DK164419B

DK164419B - Induction-logging probe with metal support

Info

Publication number: DK164419B
Application number: DK181785A
Authority: DK
Inventors: Thomas D Barber; Richard N Chandler; John F Hunka
Original assignee: Schlumberger Ltd
Priority date: 1985-04-23
Filing date: 1985-04-23
Publication date: 1992-06-22
Also published as: DK181785D0; DK164419C; DK181785A

Description

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Den foreliggende opfindelse angår et borehulsloggeapparat til undersøgelse af egenskaberne ved underjordiske formationer, som et borehul går igennem, og navnlig en induktionsloggesonde.The present invention relates to a borehole log apparatus for examining the properties of underground formations that a borehole goes through, and in particular an induction log probe.

5 Et induktionsloggeapparat omfatter i princippet en sendespole og en modtagespole, der er monteret på en understøtning og beliggende i aksial afstand fra hinanden i borehullets retning. Sendespolen energi forsynes af en vekselstrøm ved en frekvens, som typisk er 20 kHz, og frembringer et magnetfelt, der i den omgivende formation 10 inducerer hvirvelstrømme, som løber koaksialt med borehullet, og hvis styrke er proportional med formationens konduktivitet. Feltet, som igen frembringes af disse strømme, inducerer i modtagespolen en elektromotorisk kraft. Ved passende behandling af signalet fra modtagespolen fås et mål for formationens konduktivitet.In principle, an induction logger comprises a transmitting coil and a receiving coil mounted on a support and located at axial distance from each other in the direction of the borehole. The coil energy is supplied by an alternating current at a frequency typically 20 kHz, and produces a magnetic field which in the surrounding formation 10 induces eddy currents which coaxially with the borehole and whose strength is proportional to the conductivity of the formation. The field, which in turn is generated by these currents, induces in the receiving coil an electromotive force. By appropriately processing the signal from the receiving coil, a measure of the conductivity of the formation is obtained.

15 I de sædvanlige induktionsloggesonder er understøtningen for spolerne i form af en rørformet kappe af ikke ledende materiale, såsom glasfiberforstærket epoxyharpiks (se f.eks. US patentskrifterne nr. 3.179.879, 3.147.429 og 3.706.025). Det er altid blevet antaget at 20 på grund af det meget lave niveau af signalet fra modtagespolen, er det kritisk at minimere enhver tilstedeværelse af ledende materiale i nærheden af spolerne for at undgå forstyrrende strømme, som løber i nærheden af spolerne og skaber en støjkomponent ("sondefejl") se f.eks. publikation S.P.E. 12.167 (Society of Petroleum Engineers) 25 "The Electromagnetic Wave Resistivity MWD Tool" af P.R. Rodney et al, præsenteret på 58th Annual Technical Conference and Exhibition,In the usual induction log probes, the support for the coils is in the form of a tubular sheath of non-conductive material, such as fiberglass-reinforced epoxy resin (see, e.g., U.S. Pat. Nos. 3,179,879, 3,147,429 and 3,706,025). It has always been assumed that due to the very low level of the signal from the receiving coil, it is critical to minimize any presence of conductive material near the coils to avoid interfering currents running near the coils and creating a noise component ( "probe failure") see e.g. publication S.P.E. 12,167 (Society of Petroleum Engineers) 25 "The Electromagnetic Wave Resistivity MWD Tool" by P.R. Rodney et al, presented at the 58th Annual Technical Conference and Exhibition,

San Francisco, 5-8 oktober 1983, side 1, venstre spalte, 2. afsnit.San Francisco, October 5-8, 1983, page 1, left column, 2nd paragraph.

En åbenbar ulempe ved anvendelse af understøtninger af syntetisk harpiks er, at de er meget skøre under brugen og blandt de forskel -30 lige typer af loggeapparater er induktionssonderne anset for at være de mest skrøbelige. Da endvidere anordninger til måling under boring skal bygges omkring en krave af stål (eller andet materiale med høj styrke), i hvilken boremudderet kan cirkuleres, er det blevet antaget, at induktionsværktøjer ikke kan anvendes i forbindelse med 35 måling under boring, som påpeget i den ovennævnte S.P.E. publikation.An obvious disadvantage of using synthetic resin supports is that they are very brittle during use and among the different -30 equal types of loggers, the induction probes are considered to be the most fragile. Furthermore, since drilling measurement devices are to be built around a collar of steel (or other high strength material) into which the drilling mud can be circulated, it has been assumed that induction tools cannot be used for drilling measurement as pointed out in the above SPE publication.

Det skal understreges, at fuldstændig udelukkelse af metaldele i nærheden af spolerne er umulig, fordi elektriske ledninger erIt should be emphasized that complete exclusion of metal parts near the coils is impossible because electrical wires are

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2 nødvendige for at strømforsyne sendespolen og føre signalet fra modtagespolen. I sædvanlige induktionssonder er ledningerne i form af stive trykmodstandsdygtige, fieriags koaksialkabler. Disse kabler har koaksiale metal-"lag" isoleret fra hinanden, idet de indre lag 5 virker som ledere, der fører signaler, medens de ydre lag tilvejebringer den mekaniske styrke og en afskærmning for lederne. Disse kabler og diskontinuiteterne ved forbindelsen med spolerne giver under tilstedeværelsen af sendefeltet anledning til hvirvelstrømme, som frembringer en fejl i udgangssignalerne. Når der er tale om 10 formationer med lav konduktivitet, kan denne fejl være af samme størrelsesorden som nyttesignalet. Endvidere er denne fejl stærkt udsat for temperaturdrift, og dens værdi ved rumtemperatur er væsentlig forskellig fra dens værdi i borehulsmiljøet, hvor temperaturen kan være over 150°C. Fejlen kan endvidere variere med 15 alderen af udstyret, f.eks. på grund af ældning af det syntetiske harpiks og bøjningen, som kan påvirke understøtningen.2 necessary to power the transmitting coil and transmit the signal from the receiving coil. In conventional induction probes, the wires are in the form of rigid pressure-resistant, multi-layer coaxial cables. These cables have coaxial metal "layers" insulated from each other, the inner layers 5 acting as conductors conducting signals, while the outer layers provide the mechanical strength and shielding of the conductors. These cables and the discontinuities of connection to the coils, in the presence of the transmitting field, give rise to eddy currents which produce an error in the output signals. In the case of 10 low-conductivity formations, this error may be of the same magnitude as the utility signal. Furthermore, this fault is strongly exposed to temperature drift and its value at room temperature is substantially different from its value in the borehole environment where the temperature may be above 150 ° C. Furthermore, the error may vary with the age of the equipment, e.g. due to aging of the synthetic resin and the bending which may affect the support.

I US patentskrift nr. 3.249.858 er det blevet foreslået at anvende en understøtning af metal med henblik på at forøge den mekaniske 20 styrke. Dette patentskrift viser, at for at minimere frembringelsen af forstyrrende strømme i metal understøtningen, skal denne omfatte en diametral gennemgående slids, der strækker sig over i det væsentlige hele dens længde. Patentskriftet angiver også, at spolerne skal være fremstillet af cirkulære vindinger, der er forbundet med 25 hinanden ved hjælp af lineære ledende segmenter, hvis midtpunkter er placeret i det diametrale plan for slidsen. Det skal imidlertid bemærkes, at forøgelsen af den mekaniske styrke er begrænset af slidsen, som går gennem understøtningen, og også at de problemer, som opstår på grund af tilstedeværelsen af de elektriske ledninger, 30 ikke er afhjulpet.In U.S. Patent No. 3,249,858, it has been proposed to use a metal support to increase mechanical strength. This patent discloses that in order to minimize the generation of disruptive currents in the metal support, it must comprise a diametrical through-slot extending over substantially its entire length. The patent also states that the coils must be made of circular windings connected to each other by means of linear conductive segments whose centers are located in the diametrical plane of the slot. It should be noted, however, that the increase in mechanical strength is limited by the slit passing through the support, and also that the problems arising from the presence of the electrical wires are not rectified.

Fra US patentskrift nr. 3.305.771 kendes et borehulsloggeapparat, hvor sende- og modtagespoler viklet på ringkerner er anbragt på en ledende borestreng, som ved hjælp af kontaktorganer over og under 35 spolerne er i elektrisk kontakt med borehullets væg. Dette kendte apparat anvender et elektrisk felt i den omgivende formation til at frembringe et mål for formationens konduktivitet. Det er derfor nødvendigt, at borestrengen er i elektrisk kontakt med formationerne enten via direkte berøring eller ved hjælp af særligeUS Patent No. 3,305,771 discloses a borehole logging apparatus in which transmitting and receiving coils wound on annular cores are arranged on a conductive drill string which is in electrical contact with the borehole wall by means of contact means. This known apparatus uses an electric field in the surrounding formation to produce a measure of the conductivity of the formation. It is therefore necessary that the drill string be in electrical contact with the formations either by direct contact or by means of special

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3 kontaktorganer.3 contact means.

Fra GB 2.146.126 kendes et elektromagnetisk borehulsloggeapparat, hvor sende- og modtageantennespol er er anbragt i udsparinger i en 5 borestreng af stål. Apparatet drives ved højfrekvens, f.eks. 2 MHz, idet elektromagnetiske bølger fra sendeantennen efter udbredelse gennem de omgivende borehulsformationer inducerer elektriske strømme i modtagerantennerne.From GB 2,146,126 an electromagnetic borehole logger is known in which the transmitting and receiving antenna coil is arranged in recesses in a steel drill string. The apparatus is operated at high frequency, e.g. 2 MHz, electromagnetic waves from the transmitting antenna after propagation through the surrounding borehole formations induce electrical currents in the receiving antennas.

10 De to ovennævnte kendte apparater er således af andre typer end den induktive loggesonde, som den foreliggende opfindelse vedrører.Thus, the two aforementioned known devices are of different types than the inductive logging probe to which the present invention relates.

Formålet med den foreliggende opfindelse er at tilvejebringe en induktionsloggesonde med en særlig god mekanisk styrke og robusthed, 15 som frembyder en lav, stabil og forudsigelig sondefejl, hvor anvendelsen af fieriags koaksialkabler til forbindelserne til og fra spolerne er undgået, og som kan indsættes i en kombination af loggeværktøjer på et hvilket som helst sted i kombinationen samt er egnet til måle-under-boring anvendelser.The object of the present invention is to provide an induction log probe with a particularly good mechanical strength and robustness which presents a low, stable and predictable probe error where the use of multi-layer coaxial cables for the connections to and from the coils is avoided and can be inserted into a coil. combination of logging tools at any location in the combination as well as being suitable for measuring-under-drilling applications.

2020

Ifølge opfindelsen opnås dette med en induktionsloggesonde af den art, der er indrettet til forskydning i et borehul til undersøgelse af formationerne, som borehullet går igennem, omfattende i det mindste en sendesolenoidespole til frembringelse af et elektromag-25 netisk felt, som inducerer hvirvelstrømme i formationen, mindst en modtagesolenoidespole, der ligger i aksial afstand fra sendespolen til frembringelse i afhængighed af feltet, som induceres af disse hvirvelstrømme, af et signal, som er en indikation for formationens konduktivitet, og en langstrakt understøtning til montering af 30 spolerne i koaksial og med indbyrdes afstand liggende stilling, hvilken induktionsloggesonde ifølge opfindelsen er ejendommelig ved, at det elektromagnetiske felt er i det væsentlige frit for dielektriske effekter, og at understøtningen er fremstillet af elektrisk ledende materiale og i nærheden af spolerne har i det mindste en i 35 det væsentlige kontinuerlig og aksesymmetrisk ydre overflade til at begunstige passagen af hvirvelstrømme omkring overfladen.According to the invention, this is achieved with an induction log probe of the kind arranged for displacement in a borehole for examining the formation through which the borehole passes, comprising at least one transmitting solenoid coil to produce an electromagnetic field which induces eddy currents in the formation. , at least one receiving solenoid coil spaced axially away from the transmitting coil to produce, in dependence on the field induced by these eddy currents, a signal indicative of the conductivity of the formation and an elongate support for mounting the coils in coaxial and with spaced apart position, which induction log probe according to the invention is characterized in that the electromagnetic field is substantially free of dielectric effects and that the support is made of electrically conductive material and in the vicinity of the coils has at least one substantially continuous and axisymmetric outer o surface to favor the passage of eddy currents around the surface.

Når det elektromagnetiske felt således er i det væsentlige frit for dielektriske effekter, hvilket i praksis opnås ved at arbejde medThus, when the electromagnetic field is substantially free of dielectric effects, which is achieved in practice by working with

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4 frekvenser inden for området 10-400 kHz, bliver forskydningsstrømmene negligible således, at udgangssignalet ikke afhænger af formationens dielektricitetskonstant, men kun af dens konduktivitet. Når understøtningen er af et godt ledende materiale med en kontinuerlig 5 aksesymmetrisk ydre overflade, er den næsten ækvivalent med en perfekt leder. Det tangenti ale elektriske felt bliver 0 ved overfladen af understøtningen, og der frembringes derfor ikke noget elektromagnetisk felt i det lukkede indre rum i understøtningen, som derfor er en effektiv elektromagnetisk skærm. Idet direkte kobling 10 mellem lederne og spolerne derved er undgået, kan der også anvendes simple ledere. Endvidere er sondefejlen, som frembringes af hvirvelstrømmene omkring understøtningen, lille som følge af anvendelsen af godt ledende metal til understøtningen.4 frequencies in the range of 10-400 kHz, the shear currents become negligible such that the output does not depend on the dielectric constant of the formation, but only on its conductivity. When the support is of a good conductive material with a continuous 5 axis symmetrical outer surface, it is almost equivalent to a perfect conductor. The tangential electric field becomes 0 at the surface of the support, and therefore no electromagnetic field is produced in the enclosed interior space of the support, which is therefore an effective electromagnetic shield. As direct coupling 10 between the conductors and the coils is thereby avoided, simple conductors can also be used. Furthermore, the probe error produced by the eddy currents around the support is small due to the use of well-conductive metal for the support.

15 Fortrinsvis indbefatter understøtningen en ydre muffe, der er fremstillet af et metal med en høj elektrisk konduktivitet, såsom kobber, og en indre kerne af et materiale med mindre konduktivitet, men højere styrke, såsom rustfrit stål.Preferably, the support includes an outer sleeve made of a metal with a high electrical conductivity, such as copper, and an inner core of a material of less conductivity but higher strength, such as stainless steel.

20 Opfindelsen skal herefter forklares nærmere under henvisning til tegningen, hvor figur 1 skematisk viser en udførelsesform for en induktionsloggesonde ifølge opfindelsen og det dermed forbundne 25 overfladeudstyr, figur 2 et forstørret detail biIlede af en spoleenhed i apparatet i figur 1 i en første udførelsesform, figur 3 en modificeret udførelsesform for spoleenheden, figur 4 en induktionsloggesonde ifølge opfindelsen indrettet til 30 måle-under-boringdrift, figur 5 et langsgående billede delvis i snit af en foretrukken udførelsesform for induktionsloggesonden, og figur 6 et snit efter linien 6-6 i figur 5. 1 På tegningen viser fig. 1 en induktionsloggesonde 10 til undersøgelse af de geologiske formationer 11, som et borehul 12 går igennem. Borehullet er fyldt med borevæske 13. Apparatet er ophængt i et fieriederkabel 14, som er ført over en skive 15 og viklet på et spilThe invention will now be explained in more detail with reference to the drawing, in which Figure 1 shows schematically an embodiment of an induction log probe according to the invention and the associated surface equipment, Figure 2 an enlarged detail illustrated by a coil unit in the apparatus of Figure 1 in a first embodiment; Fig. 3 is a modified embodiment of the coil assembly; Fig. 4 is an induction log probe according to the invention arranged for 30 metering drilling operation; Fig. 5 is a longitudinal view partially in section of a preferred embodiment of the induction log probe; and Fig. 6 is a section along line 6-6 of Fig. 5. 1 In the drawing, FIG. 1 is an induction log probe 10 for examining the geological formations 11 through which a borehole 12 passes. The borehole is filled with drilling fluid 13. The apparatus is suspended in a feeder cable 14 which is passed over a disc 15 and wound on a play

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5 16, som er en del af overfladeudstyret i forbindelse med loggesonden nede i hullet. Overfladeudstyret forsyner apparatet 10 via kablet 14 med elektrisk energi og signaler til styring af dets drift, og modtager fra apparatet 10 målesignaler. Overfladeudstyret indbefat-5 ter organer 17 til behandling og registrering af disse signaler. Der findes en føler 17a til detektering af kablets bevægelse. Signalerne fra følerne 17a angiver den øjeblikkelige dybde af apparatet nede i hullet og føres til behandlingsorganerne for dybdetilpasning af målesignalerne.5 16, which is part of the surface equipment associated with the downhole logging probe. The surface equipment supplies the apparatus 10 via the cable 14 with electrical energy and signals to control its operation, and receives measurement signals from the apparatus 10. The surface equipment includes means 17 for processing and recording these signals. There is a sensor 17a for detecting the movement of the cable. The signals from the sensors 17a indicate the instantaneous depth of the apparatus downhole and are passed to the processing means for depth adjustment of the measurement signals.

1010

Apparatet 10 nede i hullet omfatter en elektronisk patron 18, der er forbundet med kablet 14 over et kabel hoved 19. Patronen 18 indbefatter en telemetripatron 20, som omsætter signalerne til overfladeudstyret frembragt af apparatet nede i hullet til et format, der 15 er egnet til transmission gennem kablet.The downhole apparatus 10 comprises an electronic cartridge 18 connected to the cable 14 over a cable head 19. The cartridge 18 includes a telemetry cartridge 20 which converts the signals to the surface equipment produced by the downhole apparatus into a format suitable for transmission through the cable.

Apparatet 10 nede i hullet omfatter også en langstrakt understøtning 30, hvis øverste ende er fastgjort til patronen 18. Understøtningen 30 bærer et spolesystem, som omfatter en sendespole 31 og en modta-20 gespole 32 koaksialt med og i afstand fra hinanden i den langsgående retning af understøtningen 30. Sendespolen 31 strømforsynes for at frembringe et magnetfelt, der i formationen inducerer hvirvelstrømme, som løber koaksialt med understøtningens akse. Modtagespolen frembringer i afhængighed af feltet, som skabes af disse strømme, et 25 udgangssignal, der repræsenterer konduktiviteten af formationen. Arbejdsfrekvensen for sendespolen er en sådan, at feltet, som etableres i formationerne, kan betegnes som et "quasistatisk" elektromagnetisk felt. Med andre ord er driftsfrekvensen en sådan, at forskydningsstrømmene er negligible, idet ledningsstrømme er 30 overvejende. Frekvensen ligger passende mellem ca. 10 og ca. 400 kHz. Over 400 kHz bliver forskydningsstrømme signifikante, og udgangssignalet ville afhænge ikke kun af formationens konduktivitet, men også af dens di elektricitetskonstant, hvilket ville være uønsket til den foreliggende opfindelses formål. En foretrukken øvre 35 grænse for frekvensområdet er ca. 200 kHz. En foretrukken nedre grænse for frekvensområdet er ca. 20 kHz.The downhole apparatus 10 also includes an elongate support 30, the upper end of which is attached to the cartridge 18. The support 30 carries a coil system comprising a transmitting coil 31 and a receiving coil 32 coaxially with and spaced apart in the longitudinal direction. of the support 30. The transmit coil 31 is energized to produce a magnetic field which in the formation induces eddy currents which run coaxially with the axis of the support. The receiving coil produces, in dependence on the field created by these currents, an output signal representing the conductivity of the formation. The operating frequency of the transmitting coil is such that the field established in the formations can be termed a "quasi-static" electromagnetic field. In other words, the operating frequency is such that the shear currents are negligible, with conduction currents being predominantly. The frequency is suitably between approx. 10 and approx. 400 kHz. Above 400 kHz, shear currents become significant, and the output signal would depend not only on the conductivity of the formation, but also on its di-electricity constant, which would be undesirable for the purposes of the present invention. A preferred upper limit of the frequency range is approx. 200 kHz. A preferred lower limit for the frequency range is approx. 20 kHz.

I den skematiske tegning i figur 1 er sonden vist at have kun en sendespole og en modtagespole, men det vil forstås, at hvertIn the schematic drawing of Figure 1, the probe is shown to have only one transmitting coil and one receiving coil, but it will be understood that each

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6 spolesystem kan omfatte mere end to spoler, f.eks. en eller flere sendespoler, flere modtagespoler og kompenseringsspoler i forbindelse med hver sin af modtagespolerne for at ophæve virkningen af direkte kobling mellem sendespolerne og modtagespolerne. Sonden kan 5 endvidere omfatte flere spolesystemer fordelt over sin længde.6 coil system may comprise more than two coils, e.g. one or more transmitting coils, multiple receiving coils and compensating coils in connection with each of the receiving coils to eliminate the effect of direct coupling between the transmitting coils and the receiving coils. The probe may further comprise several coil systems distributed over its length.

Understøtningen 30 har i hovedsagen rørform og er fremstillet af et metal, fortrinsvis et umagnetisk metal med god elektrisk konduktivitet. Egnede materialer indbefatter kobber og kobberlege-10 ringer og rustfrit stål.The support 30 is generally tubular in shape and is made of a metal, preferably a non-magnetic metal with good electrical conductivity. Suitable materials include copper and copper alloys and stainless steel.

Understøtningen omfatter cylindriske langsgående dele 33, hvis ydre væg 34 er i kontakt med ydersiden, det vil sige med borevæsken, og cylindriske langsgående dele 35 med en ydre diameter, der er mindre 15 end den ydre diameter af delene 33. Delene 35 danner således hulrum 35a til optagelse af spolerne 31 og 32, der er koaksiale med og elektrisk isoleret fra de respektive dele 35. Udførelsesformen vist i figur 1 indbefatter et sådant hulrum for hver spole, men det vil forstås, at en del 35 ligeså vel kan indbefatte et helt spolesystem, 20 det vil sige et hulrum 35a kan indeholde et antal aksialt fordelte spoler. De mellemliggende dele 33 har fortrinsvis en større indvendig diameter end delene 35 og danner indre rum 36, og i udførelsesformen vist i figur 1 er delene 33 og 35 forbundet med tværgående dele 37. Væggene af delen 33 har en tilstrækkelig tykkelse til selv 25 at modstå det hydrostatiske tryk af borehulsvæsken.The support comprises cylindrical longitudinal portions 33 whose outer wall 34 is in contact with the outside, that is, with the drilling fluid, and cylindrical longitudinal portions 35 with an outer diameter smaller than the outer diameter of the portions 33. The portions 35 thus form voids. 35a for receiving the coils 31 and 32 which are coaxial with and electrically insulated from the respective portions 35. The embodiment shown in Figure 1 includes such a cavity for each coil, but it will be appreciated that a portion 35 may as well include an entire coil system, i.e. a cavity 35a may contain a plurality of axially spaced coils. The intermediate portions 33 preferably have a larger internal diameter than the portions 35 and form inner compartments 36, and in the embodiment shown in Figure 1, the portions 33 and 35 are connected to transverse portions 37. The walls of the portion 33 are of sufficient thickness to withstand even 25 the hydrostatic pressure of the borehole fluid.

Respektive ledere 38, som er lagt inde i understøtningen, forbinder spolerne 31 og 32 med den elektroniske patron 18.Respective conductors 38 inserted within the support connect the coils 31 and 32 to the electronic cartridge 18.

30 Da understøtningen i delene i nærheden af spolerne er fremstillet af et godt ledende materiale og har en kontinuerlig aksesymmetrisk ydre overflade, er den næsten ækvivalent med den perfekte leder. Dette begunstiger frembringelsen af hvirvelstrømme under tilstedeværelsen af det elektromagnetiske felt, som frembringes af sendespolen, 35 hvilke strømme løber omkring overfladen af understøtningen. Som følge heraf bliver det tangentiale elektriske flet tvunget mod 0 ved overfladen af understøtningen, og der frembringes ikke noget elektromagnetisk felt i det lukkede rum, som afgrænses af det indre af understøtningen. Understøtningen udgør derfor en meget effektiv30 Since the support in the parts near the coils is made of a good conductive material and has a continuous axisymmetric outer surface, it is almost equivalent to the perfect conductor. This favors the generation of eddy currents in the presence of the electromagnetic field produced by the transmitting coil, which flows around the surface of the support. As a result, the tangential electric braid is forced toward 0 at the surface of the support, and no electromagnetic field is generated in the enclosed space bounded by the interior of the support. The support is therefore a very effective one

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7 elektromagnetisk skærm. Med f.eks. en driftsfrekvens på 20 kHz og en konduktivitet på 5,8 x 10^ S/m (kobber) repræsenterer en tykkelse på 5 mm 10 gennemtrængningsdybder (skindybder). Den forstyrrende virkning af direkte koblinger mellem lederne og spolerne er således 5 elimineret, og det er muligt at anvende simple ledertråde i stedet for de sædvanligt anvendte fieriags koaksial kabl er.7 electromagnetic display. With e.g. a operating frequency of 20 kHz and a conductivity of 5.8 x 10 6 S / m (copper) represent a thickness of 5 mm 10 penetration depths (skin depths). Thus, the disruptive effect of direct couplings between the conductors and the coils is eliminated, and it is possible to use simple conductor wires instead of the commonly used coaxial cable of the four.

Da det tangenti ale elektriske felt endvidere er i det væsentlige ophævet ved overfladen af understøtningen, er sondefejlen, som 10 frembringes af hvirvelstrømmene, der løber omkring understøtningen, lille. Det har vist sig, at sondefejlen med en fuldstændigt aksesymmetrisk metalunderstøtning er en aftagende funktion af den elektriske konduktivitet af understøtningens materiale og af frekvensen. Det matematiske udtryk for denne variation er E . k . , -1/2 . f-3/2 hvor E betegner sondefejlen, σ konduktiviteten, f frekvensen og k er en koefficient. Følgelig bliver sondefejlen minimeret, hvis der 20 anvendes et metal med høj konduktivitet. En typisk værdi for sondefejlen for understøtningen målt i luft er 2 millisiemens, hvilket er af samme størrelsesorden som udgangssignaler, der fås ved de fleste formationer med høj resistivitet. Endvidere er en meget betydelig fordel ved opfindelsen, at denne sondefejl udviser en meget lav 25 temperaturdrift og er godt forudsigelig. Det er således let at korrigere udgangssignalet for indflydelsen af metal understøtningen ved at subtrahere den veldefinerede sondefejl fra udgangssignalet.Furthermore, since the tangential electric field is substantially uplifted at the surface of the support, the probe error produced by the eddy currents running around the support is small. It has been found that the probe failure with a fully axisymmetric metal support is a decreasing function of the electrical conductivity of the support material and of the frequency. The mathematical expression of this variation is E. k. , -1/2. f-3/2 where E represents the probe error, σ conductivity, f frequency and k is a coefficient. Consequently, the probe error is minimized if a high conductivity metal is used. A typical value of the probe error for the support measured in air is 2 millisiemens, which is of the same magnitude as the output signals obtained at most high resistivity formations. Furthermore, a very significant advantage of the invention is that this probe error exhibits a very low temperature operation and is well predictable. Thus, it is easy to correct the output signal for the influence of the metal support by subtracting the well-defined probe error from the output signal.

Det forhold, at spolerne er monteret omkring metaldele, bevirker en 30 reduktion af tværsnitsarealet, som er til rådighed for magnetflux-ene, der udsendes af spolen 31 og modtages af spolen 32, idet overfladearealet er afhængigt af afstanden mellem spolerne og den ydre overflade af delene 35. Dette bevirker en reduktion i følsomheden af målingen, men denne reduktion kan der let kompenseres for 35 ved korrekt udformning af spolerne, det vil sige antallet af vindinger af spolerne forøges i forhold til det sædvanlige arrangement med en ikke ledende understøtning.The fact that the coils are mounted around metal parts causes a reduction in the cross-sectional area available to the magnetic fluxes emitted by the coil 31 and received by the coil 32, the surface area being dependent on the distance between the coils and the outer surface of the coils. The parts 35. This causes a reduction in the sensitivity of the measurement, but this reduction can easily be compensated for by the correct design of the coils, that is, the number of turns of the coils is increased relative to the usual arrangement with a non-conductive support.

Det skal bemærkes, at den aksiale afstand mellem enderne af en spoleIt should be noted that the axial distance between the ends of a coil

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8 og de nærliggende vægge af de tværgående dele 37 passende holdes over en forudbestemt værdi. Den vertikale karakteristik for sonden, når den måles langs den ydre overflade af sonden, udviser skarpe spidser ud for spolerne, idet middel bredden af spidserne er lig med 5 ca. 1 diameter af den respektive spole. For at undgå en eventuel væsentlig ændring af sondens svarkarakteristik vælges afstanden mellem enderne af spolerne og den nærliggende tværgående del lig med i det mindste én diameter af den respektive spole. Hvis et antal spoler er anbragt i ét hulrum 35a, skal afstanden mellem hver 10 tværgående del og enden af spolen beliggende nærmest denne tværgående del være mindst lig med ca. 1 diameter af den pågældende spole.8 and the adjacent walls of the transverse members 37 are suitably held above a predetermined value. The vertical characteristic of the probe, when measured along the outer surface of the probe, exhibits sharp tips next to the coils, with the mean width of the tips being equal to approx. 1 diameter of the respective coil. In order to avoid any significant change in the response characteristics of the probe, the distance between the ends of the coils and the adjacent transverse portion is chosen equal to at least one diameter of the respective coil. If a plurality of coils are disposed in one cavity 35a, the distance between each 10 transverse portion and the end of the coil located closest to this transverse portion must be at least equal to about 10 1 diameter of the coil in question.

Med andre ord skal den cylindriske del af understøtningen, som bærer en individuel spole eller et helt spolesystem have en aksial dimension, der overstiger den aksiale dimension af spolen (henholdsvis af 15 spolesystemet) på hver side af spolen (henholdsvis af spolesystemet) med mindst ca. 1 diameter af spolen (henholdsvis en diameter af endespolerne af spolesystemet).In other words, the cylindrical portion of the support carrying an individual coil or a whole coil system must have an axial dimension exceeding the axial dimension of the coil (respectively of the coil system) on each side of the coil (respectively of the coil system) by at least approx. . 1 diameter of the coil (respectively a diameter of the end coils of the coil system).

I betragtning af det foregående er en understøtning med en fuld-20 stændig aksesymmetrisk og kontinuerlig ydre overflade i delene i nærheden af spolerne det optimale, men udformninger, som afviger lidt fra dette optimum, ligger inden for opfindelsens rammer, forudsat at passagen af hvirvelstrømme omkring understøtningen ikke påvirkes væsentligt. Eksempelvis kan der anvendes et tværsnit, som 25 er i hovedsagen tilsvarende, men forskelligt fra et cirkulært tværsnit, f.eks. polygoner. Små huller dannet i understøtningen, f.eks. for passage af ledere til spolerne, vil heller ikke væsentligt ændre passagen af hvirvelstrømme. På den anden side vil langsgående slidser gennem understøtningen modvirke passagen af hvirvel-30 strømme og være skadelig for understøtningens afskærmningseffekt.In view of the foregoing, a support with a fully axially symmetric and continuous outer surface of the parts near the coils is the optimum, but designs which deviate slightly from this optimum are within the scope of the invention provided that the passage of eddy currents about the support is not significantly affected. For example, a cross-section which is substantially similar but different from a circular cross-section, e.g. polygons. Small holes formed in the support, e.g. for the passage of conductors to the coils, will also not substantially change the passage of eddy currents. On the other hand, longitudinal slits through the support will counteract the passage of eddy currents and be detrimental to the shielding effect of the support.

En yderligere fordel ved metal understøtningen er, at den giver sonden en forbedret mekanisk styrke og robusthed, og delene 33 af understøtningen er i sig selv trykmodstandsdygtige.A further advantage of the metal support is that it provides the probe with improved mechanical strength and robustness, and the parts 33 of the support are themselves pressure resistant.

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Rummene 36, der er dannet inde i delene 33, kan udnyttes til at indeholde nogle af de elektriske kredsløb i sonden. I dette tilfælde vil der i stedet for at gruppere hele kredsløbet i patronen 18, som vist i figur 1, være en sendeblok, som er forbundet med sendespolenThe compartments 36 formed within the portions 33 can be utilized to contain some of the electrical circuits in the probe. In this case, instead of grouping the entire circuit in the cartridge 18, as shown in Figure 1, there will be a transmit block connected to the transmit coil.

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9 31 og anbragt 1 et rum 36 i nærheden af denne spole, og en modtageblok, som er forbundet med udgangen på modtagespolen og på lignende måde er anbragt i et rum 36 i nærheden af modtagespolen.9 31 and disposed in a space 36 near this coil, and a receiving block connected to the output of the receiving coil and similarly arranged in a space 36 near the receiving coil.

5 Det skal også bemærkes, at som følge af den mekaniske styrke af understøtningen 30 og muligheden for at føre ledertrådene inde i understøtningen, kan den ovenfor beskrevne induktionssonde kombineres med et (eller flere) loggeapparater af forskellig type (lyd-, kerne-) fastgjort til den nederste ende af induktionssonden. Et 10 sådant apparat er vist med punkterede linier i figur 1 med henvis-ningstallet 40. Lederne, som forbinder dette apparat med telemetri-patronen 20 via det indre rum i understøtningen 30, er også vist med punkterede linier og betegnet med 41. Induktionssonden ifølge opfindelsen kan således indsættes på et hvilket som helst sted i en 15 kombination af loggesonder, medens de sædvanlige induktionssonder med en ikke metallisk understøtning kun kan placeres i bunden af kombinationen.It should also be noted that due to the mechanical strength of the support 30 and the ability to guide the conductor wires inside the support, the above-described induction probe may be combined with one (or more) loggers of different type (sound, core) attached to the lower end of the induction probe. One such apparatus is shown in dotted lines in Figure 1 with reference numeral 40. The conductors connecting this apparatus to the telemetry cartridge 20 via the inner space of the support 30 are also shown in dotted lines and denoted by 41. The induction probe of Thus, the invention can be inserted at any location into a combination of logging probes, while the usual induction probes with a non-metallic support can only be placed at the bottom of the combination.

Figur 2 viser mere detaljeret en egnet kombination af spolerne 31 og 20 32. Hver spole er i form af en spoleenhed 50. Spoleenheden er isoleret fra delen 35 af understøtningen ved hjælp af en isolerende muffe 51, f.eks. af keramik. Muffen 51 er fastgjort til delen 35 ved hjælp af et organ, såsom en stift 52. Muffen 51 bærer flere ringe 53 og flere ringe 54, som er skruet til de respektive ender af den 25 rørformede del 51 på begge sider af spoleenheden, for således at holde denne på plads.Figure 2 shows in more detail a suitable combination of coils 31 and 20 32. Each coil is in the form of a coil assembly 50. The coil assembly is insulated from the portion 35 of the support by an insulating sleeve 51, e.g. of ceramics. The sleeve 51 is secured to the member 35 by means such as a pin 52. The sleeve 51 carries several rings 53 and several rings 54 which are screwed to the respective ends of the 25 tubular member 51 on both sides of the coil assembly, thus to keep this one in place.

Spoleenheden omfatter en spoleform dannet af to i hovedsagen ringformede understøtningsdele 56, 57 af isolerende materiale, f.eks.The coil assembly comprises a coil mold formed of two generally annular support members 56, 57 of insulating material, e.g.

30 keramik, som tilsammen har et rektangulært tværsnit og afgrænser et ringformet indre rum 58. Rummet 58 optager vindingerne 60 af spolen, hvilke vindinger er anbragt koaksialt med aksen for understøtningen 30. Et antal ledende tråde 61 er viklet omkring understøtningsdelen 56, 57 i et toroidearrangement. Hver tråd er afskåret for at 35 forhindre den i at danne en lukket sløjfe, og alle trådene er forbundet med en jordring (ikke vist), og således på det samme jordpotential. Trådene 61 danner en elektrostatisk skærm, som forhindrer enhver elektrostatisk kobling af den respektive spole med den eller de andre spoler eller med borevæsken. Dette arrangement er30 ceramics, which together have a rectangular cross-section and delimit an annular inner space 58. The space 58 accommodates the coils 60 of the coil, which coils are arranged coaxially with the axis of the support 30. A number of conductive wires 61 are wound around the support member 56, 57 in a toroidearrangement. Each wire is cut to prevent it from forming a closed loop, and all the wires are connected to a ground ring (not shown), and thus to the same ground potential. The wires 61 form an electrostatic shield which prevents any electrostatic coupling of the respective coil with the other coil (s) or with the drilling fluid. This event is

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10 omhandlet mere detaljeret i en patentansøgning med benævnelsen "Shielded Solenoid Coil for Well-Logging" serie no. 551.239 (US patentskrift nr. 4.808.929) tilhørende ansøgeren, og hvortil der henvises.10, which is described in more detail in a patent application entitled "Shielded Solenoid Coil for Well-Logging" series no. 551,239 (U.S. Patent No. 4,808,929) to the applicant and to which reference is made.

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En fluidtæt muffe 62 af ikke ledende materiale, f.eks. af glasfiberforstærket epoxy, er monteret omkring spoleenheden for at beskytte denne mod kontakt med mudderet med tryktætninger 62a ved begge ender. Ringene 53, 54 understøtter muffen 62 på dens indre 10 overflade for at bringe den i stand til at modstå trykket af mudderet. Huller, såsom 63, er dannet i delen 37 af understøtningen for passagen af elektriske ledere, der er forbundet med spolen.A fluid-tight sleeve 62 of non-conductive material, e.g. of fiberglass reinforced epoxy, is mounted around the coil assembly to protect it from contact with the mud with pressure seals 62a at both ends. The rings 53, 54 support the sleeve 62 on its inner surface to enable it to withstand the pressure of the mud. Holes, such as 63, are formed in the portion 37 of the support for the passage of electrical conductors connected to the coil.

I det ovennævnte tilfælde, hvor der er flere spoler, som er monteret 15 på den samme del 35, skal yderligere ringe svarende til ringene 53 anbringes i rummene mellem spolerne for at holde disse på plads og undestøtte muffen 62, som lukker hulrummet 35a mellem spolerne.In the above-mentioned case, where there are multiple coils mounted 15 on the same part 35, additional rings corresponding to the rings 53 must be placed in the spaces between the coils to hold them in place and support the sleeve 62 which closes the cavity 35a between the coils. .

Endvidere viser figur 2 delene 35 og 33 som separate dele med gevind 20 64 ved begge ender af delene 35 for at fastgøre dem til de tværgå ende dele 37, og understøtningen er samlet, efter at spoleenhederne er blevet monteret på delene 35.Furthermore, Figure 2 shows the parts 35 and 33 as separate parts with threads 20 64 at both ends of the parts 35 to attach them to the transverse end parts 37 and the support is assembled after the coil units have been mounted on the parts 35.

Det skal også bemærkes med hensyn til materialet i understøtningen, 25 at delene 33 og 35 kan være fremstillet af forskellige materialer, f.eks. rustfrit stål i delene 33 og kobber eller kobberlegering i delene 35.It should also be noted with respect to the material in the support that parts 33 and 35 may be made of various materials, e.g. stainless steel in parts 33 and copper or copper alloy in parts 35.

En modificeret udførelsesform er vist i figur 3. Spolen 70 er 30 indesluttet i en spoleform 71, som ligner den, der udgøres af delene 56, 57 i figur 2. Spolen er elektrostatisk afskærmet af en opslidset cylindrisk del 72 fremstillet af et ledende materiale med isolerende materiale til at fylde slidserne 73. Ligesom i den ovenfor beskrevne udførelsesform holdes spoleformen på plads af ringe, der er skruet 35 på en rørformet del, hvilke ringe også indgriber med den indre væg af den opslidsede del for at støtte den imod trykket af borehulsvæsken.A modified embodiment is shown in Figure 3. Coil 70 is enclosed in a coil mold 71 similar to that constituted by parts 56, 57 of Figure 2. The coil is electrostatically shielded by a slotted cylindrical portion 72 made of a conductive material having insulating material for filling the slots 73. As in the embodiment described above, the coil shape is held in place by rings screwed 35 on a tubular member which also engages the inner wall of the slotted portion to support it against the pressure of the borehole fluid. .

En modifikation af de ovenfor beskrevne udførelsesformer ville væreA modification of the embodiments described above would be

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11 at sætte det indre af hulrummene, som optager spoleenhederne, under samme tryk som trykket af borehulsvæsken. Væskeledninger kunne lægges inde i understøtningen 30 for at forbinde disse hulrum med et sædvanligt trykkompensationsorgan. I dette tilfælde skulle der 5 tilvejebringes væsketætte elektriske gennemføringer for at føre de elektriske forbindelser gennem hulrummenes væg.11 to put the interior of the cavities which occupy the coil units under the same pressure as the pressure of the borehole fluid. Liquid lines could be laid inside the support 30 to connect these cavities with a conventional pressure compensation means. In this case, liquid-tight electrical passages should be provided to pass the electrical connections through the wall of the cavities.

Figur 4 viser en induktionssonde ifølge opfindelsen, som er indrettet til måling under boring.Figure 4 shows an induction probe according to the invention arranged for measurement during drilling.

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Sonden 80 er beliggende over borekroneenheden 82. Understøtningen for spolerne tilvejebringes af en sektion af vægtrøret 83, en rørformet del af stål, som sædvanligvis er forbundet med den ne-derste ende af borestrengen for at monteres over borekroneenheden.The probe 80 is located above the drill bit assembly 82. The support for the coils is provided by a section of the weight pipe 83, a tubular steel section usually connected to the lower end of the drill string to be mounted over the drill bit assembly.

15 Boremudderet cirkuleres under boreoperationen gennem den centrale boring 84 i vægtrøret. Vægtrøret har en stor tykkelse for at give borekronen en passende vægt til boreformål.During the drilling operation, the drilling mud is circulated through the central bore 84 of the weight pipe. The barrel has a large thickness to give the drill bit an appropriate weight for drilling purposes.

Figur 4 viser kun to spoler, en sendespole 85 og en modtagespole 86, 20 men det vil forstås, at en ikke vist kompensationsspole er forbundet med modtagespolen til det ovenfor forklarede formål, og ponden kan omfatte flere spolesæt med forskellige afstande fra sendespolen.Figure 4 shows only two coils, a transmitting coil 85 and a receiving coil 86, 20, but it will be appreciated that a compensation coil not shown is connected to the receiving coil for the purpose explained above, and the pond may comprise several coil sets at different distances from the coil.

Alle disse spoler vil være anbragt på samme måde som spolerne 85 og 86.All of these coils will be arranged in the same manner as coils 85 and 86.

25 Vægtrørsektionen 83 har dele med reduceret ydre diameter, som således danner cirkulære udsparinger eller hulrum 87, hvori spolerne er anbragt, idet hver spole er indlagt i en muffe 88 af gummi eller lignende materiale, som udfylder hulrummet. Gummi fyldningen er en 30 sådan, at den ydre overflade af muffen 88 er i det væsentlige plan med den cylindriske ydre overflade af delene 89 af vægtrørsektionen 83, som er udsat for borehulsvæskerne. Hvert hulrum 87 har en central cylindrisk del 90 med en ydre diameter Dj, der er mindre end den ydre diameter Dg af delen 89, idet den respektive spole er 35 anbragt omkring denne centrale del, og keglestubformede dele 91 forbinder den centrale del 90 med delene 89 af vægtrøret. Den aksiale dimension af de keglestubformede dele er passende lig med ca. 1. diameter af den respektive spole.The wall tube section 83 has reduced outer diameter portions thus forming circular recesses or cavities 87 in which the coils are disposed, each coil being housed in a sleeve 88 of rubber or similar material filling the cavity. The rubber filling is such that the outer surface of the sleeve 88 is substantially flush with the cylindrical outer surface of the portions 89 of the barrel section 83 which are exposed to the borehole fluids. Each cavity 87 has a central cylindrical portion 90 having an outer diameter Dj less than the outer diameter Dg of the portion 89, the respective coil 35 being disposed about this central portion, and cone-shaped portions 91 connecting the central portion 90 to the portions. 89 of the weight pipe. The axial dimension of the cone-shaped parts is suitably equal to approx. 1st diameter of the respective coil.

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Signaler, som føres til sendespolen og modtages fra modtagespolerne, overføres af ikke viste ledere, som fortrinsvis er lagt i langsgående riller, der er dannet af den ydre overflade af vægtrøret og fyldt med et egnet isolerende og beskyttende materiale. Disse ledere 5 er forbundet med en ikke vist elektronisk patron beliggende inde i vægtrøret ved det øverste af induktionssonden.Signals fed to the transmitting coil and received from the receiving coils are transmitted by conductors not shown, which are preferably laid in longitudinal grooves formed by the outer surface of the weight tube and filled with a suitable insulating and protective material. These conductors 5 are connected to an electronic cartridge not shown located inside the weight tube at the top of the induction probe.

I en foretrukken udførelsesform er et lag 92 af kobber eller andet godt ledende materiale dannet i det mindste på den centrale del 90 10 af hvert hulrum for at tilvejebringe en overflade med høj konduktivitet i nærheden af spolerne, idet vægtrørssektionen 83 ellers er af stål, som angivet ovenfor.In a preferred embodiment, a layer 92 of copper or other well-conducting material is formed at least on the central portion 90 10 of each cavity to provide a high conductivity surface near the coils, the tubular section 83 otherwise being of steel. stated above.

Figur 5 viser et billede delvis i snit af en foretrukken udførel-15 sesform for induktionssonden ifølge opfindelsen.Figure 5 is a partial sectional view of a preferred embodiment of the induction probe of the invention.

I udførelsesformen i figur 5 er en sendespoleenhed vist ved 100, og et antal sæt af solenoidespoler er tilvejebragt, idet hvert spolesæt indbefatter en modtagespole og en kompensationsspole, der er udfor-20 met og placeret således, at den ophæver virkningen af den direkte kobling af sendespolen til den respektive modtagespole. Modtagespoler med forskellige afstande fra sendespolen er vist ved 101, 102, og kompensationsspolerne, som hver for sig er knyttet til modtagespolerne, er vist ved 10Γ, 102'. Alle spolerne er anbragt omkring 25 en central understøtning 105 med en ydre cylindrisk overflade med cirkulært tværsnit, som det fremgår af snittet i figur 6. Endedelen 106, 107 med større diameter er fastgjort til understøtningen 105 ved begge dens ender. En rørformet muffe 108 af glasfiberepoxy er monteret omkring spolerne for at forhindre kontakt med borehulsvæs-30 kerne. Muffen holdes på plads mellem endedelene 106, 107, idet muffen har samme ydre diameter som endedelene 106, 107. De frie rum i det ringformede rum 110 dannet mellem den centrale understøtning 105 og muffen 108 er fyldt med under tryk stående olie, og i dette øjemed er de i forbindelse med et trykkompensationsorgan vist ved 35 111 i nærheden af den nederste endedel 107. Kompensationsorganer 111, et sædvanligt element i borehulsloggesonder, tjener til at sætte trykket, som findes i det ringformede rum 110, under tryk, som er lidt større end trykket af borehulsvæskerne, så at differenstrykket på muffen 108 er lille.In the embodiment of Figure 5, a transmitting coil unit is shown at 100 and a plurality of sets of solenoid coils are provided, each coil set including a receiving coil and a compensation coil designed and positioned to cancel the effect of the direct coupling of the coil to the respective receiving coil. Receiving coils with different distances from the transmitting coil are shown at 101, 102, and the compensation coils, each of which is associated with the receiving coils, are shown at 10Γ, 102 '. All of the coils are disposed about 25 a central support 105 having an outer cylindrical surface of circular cross section, as shown in the section in Figure 6. The larger diameter end portion 106, 107 is attached to the support 105 at both its ends. A tubular fiberglass epoxy tubular sleeve 108 is mounted around the coils to prevent contact with the borehole core. The sleeve is held in place between the end portions 106, 107, the sleeve having the same outer diameter as the end portions 106, 107. The free spaces of the annular space 110 formed between the central support 105 and the sleeve 108 are filled with pressurized oil, and in this for this purpose, in connection with a pressure compensation means shown at 35,111, near the lower end portion 107. Compensation means 111, a common element in borehole log probes, serves to depressurize the pressure present in annular space 110. than the pressure of the borehole fluids so that the differential pressure on the sleeve 108 is small.

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Snittet i figur 6 viser en foretrukket udførelsesfonn for den centrale understøtning 105. Understøtningen omfatter to dele, en ydre muffe 115, fortrinsvis af et godt ledende metal, såsom kobber eller en kobberlegering, og en indre kerne 116, fortrinsvis af et 5 metal med højere styrke, såsom rustfrit stål. Den ydre muffe er monteret over den indre kerne med en løs pasning for at tage hensyn til forskellen mellem kobber og stål i henseende til varmeudvidelse.The section in Figure 6 shows a preferred embodiment of the central support 105. The support comprises two parts, an outer sleeve 115, preferably of a good conductive metal such as copper or a copper alloy, and an inner core 116, preferably of a higher metal 5. strength, such as stainless steel. The outer sleeve is mounted over the inner core with a loose fit to take into account the difference between copper and steel in terms of heat expansion.

Den indre kerne 116 har et antal langsgående riller 117, som er dannet i dens ydre periferi, for at lederne kan passere. Som vist i 10 figur 6 optager rillerne ledere 118, der er ført inde i en rørformet skærm 119. Selv om hver rille kan optage et par ledere inde i en skærm, er kun en skærm med ledere inden i vist i figur 6. Formålet med skærmen 119 er at minimere interferenser mellem lederne placeret i hosliggende riller. Skærmen kan passende være fremstillet af 15 ferromagnetisk materiale, såsom mumetal. Foruden rillerne 117 har den indre kerne en central langsgående boring 120, som anvendes til at føre en strømforsyningsledning og eventuelt ledere, der er forbundet med andre loggeapparater ophængt i induktionsloggesonden ifølge den foreliggende opfindelse. Rillerne 117 og den centrale 20 boring 120 er i væskeforbindelse med det ringformede rum 110 gennem ikke viste radiale huller og er derfor fyldt med olie ved det samme tryk som i det ringformede rum 110. En passende metode til fremstilling af den indre kerne er ekstrudering gennem en matrice med passende udformning.The inner core 116 has a plurality of longitudinal grooves 117 formed in its outer periphery for the conductors to pass. As shown in Figure 6, the grooves receive conductors 118 inserted inside a tubular screen 119. Although each groove can accommodate a pair of conductors within a screen, only one screen with conductors is shown in Figure 6. The purpose of screen 119 is to minimize interferences between the conductors located in adjacent grooves. The screen may conveniently be made of ferromagnetic material such as mum metal. In addition to the grooves 117, the inner core has a central longitudinal bore 120 which is used to conduct a power supply line and optionally conductors connected to other logging devices suspended in the induction log probe of the present invention. The grooves 117 and central 20 bore 120 are in fluid communication with the annular space 110 through radial holes not shown and are therefore filled with oil at the same pressure as in the annular space 110. An appropriate method for preparing the inner core is extrusion through a die of suitable design.

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Spolerne kan være i form af de samme spoleenheder som beskrevet under henvisning til figur 2. Modtagespolen og den tilhørende kompensationspole kan være anbragt på den samme isolerende muffe af keramik som vist for spolerne 101 og 101', idet den respektive muffe 30 er vist ved 122, eller de kan være anbragt på separate isolerende muffer som vist ved spolerne 102, 102'. Radiale huller er dannet gennem den ydre muffe 115 af understøtningen for at føre ledere 123, der er forbundet med modtage- og kompensationsspolerne, medens en anden leder 124 forbinder spolerne i hvert par med hinanden.The coils may be in the form of the same coil units as described with reference to Figure 2. The receiving coil and the corresponding compensation coil may be disposed on the same ceramic insulating sleeve as shown for coils 101 and 101 ', the respective sleeve 30 being shown at 122. or they may be mounted on separate insulating sleeves as shown by coils 102, 102 '. Radial holes are formed through the outer sleeve 115 of the support to guide conductors 123 connected to the receiving and compensation coils, while a second conductor 124 connects the coils in each pair.

3535

Udfyldningselementer 125, f.eks. af epoxy, er anbragt i det ringformede rum 110 mellem spolerne for at reducere mængden af olie, som skal sættes under tryk af kompensationsorganet 111, og dermed længden af dette organ.Fillers 125, e.g. of epoxy, is arranged in annular space 110 between the coils to reduce the amount of oil to be pressurized by the compensating member 111, and thus the length of that member.

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1414

Den elektroniske patron, som er nødvendig for drift af senderen, er vist skematisk ved 130 i nærheden af den nederste ende af sonden med en trykskillevæg 131 anbragt mellem kompensationsorganet 111 og patronen 130. Den elektroniske patron 132, som er forbundet med 5 modtagespolerne, er anbragt i nærheden af den øverste ende af sonden ligeledes med en tryksski 11evæg 133 mellem patronen 132 og spolesektionen af sonden. Figur 5 viser også en udførelsesform for den øverste endedel og den nederste endedel af spolesektionen af sonden.The electronic cartridge required for operation of the transmitter is shown schematically at 130 near the lower end of the probe with a pressure partition 131 disposed between the compensating means 111 and the cartridge 130. The electronic cartridge 132 associated with the 5 coils is disposed near the upper end of the probe likewise with a pressure ski wall 133 between the cartridge 132 and the coil section of the probe. Figure 5 also shows an embodiment of the upper end portion and the lower end portion of the coil section of the probe.

I den nederste endedel er to halvringe 135, 136 spændt over enden af 10 den indre kerne, som har en periferisk rille 137 for indgreb med en indre krave 138 af halvringene. Halvringene ligger an mod enden af kobbermuffen og er fastgjort til hinanden ved hjælp af ikke viste bolte, så at de danner en muffe, der er drejelig omkring enden af understøtningskernen. En muffe 140 er ført ind over halvringene og 15 fastholdt imod drejning i forhold til understøtningskernen 116 ved hjælp af en kile 141, som indgriber i kilenoter dannet i understøtningen og muffen 140. Muffen 140 har en del 142 med reduceret ydre diameter, over hvilken den ydre muffe 108 passer. Huset 145 for kompensationsorganet er forbundet med muffen 140 ved hjælp af en 20 møtrik 148, der er anbragt mellem muffen 140 og endedelen af huset 145 og i gevindforbindelse med dette, idet møtrikken 148 er fastgjort mod aksi al forskydning i forhold til muffen 140 ved hjælp af et låseorgan 149. Ved at dreje møtrikken ved hjælp af en speciel skruenøgle, forskydes huset aksialt i forhold til muffen 140 og 25 dermed i forhold til understøtningen for spolerne. Endvidere er rillerne 117 ved deres ender forbundet med skrå passager 121, som fører ind i den centrale boring 120.In the lower end portion, two half rings 135, 136 are tensioned over the end of the inner core which has a peripheral groove 137 for engagement with an inner collar 138 of the half rings. The half rings abut the end of the copper sleeve and are secured to each other by means of bolts not shown, so as to form a sleeve pivotable about the end of the support core. A sleeve 140 is inserted over the half-rings and retained against rotation relative to the support core 116 by a wedge 141 which engages in wedges formed in the support and sleeve 140. The sleeve 140 has a portion 142 of reduced outer diameter over which it outer sleeve 108 fits. The compensation member housing 145 is connected to the sleeve 140 by means of a nut 148 disposed between the sleeve 140 and the end portion of the housing 145 and threaded therewith, the nut 148 being secured against axial displacement relative to the sleeve 140 by of a locking means 149. By turning the nut by means of a special wrench, the housing is axially displaced relative to the sleeve 140 and 25 relative to the support of the coils. Further, at their ends, the grooves 117 are connected to inclined passageways 121 which lead into the central bore 120.

Arrangementet ved den øverste ende af spolesektionen indbefatter en 30 muffe 160, der har gevind 161, som indgriber med gevind dannet på kernen 116 i understøtningen i nærheden af dens ende. Muffen har en del 163 med reduceret ydre diameter, over hvilken den ydre muffe 108 passer. Muffen 160 er forbundet med huset 165 for trykskillevæggen 133 ved hjælp af en møtrik 166 svarende til møtrikken 148 i gevind-35 indgreb med muffen 160 og fastholdes imod aksial forskydning i forhold til huset 165.The arrangement at the upper end of the coil section includes a sleeve 160 having threads 161 which engage threads formed on the core 116 of the support near its end. The sleeve has a reduced outer diameter portion 163 over which the outer sleeve 108 fits. The sleeve 160 is connected to the housing 165 for the pressure partition wall 133 by means of a nut 166 corresponding to the nut 148 in threaded engagement with the sleeve 160 and is retained against axial displacement relative to the housing 165.

Selve trykski 11 evæggen, der skematisk er vist ved 170, er en sædvanlig udstyrsdel i borehulsloggesonder og har aksi alt orienteredeThe pressure ski 11 egg, schematically shown at 170, is a conventional equipment part in borehole log probes and has axially all oriented

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15 passager (ikke vist), som optager trykmodstandsdygtige gennemføringer, til hvilke ledere er forbundet på begge sider. Et mellemliggende rørformet organ 171 er anbragt mellem skillevæggen 170 på den ene side og muffen 160 og enden 172 af spoleunderstøtningen på 5 den anden side. Enden 172 af understøtningskernen 116 har en reduceret ydre diameter og er i indgreb i en ringformet udsparing i det mellemliggende rørformede organ 171. En skrueformet trykfjeder 173 er anbragt mellem det mellemliggende organ 171 og enden af understøtningen 172 for at udøve et fjedrende tryk på skillevæggen.15 passages (not shown) which receive pressure resistant bushings to which conductors are connected on both sides. An intermediate tubular member 171 is disposed between the partition wall 170 on one side and the sleeve 160 and the end 172 of the coil support on the other side. The end 172 of the support core 116 has a reduced outer diameter and engages in an annular recess in the intermediate tubular member 171. A helical compression spring 173 is disposed between the intermediate member 171 and the end of the support 172 to exert a resilient pressure on the partition.

10 Aksialt orienterede passager 175, 176 er dannet henholdsvis i det mellemliggende organ 171 og muffen 160 for lederne, der er forbundet med spolerne. Passagerne 176 står i forbindelse med de respektive riller 117 i understøtningen over en del 178, der er fastgjort til understøtningen og har et respektivt antal radiale slidser for 15 ledernes passage.Axially oriented passages 175, 176 are formed, respectively, in the intermediate member 171 and the sleeve 160 of the conductors connected to the coils. The passageways 176 are connected to the respective grooves 117 in the support over a portion 178 which is attached to the support and has a respective number of radial slots for the passage of the conductors.

20 25 30 3520 25 30 35

Claims

An induction log probe adapted for displacement in a borehole (12) for examining the formations (11) through which the borehole 5 comprises, at least one transmitter solenoid coil (31; 85) for generating an electromagnetic field which induces eddy currents in the formation. at least one receiving solenoid coil (32; 86) located at axial distance 10 from the transmitting coil to produce, in dependence on the field induced by these eddy currents, a signal indicative of the conductivity of the formation and an elongated support (30; 89) for mounting the coils 15 (31,32; 85,86) in coaxial and spaced position, characterized in that the electromagnetic field is substantially free of dielectric effects and that the support (30; 89) is made of electrically conductive material and in the vicinity 20 of the coils have at least one substantially continuous and axisymmetric outer surface to favor the passage of vertebrae drums around the surface.

Probe according to claim 1, characterized in that the substantially continuous and axially symmetric outer surface extends past the end of the respective coil in the longitudinal direction by at least approx. one diameter of the coil on both sides of the coil.

Probe according to claim 1, characterized in that the support comprises an outer sleeve (115) of a first high conductivity material and an inner core (116) of a second material having a higher mechanical strength than the first material. said inner core having an outer diameter substantially equal to the inner diameter of the outer sleeve. 35

Probe according to claim 3, characterized in that the outer sleeve (115) is made of copper or copper alloy and that the inner core (116) is made of stainless steel. DK 164419 B

Probe according to claim 3, characterized in that the inner core (116) has longitudinal grooves (117) formed on its periphery, which grooves (117) together with the inner surface of the outer sleeve form respective passages, so that conductors ( 118) can be passed through the support.

Probe according to claim 5, characterized in that the inner core (116) further defines a central longitudinal bore (120). 10

Probe according to claim 1, characterized in that the operating frequency of the transmitting coil is between approx. 10 kHz and approx. 400 kHz.

Probe according to claim 1 or 7, characterized in that the support has at least one first longitudinal part (35) for mounting the coils in coaxial and spaced position and other longitudinal parts (33) on both sides of the first part. wherein at least the first portion (35) has a substantially continuous outer surface to favor the passage of vortex -20 flows circularly around the surface and the second portions (33) are subjected to the pressure of the borehole fluid.

Probe according to claim 8, characterized in that the second parts (33) of the support have a larger outer diameter than the first part.

Probe according to claim 9, characterized in that the first (35) and the second parts (33) of the support are connected by transverse parts (37) located at a distance from the end of the adjacent coil, as in the smallest is equal to the diameter of the coil.

Probe according to claim 10, characterized in that the second parts (33) of the support have a larger internal diameter than the first parts.

A probe according to claim 8, characterized in that the support is made of copper or copper alloy. DK 164419 B

Probe according to claim 1 or 7, characterized in that the elongated support (89) is arranged for connection to a drill string.

Probe according to claim 13, characterized in that during the support, parts with reduced outer diameter have to form cavities (87) in which the coils (85,86) are arranged.

Probe according to claim 13, characterized in that the coils 10 (85,86) are embedded in rubber-like material.

Probe according to claim 14 or 15, characterized in that said parts have a surface layer (92) of a metal with a higher conductivity than the support. 15

Probe according to claim 16, characterized in that the support (89) is made of stainless steel and said layer (92) is made of copper. 20 25 '30 35