EP0995877A1 - Apparatus and method for information transmission by electromagnetic waves - Google Patents

Abstract

Electromagnetic cased well information transmission comprises electrical insulation of metal casing tubes adjacent low resistivity formation layers. Information transmission from a cased well, using a downhole transmitter/receiver operating by guided electromagnetic waves created by electrical signal injection by a dipole connected to the metal casing tubes which guide the emitted waves comprises identifying low resistivity formation layers which cause transmission attenuation, and electrically insulating the tubes located at these layers. An Independent claim is also included for a system for carrying out the above information transmission method. Preferred Features: A mathematical model is used to calculate the minimum length to be insulated, taking into account the minimum characteristics of the electromagnetic transmission, especially the transmission distance and/or the information output rate. Insulation is effected by providing a cement-type insulating material in the gap between the casing tubes and certain formations. The transmitter/receiver is positioned near the lower end of a production tubing string, for transmitting bottom measurements or bottom equipment commands, or is positioned near the lower end of a well casing for transmitting bottom or drilling parameters or location measurements.

Description

The invention lies in the field of transmission of information from a hole drilled in the ground to the surface. More specifically, 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 in during production, or during 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 fluid circulating in the well. But we know that this type of transmission has the disadvantages in particular not to function properly, if not everything in a compressible fluid, such as gas or liquids charged with gas, or when there is a obstruction in the disturbing circulation channel the flow, for example a downhole motor, a valve or a duse. In addition, this system is of course inoperative during production and operation of drill string.

We also know the transmission system by electromagnetic waves guided by columns metal tubes placed in the well. This transmission system is particularly described in the document FR 2681461 of the plaintiff, cited here in reference. Transmission performance electromagnetic (EM) are dependent on the average resistivity of geological formations surrounding the well. If the resistivity of some layers is too weak, as is the case in some tertiary sedimentary land perished continental such as, those of the North Sea, or Gulf of Mexico, mitigation may become too significant along the well, which virtually excludes the use of such a device in the majority of offshore wells except drastically reducing the flow of information that we transmit.

Thus, the present invention relates to a method transmission of information from a well drilled at through layers of geological and cased formation at least in part by metal tubes, the method includes placing in said well a information transmitter / receiver operated by the using guided electromagnetic waves created by injecting an electrical signal through a connected dipole conductively to the metal tubes used for guiding waves emitted. According to the method, we identify attenuation of transmission by certain layers with a low resistivity, we isolate electrically at least partially the tubes of metal arranged in line with said layers of low resistivity.

We can determine using a model mathematical the minimum length to be isolated given minimum characteristics of said transmission electromagnetic, including the distance from transmission and / or flow of information.

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

Alternatively, the insulation can be carried out by the installation of an insulating material of the type cement to the right of said certain formations in the annular space between the tubes and the formations. We can have said transmitter / receiver close from the lower end of a column of tubing production to transmit background measurements or orders to background equipment.

You can also have said transmitter / receiver close to the lower end of a trim drilling to transmit background parameters or drilling, or location measurements.

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

Insulated tubes can be coated with layer of insulating material.

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

In the system, the isolation means can understand an insulating material that fills the space annular 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 installation with wellhead underwater.

In this application, a control line of 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 limitative, illustrated by the appended figures among which:

• FIG. 1 schematically represents 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.
• FIG. 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 borehole and the resistivity of the formations crossed.

In FIG. 1, a well 1 has already been represented drilled until reaching a geological zone 2. Zone 2 generally comprises at least one layer forming tank containing effluents to be produced. In the case in point, the land layers 3, which are between layer 2 and the surface, reduce electromagnetic waves in such a way that it is impossible to effectively use the method of known electromagnetic wave transmission. Through logging measures, we were able 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. However, zone 3c, at one resistivity greater than 20 Ω.m, for example a layer salt, a layer commonly 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 as a function of depth) of resistivity for example by extrapolating it from seismic profiles and logs of wells drilled in this zoned. Curve a in Figure 5 shows an example of this curve. This log then allows us, from a mathematical model of wave propagation electromagnetic along the drill pipes and casings of the well considered, to calculate the attenuation of the electromagnetic signal between the emission point E and the reception point R. The model used will be by example of the type described in the article SPE Drilling Engineering, June 1987, P.Degauque and R.Grudzinski. AT from this calculation we predetermine, before drilling, the signal level that we will receive, or that we should receive, on the surface throughout the descent of the transmitter. Curve b in Figure 5 shows a 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 thus allowing the actual position of the different geological layers and the real value of their resistivity. This is only possible thanks to the knowledge of the current emitted by the transmitter, which is the case for the issuer considered.

Knowing the maximum acceptable attenuation between transmitter E and receiver R for flow desired information, we can determine with precision the length of the casing to be covered in choosing to first isolate areas with low 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 curves a and b defined above, two other curves c and d are shown:

• curve c represents the signal obtained throughout the well in the case where the outside of the casing is electrically isolated from surrounding formations over the interval 500 m to 1000 m. It can be seen that the reduction in attenuation is of the order of 35 dB depending on the propagation parameters considered (carrier frequency of 5 Hz in this case);
• curve d represents the signal obtained throughout the well in the case where only the casing body is isolated. This amounts to considering, for the propagation model we have, a perfect isolation of the casing over 27 m, then an electrical conduction over 0.5 m. It can then be seen that the total gain in attenuation is of the order of 24 dB.

Thanks to this method and knowing the flow of information to be obtained 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 bottom transmitter of well and the surface and especially if the latter was located in the uncovered area of the well.

Remember 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.

Transmission is carried out by the transmitter referenced E in Figures 1, 2 and 3. The transmitter E modulates a very low frequency wave, said frequency being chosen low enough that the spread is possible. Preferably, the means of emission use waves of frequency included between 1 Hz and 10 Hz. This wave, called frequency carrier, is in an exemplary embodiment, modulated depending on the information to be transmitted, by skipping phase 0-π at a rhythm 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 downhole devices such as valves, use length codes adapted to the probability maximum error accepted. Coding can, as appropriate whether or not to be associated with detector codes and error correctors, such as redundant codes cyclic.

The wave transmitted by the transmitter E is received in surface by the receiver R of which one of the poles is connected at the wellhead and the other pole planted in the ground at sufficient distance from the wellhead. In the practical, E and R can become transmitters in turn and receiver. Electronic means send / receive E can be advantageously arranged according to the technology described in document US-A-5394141, cited here with 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 on February 23-25, 1993.

In FIG. 1, a first column of tubes 4 (surface column) is placed in well 1 and generally cemented over its entire height in the surface formation 3a. A wellhead 5 installed on the surface column allows to receive the upper end of the other columns, techniques or production, as well as the safety valves. A second column 6 is lowered into the drilled hole 7 at from the shoe of the surface column 4 and up the tank cover 2. The annular space between hole 7 and casing tube column 6 is usually filled with cement at least to the hoof from the previous column, in this example the shoe the surface column 4. A column of tubes of production 8 (tubing), whose role is to go back the effluent to the surface, passes through a packer 9 which seals the tank area relative to the annular space around the tubing 8. In the lower part of the tubing column, is installed a type E transmitter / receiver. EM transmission, the P1 and P2 poles of the dipole can be formed by the contact provided by the packer 9 with the metal column 6 and the contact provided by a blade centering device 10 placed higher in the column tubing 8. In some cases, the upper contact is directly made by the contact of the tubing with the column 6, taking into account the annular space generally weak and the geometry of the well. A insulating fitting 11, located to the right of the transmitter, can be used in casing column 6 to separate the lower contact P1 of the upper contact P2. But this insulating fitting is not necessary if using the so-called "long dipole" constitution for the antenna transmission or reception. In this case, ensure that the P2 pole is far enough from the pole P1 and there can be no other contact between column 6 and tubings 8 along the length between the poles.

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

In the present invention, it is possible to carry out said insulation of the columns of tubes with the ground by covering the outside wall of the tubes by a layer of insulating material, or almost insulating. Indeed, we have seen that according to the invention the electrical insulation required is relative since resistivity grounds greater than 20 Ω.m are sufficiently "insulating". In addition, the insulation no need to be continuous over the entire height of the thickness of the conductive layer. Tubes, casing or tubing according to the name known in the profession and standardized by API (American Petroleum Institute) include at their two ends a male thread and a sleeve, screwed onto the tube body or integral, including female thread corresponding so that we can assemble them these tubes to form a column. Of preferably, the insulating layer will only be deposited on the body of the tube, between the male thread (which obviously can not be covered) and the sleeve. In effect, the layer near the threads would be destroyed by the jaws of the screwing means, and may even be would be inconvenient for the suspension of the column or hanging 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 maritime structures, pipelines, the drill rods. It could also be a ceramic layer deposited by plasma, tar, preferably combined with polyurethane, plastic strips, such as polyethylene, PVC, a mixture of resin and sand sprayed 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, i.e. leading to resistance electric leakage far superior to resistance characteristic of the propagation line, can agree 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 an order radial isolation resistance one ohm per casing segment to obtain good effectiveness of the device.

According to the invention, it is also possible to carry out the electrical insulation of the columns of tubes in using insulating material for cementing highly conductive areas, for example annulars 3a and 3b. We know in the profession the circulation method to set up a slag of cement of formulation determined at the level of an area geological given. So we will use this technique conventional for placing insulating material or rather improvement in conductivity compared to low resistivity ground.

Figure 2 illustrates the case of the transmission according to the invention during drilling of a well 20 using a drill string 21 fitted of a drilling tool 22 at its end. A transmitter / receiver E is generally arranged in the lower part to transmit for example drilling, trajectometry, radiation parameters gamma, temperature, pressure, etc. Well 1 is here cased on the surface by a column 23 and a column intermediate 24. Zone 25 has low resistivity which too strongly attenuates the transmission by EM between E and R. According to the invention, there will be elements of insulated tubes at 26 for column 23 and at 27 for the column 24. In a variant, the ring finger between the column 23 and the formation and the ring finger between the column 24 and the formation will be filled with cement insulating. So the attenuation created by the weak resistivity of area 25 will be very noticeably decreased, correspondingly increasing the capacity or speed of transmission of E. In this system, the antenna is produced by the part of the lining between the insulating junction of the emitter E and the drilling tool 22. Note that in this case the signal from the transmitter E will be attenuated from E to the isolated or pseudo-isolated zone 27, then of the zone 26 to the surface receiver R. A mathematical model propagation taking into account the characteristics electrical of the different casings and formations, allows predetermining the minimum lengths of isolation zones 26 and 27 in order to be able 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 arrangement of the emitter E in the drill string 21 and a example of application of the invention in the case of offshore drilling with an underwater wellhead 29. Conventionally, in the case of drilling or operating with subsea wellhead, the receiver R is located at the bottom of the sea with one of its receiving poles connected to the subsea wellhead and the other made up of a piece of metal, by example an anchor 37, placed a few tens of meters from the wellhead. Communication between the surface and the bottom of the sea is done either by acoustic transmitter, either by electrical conductor installed along the casing. Soils 30 near the bottom of water are generally geologically "young" and generally of low resistivity. The column of surface 31 is therefore advantageously isolated, according to the invention, on the height corresponding to the formation 30. The emitter E is here arranged at the end of a determined 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 remote part of the rods 21. The wellhead 29 is connected to the floating support of drilling by a so-called "marine riser" unit 35. A high pressure line 36 (kill line or choke line) runs substantially parallel to the riser of the head floating support well. We can advantageously electrically isolate line 36 to couple the bottom antenna 37 with the surface and thus obtain surface reception, i.e. on the support floating line where line 36 ends.

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

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

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

The present invention therefore has all the advantages electromagnetic wave transmission and more, allows an increase in performance than it either in wells equipped for production or in drilling course. It also allows you to use more broadly the EM transmission, especially in the case deep offshore.

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

Claims (14)

Method for transmitting information from a well drilled through geological formation layers and cased at least in part by metal tubes, said method comprises the installation in said well of an information transmitter / receiver operating by the by means of guided electromagnetic waves created by the injection of an electrical signal by a dipole conductively connected to the metal tubes used for guiding the waves emitted, characterized in that: the attenuation of the transmission is identified by certain layers of formation having a low resistivity, the metal tubes arranged at right of said low resistivity layers are electrically isolated at least partially. Method according to claim 1, in which one determines using a mathematical model the minimum length to be insulated taking into account minimum characteristics of said transmission electromagnetic, including the distance from transmission and / or flow of information. Method according to one of claims 1 or 2, in which the insulation is carried out by setting place of tubes previously coated with a layer of insulating material. Method according to one of claims 1 or 2, in which the insulation is carried out by setting place of an insulating material of the cement type to the right of said certain formations in the annular space between tubes and formations. Method according to one of the claims in which we have said transmitter / receiver near the lower end a column of production tubes to transmit background measurements or orders to equipment background. Method according to one of claims 1 to 4, in which said transmitter / receiver is placed close to the lower end of a trim drilling to transmit background parameters or drilling, or location measurements. System for transmitting information from a well drilled in layers of geological formation and cased at least in part by metal tubes, said system comprising in said well a information transmitter / receiver operated by the using guided electromagnetic waves created by injecting an electrical signal through a linked dipole conductively to the metal tubes used for guiding emitted waves, characterized in that at least certain metal tubes arranged in line with said tubes low resistivity layers have means of electrical insulation with said formation. The system of claim 7, wherein said insulated tubes are coated with a layer of insulating material. The system of claim 8, wherein said insulating layer does not entirely cover the entire length of the tube. System according to claim 7, in which said isolation means comprises a insulating material which fills the annular space between said tubes and the conductive formation, said material being the result of the hardening of a liquid composition. System according to one of claims 7 to 10, wherein said transmitter / receiver is incorporated at the end of a column of production tubes. System according to one of claims 7 to 10, wherein said transmitter / receiver is incorporated at the end of a drill string. Application of the system according to one of the claims 7 to 12 to a drilling rig in sea with underwater wellhead. Application according to claim 13, in which a kill control line is externally electrically isolated from the bottom of the sea on the surface.

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