US3129517A - Means for determining the inclination of well pipes - Google Patents

Description

Ap 1964 c. J. MCWHORTER MEANS FOR DETERMINING THE INCLINATION OF WELL PIPES 2 Sheets-Sheet 1 Original Filed June 25, 1959 F a 4 Z M. Ll. J u 0 INVENTOR.

April 21, 1964 c. J. MCWHORTER MEANS FOR DETERMINING THE INCLINATION OF WELL PIPES 2 Sheets-Sheet 2 Original Filed June 25 1959 INVENTOR- ATTORNEY United States Patent- O ETERMENING THE lNCLlNATiON F WELL PIPES Cullen It. McWherter, Houston, Tex assignor to Houston Oil Field Material Company, Inc, Houston, Tex., a corporation of Delaware Original application lune 25, 1959, Ser. No. 822,903, now Patent No. 3,039,544. Divided and this application Sept. 6, 1960, Ser. No. 59,134

5 (Claims. (Cl. 33-205) This invention relates to an apparatus for logging wells, and more particularly means for determining variations in the inclination of a well pipe for the purpose of locating the point at which the pipe is stuck in a well, and to an improved inclinometer for such use. This application is a division of Serial No. 822,903 filed June 25, 1959, now Patent No. 3,039,544.

In the drilling and operation of wells, such as oil and gas wells, it is customary to produce a well bore by the use of a tubular drill string, having at its lower end a drill which is rotated with the string, the string being usually of somewhat smaller external diameter than the diameter of the bore, and drilling mud being circulated through the string and through the bore outside of the string during the drilling operation to lubricate the drill and to carry away the cuttings formed thereby. The bore of a well produced in this manner may deviate substantially from the vertical and in wells of substantial depth such deviation frequently takes place in different directions so that the bore is curved at various locations. Under some circumstances, such as when the drilling takes place in inclined formations, or when alternately soft and hard formations are encountered, the drill may be deflected in a manner to produce relatively sharp curves or bends, sometimes referred to as dog legs.

In carrying out well drilling or other operations in wells the drill stem or other well pipe will follow generally the curvature or inclination of the bore and when the well pipe is substantially smaller in diameter than the bore, which is usually the case, the pipe engages the wall of the bore at various locations throughout the length of the bore, so that the inclination of the pipe varies and is different from the inclination of the bore at some locations and may even assume a somewhat spiral shape.

It is often desirable to determine the inclination of the well bore, or of the drill stem or other pipe therein, such as the well casing or tubing, especially for the purpose of locating a dog leg or other irregularity in the bore likely to interfere with the insertion or withdrawal of the well pipe, or to locate the point at which the drill stem has become stuck in the well due to caving of the formation, settling of the drilling mud, or from other causes.

Heretofore, in attempting to locate the point at which a well pipe should be disconnected or cut olf, when such a pipe has become stuck in a well, it has been customary to make use of instruments of the strain gage type, which may be lowered into the well pipe and held stationary therein While the stress or strain on the pipe is varied to indicate by deformation of the pipe whether the pipe at a particular location is free or stuck. By this method it is possible to locate within rough limits the portion of the pipe which is stuck and the portion which is free by relatively few readings, but this method has the disadvantage that is necessary to make a separate test at each of a large number of longitudinally spaced locations in order to accurately locate the point at which the pipe is stuck.

The current procedure in determining the point at which a string of pipe may be freed is to take a series of readings in the pipe at lower and lower levels until a point is found where no readings can be obtained which is indicative of the fact that the stress or strain at this point cannot be varied due to the stuck condition of pipe above lVlEANS FUR ice this point. Generally these readings will diminish from full readings in totally free pipe to zero at some point well below the top of caved in formations or settlings that are binding the pipe. This is due to the fact that torque or tension is transmitted through the top portion of the loose material around the pipe and a certain amount of free travel is established in this loose formation by the usual working of the pipe by the operator in an effort to free the pipe. This free travel is often misleading as to the true degree of stuckness of the pipe and often results in the pipe being backed off or cut at a depth well below the top of the formation that is binding it. When this happens it is often impossible to pull the freed portion of pipe from the bore hole necessitating a second cut or back off, or, if the freed portion can be pulled out of the binding material the top portion of the fish may be filled by this material falling into it and future fishing operations may be impeded.

In the inclinometer method, described more fully hereinafter, this condition of stress and strain transmitted through the loose formation is not so much a factor. Changes in tension and in the amount of torque present in free pipe will cause the pipe to repose in the bore hole in different conditions of convolutions and/ or spirals. This is especially true if the free pipe in one condition is under a considerable tension as shown in FIGURE 1A, and another condition of being relaxed with weight of upper sections bearing down on its as shown in FIGURE 2A. Normally, under tension the pipe would reside on the low side of the bore hole (all bore holes have some deviation from a true vertical) and generally conform to the contour of this low side. When under compression, the pipe would bow out at intervals from this low side and rest approximately against the opposite wall of the bore hole. This produces a series of convolutions or curves in the pipe that causes the pipe at one point to have less inclinaton and at another point to have more inclination that it had when under tension. If there is loose formation surrounding the pipe it cannot have the freedom of side to side movement to produce changes in inclination because it would require a very considerable force to produce side movement of the pipe against the restraining formation and this force is not suflicient since it is derived from the weight of upper sections applied at the relatively small angles in the pipe in relation to the bore hole.

Thus, if an inclinometer log is run of a section of pipe, part of which is free and part stuck, under conditions of tension and compression, there will be a sharp change between the character of the two logs at the point where the binding formation begins, which is the desirable point at which to attempt a cut or back off of the pipe. This change in character of the inclinometer logs in free pipe can be induced by a change in the amount of torque applied since twisting a string of pipe will cause it to assume a spiral condition with resultant changes in inclination at difierent points.

The inclinometer instrument may be used to make readings at selected points like instruments currently in use, but the amount of change in deviation will vary from point to point. Any reading, however, will indicate that the pipe is free and readings can be checked at a slightly different depth to avoid points where the inclination of the pipe does not change appreciably between conditions of tension or compression.

The present invention has for an important object the overcoming of the above disadvantages of the methods heretofore employed in logging the variations and inclinations of a well bore or of a pipe located in such a bore, by the use of an improved means for continuously measuring the inclination of the bore or pipe throughout its length.

A further object of the invention is to provide an inclinometer of improved construction and sensitivity, for use in measuring very small variations in inclination from the vertical.

Another object of the invention is the provision of an inclinometer which is electrically operated and by which a continuous record or log of the changes in inclination of a well bore or of a pipe located therein may be made.

A still further object of the invention is to provide an inclinometer of simple design and rugged construction whose sensitivity and accuracy is substantially unaffected by the extreme conditions of hard usage to which instruments of those characteristics are likely to be subjected when used in well logging operations.

The above and other objects and advantages of the invention may best be understood from the following detailed description constituting a specification of the same, and considered in conjunction with the annexed drawings wherein FIGURE 1 is a fragmentary, partly diagrammatic view, illustratin the method and apparatus of the invention showing the inciinometer of t e invention partly broken away and partly in cross-section located in a well pipe in a well bore, the recording mechanism employed therewith being shown diagrammatically;

FIGURE 1A is a fragmentary, vertical, central, crosssectional view on a reduced scale, of a portion of a well bore showing a well pipe positioned therein, and showing a location at which the pipe is stuck in the well, the pipe being shown in the position which it occupies during one stage of the method of the invention;

FIGURE 2 is a fragmentary front elevational view of a portion of a chart showing a typical form of the continuous record made by the method and apparatus of the invention, and indicating the variation in the inclination fromthe vertical of a well pipe in a well bore;

FIGURE 2A is a view similar to that of FIGURE 1A, showing the typical variation in the inclination of a well pipe corresponding to the recording of FIGURE 2 during another stage of the method of the invention.

FIGURE 3 is a fragmentary, vertical, central, crosssectional view, on a somewhat enlarged scale, of a portion of a well bore, showing a well pipe therein with the inlinometer of the invention in an operable position in the pipe, the pipe being shown partly broken away and partly in cross-section;

FIGURE 3A is a fragmentary, front elevational view on a somewhat enlarged scale of a portion of a chart showing a typical recording indicating the variations of the inclinorneter of the invention as the inclinometer passes downwardly through the pipe, illustrated in FIG- URE 3; and

FIGURE 4 is a vertical, central, cross-sectional view, on an enlarged scale, showing details of construction of the operating elements of the inclinometer of the invention.

Referring now to the drawings in greater detail, the method and apparatus of the invention are particularly useful in connection with the drilling and operation of wells, such as oil wells, the bore of such a well being indicated at B, which bore may be provided with a casing or liner C, extending downwardly from its upper end throughout a portion of the bore, and having an inner pipe or tubing T, of substantially smaller diameter than the bore, which extends below the lower end of the casing C and which is illustrated as being stuck in the well bore, as by the caving of the surrounding formation as shown at F, or the accumulation of drilling mud, sand, or the like, in the bore about the exterior of the pipe.

Under these conditions, it is desirable to accurately locate the zone in the well bore in which the pipe is stuck, so that the pipe may be cut or disconnected at a point above the stuck portion to permit the portion above to be removed from the bore and the subsequent carrying out of washover operations by which the stuck portion of the pipe may be recovered from the well.

The apparatus by which the method of the invention is carried out comprises an inclinorneter enclosed in a suitable housing itl, connected at its upper end to the lower end of a cable 12, by which the inclinometer may be lowered into the well pipe, and which is operated by suitable winding mechanism 14 rotatably mounted in any convenient manner above the upper end of the well. The cable 12 is of the conductor line type having one or more suitably insulated conductors therein by which electric current may be supplied to the inclinometer and through which current may liow to suitable recording mechanism by which a continuous record of variations in the inclination of the well pipe may be recorded.

The inclinometer mechanism or" the invention, as best seen in FTGURES l and 4 includes an elongated tubular element 16 located in the housing lid and whose upper end 18 is closed and whose lower end extends into the upper end of an open receptacle 25) supported in the bottom of the housing. The lower end of the tube 16 opens into the interior of the receptacle it? in spaced relation to the bottom of the receptacle and the tube and receptacle contain a column of a heavy liquid, preferably mercury, whose upper end is located at a predetermined level 2-in the tube caused by the pressure of air in the housing acting upon the surface of the liquid in the receptacle. The housing ild may be completely closed and sealed to maintain the pressure in the housing at any desired pressure and to prevent variations in the pressure of the external atmosphere from causing changes in the effective length of the column of liquid. An inductance coil 24 surrounds the tube near its upper end and within the tube a core 26 of magnetic material such as ferrite or other suitable material having a high magnetic permeability is movably positioned in contact with the upper end of the mercury column in position for longitudinal movement in the tube relative to the inductance or tank coil 24 to vary the inductive effect of this coil in an oscillator circuit in accordance with the longitudinal movement of the inductor in the tube. The coil 2-4 is connected as by means of conductors 23 into an electrical circuit including an oscillator 30 of conventional construction, located in the upper end of the housing 19 and is in turn connected by the conductors of the cable 12 to the recorder mechanism at the surface.

The recorder mechanism may be of usual construction including a coupling transformer 3-2, having a primary winding 3 of low impedance connected in circuit with the oscillator 3%, through the conductors of the cable 12, and with a suitable source of direct current supply, such as that indicated at 36, and having a secondary winding 38 which is connected in circuit with a receiver 40 whose output is supplied to an electrical recorder 42 of usual construction, which includes a chart or tape 44 upon which the record is made.

The oscillator 30 is constructed to generate an alternating current at a frequency which is determined by the size of the capacitors in the oscillator and the inductance of the tank coil 24 when direct current is supplied to the oscillator from the source 36 through the primary winding 34 of the transformer 32 and through the conductors of the cable 12. The frequency of the current generated by the oscillator may be of the order of 40 kilocycles and this alternating current .is transmitted through the cable 12 to the coupling transformer 32 and through the transformer and bypass condensers, not shown, to ground and thus back to the oscillator. The alternating current from the oscillator is superimposed on the direct current and generates an alternating current of the same frequency in the secondary 3d of the coupling transformer. The direct current passing through the primary has no effect on the secondary, so that a separation of the alternating current from the direct current is effected by the coupling transformer in the receiver 40, shown in FIGURE 1. There is another oscillator whose frequency of oscillation may be set to equal the frequency being generated by the instrument in the well. The receiver also includes a frequency mixing circuit which produces no output as long as the frequency of the oscillator 30 and the frequency of the oscillator in the receiver are equal, but when one of these frequencies changes, there is generated in the mixer device an alternating potential whose frequency is the diiference between the two frequencies being fed into the device. This is known as a beat frequency. This beat frequency is amplified in the receiver and fed through a rectifier network in the receiver which produces a direct current output from the receiver whose magnitude is directly proportional to the beat frequency. The output from the receiver is fed directly into the recorder 42, shown in FIGURE 1, which produces a record on the chart 4-;- indicating variations which take place in the frequency of the current from the oscillator 30. Thus, as long as the frequencies of the currents, from the oscillator 39 and those from the oscillator in the receiver remain the same, the record on the chart 44 will be a straight line, but upon the occurrence of a variation in the frequency of the current from the oscillator 35, the direction of the line on the chart will be changed accordingly, indicating a deviation of the inclinometer from the verti cal.

In practice, the inclinometer is suspended vertically before lowering it into the well and the receiver 40 is adjusted to produce zero beat frequency or zero output, and the recorder, likewise is adjusted to indicate zero, so that the pen 46 of the recorder, shown in FIGURE 1, will make a straight line longitudinally moving on the chart 44. In this position of the inclinometer, the effective length of the mercury column supporting the core 26 will be shortest, and the core will be at its farthest point of movement relative to the tank coil 24; causing the inductance of the tank coil to be at a minimum and the frequency of the oscillator 39 to be at a maximum.

In this condition of the apparatus, any variation of the inclinometer from the vertical, regardless of the direction of such deviation, will produce a decrease in the frequency of the current from the oscillator 3i} due to movement of the core 25 toward the coil 24 caused by a change in the e ective length of the mercury column, showing the pen of the recorder to move laterally on the chart 44 to indicate such change of inclination. 1

It will be apparent that by varying the impedance in the electrical circuit between the receiver 45 and the recorder '42, the instrument may be calibrated to produce more or less lateral movement of the pen 46 upon the occurrence of a predetermined amount of change in the inclination of the inclinometer. For example, the first calibration may be such as to produce a vfull scale deflection of the recorder for a deviation of the inclinometer of 1 degree. Subsequent calibrations may be made requiring a '2 degree inclination in the inclinometer to produce full scale deflection of the recorder or the instrument may be calibrated to require 3 or 4 degrees or more inclination of the inclinometer to produce full scale deflection of the recorder to adjust the recorder to record the maximum deviation likely to be encountered in a well bore.

If this inclinometer is run in a bore hole or through a string of pipe in a bore hole it is possible to record deviation from the vertical as a function of depth as indicated in FIGURE 2. Such a recording will show sudden changes in deviation in a bore hole, commonly called dog legs, which might be missed by a directional survey made at intervals in the bore hole.

The change in the inclination of pipe as before described is necessarily sm-all because of the relatively close proximity of the walls of the bore hole to the pipe. This condition will vary as will the forces causing changes in inclination but in general it may be stated that the change will be of the order of 1 degree to 2 degrees or less. In some instances of heavy sections such as drill collars, the change may be as small as one-third of one degree. It

is apparent, therefore, that an inclinometer must be sensitive and have a high degree of resolution to successfully record such changes in deviation. As before mentioned the most sensitive calibration setting should produce a full scale deflection of the recorder for a change of only one degree. On such a scale, /3 of one degree change (or 20 minutes) will appear as /s of full scale which is easily discernable.

At the point where a string of pipe is stuck, it may be found that the deviation from the vertical is relatively large as for example 9 degrees. If the sensitivity calibration step is set high enough for example 10 degrees for a full scale deflection of the recorder, then 9 degrees will appear on the chart on the extreme right, and if the variations in deviation of the pipe were only /3 of one degree, then the changes which can be recorded in inclinometer logs between the conditions of tension and compression will appear small in comparison with the full cale of the log.

To offset this condition, the beat frequency oscillator in the receiver may be adjusted in a direction to reduce the beat frequency an amount equivalent to say 8 degrees; then a reading of 9 degrees will appear on the log in the same place as a 1 degree reading would before. This will create an artificial zero and then by using a sensitivity step of say 2 degrees for full scale, it is possible to record differential inclinometer logs to reveal positively small changes in inclination even though the total inclination of the string were large.

The inherent sensitivity of this device may be seen from the fact that the inductance of a tank coil of an oscillator whose natural frequency is in the order of 40 kc. has a very profound effect on the oscillator. In other words changes in the position of a tuning inductance within the tank coil will sharply change the natural frequency of oscillation. Specifically, a change of only .001 inch either in or out of the tank coil (shown in FIGURE 4) by the inductor will shift the frequency of oscillation by as much as 30 cycles. If an inclinometer tube 30 inches long is inclined 1 degree from the vertical, the length of the column of mercury will be increased .0045 inch, which will cause the inductor to move this amount into the tankcoil and will produce 4.5 times 30, or cycles change. This will be more than 2 cycles change for each minute of change in deviation and easily falls within the previously described minimum requirement of 1 degree for a full scale deflection of the recording equipment.

The inclinometer instrument will be sensitive to changes in the internal diameter of the pipe. In FIGURE 3, the instrument moving down inside an inclined section of pipe will be disposed on the low side and the nose of the instrument will be deflected toward the center of the pipe on reaching an internal reduction in diameter, such as may be caused by a coupling 50, thus causing a momentary increase in deviation and a kick or jog on the inclinometer log away from zero. The reverse will happen as the instrument passes through such an internal reduction back into the original pipe size, as indicated at 54. Thus internal upset points will show as a kick, followed by reversal. Reduction in pipe size will show as an outward curvature of the line of the recording and an increase in pipe size will show as an inward curvature of the line.

The inclinometer instrument may be used to find the condition at which tension and compression are equal at a given point in a string of pipe above the stuck point. If the instrument is positioned at a point where it had been observed (from logs or static readings) that a change in inclination occurred between tension and compression in the pipe and starting with a relaxed condition (compression) to slowly raise the string of pipe at the surface until a change in reading is first observed; this first show of change will be at the moment tension first arrived at the location of the instrument and will be a neutral point b and will give operator sufiicient and accurate information for backing oii the pipe at this point.

It will, of course, be apparent that any suitable device, such as a direct current meter may be substituted for the recorder mechanism 42, when it is desired merely to indicate to the operator when the stuck point is reached without making a record of the variations in inclination of the pipe.

In carrying out the method of the invention, the inclinometer is lowered inside of the string of pipe whose variation in inclination it is desired to determine and current is supplied to the inclinometer in the manner previously described, and the changes in inclination of the inclinometer are recorded as we show above, with the pipe in a relaxed condition in the bore. As the inclinometer is lowered in the bore, the deviation of the instrument from the vertical will be continuously recorded on the chart When the inclinometer reaches the bottom, an upward pull may be exerted on the string of pipe, which will tend to reduce the variations in inclination throughout the tree portion of the string, and the inclinometer may be moved upwardly through the pipe while the pipe is maintained in this condition to make a second recording of the variations in inclination. By comparing the two recordings thus produced, it will then be possible to accurately locate the portion of the pipe which is stuck in the bore and the portion which is free, to determine where the pipe shall be disconnected or cut off to permit the removal of the free portion. During the carrying out or" the method in this manner, it will be apparent that the stuck portion of the pipe will be held against being affected by the upward pull exerted on the string, so that the variations in inclination of the stuck portion will remain substantially the same While the variations in the inclination of the free portion of the pipe will be changed, so that the location where the tree portion of the pipe joins the stuck portion may be accurately located.

It will be apparent that under some conditions, the location of the stuck portion of the pipe may be determined by a single pass of the inclinometer, either with the pipe in a relaxed condition, or under the tension produced by an upward pull on the string. It will also be seen that the amount of upward pull exerted on the string need not be suificient to place the entire length of the free portion of the pipe in tension, since the method of the invention does not depend upon the tension or compression to which the pipe is subjected, but only upon the change in inclination resulting from a change in the downward force exerted on the pipe.

The invention is disclosed herein in connection with a certain specific embodiment of the apparatus employed and procedure in carrying out the method, but it will be understood that these are intended by Way of illustration only and that various changes may be made in the construction and arran ement of the parts of the apparatus as well as in the particular steps of the method, within the spirit of the invention and the scope of the appended claims.

Having thus clearly shown and described the invention, what is claimed as new and desired to secure by Letters Patent is- 1. An inclinometer comprising:

(a) an elongate liquid container,

(1)) a non-compressible liquid positioned in said container,

(c) a first gaseous pressure means acting on the top of said liquid in the container,

(d) a second gaseous pressure means acting against the second end of said liquid in the container, said second pressure means being greater than the first pressure means whereby the liquid has a substantially constant vertical head, and

(e) an electrical means for indicating a change in the angular position of said container relative to the vertical.

2. An inclinometer comprising:

(a) a first elongate liquid container,

(b) a second liquid container connected to one end of said elongate first container, said second container being of a substantially greater cross-sectional area than said first container,

(c) a non-compressible liquid positioned in said first and second containers,

(d) a first gaseous pressure in said first container acting against said liquid,

(e) a second gaseous pressure in said second container acting against the liquid, said second gaseous pressure being greater than said first gaseous pressure thereby providing a substantially constant vertical head on the liquid between said first and second gaseous pressure, and

(1) means for indicating a change in position of the upper end of the liquid relative to said first container thereby indicating a change in the angular position of said container relative to the vertical.

3. An inclinometer comprising,

an elongate liquid container, said liquid container being closed at its top,

a non-compressible liquid in said container,

at first gaseous pressure means acting on the top of said liquid in the container,

a second gaseous pressure means acting against the bottom end of said liquid in the container, said second pressure means being greater than the first pressure means whereby the liquid has a substantially constant vertical head, and

means for indicating a change in position of the upper end of the liquid relative to said container thereby indicating a change in the angular position of said container relative to the vertical.

4. The invention of claim 3 including a pressure tight housing about the container.

5. The invention of claim 3 wherein the angular indicating means include float means positioned in the liquid

Claims (1)

1. AN INCLINOMETER COMPRISING: (A) AN ELONGATE LIQUID CONTAINER, (B) A NON-COMPRESSIBLE LIQUID POSITIONED IN SAID CONTAINER, (C) A FIRST GASEOUS PRESSURE MEANS ACTING ON THE TOP OF SAID LIQUID IN THE CONTAINER, (D) A SECOND GASEOUS PRESSURE MEANS ACTING AGAINST THE SECOND END OF SAID LIQUID IN THE CONTAINER, SAID SECOND PRESSURE MEANS BEING GREATER THAN THE FIRST PRESSURE MEANS WHEREBY THE LIQUID HAS A SUBSTANTIALLY CONSTANTANT VERTICAL HEAD, AND (E) AN ELECTRICAL MEANS FOR INDICATING A CHANGE IN THE ANGULAR POSITION OF SAID CONTAINER RELATIVE TO THE VERTICAL.

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