EP1046781B1 - Method and system for detecting bit-bounce - Google Patents

Description

The present invention relates to the field of measurements in progress drilling, in particular measures concerning the behavior of a drilling tool attached to the end of a drill string. The method according to the invention proposes a solution for detecting the amplitude of vertical movements of the drilling tool or the force applied to the tool, said detections being obtained by means of a calculation program taking into account measurements made at the top of the drill string, that is to say substantially on the surface of the soil, generally by means sensors or an instrumented connector located in the vicinity of means for rotating the packing.

Measurement techniques are known for the acquisition information related to the dynamic behavior of the filling of drilling, which use a set of bottom-mounted sensors connected to the surface by an electrical conductor. In document FR / 92-02273, it is used two sets of measuring sensors connected by a cable of the type logging, one located at the bottom of the well, the other at the top of the drill string. However, the presence of a cable along the drill string is annoying for clean drilling operations say.

Document FR 2645205 or FR 2666845 disclose surface devices placed at the top of the trim that determine some drilling malfunctions according to surface measurements, but without taking into account, in a physical way, the behavior dynamic packing and drill tool in the well.

Document FR-2 750 159 discloses a device for estimating the amplitude of the vertical displacements of the drilling tool by means of a calculation program.

Between the bottom of a well and the surface of the ground, there is a train of stems along which dissipative energy phenomena take place (friction on the wall, torsion damping, ...), phenomena conservative flexibility, especially in traction-compression. There is thus a distortion between the measurements of the background and surface that depends mainly on the intrinsic characteristics of the trim (length, stiffness, geometry), characteristics of friction at the stem / wall interface and random phenomena.

Therefore, the information contained in the surface alone are not enough to solve the problem, that is to say know the instantaneous movements of the tool by knowing the instantaneous displacements of the filling on the surface. We must complete the surface measurement information by independent information, of another nature, which take into account the structure of the drill string and its behavior between the bottom and the surface: it is the role of the model of knowledge that establishes the theoretical relationships between the background and the area.

The methodology of the present invention uses the conjunction such a model, defined a priori, and surface measurements acquired in real time.

• on détermine les paramètres dudit modèle en prenant en compte les paramètres caractéristiques dudit puits et de ladite garniture,
• on réduit ledit modèle en ne conservant que certains des modes propres de la matrice d'état dudit modèle.

Thus, the present invention relates to a method of estimating the effective longitudinal behavior of a drilling tool attached to the end of a drill string and rotated in a well by means of drive located on the surface, in which uses a physical model of the drilling process based on general equations of mechanics and in which the following steps are carried out:

• the parameters of said model are determined by taking into account the characteristic parameters of said well and said lining,
• the model is reduced by keeping only some of the eigen modes of the state matrix of said model.

According to the method, at least two values Rf and Rwob are calculated in real time, Rf being a function of the main frequency of oscillations of the hook weight WOH, for example over the interval [0, 10] Hz, divided by the average instantaneous rotation speed at the surface, Rwob being a function of the standard deviation of the weight signal on the tool WOB estimated by the longitudinal model reduced from the measurement of the hook weight signal WOH, divided by the weight on the average tool WOB ₀ defined from the weight of the lining and the average hook weight, and the danger of the longitudinal behavior of said drill bit is determined from said values of Rf and Rwob.

We can compare Rf with an interval whose terminals are determined such that there can be no longitudinal behavior of the tool if Rf is not included in the interval.

Rf can be understood in the meantime, and the danger of the longitudinal behavior of the drill according to Rwob values.

Rf can be such that R _f = 20 * f _WOH / RPM ₀ where: f _WOH , expressed in Hertz, is the main oscillation frequency of the WOH over the interval [0, 10] Hz and RPM ₀ is the speed of mean instantaneous surface rotation, expressed in revolutions / min.

The bounds of the interval can be 0.95 and 0.99.

In the method, we can have: R wob = S wob WOB 0 with: s _wob is the standard deviation of the weight signal on the WOB tool estimated from that of the hook weight signal WOH and the reduced longitudinal model; and WOB ₀ is the average tool weight, defined from the weight of the lining and the average hook weight.

It can be determined that for Rwob less than 0.6, there is no danger, and for Rwob between 0.6 and 0.8, there is a danger average, and for Rwob greater than 0.8, there is extreme danger.

The invention also relates to a system for estimating the effective longitudinal behavior of a drilling tool attached to the end of a drill string driven in rotation in a well by surface-driven drive means, in which a computing installation includes means for physical modeling of the drilling process based on general equations of mechanics, parameters of the modeling means are identified taking into account the parameters of the well and the lining, the computing installation includes means for reducing the model in order to retain only some of the eigen modes of the state matrix of said model. The system comprises means for calculating, in real time, at least two values Rf and Rwob, Rf being a function of the main frequency of oscillations of the hook weight WOH, for example over the interval [0, 10] Hz, divided by the average instantaneous surface rotation speed, Rwob being a function of the standard deviation of the weight signal on the tool WOB estimated by the longitudinal model reduced from the measurement of the hook weight signal WOH , divided by the weight on the average tool WOB ₀ defined from the weight of the packing and the average hook weight. The system comprises means for alarming the danger of the longitudinal behavior of the drilling tool from the values of Rf and Rwob.

The method and system can be applied to the determination of the dangerousness of the tool's jump dysfunction drilling (bit-bouncing).

• la figure 1 représente schématiquement les moyens mis en oeuvre pour une opération de forage,
• la figure 2 représente un exemple de diagramme d'un modèle physique en traction-compression,
• la figure 3 décrit le diagramme de génération des alarmes.

The present invention will be better understood and its advantages will become clear from reading the description of an example, in no way limiting, illustrated by the appended figures, among which:

• FIG. 1 schematically represents the means implemented for a drilling operation,
• FIG. 2 represents an exemplary diagram of a physical model in traction-compression,
• Figure 3 describes the alarm generation diagram.

Figure 1 illustrates a drill rig that will be the invention. The surface installation includes a 1 comprising a lifting tower 2, a winch 3 which allow the moving a drill hook 4. Under the drill hook are suspended means 5 drive in rotation of the whole of the drill string 6 placed in the well 7. These means of training can be of the rod type of drive or kelly coupled to a table rotating 8 and mechanical drives, or head type motorized drive or power swivel suspended directly from the hook and guided longitudinally in the tower.

The drill string 6 is constituted conventionally by drill rods 10, a portion 11 commonly called BHA for "Bottom Hole Assembly" consisting mainly of drill collars, a drilling tool 12 in contact with the ground during drilling. Well 7 is filled with a fluid, called drilling, which flows from the surface to the bottom by the inner channel of the drill string and rises to the surface by the annular space between the walls of the well and the drill string.

For the implementation of the invention, a coupling is inserted instrumented 13 between the drive means and the top of the garnish. This connection makes it possible to measure the speed of rotation (RPM), the tension force (WOH) and the longitudinal vibrations of the top of the trim, and incidentally the couple. These measurements, called surface measurements, are transmitted by cable or radio to an electronic installation recording, processing, display, not shown here. To the place of the connector 13, it will be possible to use other sensors such as a tachometer on the rotary table to measure the speed of rotation, a measure of tension on the dead strand of the hauling and possibly a apparatus for measuring the torque on the motorisation apparatus, if the accuracy of the measurements thus obtained is sufficient.

Part 11 of the BHA may more specifically include, drill collars, stabilizers, and a second instrumented connector 14 which will only be used to experimentally control this invention by allowing the comparison between the displacement of the tool of drilling 12 actually measured by the instrumented connector 14 and the displacement detected through the implementation of the present invention. he it is therefore clear that the application of the present invention does not use instrument connection placed at the bottom of the well.

The driller who conducts a drilling operation with the devices described in Figure 1 has three possible actions, which are therefore the variables possible driving controls, the weight on the tool that is set by the winch which controls the position of the hook, the speed of rotation of the rotary table or equivalent, the flow of drilling fluid injected.

• un appareil de forage comprenant une installation de levage,
• un ensemble d'entraínement: organe de régulation et motorisation,
• un ensemble de tiges,
• un ensemble de masses-tiges,
• un outil de forage.

To illustrate an example of the present invention, a model of the mechanical system composed of the following technological elements will be used:

• a drilling rig comprising a hoisting installation,
• a training set: regulating member and motorization,
• a set of stems,
• a set of drill collars,
• a drilling tool.

The described model will treat the drill string as an element one-dimensional vertical. Displacements in vertical translation will be considered, lateral movements being neglected.

Figure 2 shows the block diagram of the traction-compression model. It's a classic model with finite differences that has several meshes represented by the blocks 20. Each mesh represents a part of the drill string, drill rods and drill collars. he are mass-spring-damping triplets represented by the diagrams referenced 21, 22, 23. Each block is provided with two inputs and outputs represented by the pairs of arrows 24 and 25 which represent the input and output voltages and vertical velocities of inputs and outputs. This representation shows how to digitally connect several stems (or meshes) as you connect physically the stems of the filling.

Block 26 represents the drilling rig. It's a set of masses, springs and friction.

Block 27 represents the tool in its longitudinal behavior.

The main object of the invention is to provide a system of alarms dedicated to bit-bouncing, using only the signals available on the surface: pad rotation speed (RPM) and weight hook (WOH). This alarm detects longitudinal oscillations of the tool, and gives the scale.

The application includes the construction of a model capable of reproduce the longitudinal behavior of all the elements of drilling. The classical model is obtained from the equation fundamental dynamics and the expression of the different forces, which in particular, the one reflecting the stiffness of the spring of the element. The friction force is a force proportional to the speed of moving the element. This model has two parts: the drilling (rig) on the one hand, the gasket and the tool on the other hand. These two parts are therefore composed of {mass-spring-friction} elements to each other by a transfer of power in the form of forces and longitudinal speeds. These equations, expressed here in the field continuous, are discretized to finite differences for each element.

These different elements are identified from the data geometrical construction: composition of the packing, type of apparatus drilling, mud density, well tilt, etc.

   avec:

X = le vecteur d'états du modèle (déplacements et vitesses longitudinales de tous les éléments du modèle);

A, B, C, D = les matrices d'état, de commande, d'observation et directe du modèle;

U = le vecteur des entrées du modèle. Dans le cas présent, le modèle n'a qu'une seule entrée, le poids sur l'outil WOB;

Y = vecteur des sorties du modèle, le poids au crochet WOH pour cette application.

The model thus constituted is written in the form of equations of states:

with:

X = the state vector of the model (displacements and longitudinal velocities of all the elements of the model);

A, B, C, D = the state, control, observation and direct matrices of the model;

U = the vector of the inputs of the model. In this case, the model has only one input, the weight on the WOB tool;

Y = vector of model outputs, hook weight WOH for this application.

After formatting state equations, we reduce the model to keep only the relevant information it contains, vis-à-vis malfunction of jumping the tool on the bottom, called "bit-bouncing". More precisely, we keep only the first 5 oscillating modes of the system, which are the ones whose associated frequencies correspond to the frequency range of the surface rotation speed usually used in drilling with a tricone tool (about 50 to 200 revolutions / min).

This model is able to give an approximation of WOB signal characteristics from the weight measurements to the hook (WOH).

The reduced state equations are translated as an H transfer function between WOB input and WOH output of the model. For any frequency f belonging to the domain scanned by the reduced model, we have: WOH ( f ) = H ( f ) WOB ( f )

• d'une part un critère fréquentiel,
• d'autre part un critère d'amplitude.
• a) Critère fréquentiel: dans le cadre d'un forage avec un outil du type tricône, il n'y a possibilité d'obtenir le dysfonctionnement de "bit-bouncing" que dans le cas où un coefficient Rf exprimant le rapport entre la fréquence principale d'oscillations du poids au crochet (WOH) et la vitesse de rotation (RPM) de la garniture en surface est comprise entre deux bornes : Rf = 20*fWOH RPM 0    où :
• f_WOH, exprimée en Hertz, est la fréquence principale d'oscillations du WOH sur l'intervalle [0 , 10] Hz.
• RPM₀ est la vitesse de rotation instantanée moyenne en surface, exprimée en tours/min.

To obtain an estimation of the behavior of the tool from the reduced model, two criteria come into play:

• on the one hand, a frequency criterion,
• on the other hand a criterion of amplitude.
• a) Frequency criterion: in the case of drilling with a tool of the tricone type, it is possible to obtain the "bit-bouncing" dysfunction only in the case where a coefficient Rf expressing the ratio between the frequency principal of oscillations of the hook weight (WOH) and the speed of rotation (RPM) of the surface lining is between two terminals: R f = * 20 f WOH RPM 0 or :
• _WOH , expressed in Hertz, is the main oscillation frequency of WOH over the interval [0, 10] Hz.
• RPM ₀ is the average instantaneous surface rotation speed, expressed in revolutions / min.

The frequency criterion is expressed by: 0.95 <R f <0.99:

The two bounds, 0.95 and 0.99, are set here from results experimental.

In fact, it has been found that the tricone tools generate at the bottom of well a trilobed form. The longitudinal oscillation frequency of the drilling set, when bit-bouncing, is about three times more high than its frequency of oscillation in rotation. Having noticed by elsewhere, from a 2D model of tool / rock contact that the field plays a role of frequency modulator between the rotational speed signal and that of the longitudinal velocity of the tool, the ratio between these two frequencies is not strictly equal to 3, but slightly lower. This is expressed by the values of these two limits: 0.95 and 0.99.

b) Critère d'amplitude : On peut caractériser l'amplitude des mouvements de l'outil en fond de puits en déterminant un rapport entre la moyenne du poids sur l'outil (WOB₀) et son écart-type (S_WOB0)_. En effet, pour un poids sur l'outil moyen donné, l'écart-type calculé sur une certaine fenêtre temporelle permet de quantifier si les oscillations du signal autour de sa moyenne sont dangereuses ou non, c'est à dire devront être signalées ou non.

It is important to note that their values are given in theory, but that, in practice, these two terminals may be subject to weighting coefficients depending in particular on the quality of the sensors used to measure the rotation speed RPM and the weight at WOH hook. In fact, the more imprecise these sensors will be, and the longer the interval in which R _{f is} in the presence of bit-bouncing will be wide, since it will have to include this degree of inaccuracy of the measurements.

b) Amplitude criterion: One can characterize the amplitude of the movements of the tool downhole by determining a ratio between the average of the weight on the tool (WOB ₀ ) and its standard deviation (S _WOB0 ) _. Indeed, for a weight on the given average tool, the standard deviation calculated over a certain time window makes it possible to quantify if the oscillations of the signal around its mean are dangerous or not, ie will have to be signaled or no.

• s_wob est l'écart-type du signal de poids sur l'outil WOB estimé à partir de celui du signal de poids au crochet WOH et du modèle longitudinal réduit;
• WOB₀ est le poids sur l'outil moyen, défini à partir de la masse de la garniture et du poids au crochet moyen.

Thus, we define R _wob such that: R wob = s wob WOB 0 or :

• s _wob is the standard deviation of the weight signal on the WOB tool estimated from that of the hook weight signal WOH and the reduced longitudinal model;
• WOB ₀ is the average tool weight, defined from the weight of the lining and the average hook weight.

The diagram of FIG. 3 shows how the two ratio values R _f and R _{w w} are used to generate a set of alarms on the "bit-bouncing" malfunction.

The main frequency of oscillations of the hook weight, _WOH , is calculated from an FFT over a time window whose width depends directly on the acquisition frequency of the hook weight signal. The average instantaneous rotation speed RPM ₀ is also calculated, which is the average rotational speed given at a regular time interval from the measurements included in a certain time window.

The standard deviation _WOH and the instantaneous average of the hook weight WOH _{0 are} jointly calculated. These two quantities are calculated on a sliding window corresponding to a certain period of time (for example 3s). This period of time is determined according to the acquisition frequency of the hook weight signal WOH.

The calculation of the estimate of the average weight on the tool WOB ₀ is directly derived from the difference between the hook weight and the weight of the drill string. The estimate of the standard deviation s _WOB of the weight on the tool is given by the following expression: s WOB = s WOH H ( f WOH )

The two ratios R _f and R _{W w are} then calculated simultaneously in real time.

We compare Rf with the two bounds delimiting the interval "at risk" dysfunction of the "bit-bouncing" type.

If Rf is not in this range, there can not be bit-bouncing, the alarm indicates the green light (reference 28).

Otherwise, for example, Rf is between 0.95 and 0.99, there is risk bit-bouncing.

We then consider the second criterion R _wob .

If R _wob is low (here, for example, less than 0.6), this means that oscillations of WOB around its mean are small. So there is a potential risk of "bit-bouncing", but it does not really appear, or is not observable, the fire remains green (28).

If R _wob is average (for example between 0.6 and 0.8), then the light becomes orange (reference 29), because there is probably a bit-bouncing, but still of medium force. does not bounce again, but the weight on the tool has already significant longitudinal oscillations, and at a dangerous frequency.

Finally, if R _wob is strong, there is likely to be a large bit-bouncing. The fire alarm is red (reference 30).

Without departing from the scope of the present invention, it would be possible not to limit the graduation of the malfunction on the basis of three colors, but to associate a color with each degree of severity of the oscillations (for example every 0.1 points for R _wob, which would avoid having to choose "fateful" thresholds, such as 0.6 and 0.8).

The physical model is validated using data recorded on site using instrumented bottom fittings and area.

The drilling fluid and the walls of the well intervene only in to the extent that they generate a friction-resistant torque. By experiment, and using the bottom and surface measurements, we can establish a law friction along the linear rods as a function of rotational speed and longitudinal velocity.

The reduction method used is the method of singular disturbances. It consists of keeping the state matrix and the control matrix, the rows and columns corresponding to the modes to keep. To keep static gains, fast modes replaced by their static value, which has the consequence to introduce a direct matrix.

The method assumes that fast modes take their equilibrium in a negligible time, that is, they establish themselves instantly (quasi-static hypothesis).

The present invention is advantageously implemented on a drilling site in order to have as precise a detection as possible the dangerousness of the vertical displacement of the drilling tool in time real, and that from the only surface measurements, including fluctuations in longitudinal acceleration and rotational speed of conventional means for rotating the drill string, and a surface installation equipped with electronic means and computer. It is very interesting to prevent malfunctions known, for example the so-called "bit bouncing" behavior characterized by a jump and a detachment of the tool from the face although the head of the drill string remains substantially fixed and that a compressive force important is applied to the tool. This dysfunction may have for consequences of the adverse effects on the tool life, on the increase in mechanical fatigue of the drill string and the frequency breaks in connections.

Claims (9)

1. Method for estimating the effective longitudinal behaviour of a drilling bit (12) fixed to the end of a drilling string and entrained in rotation in a well (7) by entrainment means situated on the surface, in which use is made of a physical model of the drilling process based on general equations of mechanics and in which the following steps are carried out:

   the parameters of said model are determined taking into account the characteristic parameters of said well and said string,

   said model is reduced retaining only some of the characteristic modes of the matrix defining the state of said model

   characterised in that at least two values Rf and Rwob are calculated in real time, Rf being a function of the main oscillation frequency of the weight on the hook WOH divided by the mean instantaneous speed of rotation on the surface, Rwob being a function of the typical deviation of the signal for the weight on the bit WOB estimated by the reduced longitudinal model from the measurement of the signal for the weight on the hook WOH, divided by the mean weight on the bit WOB₀ defined from the weight of the string and the mean weight on the hook, and in that the level of danger of the longitudinal behaviour of said drilling bit is determined from said values of Rf and Rwob.
2. Method according to claim 1, in which Rf is compared with a range the limits of which are determined such that no dangerous longitudinal behaviour of the bit can take place therein if Rf does not fall within said range.
3. Method according to claim 2, in which Rf falls within said range, and in that the level of danger of the longitudinal behaviour of the drilling bit is quantified as a function of the values of Rwob.
4. Method according to one of the preceding claims, in which R_f = 20*f_WOH / RPM₀ in which f_WOH, expressed in Hertz, is the main oscillation frequency of the WOH over the interval [0, 10] Hz and RPM₀ is the mean instantaneous speed of rotation on the surface, expressed in revolutions per minute.
5. Method according to one of the preceding claims, in which said limits of said interval are 0.95 and 0.99.
6. Method according to one of the preceding claims, in which Rwob = Swob WOB0 in which s_wob is the typical deviation of the signal for the weight on the bit WOB estimated from that of the signal for the weight on the hook WOH and the reduced longitudinal model, and WOB₀ is the mean weight on the bit defined from the mass of the string and the mean weight on the hook.
7. Method according to claims 3 and 6, in which it is determined that there is no danger when Rwob is less than 0.6, and that there is a moderate danger when Rwob is between 0.6 and 0.8, and that there is extreme danger when Rwob is greater than 0.8.
8. System for estimating the effective longitudinal behaviour of a drilling bit fixed to the end of a drilling string entrained in rotation in a well by entrainment means situated on the surface, in which a calculating installation comprises means for physical modelling of the drilling process based on general equations of mechanics, in that parameters of said modelling means are identified taking account of the parameters of said well and of said string, in that the calculating installation comprises means for reducing said model so as to retain only some of the characteristic modes of the matrix defining the state of said model, characterised in that said system comprises means for calculating at least two values Rf and Rwob in real time, Rf being a function of the main oscillation frequency of the weight on the hook WOH divided by the mean instantaneous speed of rotation on the surface, Rwob being a function of the typical deviation of the signal for the weight on the bit WOB estimated by the reduced longitudinal model from the measurement of the signal for the weight on the hook WOH, divided by the mean weight on the bit WOB₀ defined from the weight of the string and from the mean weight on the hook, and in that said system comprises alarm means for the level of danger of the longitudinal behaviour of said drilling bit from said values of Rf and Rwob.
9. Application of the method and the system according to one of the preceding claims to determination of the level of danger of the malfunction of bit bouncing.

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