EP0500877B1 - Method for conducting an oil drilling operation - Google Patents

Abstract

PCT No. PCT/FR91/00721 Sec. 371 Date Jul. 13, 1992 Sec. 102(e) Date Jul. 13, 1992 PCT Filed Sep. 12, 1991 PCT Pub. No. WO92/05337 PCT Pub. Date Apr. 2, 1992.Method for conducting an oil drilling operation, during which a drill-stem produces the rotation of a tool in an oil well. The method consists of the following steps: continually measuring the rotational speed of the upper end of the drill-stem; continuously measuring the torque applied to that end of the drill-stem; determining the torque applied to that end of the drill-stem; determining the torque variation; establishing the period of torque variation if the amplitude of the variation exceeds a predefined threshold; verifying the stability of this period; comparing the latter, if stable, with at least one predefined theoretical period; and reporting the results obtained to the user in order to control the drilling operation.

Description

The present invention relates to a method of conducting a borehole.

When drilling an oil well, the drill string motor, which is mounted to the surface, rotates at a constant speed of about 50-150 rpm. However, the friction produced between the drilling tool and the bottom of the well, or between the rods and the wall of the well, can cause slowing down or even periodic stops of the tool. Since, during this time, the motor continues to rotate at one end of the drill string, the latter tends to twist around its longitudinal axis until the force exerted is greater than the friction effect braking the tool. At this time, the drill string relaxes and the tool starts to rotate again, reaching peak rotational speeds of the order of 150 to 400 revolutions / minute. As wells often follow opposite paths, contact between the lining and the wall of the well occurs quite frequently.

It is obvious that the behavior of the tool has a significant effect on the progress of the drilling. Thus, it is desirable that the master driller be informed of the periodic instability of the tool's rotation speed so that he can modify the drilling parameters - engine rotation speed, weight applied to the tool or the mud flow rate. - and thus ensure optimal drilling.

The present invention therefore relates to a method of conducting a borehole which makes it possible to provide a user, in a simple manner, with data on the state of rotation of the rod.

Document US-E-28,436 describes a method of conducting a borehole in which the torque applied by the motor for rotating the drill pipe is measured and in which a user is informed if the torque exceeds a threshold predetermined.

This process does not make it possible to signal to a user the presence, the absence or the possible presence periodic instabilities in rotation of the drill pipe so that this user can modify the drilling parameters as a function of the behavior of the drill pipe.

• mesure de la vitesse de rotation de l'extrémité supérieure de la tige de façon continue ;
• mesure en continu du couple appliqué à cette extrémité supérieure de la tige, caractérisé en ce que le procédé comporte les étapes additionnelles suivantes :
• recherche de la variation du couple ;
• détermination de la période de variation du couple, si l'amplitude de cette variation dépasse un seuil prédéterminé ;
• vérification de la stabilité de cette période ;
• comparaison, si cette période est stable, de la dite période avec au moins une période théorique prédéterminée, la période théorique prédéterminée étant une caractéristique de la tige de forage calculée à partir des modes propres de vibration en torsion de la garniture ;
• signalisation des résultats obtenus à un utilisateur afin de pouvoir contrôler le forage, de manière que :
• si l'amplitude de la variation du couple ne dépasse pas le seuil prédéterminé, on signale à l'utilisateur que les paramètres du forage peuvent être maintenus ;
• si la période n'est pas stable ou si la période stable ne correspond pas à une période théorique prédéterminée, on signale cette condition à l'utilisateur afin de lui permettre de modifier les paramètres du forage ; et
• si la période est stable et correspond à une période théorique prédéterminée, on signale la présence d'instabilités en rotation à l'utilisateur afin qu'il puisse agir activement et modifier les paramètres du forage.

The invention provides a method of conducting a borehole in which a tool is rotated in a well by a drill rod, the method being intended to detect and report the presence of periodic instabilities in rotation of the drill rod drilling and involves the following steps:

• measuring the speed of rotation of the upper end of the rod continuously;
• continuous measurement of the torque applied to this upper end of the rod, characterized in that the method comprises the following additional steps:
• looking for torque variation;
• determining the period of variation of the torque, if the amplitude of this variation exceeds a predetermined threshold;
• verification of the stability of this period;
• comparison, if this period is stable, of said period with at least one predetermined theoretical period, the predetermined theoretical period being a characteristic of the drill pipe calculated from the natural modes of torsional vibration of the lining;
• signaling of the results obtained to a user in order to be able to control the drilling, so that:
• if the amplitude of the torque variation does not exceed the predetermined threshold, the user is informed that the drilling parameters can be maintained;
• if the period is not stable or if the stable period does not correspond to a predetermined theoretical period, this condition is signaled to the user in order to allow him to modify the parameters of the drilling; and
• if the period is stable and corresponds to a predetermined theoretical period, the presence of rotation instabilities is signaled to the user so that he can act actively and modify the parameters of the drilling.

• la figure 1 est une vue schématique en coupe d'un ensemble de forage ;
• la figure 2 est un logigramme de certaines étapes du procédé de l'invention ; et
• les figures 3A, 3B et 4 montrent chacune des paires de courbes de couple et de vitesse de rotation.

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 sectional view of a drilling assembly;
• FIG. 2 is a flow diagram of certain steps of the method of the invention; and
• Figures 3A, 3B and 4 each show pairs of torque and speed curves.

As shown in FIG. 1, a drilling assembly comprises a mast 10 provided, in a manner known per se, with a hook 12 to which is suspended a drill string, generally represented at 14. The drill string 14 comprises a tool drill 16, drill rods 18 and drill rods 20 forming an assembly called drill string. In the example illustrated, the drill string 14 is rotated by a rotation table 22. Any other device can be used. The rotation table 22 is provided with a rotation speed sensor 24 and a torque sensor 26 applied to the drill string 14.

From the data representing the speed of rotation and the torque, it is possible, according to the invention, to detect periodic rotation instabilities.

To do this, the following steps must be carried out:
- Search for torque variation:

In order to see if the variations in torque are significant during a given period of time, the difference between the maximum torque and the minimum torque is determined and this result is divided by the average torque. If the result of this calculation is greater than 10%, it can be assumed that there are periodic instabilities in the speed of rotation of the lining.

This step is represented in FIG. 2 by:

A result of less than 10% implies a small variation in torque which makes it possible to deduce therefrom that there is no instability in the speed of rotation of the lining. In this case, the method makes it possible to signal to the master driller that he can maintain the drilling parameters.
- Calculation of period P:

If the variation in the torque is significant, the next step of the process is carried out in which the period P of the variation in the torque is calculated. Then we are led to check if this period P is constant for a predetermined number of cycles.

If it turns out that the period P is not constant, we cannot deduce that there are, or that there are not, rotational speed instabilities. However, as there are significant variations in the torque, the process allows this situation to be reported to the master driller so that he can, if necessary, modify the drilling parameters.

If the period P is constant, we can go to the next step:
- Comparison of period P with a theoretical period:
The theoretical period P _th is a characteristic of the packing used. It is calculated from the natural modes of vibration in torsion of the lining. As there are several eigen modes of vibration, it follows that there are several values for P _th which one can call P _th,; P _th2 ,
We therefore proceed to a comparison of the current P value with each of the predetermined theoretical values in order to see if the value P is in a range between 0.8 and 1.2 times the value of one of the theoretical values P _th ,
If the value P is within such a range it can be deduced therefrom that there are periodic instabilities of rotational speed. The system allows this fact to be reported to the master driller so that he can act and modify one or more drilling parameters. On the other hand, if the value P is not within such a range there is uncertainty regarding the behavior of the drill string. However, the system allows this uncertain situation to be reported to the master driller so that he can modify the drilling parameters if necessary.

Then it is necessary to proceed to a last step:
- the characterization of the phenomenon.

This step has two parts: calculating the percentage of tool downtime and calculating the maximum tool rotation speed.

The% _tar tool downtime percentage is defined by the formula

The recovery time, time during which the engine runs and the tool stopped, is the time necessary for the engine to overcome the friction between the lining and the well.

   où DN est le nombre de tours de garniture nécessaire pour vaincre les frottements.
   et VR_moy est la vitesse de rotation moyenne de l'outil.This time is equal to $$\text{60 x}\frac{\text{DN}}{{\text{VR}}_{\text{avg}}}$$

where DN is the number of turns of packing necessary to overcome friction.
and VR _avg is the average speed of rotation of the tool.

The propagation time is given by the expression

   où j est un coefficient de profil qui est, par exemple 1,7 pour le premier mode de vibration.The maximum rotation speed of the VR tool _max

where j is a profile coefficient which is, for example 1.7 for the first vibration mode.

As shown in Figure 2, the present invention makes it possible to signal to the master-driller, in a simple manner, the presence or absence of rotational speed instabilities. In the example illustrated, a set of indicators, analogous to conventional lights intended to regulate road traffic, is used. Any other signaling means, for example auditory or graphic, can be used.

In the example illustrated, a green light indicates to the master driller that he can maintain the parameters of the drilling, an orange light leaves him the choice to modify the parameters, taking into account the uncertain diagnosis, and the red light indicates to him that we must act actively.

FIGS. 3A and 3B are two pairs of curves, at a different time scale, of the variation of the torque C and of the speed of rotation of the tool VR over time. The measurements were carried out by a recording device placed at the bottom of the well. These measurements make it possible to visualize the relationship between the torque and the speed of rotation and to confirm that this relationship corresponds to the hypotheses on which the method according to the present invention is based. Figure 4 shows in more detail the variation of the torque and the rotation speed.

Claims (1)

1. Process for performing drilling, in the course of which a tool is rotated in a well by a drill string, the process being intended to detect and to indicate the presence of periodic instability in rotation of the drill string, and comprising the following steps:

   - measurement of the speed of rotation of the upper end of the drill string in the known manner;

   - continuous measurement of the force applied to this upper end of the string, characterised in that the process comprises the additional following steps:

   - determining the variation of the force;

   - determining the period of variation of the force if the amplitude of this variation exceeds a predetermined threshold;

   - verification of the stability of this period;

   - comparison, if this period is stable, of the said period with at least one predetermined theoretical period, the predetermined theoretical period being a characteristic of the drill string calculated from suitable methods with respect to the torsional vibration of the equipment;

   - indicating the results obtained to a user in order to be able to control the drilling, in such a manner that:

   - if the amplitude of the variation of the force does not exceed a predetermined threshold, it is indicated to the user that the drilling parameters may be maintained;

   - if the period is not stable, or if the stable period does not correspond to a predetermined theoretical period, this condition is indicated to the user in order to allow him to modify the drilling parameters; and

   - if the period is stable and corresponds to a predetermined theoretical period, the presence of instabilities of rotation are indicated to the user in order that he may act actively and modify the drilling parameters.

Images