CN106814402B - Transient electromagnetic signal Prestack Noise Suppression Methods - Google Patents

Transient electromagnetic signal Prestack Noise Suppression Methods Download PDF

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CN106814402B
CN106814402B CN201611201090.6A CN201611201090A CN106814402B CN 106814402 B CN106814402 B CN 106814402B CN 201611201090 A CN201611201090 A CN 201611201090A CN 106814402 B CN106814402 B CN 106814402B
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field
window
value
time
transient electromagnetic
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CN106814402A (en
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陈孝雄
严良俊
张武中
谢兴兵
王友胜
周磊
姚本全
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中石化石油工程技术服务有限公司
中石化石油工程地球物理有限公司地理地质信息勘查分公司
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01VGEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS
    • G01V3/00Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/38Processing data, e.g. for analysis, for interpretation, for correction

Abstract

The invention discloses a kind of Prestack Noise Suppression Methods of the time series signal of transient electromagnetic exploration, comprising the following steps: S1, storage transient electromagnetic time series;S2, inverted order time-recursive filtering is carried out to each periodic attenuation curve of the field component time series of Transient electromagnetic measure;S3, windowing process is carried out to the field component attenuation curve in period each after filtering, obtains the equally spaced field of logarithm and is worth attenuation curve;S4, the statistical stacking processing method for taking given threshold carry out flying spot to same a period of time window field value of multiple observation cycles in the equally spaced field value attenuation curve of logarithm and are superimposed.The invention enables the processing of LOATEM method data quickly and effectively, and signal-to-noise ratio is obviously improved, and data distortion is obviously reduced, and data quality significantly improves, and calculates for apparent resistivity curve, and solid foundation has been established in high-resolution fine inverting.

Description

Transient electromagnetic signal Prestack Noise Suppression Methods

Technical field

The present invention relates to geophysical signal processing to explore with analytical technology research field more particularly to a kind of transient electromagnetic Time series signal prestack noise-removed technology.

Background technique

Long offset transient electromagnetic Array Method (LOATEM) as an emerging technology in electromagnetic prospecting, more and more by To the attention of exploration geophysics circle.Since the nineties in last century, domestic scholars are taken to this method and are led in oil exploration Method test and Interpreting Method in domain are successively successfully carried out in Carbonate Rock Areas, Southern China area and Ordos Basin Method test achieves some encouraging as a result, further developing and laying a good foundation for this method.

Although LOATEM method has solid theoretical basis, although it is excellent in terms of the factors such as resolution ratio, signal-to-noise ratio In domain electromagnetic exploitation method, but in terms of data processing and interpretation, there are still some very distinct issues.Firstly, since should Method record is time series, and sampled point is intensive (0.1 to 0.5 millisecond of sampling interval), and the period is long (general 8 to 64 seconds), battle array Data volume is huge when column acquisition, and processing is quite heavy with inverting task, and scene cannot generally provide electric section in time, thus shadow The evaluation to the acquisition quality of data and exploration effects is rung.

With the quickening of process of industrialization, though electromagnetic prospecting, in remote mountain area, cultural barriers still remain, and Intolerable stage, needless to say developed regions are arrived.Although LOATEM has, transmission power is big, depth of exploration is deep, anti- The features such as interference performance is strong, convenient, flexible, but still there are many measuring point due to being influenced by cultural barriers, signal-to-noise ratio is very low, number According to often without method interpretation.Quality is explained in order to improve letter, and " denoising " is the prelimi nary work of electromagnetic method data processing.Currently, There are many method of denoising.At, big, the live superposition of Single time series record data volume high for LOATEM method time sampling density The features such as reason is difficult, the invention proposes a kind of prestack noise-removed technologies of transient electromagnetic time series signal.

Transient electromagnetic signal has early signal amplitude high, and decaying is fast, and advanced stage signal is weak, and decaying is slow, and dynamic range is big etc. Feature.Conventional FFT method is because it is mainly from the frequency district characteristic analysis of all the period of time, it is difficult to window when to transient electromagnetic difference Time series signal in noise preferably eliminate.Three vertex degrees of some scholars' research and development approach nonlinear smoothing It makes an uproar and the signal denoising technology based on wavelet threshold, achieves certain effect.Transient electromagnetic method improves the side of signal-to-noise ratio at present Method mainly by be superimposed and increase transmitting ource electric current come.Since the raising of signal-to-noise ratio and the index of stacking fold are directly proportional again, It is thus limited to improve signal-to-noise ratio by stacking fold.Improve emission current is influenced by instrument power, device and ground connection, also can only It is a limited means.Carry out signal identification and Study on Extraction Method, under the premise of superposition is with supply current is increased, exploitation New noise-removed technology is the important channel that current transient electromagnetic method improves data quality.

Summary of the invention

The technical problem to be solved in the present invention is that high, the single-point time for prior art LOATEM method time sampling density The defect of big, the live superposition processing difficulty of sequential recording data volume etc., providing one kind may make the processing of LOATEM method data fast Fast effectively signal-to-noise ratio is obviously improved, and data distortion is obviously reduced, and data quality significantly improves, and calculates for apparent resistivity curve, high Solid foundation has been established in the fine inverting differentiated.

The technical solution adopted by the present invention to solve the technical problems is:

A kind of Prestack Noise Suppression Methods of the time series signal of transient electromagnetic exploration are provided, comprising the following steps:

S1, storage transient electromagnetic time series;

S2, the filter of inverted order Temporal Recursive is carried out to each periodic attenuation curve of the field component time series of Transient electromagnetic measure Wave;

S3, windowing process is carried out to the field component attenuation curve in period each after filtering, obtains the equally spaced field value of logarithm Attenuation curve;

S4, the statistical stacking processing method for taking given threshold, to multiple in the value attenuation curve of logarithm equally spaced field Same a period of time window field value of observation cycle carries out flying spot and is superimposed.

In method of the present invention, in step S1, the signal after shutdown is only extracted, and by the pass twice in each period The attenuation curve of secondary field having no progeny is average again after being added, and forms an attenuation curve, carries out K period observation in a measuring point When, then it is average after being added for the field value of the same delay time of K periodic attenuation curve.

When carrying out windowing process in method of the present invention, in step S3, the time after shutdown is divided into N number of logarithm etc. Window when interval, the interval width in log-domain is Δ, and the center time point of window is denoted as t when each1,t2......tN, corresponding to Field value be calculated as EMF (t respectively1),EMF(t2),.......EMF(tN), N is natural number;Window is divided into 4 parts when will be each, successively It is denoted as ti+Δ/4,ti+Δ/2,ti+3Δ/4,ti+Δ;In order to calculate the field component value EMF (t at center time pointi), by when window width expand Greatly to 3 Δ/2, window has the overlapping of Δ/2 when guaranteeing each;

K sampled point when falling into window is subjected to least square fitting;If y is sampling time ts and parameterFunction, (yi,tsi) it is K to observation, wherein yiIt is observation field values, tsiWhen being corresponding sampling Between, i=1 ..., K, K, M are natural number;Seek parameterMake objective functionReach minimum, wherein σiFor observation field values yiThe standard deviation of error;Window center point when then Corresponding field value isWherein i=1 ..., N, N are natural number.

In method of the present invention, when observation field values points are less than 3 in window at that time, intermediate value or spline interpolation side are taken Field value corresponding to window center point when method is sought.

In method of the present invention, set in step S4 transient electromagnetic field component attenuation curve when window number as N, observation week Issue is M, and the field value in j-th of period after adding window is denoted as EMFj(ti), wherein i=1 ..., N;J=1 ..., M, M, N is natural number;And set threshold value as ε, then M period superposition processing is as follows:

1. calculating different cycles with the average value of a period of time window center field of points value:

2. given threshold ε is rejectedField value, wherein j=1 ..., M;

3. window center field of points value when being recalculated to remaining field value by formula in 1..

Beneficial effects of the present invention: the invention enables the processing of LOATEM method data quickly and effectively, and signal-to-noise ratio is obviously improved, Data distortion is obviously reduced, and data quality significantly improves, and calculates for apparent resistivity curve, and heavily fortified point has been established in high-resolution fine inverting Real basis.

Detailed description of the invention

Present invention will be further explained below with reference to the attached drawings and examples, in attached drawing:

Fig. 1 is Z plane inpolar and O point distribution situation, wherein+it is pole, O is zero point;

Fig. 2 is the amplitude-frequency characteristic of trapper;

Fig. 3 is that 50Hz standard signal sequence is compared with inverted order filter effect;

Fig. 4 is actual measurement die-away time sequence (Hz noise is serious);

Fig. 5 is inverted order and positive sequence time-recursive filtering Contrast on effect;

Fig. 6 is the overlapping windowing process of transient electromagnetic field data;

Fig. 7 (a) is that transient electromagnetic magnetic data prestack filters apparent resistivity curve figure;

Fig. 7 (b) is that transient electromagnetic magnetic data poststack filters apparent resistivity curve figure.

Specific embodiment

In order to make the objectives, technical solutions, and advantages of the present invention clearer, with reference to the accompanying drawings and embodiments, right The present invention is further elaborated.It should be appreciated that described herein, specific examples are only used to explain the present invention, not For limiting the present invention.

Pre-stack processing Method And Principle and process

Due to electric dipole source transient electromagnetic exploitation method have depth of exploration it is big, it is adaptable, multi -components observe when pair High resistant thin layer has higher resolution capability, is widely used in oil-gas exploration.Currently, record magnanimity electric dipole source transient electromagnetic Depth measurement multi -components time series is possibly realized, and is provided solid data for the signal-to-noise ratio that Enhanced time sequence data gives processing and is protected Card.

1. transient electromagnetic time series stores journey

Usually power supply wave mode is bipolar square wave, duty ratio 50%, Zhou Wei T.It is only mentioned in the signal that collection terminal receives Signal after taking shutdown.The attenuation curve of secondary field after shutdown twice in each period adds up average production, forms one and declines Subtract curve (note: every secondary extinction curve is added with attenuation of the first kind curve divided by 2 multiplied by negative sign).In this way, a measuring point into It is that the field value of the same delay time of K periodic attenuation curve is added up and is averaged when the observation of K period of row.For folded Pre-treatment, it is not necessary to which retention time sequence data, only constantly superposition, retains last stack result.

2. pre-stack processing method and technology

(1) prestack inverted order time-recursive filtering

Basic principle

If the time series recorded in YUTEM sampling time section is { xi, i=1,2 ..., N, filtering factor hi, then filter Time series { y after waveiAre as follows:

In actual operation, filtering factor hjFinite term can only be taken, this just unavoidably generates error, misses to reduce Difference, hjIt takes into finite term but number wants quite a lot of, maxitem N is 4800 in YUTEM mode, and such operation, which is got up, both to be occupied Memory is big, and Fei Jishi, and recursive filtering can well solve this problem.

The thought of recursive filtering is: thinking output valve yiBetween it is associated with each other, therefore calculate yiWhen, it to utilize pervious Calculated result yi-1,yi-2....According to this thought, conventional recursive filtering formula are as follows:

yi=a0xi+a1xi-1+…+anxi-n-(b1yi-1+b2yi-2+…+bmyi-m) (2)

Wherein m, n are natural number, aj、bjFor recursive filtering parameter.

Z plane method designs filter

What LOATEM measuring signal suffered from is the interference of certain fixed frequencies, thus the design of filter should be directed to The trapper of some fixed frequency.Temporal Recursive trapper is designed with Z plane method with can be convenient.So-called Z plane method design Filter exactly selects 0 point appropriate and pole on Z plane, designs according to the requirement to filter to amplitude and phase Filter.According to the basic theories of transform, the transform of the amplitude-frequency characteristic of temporal recursive filter can be written as

Z plane method is that have to fall into amplitude-frequency function corresponding to the point using 0 point on Unit Circle and the pole near it Wave property (as depicted in figs. 1 and 2) quickly determines W (z), i.e., in-fr,frAmplitude should be 0 at point, and except this two o'clock Amplitude is 1 (normalized value).Meet above-mentioned two condition, then requires amplitude function that must contain and pole, and 0 simultaneously at 0 point Point and pole should be very close to.For this purpose, (3) formula can be written as

W (z) is quickly determined below by Z plane method.

The plural form of zero point and pole in Z plane can be written as

zz=cos Ωr±sinΩr=Rz±iIz (5)

zp=rp cosΩp±rp sinΩp=Rp±iIp (6)

Wherein rpFor filter factor, ΩrFor the angular frequency for wanting trap, mathematic(al) representation are as follows:

Ωr=± 180 ° of fr/fN

frFor the frequency for wanting trap, fNFor nyquist frequency, had according to sampling thheorem:

fN=1/ (2 Δ t)

(5), (6) formula are substituted into (4) formula and by simple mathematical operation, then the frequency response of trapper can be written as

G is by nyquist frequency ωNWhen=π, enables W (z)=1 and obtains, it may be assumed that

According to the property of recursion filter, we write out the mathematic(al) representation of temporal recursive filter in which can be convenient:

? Sequence filtering

In practical filtering, first time series data is fallen to arrange, then carry out above-mentioned filtering processing, then fall again Row obtains last filter result, this ensure that the filter quality of time series front end data, because of the transient signal after shutdown It is most important with inverting to data processing.By taking the filtering of 50Hz sine wave as an example, as shown in Figure 3.Black dotted line is 50Hz sine wave letter Number, for red line to use (8) formula filter effect under the conditions of positive sequence, blue line is inverted order filter effect.As can be seen that the leading portion of positive sequence filtering There is one section of resistance decaying, signal obviously distorts, and effect is poor, and the leading portion data filtering effect for arranging filtering is very ideal.It is based on Inverted order filtering technique, we handle real data, and as shown in figs. 4 and 5, inverted order filters when making leading portion treatment effect Between sequence signal-to-noise ratio greatly improve, and ensure that the authenticity of signal.

(2) it is overlapped windowing process

After field component attenuation curve in each period is filtered, it is desirable that window curve when taking log-domain, formation pair Number field at equal intervals when window data.In order to guarantee that curve is continuous, smooth, we take overlapping windowing process.Its Method And Principle such as Fig. 6 It is shown.

Window when time after shutdown is divided into N number of logarithm at equal intervals, the interval width in log-domain are Δ, center time point It is denoted as t1,t2......tN, corresponding to field value be calculated as EMF (t respectively1),EMF(t2),..EMF(tN).Window point when will be each At 4 parts, it is successively denoted as ti+Δ/4,ti+Δ/2,ti+3Δ/4,ti+Δ.In order to calculate the field component value EMF (t at center time pointi), it will When window width be expanded to 3 Δ/2, window has the overlapping of Δ/2 when guaranteeing each in this way, as shown in Figure 3.

K sampled point when falling into window is subjected to least square fitting.If y is sampling time ts and parameterFunction, (yi,tsi), (i=1 ..., K) is K to observation, wherein yiIt is observation field values, tsiIt is the corresponding sampling time.Seek parameterMake objective function

Reach minimum, wherein σiFor observation field values yiThe standard deviation of error.Field value corresponding to window center point is when then

When observation field values points are less than 3 in window at that time, window center point when intermediate value or Spline Interpolation Method can be taken to seek Corresponding field value.

(3) the statistical stacking processing of given threshold

If the when window number of transient electromagnetic field component attenuation curve is N, observation cycle number is M, in j-th of period after adding window Field value be denoted as EMFj(ti), (i=1 ..., N;J=1 ..., M), and set threshold value as ε, then M period superposition processing By as follows:

1. calculating different cycles with the average value of a period of time window center field of points value:

2. given threshold ε is rejectedField value.

3. to remaining field value by 1. formula recalculates when window center field of points value.

Fig. 7 (a) and 7 (b) is single-point prestack and post-stack data processing apparent resistivity curve.As can be seen that the view electricity of prestack filtering Resistance rate curve quality significantly improves.

Large power long offset distance transient electromagnetic array exploitation method of the invention is a kind of for deep prospecting, especially oily Electromagnetic exploration method in gas exploration.It, can with the fast development of electronics and computer technology and instrument weak signal acquisition technique Simultaneously mass storage multi -components multiple tracks observation field values time series data, for this method prestack signal processing provide it is solid Data guarantee.This technology invention first carries out each periodic attenuation curve of the field component time series of Transient electromagnetic measure Inverted order time-recursive filtering preferably eliminates periodic cultural barriers, and has higher fidelity, and core technology is down Sequence filtering.Secondly, carry out obtaining the equally spaced attenuation curve of logarithm to each period field component attenuation curve windowing process, Window center field of points value when window overlapping is solved with nonlinear least square method when core technology is.Finally take multiple weeks of given threshold Phase statistical stacking processing technique carries out flying spot superposition processing to same a period of time window field component value of multiple observation cycles, mentions significantly The high precision of field value estimation.

The invention enables the processing of LOATEM method data quickly and effectively, and signal-to-noise ratio is obviously improved, and data distortion is obviously reduced, Data quality significantly improves, and calculates for apparent resistivity curve, and solid foundation has been established in high-resolution fine inverting.

It should be understood that for those of ordinary skills, it can be modified or changed according to the above description, And all these modifications and variations should all belong to the protection domain of appended claims of the present invention.

Claims (2)

1. a kind of Prestack Noise Suppression Methods of the time series signal of transient electromagnetic exploration, which comprises the following steps:
S1, storage transient electromagnetic time series;
S2, inverted order time-recursive filtering is carried out to each periodic attenuation curve of the field component time series of Transient electromagnetic measure;
S3, windowing process is carried out to the field component attenuation curve in period each after filtering, obtains the equally spaced field value decaying of logarithm Curve;
S4, the statistical stacking processing method for taking given threshold, to multiple observations in the value attenuation curve of logarithm equally spaced field Same a period of time window field value in period carries out flying spot and is superimposed;
In step S1, only extract shutdown after signal, and by each period twice turn off after attenuation curve of secondary field phase It is average again after adding, an attenuation curve is formed, is then K periodic attenuation curve when a measuring point carries out K period and observes The field value of same delay time is average after being added;
When carrying out windowing process in step S3, the window when time after shutdown is divided into N number of logarithm at equal intervals, the interval in log-domain Width is Δ, and the center time point of window is denoted as t when each1,t2......tN, corresponding to field value be calculated as EMF (t respectively1), EMF(t2),.......EMF(tN), N is natural number;Window is divided into 4 parts when will be each, is successively denoted as ti+Δ/4,ti+Δ/2,ti+3Δ/4, ti+Δ;In order to calculate the field component value EMF (t at center time pointi), by when window width be expanded to 3 Δ/2, when guaranteeing each Window has the overlapping of Δ/2;
K sampled point when falling into window is subjected to least square fitting;If y is sampling time ts and parameterFunction, (yi,tsi) it is K to observation, wherein yiIt is observation field values, tsiWhen being corresponding sampling Between, i=1 ..., K, K, M are natural number;Seek parameterMake objective functionReach minimum, wherein σiFor observation field values yiThe standard deviation of error;Window center point when then Corresponding field value isWherein i=1 ..., N, N are natural number;
Set in step S4 transient electromagnetic field component attenuation curve when window number as N, observation cycle number is M, j-th week after adding window Interim field value is denoted as EMFj(ti), wherein i=1 ..., N;J=1 ..., M, M, N are natural number;And set threshold value For ε, then M period superposition processing is as follows:
1. calculating different cycles with the average value of a period of time window center field of points value:
2. given threshold ε is rejectedField value, wherein j=1 ..., M;
3. window center field of points value when being recalculated to remaining field value by formula in 1..
2. the Prestack Noise Suppression Methods of the time series signal of transient electromagnetic exploration according to claim 1, which is characterized in that When observation field values points are less than 3 in window at that time, field corresponding to window center point when intermediate value or Spline Interpolation Method being taken to seek Value.
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