EP0526619B1 - Method for automatically monitoring the vibrational condition of a drill string - Google Patents

Abstract

PCT No. PCT/FR92/00169 Sec. 371 Date Nov. 20, 1992 Sec. 102(e) Date Nov. 20, 1992 PCT Filed Feb. 25, 1992 PCT Pub. No. WO92/14908 PCT Pub. Date Sep. 3, 1992.A method for automatically monitoring the vibrational condition of a drill string fitted with detectors comprises the following steps: obtaining a reference spectrum for each detector; obtaining a spectrum for each detector representing the actual situation; comparing the two spectra to detect possible instabilities in the values measured by the detectors; indication of said instabilities by means of audio and/or visual devices.

Description

The present invention relates to a method for automatically monitoring the vibrational state of a drill string.

Research in the oil industry has led to equip the drilling rigs at their top with numerous sensors such as accelerometers and / or strain gauges, making it possible to access quantities such as torsional, axial or transverse accelerations, the axial force, torque and bending moments.

However, the vibrational information emanating from these sensors conceals an obvious complexity for a non-specialist wishing to use it. Indeed, traditional spectrum analyzers generally only produce curves whose analysis is not immediate. However, the master driller must instantly know the vibratory behavior of its lining, and in particular a possible instability of said behavior in order to be able to adjust the various drilling parameters as quickly as possible, namely the weight on the tool, the speed of rotation as well as the flow of mud.

These instabilities arise from the fact that the lining constitutes a mechanical assembly having its own modes which is capable of responding to the various mechanical stresses occurring during drilling, such as the work of the tool on the rock and the interactions between the well and said lining, this being true both axially as well as laterally or in torsion.

Such instabilities are to be avoided because they are at the origin of an additional stress brought to the material likely to cause a rupture of the lining; moreover, they consume a share of energy which it would be preferable to transmit directly to the tool, the latter then transforming it into energy for destroying the rock, which contributes to a more efficient advancement of drilling.

Document WO 90/12195 describes a device intended to present, acoustically or visually, to a user, the mechanical phenomena of a borehole. The device comprises an accelerometric sensor at the top of the drill string which emits a signal, which, after treatment with filters, and converted into an auditory or visual signal.

In US patents 4,150,568, a method of analysis, downhole, of the vibrations generated in the lining during drilling is described. The signal representing the vibrations is filtered in stages during a series of operations. The magnitude and frequency of vibrations in each passband are represented by two DC signals.

A method of detecting the wear of a drilling tool in order to prevent the tool from breaking at the bottom of the well is described in document US-Re-28,436. The method is based on the detection of oscillations characteristic of the drill string, oscillations having a predetermined amplitude and frequency. If such oscillations are detected, an alarm alerts an operator.

Document US Pat. No. 4,903,245 describes a method for detecting vibrations which may be harmful to the drill string, or which may cause it to rupture.

The present invention therefore relates to a method for automatically monitoring the vibrational state of a drill string which makes it possible to use the measurements provided by a set of sensors located at the top of a drill string, in particular by warning a user in a simple way of possible instabilities in these measurements.

• obtention d'un spectre de référence (32) pour chacun des capteurs (14),
• obtention d'un spectre pour chacun des capteurs (14) en situation réelle,
• comparaison des deux spectres afin de détecter d'éventuelles instabilités au niveau des grandeurs mesurées par les capteurs,
• signalisation desdites instabilités au moyen de dispositifs auditifs (34) et/ou visuels (36), caractérisée en ce que le traitement des spectres s'effectue sur une gamme de fréquences s'étendant au moins de 0,1 Hz à 400 Hz, et en ce que on signale les résultats obtenus à un utilisateur afin de pouvoir contrôler le forage, de manière que :
• si le rapport entre le spectre réel et le spectre de référence n'excède pas une valeur de sécurité, on signale à l'utilisateur que les paramètres de forage peuvent être maintenus,
• si le rapport entre spectre réel et spectre de référence est compris entre la valeur de sécurité et la valeur d'alerte, on signale cet état à l'utilisateur afin de lui permettre de modifier le cas échéant les paramètres de forage
• si le rapport entre spectre réel et spectre de référence excède une valeur d'alerte, on signale cet état à l'utilisateur afin qu'il puisse agir activement et modifier les paramètres de forage.

To do this, the invention proposes a method for automatically monitoring the vibrational state of a drill string (16) provided with sensors (14), said method comprising the following steps:

• obtaining a reference spectrum (32) for each of the sensors (14),
• obtaining a spectrum for each of the sensors (14) in real situation,
• comparison of the two spectra in order to detect possible instabilities in the quantities measured by the sensors,
• signaling of said instabilities by means of hearing (34) and / or visual (36) devices, characterized in that the processing of the spectra is carried out on a frequency range extending at least from 0.1 Hz to 400 Hz, and in that the results obtained are reported to a user in order to be able to control the drilling, so that:
• if the ratio between the actual spectrum and the reference spectrum does not exceed a safety value, the user is informed that the drilling parameters can be maintained,
• if the ratio between real spectrum and reference spectrum is between the safety value and the alert value, this state is signaled to the user in order to allow him to modify the drilling parameters if necessary
• if the ratio between the actual spectrum and the reference spectrum exceeds an alert value, this state is signaled to the user so that he can act actively and modify the drilling parameters.

• la figure 1 est un dessin schématique de l'ensemble du système de surveillance ;
• la figure 2 est un logigramme décrivant certaines étapes de la signalisation à l'utilisateur ; et
• les figures 3a, 3b et 3c sont des courbes explicatives de la présente invention.

Other characteristics and advantages of the present invention will appear more clearly on reading the description below made with reference to the appended drawings in which:

• Figure 1 is a schematic drawing of the entire surveillance system;
• FIG. 2 is a flow diagram describing certain stages of signaling to the user; and
• Figures 3a, 3b and 3c are explanatory curves of the present invention.

As shown in FIG. 1, the monitoring system comprises a battery of programmable filters 8 as well as quadratic mean converters, more commonly called "root mean square" RMS 10 or anti-aliasing filters 12 making it possible to process the signals from sensors 14 arranged on the drill string 16; the data coming from the converters 10 are grouped together at the level of a multiplexer 18 then transmitted to an analog-digital converter 20 and finally to one or several processors 22. The microprocessor (s) 22 are optionally assisted by one or more signal processors 24 and are coupled to an interface 26; the user can transmit information to the processor (s) 22 by means of a keyboard 28 and a communication link 30. It is possible to enter certain information concerning the reference spectra 32 at the interface 26 relating to each sensor, said interface 26 being connected to auditory 34 and / or visual signaling means 36.

• Obtention d'un spectre de référence pour chacun des capteurs :
     Pour ce faire, deux méthodes sont possibles. Le maître-foreur détermine dans le premier cas un état qu'il juge adéquat à un forage efficace, assisté éventuellement en cela par un spécialiste des vibrations dans le domaine du forage. A cet état correspondent différentes mesures vibratoires fournies par les capteurs, ces mesures étant traitées de la façon décrite ci-après de manière à obtenir des spectres de référence relatifs à chacun des capteurs. Le traitement des mesures vibratoires peut être effectué soit de manière grossière, c'est-à-dire qu'elles sont échantillonnées à une fréquence faible, par exemple 0,1 Hz, et que seule est retenue leur valeur efficace, soit de manière plus fine, à savoir qu'elles sont échantillonnées à une fréquence supérieure à 400 Hz après un filtrage anti-repliement soigné.

In order to detect possible instabilities in the quantities measured by the sensors, the following steps should be carried out:

• Obtaining a reference spectrum for each of the sensors:
  There are two ways to do this. The master driller determines in the first case a state which he considers adequate for effective drilling, possibly assisted in this by a vibration specialist in the field of drilling. This state corresponds to different vibration measurements provided by the sensors, these measurements being processed in the manner described below so as to obtain reference spectra relating to each of the sensors. The processing of the vibration measurements can be carried out either roughly, that is to say that they are sampled at a low frequency, for example 0.1 Hz, and only their effective value is retained, or more fine, namely that they are sampled at a frequency greater than 400 Hz after careful anti-aliasing filtering.

• Obtention d'un spectre en situation réelle :
     A cette fin, les mesures vibratoires fournies par les capteurs sont traitées de la même manière que pour l'obtention du spectre de référence, ladite manière étant décrite ci-dessus ; dans l'exemple illustré, les grandeurs mesurées par les capteurs sont respectivement la composante dynamique de la force au crochet (FCD), l'accélération longitudinale (AL), la composante dynamique du couple (CD), l'accélération de torsion (AT) et l'accélération de flexion (AF). L'information est alors transmise au processeur après une conversion analogique - numérique des mesures.
• Comparaison des données et signalisation d'éventuelles instabilités :
     Cette comparaison peut se faire soit au niveau des valeurs efficaces uniquement, soit au niveau du spectre tout entier.

In the second case, simulation software to which mechanical information is supplied on the drill string produces the spectra relating to each of the sensors, the simulation software possibly being integrated into the system itself. The information thus produced is introduced at the level of the processor or processors by means of a communication interface, said processor then only working by comparison with these reference elements.

• Obtaining a spectrum in real situation:
  To this end, the vibration measurements provided by the sensors are processed in the same manner as for obtaining the reference spectrum, said manner being described above; in the example illustrated, the quantities measured by the sensors are respectively the dynamic component of the hook force (FCD), the longitudinal acceleration (AL), the dynamic component of the torque (CD), the torsional acceleration (AT ) and bending acceleration (AF). The information is then transmitted to the processor after an analog-digital conversion of the measurements.
• Data comparison and reporting of possible instabilities:
  This comparison can be made either at the level of the effective values only, or at the level of the entire spectrum.

With regard to the effective values, the processor compares said value with that of reference previously determined, this comparison being carried out in the form of the ratio of the two values, which makes it possible to dispense with a calibration of the always delicate sensors.

As shown in Figure 2, if no RMS exceeds 10 times its reference level, the situation is considered stable, and no warning is sent to the master driller.

If the level of at least one of them is between 10 and 100 times its reference level, the master driller is alerted and can, if he deems it necessary, vary the drilling parameters.

If the level of at least one of them exceeds 100 times its reference level, the master driller is alerted to the existence of a very unstable situation and must remedy it as soon as possible.

The processing at the spectra level is of the same type. Indeed, the spectra developed on each measurement by the processor are compared lines to lines with those of reference. As for the effective values, the criteria corresponding to ratios respectively 10 and 100 times larger than the reference are retained in the illustrated example. In either case, the values 10 and 100 are arbitrary and are subject to change.

As shown in FIG. 2, the present invention makes it possible, in a simple manner, to signal to the master-driller the level of instability of the various quantities measured by the sensors. In the example illustrated, a set of warning lights is used, similar to conventional lights intended to regulate road traffic, as well as various auditory signals.

In the example illustrated, a green light indicates to the master driller the existence of a stable situation, an orange light supplemented by a disengageable discontinuous sound signal warns him of a relative instability and a red light supplemented by a sound signal continues the alert of high instability.

Figures 3a, 3b and 3c are explanatory curves of the present invention. The curves 3a and 3b are spectra obtained for the same sensor, one 3A being a reference spectrum and the other 3B being an instantaneous spectrum corresponding to a real situation, said spectra extending over a frequency range of 0 , 5 to 50 Hz. The curve 3C represents the ratio of the instantaneous spectrum to the real spectrum over the preceding frequency domain. From the different values of this report, the device is able to signal to the user if it is necessary to make, if necessary, a modification to the different drilling parameters.

It should be noted that this monitoring system can be supplemented by numerous algorithms allowing it to significantly expand its possibilities. Thus, it can detect a possible disappearance of the vibrations, corresponding respectively to 1/10 ratios between the real spectrum and the reference spectrum for a relative disappearance and 1/100 for a notable disappearance. The disappearance of vibrations is just as worrying as the increase in amplitudes, because it reflects, among other things, the collapse of the well above the tool.

In addition, the system object of the present invention allows the processing of data transmitted from the bottom by an appropriate tool and transmitted to the surface by any measurement method during drilling.

Thus, on the basis of the various auditory and / or visual signals which reach it, the master driller can, if necessary, make the modifications which seem to him necessary in terms of the various drilling parameters, such as the weight on the tool, the speed of rotation and the flow of mud.

Claims (3)

1. Method for the automatic monitoring of the state of vibration of a drilling fitting (16) provided with sensors (14), the said method comprising the following stages:

   - obtaining a reference spectrum (32) for each of the sensors (14);

   - obtaining a spectrum for each of the sensors (14) in an actual situation;

   - comparison of the two spectra in order to detect any instabilities in the quantities measured by the sensors;

   - indication of the instabilities by means of audio (34) and/or visual (36) devices, characterised in that the processing of the spectra is effected over a range of frequencies extending at least from 0.1 Hz to 400 Hz, and in that the results obtained are indicated to a user in order to be able to control the drilling, in such a manner that:

   - if the ratio between the actual spectrum and the reference spectrum does not exceed a safety value, the user is informed that the drilling parameters can be maintained;

   - if the ratio between the actual spectrum and the reference spectrum is between the safety value and the alarm value, the user is informed of that state in order to enable him to modify, where appropriate, the drilling parameters;

   - if the ratio between the actual spectrum and the reference spectrum exceeds an alarm value, the user is informed of that state so that he is able to respond actively and modify the drilling parameters.
2. Method according to Claim 1, characterised in that the signals supplied by the sensors (14) pass in succession via programmable filters (8), RMS converters (10) or anti-aliasing filters (12), a multiplexer, an analogue-digital converter (20) and one or more processors (22).
3. Method according to either Claim 1 or Claim 2, characterised in that the comparison is effected either in respect of the virtual values only or in respect of the entire spectrum.

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