EP1046781A1 - Method and system for detecting bit-bounce - Google Patents

Abstract

The present invention relates to a system and a method for generating an alarm on the effective longitudinal behavior of a drilling tool fixed to the end of a drilling rig driven in rotation in a well by drive means located in surface, using a physical model of the drilling process based on general mechanical equations. The following steps are carried out: the model is reduced to keep only the relevant modes, at least two values Rf and Rwob are calculated, Rf being a function of the main frequency of oscillations of the hook weight WOH divided by the speed of rotation instantaneous mean at the surface, Rwob being a function of the standard deviation of the weight signal on the WOB tool estimated by the longitudinal model reduced from the measurement of the hook weight signal WOH, divided by the weight on the WOB0 medium tool defined from the weight of the trim and the average hook weight; The dangerousness of the longitudinal behavior of said drilling tool is determined from said values of Rf and Rwob. <IMAGE>

Description

The present invention relates to the field of measurements in progress drilling, in particular measurements concerning the behavior of a drilling tool attached to the end of a drill string. The method according to the invention provides 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 ground surface, generally by means sensors or an instrumented connection located in the vicinity of means for rotating the lining.

We know measurement techniques for acquisition information related to the dynamic behavior of the gasket drilling, which use a set of bottom sensors connected to the surface by an electrical conductor. In document FR / 92-02273, it is used two sets of measurement sensors connected by a cable of the type logging, one being 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 inconvenient for proper drilling operations say.

We know from documents FR 2645205 or FR 2666845 of surface devices placed at the top of the lining which determine certain drilling malfunctions based on surface measurements, but without taking physical behavior into account dynamics of the lining and the drilling tool in the well.

Between the bottom of a well and the ground surface, there is a train of rods along which dissipative energy phenomena take place (friction on the wall, torsional damping, ...), phenomena flexibility preservatives, especially in traction and compression. There is thus a distortion between the measurements of the bottom displacements and of surface which mainly depends on the intrinsic characteristics of the lining (length, stiffness, geometry), characteristics of friction at the rods / wall interface and random phenomena.

This is why the information contained in the measurement surface alone are not sufficient to solve the problem posed, that is to say know the instantaneous movements of the tool by knowing the instantaneous movements of the lining on the surface. You 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: this is the role of the model of knowledge which establishes the theoretical relations between the substance and the area.

The methodology of the present invention uses the conjunction of such a model, defined a priori, and of 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 for estimating the effective longitudinal behavior of a drilling tool attached to the end of a drilling rig and rotated in a well by drive means located on the surface, in which uses a physical model of the drilling process based on general mechanical equations 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 of said lining,
• said model is reduced by retaining 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 surface speed, Rwob being a function of the standard deviation of the weight signal on the WOB tool 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 dangerousness of the longitudinal behavior of said drilling tool is determined from said values of Rf and Rwob.

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

Rf can be included in the interval, and we quantify the danger of the longitudinal behavior of the drilling tool in function Rwob values.

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

The limits 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 weight on the average tool, defined from the mass of the trim and the average hook weight.

We can determine that, for Rwob less than 0.6, there is no danger, and that for Rwob between 0.6 and 0.8, there is a danger medium, 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 fixed to the end of a drilling rig rotated in a well by drive means located on the surface, in which a calculation installation comprises means of physical modeling of the drilling process based on general mechanical equations, parameters of the modeling means are identified taking into account the parameters of the well and the lining, the calculation installation comprises means of reduction of the model in order to keep 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 speed of rotation, Rwob being a function of the standard deviation of the weight signal on the WOB tool estimated by the reduced longitudinal model from the measurement of the weight signal on the hook WOH , divided by the weight on the average tool WOB ₀ defined from the weight of the trim and the average hook weight. The system includes means for alarming the dangerousness 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 danger of the tool jumping malfunction 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 on reading the description of an example, in no way limiting, illustrated by the figures below appended, among which:

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

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

The drill string 6 is conventionally constituted by drill rods 10, part 11 commonly called BHA for "Bottom Hole Assembly" comprising mainly drill-drills, a drilling tool 12 in contact with the ground during drilling. Well 7 is filled with a fluid, called a drilling fluid, which circulates 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 fitting is inserted instrumented 13 between the drive means and the top of the garnish. This connector measures the speed of rotation (RPM), the tensile force (WOH) and longitudinal vibration from the top of the trim, and incidentally the couple. These so-called surface measurements are transmitted by cable or radio to an electronic installation recording, processing, display, not shown here. To the place of the fitting 13, other sensors such as a tachometer on the rotation table to measure the rotation speed, a tension measurement on the dead strand of hauling and possibly a torque measurement device on the motorization device, if the accuracy of the measurements thus obtained is sufficient.

Part 11 of the BHA may more specifically include, rods, stabilizers, and a second instrumented fitting 14 which will only be used to experimentally control this invention by allowing the comparison between the displacement of the tool borehole 12 actually measured by the instrumented fitting 14 and the displacement detected thanks to 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 command for driving, the weight on the tool which is adjusted by the winch which controls the hook position, the speed of rotation of the rotary table or equivalent, the drilling fluid flow 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 lifting installation,
• a set of drive: regulator and motor,
• a set of rods,
• a set of drill sticks,
• a drilling tool.

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

Figure 2 shows the block diagram of the traction-compression model. It is a classic model with finite differences which has several meshes represented by blocks 20. Each mesh represents part of the drill string, drill pipe and drill collars. he these are mass-spring-damping triples shown in the diagrams referenced 21, 22, 23. Each block has two inputs and outputs represented by the pairs of arrows 24 and 25 which represent the input and output voltages and vertical displacement speeds inputs and outputs. This representation shows the way of digitally connect several rods (or meshes) as we connect physically the stems of the trim.

Block 26 represents the drilling rig. It is 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 alarms dedicated to bit-bouncing, using only the signals available at the surface: speed of rotation of the lining (RPM) and weight crochet (WOH). This alarm detects the 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 classic model is obtained from the equation fundamental of the dynamics and the expression of the different forces, including in particular, that translating the stiffness of the spring of the element. The friction force is a force proportional to the speed of moving the item. This model has two parts: the drilling (rig) on the one hand, the lining and the tool on the other hand. These two parts are therefore composed of elements {mass-spring-friction} linked the 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 the finite differences for each element.

These different elements are identified from the data site geometries: composition of the trim, type of appliance drilling, mud density, slope of the well, 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 formed is written in the form of state equations:

with:

X = the vector of states 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 model inputs. In this case, the model has only one entry, the weight on the WOB tool;

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

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

This reduced model is capable of giving an approximation of the WOB signal characteristics from weight measurements at hook (WOH).

We translate the reduced state equations in the form of a transfer function H between WOB input and WOH output of the model. For any frequency f belonging to the domain swept 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.

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

• on the one hand a frequency criterion,
• on the other hand a criterion of amplitude.

• 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.

a) Frequency criterion: within the framework of drilling with a tool of the tricone type, there is no possibility of obtaining the "bit-bouncing" dysfunction except 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 lining on the surface is between two limits: R f = 20 * f WOH RPM 0 or :

• f _WOH , expressed in Hertz, is the main frequency of oscillations of WOH over the interval [0, 10] Hz.
• RPM ₀ is the average instantaneous speed of rotation at the surface, expressed in revolutions / min.

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

The two limits, 0.95 and 0.99, are fixed here from results experimental.

Indeed, it has been found that the tricone tools generate at the bottom of well a three-lobed shape. The longitudinal oscillation frequency of the drilling set, during bit-bouncing, is therefore approximately three times more higher than its rotating oscillation frequency. Having noted by elsewhere, from a 2D tool / rock contact model that the terrain plays a role of frequency modulator between the speed signal and that of the tool's longitudinal speed, the relationship between these two frequencies is therefore not strictly equal to 3, but slightly lower. This is expressed by the values of these two limits: 0.95 and 0.99.

It is important to note that their values are given in theory, but that, in practice, these two limits can be subjected to weighting coefficients depending in particular on the quality of the sensors used to measure the speed of rotation RPM and the weight at WOH hook. In fact, the more imprecise these sensors are, the wider the interval in which R _f is located in the presence of bit-bouncing, since it must include this degree of inaccuracy of the measurements.

b) Amplitude criterion: The amplitude of the tool's movements at the bottom of the well can be characterized by determining a ratio between the mean 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 whether the oscillations of the signal around its average are dangerous or not, that is to say must be reported 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 weight on the average tool, defined from the mass of the trim and the average hook weight.

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

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

We calculate jointly the standard deviation S _WOH and the instantaneous average of the hook weight WOH ₀ . 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 as a function of the frequency of acquisition of the WOH hook weight signal.

The calculation of the average weight estimate on the WOB ₀ tool 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 _{wob are} then calculated simultaneously and in real time.

We compare Rf to the two bounds delimiting the “at risk” interval bit-bouncing type dysfunction.

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

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

We then consider the second criterion R _wob .

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

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

Finally, if R _wob is strong, there is probably significant bit-bouncing. The alarm is on fire is red (reference 30).

We could, without departing from the scope of the present invention, not limit the graduation of the dysfunction on the basis of three colors, but associate a color with each degree of severity of the oscillations (for example all 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 bottom instrumented fittings and area.

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

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

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

The present invention is advantageously implemented on a drilling site in order to have as precise detection as possible of the danger of vertical movement of the drilling tool in time real, and this from only surface measurements, in particular fluctuations in longitudinal acceleration and rotational speed of conventional means for rotating the drilling string, and a surface installation equipped with electronic means and IT. 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 while the head of the drill string remains substantially stationary and only a compressive force important is applied to the tool. This malfunction may have consequences of adverse effects on the life of the tools, on increased mechanical fatigue of the drill string and the frequency broken connections.

Claims (9)

Method for estimating the effective longitudinal behavior of a drilling tool (12) fixed to the end of a drilling rig and rotated in a well (7) by drive means located on the surface, in which we use a physical model of the drilling process based on general mechanical equations 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 of said lining, said model is reduced by keeping only some of the eigen modes of the state matrix of said model, characterized in that 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 divided by the average instantaneous speed of rotation at the surface, Rwob being a function of the standard deviation of the weight signal on the WOB tool estimated by the reduced longitudinal model 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 in that the dangerousness of the longitudinal behavior of said drilling tool is determined from said values of Rf and Rwob. Method according to claim 1, in which Rf is compared with an interval whose limits are determined such that it cannot no dangerous longitudinal behavior of the tool if Rf is not not included in said interval. Method according to one of claims 2, in which Rf is included in said interval, and in that we quantify the dangerousness of the longitudinal behavior of the drilling tool as a function of the values of Rwob. Method according to one of the preceding claims, in which R f = 20 * f WOH RPM 0 where: f _WOH , expressed in Hertz, is the main frequency of oscillations of WOH over the interval [0, 10] Hz and RPM ₀ is the average instantaneous rotation speed at the surface, expressed in revolutions / min. Method according to one of the preceding claims, in which said limits of said interval are 0.95 and 0.99. Method according to one of the preceding claims, in which 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 weight on the average tool, defined from the mass of the trim and the average hook weight. Method according to claims 3 and 6, in which determines that, for Rwob less than 0.6, there is no danger, and that for Rwob between 0.6 and 0.8 there is a medium danger, and for Rwob greater than 0.8 there is extreme danger. System for estimating the effective longitudinal behavior of a drilling tool attached to the end of a drilling rig rotated in a well by drive means located on the surface, in which a calculation installation comprises means physical modeling of the drilling process based on general mechanical equations, in that the parameters of said modeling means are identified taking into account the parameters of said well and of said lining, in that the calculation installation includes means for reducing said model in order to keep only some of the eigen modes of the state matrix of said model, characterized in that said system comprises means for calculating, in real time, at least two values Rf and Rwob, Rf being a function of the main frequency of oscillation of the hook weight WOH divided by the average instantaneous speed of rotation at the surface, Rwob being a function of the standard deviation of the weight signal on the WOB tool 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 weight of the lining and the average hook weight, and in that said system includes means for alarming the danger of the longitudinal behavior of said drilling tool from said values of Rf and Rwob. Application of the method and system according to one of the previous claims, to the determination of the dangerousness of the drilling tool jump malfunction

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