Exploration seismology method

FIELD: geophysics.

SUBSTANCE: in accordance to the method, dispersive curve of micro-seismic waves is determined preliminarily. Wave lengths λ are determined as well as frequency spectrum of micro-seismic signal on basis of analysis of apparent speeds, wherein it consists of Raleigh waves. Seismic indicators are positioned across researched territory in such a way, that distance between them was not more than half the shortest length of Raleigh wave. Then, amplitude difference of measuring channels of seismic indicators is determined within frequencies band of micro-seismic signal. Micro-seismic signal is registered by no less than two seismic stations, one of which is mounted in stationary manner in the central portion of researched territory, and the rest are moving across researched territory. Accumulation of power spectrum of micro-seismic signal is performed in each measurement point during time, enough to reach stationary spectrum. Spatial variations spectrum of micro-seismic signal is connected for each measurements point. Maps of amplitude variations of micro-seismic signal are built for each spectrum frequency of spatial variations. Alignment of each received map is performed to appropriate depth H.

EFFECT: increased depth capacity of exploration seismology with simultaneous increase in trustworthiness of results.

2 dwg

 

The invention relates to the field of seismic exploration and can be used for mapping deep inhomogeneities of the Earth, to search for ore deposits and oil and gas fields, for the assessment of commercial reserves of oil and gas fields, for optimal selection of drilling locations in the development field, to determine the superficial and deep fault structures, for monitoring the environment in forecasting earthquakes.

There is a method of seismic exploration comprising determining in the study area spectral characteristics of the field MicroSAM and the deep structure of the environment, the selection of resonant frequencies, of which there are three frequencies, the generation of seismic vibrations on three frequencies, from the lowest continuous recording of seismic signals (SU, No. 996964, G 01 V 1/00, 1981).

The disadvantage of this method is the low reliability due to the fact that the resonant frequency is not always present in microseismic signal.

Closest to the proposed invention is a method of seismic exploration, including the registration of natural seismic background on the three components is not less than two geophones before and after the generation of seismic vibrations with a frequency of 0.1-70 Hz, the judgment about the presence of oil and gas fields to increase the area under the curve spectrasystem background on all three components after generating seismic vibrations compared to the original (RU # 2119677, G 01 V 1/00, 1998).

The disadvantage of this method is the low validity and reliability as to make the generation of a signal in the range 0.1-1 Hz represents a technical challenge.

The invention solves the technical problem of improving the efficiency of seismic exploration for large depths. The technical result is an increase in the depth of the seismic while increasing the reliability and efficiency of seismic at different depths through the use of the entire frequency range of the microseismic signal, including ultra-low frequencies.

The technical result is achieved in a method of seismic exploration, including a preliminary determination of the dispersion curve of the microseismic waves, characteristic of the study area, by conducting simultaneous registration of microseismic signals at least three seismic stations with vertical seismic sensors with evaluation data obtained dependence of the apparent velocities of propagation of seismic waves from the signal frequency, the definition of wavelengths (λ) and frequency range based on the analysis of apparent velocities in which the microseismic signal is composed of Rayleigh waves, the placement of the seismic sensors in the study area so that the distance between the at them was not more than half the shortest wavelength of the Rayleigh, determination of the amplitude of identical measuring channels of seismic sensors in the frequency band of the microseismic signal by simultaneous recording microseismic signal all the seismic sensors at the same point in a period of time sufficient to determine the stationarity of the power spectrum of the microseismic signal, with subsequent determination of the logarithmic difference of the spectra of all measuring channels of seismic sensors, recording microseismic signal by at least two seismic stations, one of which is stationary in the Central part of the study area, while the others move around the area, the accumulation of the power spectrum of the microseismic signal at each measurement point in a period of time sufficient to determine the stationarity of the spectrum, the calculation of the spectrum of spatial variations in microseismic signal for each point measurements by determining the logarithmic difference of the power spectrum for each point measurement and power spectrum of the microseismic signal accumulated in the recording truck, installed within the equivalent time in the same time period taking into account the amplitude of identical measuring channels of seismic sensors, the mapping of the amplitude variations of microseismic signals is the frequency spectrum of the spatial variations binding each of the cards corresponding to the depth H according to the equation:

N=λ×,

where It is experimentally established numerical factor depending on the outgoing rocks,

λ - wavelength Rayleigh determined from the dispersion curve, m

Distinctive features of the proposed method are the determination of the dispersion curve of the microseismic waves adhesive, followed by estimation of the dependence of the apparent velocities of propagation of seismic waves from the signal frequency, the definition of wavelengths (λ) and frequency range, consisting of Rayleigh waves, the placement of the seismic sensors of the above method, the determination of the amplitude of identical measuring channels of seismic sensors with subsequent determination of the logarithmic difference spectra, registration microseismic signal seismic stations, one of which is stationary, the accumulation of the power spectrum of the microseismic signal to establish the stationarity of the spectrum, the calculation of the spectrum of spatial variations in microseismic signal for each measurement point, the mapping of the amplitude variations of the microseismic signal for each frequency spectrum spatial variation, binding each received a card corresponding to the depth according to the above value, that poses the s to increase the propagation distance of seismic while increasing the reliability and efficiency of seismic at different depths through the use of the entire frequency range of the microseismic signal, including ultra-low frequencies. Microseismic signals are represented in the General case the sum of bulk and surface waves type of love waves and Rayleigh. The energy of surface waves in the seismic signal is much higher volumetric energy waves and implementing a way they are not taken into account. The use of vertical sensors allows to isolate from surface waves only Rayleigh waves, which contain zero fashion even in the absence of bright reflecting boundaries, in contrast to the waves of love. Placing seismic sensors at a distance from each other not more than half the shortest wavelength of the Rayleigh will allow you to achieve maximum resolution of the method according to the horizontal. Accounting amplitude of identical measuring channels of seismic sensors allows you to exclude individual characteristics measuring channels when building maps. The accumulation of the power spectrum of the microseismic signal at each point of measurement to establish the stationarity of the spectrum must be made in view of the duality of the nature of the microseismic signal, which consists of determenirovana of trains with random initial phases, random frequencies, amplitudes and directions of arrival. At sufficiently large times, these deterministic trains are stationary random signal. These stationen the e characteristics, including the power spectrum, are determined during measurements. The calculation of the spectrum of spatial variations in microseismic signal for each point of measurement is necessary in order to exclude the influence of the springs forming the microseismic signal. The mapping of the amplitude variations of the microseismic signal and bind them to a depth of produce to obtain the mechanical characteristics of the environment at different depths.

Method of seismic exploration is illustrated by a drawing, in which figure 1 presents a map of the amplitude variations of the microseismic signal for different frequencies and the corresponding depths, figure 2 - construction of three-dimensional heterogeneity.

Method of seismic exploration is carried out as follows. Pre-determine the dispersion curve of the microseismic waves, characteristic of the study area by conducting simultaneous registration of microseismic signals at least three seismic stations with vertical seismic sensors with evaluation data obtained dependence of the apparent velocities of propagation of seismic waves from the signal frequency. Determine the wavelengths (λ) and the frequency range of the microseismic signal based on the analysis of apparent velocities, in which it consists of Rayleigh waves. The seismic sensors are placed on the investigated territory is thus to the distance between them was not more than half the shortest wavelength of Rayleigh. Then determine the amplitude non-identity of measuring channels of seismic sensors in the frequency band of the microseismic signal by simultaneous recording microseismic signal all the seismic sensors at the same point in a period of time sufficient to determine the stationarity of the power spectrum of the microseismic signal, with subsequent determination of the logarithmic difference of the spectra of all measuring channels of seismic sensors. Register microseismic signal by at least two seismic stations, one of which is stationary in the Central part of the study area, while the others move around the study area. Spend the accumulation of the power spectrum of the microseismic signal at each measurement point in a period of time sufficient to determine statsionarnosti spectrum. Calculate the range of spatial variations in microseismic signal for each point of measurement by determining the logarithmic difference of the power spectrum for each point measurement and power spectrum of the microseismic signal accumulated in the recording truck, installed within the equivalent time in the same time period taking into account the amplitude of needent the surface of the measuring channels of seismic sensors. Build maps of the amplitude variations of the microseismic signal for each frequency of the spectrum of spatial variations. Do bind each received a card corresponding to the depth H according to the equation:

H=λ×K,

where It is experimentally established numerical factor depending on the outgoing rocks,

λ - wavelength Rayleigh determined from the dispersion curve, m

An example of the method of seismic prospecting.

Seismic survey conducted on the island of volcanic origin Spruce, Iero included in the Canary archipelago. The size of the island was about 25×30 km2. For the seismic survey used three seismic stations with vertical seismic sensors with the following technical characteristics: sensitivity of the measuring channel of 400,000 volts/meter/sec with the possibility of attenuation of the gain, frequency range channel: 0.03-15 Hz. The distance between the measurement points averaged 1.5 km While the length of the shorter wavelength Rayleigh amounted to 3 km. the Total number of measurement points was 62. Pre-determined dispersion curve of microseismic waves, characteristic of the study area by conducting simultaneous registration of microseismic signals from three seismic stations with vertical seismic sensors. Assess the Wali on the data dependencies of the apparent velocities of propagation of seismic waves from the signal frequency. Was determined on the basis of the analysis of apparent velocities of wavelengths α and a frequency range of microseismic signal, in which it consists of Rayleigh waves. The apparent velocities are in the range: 1.5-2.5 km/sec. The frequency range is 0.03-0.75 Hz and wavelengths α set of dependencies: λ=V/f where V is the velocity of the Rayleigh wave for the frequency f. Then determined amplitude non-identity of measuring channels of seismic sensors in the frequency band of the microseismic signal by simultaneous recording microseismic signal all the seismic sensors at the same point in a period of time sufficient to determine the stationarity of the power spectrum of the microseismic signal, with subsequent determination of the logarithmic difference of the spectra of all measuring channels of seismic sensors. Recorded microseismic signal two seismic stations, one of which was stationary in the Central part of the study area, and the other moved around the study area. Spent the accumulation of the power spectrum of the microseismic signal at each measurement point in a period of time sufficient to determine the stationarity of the spectrum. Expected range of spatial variations in microseismic signal for each point of measurement by determining the logarithmic difference spectrum power the spine for each point measurement and power spectrum of the microseismic signal, accumulated in the recording truck, installed within the equivalent time in the same time period taking into account the amplitude of identical measuring channels of seismic sensors. Built maps of amplitude variations of the microseismic signal for each frequency of the spectrum of spatial variations. Did bind each received a card corresponding to the depth H according to the ratio H=λ×K, where K=0.5. The value of K was determined experimentally in the course of mathematical modeling based on the finite element method for the propagation of Rayleigh waves in an inhomogeneous half-space, folded rocks close to the rocks of volcanic origin.

Figure 1 shows the 4 cards of the amplitude variations of the microseismic signal, for frequency (f): 0.0769, 0.0897, 0.094, 0.1068 Hz, and the corresponding wavelengths (λ) 26.0, 22.1, 21,2 and 18.8 km, which was calculated at V=2 km/sec. Depth was calculated For K=0.5 in the above formula and amounted to 13.0, 11.1, 10.6, 9.4 km figure 2 shows the principle of construction of three-dimensional Intrusive body.

The use of the proposed method of seismic data can improve the accuracy of seismic gives the principal the opportunity to conduct a seismic survey in the places inaccessible to the application of artificial sources, allows producers who seismic survey at great depths, allows seismic survey in the monitoring mode without the use of springs. The method is technically simple, clean, efficient from a cost perspective.

Method of seismic exploration, including a preliminary determination of the dispersion curve of the microseismic waves, characteristic of the study area, by conducting simultaneous registration of microseismic signals at least three seismic stations with vertical seismic sensors with evaluation data obtained dependence of the apparent velocities of propagation of seismic waves from the signal frequency, the definition of wavelengths (λ) and frequency range based on the analysis of apparent velocities in which the microseismic signal is composed of Rayleigh waves, the placement of the seismic sensors in the study area so that the distance between them was not more than half the shortest wavelength of the Rayleigh, the determination of the amplitude of identical measuring channels the seismic sensors in the frequency band of the microseismic signal by simultaneous recording microseismic signal all the seismic sensors at the same point in a period of time sufficient to determine the stationarity of the power spectrum of the microseismic signal, with subsequent determination of logarifmicheskoi spectra of all measuring channels of seismic sensors, registration microseismic signal by at least two seismic stations, one of which is stationary in the Central part of the study area, while the others move around the area, the accumulation of the power spectrum of the microseismic signal at each measurement point in a period of time sufficient to determine the stationarity of the spectrum, the calculation of the spectrum of spatial variations in microseismic signal for each point of measurement by determining the logarithmic difference of the power spectrum for each point measurement and power spectrum of the microseismic signal accumulated in the recording truck, installed within the equivalent time in the same time period taking into account the amplitude of identical measuring channels of seismic sensors, the mapping of the amplitude variations microseismic signal for each frequency of the spectrum of spatial variations, binding each received a card corresponding to the depth H according to the value

N=λ×,

where It is experimentally established numerical factor depending on the outgoing breeds;

λ - wavelength Rayleigh determined from the dispersion curve, m



 

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2 dwg

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