RU2500888C1 - Acoustic method for determination of fluid crossflow point in borehole annulus - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: acoustic method for determination of fluid crossflow point in borehole annulus involves equal movement of acoustic transducer along the borehole and processing of noise signal received at its output, which is used for depth determination of fluid crossflow point. At that in output noise signal of acoustic transducer frequency-stable discreet component f₀ is defined and instant Doppler-beat frequency f(t) is registered as transducer moves along the borehole with equal speed. At the moment when instant Doppler-beat frequency f(t) is equal to discreet component f₀, time t₀ is recorded and depth h₀ for noise source is defined against specified mathematical expression.

EFFECT: method reduces labour intensity for determination of fluid crossflow point in borehole annulus.

2 cl, 2 dwg

Description

The invention relates to the oil and gas industry and can be used, for example, to determine the quality of cementing wells.

A known method for a similar purpose, according to which to determine the presence of annular movement of fluid in the well, vibroacoustic vibrations are created by pumping fluid into the well, followed by multiple recording of vibroacoustic vibrations. Moreover, the determination of the annular movement of fluid in the well is carried out by changing the amplitudes of the vibro-acoustic vibrations / RF Patent No. 2066751, class. ЕВВ 47/10, 1996 /.

The disadvantage of this method is its limited use only in the case of detecting the presence of a fact of annular fluid flow.

There is a method of the same purpose, adopted as a prototype, which consists in uniformly moving along or parallel to the axis of the well with a uniform speed V of the acoustic transducer and working out the noise signal received at its output, which is used to judge the depth h _{0 of the} location of the fluid flow.

In the prototype, the distribution of temperature anomalies along the wellbore is pre-recorded using a downhole thermometer and the intervals of their deviations from the geotherm are distinguished. Then, noise signals are recorded twice by an acoustic transducer — with the waveguide levers open and closed at the locations of the temperature anomalies (RU 2405936 C2, class Е21В 47/14, published on December 10, 2010).

The disadvantage of the prototype is the complexity of the practical implementation of the method, resulting from the need to use research in addition to acoustic and thermal logging, as well as the need to use special leverage waveguides in acoustic logging.

The technical result obtained from the implementation of the invention is to simplify the practical implementation of the method.

This technical result is achieved due to the fact that in the known acoustic method, which consists in uniformly moving along or parallel to the axis of the well with a uniform speed V of the acoustic transducer and working out the noise signal received at its output, which is used to judge the depth h _{0 of the} location of the fluid flow, first, a discrete component f ₀ stable in frequency is isolated from the noise signal, and at the output of the acoustic transducer as it moves along or parallel to the axis of the wells s register the instantaneous Doppler frequency f (t) and at time t ₀ , at which the value of the instantaneous Doppler frequency f (t) = f ₀ , determine the depth h ₀ by the formula:

$$h_0=V{t}_0\left(\mathrm{one}\right)$$

In addition, a frequency-stable, discrete component with a frequency above 500 Hz is isolated from the noise signal.

The invention is illustrated by drawings. Figure 1 presents a diagram of the implementation of the method; figure 2 - the trajectory of the time-frequency trace to explain the essence of the method.

The circuit that implements the method includes an acoustic logging system consisting of a hoisting device 1 (SPU 1), a cable cable 2 and an acoustic transducer 3. There is also a secondary electronic equipment 4, made, for example, in the form of a frequency discriminator and a computer, the input of which the output of the converter 3 is connected via a cable-cable 2.

The method is implemented as follows.

Acoustic transducer 3 is lowered or raised at a uniform speed V using SPU 1 and cable-cable 2. At the same time, using a secondary electronic equipment 4, the noise output signal at the output of transducer 3 is detected. The frequency-stable discrete component f is isolated from the noise output of acoustic transducer 3 ₀ using tunable band-pass filters of the frequency discriminator.

Since between the acoustic transducer 3 and the noise source 5 (Fig. 1) there is uniform motion with speed V, the Doppler effect occurs, which manifests itself in the fact that the instantaneous Doppler frequency f (t) on the selected discrete component f ₀ will change with time t as the distance d between the transducer 3 and the noise source 5 changes.

The nature of the change in instantaneous Doppler frequency obeys the mathematical relation (Measuring technique, 1997, No. 3, p. 48-52):

$$f(t)=f_0\left[\mathrm{one}+\frac{V^2(t_0-t)}{c\sqrt{d^2+V^2{(t-t_0)}^2}}\right]\left(2\right),$$

where c is the speed of sound; t ₀ is the point in time at which the transducer 3 will be located at a traverse distance from the noise source 5 (essentially, it will be located opposite the noise source 5, as shown in figure 1).

The nature of the change in the instantaneous Doppler frequency f (t) is shown in FIG. 2, from which it can be seen that at times t << t ₀ and t >> t ₀ $$f(t)=f_{\mathrm{one}}=f_2=f_0\pm f_0\frac{V}{c}.$$

At time t ₀ , when the converter 3 is located at a traverse distance from the noise source 5 (opposite the noise source 5), f (t) = f ₀ .

Secondary equipment 4 fixes a point in time t ₀ on a computer and determines the depth h ₀ from it using formula (1).

High measurement accuracy of the instantaneous Doppler frequency f (t) is observed at f ₀ > 500 Hz.

Claims (2)

1. The acoustic method of determining the place of fluid flow in the annulus of the well, which consists in uniformly moving along or parallel to the axis of the well with a uniform velocity V of the acoustic transducer and working out the noise signal received at its output, which judges the depth h _{0 of the} location of the place of fluid flow, different in that the pre-noise signal from isolated stable discrete frequency component f _0, a output acoustic transducer as it travels along or arallelno axis of the borehole is recorded instantaneous Doppler frequency f (t) and at time ₀ t, in which the instantaneous Doppler frequency f (t) = f _0, the depth h is determined by the formula h _{0 0 0} = Vt. 2. The acoustic method according to claim 1, characterized in that a frequency-stable discrete component with a frequency above 500 Hz is isolated from the noise signal.

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