SU1053044A1 - Method of electromagnetic wave logging - Google Patents

Abstract

1. METHOD OF WAVE ELECTRICAL TIRAGETIC CARROLL, including the excitation of a high-frequency electromagnetic field at ONE point of the axial hole of the well and its reception at one or several other points on the axis of the well, far from the excitation point for a distance longer than the wavelength of the signal, amplitude measurement. and phases of received signals and computations. using them, the electrical conductivity and dielectric constant of rocks intersected by the borehole differ by 14 so that, in order to increase the reliability and accuracy of measurements of the electrical parameters of the rocks, the excitation signal is modulated in frequency, the correlated functions of the received and excited signals and / or received signals among themselves, separate the maximum values of the calculated cross-correlation functions corresponding to the signals propagating over the rock, determine: these parameters signals and uses them to calculate electrical parameters of breeds. 2, the method according to claim 1, from which the reception points are removed from the excitation point so that the transit time of the head and refracted waves over the rock is less than the propagation time t of all other types of waves between point (lm of excitation and reception. 3. The method according to claim 1, which is also distinguished by the fact that the frequency of the excited electromagnetic field varies linearly with the pick-up period of the NIN cycles not longer than the time of movement of the excitation and reception points on the interval is equal to the minimum wavelength of the excited field in the medium. t: o about 4 4

Description

The invention relates to field geophysics, and more specifically to electromagnetic methods for the study of oil and gas wells. Electromagnetic well logging methods are known that provide for a relatively low frequency (in the 10100 kHz range) harmonic electromagnetic field at a point on the I-well axis and for receiving a signal induced by it at one or several other points on the well axis that are remote from the point of excitation, shorter wavelengths of the electromagnetic signal, measuring the amplitude of the received signals and calculating the specific electrical conductivity of rocks with the introduction of corrections for the effect of the conductivity of the liquid in the station the will of the well one way or another 1. The disadvantage of these methods is ow. It is impossible to separate with them the oil-and-gas-saturated rocks and the rocks saturated with fresh water, since the conductivity of fresh water differs little from the conductivity of hydrocarbons. The closest to the invention is a wave electromagnetic logging method, which provides for a wake-up excitation of a high-frequency (in the range of 1-100 MHz) electromagnetic field at one point on the well axis and its reception at one or several other points on the borehole a distance greater than the wavelength of the field, measuring the amplitude and phase of the received signals and calculating from them the specific electrical conductivity and dielectric constant of rocks intersected by the well. To reduce the effect of produce a borehole and filling fluid with an experimental selection of the frequency of the excited signal and the distance between the points of excitation and reception. Since the dielectric constant of water depends little on its mineralization and differs significantly from the dielectric constant of oil and gas, this method in principle provides for the separation of water and oil-saturated tegazonasirovannyh rocks regardless of the mineralization of formation water 2,. However, the results obtained when using the known method in practice are quite unambiguous, since the measured values of dielectric constant and specific electrical conductivity for water and oil and gas saturated rocks overlap so much especially especially in the case of thin layers and well diameter, which distinguish water and oil and gas saturated rocks by these parameters is impossible. The aim of the invention is to increase the reliability and accuracy of measuring the electrical parameters of rocks. The goal is achieved according to the wave electromagnetic logging method, which includes the excitation of a high-frequency electromagnetic field at one point on the well axis and its reception at one or several other points on the well axis, which are more distant from the excitation point on the distance the amplitudes and phases of the received signals, and the calculation by them of the specific electrical conductivity and dielectric constant of rocks intersected by the well, the excited signal modulate the frequency, num dissolved crosscorrelation function of the received signal and excited and / or received signals between .soboy isolated maximum values calculated. The correlation functions corresponding to the signals propagating along the rock determine the parameters of these signals and use them to calculate the electrical parameters of the rocks. Moreover, the points n {the distance is removed from the point of excitation so that the time of passage of the head or refracted waves over the rock is less than the time of propagation of all other types of waves between the points of excitation and reception. . In addition, the frequency of the electromagnetic field excited is changed by. linear law with a repetition period of cycles, not longer than the time of moving the excitation points and receiving for an interval equal to the minimum wavelength of the excited field in the medium. :,. . Practically, with proper selection of the removal of the receiving point from the exact excitation, it is always possible to ensure that the forward, head or refracted wave propagating over the rock reaches the reception point before the wave propagating at a lower velocity through the fluid in the wellbore (which always has a higher dielectric constant and, consequently, a slower rate of propagation of electromagnetic waves than rocks), and especially earlier waves that have undergone multiple reflections at the boundaries of the layers and the wall wells. The proposed method performs time selection of the useful wave, while in the known methods a complex total signal is recorded, due to the entire aggregate

of various types of waves reaching the receiver, which, depending on the geometry and electrical properties of the section and well, may differ significantly from the useful signal induced by the wave passing through the rock.

Figure 1 shows the block diagram of aiC | napaTyi fci; allowing to implement the proposed method, option) in FIG. Figures 2-7 show his work.

The method is carried out as follows.

At a given point on the axis of the well, a high-frequency electric electromagnetic signal is excited (for example, using a coil / powered by alternating current), the frequency of which is periodically changed within certain limits, for example, in the range from 10-20 to 60-100 MHz in 10-100 μs. At one or several other points on the well axis, which are remote from the point of excitation by a distance substantially greater than the wavelength of the signal in the medium, for example, at points that are at a distance of 0.7 and 1 m from the point of excitation, receive an excited signal, for example, also with. using coils and amplify it for ease of further operation and transmission; With the help of an analog or digital device, the functions of mutual correlation of each of the received signals with excited and / or with each other are calculated. Then, the maximum values of the mutual correlation functions are selected, the corresponding ones. in the wave propagating through the rocks (for example, the first maximum exceeding a given threshold level)

The amplitude of the wave propagating over the rock is determined by the measured value of the maximum of the cross-correlation function, and its phase shift is determined by the value of the time shift at; 1 this and the excited signals corresponding to MciK to the maximum value of the cross-correlation function for each point .. reception. The attenuation and relative phase shift of the wave propagating through the rock are calculated between the receiving points and calculated from these values; dielectric constant and electrical specificity of contiguous rocks; KOTOptm considers the nature of the fluid in the porous space of the rock. .

For the implementation of the method, it is possible to use conventional wave dielectric carote A equipment, subjected to some modifications of the emitting Kaxjaa,

ki perform frequency controlled and receive channels (coils and amplifiers) with relatively broadband; The processing circuits incorporate blocks for calculating the functions of mutual correlation and extracting its maximum quantities corresponding to the wave propagating predominantly over the rock.

Such apparatus includes (figure 1)

0 robust dielectric case 1, emitting coil 2, its exciter (generator) 3j block 4 controlling frequency, wideband receiving coils 5 and 6, amplifiers 7 and 8,

5 telemetry scheme 9, which provides a signal from the outputs of amplifiers 7 and 8 and the reference signal from the output of the exciter 3 to the surface via high-frequency coaxial or

0 light guide 10, teleme.retime receiver circuit 11, which provides for the separation of transmitted signals, blocks 12 and 13 of the calculation of the cross-correlation functions, maxi-selection blocks. the cross-correlation functions corresponding to the head or refracted wave propagating over the rock, and determining their parameters — amplitudes and phases 14 and 15;

0, blocks 16 and 17 for calculating the amplitude ratio (attenuation) and relative to the phase shift, respectively, and block 18 for calculating the dielectric constant and the specific electrical conductivity of the rocks.

The signal emitted by the radiating coil 3 (FIG. 4), frequency-modulated by the signal of block 4 (FIG. 3), propagates in several different ways (dashed lines in FIG. 1) corresponding to different types of waves (head or refracted in rock , repeatedly reflected from the walls of the well and the device core, etc.), and a 5 nb coil is received in the form of several delayed and strongly distorted signals shown in fng "4 and 5. After amplification with amplifiers 7 and 8 and transfer to the surface of these signish

0 are subject to cross-correlation in blocks 12 and 13 with an excited signal, resulting in signals corresponding to the cross-correlation functions shown in FIG. b and 7, according to which the parameters (the amplitude of the unnormalized value and the time shift) of the maxima corresponding to the wave propagating over the rock (maxima A || and A2 in Figs. 7 and 7) are determined. These parameters determine in blocks 16 and 17 the attenuation and relative phase shift of the signals between the receiving coils 5 and b, and in block 18

5, a calculation is performed using the known

formulas of electrical conductivity and dielectric constant of rocks.

With moderate requirements to the thermal stability of the equipment, it is advisable to place most of the circuits in the upstream part of the equipment, which allows information to be transmitted via conventional logging cables. In the presence of high-speed converters analog - code, all processing can be performed on a computer.

The use of the proposed wave electromagnetic logging method makes it possible to drastically improve the reliability and accuracy of measuring the electrical properties of rocks and, on this basis, the reliability of determining the nature of reservoir saturation, especially when they are flooded with fresh water, which plays a very important role in the study of wells in the fields operated using various water flooding systems.

AND.

FIG. 2

Fsh

Fu four

OLAALLL / / / l

Fig.b

Claims (3)

1. METHOD OF WAVE ELECTRIC - V | MAGNETIC LOGGING ;; including the excitation of a high-frequency electromagnetic field at one point on the axis of the well and its reception at one or more other points on the axis of the well, remote from the point of excitation at a distance greater than the wavelength of the signal, measuring the amplitude. ' and the phases of the received signals and of them electrical conductivity and permittivity rock intersected borehole, characterized in that, in order to increase the reliability and accuracy of the measurements of electric parameters of breeds my excite signal is modulated in frequency, is calculated mutual correlation function ¹ tion received and excited signals and / or received signals between each other ', the maximum values of the calculated cross-correlation functions corresponding to the signals propagating throughout the breed are extracted, the parameters of these signals are determined and in. · uses them to calculate electrical parameters of breeds. 2, the Method according to claim 1, with the fact that the reception points are removed from the excitation point so that the travel time of the head or the refracted waves through the rock has _a shorter propagation time] of injuries other types of waves between the point: mi excitation and reception. 3. The method according to claim 1, with respect to the fact that the frequency of the excited electromagnetic field is changed according to the linear law c. the period of the repetition of the cycles is not greater than the time of movement of the points of excitation and reception by an interval equal to the minimum wavelength of the excited field in the medium. > 1 * - 1053044