USRE23621E - Sleeve supported electrode fob - Google Patents

Description

Feb. 24, 1953 A. B. HILDEBRANDT 23,521

SLEEVE SUPPORTED ELECTRODE FOR WELL LOGGING Original Filed Sept. 21, 1949 5 Sheets-Sheet 1 F I C, i

Glexarzder 5. Hildebrarldi Jnventor 'Clbbori'zes Feb. 24, 1953 A. B. HILDEBRANDT 23,521

' SLEEVE SUPPORTED ELECTRODE FOR WELL LOGGING 5 Sheets-Sheet 2 Original Filed Sept. 21, 1949 Cllexarider b. HildebrandtCSrzvenbor A. B. HILDEBRANDT SLEEVE SUPPORTED ELECTRODE FOR WELL LOGGING I Feb. 24, 1953 s Sheets-Shet 5 Original Filed Sept. 21, 1949 ClZea cancler b. Hzlldebrandt {Inventor 238w- Clbbol neg I Feb. 24, 1953 A. B. HILDEBRANDT Re. 23,621

SLEEVE SUPPORTED ELECTRODE FOR WELL LOGGING Original Filed Sept. 21-, 1949 SSheets-Sheet 4 6i 52 52 s4 s5 50 FLQ-JO G Lcxarzder 6b- HL Ldcbrandt -{n.ver1bor $5 5 111 (2 Cbborneg Feb. 24, 1953 A. B. HILDEBRANDT Re. 23,621

sLEEvE SUPPORTED ELECTRODE FOR WELL LOGGING 5 Sheets-Sheet 5 Original Filed Sept. 21, 1949 Cltb orneg bg w Rama-m. :4; 953 a Re. 23,621 UNITED STATES; PATENT OFFICE sum surroa'ran anac'raona roa WELL LoGGmo Alexander B. Hildebrandt, Tulsa, Okla, alsignor to Standard Oil Development Company. a corporation of Delaware Original No. 2,552,428, dated May 8, 1951, Serial No. 117,058, September 21, 1949. Application for reissue September 26, 1952, Serial No.

2; Claims. (01. 175-182) Hatter enclosed in heavy when l: 1 appears in the ii -mun patent but forms no part of unrel-lie specification: matter printed in italics indicates the additions made by reissue.

This invention. is concerned with apparatus for the electrical logging of bore-holes in the' earth. such as oil wells; and more particularly with an improved type of electrode for use in electrical 1088 8 .to determine the nature of strataencountered by a bore hole.

. Methods and apparatus for the logging of bore holes by measuring impedance self potentials, resistance or-some other electrical property of the' various strata through whichthe bore hole well known. Some of these are de- -,-scribed'for example in the Schlumberger patents such as. 1,819,923; 1,894,328; 1,913,293 and 2,165,013. 'These methods involve the lowering of one or more electrodes into a bore hole filled with.water or with aqueous drilling mud, sending "currents into the formation and observing the electrical phenomena produced.

One of the more common procedures is to mak electrical measurements indicative ofthe diiference in apparent resistivity of the various types of rocks encountered as the. electrodes are raised up throughthe bore hole. A particular dimculty arising in suclimeasurements, however, is that the resistivity of the mud or water in .the bore hole enters into the measurement and in some .lnstances causes anomalous or misleading results, as will beexplained more fully hereinafter.

It is one object of the present invention to provide an electrode assembly for electrical well loggin which will eliminate or minimize the sources of error in conventional methods of electric logging of bore holes. Another object of the invention is to provide well logging electrodes which will besubstantialiy shielded electrically -from the mud column in a well and thus substantially eliminate erroneous well log ing readings. Other and further objects and advantages of this invention will be apparent from the ensuing description taken in conjunction with the accompanying drawing in which Fig. 1 is a vertical cross sectional view of a section of a bore hole together with the conventional apparatus placed therein and on the earths surface for making an electric log of the bore hole and illustrating particularly the disadvantage of theconventional well loggin Procedure.

2 show the assembly in its operating or open position for traveling up the bore hole and making an electric log thereof;

Fig. 6 is a cross sectional view along line A-li' of Fig. 2;

Fig. '7 is a detailed view of the lower end of the mechanism of Fig. 3, showing particularly the sleeve fastening means;

Fig. 8 is a cross, sectional view taken along line 13-13 of Fig. 4;

Fig. 9 is a crow sectional view taken along lineC-CofI ig.8;and,

Fig. 10 is a view of a typical record obtained in a modification of the device of this invention to enable the determination of dip and strike of strata encountered.

Referring to the drawing in detail and in particular to Fig. '1 thereof, reference numeral I denotesa bore hole filled with drilling mud 2 and into which is suspended a cable 3 carrying a plurality of conductors l, I, 6,,each having an electrode I, I, 9. The cable is supported over the bore hole on a pulley Iii and is wound onto a reel II. By suitable collector rings l2, electrical contact is made between conductors ta, 5a, 8a and the corresponding conductors l, 5 and 8 in cable 2.- Conductor la is connected to one terminal of potential source I, the other end of which is connected to ground. Surface casing ll may suitably serve as the ground electrode,

Conductors Ia and 6a connect into a recording potentiometer or similar recording device it provided with means for feeding a roll of paper past a recording stylus or the like in proportion to the length of cable being wound on reel ll. Means for measuring the length of cable in the bore hole and the tension on the cable, and for Figs. 2 and 3 are vertical cross sectional views .of a bore hole' with the electrode assembly of the present invention suspended therein, the assembly being depicted in cross section in its initial or closed condition for lowering into the bore hole, Fig. 3 representing a lower continuation of Fig. 2:

Figs! and'ii co nd to Figs. 2 and 3 and relating the recording paper movement to the movement of the cable, are not depicted here,

as these devices are conventional and their description is not pertinent to the discussion of the present invention.

The theory of formation resistivity measurements is fully explained in the aforementioned Schlumberger patent, 1,819,923 and is briefly as follows: Current enters the ground through electrode I and flows to the ground electrode, i. e. the surface casing it. The flow of electrical current is represented by lines 0. Now if the distances from electrode 1 to electrode 8 and from electrode 1 to electrode 9 are relatively large with respect to the diameter of the bore hole,

say 10 to 20 times saiddiameter, there will be created a difference in potential between electrode I and I, which'can be measured with repointed out by 'Schlumberger, that the current flowing from'electrode 1 produces by ohmic effect equipotential surfaces which are essentially spherical surfaces centered on electrode 1. It

' is assumed that since the cross sectional area of the bore hole is small compared to the distances fromelectrode 1 to electrodes '8 and 9 there is no appreciable deformation of the spheres by the column of water or drilling mud in the bore hole. so that the measure of potential between electrodes 3 and 9 is eouivalent to a measure of the difference in potential in the adjacent formation at equivalent distances from electrode 1.

The res stivity measured b the above method is approximately the real resistivity only if it is assumed that the formations in the vicinity of the electrodes 1, 3 and 9 are homo eneous and .that the effect of the co u n of mud or water is negligible. Fuch is not the case, however. and in act al pract ce what is measured is not t e real resistivitv but what is called ap arent resistivitv. influenced b b th the resist vity of the drilling mud and the different types of rocks encountered. Nevertheless, rock lavers having differences in resistivltv are detected with reasonable accuracy by means of the usual apparent resistivity measurements. However, when it is desired to obtain indication between different layers with a high de ree of definition. especially when the lavers are relatively thin. the resistivity of the drilling mud or water relative to the re sistivity of the formation levers enters into the picture. For exam le, if a thin bed I! of high resistivity is encountered, its presence may not show up on the record, because of the short circuiting of current through the drilling mud from electrode 9 to electrode 9, giving a resistivity reading which will be lower than would be obtained if the resistivity through layer l9 were the only factor.

Reference will now be made to the remaining figures of the drawing, showing the features of the present invention. Referring particularly to Figs. 2 and 3, a case 2| is suspended by cable 3 in a bore hole I fllled with drilling mud 2. Pivotally attached to the lower end of case 2| are a plurality of arms 25. A centrally disposed elongated rod member 26 is screwed into base 66 in case 2|. Slidably fitted over rod 26 is a rotatable sleeve 21 provided at its lower end with curved pins 29 adapted to engage holes 29 at the lower ends of arms 25 and to release said arms upon rotation of sleeve 21. This is shown in detail in Fig. 6, which is a cross-sectional view along line A-A of Fig. 2. The mechanism for rotating sleeve 21 to release arms 25 is contained in case 2| and will be described in more detail later in the specification.

Attached to the lower end of the arms 25 is a flexible, open, elongated, rubberized sleeve 39 extending for almost the full length of rod 26 as shown in Fig. 3. Sleeve 39 is yieldably fastened at its lower end to rod 26 by fastening means 3|. Embedded in the wall of sleeve 39 are a plurality of sets of electrodes, 33, 36, an of the electrodes 33 being electrically connected and all ofthe electrodes 36 being electrically connected. Insulated leads 31 and 3B embedded in sleeve 39 con- Depending upon the particular use that is to be made of the device, only a single set oi electrodes such as 33 might be utilized or both sets 33 and 36 might be employed. In the preferred embodiment of the invention both sets are employed and in addition rod 26 is an insulated rod on the lower end of which is fitted an additional electrode which is connected electrically to surface equipment by means of lead 6| running up through rod 26, case 2 I and cable 3. Thus electrodes 69, 33 and 36 correspond in their function to electrodes I, 8 and 9 of Fig. l.

The apparatus of the invention is depicted in its non-logging position in' Figs. 2 and 3 and in this position is adapted to be lowered into the well to be logged. When the desired depth has been reached the tripping mechanism contained within case 2| rotates sleeve 21, releasing pins 28 from engagement with holes 23, thereby permitting arms 25 to move outwardly because of the tension exerted by springs 23, which are attached to the ends of arms 25 and to bracket 58. Since the arms 25 move independently of each other, each will move outwardly until it touches the walls of the bore hole, causing the upper rim of flexible sleeve 39 to conform to the cross section of the bore hole walls In other words, substantially the entire upper or leading edge of the sleeve will be brought into contact with the periphery of the bore hole. As the assembly moves up the bore hole, drilling mud 2 will enter sleeve 39 and cause [it] the sleeve to contact the bore hole wall, thus bringing electrodes 33 and 36 into contact with the wall of the bore hole. As drilling mud reaches the bottom of the sleeve 39, the differential pressure resulting from upward motion of the sleeve will cause the lower end of the sleeve to pull free from holding means 3|, thus allowing substantially all ofthe drilling mud to be bypassed through sleeve 39 at the device moves upwardly through the bore hole. Potential measurements are made in the conventional manner with electrodes 33 and 36, using a current introduced by electrode 69.

Details of the holding means 3| and the manner in which it functions are illustrated in Fig. '7. Holding means 3| comprises a semi-rigid material such as heavy rubber or rubber-impregnated fabric which is tightly bound to rod 26 by means of wire or similar material 32. The wall thickness of means 3| is considerably [thicker] greater at its uppermost portion in order to form a rim 3|a which will hold the lower end of the sleeve 39 against rod 26. The wall of holding means 3| is sufilciently flexible so that as suiii cient mud pressure is built up inside the sleeve the lower end of the sleeve will be permitted to slide past rim 3 a.

To ensure that the upper or leading edge of open flexible sleeve 39 will follow the contour of bore hole I as the device is raised up through the bore hole, arms 25 are provided with shorter arms 26 which are pivotall fastened to arms 25 by means of pins 22. The short arms 26 are of flat cross-section as illustrated in Fig. 9, which is a cross-section taken along line 0-0 of Fig. 8. The ends of the short arms 26 are fastened to sleeve 39 at intermediate points between the ends similar material to ensure maximum flexibility in following the contour of the hole.

The mechanism for releasing arms 2! is also depicted in Figs. 2 and 4. Rotatable sleeve 21- is supported by bearings 42 and 43 and has attached to its upper end a gear 45 which meshes with a spur gear 46 attached to rotatable shaft I, supported on bearings 49 and II. A lever 52 extending at right angles to the axis of shaft 41 is secured to the shaft just above base 44. Spring ll, wound about shaft 41, has its upper end attached to support member 59 and its lower end secured to lever 52, so that spring 5| exerts a bias on shaft 41 in the clockwise direction, viewing shaft 41 from its lower end. A Jointed bar ii is provided, being constructed with arms BI and 84 secured together by a pin -58. Arm ll is secured to lever arm 52 of shaft II by pin 58 and arm 54 is secured to a portion of case II by pin 51.

The means for actuating the releasing mechanism consists of an armature 62 having a vertical axis and slidably arranged in a coil of wire 83. An electric current can be sent through coil 83 through leads 64 and 65 which run to the surface equipment through cable 3. Passage of such a current through coil 63 will cause armature 62 to be drawn upwardly so that it strikes the center of bar 60. The resulting movement of pivot 65 of jointed bar 60 above the line joining pivots 56 and 51 causes the bar to buckle because of the bias exerted by spring 5|, thus causing shaft 41 to rotate through an angle of about 90. Gear 48 likewise rotates through the same angle and causes gear 45 and sleeve 21 to rotate in the opposite direction through a sufficient angle to disengage pins 28 and holes I! in the lower ends of arms 25, the gear ratio; between gears 45 and 46 being so selected that the pins II will be pulled clear of arms 25.

The advantages of the present invention will be readily apparent to those skilled in the art of electric logging of wells. Since the electrodes 33 and N are in substantial contact with the walls of the bore hole at all times and are insulated from the main column of mud, the resistivity readings obtained will not be, seriously affected by variations in hole size nor by mud in the hole. It is anticipated that sleeve 30 will not completely prevent mud from passing between the sleeve and the walls of the bore but nevertheless the amount of mud remaining in this vicinity will be so small and of such narrow cross section that its resistivity will be high, compared to that of the adjacent formation, so that the mud resistivity will be a negligible factor in the measurement. Since the sleeve can accommodate a large volume of drilling mud, the device will meet but little resistance on its way up the bore hole, thus permitting a rapid log of the bore hole to be made.

It is obvious that modification of the assembly described can be made without departing from the scope and spirit of the invention. For example by using three or four electrodes in each of the groups I3 and 34 and spacing the electrodes in each group uniformly in a horizontal plane about the circumference of sleeve 30 and providing separate electrical leads 31 and 38 from each individual electrode to surface instruments it is possible to obtain measurements that will be indicative of the dip and strike of strata encountered. Assume that four electrodes are used in each group and that they are designated as Ila, "b, He. 33d, a, etc., 33a and 34a as shown in Fig. 9, 8| being the trace of the potentia] measured from electrodes 33a and 34a,

82 for electrodes 33b and 34b, and so on. A fifth trace, 85 may be made to show the orientation of one of the electrodes, say 33a with respect to North on the compass by providing wthin case 2i in the bore hole a suitable orienting apparatus, such as that described and claimed in the Boucher patent, 2,332,777, and tracing the impulses on moving paper 80 simultaneously with the other traces Ola, etc. A sixth trace 86 may designate the depth of the instrument at any time on the record by means well known in the art, or the depth may be recorded manually on the chart from readings of suitable depth measuring instruments.

Assume further, for the purpose of simplifying the explanation, that measurements on trace 85 indicate, by the method outlined in the aforementioned Boucher patent, that electrodes 33a and 34a are oriented North; then electrodes 33b and 34b will lie East, 330 and 340 South, and 33d and 34d West. With paper 80 moving in the direction indicated by the arrow, peaks 8! on traces BI, 82, etc. show that a stratum of different resistivity was encountered first by North electrodes 33a and 34a, then by East and West electrodes 33b, 34b, 33d, and 34d and finally by South electrodes 33c and 340. This indicates that this particular stratum dips in a northerly direction.

It is not intended that the invention be restricted to the specific embodiments described, which have been presented merely by way of example. The invention is to be limited only by the following claims.

What is claimed is:

[1. An electrode assembly for the electric logging of bore holes comprising an elongated flexible insulat ng sleeve adapted to contact substantially the entire periphery of the bore hole, at least one electrode carried by said sleeve in a section intermediate its ends, said electrode being insulated from the interior of ,said sleeve but electrically accessible from the exterior of said sleeve, and means for supporting said sleeve in said bore hole and for pressing its upper periphery into contact with the periphery of the bore hole] [2. An electrode assembly according to claim 1 in which an additional electrode is supported adjacent the lower end of said sleeve on insulated supporting means disposed within said sleeve] 3. An electrode assembly for the electric logging or bore holes comprising a supporting body adapted to besuspended within said bore hole on a cable, a plurality of arms pivotally attached to the lower portion of said body, each arm being adapted for independent movement outwardly from said body, means urging each of said arms outwardly from said body, an elongated flexible insulating sleeve attached at its upper end to the lower extremities of said arms, and at least one electrode carried by said sleeve in a section intermediate its. ends, said electrode being insulated fromt he interior of said sleeve but electrically accessible from the exterior of said sleeve.

4. Electrode assembly according to claim 3 in oi the flexible sleeve.

I which a plurality ot electrically connected electrodes are carried by said sleeve about a horiaontal periphery thereof.

5. Electrode assembly according to claim 3 in which said sleeve carries at least two groups of electrodes, the electrodes in each group being electrically connected to each other and dispos about a horizontal periphery of said sleeve, the electrode groups-being placed in vertical relation to each other in a section intermediate the ends 8. Electrode assembly according to which an additional electrode is supported adjacent the lower end of said sleeve on an insulated supporting means disposed within said sleeve and attached to said supporting body.

7. An electrode assembly for the electric loggins oi bore holes comprising a supporting body adapted to be suspended within said bore hole on a cable, a plurality of arms pivotally attached claim 3 in to the lower portion of said body, spring means independently urging each 01' said arms outward- 1y from said body, releasable locking means for holding said arms inwardly in opposition to said spring means, electrically operable I releasing means for said locking means, an elongated-flexible insulating sleeve attached at its upper edge to the lower extremities of said arms. an elongated rod attached at its upper end to said supsaid electrode being insulated from the interior l a of said sleeve but electrically accessible from the exterior of said sleeve. I

8. Electrode assembly according to claim 7 in which said elongated rod is an insulated rod and in which an additional electrode is supported by the lower end of said insulated rod.

9. An electrode assembly for the electric logplay of bore holes comprising an open elongated flexible insulating sleeve adapted to contact substantially the entire periphery of the bore hole, at least one electrode carried by said sleeve in a section intermediate its ends, said electrode being insulated from the interior of said sleeve but electrically accessible from the exterior of said sleeve, means for supporting said sleeve in said bore hole and means {or pressing substantially the entire upper edge of said sleeve into contact with the periphery ofthe bore hole, whereby substantially all of the fluid in the bore hole in the vicinity of,

the sleeve will pass through said sleeve as said sleeve is raised through the bore hole by said supporting means.

10. An electrode assembly according to claim 9,

including insulated supporting means disposed within said sleeve and an additional electrode supported ada'aeent the lower end of said sleeve on said insulated supporting means.

' ALEXANDER. B. HILDEBRANDT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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