RU2265235C1 - Method for searching and reconnaissance operations concerning oil and gas deposits - Google Patents

Abstract

FIELD: geophysics.

SUBSTANCE: in accordance to method by transformation of excited and registered wave fields, amplitude-frequency and transfer characteristics of deposits of hydrocarbon resources are formed along lateral line and below face of control well, which are used to determine position and depth of oil-gas deposits. After transformation and comparison of frequency characteristics of longitudinal and transverse resilient oscillations, character of saturation and filtering-capacity properties of oil-gas deposits are determined.

EFFECT: higher efficiency, higher trustworthiness.

2 cl, 6 dwg

Description

The invention relates to geophysical methods for prospecting and exploration of oil and gas fields and can be used in the search and exploration of hydrocarbon deposits on land and in the water.

It can be most effectively used in the search and exploration of hydrocarbon deposits, characterized by a multi-tiered geological structure, in which the hydrocarbon deposits are separated, located at great depths and are associated with non-structural type hydrocarbon traps, as well as with hydrocarbon traps in the form of low-amplitude elevations. The invention can be used to control the development and further development of hydrocarbon deposits at a late stage of operation, when it is extremely necessary to engage weakly drained, deadlock and stagnant zones in operation.

A known method for the search and exploration of hydrocarbon raw materials (RU, patent 2217778, G 01 V 1/00, 2003), according to which it is proposed to register the earth's seismic background with subsequent analysis and compare it with the standard form of the information signal measured at a known hydrocarbon field.

Significant disadvantages of the method are its low depth, accuracy, noise immunity and resolution, because the productive part of the reservoir has a small relative power in the studied geological section and is a thin heterogeneity in the recorded wave field; in addition, the implementation of the method requires a laborious study of areas with known geological structure.

There is also known a method for searching and exploration of hydrocarbon raw materials (RU, patent 2161809, G 01 V 1/00, 2001), when the characteristics of the microseismic noise of the Earth are also used as an information signal and they are compared with the results of additional generation of seismic vibrations by a ground seismic vibrator.

The disadvantages of this method are low accuracy, noise immunity and reliability of measurements, because the contrast of the diagnostic features of the recorded wave fields for the direct search of hydrocarbon deposits is small, and the dynamic range of their change is extremely low; the additional difficulties of extracting useful waves in a wide frequency range due to the superposition of multiple-reflected waves and other interference makes its practical application quite problematic. In addition, this method does not exclude the inherent limitations of ground-based methods of recording the wave field due to insufficiently reliable a priori information about the model of the studied geological environment, which casts doubt on the subsequent correct choice of the location of prospecting and exploratory wells.

The closest in technical essence to the invention is a method for prospecting and exploration of oil and gas fields (RU, patent 2045079, class G 01 V 1/00, 1995), including the excitation of seismic vibrations by a seismic vibrator, registration of three-way seismic receivers of the wave field and its comparison with natural ground-based seismic by the field.

According to the known method, seismic vibrations are excited by a ground vibrator in a narrow-band seismic frequency range from 10 to 20 Hz. As an information signal, a natural seismic background is recorded, recorded both before and after the excitation of vibrational vibrations, and the presence of a field is judged by the increase in the area under the mutual spectrum curve of the components of the same name when registering a seismic background after excitation of seismic vibrations compared with registration before excitation. The disadvantages of this method, along with low noise immunity, reliability and accuracy of measurements is the complete lack of information about the depth of the oil and gas deposits, since this method allows you to predict only the contours of oil and gas deposits in the conditions of traditional single traps of hydrocarbon structured type, which is extremely insufficient when searching and exploring complex deposits UVS characterized by a multi-tiered structure; in addition, the known method does not allow to evaluate the spatial contours of oil and gas deposits, their fluid saturation and reservoir properties.

The aim of the invention is to improve the accuracy of predicting spatial position, geometric dimensions, reservoir properties and the nature of saturation of geological objects.

This goal is achieved by the fact that according to the method of prospecting and exploration of oil and gas fields, including the multiple excitation and registration of elastic vibrations on the earth's surface in the seismic frequency range, the registration of the natural seismic background in the infra-low range of 1-10 Hz and subsequent comparison of the data obtained during the opening of the interval the geological section of the control well carry out additional periodic excitation of elastic vibrations at internal points of the medium in seismic frequency range of 10-1000 Hz, consistent in time with radiation on the earth's surface, the wave field of induced seismic emission in the range of 0.1-1 Hz is recorded on the earth's surface simultaneously with the reception of elastic vibrations in the upper part of the drill string, after opening the interval of the geological section register the natural seismic-acoustic background at internal points of the medium in the high-frequency range of 1-50 kHz, after which elastic vibrations inside and outside the drill string are excited at the same points in the range frequency range 1-50 kHz and the induced acoustic emission is recorded, the measured spectral densities of longitudinal and transverse elastic vibrations are summarized and compared in the range of the restored amplitude-frequency characteristic of the medium 0.1 Hz-50 kHz and with respect to the spectral densities of longitudinal and transverse vibrations as a function of depth wells and their correlation with the ratio of the spectral densities of reflected oscillations in the lateral and below the bottom of the well determine the spatial position, the depth, the nature of yscheniya and reservoir properties of oil and gas deposits.

The values of spectral densities and correlation functions of longitudinal and transverse elastic vibrations recorded at internal points of the geological environment exposed by the control well or at the top of the drill string at depths corresponding to reflecting seismic boundaries are used as a correlated signal when extrapolating laterally and below the bottom of the control well .

Figure 1 presents a list of sequences for implementing the method in the form of a functional diagram.

The functional diagram includes a control well 1, a drill string 2, downhole acoustic receiving transducers 3 and 4, a downhole high-frequency acoustic emitter 5 in the range of radiation frequencies 1-50 kHz, a downhole low-frequency emitter 6 in the range of radiation frequencies 10-1000 Hz, installed in the lower part drill string, ground emitter 7 low-frequency oscillations in the frequency range of radiation 10-20 Hz, moved on the earth's surface according to a given system of excitation of elastic waves, ground 3-component acoustic transducer 8 installed in the upper part of the drill string and operating in the radiation mode in the frequency range of 1-10 Hz and reception in the frequency range of 1-1000 Hz, ground-based acoustic 3-component receiving transducers 9 installed by specified linear or areal monitoring systems near wellhead, signal amplification and filtering unit 10, correlator 11 for the low-frequency range, adder 12, correlator 13 for the high-frequency range, unit 14 for measuring the spectra of longitudinal and transverse high-frequency oscillations, block 1 5 measurements of spectra of longitudinal and transverse low-frequency oscillations, block 16 for controlling the emission spectrum of emitters 5, 6 and 7, block 17 for synchronization, block 18 for summing and measuring the ratio of the same spectra and spectra of longitudinal and transverse oscillations, depth gauge 19 for the well, block 20 for deep reflection to the horizons of the geological section, block 21 converting the relations of the spectra of longitudinal and transverse vibrations into values of reservoir properties and oil and gas saturation of reservoir layers, block 22 registration and sampling zheniya information into a function of depth, frequency and time.

Figure 2 shows the palette (dependence 23) to determine the coefficient of porosity K _P productive collectors.

Figure 3 shows an example of determining the nature of the saturation of the reservoir by the ratio of the spectral densities of the longitudinal W _P (w) and transverse W _S (w) elastic vibrations with the following dependencies:

24 - for a gas-saturated collector;

25 - for oil saturated reservoir;

26 - for water-saturated collector.

The method is implemented according to the following sequence of operations.

After recording the natural seismic background by the receiving acoustic transducers 9, periodic low-frequency emission of elastic vibrations on the earth’s surface by the emitter 7 in the range of 10-20 Hz, coordinated in time with the emission of elastic vibrations at the internal points of the medium using the emitter 6 located in the lower part of the drill string 2 is produced (as the emitter 6 can be used downhole signal from the interaction of the bit with the drilled rock, downhole hydrodynamic emitter type "Siren" mechanical emitter et al.).

The spectra of elastic oscillations of the emitter 9 are controlled in the frequency range 10-20 Hz and the emitter 6 in the frequency range 10-1000 Hz using block 16. The emitters are synchronized in time using block 17.

Using ground-based acoustic transducers 8 and 9, after temporary selection, synchronized reception of reflected (refracted) interference elastic vibrations in the frequency range of 10-1000 Hz is performed using the synchronization unit 17 and the amplification and filtering unit 10.

At the same time, using an acoustic transducer 8 installed in the upper part of the drill string in the flow of drilling fluid, radiation and reception of elastic vibrations reflected from the bottom of the well in the range of 1-10 Hz are carried out. In this case, induced seismic emission in the infra-low frequency range of 0.1-1 Hz is recorded on the earth's surface. The presence of two ground emitters 7 and 8 in the seismic frequency range along with the registration of induced seismic emission allows us to achieve broadband radiation and the reception of elastic vibrations in the range of 0.1-1000 Hz, which is necessary to study the frequency characteristics of complex oil and gas fields.

The resolution of the recorded wave field is achieved by adjusting the duration of the emission of elastic vibrations on the earth's surface and at internal points of the medium using the control unit 16.

The control of the total radiation front of the elastic vibrations of the emitters 6, 7 and 8 by adjusting the time delay with sequential time excitation allows controlling the directivity of the radiation, which is especially relevant in the presence of oblique directional boundaries of reflecting horizons in complex media.

The choice of the frequency ranges for the analysis of elastic waves in the infra-low 0.1-10 Hz, seismic 1-1000 Hz and high-frequency 1-50 kHz frequency ranges is justified by the results of numerous experimental trials of this method, when the oil and gas reservoir is considered as an anomalous energy zone with the corresponding broadband frequency response and pulse transient response.

In the absence of a downhole radiation source 6, when implementing the method, a ground-based excitation source in the seismic frequency range can be used; in this case, elastic vibrations are received at internal points of the medium by receiving acoustic transformations 3, 4 as a function of the depth of the control well.

The recorded interference signals from the outputs of the ground receiving transducers 8 and 9 after amplification, filtering, and temporal selection in block 10 are fed to the inputs of the correlator 11, where the mutual correlation (CVF) and autocorrelation (FAK) functions of low-frequency oscillations are measured. The values of FVK and FAK measured in correlator 11 are fed to the input of block 15 for measuring the spectral densities of longitudinal and transverse vibrations W _{P (LF)} and W _{S (LF)} and to the input of adder 12, where the operation of simultaneous summation of FVK, which improves the noise immunity of measurements.

After opening the specified interval of the geological section, the acoustic probe containing the acoustic emitter 5, exciting elastic vibrations in the frequency range 1-50 kHz, and acoustic receiving transducers 3 and 4 are received into the drill string by the flow of flushing fluid or on the cable. the vibrations go to the input of block 10 and, after amplification and filtering, to the input of the correlator 13 and then to the input of the block for measuring the spectra of longitudinal and transverse elastic vibrations, where Ia spectra W _{P (HF)} and W _{S (HF)} in the high frequency range 1-50 kHz.

From the outputs of blocks 14 and 15, the measured values of W _{P (HF)} and W _{S (HF)} are sent to the unit 18 for summing and measuring the ratio of the spectra of the same name and the spectra of longitudinal and transverse elastic vibrations W _P / W _S. The summation of spectral densities in the range of 0.1 Hz-50 kHz is carried out in order to restore the full frequency response of the oil and gas field. Measurement of the ratio of the spectra of the same name W _P and W _S allows you to study in detail the transfer and transition characteristics of a thin-layered geological section.

In block 20, the depth spectra W _{P (LF)} and W _{S (LF) of the} reflected low-frequency signals are deeply referenced to the high-frequency spectral components of the elastic vibrations W _{P (HF)} and W _{S (HF)} recorded at internal points of the medium as a function of the depth of the control well Ngl , which produce their conversion to synthetic spectral diagram with sequentially changing the coordinate X ₀ along the ground profiles converters 9 using parameters relative spectral densities as a function of depth control HP well known us 1.

The relative parameter of the spectral density of elastic vibrations recorded inside the well 1 by transducers 3, 4 (or in the upper part of the drill string using transducer 8) is defined as

where Hi is the current depth;

ΔH is the sampling step in depth, selected depending on the resolution of the measurement W _P (Ngl).

The relative parameter of the spectral density of the reflected elastic vibrations recorded on the day surface using transducers 9, is defined as

For each fixed position obtained in the function of the depth Ngl of the diagrams α _SLE and α _naz, the correlation coefficient R (α _SLE ; α _naz ) is calculated. The deep and lithological-stratigraphic binding of the diagrams of α _well and α _{naz is} carried out according to the position on the depth axis Ngl, for which the correlation coefficient R has a maximum value.

The correlation coefficient is estimated as follows:

а коэффициент пористости оценивается с помощью зависимости W_P/W_S=a_K+m_KK_п, где a_R; a_K точки пересечения зависимостей W_P/W_S и W_S/W_P с осью ординат;For sections of the geological section, characterized by the corresponding identical (with a spread of ± 5%) values of the correlation coefficients R for the desired reservoir layers, the nature of saturation is determined by the frequency dependence of the ratio

and the porosity coefficient is estimated using the dependence W _P / W _S = a _K + m _K K _p where a _R ; a _{K are} the intersection points of the dependences W _P / W _S and W _S / W _P with the ordinate axis;

m _R ; W _K - angular coefficients.

From the outputs of blocks 11, 12, 14, 15, 18, 21, the signals are fed to the inputs of the block 22 of the visualization and display of information, where they are spatially-temporally linked.

As an example, figure 2 and figure 3 shows graphs for determining the coefficient of porosity and oil and gas saturation of productive horizons, constructed according to the dependencies W _P / W _S and W _S / W _P , in one of the search areas of the Orenburg oil and gas region.

The advantages of the proposed method in comparison with the known ones are that it allows one to predict with high efficiency the oil and gas content of multilevel deposits laterally and before drilling the productive horizons below the slaughter. The method allows to separately contour and determine the spatial position and the filtration and reservoir properties of the studied productive deposits with a high degree of detail in depth, reaching 0.1-0.5 m, which makes it possible to optimize the choice of location and profiles of exploration and production wells.

Moreover, the restoration of three-dimensional images of oil and gas deposits using spectral-correlation reception and control of the spectrum and radiation pattern of the source of excitation of elastic vibrations significantly increase the accuracy, noise immunity and resolution of the method.

Claims (2)

1. The method of prospecting and exploration of oil and gas fields, including multiple excitation and registration of elastic vibrations on the earth's surface in the seismic frequency range, registration of the natural seismic background in the infra-low range and subsequent comparison of the obtained data, characterized in that, in order to improve the accuracy of predicting the spatial position, geometrical dimensions, reservoir properties and the nature of saturation of geological objects in the process of opening the interval of geological fracture behind the control well, additionally periodic excitation of elastic vibrations at internal points of the medium in the seismic frequency range of 10-1000 Hz, coordinated in time with radiation on the earth's surface, is carried out, the wave field of the induced seismic emission in the range of 0.1-1 Hz is recorded on the earth's surface simultaneously with receiving elastic vibrations in the upper part of the drill string, after opening the interval of the geological section, the natural seismic-acoustic background is recorded at internal points medium in the high-frequency range of 1–50 kHz, after which elastic vibrations inside and outside the drill string are excited at the same points in the frequency range of 1–50 kHz and the induced acoustic emission is recorded, and the measured spectral densities of longitudinal and transverse elastic vibrations are summarized and compared in the restored amplitude-frequency characteristics of the medium 0.1 Hz ÷ 50 kHz and the ratio of the spectral densities of longitudinal and transverse vibrations as a function of well depth and their correlation with the ratio of spectral lotnostey vibrations reflected laterally and below the bottom of the well determine the spatial position, the depth, the saturation nature and reservoir properties of the oil and gas deposits. 2. The method according to claim 1, characterized in that after the restoration of the frequency response of the medium as a correlated signal during extrapolation along the lateral and below the bottom of the control well, the values of spectral densities and correlation functions of longitudinal and transverse elastic vibrations recorded at internal points of the geological environment are used, an open control well, or in the upper part of the drill string at depths corresponding to reflecting seismic boundaries.

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