EP0995877B1 - Apparatus and method for information transmission by electromagnetic waves - Google Patents

Description

The invention lies in the field of transmissions of information from a drilled hole in the ground to the surface. More particularly, the invention relates to an optimized method of transmission of information between the bottom of a well drilled and the surface, the well being either already drilled and production course, being in the course of drilling.

We know different transmission systems information between the bottom of a well and the surface, for example by pressure waves ("Mud pulse") in a circulating fluid in the well. But we know that this type of transmission has particular disadvantages to not function properly, if it is not everything in a compressible fluid, such as gas or liquids charged with gas, or where there is a obstruction in the traffic channel that disturbs the flow, for example a bottom motor, a valve or a trick. Moreover, this system is of course inoperative during production and maneuvering drill string.

We also know the transmission system by electromagnetic waves guided by the columns Metallic tubes set up in the well. This transmission system is described in particular in the document FR 2681461 of the applicant, quoted here in reference. The performance of the transmission electromagnetic energy (EM) are dependent on average resistivity of geological formations surrounding at the well. If the resistivity of some layers is too weak, as is the case in some Tertiary tertiary sedimentary such as those of the North Sea, Gulf of Mexico, mitigation can become too along the well, which virtually excludes the use of such a device in the majority of offshore wells unless drastically reducing flow information that is transmitted.

Thus, the present invention relates to a method transmission of information from a well drilled to through layers of geological formation and cuvelé at least partly by metal tubes, the method comprises placing in said well a information transmitter / receiver operating by the medium of guided electromagnetic waves created by the injection of an electrical signal by a connected dipole conductively to the metal tubes used for guiding waves emitted. According to the method, we identify mitigation of transmission by some layers with low resistivity, one isolates electrically at least partially the tubes arranged in line with the said layers of low resistivity.

We can determine using a model mathematical the minimal length to isolate considering minimum characteristics of said transmission electromagnetic, including the distance of transmission and / or information rate.

Insulation can be done by place tubes previously coated with a layer of insulating material.

In a variant, it is possible to carry out the isolation by placing an insulating material of the type cement to the right of said certain formations in the annular space between the tubes and formations.

This near transmitter / receiver can be arranged of the lower end of a column of tubes of production to transmit substantive measures or orders to background equipment.

It is also possible to have said transmitter / receiver near the bottom end of a pad of drilling to transmit background or drilling, or location measurements.

The invention also relates to a system of transmission of information from a well drilled in layers of geological formation and cuvelé at least partly by metal tubes, the system comprising in said well a transmitter / receiver of information operating by the means of waves guided electromagnetic waves created by the injection of a electrical signal by a dipole conductively connected to metal tubes for guiding the emitted waves. In the system, at least some metal tubes arranged at the right of low resistivity layers include means of electrical insulation with said formation.

Insulated tubes may be coated with layer of insulating material.

Insulating layer may not cover entirely the entire length of the tube.

In the system, the isolation means can understand an insulating material that fills the space ring between the tubes and the conductive formation, the material being the result of the hardening of a liquid composition.

The transmitter / receiver can be incorporated into the end of a column of production tubes.

The transmitter / receiver can also be incorporated into the end of a drill string.

The system according to the invention can be applied to an offshore drilling rig with wellhead underwater.

In this application, a control line kills (kill-line) can be externally isolated electrically from the bottom of the sea to the surface

• La figure 1 représente schématiquement une mise en oeuvre de l'invention pour un puits en production.
• La figure 2 illustre un autre mode de mise en oeuvre de l'invention dans le cas de l'opération de forage d'un puits.
• La figure 3 illustre une variante en forage.
• La figure 4 montre en coupe l'exemple d'un élément de tube de cuvelage revêtu extérieurement d'un isolant électrique.
• La figure 5 représente un exemple d'atténuation du signal en fonction de la profondeur du forage et de la résistivité des formations traversées.

The present invention will be better understood and its advantages will appear more clearly on reading the following examples, which are in no way limiting, illustrated by the appended figures in which:

• Figure 1 shows schematically an implementation of the invention for a well in production.
• FIG. 2 illustrates another embodiment of the invention in the case of the drilling operation of a well.
• Figure 3 illustrates a variant in drilling.
• Figure 4 shows in section the example of a casing tube element coated externally with an electrical insulator.
• FIG. 5 represents an example of attenuation of the signal as a function of the depth of the drilling and the resistivity of the formations traversed.

In FIG. 1, there is shown a well 1 already drilled to a geological zone 2. Zone 2 generally comprises at least one layer forming reservoir containing effluents to be produced. In the case, the layers of land 3, which are between layer 2 and the surface, attenuate electromagnetic waves in such a way that it is impossible to use the method of transmission by electromagnetic waves known. Through logging measures, it was possible to measure that the layers 3a and 3b have resistivities much lower than 20 Ω.m, for example of the order of a few Ω.m, or even less than 1 Ω.m. On the other hand, zone 3c, at a resistivity greater than 20 Ω.m, for example a layer of salt, a layer frequently encountered in drilling. Before drilling a well, in which we will have to apply the technique object of this invention it is almost always possible to get a log (recording according to the depth) of resistivity for example by extrapolating it from the seismic profiles and well logs drilled in this zoned. Curve a of Figure 5 shows an example of this curve. This log then allows us, from a mathematical model of wave propagation electromagnetic waves along the drill rods and well casing, to calculate the attenuation the electromagnetic signal between the emission point E and the receiving point R. The model used will be example of the type described in the SPE Drilling article Engineering, June 1987, P.Degauque and R.Grudzinski. AT from this calculation it is predefined, before drilling, the signal level that we will receive, or that we should receive, surface all along the descent of the transmitter. The curve b of FIG. example of this signal. The signal obtained during drilling of the well will be recorded and compared in real time with the signal calculated from the forecast log allowing to adjust the actual position of different geological layers and the actual value of their resistivity. This is only possible thanks to the knowledge of the current emitted by the issuer, which is the case for the issuer concerned.

Knowing maximum acceptable attenuation between transmitter E and receiver R for flow desired information, it will be possible to determine the length of the casing to be covered choosing to isolate low areas first resistivity such as those between 500 and 1000 m in Figure 5.

• la courbe c représente le signal obtenu tout au long du puits dans le cas où on isole électriquement de manière parfaite l'extérieur du casing des formations environnantes sur l'intervalle 500 m à 1000 m. On constate que la réduction d'atténuation est de l'ordre de 35 dB selon les paramètres de propagation considérés (fréquence porteuse de 5Hz dans ce cas);
• la courbe d représente le signal obtenu tout au long du puits dans le cas où on isole uniquement le corps des casings. Ceci revient à considérer, pour le modèle de propagation que nous avons, une isolation parfaite du casing sur 27 m, puis une conduction électrique sur 0,5 mètre. On constate alors que le gain total en atténuation est de l'ordre de 24 dB.

In FIG. 5, from the curves a and b defined above, two other curves c and d are represented:

• curve c represents the signal obtained throughout the well in the case where the outer casing of the surrounding formations is isolated in a perfect manner over the interval 500 m to 1000 m. It can be seen that the attenuation reduction is of the order of 35 dB according to the propagation parameters considered (carrier frequency of 5 Hz in this case);
• the curve d represents the signal obtained throughout the well in the case where only the casings body is isolated. This amounts to considering, for the model of propagation that we have, a perfect insulation of the casing on 27 m, then an electrical conduction on 0,5 meter. It can be seen that the total attenuation gain is of the order of 24 dB.

Thanks to this method and knowing the flow information to obtain, it will always be possible technically to determine and install the casing necessary for the desired transmission.

It should be noted that this would not change the method if the electromagnetic signal was relayed by a transmitter / receiver located between the base transmitter of well and the surface and especially if the latter was located in the uncapped area of the well.

It is recalled that the information rate Df is calculated by the following formula: Df = ΔF log 2 (1 + S / B) with ΔF useful modulation bandwidth, S signal and B the noise in the useful band.

The transmission is carried out by the issuer referenced E in FIGS. 1, 2 and 3. The emitter E modulates a very low frequency wave, said frequency being chosen low enough so that the propagation is possible. Preferably, the means transmitters use frequency waves included between 1 Hz and 10 Hz. This wave, called frequency carrier, is in an exemplary embodiment, modulated according to the information to be transmitted, by phase 0-π at a rate compatible with the frequency carrier. Other types of modulation can be used without departing from the scope of this invention. The modulation rate is of the order of bit / second, but it can be adapted according to transmission needs. In the case of orders from bottom devices such as valves, we will be able to use length codes adapted to the probability maximum error accepted. The coding may as appropriate whether or not associated with detector codes and error correctors, such as redundancy codes cyclic.

The wave emitted by the transmitter E is received in surface by the receiver R which one of the poles is connected at the wellhead and the other pole planted in the ground at a sufficient distance from the wellhead. In the practice, E and R can become alternately transmitters and receiver. Electronic means

transmission / reception E can be advantageously arranged according to the described technology in US-A-5394141, incorporated herein by reference. We can also refer to the publication SPE / IADC 25686 presented by Louis Soulier and Michel Lemaitre to the SPE / IADC Drilling Conference held in Amsterdam February 23-25, 1993.

In FIG. 1, a first column of tubes 4 (surface column) is placed in well 1 and usually cemented all the way up into the surface formation 3a. Wellhead 5 installed on the surface column can receive the top end of the other columns, techniques or production, as well as safety valves. A second column 6 went down into the drilled hole 7 to from the hoof of the surface column 4 and up the tank cover 2. The annular space between the hole 7 and the casing tube column 6 is usually filled with cement at least up to the hoof from the previous column, in this example the hoof of the surface column 4. A column of tubes of production 8 (tubing), whose role is to the effluent to the surface, passes through a packer 9 which seals the reservoir zone relative to the annular space around the tubing 8. In the lower part of the tubing column, is installed an E-type transmitter / receiver. EM transmission, the P1 and P2 poles of the dipole can be constituted by the contact provided by the packer 9 with the metal column 6 and the contact provided by a blade centraliser 10 placed higher in the column 8. In some cases, the upper contact is directly made by the contact of the tubing with the column 6, considering the annular space generally low and well geometry. A insulating connector 11, located to the right of the transmitter, can be used in the casing column 6 to separate the lower contact P1 of the upper contact P2. But this insulating connection is not necessary if one uses the so-called "long dipole" constitution for the antenna transmission or reception. In this case, it is necessary ensure that the P2 pole is sufficiently far from the pole P1 and that there can be no other contact between column 6 and tubings 8 on the length between the poles.

According to the invention, the performance is improved of the emitter E by electrically insulating the column 6 of the highly conductive geological formation 3b. This insulation is represented by the frame referenced 12. It is important to note that zone 3c, which is known to have sufficient resistivity to not provide a penalizing attenuation, for example greater than about 20 Ω.m, so does not need to be electrically isolated. In this example, the lands 3a surface are not favorable to a good transmission. The surface column 4 will be, depending information flow requirements, also isolated from training 3a (represented by the referenced frame 13).

In the present invention, it is possible to realize said insulation of the columns of tubes with the lands by covering the outer wall of the tubes by a layer of insulating material, or almost insulating. Indeed, we have seen that according to the invention the necessary electrical insulation is all relative since resistivity fields greater than 20 Ω.m are sufficiently "insulating". In addition, insulation has no need to be continuous all the way up from the thickness of the conductive layer. The tubes, casing or tubing according to the name known in the profession and standardized by the API (American Petroleum Institute) include at both ends a male thread and a sleeve, screwed onto the body of the tube or integral, with female thread corresponding so as to be able to assemble them these tubes to form a column. Of preferably, the insulating layer will be deposited only on the body of the tube, between the male thread (which obviously can not be covered) and the sleeve. In indeed, the layer near the threads would be destroyed by the jaws of the screwing means, and may even be would be embarrassing for the suspension of the column or clinging of the jaws. The insulating layer can be an epoxy coating loaded with ceramic, by example of the type of coating used as protection anticorrosion on marine structures, pipelines, the drill rods. It could also be of a ceramic layer deposited by plasma, tar, preferably combined with polyurethane, plastic strips, such as polyethylene, PVC, a mixture of resin and sand projected onto the tube, a coating of impregnated glass fibers and wound around the body of the tube. All coatings sufficiently insulating according to the needs of this application, ie leading to a resistance Electric leakage far superior to the resistance characteristic of the propagation line, can be suitable without departing from the scope of the present invention. In practice, this characteristic resistance being of the order of a few milliohms, it will suffice to have a radial isolation resistance of the order of one ohm per casing segment to get a good effectiveness of the device.

According to the invention, it is also possible to realize electrical insulation of the columns of tubes using an insulating material for the cementing of strongly conductive areas, for example rings 3a and 3b. We know in the profession the circulation method to set up a slag of formulation cement determined at the level of a zone geological data. We will use this technique conventional way to place insulating material or rather to improve the conductivity compared to the low resistivity ground.

Figure 2 illustrates the case of the system of transmission according to the invention while drilling a well 20 by means of a drill string 21 equipped a drilling tool 22 at its end. A emitter / receiver E is generally located in the lower part to transmit for example parameters of drilling, trajectories, radiation gamma, temperature, pressure, etc. Well 1 is here cuvelé surface by a column 23 and a column Intermediate 24. Zone 25 has low resistivity which mitigates too strongly the transmission by EM between E and R. According to the invention, the elements of insulated tubes at 26 for column 23 and at 27 for the 24. In a variant, the ring finger between the column 23 and the formation and the ring finger between the column 24 and the training will be filled with cement insulating. Thus, the attenuation created by the weak resistivity of zone 25 will be very substantially decreased, increasing the capacity or speed of transmission of E. In this system, the antenna is made by the part of the trim between the insulating junction of the emitter E and the tool 22 drilling. Note that in this case the signal emitted by the transmitter E will be attenuated from E to isolated or pseudo-isolated zone 27, then zone 26 to the surface receiver R. A mathematical model of propagation taking into account characteristics electric casings and formations, allows to predetermine the minimum lengths of isolation zones 26 and 27 in order to guarantee the transmission.

It should be noted that the part of the tubes of the column 24 included in column 23 does not require insulation.

Figure 3 shows an alternative layout of the emitter E in the drill string 21 and a example of application of the invention in the case of offshore drilling with a subsea wellhead. Conventionally, in the case of drilling or operating with underwater wellhead, the receiver R is located at the bottom of the sea with one of its reception poles connected to the underwater wellhead and the other constituted by a piece of metal, by example an anchor 37, placed a few dozen meters from the wellhead. Communication between the surface and the bottom of the sea is done either by acoustic transmitter, or by electric conductor installed along the casing. Soils 30 close to the bottom of water are generally geologically "young" and generally low resistivity. The column of surface 31 is therefore advantageously isolated, according to the invention, on the height corresponding to the 30. The transmitter E is here at the end of a given length of cable 32 to create a "long dipole". The cable is fixed by a support 33 to inside of rods and is electrically connected to the transmitter located at a distant part of the rods 21. The wellhead 29 is connected to the floating support of drilling by a set called "marine riser". high pressure line 36 (kill-line or choke-line) runs substantially parallel to the riser of the head of floating support well. We can advantageously electrically isolating the pipe 36 to couple the bottom antenna 37 with the surface and so get surface reception, ie on the support floating where line 36 ends.

It is clear that the provision "long dipole" described in Figure 3 applies in all other drilling configurations and not just in the offshore case. In the case of operations where uses aerated mud with gas, or even foam, the EM transmission is the only transmission possible and has increased performance thanks to improvement according to the invention.

FIG. 4 shows in section a tube element 40 that can be used to caster a drilled hole in a zone of too low resistivity. A tube body steel 41 is obtained by hot rolling. We factory at both ends a male thread 42 and 43. A sleeve 44 having female threads 45 is screwed on one end. Insulating coating (as defined above) is filed on the central zone 48. Zones 46 and 47 may be left raw so that the jaws of the robots screws have direct contact with the steel of the tube, the same with respect to the corners of the table suspension of the casing column.

It is clear that it is quite possible to completely isolate the outer surface of the tube casing, before screwing or after screwing, however this operation faces many difficulties operating. Practically and economically this is not desirable. This is why the present invention that does not require perfect isolation is particularly advantageous.

The present invention therefore has all the advantages of transmission by electromagnetic waves and more, allows an increase in performance that this in wells equipped for production or in drilling course. It also allows you to use more largely the EM transmission, especially in the case deep offshore.

The tubes thus coated are also more effectively protected cathodically since the current to inject for cathodic protection will be decreased and otherwise it will only go to places not which therefore require a potential electrical protection against electro-corrosion. The coating can also promote cement adhesion on the tubes.

Claims (16)

1. Method of transmitting information from a well drilled through geological formation layers and at least partly lined with metal tubes (6), said method comprising placing in said well an information transmitter/receiver (E) operating by means of guided electromagnetic waves created by injecting an electrical signal through a dipole (P1, P2) conductively connected to the metal tubes (6) serving to guide the waves emitted, characterised in that:

   the attenuation of the transmission through certain formation layers (3a, 3b) with low resistivity is identified;

   the metal tubes (6) disposed level with said layers of low resistivity are at least partly insulated electrically.
2. Method according to claim 1, wherein the minimum length to be isolated, taking into account the minimum characteristics of said electromagnetic transmission, notably the transmission distance and/or the information flow rate, are determined using a mathematical model.
3. Method according to one of claims 1 or 2, wherein the insulation is provided by putting into place metal tubes (6) which have previously been coated with a layer of insulating material (12, 13).
4. Method according to one of claims 1 or 2, wherein the insulation is provided by putting into place a cement-type insulating material level with said certain formations (3a, 3b) in the annular space between the metal tubes (6) and the formations.
5. Method according to one of the preceding claims, wherein the transmitter/receiver (E) is placed close to the lower end of a column of metal production tubes (8) for transmitting measurements from the bottom or commands to equipment at the bottom.
6. Method according to one of claims 1 to 4, wherein the transmitter/receiver (E) is placed close to the lower end of a drill string (21) for transmitting the bottom parameters or drilling parameters, or location measurements.
7. Method according to any one of the preceding claims, wherein the metal tubes (6) comprise two ends, a male screw thread (42, 43) at both ends and a sleeve (44) screwed onto the tube (6) or integral therewith, comprising the corresponding female screw thread (45) so as to fit the tubes together, and the metal tubes (6) located level with the layers (3a, 3b) of low resistivity are electrically insulated only at their central zone (48) situated between their ends.
8. Information transmission system comprising a well drilled into geological formation layers and at least partly lined with metal tubes (6), said system comprising in said well an information transmitter/receiver (E) operating by means of guided electromagnetic waves created by injecting an electrical signal through a dipole (P1, P2) conductively connected to the metal tubes (6) serving to guide the waves emitted, characterised in that at least some metal tubes (6) located level with the layers (3a, 3b) of low resistivity comprise means of electrical insulation (12, 13) with said formation.
9. System according to claim 8, wherein said insulated metal tubes are coated with a layer of insulating material (12, 13).
10. System according to claim 9, wherein said insulating layer (12, 13) does not totally cover the length of the metal tubes.
11. System according to claim 8, wherein said insulating means (12, 13) comprise an insulating material which fills the annular space between said metal tubes (23) and the conductive formation, said material being the result of the hardening of a liquid composition.
12. System according to one of claims 8 to 11, wherein said transmitter/receiver is incorporated at the end of a column of metal production tubes (8).
13. System according to one of claims 8 to 11, wherein said transmitter/receiver (E) is incorporated at the end of a drill string (21).
14. System according to any one of claims 8 to 13, wherein the metal tubes (6) comprise two ends, a male thread (42, 43) at these two ends and a sleeve screwed to the tube (6) or integral therewith, comprising the corresponding female thread, so as to fit the tubes together, and the electrical insulating means (12, 13) comprise an insulating layer which is deposited only on the central zone (48) of said metal tubes (6) located level with the layers (3a, 3b) of low resistivity.
15. Offshore drilling installation with a subsea wellhead (29), comprising an information transmitting system according to any one of claims 8 to 14.
16. Installation according to claim 15, wherein a line for controlling kicks (kill-line)(36) is electrically insulated on the outside from the bottom of the sea to the surface.

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