EP0026706A1 - Process and device for determining the directional parameters of a continuously explored well - Google Patents

Abstract

This method and this device use the measurement signals of an accelerometer and a magnetometer with three sensitive axes housed in a probe exploring the well. The probe is continuously moved into the well during the measurement. In the most common case, the accelerometer signal is prefiltered, then combined with the magnetometer signal to rid it of the alteration it undergoes due to the displacement of the probe in the well, then subjected to pass filtering. - very selective bottom, and finally again combined with the signal from the magnetometer for the determination of well direction parameters. This method and this device allow rapid exploration of the well and improve the quality of the measurements.

Description

The present invention relates to a method and apparatus for determining direction parameters of a well as a function of depth, and more particularly to a method and apparatus which use the measurement signals of an accelerometer and a magnetometer to three sensitive axes housed in a probe exploring the well. The probe is continuously moved into the well during the measurement. In the most common case, the accelerometer signal is prefiltered, then combined with the magnetometer signal to rid it of the alteration it undergoes due to the displacement of the probe in the well, then subjected to pass filtering. - very selective bottom, and finally again combined with the signal from the magnetometer for the determination of well direction parameters.

The crust of the earth is made up of layers of different natures, thicknesses and inclinations, and it has long been apparent that all information concerning the successive layers, and in particular their inclination, is of definite interest in fields such as that of oil research. However, since such information on the inclination of the layers is not directly accessible in the current state of the art, it is conventionally used to use probes, which are moved in a well passing through these layers, and which provide information on their orientation in relation to the layers crossed by the well.

It is easy to understand that this information representative of a relative orientation is insufficient and that it is therefore necessary, in order to know the orientation of the layers, to determine the three-dimensional topographic orientation of the well and the position taken by the probe in the well at the depth of investigation.

It is also well known, in aviation techniques, that the three-dimensional topographic orientation of an airplane or a rocket can be determined by using the measurement signals of an accelerometer and a magnetometer with three sensitive axes. . These signals are immediately usable when the aircraft is flying at a constant speed and has a trajectory regular. When there are sudden disturbances or accelerations, the signals from the accelerometer and magnetometer generally lose their interest in this orientation determination.

It is within this very general framework that the process described in United States patent no. 3,862,499 issued to CE Isham et al, as well as that of the present invention, which aims at determining parameters representative of the topographic orientation of the well and, although optionally, the determination of the position taken by the probe in the well.

According to the known method, the probe is lowered into the well and stabilized at a certain depth. The signals from an accelerometer and a magnetometer mounted in the probe are recorded while the probe is fixed in the well in the absence of any disturbance. These stationary component signals are combined to obtain two well direction parameters, namely the deflection angle, defined as the angle formed between the longitudinal axis of the well and the vertical, and the azimuth, defined as the angle formed between two vertical planes, one of which contains the longitudinal axis of the well and the other the north direction. Then the probe is moved into the well and stabilized at another depth. New signals are produced when the probe is fixed, and are combined to obtain new values for the deflection angle and azimuth.

This method, despite the fact that it allows satisfactory accuracy to be obtained on the parameters measured at each station of the probe, has several limitations, and in particular the two significant drawbacks below.

The first, immediate, is that the need to stabilize the probe for each measurement causes a detrimental increase in the duration of exploration of the well.

The second is that the orientation of the well between two measurements being physically unobservable, any variation in orientation, which appears and disappears between two successive measurements, critically increases the error on the location of the points of the well located below of this orientation variation.

In this context, the present invention aims to propose a method for determining parameters of a well which is faster than the known method described above.

Another object of the present invention is to propose a method making it possible to physically determine variations in the orientation of the well at any point of an explored longitudinal portion of this well.

The method of the invention is essentially characterized in that the phases consisting in producing said acceleration and locating signals and in moving the probe are simultaneous and substantially continuous, in that said phase of determining the direction parameters is divided into a virtual stabilization step by which the effects of the displacement of the probe are eliminated, in the components of one of the signals, constituting a signal to be stabilized, by means of the components of the other signal, constituting a stabilizing signal, and by a final step of combining the components of said signals, said phase of determining the parameters comprising an intermediate low-pass filtering operation involving at least stabilized components of said signal to be stabilized and by which frequency variations greater than the maximum frequency of variations due to the acceleration of gravity.

Preferably, said phase of determining the steering parameters further comprises a step preliminary to said step of virtual stabilization, comprising an operation of prefiltering the components of the acceleration signal, by which the variations in these components are substantially attenuated. signal having a frequency greater than the greatest possible frequency of the rotational movement of the probe around its longitudinal axis.

In a simple manner, one uses respectively, to produce said acceleration and locating signals, an accelerometer and a direction indicator, this accelerometer and this direction indicator each having a first and a second sensitive transverse axis, perpendicular to each other and to the longitudinal axis of the probe, and a third sensitive axis, of longitudinal direction and coincident with the axis of the probe, said signals each comprising two transverse axial components and a longitudinal axial component and said direction indicator being for example a magnetometer giving in the coordinate system of its three sensitive axes the direction of the earth's magnetic field vector.

The preliminary step of the direction parameter determination phase comprises determining a transverse diagonal component of the stabilizing signal from the transverse axial components of this signal and eliminating the effects of rotation, using the axial and diagonal components. transverse of this same signal, in the transverse axial components of the signal to be stabilized to obtain components stabilized in rotation, corresponding to a reference position of the probe around its longitudinal axis.

The preliminary step comprises the operations consisting in: determining a transverse diagonal component of the locating signal from the transverse axial components of this signal; determine from this transverse diagonal component and the longitudinal axial component of this same locating signal the sign of the difference between a first angle, formed between said vector of fixed direction and the longitudinal axis of the probe, and a limit angle of predetermined value; defining the stabilizing and stabilizing signals, respectively by the locating and acceleration signals when the sign of said difference is positive, and by the acceleration and locating signals when this sign is negative; and determining a transverse diagonal component of the stabilizing signal from its transverse axial components when said stabilizing signal is defined by said acceleration signal.

The final step of combining the components of said signals comprises a preliminary normalization operation consisting in determining at least one standard, a normalized longitudinal component, and a normalized transverse diagonal component of the acceleration signal.

The final step of combining the components of the signals comprises an operation of determining a first of said direction parameters, this operation involving the combination of diagonal transverse and longitudinal axial components, filtered and normalized, of said acceleration signal, this first parameter representing the angle formed between the vertical and. the longitudinal axis of the probe.

This final step of combining components of the signals also comprises an operation of determining a second of said direction parameters, this operation involving the combination of the three normalized and stabilized axial components of said signal to be stabilized, and of the normalized longitudinal and diagonal transverse components of said stabilizing signal, this second parameter representing the angle formed between the horizontal trace of the vertical plane passing through the longitudinal axis of the probe and the horizontal projection of said fixed direction vector different from the vertical.

When the sign of the difference determined during said preliminary step is positive, said final step comprises an operation of reintroducing the effects of rotation of the probe, supplying from the two stabilized transverse axial components of the acceleration signal and the transverse components diagonal and axial of the locating signal rage, two transverse axial components of the acceleration signal which are no longer stabilized again with respect to said reference position of the probe around its longitudinal axis.

The final step of combining the components of the signals advantageously comprises an operation of determining a third of said direction parameters, this operation involving the combination of the three unstabilized axial components of said acceleration signal and the three unstabilized axial components of said signal marking, this third parameter representing the angle formed between the horizontal projection of said vector of fixed direction different from the vertical and the horizontal projection of a vector perpendicular to the longitudinal axis and joining this axis to a fixed point of the probe.

Furthermore, this final step of combining the components of the signals can also comprise an operation of determining a fourth of said direction parameters, this operation involving the combination of the two non-stabilized transverse axial components of the acceleration signal, this fourth parameter representing the dihedral angle formed between a vertical plane containing the longitudinal axis of the probe and a plane containing the axis of the probe and passing through said fixed point of the probe.

Preferably, the final step of combining the components of the signals comprises, after the operation of determining the first direction parameter, an operation of comparing this parameter with a predetermined minimum value and, when the first parameter is less than this minimum value , an operation consisting in forcing the second and / or fourth parameters to zero.

Under current conditions of exploration of the well, it is advantageous that the low-pass filtering eliminates, by a rapidly increasing attenuation from 3 dB, the signal variations having a frequency higher than 8.10 2 Hz and that the pre-filtration consists an attenuation, increasing from 3 dB, of signal variations having a frequency greater than 2.5 Hz.

• - La figure 1 est une vue schématique représentant, en coupe, un puits exploré par une sonde ;
• - La figure 2 est un diagramme fonctionnel (flov-chart) représentant les. principales opérations de la phase de détermination de valeurs de paramètres dans le procédé de l'invention ;
• - Les figures 3a et 3b sont des représentations schématiques de circuits multifilaires pour la circulation et le traitement des composantes des signaux d'accélération et de repérage dans la phase de détermination des paramètres, et sur lesquelles chaque conducteur est assigné à une seule composante d'un des deux signaux ces figures sont raccordées par les faisceaux de conducteurs φ₁et φ₂;
• - La figure 4 est un diagramme représentant les caractéristiques du filtre de préfiltrage ;
• - La figure 5 est un diagramme représentant les caractéristiques du filtre passe-bas.

A particular embodiment of the invention will be described below, by way of indication and in no way limitative, with reference to the appended drawing, in which:

• - Figure 1 is a schematic view showing, in section, a well explored by a probe;
• - Figure 2 is a functional diagram (flov-chart) representing the. main operations of the phase of determining parameter values in the method of the invention;
• - Figures 3a and 3b are schematic representations of multi-wire circuits for the circulation and processing of the components of the acceleration and location signals in the phase of determining the parameters, and on which each conductor is assigned to a single component of one of the two signals these figures are connected by the bundles of conductors φ ₁ and φ ₂ ;
• - Figure 4 is a diagram showing the characteristics of the pre-filter;
• - Figure 5 is a diagram showing the characteristics of the low-pass filter.

As previously indicated, the method of the invention aims to determine different parameters, related to the topographic orientation taken by a well 1 at a given depth.

To this end, there is an elongated probe 2 which is initially lowered into the well 1 by means of a cable 3 secured to the probe and wound on a winch 4.

Between the winch and the upper edge of the well, the cable passed over a measuring wheel 5 connected to a counter 6 recording the rotations of the wheel 5. The depth at which the probe is in the well, which obviously depends on the length of the cable unwound from the winch, can, in known manner, be deduced from the indication of the counter 6.

The probe 2 comprises centering poles 7 enabling it to always adopt a position in the well in which its longitudinal axis 2a is, over: the length of this probe at least, substantially coincident with the longitudinal axis 1a of the well, the orientation of the probe axis thus assimilating to the orientation of the well at the exploration depth.

Inside the probe are housed an accelerometer 8 and a magnetometer 9 firmly attached to the probe.

The accelerometer provides a signal with three axial components whose amplitudes represent the lengths of the projections, on three respective sensitive axes, of the vector associated with the set of accelerations undergone by the probe, and the magnetometer provides a signal with three axial components of which the amplitudes represent the lengths of the projections, on three respective sensitive axes, of the vector associated with the magnetic field passing through the probe, that is to say in practice with the terrestrial magnetic field.

However, the magnetometer 9 could be replaced by a gyroscope delivering a three-component signal constituting location information of the probe with respect to the characteristic direction of the gyroscope, or by any other direction indicator, provided on the one hand that the direction of the vector represented by the signal that this indicator would provide is fixed and known and on the other hand that it is different from the vertical.

The sensitive axes of the accelerometer and the magnetometer form a fixed rectangular trihedron with respect to the probe, the accelerometer and the magnetometer having a first sensitive axis in. the longitudinal direction of the probe and two transverse sensitive axes.

The probe having been lowered into the well to a known depth is raised using the winch and the cable at a substantially constant speed while the accelerometer and the magnetometer produce their respective signals, which are transmitted to the surface by the cable. 3, and recovered at the surface in correlation with the signal from counter 6.

Due in particular to the irregularities in the wall of the well and the elasticity of the cable 3, the probe 2 is subjected to accelerations which, in addition to the acceleration of gravity, include the acceleration due to the movement of the probe 2 in the well. Indeed, on the one hand the probe undergoes transverse movements and shocks against the wall and on the other hand, despite the fact that the cable is rewound at substantially constant speed, the probe advances in the longitudinal direction by jerky progressions a movement called "yo-yo". In addition, the probe generally undergoes an additional movement of rotation about its longitudinal axis.

If we can consider the components of the tracking signal, coming from the magnetometer, as appreciably independent of the sudden movements of the probe, on the other hand the components of the acceleration signal, coming from the accelerometer, are, to a very large extent, representative of these parasitic movements of limited amplitude, which critically disturb it.

The phase of determining the direction parameters of the well from the signals from the accelerometer and the magnetometer therefore requires different steps and operations aimed in particular at recovering from these signals the information that they would have provided directly if they had been produced while the probe was at rest and had not undergone any rotation around its longitudinal axis.

• - S désigne un signal quelconque de nature vectorielle, de composantes axiales S_x, S_y et S_z;
• - S désigne la norme partielle ou composante diagonale de ce signal
  
• - S_xyz désigne la norme :
  
  du signal S ;
• - S_ζo et S_ζ désignent une même composante axiale du signal S, respectivement avant et après une opération modifiant cette composante ; _ζo et ζ peuvent respectivement adopter les significations suivantes : x_o et x; ^y0 et y ; z_o et ^z ; x_oy_o et xy ;
• - S_ζ désigne une composante normée si
  
• - ^γS et ^µS désignent respectivement les signaux d'accélération et de repérage, de nature vectorielle, respectivement issus de l'accéléromètre et du magnétomètre et ayant les composantes axiales respectives ^γS_x, γS_y, γS_z et ^µS_x, ^µS_y et ^µS_z;
• - ^aS et ^pS (a = actif p = passif) désignent respectivement un signal stabilisateur et un signal à stabiliser, la nature de la stabilisation étant expliquée en détail ultérieurement.

In the description which is given below of these different steps and operations, the following definitions will be used:

• - S denotes any signal of a vector nature, of axial components S _x , S _y and S _z ;
• - S denotes the partial norm or diagonal component of this signal
  
• - S _xyz denotes the standard:
  
  signal S;
• - S _ζo and S _ζ denote the same axial component of the signal S, respectively before and after an operation modifying this component; _ζo and ζ can respectively take the following meanings: x _o and x; ^y0 and y; z _o and ^z ; x _o y _o and xy;
• - S _ζ denotes a normalized component if
  
• ^γ S and ^µ S respectively designate the acceleration and location signals, of vectorial nature, respectively from the accelerometer and the magnetometer and having the respective axial components ^γ S _x , γS _y , γS _z and ^µ S _x , ^µ S _y and ^µ S _z ;
• - ^a S and ^p S (a = active p = passive) respectively designate a stabilizing signal and a signal to be stabilized, the nature of the stabilization being explained in detail later.

Referring to FIG. 2, which represents the phase for determining the values of the parameters, it can be seen that this phase comprises a preliminary step ETO, a virtual stabilization step ET1, itself comprising an operation D ₁ or D ₂ of elimination of the effects of rotation, and a final step ET2 of combining the processed components of the signals YS and ^μ S, the step ET1 and the final step ET2 being separated by an intermediate operation OIF of low-pass filtering F ₂ 13 or F2 47.

The preliminary step ETO comprises, in addition to possible operations I 13 and I 46 of inverting the sign of the components of the signals ^Y _S and ^µ S, prefiltering operations F ₁ of the signal ^Y S, of delay R ₁ of the signal ^µ S, of normalization N ₁ of the signal ^µ S, of choice with test "T = 0?" and, optionally of normalization N ₃ of the signal ^Y S.

The operations I 13 and 1 46 consist in changing the sign of the components of the signals ^Y S and ^μ S and are only necessary when the ETO step relates to the signals directly supplied by the accelerometer _' and the magnetometer as representative of vectors of directions opposite to those of the acceleration vectors on the one hand and the earth's magnetic field on the other.

The pre-filtering operations F ₁ and delay R ₁ will be explained in detail later.

In addition to obtaining pre-filtered components of the acceleration signal, the preliminary ETO stage has two essential purposes. In fact, as previously mentioned, the components of the acceleration and location signals generally carry information coming from a parasitic phenomenon, namely the rotation of the probe around its axis. To eliminate the effects of this rotation on the values of the transverse axial components of one of the signals hereinafter called "signal to be stabilized", use is made, in the subsequent step of virtual stabilization ET1, of the use of the components transverse axial and a transverse component, called diagonal, of the other signal, hereinafter called "stabilizing signal". However, according to the topographic orientation of the longitudinal axis of the probe, it may be preferable either to use the components of the signal from the magnetometer to correct the components of the signal from the accelerometer, or, conversely, to use the accelerometer signal components to correct the magnetometer signal components. The preliminary stage ETO therefore appears to have the function, on the one hand, of making it possible to determine which of the two signals ^Y S and ^µ S must play the role of signal to stabilize ^p S, the other signal obviously having to play the role of signal stabilizer ^a S, and on the other hand to supply, for the needs of the virtual stabilization step ET1, the diagonal transverse component of the stabilizer signal, that is to say ^a S according to the notation previously introduced.

The operation for determining ^a S, is included in block N ₃ or in block N ₁ according to, respectively, whether the role of S is held by the signal ^Y S or by the signal ^µ S. However, as the choice with test "T ₁ = 0?" suppose, as will appear below, the use of the diagonal component of one of the two signals, and very preferably of ^µ S, we first determine ^µ S _xy during the operation N ₁ , we then use ^µ S _xy to conduct the test "T ₁ = 0?" which makes it possible to decide which of the two signals should play the role of stabilizing sigral - t _eur a _S and one determines ^a S _xy = ^Y S _xy during the operation N ₃ if the test "T _l = 0?" has led to assign to S the role of stabilizing signal S.

The detailed description of the various operations of the whole parameter determination phase generally refers hereinafter to Figures 3a and 3b on which are represented the lines of material flow or virtual information, each assigned, con- _tr a _ir in no way Figure 2, single component or signal standard.

In blocks I 13, 1 46; F ₁ ; R ₁ , R ₂ .14, R ₂ .59; F ₂ .13 and F ₂ .47 in FIG. 2 correspond respectively to the inverters I ₁ to I ₁₃ and I ₄ to I6, the pre-filtration filters F ₁ .1 to F ₁ .3, the buffer cells R ₁ .1 to R ₁ .5, R ₂ .1 to R ₂ .4 and R ₂ .5 to R ₂ .9 and filters F ₂ .1 to F ₂ .3 and F ₂ .4 to F ₂ .7 in Figures 3a and 3b.

The blocks N ₁ to N ₄ , D ₁ and D ₂ , E ₁ , DEV 1, DEV 2, RB 1 and RB 3 AZI1.1 and AZI1.2, AZIM1 and AZIM3 are to be considered as operations in FIG. 2, and as function generators, suitable for carrying out these operations, in FIGS. 3a and 3b.

In FIGS. 3a and 3b, the notations of the components of the signals do not take account, for reasons of simplification, of the fact that these components obviously keep, at all levels, the memory of the processing operations which have been applied to them in the blocks that 'they have crossed .. previously.

The axial components ^Y S _xo , ^Y S _yo , S and ^µ S _xo , ^µ S _yo , and ^µ S of the accelerometer and magnetometer output, available at the start of the parameter value determination phase, can be considered as each having on each of the elementary time intervals At, a constant amplitude.

The axial components of the magnetometer, of sign possibly corrected by the inverters I ₄ ; I ₅ and I6 are applied to the function generator N ₁ , which outputs the standard ^µ S _xyz , the normalized axial components ^µ S _x = ^µ S _xo / ^µ S _xyz , ^µ S _y = ^µ S _yo / ^µ S _xyz , ^µ S _z = ^µ S _zo / ^µ S _xyz . and the normalized transverse diagonal component

The axial components of the accelerometer, sign possibly corrected by inverters I _1, I ₂ and I _3, are applied to the filtered t _r are identical prefilter F ₁ to F ₁ .1 .3 ·

avec. a_k = 0,54 - 0,46 cos

If _ζo represents x _o , y _o or z for a component before filtering, if ζ represents x, y, z for a component after filtering, if k and ℓ represent whole numbers and if YS _{ζ, iΔt} represents the amplitude of the component ζ of the signal ^Y S during the i ^th interval of time Δt, the characteristic of filters F ₁ .1 to F ₁ .3 is to deliver for all ℓ, an output signal such as:

with. a _k = 0.54 - 0.46 cos

The characteristic of these filters F ₁ is represented in FIG. 4 which carries, on the abscissa, the frequency and, on the ordinate, the attenuation, in the case where the value of each component of the sigrial ^Y S of the accelerometer is sampled all 8.3 milliseconds (Δt = 8.3 ms). New filtered components therefore appear every 15.5Δt, or approximately every 1 / 7.5 seconds. The role of filters F ₁ is to very substantially attenuate, in the filtered components, the signal variations having a frequency greater than the maximum possible frequency of the rotational movement of the probe around its axis. It can be seen in FIG. 4 that the frequencies above 2.5 Hz undergo an attenuation greater than 3 dB.

As the appearance of the filtered component ^Y S _{ζ, 15.5Δt} supposes the previous appearance of the unfiltered component ^Y S _{ζo, (15.5 ) (ℓ + 1) Δt} the output signal of the filter F ₁ has a certain delay from the input signal. As it is obviously necessary to use together the components of the signals from the accelerometer and the magnetometer relating to the same instantaneous depth of the probe in the well, the components ^µ S _x , ^µ S _y , µS _z , ^µ S _xy and the standard ^µ S _xyz of the locating signal, coming from the magnetometer, undergo in cells R ₁ .1 to R ₁ .5 a delay equivalent to that caused by filtering F ₁ on the components of the acceleration signal.

est positive ou nulle, la sortie du comparateur COMP 1 se met dans l'état T₁ = 0 (cas général), et, si u est négatif, dans l'état T₁ = 1(cas particulier, le moins fréquent), T₁ étant par exemple défini par la fonction explicite T₁=1- INT 2 u |u| où "INT" désigne la fonction "partie entière de". Ainsi, pour la valeur, généralement appropriée, de 5.10^-2 pour L1, la sortie T₁ ducomparateur COMP 1 sera désactivée si l'angle

est supérieur ou égal à 3° (cas général).The divider DV, to which the components µS _z and ^µ S _xy are then applied, performs the ratio ^µ S _xy / ^µ S _z , which represents the tangent of the angle a formed between the direction of the earth's magnetic field vector and that of the axis of the probe. The information ^µ S _xy / ^µ S _z is then applied to the comparator COMP 1 which compares to a predetermined value limit L ₁ . If the quantity

is positive or zero, the output of comparator COMP 1 is put in the state T ₁ = 0 (general case), and, if u is negative, in the state T ₁ = 1 (particular case, the least frequent), T ₁ being for example defined by the explicit function T ₁ = 1- INT 2 u | u | where "INT" denotes the "whole part of" function. Thus, for the generally appropriate value of 5.10 ^-2 for L1, the output T _{1 of the} comparator COMP 1 will be deactivated if the angle

is greater than or equal to 3 ° (general case).

T₁ de le sortie du comparateur COMP 1 permet d'opérer un aiguillage, symboliquement réalisé par deux relais MT₁ et MT1. Le relais KT₁ ferme ses contacts lorsque T₁ = 1 - T₁ est égal à 1 et le relais MT₁ ferme ses contacts lorsque T₁ est égal à 1. Lorsque T₁ est nul,(cas général), c'est-à-dire lorsque T₁ est égal à 1 (fig.3a) le signal ^µS du magnétomètre est utilisé comme signal stabilisateur ^aS et le signal ^YS de l'accéléromètre comme signal à stabiliser ^pS, ce qui signifie que le signal du magnétométre est utilisé pour corriger le signal de l'accéléromètre des effets de rotation de la sonde. Inversement lorsque T₁ est égal à 1 (cas particulier), c'est-à-dire lorsque T₁ est nul, le signal stabilisateur ^aS est le signal ^YS de l'accéléromètre, qui sert à corriger le signal ^µS du magnétomètre, constituant le signal à stabiliser ^pS.

T ₁ of the output of the comparator COMP 1 makes it possible to operate a switch, symbolically produced by two relays MT ₁ and MT1. Relay KT ₁ closes its contacts when T ₁ = 1 - T ₁ is equal to 1 and relay MT ₁ closes its contacts when T ₁ is equal to 1. When T ₁ is zero, (general case), i.e. when T ₁ is equal to 1 (fig. 3a) the signal ^µ S of the magnetometer is used as the stabilizing signal ^a S and the signal ^Y S of the accelerometer as the signal to stabilize ^p S, which means that the signal a magnetometer is used to correct the accelerometer signal for the effects of rotation of the probe. Conversely when T ₁ is equal to 1 (special case), that is to say when T ₁ is zero, the stabilizing signal ^a S is the signal ^Y S of the accelerometer, which is used to correct the signal ^µ S of the magnetometer, constituting the signal to be stabilized ^p S.

pour les deux valeurs de T₁.More concisely, the MT ₁ and MT relays achieve the definition:

for the two values of T ₁ .

In the. case = T ₁ = ¹ (special case), the components ^Y S _xo and ^Y S _xy coming from F ₁ .1 and F, .2 are combined in N ₃ to obtain the diagonal transverse component

^pS_xo et ^pS_yo proviennent de F₁.1 et F₁.2 si T₁ = 0 (cas général) et de R₁.1 et R₁.2 si T₁ = 1 (cas particulier) ; ^aS_x et ^aS_y proviennent de

R₁.1 et R₁.2 si T₁= 0 (cas général) et de F₁.1 et F 2 si T_l = 1 (cas particulier) et ^aS_xy provient de N₁ par R₁.4 lorsque T₁= 0 (cas général), et de N lorsque T₁= 1 (cas particulier). Les composantes ^pS _x et ^pS stabilisées sont sensiblement celles qui auraient été obtenues en y absence de rotation de la sonde autour de son axe longitudinal. Les composantes ^pS_x et ^pS_y provenant des blocs D₁ ou D₂, la composante axiale longitudinale S du signal de l'accéléromètre (définissant ^pS _z si T₁= 0 et ^aS₂ si T₁= 1), et, si T₁ =1 (cas particulier), la composante diagonale ^aS_xy du signal stabilisateur, subissent ensuite, dans les blocs F₂.1 à F₂.7 un filtrage passe-bas dont la caractéristique est donnée par

avec b_k = 0,54 - 0,46 cos

The virtual stabilization step ET1 essentially consists in correcting the transverse axial components of the signal to be stabilized, by eliminating in these components the effects of the rotation of the probe, by means of the diagonal and axial transverse components of the stabilizing signal, in the blocks D ₁ or D ₂ ; for components ^p S _xo , ^p S _yo , ^a S _x , ^a S _y , ^a S _xy input D ₁ and D ₂ output the new components ^p S _x and ^p S _y such that :

^p S _xo and ^p S _yo come from F ₁ .1 and F ₁ .2 if T ₁ = 0 (general case) and from R ₁ .1 and R ₁ .2 if T ₁ = 1 (particular case); ^a S _x and ^a S _y come from

R ₁ .1 and R ₁ .2 if T ₁ = 0 (general case) and of F ₁ .1 and F 2 if T _l = 1 (particular case) and ^a S _xy comes from N ₁ by R ₁ .4 when T ₁ = 0 (general case), and of N when T ₁ = 1 (special case). The stabilized components ^p S _x and ^p S are substantially those which would have been obtained in the absence of rotation of the probe around its longitudinal axis. The components ^p S _x and ^p S _y coming from blocks D ₁ or D ₂ , the longitudinal axial component S of the accelerometer signal (defining ^p S _z if T ₁ = 0 and ^a S ₂ if T ₁ = 1), and, if T ₁ = 1 (special case), the diagonal component ^a S _xy of the stabilizing signal, then undergo, in blocks F ₂ .1 to F ₂ .7 a low-pass filtering whose characteristic is given by

with b _k = 0.54 - 0.46 cos

The characteristic of these filters F ₂ is shown in Figure-5 which carries, on the abscissa, the frequency and on the ordinate, the transmitted amplitude, in the case where the value of each component to be filtered is sampled every 1/7 , 5 seconds (Δt = 1 / 7.5 s). New filtered components therefore appear every 31.5Δt, or approximately every 4.2 seconds.

The role of the filters F ₂ is to eliminate, from the filtered components, the variations in the amplitude having a frequency greater than the maximum frequency of the amplitude variations which are attributable to the acceleration of gravity and which essentially derive from the variations the angle formed between the vertical and the longitudinal axis of the probe. We see in Figure 5 that frequencies above 8.10 ^-2 Hz undergo an attenuation greater than 3 dB and very rapidly increasing.

As the appearance of a filtered component S _ξ, (31.5) ℓΔt ^SUP pose previous occurrence of the ^unfiltered component S _ξ o, (31.5Xℓ + 1) .DELTA.t components at the output of filters F2.1 F2.7 undergo a delay of 31.5 Δt. To eliminate the impact of this. delay, the unfiltered components undergo equivalent delays in the buffer cells R ₂ .1 to R ₂ .9.

After the low-pass filtering, the components of the accelerometer signal are normalized. When T ₁ = 0 (general case), the components of ^γ S = ^p S are normalized in N ₂ , which provides the norm ^γ S _xyz = ^p S _xyz and the diagonal normalized components ^γ S _xy = ^p S _xy and axial γS _x = ^p S _x , ^γ S _y = ^p S _y and ^γ S _z = ^p S _z . When _T1 = 1 (special case), the components of ^γ S = ^a S are normalized in N ₄ , which provides the norm ^γ S _xyz = ^a S _xyz and the normalized longitudinal components ^γ S _z = ^a S _z and diagonal ^γ S _xy = ^a S _xy .

Further, when T ₁ = 0 (general case), new compo- _s antes transverse ^γ S ^p _x = S _x and S _y = ^γ S ^p _y of the accelerometer signal are obtained in E _1, to the output of N ₂ , using the transverse components ^a S _x = ^µ S _x , ^a S _y = ^µ S _y and ^a S _xy = ^µ S _xy of the locating signal from the magnetometer. This operation E ₁ constitutes the opposite operation to the operation D previously mentioned and has the effect of reintroducing, into the components of the accelerometer signal, the information relating to the rotation of the probe around its longitudinal axis.

If ^γ S _xo and ^γ S _yo are the components of ^γ S at the exit of N ₂ and ^µ S _x , ^µ S _y , ^µ S _xy the transverse components of ^µ S at the exit of R ₂ .1, R ₂ . 2 and R _2. 4, the new components of ^γ S at the output of E ₁ are:

It should be noted here that these components ^γ S _x and ^γ S _y are not at all identical or proportional to the components of the accelerometer output signal. If, indeed, these new components ^Y S _x and ^γ S y again contain the information relating to the rotation of the probe around its longitudinal axis with respect to a reference position, on the other hand they are rid of disturbing information originating impacts of the probe against the wall of the well.

The final step ET2 of combining the components of the acceleration and locating signals results, by different operations described below, in the determination of different parameters representative of the topographic orientation of the well and of the position of the probe in the well relative to a reference position corresponding to a setting of the probe for the rotational movements around its longitudinal axis.

The diagonal transverse components γS _xy and longitudinal ^Y S _z of the accelerometer signal, normalized in N ₂ or in N ₄ , are combined to obtain the value of a first parameter, DEV, representing the angle β formed between the vertical and the longitudinal axis of the probe.

If T ₁ = 0 (general case), the DEV parameter is obtained in DEV 1 which provides the information with the same name DEV 1, and if T ₁ = 1, DEV is obtained in DEV 2, providing the information DEV 2. The function generators DEV 1 and DEV 2 are identical and provide the information defined by

et

Autrement dit, J(N,D) est égal à : Arctg

+ π si D est négatif, et à Arctg

si D est positif, 2π étant ajoutés si Arctg

est négatif.In the case T ₁ = 0 (general case), the information DEV 1 is, in the comparator COMP 2, compared with an angle L2 of predetermined value, for example equal to 0.5 °; according to the result of this comparison, the value of two other pieces of information RB1 and AZIM 1 is multiplied by 0 or 1, which will be defined later. This is, schematically, represented by the possibility, for the comparator COMP 2, of controlling two relays MT ₂ .1 and MT ₂ .2 closed or switched to ground. The comparator COMP 2 and the relays MT ₂ .1 and MT ₂ .2 are equivalent to a test "T2 = 0?" in which T ₂ is a function with value 1 if the angle v defined by .v = DEV 1 - L2 is positive or zero and with zero value if-v is negative. The function T ₂ can for example take the explicit form: T ₂ = INT 2 ^{v- | v |} where INT indicates the function "whole part of". To define the information RB1 and AZIM 1, previously mentioned, it is advantageous to define two functions, H and J, of two variables N and D, such as:

and

In other words, J (N, D) is equal to: Arctg

+ π if D is negative, and to Arctg

if D is positive, 2π being added if Arctg

is negative.

The two axial transverse components of the signal to be stabilized ^p S _x , ^p S _y , rid of the effects of rotation of the probe and filtered, coming from N ₂ when T ₁ = 0 (general case) and from F ₂ .6 and F ₂ .7 when T ₁ = 1, the normalized longitudinal component ^p S _z of this same signal, coming from N ₂ when T ₁ = 0 (general case) and from R ₂ .9 when T ₁ = 1, and the diagonal components and longitudinal S _x y and S _z of the stabilizing vector, coming from R ₂ .4 and R ₂ .3 when T ₁ = 0 (general case) and from N ₄ when T ₁ = 1, are combined to obtain the value of a second parameter, AZIM, representing the angleζ formed between the horizontal trace of the vertical plane passing through the longitudinal axis of the probe and the horizontal projection of the earth's magnetic field vector.

• AZIM 1 = J(N,D) avec
  
  Après le test "T₂ = 0 ?", l'information AZIM 1 devient AZIM 2 telle que AZIM 2 = T₂.AZIM 1.
• Pour T₁ = 1, le bloc AZIM 3 réalise la fonction élaborant l'information AZIM 3, définie par :
• AZIM 3 = J(N,D) avec
  
  Le paramètre AZIM est donc égal à AZIM 2 si T₁ = 0 (cas général) et à AZIM 3 si T₁ = ¹.

For T ₁ = 0 (general case), the AZIM 1 block performs the function elaborating the information of the same name, AZIM 1, previously mentioned and defined by:

• AZIM 1 = J (N, D) with
  
  After the test "T ₂ = 0?", The AZIM 1 information becomes AZIM 2 such that AZIM 2 = T ₂ .AZIM 1.
• For T ₁ = 1, the AZIM 3 block performs the function developing the AZIM 3 information, defined by:
• AZIM 3 = J (N, D) with
  
  The AZIM parameter is therefore equal to AZIM 2 if T ₁ = 0 (general case) and to AZIM 3 if T ₁ = ¹ .

et

Lorsque T₁ = 1, la combinaison des six composantes axiales des signaux est réalisée par AZI1.2, de la même façon, c'est-à-dire avec les mêmes expressions pour N et D. Le paramètre AZI 1 est donc égal à AZI1.1 si T₁ = 0 et à AZI1.2 si T₁ = 1.The three axial components ^γ S _x , ^γ S _y and ^γ S _z of the accelerometer signal, containing the effects of rotation of the probe, i.e. coming from, when T ₁ = 0 (general case) of F ₁ with regard to ^γ S _x and ^γ S _y and N ₂ for ^γ S _z , and, when T _l = 1, of R ₂ .5 and R ₂ .6 with regard to ^γ S _x and YS , and of N ₄ for ^γ S _z , and the three axial components ^µ S _x , ^µ S _y and ^µ S _z of the signal from the magnetometer, also containing the effects of rotation of the probe, i.e. coming from, when T ₁ = 0 (general case) of R2.1, R ₂ .2 and R ₂ .3 and, when T ₁ = 1, of R ₂ .7, R ₂ .8 and R ₂ .9, are combined to obtain the value of a third parameter, AZI 1, representing the angle δ formed between the horizontal projection of the earth's magnetic field vector and the horizontal projection of a vector perpendicular to the longitudinal axis of the probe and joining this axis at a fixed point P of the probe, distant from this same axis. This combination is made, when T ₁ = O (general case) by AZI1.1 which provides the information AZI1.1 such that AZI1.1 = J (N, D) with

and

When T ₁ = 1, the combination of the six axial components of the signals is carried out by AZI1.2, in the same way, that is to say with the same expressions for N and D. The parameter AZI 1 is therefore equal to AZI1.1 if T ₁ = 0 and AZI1.2 if T ₁ = 1.

The two transverse axial components ^Y S _x and ^γ S _y of the accelerometer signal, containing the effects of rotation of the probe, i.e. coming from El when T _l = 0 (general case) and from R ₂ .5 and R ₂ .6 when T ₁ = 1, are combined respectively in RB1 and RB3 to obtain the value of a fourth parameter, RB, representing the maximum angleθ, or dihedral angle, formed between a vertical plane containing the longitudinal axis of the probe and a plane containing the axis of the probe and passing through the fixed point P thereof. The information RB1 and RB3 are expressed by the same combination of components, namely J (N, D) with N = ^γ S _y and D = - ^γ S _x . After the test "T ₂ = 0?", The information RB1 becomes RB2 such that RB2 = T ₂ .RB1. The parameter RB is therefore equal to RB2 if T ₁ = O and to RB3 if T ₁ = 1.

In FIG. 3b, the double contact relay T ₁ T ₁ , controlled by the comparator COMP 1, schematically represents the connection of the phase for determining the value of the parameters to a display operation AFF of these parameters. Thus this relay T ₁ T ₁ makes it possible to obtain, at the end of the determination phase, the parameters DEV, AZIM, AZI1 and RB which, in an explicit form, are expressed by:

It is however possible, and possibly advantageous, to determine during the final step ET2, the value of other parameters such as Sin i, i being the angle of inclination of the earth's magnetic field vector. This possibility is illustrated in FIG. 3b (case T ₁ = 1). The parameter Sin i is given by:

On the other hand, the display of quantities such as the norm ^µ S _xyz of the signal of the magnetometer, and the norm ^γ S _xyz of the signal of the accelerometer, after low-pass filtering, makes it possible to exercise control over the meaning actual values obtained for the different parameters.

As mentioned above, the value of L1 should be chosen to be quite low. preferably less than or equal to 5.10 ^-2 (5.10 ^-2 = tg 3 °). Indeed, the signal ^Y S of the accelerometer being very disturbed by the accelerations undergone by the probe due to its newness, it is advantageous to limit as much as possible the use of the signal S of the accelerometer as stabilizing signal ^a S to rid the magnetometer signal of the effects of rotation of the probe , therefore to limit to the maximum the cases T ₁ = 1.

Although, in the method of the invention, the phase of determining the value of the parameters can, using the preceding indications, be carried out according to various methods, and for example by means of a hardware device specially designed for To this end and responding to the diagram of FIGS. 3a and 3b, it appeared that the most suitable way consisted in resorting to automatic data processing by means of a computer. In such a component, the blocks in FIGS. 2, 3a and 3b represent subroutines, with the exception of the comparators in FIG. 3a which represent tests, and relays in FIGS. 3a and 3b, which represent conditional connections.

Claims (14)

1. Method for determining at least two parameters of direction of a well as a function of the depth, comprising the phases consisting in: producing an acceleration signal with three components representing a set of accelerations undergone by a probe which is moved into the well and detected along three reference axes linked to this probe; producing a three-component locating signal representing a vector of fixed direction different from the vertical, related to said three reference axes; determining said direction parameters by a combination of the components of said signals, characterized in that the phases consisting in producing said acceleration and locating signals and the displacement of the probe are simultaneous and substantially continuous, in that said phase of determining the direction parameters is split into a virtual stabilization step by which the effects of the displacement of the probe in the components of one of said signals, constituting a signal to be stabilized, are eliminated, by means of the components of the other signal, constituting a stabilizer signal. 2. Method according to claim 1, characterized in that said phase of determining the parameters further comprises an intermediate low-pass filtering operation, carrying at least on stabilized components of said signal to be stabilized and by which the components are eliminated frequency variations greater than the maximum frequency of variations due to the acceleration of gravity. 3. Method according to claim 1, characterized in that said phase of determining the steering parameters further comprises a step preliminary to said step of virtual stabilization, comprising an operation of prefiltering the components of the acceleration signal, by which one attenuates substantially, in these components, the signal variations having a frequency greater than the greatest possible frequency of the rotational movement of the probe around its longitudinal axis. 4. Method according to claim 1 or 3, characterized in that said acceleration and location signals are related to a first and a second transverse sensitive axis, perpendicular to each other and to the longitudinal axis of the probe, and to a third sensitive axis, of longitudinal direction and coincident with the axis of the probe, said signals each comprising two transverse axial components and a longitudinal axial component. 5. Method according to claim 4, in which the phase of determining said direction parameters comprises a step preliminary to the virtual stabilization step, characterized in that a transverse diagonal component of the stabilizing signal is determined in this preliminary step from the transverse axial components of this signal, and in that eliminating said effects of rotation, by means of the transverse axial and diagonal components of this same signal, in the transverse axial components of the signal to be stabilized, in order to obtain components thereof stabilized in rotation, corresponding to a reference position of the probe around its longitudinal axis. 6. Method according to claim 5, characterized in that the preliminary step comprises the operations consisting in: determining a transverse diagonal component of the locating signal from the transverse axial components of this signal; determine from this transverse diagonal component and the longitudinal axial component of this same locating signal the sign of the difference between a first angle, formed between said vector of fixed direction and the longitudinal axis of the probe, and a limit angle of predetermined value; defining the stabilizing and stabilizing signals, respectively by the locating and acceleration signals when the sign of said difference is positive, and by the acceleration and locating signals when this sign is negative; and determining a transverse diagonal component of the stabilizing signal from its transverse axial components when this stabilizing signal is defined by said acceleration signal. 7. Method according to claim 6, characterized in that said final step of combining the components of the signals comprises an operation of determining a first of said direction parameters, this operation involving the combination of transverse diagonal and longitudinal axial components, filtered and normalized, of said acceleration signal, this first parameter representing the angle formed between the vertical and the longitudinal axis of the probe. 8. Method according to claim 6 or 7, characterized in that said final step of combining components of the signals comprises an operation of determining a second of said direction parameters, this operation involving the combination of the three normalized and stabilized axial components of said signal to be stabilized and normalized longitudinal and diagonal transverse components of said stabilizing signal, this second parameter representing the angle formed between the horizontal trace of the vertical plane passing through the longitudinal axis of the probe and the horizontal projection of said vector of fixed direction different from the vertical. 9. Method according to claim or 5, characterized in that, when the sign of the difference determined during said preliminary step is positive, said final step comprises an operation of reintroducing the effects of the displacement of the probe, providing, from of the two stabilized transverse axial components of the acceleration signal and of the diagonal and axial transverse components of the locating signal, two transverse axial components of the acceleration signal which are no longer stabilized with respect to said reference position of the probe. 10. Method according to claim'7, characterized in that said final combining step comprises, after the operation of determining the first direction parameter, an operation of comparing this parameter with a predetermined minimum value and, when the first parameter is less than this minimum value, an operation. consisting in forcing a second direction parameter at zero, representing the angle formed between the horizontal trace of the vertical plane passing through the longitudinal axis of the probe, and the horizontal projection of said fixed direction vector different from the vertical. 11. Apparatus for determining direction parameters of a well, comprising: - a probe, - means for centralizing the probe in a well, - first means, included in the probe, for producing signals representing the accelerations undergone by the probe when the probe is moved in the well, second means, included in the probe, for producing signals representing a vector of fixed direction different from the vertical, and means for determining said direction parameters by processing and combining said signals,
characterized in that said processing and combining means further comprises additional means for processing and combining the signals in order to determine the direction parameters, representing the position of the probe in the well at each depth, so that said parameters are rid of the effects of displacement of the probe in the well. 12. Apparatus according to claim 11, characterized in that said additional processing and combining means further comprise: means for ridding the signals produced by said first means of the effects of the displacement of the probe, by a combination of the components of the signals produced by said first and second means, and - of. means for determining said direction parameters by a combination of the components of said signals rid of the effects of the displacement of the probe and of the signals produced by said second means. 13. Apparatus according to claim 11, characterized in that it further comprises: means for moving the probe in the well, and - Means for producing measurements representing the displacement of the probe in the well. 14. Apparatus according to claim 13, characterized in that it further comprises: - Means for coordinating said displacement measurements with said direction parameters.

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