RU2012018C1 - Acoustic logging method - Google Patents

Abstract

FIELD: geophysical testing of wells. SUBSTANCE: probing acoustic pulses are modulated by pseudorandom periodical sequence. In this case at least one period of pseudorandom periodic sequence is radiated. This period consists of single acoustic pulses which have initial phases of 0 and K=(q⁽²ⁿ⁺¹⁾-1)/(q-1),, as well as misses of radiation. Number of single acoustic pulses and radiation misses in the sequence period are set to be equal to K₊=(q²ⁿ+qⁿ)/2,, K_-=(q²ⁿ-qⁿ)/2, π, where K is general number of single acoustic pulses with initial phases 0 and p and misses of radiation in sequence period; K is number of single acoustic pulses with initial phase to be equal to 0; K is the number of single acoustic pulses with initial phase q=p^m, p is a prime number, m and n are natural numbers. Durations of radiation misses and time intervals, at which acoustic pulses have to be radiated, are equal. Law of single acoustic pulses and radiation misses sequence in the period of the sequence are set in such a manner, that periodic autocorrelation function of modulating sequence could not have non-zero lobes during the whole period. Correlation of the signals being received are performed with the same period of modulating sequence, moreover, signals are selected in M+2 time intervals, where M is number of periods in sequence radiated. Duration of any time interval is equal to period of the sequence. Selected signals are synchronously stored during the time interval being equal to the duration of medium response under testing. EFFECT: improved precision of testing. 2 cl, 2 dwg, 2 tbl

Description

 The invention relates to geophysical methods for researching wells, in particular to methods of acoustic logging.

 A known method of acoustic logging of wells, in which with continuous movement of the downhole tool and periodic excitation of the emitters, the converted signals of each package are summed with the signals stored in the random access memory of several previous packages, and after the accumulation of a given number of packages is completed, the total signal is recorded on a magnetic medium [1 ].

 A disadvantage of the known method of acoustic well logging is the low productivity of logging operations due to the low frequency of sending sounding acoustic signals.

 Also known is a method of acoustic logging of wells, consisting in the continuous movement of the downhole tool and periodically exciting emitters, receiving signals and summing the signals of several packages, while increasing the frequency of the probe pulses, modulating them in phase with a binary pseudorandom periodic sequence, the received signals of each package are subjected to a synchronous phase demodulations using the same sequence and summarize them with each other within its period [2].

 The disadvantage of this method of acoustic well logging is the lack of complete suppression of correlation noise, since they are determined by the level of the side lobes of the periodic autocorrelation function of the emitted sequence.

 The closest in technical essence to the claimed object is the method of acoustic logging, which consists in the fact that the modulation of the probing signals is carried out within at least three periods by a modulating M-sequence, followed by additional excitation in the test medium of a sequence of acoustic pulses with zero initial phase through a time interval not less than the period of the M-sequence. Moreover, the duration of the excited sequence is equal to no less than two periods of the modulating M-sequence. The amplitude of the acoustic pulses is equal to the amplitude of the probing signals, and the repetition rate of the acoustic pulses is equal to the repetition rate of the pulses in the M-sequence. Then, the received additionally excited signals are converted into a digital code and summed with the result of the correlation processing of the signals of the previous packages [3].

 A disadvantage of the known method of acoustic logging is the low productivity of logging operations and the incomplete use of the energy of the emitted signals when they are extracted, which leads to a decrease in the signal / random noise ratio.

 The aim of the invention is to increase productivity by increasing the speed of logging.

The goal is achieved due to the fact that in the acoustic logging method based on the continuous movement of the downhole tool and periodically sending probing signals in the form of acoustic pulses modulated by a pseudorandom periodic sequence to the test medium, correlation processing of the received signals, the following differences are provided: radiation of at least one pseudorandom period periodic sequence, the period of which consists of single acoustic pulses with initial phase mi O and π and radiation gaps; the number of unit acoustic pulses and gaps in the period of the sequence is set equal to
K = (q ^{(2n + 1)} -1) / (q-1), K ₊ = (q ²ⁿ + q ⁿ ) / 2, K _- = (q ^2n- q ⁿ ) / 2, where K is the total number single acoustic pulses with initial phases O and π and radiation gaps; K ₊ is the number of unit acoustic pulses with an initial phase O; K _- is the number of unit acoustic pulses with an initial phase π; q = p ^m , p is a prime number; n and m are natural numbers; the duration of the radiation pass and the time interval over which a single acoustic pulse is emitted are set equal; the law of succession of single acoustic pulses and gaps in the period of the sequence is formed so that the periodic autocorrelation function of the modulating sequence does not contain non-zero side lobes throughout the period; correlate the received signals with one period of the modulating sequence, while allocating signals at M + 2, where M is the number of periods in the emitted sequence, time intervals, each of which is equal in duration to the period of the sequence, and synchronously accumulate them in a time interval equal to the duration investigated response environment.

 In addition, the proposed method is characterized in that the law of succession of single acoustic pulses and radiation gaps during the sequence period is formed by generating a linear recurrent pseudorandom sequence of numbers, converting numbers that are quadratic residues into unit acoustic pulses with an initial phase O, numbers that are quadratic residues, into unit acoustic pulses with an initial phase π, and numbers zero - into excitation gaps.

 Thus, the presence in the claimed method of acoustic logging of distinctive features from the prototype allows us to conclude that it meets the criterion of "novelty."

 When studying other well-known technical solutions in this technical field, signs that distinguish the claimed technical solution from the prototype were not identified, and therefore we can conclude that the claimed object meets the criterion of "significant differences".

 The achievement of a positive effect in the implementation of the proposed method is ensured by the choice of the structure of the emitted signals, characterized by the absence of correlation noise during the separation of signals and an increase in the amount of energy used to separate the signals, since signals caused by the complete emission of the sequence are recorded and processed.

To ensure that no or a minimum level of noise correlation in the allocation signals during the period radiated sequence set the total number K of single acoustic pulses and the radiation passes, the number of K ₊ acoustic pulses with the initial phase and the number of O K _- - with the initial phase equal to π acoustic pulses:
K = (q ^{(2n + 1)} -1) / (q-1), K ₊ = (q ²ⁿ + q ⁿ ) / 2, K _- = (q ^2n- q ⁿ ) / 2, (1) for q = p ^m ; p is a prime number; n and m are natural numbers.

To obtain the structure of periods of sequences with ideal periodic autocorrelation functions, the following actions are performed: in the final Galois field GF (q) find an irreducible polynomial of the form
x ³ - ax ² - bx - c = 0. (2) To do this, you can use the tables of irreducible polynomials given, for example, in: Gill A. Linear sequential machines. M.: Science, 1974, p. 263-276, tab. II 4; based on the selected irreducible polynomial of the form (2) for a given q, the corresponding recurrence equation is constructed
S _j = a ˙ S _j-1 + b ˙ S _j-2 + c ˙ S _j-3 , (3) where S _j , S _j-1 , S _j-2 , S _j-3 are calculated and preceding time elements. To calculate the elements of a sequence, the values of its initial conditions are set, for example, S _j-3 = S _j-2 = 0, S _j-1 = 1.

The construction of recurrence equations on the basis of irreducible polynomials is described in a number of works, for example, N. Zirler. Linear return sequences. - In the book. : Cybernetic collection. M.: Publishing house of foreign countries. lit. , 1963, no. 6, p. 55-79; based on the recurrence equation (3) form a q-ary pseudo-random sequence of numbers; from the q-ary pseudo-random sequence of numbers {S _j } thus obtained, the sequence {α _j } is formed, consisting of the symbols -1, 0, +1 and having an ideal periodic autocorrelation function.

(4) где α_j - j-й элемент формируемой последовательности,
j = 0,

,
Ψ (S_j) - индекс числа S_j, устанавливаемый на основании теоремы о квадратичных вычетах (см. , например, Варакин Л. Е. Теория сложных сигналов. М. : Советское радио, 1970, с. 238-239, где показано, что квадратичные вычеты определяются из тождества x²≡ S_j(mod q), при этом значения S_j, при которых сравнение x²≡ S_j имеет решения, называются квадратичными вычетами и им присваивается символ +1, а значения S_j, при которых сравнение не имеет решений, называются квадратичными невычетами и им присваивается значение -1). Индексы чисел приведены в ряде работ, например. Виноградов И. М. Основы теории чисел. М. : Наука, 1981, с. 176; для подтверждения идеальности периодической автокорреляционной функции, полученного периода последовательности, состоящего из символов +1, 0, -1, проверяют выполнение соотношений (1).To do this, apply the rule:
α _j =

(4) where α _j is the jth element of the generated sequence,
j = 0,

,
Ψ (S _j ) is the index of the number S _j established on the basis of the quadratic residue theorem (see, for example, L. Varakin, Theory of Complex Signals. M.: Soviet Radio, 1970, pp. 238-239, where that quadratic residues are determined from the identity x ² ≡ S _j (mod q), while the values of S _j for which the comparison x ² ≡ S _j has solutions are called quadratic residues and they are assigned the symbol +1, and the values of S _j , for which the comparison has no solutions, they are called quadratic residues and they are assigned the value -1). Indexes of numbers are given in a number of works, for example. Vinogradov I. M. Fundamentals of number theory. M.: Science, 1981, p. 176; to confirm the ideality of the periodic autocorrelation function, the obtained period of the sequence, consisting of symbols +1, 0, -1, check the fulfillment of relations (1).

(5)
Анализ решающих правил (4) и (5) показывает их идентичность, отличие состоит в том, что при использовании решающего правила (5) символы, находящиеся на нечетных позициях в сформированной последовательности, инвертируются по знаку, то есть символ +1 заменяется на -1, а символ -1 заменяется на +1.If the calculated number of characters +1, -1 and 0 according to formulas (1) and the generated number of characters according to rule (4) coincide, the process of forming the sequence period is completed. By calculating the periodic autocorrelation function of a sequence, its ideality can be confirmed; if, in the generated period of the sequence, the calculated, according to (1), the number of characters +1, -1, 0 does not coincide with the values of the number of characters +1, -1, 0 in the period of the sequence generated by rule (4), then instead rules for the formation of a sequence period apply the following rule:

(5)
The analysis of decision rules (4) and (5) shows their identity, the difference is that when using decision rule (5), characters located at odd positions in the generated sequence are inverted by sign, that is, the +1 symbol is replaced by -1 , and -1 is replaced by +1.

 After that, as in the case of using rule (4), check the estimated number of characters +1, -1, 0 in the sequence period using formulas (1) and the generated number of elements +1, -1, 0 in the period of the sequence based on the decisive rules (5) and when they coincide, by calculating the periodic autocorrelation function of the sequence confirm its ideality.

a_i·a_i+k=

На основании изложенного в табл. 1 даны примеры периодов последовательностей с идеальной структурой для К = 13, 31 и 57.Thus, the generated sequence according to the rules (4) or (5) has an ideal periodic autocorrelation function, which can be written in mathematical form
R _k =

a _i · a _{i + k} =

Based on the above table. Table 1 gives examples of periods of sequences with an ideal structure for K = 13, 31, and 57.

. В приведенных примерах последовательности { α_j} получены из последовательностей { S_j} для q = 3 и q = 7 (К = 13 и К = 57) по правилу (4), а для q = 5 (К = 31) - по правилу (5). При этом использовались следующие замены ненулевых чисел Sj символами +1 и -1: для q = 3 Ψ (1) = 1; Ψ (2) = -1; для q = 5 Ψ (1) = Ψ (4) = 1, Ψ (2) = Ψ (3) = -1; для q = 7 Ψ (1) = Ψ (2) = Ψ (4) = 1, Ψ(3) = Ψ (5) = Ψ (6) = -1.In the table. 1 characters - 1 sequences {α _j } are marked with a dash for ease of writing

. In the above examples, the sequences {α _j } were obtained from the sequences {S _j } for q = 3 and q = 7 (K = 13 and K = 57) according to rule (4), and for q = 5 (K = 31) - from rule (5). The following replacements of nonzero numbers Sj with the symbols +1 and -1 were used: for q = 3 q (1) = 1; Ψ (2) = -1; for q = 5 Ψ (1) = Ψ (4) = 1, Ψ (2) = Ψ (3) = -1; for q = 7 Ψ (1) = Ψ (2) = Ψ (4) = 1, Ψ (3) = Ψ (5) = Ψ (6) = -1.

 The analysis shows that the tab. 1 sequences have an ideal periodic autocorrelation function.

 In FIG. 1 is a structural diagram of a device for implementing the method; in FIG. 2 is a timing chart illustrating the method.

 The device (Fig. 1) contains a clock generator 1, a pseudo-random periodic sequence generator 2, a driver 3 pulses, a transmitter 4, a receiver 5, an analog-to-digital converter 6, a multiplier 7, an adder 8, and random access memory (RAM) 9.

 In FIG. 2 shows signals 10 at the output of a clock generator, signals 11 at the output of a clock generator of a pseudo-random periodic sequence, signals 12 at the output of the emitter, radiation passes 13, a single delta-shaped pulse 14 corresponding to the +1 symbol, a single delta-shaped pulse 15 corresponding to the -1 symbol, a single an acoustic pulse 16 with an initial phase O and a single acoustic pulse 17 with an initial phase π.

 To implement the method, well-known means are used, for example, as a clock generator 1, a highly stable pulse generator is used, the frequency of which is determined by a quartz element, the pseudo-random periodic sequence generator 2 is made by a. with. USSR N 1499437, class H 03 K 3/64, the driver of 3 pulses of the excitation of the emitter is made according to the scheme of the site of pulsed radiation (Ivakin B.N. et al. Acoustic method for researching wells. M.: Nedra, 1978, pp. 144-145), in which the bridge a circuit of discharge thyristors, which allows you to manipulate the phase of the discharge current to the emitter 4, which is used as a magnetostrictive transducer or spark spark gap. Well-known elements are used as a receiver 5, an analog-to-digital converter 6, a multiplier 7, an adder 8, and a random access memory 9.

, где F - ширина спектра единичного акустического сигнала, а также скоростью заряда накопительного конденсатора формирователя 3 импульсов возбуждения излучателя. Практически Δτ выбирают в пределах 0,5-10 мс, за это время накопления энергия в формирователе 3 полностью преобразовывается излучателем 4 в упругие колебания и накопительный конденсатор формирователя 3 успеет зарядиться.The method is as follows. The clock generator 1 generates a continuous sequence of pulses, the repetition rate (1 / Δτ) of which determines the frequency of sending sounding acoustic pulses and radiation passes. The choice of Δτ is determined based on the condition Δτ ≫

where F is the width of the spectrum of a single acoustic signal, as well as the charge rate of the storage capacitor of the shaper 3 pulses of excitation of the emitter. In practice, Δτ is chosen in the range of 0.5-10 ms, during this accumulation time the energy in the shaper 3 is completely converted by the emitter 4 into elastic vibrations and the storage capacitor of the shaper 3 has time to charge.

N= (q⁽²ⁿ⁺¹⁾-1)/(q-1), где q = p^m; p - простое число; m и n - натуральные числа. При этом число символов +1 равно K₊= (q²ⁿ+qⁿ)/2 , число символов -1 равно K_-= (q²ⁿ-qⁿ)/2, а число символов 0 равно К_о = К - К₊ - К_-. При выборе числа символов в периоде последовательности необходимо учитывать, что увеличение q дает возможность получать периоды большей длины при одновременном уменьшении числа символов О в периоде последовательности. Структура периода последовательности определяется рекуррентным уравнением (3), полученным на основании неприводимого полинома вида (2). При этом закон следования единичных акустических импульсов и пропусков излучения в периоде последовательности формируют путем генерирования линейной псевдослучайной рекуррентной последовательности чисел, преобразования чисел, которые являются квадратичными вычетами, в единичные акустические импульсы с начальной фазой О, чисел, которые являются квадратичными невычетами, в единичные акустические импульсы с начальной фазой π, а чисел нуль - в пропуски излучения. Устанавливают длительности пропусков излучения и временные интервалы, на которых излучают единичные акустические импульсы равными между собой. Общая длительность псевдослучайной периодической последовательности, т. е. число периодов последовательности, определяется из необходимой энергии излучения для получения заданного отношения сигнал/шум.Clock pulses are fed to the input of the generator 2 of a pseudo-random periodic sequence. The period of the sequence generated by it is equal to τ, and the pulse repetition rate and gaps is equal to 1 / Δτ. Moreover, the total duration of the generated pseudo-random periodic sequence is equal to M periods, where M is a natural number. The duration of the pseudo-random sequence period is determined from the condition τ ≥ τ and _o , where τ and _o are the duration of the studied response of the medium. To ensure the absence of interference (correlation) interference, the duration of the pseudo-random sequence should be longer than the maximum duration of the total acoustic signal recorded per one probe acoustic pulse. Based on the specified in this way, τ, Δτ, τ and _o , determine the possible minimum number of characters in the sequence period, equal to the integer part of the ratio τ / Δτ, and based on it select the required number of characters in the sequence by the formula

N = (q ^{(2n + 1)} -1) / (q-1), where q = p ^m ; p is a prime number; m and n are natural numbers. The number of characters +1 is K ₊ = (q ²ⁿ + q ⁿ ) / 2, the number of characters -1 is K _- = (q ^2n- q ⁿ ) / 2, and the number of characters 0 is K _o = K - K ₊ - To _- . When choosing the number of characters in a sequence period, it must be taken into account that an increase in q makes it possible to obtain periods of longer length while reducing the number of O symbols in the sequence period. The structure of the sequence period is determined by the recurrence equation (3) obtained on the basis of an irreducible polynomial of the form (2). Moreover, the law of succession of single acoustic pulses and gaps in the period of the sequence is formed by generating a linear pseudorandom recurrent sequence of numbers, converting numbers that are quadratic residues into unit acoustic pulses with an initial phase O, numbers that are quadratic residues, into unit acoustic pulses with the initial phase π, and the numbers zero - in the transmission of radiation. Set the duration of the omissions and the time intervals at which emit single acoustic pulses equal to each other. The total duration of the pseudo-random periodic sequence, i.e. the number of periods of the sequence, is determined from the necessary radiation energy to obtain a given signal-to-noise ratio.

 Delta-shaped single pulses of positive (symbol +1) and negative (symbol -1) polarity are supplied to the driver 3 of the excitation pulses of the emitter, in which they cause the formation of pulses supplied to the emitter 4. As a result, the emitter 4 will be excited by acoustic pulses with an initial phase O and π depending on the modulating pseudo-random periodic sequence coming from the generator 2.

 A downhole tool with an emitter and a receiver is continuously moving and periodically sending probing signals to the test medium in the form of acoustic pulses modulated by a pseudorandom periodic sequence.

The acoustic signals that passed through the rocks are fed to the receiver 5 and converted into electric ones, after which they are converted in the analog-to-digital converter 6 into a digital code. After that, the received acoustic signals are correlated over a time interval equal to the sum of the duration of the emitted M periods of the pseudo-random sequence, where M is the natural number of the investigated medium response τ and _o with one period of the modulating pseudo-random periodic sequence. After the correlation is performed, the signals are extracted at M + 2, where M is the number of periods in the emitted sequence, time intervals, each of which is equal in duration to the period of the sequence, and synchronously they are accumulated over a time interval equal to the duration of the studied medium response.

 In this case, in the multiplier 7, during the correlation processing, an operation of synchronous phase demodulation of the signal in analog form is performed. The proposed method for the synchronous accumulation of selected signals at M + 2 intervals with a length of a period eliminates correlation noises that complicate useful signals without loss of excited energy. In known methods of acoustic logging, the energy of the extreme periods of sequences is lost in order to eliminate correlation noise. This defect is eliminated in the claimed facility.

 PRI me R. The example in question is illustrated by the timing diagrams shown in FIG. 2. In the considered variant of the method, a pseudo-random sequence consisting of one period containing 13 characters is emitted.

The clock generator 1 generates a continuous sequence of 10 pulses, the pulse repetition rate 1 / Δτ of which determines the frequency of sending acoustic pulses and radiation passes. The parameters Δτ are chosen as described above. Clock pulses 10 arrive at the input of a pseudo-random periodic sequence generator 2, the period of the sequence generated by it consists of 13 delta-shaped pulses with initial phases O and π and gaps, and the pulse repetition rate and gaps are equal to 1 / Δτ. To generate such a period of the pseudo-random sequence with q = 3, an irreducible polynomial of the form X ³ + 2X + 2 is chosen in the Galois field GF (q). Based on it, the recurrence equation S _j = S _j-2 + S _{j-3 is} obtained. Then, under the initial conditions S _j-3 = S _j-2 = 0, S _j-1 = 1, the following period of the pseudo-random sequence of numbers 0 0 1 0 1 1 1 2 2 0 1 2 1. will be formed. Since for q = 3 the number 1 is a quadratic residue, and the number 2 is a quadratic residue, the indicated number sequence can be converted to the following sequence of characters 0 0 1 0 1 1 1 -1 -1 0 1 -1 1. The indicated values of the characters are encoded and stored in the memory of generator 2, which forms one period of the sequence 11, consisting of 6 delta-shaped unit positive pulses 14, 3 delta-shaped single negative pulses 15 and 4 radiation passes 13, which corresponds to the calculated values according to formulas (1). The periodic autocorrelation function of such a sequence is. . . 9,000,000,000,000 9.. . That is, it does not have side lobes. The radiation time of the period of such a sequence should exceed the duration of the studied response of the medium. The pulse sequence 11 from the generator 2 is supplied to the driver 3 of the emitter excitation pulses, where powerful current pulses of the corresponding polarity are generated, supplied to the emitter 4, which generates in the medium a sequence of 12 acoustic pulses modulated in phase by the sequence 11. As a result, the emitter is generated in the generated sequence 12 4 will contain 4 radiation passes 13, 6 unit acoustic pulses 16 with an initial phase O corresponding to unit positive delta-shaped pulses 14, 3 single acoustic pulses 17 with an initial phase π corresponding to a single negative delta-shaped pulses 15. Set the duration of each radiation pass 13 equal to the duration of the time interval in which an acoustic pulse with an initial phase of O or π is excited.

 The downhole tool with the emitter and receiver is continuously moved and periodically send probing signals to the test medium in the form of acoustic pulses modulated by a pseudorandom periodic sequence 11.

,

,

,

,

, где черта сверху над Х означает инвертирование полярности. Здесь для простоты отсчеты отклика среды задаются через временные интервалы, соответствующие временным интервалам следования акустических импульсов и пропусков излучения, то есть равными Δτ. В табл. 2 приведен зарегистрированный приемником 5 сигнал на возбуждение последовательности 12.The acoustic signals that passed through the rocks are fed to the receiver 5 and converted into electric ones, after which they are converted in the analog-to-digital converter 6 into a digital code. After that, the received acoustic signals are correlated over a time interval equal to the sum of the duration of the emitted period of the pseudo-random periodic sequence and the investigated response of the medium τ _io with the period of the pseudo-random periodic sequence 11. Suppose that a single acoustic pulse 16 with the initial phase O causes a response of the medium X ₁ , X ₂ , X ₃ , X ₄ , X ₅ , and a single acoustic pulse 17 with an initial phase π causes a response from the medium

,

,

,

,

where the bar above X means inverting polarity. Here, for simplicity, the samples of the response of the medium are set at time intervals corresponding to the time intervals of the repetition of acoustic pulses and transmission gaps, that is, equal to Δτ. In the table. 2 shows the signal registered by the receiver 5 for the excitation of the sequence 12.

+ Х₅;

; 0;

; Х₁ +

), а на остальных отсчетах - корреляционные шумы. Сложение (накопление) сигналов на отсчетах 38, 0. . . 11 и 12. . . 24 и 25. . . 37 позволяет выделить полезный сигнал, не осложненный корреляционными шумами, а именно 9Х₁, 9Х₂, 9Х₃, 9Х₄, 9Х₅. Этот сигнал соответствует полной возбужденной энергии в последовательности (9 единичным акустическим импульсам) и не содержит корреляционных шумов.As a result of correlation between the registered signal by the receiver 5 (Table 2) and the pulse sequence 11 modulating the excited signal, a correlation conversion signal is obtained. Moreover, on the counts 12.. . 16 contains a useful signal complicated by correlation noise (

+ X ₅ ;

; 0;

; X ₁ +

), and in the remaining samples - correlation noises. Addition (accumulation) of signals at samples 38, 0.. . 11 and 12.. . 24 and 25.. . 37 allows you to select a useful signal, not complicated by correlation noise, namely 9X ₁ , 9X ₂ , 9X ₃ , 9X ₄ , 9X ₅ . This signal corresponds to the total excited energy in the sequence (9 unit acoustic pulses) and does not contain correlation noises.

 The proposed method of acoustic logging in comparison with the prototype allows to increase the productivity of logging by reducing the number of excited sequences and using all periods of the emitted sequence during correlation processing, this simultaneously allows to improve the ratio of signal to random noise.

 The proposed method can also find application in interwell sounding when using a powerful emitter built, for example, on the electromechanical principle.

Claims (2)

1. ACOUSTIC LOGGING METHOD based on the continuous movement of the downhole tool, periodically sending probing signals into the test medium in the form of acoustic pulses with initial phases 0 and π modulated by a pseudorandom periodic sequence, and correlation processing of the received signals, characterized in that, in order to increase signal-to-noise ratios emit a pseudo-random sequence of unit acoustic pulses into the medium under study, into which additional emission gaps are introduced In its period set unit number of acoustic pulses and the radiation passes equal
(q ^{2n + 1} - 1) / (q - 1),
and the number of unit acoustic pulses with an initial phase of 0 and π are respectively equal to (q ²ⁿ + q ⁿ ) / 2 and (q ^2h - q ⁿ ) / 2, where q = p ^m ;
p is a prime number;
m and n are natural numbers,
at the same time, a recursive pseudorandom sequence of numbers is generated, numbers corresponding to quadratic residues are converted into unit acoustic pulses with an initial phase of 0, numbers corresponding to quadratic residues are transformed into unit acoustic pulses with an initial phase of π, and numbers “0” are converted to radiation passes, moreover, the duration of the radiation pass is set equal to the time interval over which a single acoustic pulse is emitted, the signals recorded by the receiver correlate with one period of the modulating sequence, while the signals selected during correlation at M + 2 time intervals, each of which is equal to the length of the sequence period, where M is the number of periods in the emitted sequence, are synchronously summed.  2. The method according to p. 1, characterized in that the probing signals are sent to the test medium in the form of acoustic pulses modulated by a pseudo-random periodic sequence containing two periods.

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