US2298216A - Weight indicator for rotary drilling - Google Patents

Description

0d. 1942- E H. LAMBERGER EIAL 2,298,216

WEIGHT INDICATOR FOR ROTARY DRILLING Filed Sept. 26, 1939 3 Sheets-Sheet 1 fl I wrmsssss;

INVENTORS ATTORNEY 1942- E. H. LAMBERGER ETAL 2,298,216

WEIGHT INDICATOR FOR ROTARY DRILLING Filed Sept. 26, 1939 3 Sheets-Sheet 2 Fly. 2.

Edward II. Zambe Bernard F L WITNESSES:

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glmk Juli ATTORNEY 1942- E. H. LAMBERGER ETAL ,298,216

WEIGHT INDICATOR FOR ROTARY DRILLING 12 13 32 31a mDj Total Load on Load Bottom 4.0. Supply WITNESSES: INVENTORS g l I 1 Edward HLambez-ga' 8 I W Bernarz l F'Lanyer.

ATTORNEY Patented Oct. 6, 1942 WEIGHT INDICATOR FOR ROTARY DRILLING Edward H. Lamberger, Wilkinsburg, and Bernard F. Langer, Pittsburgh, Pa., assignors to Westinghouse Electric 4; Manufacturing Company, East Pittsburgh, I'a., a corporation of Pennsyl- Vania Application September 26, 1939, Serial No. 296,596

6 Claims. (01. 265-1) Our invention relates to drilling equipment for use in oil or gas wells or the like, and is more specifically directed to weight indicating means for determining the total weight of the suspended drilling equipment as the string of pipe and the bit. When the bit is set on the bottom of the well the unsuspended weight is usually referred to as the weight on the bottom. Our invention is not confined to drilling equipment but may be used generally to indicate weight of heavy apparatus.

The present application is related to our previously filed copending application Serial No. 268,500, entitled Oil well strain gauge, filed April 18, 1939, and is an improvement of the copending application of B. F. Langer which has matured into Patent 2,275,532 and S. L. Burgwin, Serial No. 258,510 entitled Strain gauges illed February 25, 1939, which has matured into Patent 2,231,702 and assigned to the present assignee.

When drilling a well with rotary drilling equipment, it is important to know: (1) the weight on the bit, that is, the unsuspended weight, (2) the total weight on the drill string, (3) the suspended weight of the drill string, and (4) the pull being exerted'when pulling on a stuck drill stem or stuck casing. It is particularly important to know the weight on the bit because that weight affects the (a) rate of penetration, (b) duration of bit sharpness, (c) straightness of hole, (d) life of the drill stem, (e) life of drilling bit, and (f) wobble of drill stem against side of hole. It is apparent that improper weight on the bit can easily increase the cost of drilling, as insuflicient weight means reduced rate of penetration, and excessive weight means extra expense and loss of time due to shortened life of equipment, premature dulling of bit, and possibly fishing for broken tools.

The present commonly used device for indicating these loads is a shunt dynamometer placed on the tail rope of the hoisting cable. It is actuated by the pull on the cable attempting to straighten a kink in the cable which is made when mounting the gauge on the tail rope. The accuracy of the device is affected by the friction of the sheaves in the blocks, and by the bending of the cables over the sheaves. Also, as the number of lines between blocks is changed, the proper dial must be placed on the gauge in order that it may indicate the total suspended load.

The weight on the bit is determined by observing the weight of the suspended string when of! bottom, then setting the tool on bottom until the indicated weight has decreased by that amount desired as the load on the bit. This reduction'iii weight is usually referred to as the weight on bottom.

Our invention covers a new arrangement of one or more magnetic strain gauges which may be placed within an elastic element which is mounted in the string of suspended equipment above the ground surface. It consists essentially of a single, a compound, or a multiplicity of strain gauges in conjuction with a reference rod mounted on the centerline of the elastic element. The arrangement is such that the elongation of a definite portion of the elastic element is transmitted mechanically to the strain gauge (or gauges). By proper electrical circuits and instruments, the total load and the reduction in load as the tool is set on bottom are indicated and recorded. 7

The device must have a very high accuracy when measuring the weight on bottom. For example, suppose the total weight of a suspended drill string is 200,000 pounds. It is desired to maintain weight on bottom of 20,000 pounds within limits of +500 pounds. Such a variation is +25% of the weight on bottom, but only +25% of the total weight.

Tests have shown that such accuracy is not possible with an instrument mounted in the tail rope.

In order to avoid (1) the inaccuracy of the measurement in the tail rope, (2) the use of a bulky elastic element in series with the hook, and (3) the need for very high precision in the voltage regulation and recording instruments, we propose, in accordance with our invention, the use of a compound electric strain gauge mounted in the shank of the lifting hook.

An object of our invention is to provide a compound electric strain gauge which will accurately determine the total weight of the string of drilling tools when suspended freely from the hook, and which will also indicate with accuracy the weight on the bottom, that is, the total weight on the bit when the bit is in contact with the bottom of the well.

Another object of our invention is to provide a new type of compound magnetic strain gauge and to dispose it in such manner in the string of drilling tools so as to take up a minimum amount of space and cause minimum added length to the string and at the same time to be effective to indicate weights with precision.

Other objects and advantages will become more apparent from a study of the following specificaof the hook incorporated in Fig. 1 showing the disposition of a compound magnetic strain gauge within the shank of the hook;

Fig. 3 is an enlarged sectional view of the compound magnetic strain gauge incorporated in Fig.

2 takenalong line III-III' of Fig. 4.

Fig. 4 is a partial-side view of the strain gauge taken along line IV-IV of Fig. 3; and

Fig. 5 is a schematic showing of a pair of electrical metering circuits, each of which includes an impedance bridge which includes a pair of coils of a single magnetic strain gauge; and

Fig. 6 is a front view in cross-section of a modification of our invention.

Referring more particularly to Figure 1, the numeral denotes an oil well drilling derrick, at the top of which is supporteda crown block 2 which carries a plural-wound cable 3, which cable supports-a traveling block 4. The traveling block 4 supports a block bail 5 which in turn supports a hook bail 6, the latter finally yieldingly supporting a hook I through intermediary elements hereinafter described. Supported on hook I is a swivel and a string of pipe forming the drill string 3 of any conventional type. One end of cable 3 is wound about a drum 9 of any conventional type. It is thus seen that by applying power to the drum, the hook is raised, and by applying braking pressure to the drum, the

hook is held at any desired height. .An electrical cable III, which supplies electrical energy to the compound magnetic strain gauge mounted in shank H of the hook (which will appear more clearly in Fig. 2), is shown supported halfway up the derrick in order to allow full travel of the hook, finally leading to a pair of meters I2 and I3 located near the ground surface.

\ Fig. 2 shows the hook in greater detail. Pivoted on the hook bail 6 is a support member H which has screw-threaded on the top thereof a sleeve l5. Surrounding shank H is a helical spring l6 which supports a pair of race plates II which in turn support a nut l8, which nut is screw-threadedly connected to the upper end of hook shank II. The hook shank II has drilled therein from the top or upper end thereof a cavity which is suitably shaped so as to accommodate a compound magnetic strain gauge IS. The details of the compound magnetic strain gauge are more clearly shown in Fig. 3, which is an enlarged sectional view thereof.

Referring more particularly to Fig. 3, the compound magnetic strain gauge I 3 comprises essentially a pair of electromagnets and 2|, which are separated by a partition member 22 made of brass or other suitable non-magnetic material for magnetically separating the two electromagnets 23 and 2|. Each of the electromagnets 20 and 2| is of the construction described in detail in our copending application previously referred to. Briefly, each of them, such as 20, comprises an armature 23 which is rigidly fastened to. an armature framework 24, which in turn is rigidly secured to a top plate 25 and screw-threaded pin 25a. Threaded to pin 25a is a cap assembly 26 which is rigidly secured to a cylindrical shell 21, which in turn is rigidly secured to a flanged pipe 28 which is threaded at 23- to the shank ll. Thus, in efiect, it will be seen that the two armatures (one from each electromagnet 20 and 2|), such as 23, are rigidly connected through the medium of a number of elements formed substantially as a box to'the point 29. The cylindrical shell 2'! has a hole surrounded by an insulating ring 21a through which cable i0 is led to energize the electromagnets. The electromagnet 20 has cooperating with the armature 23 a core structure 30, upon which is wound a pair of coils 3| and 32. The core structures of both of the electromagnets 20 and 2| are rigidly supported on partition 22 by suitable rivets as illustrated in Fig. 3 by a cross-section taken partly along line lIL-III of Fig. 4 and are secured to a common screwthreaded pin 33 which is integral with a reference rod 34. The bottom of the reference rod 34 is screw-threaded at point 35 to the shank Thus, in-efiect, the core and the coils mounted thereon are secured by meansof a number of intermediary elements to point 35. The hook shank H is made of a suitable elastic metal which will stretch or elongate a desirable amount as a result of the weight of the drilling string of tools supported by the hook,

As the shank stretches as the result of increased weight on the hook, points 29 and 35 in Fig. 3 are pulled farther and farther apart. Hence, armature 23 moves somewhat farther from coil 32a, but moves closer to coil 3 la, thereby changing the effective magnetic path and the impedances of coils 3Ia and 32a. It should be noted that point 29 is selected so as to be located below the threads of the nut I8. This is done because the threads carry the entire load, and- Hence the redistribution of loads due to creep would tend to introduce inaccuracy in the magnetic strain gauge if point 29 were located within the confines of the threaded section; that is, if

point 29 were chosen immediately adjacent the electromagnetic structure of the strain gauge.

The construction of the magnetic strain gauge is such that it can be assembled into the hook shank and all the threaded connections securely tightened without damaging the more delicate parts of the gauge. The flanged pipe 28 is first screwed into the shank with a suitable wrench. The strain gauge itself, consisting of parts 20, 2|, 22, 23, 24, 25, 25a, 30, 3| and 32 is then connected to the rod 34 by means of the screw threaded pin 33, The rod 34 is then passed through the pipe 28 and threaded into the shank at 35. Part 22 moves longitudinally relative to part 25. After this, the cylindrical shell 21 and the cap 26 are easily installed to complete the assembly.

In order to minimize temperature errors, the space surrounding the reference rod 34 and the compound electromagnet is filled with transformer oil to keep the rod and electromagnets at the same temperature as the hook shank. The cylindrical shell 21 is made of the same material as the armature framework 24 and the partition 22 to which the electromagnets are attached. Also the rod 34 is made of the same material as the hook shank ll so that temperature changes will not produce errors.

One of the main difficulties encountered when pound magnetic strain gauge, as described below,

suflicient accuracy can be obtained for both weight on bottom and total load measurements of the drilling string of tools without using extreme accuracy in the regulation of the voltage applied to the gauge. The schematic circuit of the proposed gauge is shown in Fig. 5. It is, in eifect, two independent magnetic strain gauges, one for measuring total load and the other for measuring weight on bottom." The bridge circuit of the total load gauge including coils Ma and 32 and variable inductance coil 38 is adjusted so that balance is obtained atzero total load." The current flowing through the meter at any given load is then proportional to the load and to the applied voltage, and a voltage change of 2% will produce an error of 2% in the load reading, which we can assume is within the required accuracy. The bridge circuit of the "load on bottom" gauge is adjusted so that balance is obtained at zero bit pressure" instead of at zero hook load. The current flowing through the load on bottom" meter is thus proportional to bit pressure and voltage, so that a voltage change of 2% produces an error of only 2% in the pressure reading. If the same gauge were used for both total load and load on bottom then for the weights assumed hereinbefore, a voltage shift of 2% would produce of error in the bit pressure reading, which could not be tolerated.

The compound gauge can be made in various ways. It can take the form of two independent gauges located at different points along the string suspended from the derrick, or it can be made as a single gauge with double windings. If it is not necessary to obtain simultaneous readings of total load and bit pressure, a single gauge can be used with two sets of controls (1. e. immdance bridge metering circuits) and means for switching a single electromagnet back and forth from one set of controls to the other.

In some instances coils 3i and 32 may be connected in series with a variable inductance such as 31 to form a magnetic bridge circuit. However, in order to minimize the introduction of error due to bending of the hook shank, it is preferable to connect diagonally opposite coils of the compound strain gauge in each ofthe bridge circuits; that is, for example, in one bridge circuit the upper left-hand coil 3| of Fig. 3 is connected with the lower right-hand coil 32a, thus, together with the variable inductance coil 31, forming one of the bridge circuits, which bridge circuit is connected to a meter l3 which may be either an indicating, recording or a combined indicating and recording type of electrical meter suitably calibrated to read "load on bottom." if of the direct-current milliammeter type, will also include a rectifier, preferably a bridge type copper oxide rectifier (not shown), inasmuch as the source of supply is an alternating-current source, as shown. Meter l3 may be calibrated to indicate the load on the bottom. Adjustable resistors 49 and 50 are provided so as to make it possible to set the pointer of meter II to zero while the total load is still suspended. Likewise the meter il, in a similar bridge circuit embodying the remaining two coils 32 and 31a Meters l2 and I3,

of the compound electromagnetic structure, is

has been shown as being positioned within the hook shank, it will be apparent that it may likewise be positioned in other parts of the string suspended by the derrick, either above or below the hook shank. For example, it-may be a separate unit which is added between the hook ball 8 and the block ball 5, or which separate unit may be inserted somewhere along the string 3 of the drilling tools. In some instances, it is more desirable to mount it in parts other than the hook, because by so doing a conventional type of hook may be used rather than to make the hook of special construction.

Fig.- 6 illustrates a modification of the strain gauge mounting in which the strain gauge unit is mounted on a structure which is independent of the hook and which can be attached to the lower removable ball of the traveling block, or in fact to any element in the suspended string. Numeral l0 denotes an elastic element which has a hole 4i drilled or bored on the axis thereof and being of suitable dimension to accommodate a magnetic strain gauge unit. Numeral 41 denotes a cap nut connected on one end of the elastic element. This cap nut permits introduction of the strain gauge unit and assembly of yokes l3 and 44 on the element. A second cap nut ll is also shown but this could be integral with the elastic element. Balls 46 and 41 respectively engage the bails of the traveling block and the hock. Qne of these bails must be removable. Numeral 48 represents the removable trunnions of the yoke 44 which is necessary so that ball 41 can be removed so that it may be connected with the hail of the hook. The strain gauge unit, the means for locking the cap nut, and the means for bringing out the leads of the gauge are not indicated but are substantially the same as illustrated in the previous embodiment.

The embodiment shown in Fig. 6 results in a minimum of overall length of the strain gauge unit since yokes 43 and 44 cover the same longitudinal space as that taken up by elastic element 40. Other means for opening bail 41 for engagement with the bail of the hook are of course possible. For example, the lower portion of this bail may be a separate piece with clevis ends secured to the ends of the upper portions or arms of the ball by removable pins. The outstanding advantage of the modification illustrated in Fig. 6 is that the strain gauge is a unit which is separate and independent of the hook or of any other element of the string so that it can be used with any standard equipment in the string, so that a standard type of hook can be used. In the previously described modification, the hook had to be modified to accommodate the strain gauge.

To summarize, we propose an instrument for indicating and recording the total load and the reduction in total load when the bit is set on the bottom of the well (the "weight on bottom") on a rotary well drilling rig. The instrument consists of a compound magnetic strain gauge (or a combination oi gauges) so mounted with the hook shank that the strain in a portion of the shank of the lifting hook is measured. Some of the advantages of our specific strain gauge over other devices which have been used or proposed are:

(1) It avoids the errors due to frictional losses in the hoisting system by making the measurement in the hook instead of the tail rope.

(2) It puts the measuring device in a protected location, and where it is not in the way of the operator.

(6) It avoids the necessity for extreme accuracy in voltage regulation by using two independent bridge type strain gauges, one for "total load and the other for load on bottom.

We are, of course, aware that others particularly after having had the benefit of the teachings of our invention, may devise other devices embodying our invention, and we, therefore, do not wish to be limited to the specific showings made in the drawings and the descriptive disclosure hereinbefore made, but wish to be limited only by the scope of the appended claims.

We claim as our invention:

1. In a drilling apparatus for wells and the like, a hook for supporting a drilling string of tools, said hook having a substantially cylindrical shank portion, said shank portion having an elongated cavity located inside thereof along its axis, a magnetic type strain gauge which includes an electromagnet and an electrical metering circuit electrically connected thereto which provides a zero reading for a fully suspended load, said electromagnet being mounted within said cavity and having its core and its armature rigidly attached to spaced concentric threaded connections on said shank and being adapted for relative motion as the result of separation of said spaced connections due to elongation of said shank due to the load of said drilling string of tools, partition means extending substantially along the axis or said shank portion for rigidly supporting said core, said electrical metering circuit being adjusted to give a reading inversely proportional to the elongation of said shank portion.

2. In a drilling apparatus for wells and the like, a hook for supporting a drilling string of tools,.said hook having a substantially cylindrical shank portion, said shank portion having an elongated cavity located inside thereof along its axis, a magnetic type strain gauge which includes an electrical impedance bridge circuit, an electromagnet having a pair of coils and armature means movable therebetween, said coils forming two legs of said bridge circuit, metering means electrically connected to said bridge circuit which provides a zero reading for the string of tools when fully suspended, said electromagnet being mounted within said cavity and having its core and its armature rigidly attached to spaced threaded, concentric parts of said shank and being adapted for relative motion as the result of separation of said spaced parts due to elongation of said shank due to the load of the drilling string of tools, said electrical metering means thereby being adapted to provide an indication of the weight on bottom of said drillin string of tools.

'3. In a drilling apparatus for wells and the like, a hook for supporting a drilling string of ed between said electromagnets and mechani-v cally supporting the two cores thereof, two impedance bridge circuits, each of which includes one of each of said pair of coils as two of its legs, two impedance means, each forming the other two legs of the respective bridge circuits, said electromagnets being mounted within said cavity and having its cores and armatures rigidly attached to spaced parts of said shank and being adapted for relative motion as the result of separation of said spaced parts due to elongation of said shank due to the load of the drilling, a pair of electrical meters each electrically connected to one of said bridge circuits for measuring different portions or said load depending upon whether said drilling string of tools is supported or unsupported at the bottom thereof.

4. In a drilling apparatus for wells and the like, a hook for supporting a drilling string of tools, said hook having a substantially cylindrical shank portion, said shank portion having an elongated cavity located inside thereof along its axis, a magnetic type strain gauge which includes a pair of electromagnets each comprising a pair of coils on a core and an armature movable between said coils, a non-magnetic partition member located between said electromagnets and mechanically supporting the two cores thereof, said electromagnets being mounted within said cavity and having their cores and armatures rigidly attached to spaced parts of said shank and being adapted for relative motion as the result of separation of said spaced parts due to elongation of said shank due to the load of said drilling string of tools, a pair of metering circuits, each connected to one of the coils of each of said electromagnets and each being adapted to indicate the amount of load on said hook for various positions of said drilling string of tools.

5. In a drilling apparatus for wells and the like, a hook for supporting a drilling string of tools, said hook having a substantially cylindrical shank portion, said shank portion having an elongated cavity located inside thereof along its axis, a magnetic type strain gauge which includes a compound electromagnet structure comprising in effect two separate electromagnets, each of which has a pair of coils on its core structure a and an armature movable therebetween, a partition member located between and mechanically interconnecting the cores of each electromagnet, two impedance bridge circuits, each of which includes one of each of said pair of coils as two of its legs, variable inductance coils, each forming the other two legs of the respective bridge cirsaid load depending upon whether said drilling string of tools is supported or unsupported at the bottom thereof.

6. In a drilling apparatus for Wells and the like, a hook for supporting a drilling string of tools, said hook having a substantially cylindrical shank portion subjected to strain by the weight of said string of tools, said shank portion having an elongated cavity located inside thereof along its axis, a nut which is screw threaded to the top of said shank portion for forming a sealed enclosure, support means for suppoi'thig said. nut thereby imparting strain to threaded por tion due to the weight of said string of tools, a magnetic type strain gauge which includes an electromagnet and an electrical metering circuit electrically connected thereto, said electromagnet being mounted within said cavity and having its core and its armature rigidly attached to spaced concentric, threaded pa s of said shanlz, both of which are below said so "hr-eaded con nection and being adapted to. relative motion as the result of separation of spaced parts due to elongation of said shank due to the load of the drilling string of tools, said eieotrioal metering circuit ther h vide an ind: string of tools.

ED'W 1 BERNARD 1;

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