SU909660A1 - Method of measuring time intervals in acoustic well-logging - Google Patents

Description

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The invention relates to a measurement technique and can be used in acoustic logging of wells.

Known cnocojS time measurement, based on the fixation of the moments of arrival of elastic waves from the radiator to the receiver 1.

The closest in technical essence is the method according to which the time interval is fixed at the moment when the signal passes the threshold voltage 2.

However, the known methods have a low measurement accuracy.

The purpose of the invention is to improve the measurement accuracy.

This goal is achieved by the fact that in the known method, which includes fixing the time interval at the moment when the signal passes the threshold voltage, the operations of forming the time interval that precedes the moment of fixation are introduced.

detecting the signal in the generated time interval; comparing with the reference level i - when the detected signal exceeds the reference level, a time correction for the measurement is introduced.

FIG. 1 shows one of the devices that implements this method; in fig. 2 - diagrams illustrating the operation of the device.

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The device comprises a threshold device 1, a shaper 2 interval pulses, a selection circuit 3, a subtraction circuit t, shaper pulses 5 and 6, peak detectors 7 and 8, a comparator 9, a correction device 10 and a switch 11.

Information signals 12 and 13 from alternately excited near and far emitters in the system with

20 by a three-element acoustic probe arrive at the threshold device 1-, where, with a sufficient signal amplitude, the moments of the 390 second firing are recorded by the second inputs of the trigger level information signals. Short pulses corresponding to the moment of fixation from the output of the threshold device arrive at the shaper 2 interval pulses, forming interval pulses H and 15, corresponding to the duration of the propagation time of the oscillations, respectively, from the near emitter to the receiver T and from the far radiation to the TQ receiver. Using the selection scheme 3, these pulses are separated with and separately - the pulse k is directly, and the pulse 15 through the switch is fed to the subtraction circuit 4, the voltage at the output of which is proportional to the difference of the specified times, which is equal to the propagation time of elastic oscillations in the interval between far and near emitters lt. The shaper 5 and 6 gating pulses form time intervals 16 and 17 in the form of pulses, the first of which is the moment of fixing the signal from the near emitter, the second is the moment of fixing the signal from the far emitter. The leading edges of the pulses are shifted relative to the fixation moments by a time corresponding to several periods of oscillation of the information signal. The rising edges of the pulses 16 and 17 coincide with the falling edges of the corresponding interval pulses 14 and 15. The pulses 16 and 17 arrive at the control inputs of the detectors, respectively 7 and 8, ensuring detection of information signals arriving at the signal inputs of the detectors at intervals of gating pulses. The detected signal from the output of the detector 7 as a dynamic reference voltage is fed to the inverted input of the comparator 9 The detected signal from the output of the detector 8 is fed to its direct input. When the threshold device on the second inputs of the near and far emitter drivers (plots 12 and 13) is triggered, only the lane at intervals of gating pulses fall into the intervals of gating pulses. entry, with the first entry of the far-emitter signal always less than the first entry of the near-emitter signal. In this case, the voltage at the direct input of the comparator is always less than the reference voltage, due to which the comparator retains its original state without affecting the switch connected to its output. In rocks with increased attenuation, the information signals from the near (plot 18) and the far (plot 19) emitters are reduced so that the second signal entry from the far emitter may not reach the trigger level of the threshold device. In this case, the threshold device is triggered at a more distant entry, for example, the fourth, shifted relative to the second entry at time t, corresponding to one period of oscillation of the information signal and determining the overestimation of the values of Tg and dT due to fixation of non-named arrivals. At the same time, the gate-pulse 17 in front of the far-emitter signal, maintaining its temporary position relative to the moment of fixation, approaches the information signal, and in the time interval determined by this pulse, a relatively large third entry of the information signal falls, while, in the interval, At the same time, as in the previous case, a small first entry remains before the signal from the near-emitter. As a result of detection, the direct voltage input voltage exceeds the reference voltage at the inverse input, which will trigger the comparator and cause a short pulse at its output to the control input of the switch 11. The comparator pulse switches the switch in the next cycle instead of pulse 15, a correction device pulse 20 is fed through the switch to the input of the subtraction circuit, which has a shorter duration by t compared to pulse 15. A decrease in pulse width 20 provides delay by the amount t of its leading edge as compared with the leading edge of the pulse 15; A decrease in the pulse duration of 20, and hence the value of dT at the output of the subtraction circuit, compensates for their overestimation due to

triggered threshold device on non-named entries.

The method provides high accuracy of measurement, regardless of whether the information signals from the near and far radiators are recorded on the same or opposite entries, ensuring high accuracy of geophysical information in an environment with a wide range of attenuation coefficient.

Claims (2)

1.Di Konova D.I. et al. General geophysical well survey M., 1977. 2. USSR author's certificate number 607176, cl. G F 10/0, 1976 (prototype). 1 Sync pulse Uroyen ipuKcautUu. I Ta 7577 Tz 2.