阅读说明：本技术 用于近地表品质因子q值反演的衰减曲线层析剥离方法 (Attenuation curve chromatographic stripping method for near-surface quality factor Q value inversion ) 是由 郑浩 蔡杰雄 郭恺 于 2018-08-08 设计创作，主要内容包括：本发明提供了一种用于近地表品质因子Q值反演的衰减曲线层析剥离方法,包括：通过微测井观测系统的检波器采集经由不同激发深度处的多个炮激发而产生的地震信号,形成共检波点道集；拾取共检波点道集中的地震信号到达检波器的初至时间,并且由此建立近地表速度模型；基于近地表速度模型,选取共检波点道集中的未受到噪声干扰的地震信号；对所选取的地震信号进行频谱分析,以获得包含近地表结构中的多个层的品质因子Q值的等效衰减曲线；基于所选取的地震信号的传播旅行时间,利用多炮组合消元方法,对等效衰减曲线进行层析剥离,以分别得到近地表结构中每层的衰减曲线。(The invention provides an attenuation curve chromatographic stripping method for near-surface quality factor Q value inversion, which comprises the following steps: collecting seismic signals generated by excitation of a plurality of guns at different excitation depths through a detector of a micro-logging observation system to form a common detection point gather; picking up the first arrival time of the seismic signals in the common survey point channel set to reach the detector, and establishing a near-surface velocity model according to the first arrival time; selecting seismic signals which are not interfered by noise in a common detection point channel set based on a near-surface velocity model; performing spectral analysis on the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values of a plurality of layers in the near-surface structure; and carrying out chromatographic stripping on the equivalent attenuation curve by utilizing a multi-gun combination elimination method based on the propagation travel time of the selected seismic signal so as to respectively obtain the attenuation curve of each layer in the near-surface structure.)

1. An attenuation curve chromatographic stripping method for near-surface quality factor Q value inversion comprises the following steps:

establishing a near-surface velocity model based on micro-logging data;

selecting seismic signals which are not interfered by noise in a common detection point channel set based on a near-surface velocity model;

performing spectral analysis on the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values of a plurality of layers in the near-surface structure; and

and carrying out chromatographic stripping on the equivalent attenuation curve by utilizing a multi-gun combination elimination method based on the propagation travel time of the selected seismic signal so as to respectively obtain the attenuation curve of each layer in the near-surface structure.

2. The method of claim 1, further comprising:

and estimating the Q value of the quality factor of each layer in the near-surface structure by using a spectral ratio method.

3. The method of claim 2, wherein building a near-surface velocity model based on the micro-log data comprises:

collecting seismic signals generated by excitation of a plurality of guns at different excitation depths through a detector of a micro-logging observation system to form a common detection point gather; and

the first arrival time of the seismic signals in the common survey point trace set arriving at the geophone is picked up, and a near-surface velocity model is built accordingly.

4. The method of claim 3, wherein establishing a near-surface velocity model further comprises: and acquiring the number of horizons, the thickness and the speed of each layer of the near-surface structure, so as to calculate the propagation travel time of the seismic signals in each layer by using a ray tracing method.

5. The method of claim 4, wherein selecting the seismic signals in the common gather of geophone traces that are not disturbed by noise comprises:

and selecting three seismic signals which are not interfered by noise in the common survey point channel set.

6. The method of claim 5, wherein performing spectral analysis on the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values for a plurality of layers in the near-surface structure comprises:

obtaining an equivalent attenuation curve containing Q values of quality factors of two layers in the near-surface structure by using the two selected seismic signals:

wherein the upper line represents the logarithmic value of each variable, i.e.

wherein k represents the kth layer, g_ijRepresenting a constant term independent of frequency, t_ijkAnd representing the propagation travel time of the seismic signal excited by the ith gun and received by the jth trace detector on the kth layer, wherein j is 1.

7. The method of claim 6, further comprising:

selecting two seismic signals, and calculating a reference attenuation curve:

8. the method of claim 7, wherein chromatographically stripping the equivalent attenuation curves using a multi-shot combination apogee method based on the travel time of the selected seismic signals to obtain an attenuation curve for each layer of the near-surface structure, respectively, comprises:

establishing an equation set by combining the reference attenuation curve and the formula of the equivalent attenuation curve:

and by solving the system of equations, an attenuation curve is obtained that contains only one layer of quality factor Q:

wherein

9. The method of claim 8, wherein estimating the quality factor Q for each layer in the near-surface structure using a spectral ratio method comprises:

by respectively pairing R₁(f) And R₂(f) Linear fitting to obtain its slope p₁＝-πQ₁ ^-1Δt₁And p₂＝-πQ₂ ^-1Δt₂The quality factor Q of each layer can be obtained by inversion₁、Q₂：

10. A storage medium having stored therein a computer-executable program, which when executed, is adapted to implement an attenuation curve tomographic stripping method for near-surface quality factor Q-value inversion, the method comprising:

establishing a near-surface velocity model based on micro-logging data;

selecting seismic signals which are not interfered by noise in a common detection point channel set based on a near-surface velocity model;

performing spectral analysis on the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values of a plurality of layers in the near-surface structure; and

and carrying out chromatographic stripping on the equivalent attenuation curve by utilizing a multi-gun combination elimination method based on the propagation travel time of the selected seismic signal so as to respectively obtain the attenuation curve of each layer in the near-surface structure.

Technical Field

The invention relates to the technical field of geophysical exploration, in particular to an attenuation curve chromatographic stripping method for near-surface quality factor Q value inversion, which can be applied to seismic data absorption attenuation inversion and compensation stages in petroleum geophysical exploration.

Background

The earth medium is not an elastic medium but a viscoelastic medium with an absorptive damping effect. The seismic waves are propagated in the optical fiber, absorption attenuation is inevitable, the resolution ratio of seismic data is reduced, and the final imaging result has large errors on the thin interbed and micro-structure drawing. Therefore, how to accurately calculate the absorption attenuation of the seismic waves in the propagation process and realize frequency and energy compensation are the key of the current high-resolution seismic exploration.

Generally, absorption attenuation is quantitatively characterized by a quality factor Q. With the continuous development of technology, there are several dozen methods, including a time domain method, a frequency domain method and a time-frequency domain method. The spectral ratio method is simple in calculation, convenient to operate, and directly derived from a wave equation, and high in precision, so that the spectral ratio method is widely applied to the industry at present. According to the method, effective signals of signals at different moments are extracted, the signals are converted into a frequency domain by means of Fourier transform, then an attenuation curve (log-spectral ratio curve) is obtained according to the change of an amplitude spectrum, and then the slope of the attenuation curve is used for inverting a quality factor Q value. The method has a good effect when a large set of stable wave groups are obtained, but because the layer-by-layer separation of the attenuation curve is difficult to realize, the obtained Q value model is often a macroscopic low wave number result. The influence of the model on the middle-deep layer data is small, and the absorption attenuation of the middle-deep layer is small along with the enhancement of the stratum compaction degree; however, for shallow layers, particularly low-velocity zone strong absorption attenuation areas, the requirement of high-resolution seismic exploration on the accuracy of a quality factor Q value model is obviously not met.

At present, for modeling the quality factor Q value of a shallow layer, because the shallow signal-to-noise ratio of conventional seismic data is low, and the dynamic correction stretching and cutting off enables that the region has almost no available effective signal for modeling the quality factor Q value of the near-surface, the modeling of the quality factor Q value of the near-surface region is often carried out by adopting micro logging information. The method comprises the steps of establishing a near-surface velocity model through first arrival picking of micro-logging information, then carrying out horizon constraint on a near-surface quality factor Q value according to an interpretation result, designing a proper mathematical algorithm by utilizing the advantage of more excited cannons in the micro-logging information, realizing layer-by-layer separation of attenuation curves, further carrying out quality factor Q value inversion on the attenuation curves of each layer, and achieving the purpose of modeling the near-surface high-precision quality factor Q value, wherein the key is how to strip the attenuation curves layer-by-layer.

Disclosure of Invention

Aiming at the problems that the Q value modeling precision of the near-surface structure quality factor is low and the high-resolution seismic exploration requirement is not met, the method is based on micro-logging information, a near-surface velocity model is established through first arrival picking, the model comprises the number of strata and the velocity of each layer, the number of strata and the velocity of each layer are used for horizon constraint of near-surface attenuation curve stripping, seismic signals generated by different shot excitation are concentrated through selecting common detection wave point channels, the attenuation curves of each layer are calculated through a multi-shot combined elimination algorithm, the Q value of the quality factor of each layer can be obtained through combining a spectral ratio method, the purpose of near-surface high-precision quality factor Q value modeling is achieved, and therefore the attenuation curve chromatography stripping algorithm for near-surface absorption attenuation parameter inversion is achieved.

According to an aspect of the invention, there is provided an attenuation curve chromatographic stripping method for near-surface quality factor Q value inversion, comprising:

establishing a near-surface velocity model based on micro-logging data;

selecting seismic signals which are not interfered by noise in a common detection point channel set based on a near-surface velocity model;

performing spectral analysis on the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values of a plurality of layers in the near-surface structure; and

and carrying out chromatographic stripping on the equivalent attenuation curve by utilizing a multi-gun combination elimination method based on the propagation travel time of the selected seismic signal so as to respectively obtain the attenuation curve of each layer in the near-surface structure.

According to an embodiment, the method further comprises:

and estimating the Q value of the quality factor of each layer in the near-surface structure by using a spectral ratio method.

According to an embodiment, wherein building a near-surface velocity model based on the micro-log data comprises:

collecting seismic signals generated by excitation of a plurality of guns at different excitation depths through a detector of a micro-logging observation system to form a common detection point gather; and

the first arrival time of the seismic signals in the common survey point trace set arriving at the geophone is picked up, and a near-surface velocity model is built accordingly.

According to an embodiment, wherein building the near-surface velocity model comprises: and acquiring the number of horizons, the thickness and the speed of each layer of the near-surface structure, so as to calculate the propagation travel time of the seismic signals in each layer by using a ray tracing method.

According to an embodiment, wherein selecting seismic signals in the common geophone gather that are not disturbed by noise comprises:

and selecting three seismic signals which are not interfered by noise in the common survey point channel set.

According to an embodiment, wherein the spectral analysis of the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values for a plurality of layers in the near-surface structure comprises:

obtaining an equivalent attenuation curve comprising quality factor Q values of two layers in the near-surface structure by using the two selected seismic signals:

wherein the upper line represents the logarithmic value of each variable, i.e.Denotes x_i1(f) Is 2,3, m, m represents the number of excitation points in the micro-logging observation system, f represents the frequency, a represents the frequency₁Represents a constant independent of frequency, wherein the amplitude spectrum of the seismic signal received by the ith shot excitation and the jth receiver can be expressed as:

wherein k represents the kth layer, g_ijRepresenting a constant term independent of frequency, t_ijkAnd the propagation travel time of the seismic signal excited by the ith shot and received by the jth channel detector on the kth layer is shown, wherein j is 1.

In a preferred embodiment, only one reception point may be set, so in the above formula j ═ 1, i.e.:

according to an embodiment, the method further comprises:

selecting two seismic signals, and calculating a reference attenuation curve:

according to an embodiment, wherein the tomographic stripping of the equivalent attenuation curve to obtain the attenuation curve of each layer in the near-surface structure respectively by using a multi-shot combined elimination method based on the propagation travel time of the selected seismic signal comprises:

establishing a system of equations by combining equations representing the reference attenuation curve and the equivalent attenuation curve:

and by solving the system of equations, an attenuation curve is obtained that contains only one layer of quality factor Q:

wherein

R₁(f) And R₂(f) Respectively representing attenuation curves which, after solution, contain only one layer of quality factor Q value, c₁And c₂Two frequency independent terms are represented, i is 2, 3.

According to an embodiment, wherein the estimating the quality factor Q value for each layer in the near-surface structure using a spectral ratio method comprises:

by respectively pairing R₁(f) And R₂(f) Linear fitting to obtain its slope p₁＝-πQ₁ ^-1Δt₁And p₂＝-πQ₂ ^-1Δt₂And inverting to obtain the quality factor Q1, Q2:

according to another aspect of the present invention, there is also provided a storage medium having stored therein a computer-executable program which, when executed, is adapted to implement an attenuation curve tomographic stripping method for near-surface quality factor Q-value inversion, the method comprising:

establishing a near-surface velocity model based on micro-logging data;

selecting seismic signals which are not interfered by noise in a common detection point channel set based on a near-surface velocity model;

performing spectral analysis on the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values of a plurality of layers in the near-surface structure; and

and carrying out chromatographic stripping on the equivalent attenuation curve by utilizing a multi-gun combination elimination method based on the propagation travel time of the selected seismic signal so as to respectively obtain the attenuation curve of each layer in the near-surface structure.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 illustrates a single well micro-logging observation system used in embodiments of the present invention;

FIG. 2 illustrates a common-probe gather received by a 5m offset detector in a microlog observation system used in an embodiment of the present invention, where the abscissa represents depth of excitation (m) and the ordinate represents time (ms);

FIG. 3 illustrates a near-surface velocity model derived from a first-arrival time interpretation of seismic signals using the common-geophone gather shown in FIG. 2, wherein the ordinate represents depth (m) and the abscissa represents time (ms) and velocity (m/s);

FIG. 4 shows three seismic signal direct arrivals extracted from the common geophone gather shown in FIG. 2 at different depths, with excitation depths of 150m, 130m, and 106m, respectively, where the abscissa represents the excitation depth (m) and the ordinate represents time (ms);

FIG. 5 shows the corresponding amplitude spectra of the three direct wave signals of FIG. 4, where the abscissa represents frequency (Hz) and the ordinate represents amplitude;

FIG. 6 shows the attenuation curves of each layer of the low and reduced velocity bands calculated by the multi-shot combined elimination algorithm of the present invention, wherein the abscissa represents frequency (Hz) and the ordinate represents the attenuation;

fig. 7 shows a graph comparing an attenuation curve forward-simulated by the calculation result of the quality factor Q value of the attenuation curve after peeling off with a real attenuation curve, in which the abscissa represents frequency (Hz) and the ordinate represents attenuation amount.

Detailed Description

The following detailed description of the embodiments of the present invention will be provided with reference to the drawings and examples, so that how to apply the technical means to solve the technical problems and achieve the technical effects can be fully understood and implemented. It should be noted that, as long as there is no conflict, the embodiments and the features of the embodiments of the present invention may be combined with each other, and the technical solutions formed are within the scope of the present invention.

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details or with a specific implementation described herein.

As mentioned above, aiming at the problems that the modeling precision of the quality factor Q value of the near-surface structure is low and the high-resolution seismic exploration requirement is not met, the invention establishes a near-surface velocity model including the number of strata and the velocity of each stratum through first arrival picking based on micro-logging data, then uses the model for the horizon constraint of near-surface attenuation curve stripping, selects seismic signals generated by different shot excitation in a common detection wave point channel set, calculates the attenuation curve of each stratum through a multi-shot combined elimination algorithm, and then combines a spectral ratio method to obtain the quality factor Q value of each stratum so as to realize the purpose of modeling of the near-surface high-precision quality factor Q value, thereby realizing the attenuation curve chromatographic stripping algorithm for the inversion of near-surface absorption attenuation parameters.

Specifically, the invention provides an attenuation curve chromatographic stripping method for near-surface quality factor Q value inversion, which comprises the following steps:

establishing a near-surface velocity model based on micro-logging data;

selecting seismic signals which are not interfered by noise in a common detection point channel set based on a near-surface velocity model;

performing spectral analysis on the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values of a plurality of layers in the near-surface structure; and

and carrying out chromatographic stripping on the equivalent attenuation curve by utilizing a multi-gun combination elimination method based on the propagation travel time of the selected seismic signal so as to respectively obtain the attenuation curve of each layer in the near-surface structure.

Wherein, based on the micro-logging data, establishing a near-surface velocity model, comprising:

collecting seismic signals generated by excitation of a plurality of guns at different excitation depths through a detector of a micro-logging observation system to form a common detection point gather; and

the first arrival time of the seismic signals in the common survey point trace set arriving at the geophone is picked up, and a near-surface velocity model is built accordingly.

Specifically, the process of establishing a near-surface velocity model based on micro-logging data is described below with reference to fig. 1 to 3.

FIG. 1 illustrates a single well micro-logging observation system used in embodiments of the present invention. As shown in figure 1, the single-well micro-logging observation system is used for collecting data, the minimum excitation depth is 1m, the maximum excitation depth is 150m, and the constant explosive quantity is adopted for continuous excitation from deep to shallow, wherein one cannon is excited at each interval of 4m in the depth range of 30-150m, one cannon is excited at each interval of 2m in the depth range of 10-30m, one cannon is excited at each interval of 1m in the depth range of 1-10m, and 50 cannons are excited together.

FIG. 2 illustrates a common-probe gather received by a 5m offset receiver in a microlog observation system used in an embodiment of the present invention. As shown in FIG. 2, a common detector gather of 5m offset is acquired using the microlog observation system of FIG. 1, where the abscissa represents the depth of excitation (m) and the ordinate represents time (ms). The seismic signals are rejected when the attenuation curve is calculated when excitation abnormality occurs in the signals with the excitation depth of 22 m.

FIG. 3 illustrates a near-surface velocity model derived from a first arrival time interpretation of seismic signals using the common-geophone gather shown in FIG. 2. As shown in FIG. 3, the first arrival times of the seismic signals in FIG. 2 are picked up for interpretation to obtain a near-surface velocity model, where the ordinate represents depth (m) and the abscissa represents time (ms) and velocity (m/s). It can be seen that in this embodiment, the near-surface may be divided into two layers of low and reduced velocity zones, the first layer being a low velocity zone with a thickness of 7.61m and a velocity of 402 m/s; the second is the deceleration layer, with a thickness of 142.39m and a velocity of 1503 m/s.

In an embodiment, based on the obtained number of horizons, thickness and velocity of each layer of the near-surface structure, the travel time of the seismic signal in each layer can be calculated by using a ray tracing method.

Hereinafter, for convenience of explanation of the method of the present invention, a two-layer near-surface structure is taken as an example.

FIG. 4 shows three direct arrivals of seismic signals at different depths extracted from the common geophone gather shown in FIG. 2. As shown in fig. 4, in the common-probe channel set, these are direct wave signals with excitation depths of 150m, 130m, and 106m, respectively, where the abscissa represents the excitation depth (m) and the ordinate represents time (ms). It can be seen that the three signal waveforms are stable and not disturbed by noise.

Fig. 5 shows the amplitude spectra corresponding to the three direct wave signals in fig. 4, wherein the abscissa represents frequency (Hz) and the ordinate represents amplitude. As shown in fig. 5, the results obtained by performing the spectrum analysis on fig. 4. Analysis can obtain that the main frequencies of the three signals are reduced along with the increase of the excitation depth, that is, the deeper the excitation depth, the larger the propagation distance, the lower the corresponding main frequency of the signals, and the narrower the frequency band, which is just caused by the absorption attenuation effect of the stratum, and the frequency spectrum can be used for carrying out attenuation curve stripping.

Specifically, an equivalent attenuation curve including quality factor Q values of two layers in the near-surface structure is obtained using the two selected seismic signals:

wherein the upper line represents the logarithmic value of each variable, i.e.Denotes x_ij(f) Is 2,3, m, m represents the number of excitation points in the micro-logging observation system, f represents the frequency, a represents the frequency₁Represents a constant independent of frequency, wherein the amplitude spectrum of the seismic signal received by the ith shot excitation and the jth receiver can be expressed as:

wherein k represents the kth layer, g_ijDenotes a constant term, t, independent of frequency, such as spherical diffusion and transmission loss_ijkAnd the propagation travel time of the seismic signal excited by the ith gun and received by the jth trace detector on the kth layer is shown. In the present embodiment, the calculation is performed using only one reception point, and therefore j is 1.

In an embodiment, the method of the invention further comprises:

selecting two seismic signals, and calculating a reference attenuation curve:

further, the equation set is established by combining the formula representing the reference attenuation curve and the equivalent attenuation curve:

and by solving the system of equations, an attenuation curve can be obtained that contains only one layer of quality factor Q:

wherein

R₁(f) And R₂(f) Respectively representing attenuation curves which, after solution, contain only one layer of quality factor Q value, c₁And c₂Two frequency independent terms are indicated, i 2, 3.

In the examples, by separately pairing R₁(f) And R₂(f) Linear fitting to obtain its slope p₁＝-πQ₁ ^-1Δt₁And p₂＝-πQ₂ ^-1Δt₂The quality factor Q of each layer can be obtained by inversion₁，Q₂：

Fig. 6 shows the attenuation curves of the layers of the low and reduced velocity bands calculated by the multi-shot combined elimination algorithm of the present invention, wherein the abscissa represents frequency (Hz) and the ordinate represents attenuation. As shown in fig. 6, the attenuation curves of the low-speed layer and the deceleration layer are obtained by the multi-shot combined elimination algorithm according to the three signal spectrums shown in fig. 5 through attenuation curve stripping, wherein fig. 6(a) shows the attenuation curve of the low-speed layer, and fig. 6(b) shows the attenuation curve of the deceleration layer.

Fig. 7 shows a graph comparing an attenuation curve forward-simulated by the calculation result of the quality factor Q value of the attenuation curve after peeling off with a real attenuation curve, in which the abscissa represents frequency (Hz) and the ordinate represents attenuation amount. Specifically, fig. 7(a) shows a comparison between a simulation result of the low-speed belt and a real value obtained by solving the attenuation curve of the low-speed belt and performing forward simulation using the quality factor Q value, and fig. 7(b) shows a comparison between a simulation result of the low-speed belt and a real value obtained by solving the attenuation curve of the velocity reduction belt and performing forward simulation using the quality factor Q value.

As can be seen from fig. 7(a) and (b), the two substantially coincide, which also demonstrates that the peeling results are very reliable.

In summary, the invention provides an attenuation curve chromatography stripping method for near-surface quality factor Q value inversion, which is based on micro-logging data, establishes a near-surface velocity model including the number of strata and the velocity of each stratum through first arrival picking, then uses the near-surface attenuation curve stripping horizon constraint, collects seismic signals generated by different shot excitations through a common detector point channel, calculates the attenuation curve of each stratum through a multi-shot combined elimination algorithm, and then combines a spectral ratio method to obtain the quality factor Q value of each stratum, thereby realizing the purpose of near-surface high-precision quality factor Q value modeling, and further realizing the attenuation curve chromatography stripping algorithm for near-surface absorption attenuation parameter inversion. Compared with the prior art, the method has the advantages that reasonable gun combination is selected, the overall attenuation curve is stripped layer by layer, the attenuation curves of all layers are respectively obtained, and the quality factor Q of each layer is solved by combining a corresponding algorithm, so that the precision of near-surface quality factor Q value modeling is improved, and the problem of low precision of a Q model solved before is solved.

In another aspect, the present invention also provides a storage medium having stored therein a computer-executable program adapted to, when executed, implement an attenuation curve tomographic stripping method for near-surface quality factor Q-value inversion, the method comprising: establishing a near-surface velocity model based on micro-logging data; selecting seismic signals which are not interfered by noise in a common detection point channel set based on a near-surface velocity model; performing spectral analysis on the selected seismic signals to obtain an equivalent attenuation curve comprising quality factor Q values of a plurality of layers in the near-surface structure; and carrying out chromatography stripping on the equivalent attenuation curve by utilizing a multi-gun combination elimination method based on the propagation travel time of the selected seismic signals so as to respectively obtain the attenuation curve of each layer in the near-surface structure.

It is to be understood that the disclosed embodiments of the invention are not limited to the particular process steps or materials disclosed herein, but rather, are extended to equivalents thereof as would be understood by those of ordinary skill in the relevant art. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

Reference in the specification to "an embodiment" means that a particular feature, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase "an embodiment" appearing in various places throughout the specification are not necessarily all referring to the same embodiment.

It will be appreciated by those of skill in the art that the elements and algorithm steps of the examples described in connection with the embodiments disclosed herein may be embodied in electronic hardware, computer software, or combinations of both, and that the components and steps of the examples have been described in a functional general in the foregoing description for the purpose of illustrating clearly the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

Although the embodiments of the present invention have been described above, the above description is only for the convenience of understanding the present invention, and is not intended to limit the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.