above an oil reservoir, and the data is then used to monitor the evolution of the reservoir.
Further, the method 600 includes estimating a time-variable wavelet corresponding to unwanted waves, at S620. The unwanted waves include noise and other wave reflections due to reflection at other locations than the subsurface. These unwanted waves may be represented as a convolution of a wavelet and a propagation operator none of which is known. Both the wavelet and the propagation operator may be variable in time. However, one can use a reasonable assumption that the wavelet varies in time while the propagator is constant in time.
The time-variable wavelet may be estimated by identifying unwanted waves that do not interfere with the target waves. For example, in
However, in another example discussed below, the time-variable wavelet may be estimated using seismic data detected in another sensor receiving substantially the same unwanted waves as the first sensor, but (due to its location) the unwanted waves detected by the other sensor do not interfere with the target waves.
The method 600 also includes determining a propagation of the time-variable wavelet, at S630. This propagation is assumed to be constant over the calendar time (i.e., over all the measurements), and is determined by solving an inverse problem using the repeated seismic data and the estimated time-variable wavelet. For example, if rsr is the repeated seismic data of m measurements, each measurement having n samples as illustrated in
Finally, the method 600 includes extracting signal data (i.e., corresponding to waves reflected by the target) by subtracting a convolution of the estimated time-variable wavelet and the propagation from the repeated seismic data, at S640. For example, following the notation described above and tr being the signal data in time domain, while TR being the Fourier transform of tr, TR=RSR−(PUW·X). The inverse Fourier transform of PUW·X is illustrated in
Steps S630 and S640 may be performed in frequency domain or in time domain as illustrated relative to another embodiment in
The signal data is then extracted by subtracting a convolution of the estimated time-variable wavelet and the propagation from the repeated seismic data, is illustrated in
By comparing
Method 600 and other similar embodiments may be performed by a seismic data processing device 1600 as illustrated in
The data processing unit 1620 may further be configured to estimate the time-variable wavelet by selecting a subset of the seismic data corresponding to a propagation time range for the multiple days.
The data processing unit 1620 may be configured to determine the propagation by (A) applying a Fourier transformation to the estimated wavelet to obtain a Fourier transform of the estimated wavelet, (B) calculating an inverse matrix of a product of a transposed of the Fourier transform of the estimated wavelet and the Fourier transform of the estimated wavelet, (C) applying a Fourier transformation to the repeated seismic records to obtain a Fourier transform of the repeated seismic records, (D) calculating a product of the transposed of the Fourier transform of the estimated wavelet and the Fourier transform of the repeated seismic records, and (E) determining a Fourier transform of the propagation as a convolution of the inverse matrix and the product.
The seismic data processing device 1600 may also includes a memory 1630 configured to non-transitory storing executable codes which when executed on the data processing unit 1620, and the interface 1610 makes the seismic data processing device 1600 process repeated seismic data gathered from sets of seismic data acquired using the same seismic survey setup over multiple days, according to a method including: (i) estimating a time-variable wavelet corresponding to unwanted waves, (ii) determining a propagation of the time-variable wavelet, which propagation is assumed to be constant in time, by solving an inverse problem in a frequency domain using the repeated seismic data and the estimated time-variable wavelet, and (iii) extracting signal data by subtracting a convolution of the estimated time-variable wavelet and a Fourier transform of the propagation from the repeated seismic data.
The step of estimating the time-variable wavelet (i.e., step i above) may include selecting a subset of the repeated seismic data corresponding to a propagation time range for the multiple days.
The step of determining the propagation (step ii above) may include (A) applying a Fourier transformation to the estimated time-variable wavelet to obtain a Fourier transform of the estimated time-variable wavelet, (B) calculating an inverse matrix of a product of a transposed of the Fourier transform of the estimated time-variable wavelet and the Fourier transform of the estimated time-variable wavelet, (C) applying a Fourier transformation to the repeated seismic records to obtain a Fourier transform of the repeated seismic records, (D) calculating a product of the transposed of the Fourier transform of the estimated wavelet and the Fourier transform of the repeated seismic records, and (E) determining a Fourier transform of the propagation as a convolution of the inverse matrix and the product.
The signal wave may include target waves due to a monitored underground reservoir, and the unwanted waves may include noise and other wave reflections due to reflection sources other than the monitored underground reservoir.
The memory 1630 may be configured to store the repeated seismic data.
The seismic data processing device 1600 may also include a display 1640 configured to display images of an underground formation generated by the data processing unit 1620 using the signal data.
Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. The methods or flowcharts provided in the present application may be implemented in a computer program, software or firmware tangibly embodied in a computer-readable storage medium for execution by a specifically programmed computer or processor.
The disclosed exemplary embodiments provide methods and devices for processing seismic data gathered during multiple days. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.
Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.
This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.
This application claims priority and benefit from U.S. Provisional Application No. 61/617,918, filed on Mar. 30, 2012, for “Time-Lapse Wave Separation,” the entire content of which is incorporated herein by reference.
Number | Date | Country | |
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61617918 | Mar 2012 | US |