US2857677A - Apparatus for surveying bore holes - Google Patents

Description

oef. 2s, 195s C. L. NORDEN APPARATUS FOR SURVEYING BORE HOLES Filed March 6, '1953 4 Sheets-Sheet 1 INVENTOR.

vCAI/ez. A/o/PDEA/ BY Afp-`L-Smm Oct. 28, 1958 c. L. NORDEN 2,857,677

APPARATUS FOR SURVEYING BORE HOLES Filed March 6, l955 4 Sheets-Sheet 2 IN V EN TOR.

12.1.5 E Cnel. A/QQDEA/ BY Mm@ 7'7 ORME Y Oct. 28, 1958 C. L. NORDEN APPARATUS FOR SURVEYING BORE HOLES Filed March 6, 1953 4 Sheets-Sheet 3 44 Il, 5o I 46 sa o 48 4o ,n I

|| f H n l u 58 62' Zo v INVENToR. @22A L A/oQoE/V HTTOP/VEY Oct. 28, 1958 c. L. NoRDl-:N '2,857,677

APPARATUS FOR SURVEYING BORE HOLES Filed March 6, 1953 4 Sheets-Sheet 4 INDlATED REFERENCE.

O\QE ;T|ON

TQQE QEr-Er-zENea 'DlQEC-TION PLANE NORMAL TO AXIS OF BOQE HOLE INVENTOR. C nel. L. A/o/@DEA/ BY MLM 4 TTOENE Y PLANE oF Hok/zou the surface of the earth.

United States Patent 1 APPARATUS FOR SURVEYIN G BORE HOLES Application March 6, 1953, Serial No. 340,799

8 Claims. (Cl. 315-2055) My invention relates to apparatus for surveying bore holes and more particularly to a device for measuring the inclination of bore holes from the vertical and the direction of the inclination in azimuth with reference to a selected direction. i

This application is a continuation in part of my copending application Serial No. 2,975,'led January 19, 1948, for Apparatus for Surveying Bore Holes, now Patent No. 2,699,611 issued Ianuary18, 1955.

In the drilling of oil wells, the drill bit must pass through various geological strata having different characteristics. These different characteristics cause the drill bit to deviate from the vertical, and a whipstock is employed to bring the bit back to vertical. However, the resultant bore hole will not be truly vertical. Occasionally a suitable drilling location will not be found directly over the deposit of oil and drilling must be done from a site at some distance from the point over the deposit. In such a case, the bore hole must be drilled at a predetermined inclination and direction from the chosen site in order to reach the deposit. The provision of apparatus for surveying such bore holes to produce a record of the inclination of the hole at various points and the direction of this inclination is exceedingly dilcult. This is especially true of many wells being drilled today, since the deposit is often located many thousands of feet below In addition, such a surveying instrument must occupy a space of limited cross-sectional area in order that it may iit within the bore hole.

Measurements of the inclination of the hole present no great problem, since any number of levels or pendulums may be used to indicate lthe amount of the inclination. Measurements of the direction of the inclination, however, present a more serious problem. Magnetic compasses have been unsatisfactory for indicating such direction, since the magnetic characteristics of the strata through which the instrument is passing are random and vary with time and are, therefore, exceedingly difficult to determine. Very often the bore hole itself is provided with a casing which acts as a shield for the magnetic compass, further complicating the problem.

It has been suggested that a gyrocompass be used to provide a reference direction from which the direction of the inclination can be measured. However, errors will be introduced in the case of the gyrocompass by precessions caused by friction in the bearings of the gyro scope 'rotor and by the rotation of the earth. No suitable means is provided in the prior art for compensating for these errors. In addition, in instruments of the prior art employing -gyrocompasses, electrical leads from the inin the gyroscope rotor bearings and the rotation of the earth.

In my copending application Serial No. 2,975, previously referred to, I have disclosed apparatus for surveying bore holes in which the spin axis is maintained in a plane normal to true gravity so that the gyroscope ernployed therein gives true directions with reference to the plane of the horizon. The azimuth scale, however, on which the directions are indicated, is iixed in a plane which is perpendicular to the axis of the instrument and, therefore, to the axis of the bore h ole." Sincek the indicated directions are given in this plane, they must kbe referred to the plane of the horizon to obtain the true directions, and it is necessary to calculate the true direction for each reading or ,observationv of indicated direction. l have also developed apparatus for surveying bore holes which is provided with means for maintaining the spin axis of the gyroscope ina plane which is perpendicular to the axis of the instrument and, therefore, perpendicular to the axis of the bore hole. It is this latter apparatus which is the subject matter of lmy invention. When the spin axis of the 'gyroscope is maintained ina plane perpendicular to the axis of the bore hole, the gyroscope Will give true directions with reference to that plane. Since the azimuth circle is fixed in a plane perpendicular to the instrument and bore hole axes, the gyroscope will give true directions in the plane ot the azimuth. Most bore holes have inclinations which'l are in a single vertical plane, and the'indicated directions will be true directions. It is therefore not necessary to correct the indicated directions as must be `done in the case where the spin axis is maintained in a plane normal to true gravity. Some bore holes are helical in shape and introduce a gyratory motion of the instrument around a vertical axis.

Since the Cardan ring is insensitive to rotation about anyv axis at right angles to the Cardan, an error will be introduced by the gyratory motion and a correction must be made, as will be described in detail hereinafter. However, as is pointed out above, most bore holes have all their inclinations in asingle vertical plane and no cor-v rections need be made. The gyroscope of my improved apparatus -is automatically corrected for errors introduced by friction in the rotor bearings and by the rotation of the earth on its axis.

One object of my invention is to provide an apparatus for surveying bore holes which eliminates the disadvantages of the prior art. i

Another object of my invention is to provide an irnproved apparatus for surveying bore holes to determine the amount of inclination of the hole and the direction of the inclination with reference to a predetermined direction.

Another object of my invention is the provision of apparatus for surveyingv bore holes in which a reference direction is accurately and constantly maintained.

AV further object of my invention is to provide an apparatus for surveying bore holes in which a record of the anglel of inclination of the hole frornthe vertical and the direction of the inclination .with respect to a predetermined direction is made.

A still further object of my invention is to provide apparatusV for surveying bore holes having inclinations generally in a single vertical plane, which apparatus gives a record of inclinations and the directions of the inclinations which requires no correction.

Other and further objects of my invention will appear from the following description.

In generalmy invention contemplates the provision of a liquid-tight casing having an outside diameter such that it may readily be lowered into a bore hole. A number of housings are mounted within the casing. Disposed respectively within the various housings are a camera Patented oct. .28, 1958 `of the bore `hole at the position of the instrument. I

accomplish this by applying correctional precessions from the servomotor and a switch. Means are provided `for correcting the servomotor for errors in azimuth intro- -duced by precessions caused by the rotation of the earth onitsaxis and friction in the gyroscope rotor bearings. In the accompanying drawings which form part of the instant `specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

Figure lis a elevation of a unit embodying my apparatus `forsurveying bore holes with a part broken away.

Figure 2 is a sectional View on an enlarged scale with part of the case removed taken generally on the line 2 2 of Figure 1.

Figure 3 is a sectional view taken along the line 3--3 of Figure 2.

Figure 4 is an elevation taken on the line 4-4 of Figure 2 with the casing and housing removed.

Figure 5 is a sectional view taken along the line 5-5 of Figure 4.

Figure 6 is a sectional view taken along the line 6-6 of Figure 3.

Figure 7 is a diagrammatical view showing the electrical circuits-employed in my apparatus.

Figure 8 is a diagrammatic elevation showing the generation of corrections when the spin axis of the gyroscope is maintained normal to the axis of the bore hole.

Figure 9 is a plane view of the diagram shown in Figure 8.

More particularly, referring now to the drawings, I provide aliquid-tight casing 12 having removable top and bottom members 14 and 16, respectively. Casing 12 has an outside diameter such that it may be lowered in a bore hole. For example, the outside diameter of casing 12 may be three and one-half inches and the wall thickness SAG of an inch. Appropriate means such as an eye 18 is fixed to the top member 14 by suitable means such as straps to provide means for-lowering the apparatus into the bore hole. The interior of casing 12 contains a number of housings 22, 24, 26, 28 and 30, in which housings a battery, a servomotor and shockabsorbing means, a gyroscope unit, a scale unit and a camera unit are respectively disposed. The housings are separated from one another by partitions 32. Referring to Figures 3 and 6, the rotor 34 of my gyroscope is selected to have as large a moment of inertia as is possible within limits imposed by the available space and, therefore, is made of some heavy metal such as tungsten which is placed on a plate 36 carried by the shaft 38 of the unit. Shaft 38 is supported by a pair of ball bearings 40 and 42 mounted in the gyroscope housing 44. Tubular member 46 is'xed to the housing by suitable means such as bolts 48 and `has .pole pieces `50 and 52 formed thereon which carry respective windings 54 and 56. Current is supplied to the gyroscope armature winding 58 through brushes 60 and 62.

As is shown in Figure 6, the gyroscope housing 44 is supported on a'pair of ball bearings 64and 66 mounted on stub shafts 68 and 70, respectively, fixed to the Cardan ring 72 of the `gyroscope by appropriate means such as bolts 74. It is to be noted that stub shafts 68 and 70 are aligned at right angles to the shaft 38. The Cardan ring 72 is mounted for rotation about a normally vertical axis in an upper ball bearing 76 and a lower ball bearing 78, as can readily be seen by reference to Figures 2 and 3. For purposes of convenience the axis CTI of shaft 38 about which the rotor y34 ofthe 'gyroscope rotates is referred to as the spin axis. The axis which passes through stub shafts 68 and 70 around which the gyroscope housing 44 pivots is referred to as the tilt axis. The vertical axis around which the Cardan ring 72 is pivoted is referred to as the azimuth axis.

The lower bearing 78 in which the Cardan ring is carried is supported by a boss on the bottom member 80 of the housing 26. The member 80 is formed 'with a bracket 82 to which the housing 86 of a servomotor is attached. The motor shaft 84 is attached to a stub shaft 8S on the bottom 4of the Cardan ring by means of a universal joint 90. Shaft 88 is formed a't its upper end with a flange or plate 92 secured to the bottom of Cardan ring 72 by suitable means so that when shaft 84 rotates, it will rotate shaft 38 and thereby the Cardan ring. Shaft 88 is hollow and carries an insulating bushing 94 and supports a plurality of slip rings 96 through which electrical connections to the gyroscope are made. The -base 98 of housing 24 has an upstanding annular boss 100 formed thereon which guides a spring 102 seated on base 98 -and extending upwardly tothe underside of base 80. A boss 104 formed on the underside of base 80 holds the spring in position. The lower portion of the servomotor housing `86 carries a guide member 106 which is slidably received in an opening formed in a bracket 108 attached to base 98 by a screw 110. Spring 102 provides means to absorb any shocks encountered when the assembly is lowered into the bore hole. When a shock is encountered, the kinetic energy of the unit enclosed in housing -26 compresses spring 102 which absorbs the shock, and guide member 106 may slide downwardly in the recess in bracket 108. The openings 112 in base 98 and 114 in the separator 32 covering the housing 22 permitfmovementof guide member 106 downwardly through the opening in bracket 108.

The upper portion of Cardan ring 72 is secured to a flange 116 formed on a shaft 1-18 rotatably mounted in bearing 76. A disk 120 of light aluminum is carried on a pin 122 at the upper end of shaft 118 and is clamped to the shaft by a clamping nut 124. A cylindrical member 126 at the periphery of the disk 120 has an upper flange 128 which may be calibrated in azimuth in any appropriate manner. K The Cardan ring 72 is formed with a depending portion 130 to which is secured by means of machine-screws 132 a plate i134. A bracket 136 on the bottom of Cardan ring 72 has a recess therein in which is carried a stub shaft 138. Stub shaft 138 is securely held in bracket 136 by a screw 140. A bracket 142 is adjustably fixed on shaft 138 by a set screw 144. Carried by the bracket 142 and insulated therefrom by an insulating member 146 are a pair of conducting segments 148 and 150. The segments 14S and 150 are separated by a portion 147 of the insulating member 146 extending between them as can be seen by reference to Figure 4. The end of the stub shaft 138 carries a ball bearing 149 in which bearing and another ball bearing 151 carried by `plate 134, I pivot a shaft 152. A lever 154 is secured to shaft 152 for rotation therewith. A conducting arm 156 is xed to the lever 154 by a screw 158 and insulated therefrom by an insulator 160. If desired, the lever 156 may itself be made of insulating material.

As can readily be seen by reference to Figures 4 and 6, an angle plate 162 is secured to the `housing 44 Yof the gyroscope by a machine screw 164. A connecting rod 166 is pivoted on a pin 168 on plate 162 and held in the connected position by a spring attached to housing 44 by `a screw 172. The lower end of connecting vrod 166 is pivoted around a pin 174 yon lever 154- and the connection maintained by a spring 176 fixed to the lever 154 by a screw 178. It is -to bc noted that the distance between the axis of shaft 70 and the axis of `pin 168 is exactly the same as `the distance between the axis of bearing 151 and the axis of pin center.

174. Similarly, the length of the connecting rod 166 between the axis of pin 168 and the axis of pin 174 is thev same as the distance between the axis of bearing 66 and the axis of bearing 151. Thereby, I have provided a parallel motion connection so that the lever 154 will always be parallel to the axis of spin of the gyroscope. Relative movement between the spin axis and the direction of the bore hole as represented by the portion 147 of the insulating member 14 extending between segments 148 and 150 will cause relative movement of contact arm 156 with respect to the conducting segments. In the normal position of operation when the spin axis is exactly perpendicular to the axis of the bore hole, the end of contact arm 156 will rest on the insulation 147 between the segments 148 and 150.

The upper portion of the scale unit housing 28 is closed by an annular member 180 iixed to the housing 28 by suitable means such as screws 182 and provided with a depending ange 184 forming an opening 186. The lower end of flange 184 as viewed in Figure 3 has a peripheral lip 188 on which is supported a heavy glass plate 190 having a ball bearing 192 seated in its This ball bearing casts a shadow at the base of the scale compartment and, accordingly, I place all indicators, scales and the watch out of the shadow zone. A shaft 194 carries a spherical bearing member 196 which rests upon the balls of bearing 192. A shaft 198 is supported from shaft 194 by suitable means such as lpins 200 and carries a base 202 for the support of the indicators at its lower end. Base 188 is screwed onto threads 204 on the end of shaft 198. A thermometer (not shown) is mounted on base 202. Shaft 198 is formed with a laterally extending bearing 206 in which is supported'a shaft 208. A pendulum 210 is mounted on shaft 208 for rotation therewith and cooperates with a scale 212 calibrated to show inclinations up to 40 degrees. Likewise, secured to the base 202 in any suitable manner is an indicator 214 calibrated in inclinations up to 20 degrees. I also mount a ball indicator 216 on the base 202 which has a ball 218 retained on a spherical lapped surface 220 by means of a curved glass cover 222. The curvature of the ball support 220 is such that it is adapted to indicate inclinations up to the vicinity of 71/2 degrees. The glass cover is also provided wtih a plurality of circular etched lines to indicate 1 degree of inclination in any direction. In addition to the indicators already described, I provide a watch 215 on base 202. The details of the indicating means just i described are shown 'and described in detail in the aforesaid copending application, Serial No. 2,975.

A U-shaped guide member 224 is secured to the underside of base 202 and surrounds clamping nut 124 which is formed with a cylindrical exterior surface. A roller 228 is mounted for rotation about a shaft 230 carried by the base 202. The roller 228 is adapted to contact the surface of nut 124. The interior sides of the guide member 224 are likewise adapted to contact the cylindrical nut 124. When the instrument is vertical, the assembly of scales suspended from the bearing 192 is such that the roller 228 and the interior sides of guide 224 just clear the lateral sides of nut 124. The base 202 is formed with a thickened portion 232 which gives olset weight to the base on aline drawn through the axis of -roller 228 and the axis of cylindrical nut 124. This arrangement provides friction damping permitting the base and scale assembly to stabilize at a low gravity position without undue oscillation. As the instrument is inclined, weight 252 will cause the base to rotate to a position where weight 232 is in the low gravity position. The lower the inclination, the greater will be the friction damping of guide plate 224 against the nut 124.

The annular cover member 180 of housing 28 supports a pair of bases 234 and 236 in which are mounted, respectively, incandescent lamps 238 and 240. Above the scale unit in the housing 30 I mount the camera unit 6 242, the lens 244 of which is shown. This cameraunit may be of any appropriate design and is well known in the art.

Referring now to Figures 2 and 6, I mount a pair of guide members 246 and 248 on the gyroscope housing 44. Guide member 246 extends vertically of the housing in a direction parallel to the azimuth axis, as can be seen by reference to Figure 2. The guide member 248 extends horizontally in a direction parallel to the spin axis of the gyroscope, as can be seen by reference to Figure 6. An internally threaded weight 250 is mounted on a screw 252 mounted within suitable bearings in guide member 246. The shape of the weight 250 is such that it engages a portion of the guide member and is prevented from rotating relatively thereto. An adjusting head 254 is provided so that on rotation thereof, weight 250 will be moved up or downwardlyl along the length of screw 252. By rotating nut 254 I can thereby raise or lower the center of gravity of the gyroscope housing and assembly to a point where it will coincide with the horizontal plane passing through the tilt axis.

A second internally threaded weight 256 is mounted on a screw 258 carried in suitable vbearings in guide member 248. This weight is also so shaped as to cooperate` with the guide 248 so that it cannot rotate relative thereto. By means of an adjusting head 260, weight 256 can be moved back and forth along the lengthof screw 258. The screw carries a scale which is calibrated as a function of the 'cosine of latitude, and the weight is constructed such that it produces a moment about the tilt axis which is a function of the distance of the center of gravity of the weight from the tilt axis and of the magnitude of the weight. The resultant` torque will cause the gyroscope to precess in azimuth and is adapted to introduce a correction for the error introduced by precession due to the rotation of the earth.

The electrical connections of my assemblyare made -through the gyroscope housing and `are diagrammatically illustrated in Figure 7. A battery 262 has one of its terminals grounded at a point indicated by the reference character 264 and its other'terminal connected to a conductor 266 common to all circuits. A conductor 268 connects the contact arm 156 to the conductor 266. Conducting segment 148 on the bracket 142 is connected to one of the windings 270 of the gyroscope servomotor by la conductor 272 and the other conducting segment on bracket 142 is similarly connected to the other winding 274 of the servomotor by a lead 276. Both of the windings 270 and 274 are connected to a brush 276 of the servomotor, and the other servomotor brush 278 is grounded. It is to be noted that windings 270 and 274 connected respectively to conducting segments 148 and 150 are oppositely wound with the result that the current through one will befopposite to the current flowing through the other in the event that its respective conducting segment is contacted by contacting arm 156. As a result, the servomotor armature will rotate in one direction or the other depending upon which of the conducting segments is contacted by arm 156. A conductor 280 connects lead 266 with one of the brushes 60 of the gyroscope motor and also with winding 284 -of the gyroscope motor. Brush 62 of the gyroscope motor and the other end of winding 284 are grounded. A lead 288 connects conductor 266 with a brush 290 and the winding 292 of thecamera motor. Brush 294 and rthe other end of the winding 292 of the camera motor are grounded. Incandescent lamps 238 and 240 are likewise connected between conductor 266 and ground.

In use, the camera unit of the apparatus is loaded v with lm and 'the switch to the current supply of the p camera and incandescent lampsis closed. The scale on and the azimuth scale has been oriented to the desired direction, the units areassembled -as shown in Figure 'l and a lowering cable attached tothe eye 18. The-instrument is then lowered into the bore hole and its position in depth ascertained by a suitable calibrated lowering reel or by appropriate markings onthe lowering cable or both. These depthreadings are correlated with time by the synchronized watch at the surface.

The gyroscope rotor will tend to remain xed inspace. Friction about the tilt axis which isiminirnized by the use of ball bearings 64 and 66 will `produce a slight tendency for the gyroscope to precess in azimuth. The directional effectof the gyroscope,however, is suciently great to overcome the small precessional force occasioned by slight friction about'the tilt axis 'so'that my gyroscope will indicate substantially true `direction for alon'gperiod of time, much longer than bythe time consumed by lowering the instrument into a bore hole and removing it therefrom.

Since the azimuth scale on flange 1 28 is fixed in a plane normal to the axis of the bore hole, to-achieve correct indications in the passage of the instrument down the bore hole, I maintain thespin axis of the gyroscope in a plane normal to the axis of the instrument. Any inclination'of the instrument 'will cause the contacting point carried Iby the arm 156 to contact one or the other of the segments 14S or 150. This contact will complete the circuit of the gyroscope servomotor to apply a torque around the azimuth axis in a direction to process the gyroscope aboutthe tilt axis until the spin axis is in a plane normal to the axis of the instrument. VIt is to be noted that the axis of the instrument coincideswith the axis of the borehole. Since most `bore holes-have inclinations which lie generally in a single vertical plane, thc direction indicated by the azimuth scale will be a true direction, and it will be unnecessary toapply a correction for angularity between the azimuth scaleand the horizon as must be done when the spin axis is maintained in a plane normal to true gravity, as disclosed in my copending application, Serial No. 2,975. This correcting torque also overcomes the disturbing precessions due to friction in the gyroscope rotor bearings 40 and 42, which precessions tend to reduce thedircctional effect of the gyroscope.

The gyroscope rotor will always maintain a fixed position with respect to space. As the earth rotates, the spatial direction and the terrestrial direction in azimuth will have a relative movement, which at the equator amounts to l degrees an hour. That is, a point on the equator of the earth moves at'the rate of l5 degrees an hour so that the direction from the rst point to the pole will malte an angle of 15 degrees with the direction `tothe pole from that point one hour later. At intermediate points between the pole and the equator, this rate of change of direction with respect to space varies as a vfunction of the cosine of the latitude.

in order to enable my gyroscope to indicate a true terrestrial direction, it is necessary to precess the gyroscope in azimuth in a direction to 'compensate for the rotation of the earth. The direction of precession must be from the elevated pole toward west, since the earth rotates on its axis from west toward east. fFor example, if the location of the bore hole to be surveyed were 41 100 north, the rate at which the gyroscope must be processed in azimuth is ll1724" an hour. Such a precession in azimuth is produced by a torque applied around the tilt axis in a direction depending on the direction of spin. i accomplish this by means of the weight 256 and the scale 258. Scale 258 is calibrated so that when the weight is set to a value corresponding to the cosine of the latitude of a place, the weight will cause a torque about the tilt axis which produces a precession about the azimuth axis in the correct direction at a rate which is represented .by 15 cos L per hour. Since I attach my weight-256 on only one side ofthe gyroscope housing, it will be necessary to change the direction of rotation of` the gyroscope motor in south latitudes.

As the instrument is lowered into the bore hole, the Cardan ring 72 will'remain inthe alignment to which it was originally set. The azimuth scale 128 is carried by the'Caidan ring sothatit will remain in a fixed direction irrespective of axial rotation of the instrument during lowering. When the instrument is inclined due to deviations V,from the vertical in the bore hole, the base 202 which carries the scales rotates until the weight 232 occupies the lowgravityfposition. The roller 228 and a plate 224 produce frictional damping tending to stabilize the base in its low gravity position without undue oscillation. The arrangement is such that the friction damping is proportional tothe angle of inclination. The arrangement furthermore permits settling at low angles, since the friction in the upperbearing 192 is very small. The devices 212, 214 and 216 mounted on the base 202 will indicate the inclination and azimuth as is explained in detail in my copending application, Serial No. 2,975.

Where the bore hole is generally helical in shape, there will be a gyratory motion of the instrument around a vertical axis. Since the Cardan ring is insensitive to rotation about any axis at right angles to the Cardan axis, an errorv will be introduced by this gyratory motion. Referring now to Figures 8 and 9, the line A lnclicates the direction of true gravity, and the line A indicates the axis of the bore hole B. Since the Cardan ring axis is located with respect to the gyroscope housing and the instrument must align itself with the bore hole, the Cardan axis will coincide with the axis A. Let w represent the angular velocity around the axis of true gravity A and represent the angle between axis A and the direction of true gravity A. The angular velocity w which `tends to cause rotation about the axis A of true gravity may be represented as a vector in the direction of the axis A. This vector may be resolved into two components, w cos in the direction of the bore hole axis and w sin at right angles to the bore hole axis. The component w sin tends to cause rotation about an axis at right angles to the Cardan axis and will not induce any error in indicated direction since 'the Cardan is insensitive to forces tending to cause rotation about axes at right angles'to the Cardan axis. The components w cos however, tends to cause rotation about the `Cardan axis and will therefore induce an error. During any time t the angular displacement in the plane of the horizonowing to the vector w may be represented as wt. At the same time the angular displacement in the plane of the bore hole as a result of the vector w will be wt cos Let us assume that, in the absence of a velocity w, the reference direction selected lies along tilt axis. Let p represent the angle between the tilt axis and the true reference direction measured in the plane of the horizon in the presence of a velocity w. Let tp' represent the angle between the tilt axis and the indicated reference direction measured in a plane normal to the axis of the bore hole in the prescnceof a velocity w.

lf a measurement Yis made in the plane of the horizon in -the presence of the velocity w, at any time l the angle p equals wt. If the same measurement is made in a plane making an angle with the horizontal plane the angle equals wt cos 6. From Ythe foregoing it wlll lreadily be appreciated that the relationship between fp and p may be expressed as:

direction referred to the plane of the horizon. I The difference A between the true direction of maximum tilt and the indicated direction of maximum tilt will be the same as the deviation between the reference direction qa in the plane of the bore hole and the reference direction o in the horizontal plane. The difference in direction Agb, or the error of the indicated direction from true direction at any given point in the bore hole may be represented by:

Where p1 is an angle at the point in the borehole where the measurement is started and p2 is an angle at the point in the bore hole at which the measurement ends.

IIt will be seen that I have accomplished the objects of my invention. I have lprovided a self-contained apparatus for surveying bore holes in which the direction of the inclination of the bore hole is indicated Wi-th reference to an azimuth scale oriented by a gyroscope. I have provided the gyroscope with means for maintaining the spin axis in a plane normal to the axis of the bore hole so that for holes having inclinations generally in a single vertical plane, the direction indications will be true and require no correction. This means also maintains the maximum directional efect of the gyroscope by correcting for errors which would otherwise be introduced by processions resulting from friction in the gyroscope rotor bearings. In addition my gyroscope is automatically corrected for errors due to procession caused by the component of the rotation of the earth on its axis. My self-contained unit has means for indicating inclinations with respect to the vertical and a photographic unit for making a record of the amount and direction of the inclinations at predetermined times.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. It is further obvious that various changes may be made in details within the scope of the claims without departing from the spirit of the invention. It is therefore to be understood that this invention is not to be limited to the specic details shown and described.

Having thus described my invention, what I claim is:

1. In an apparatus for surveying bore holes, an elongated casing adapted to be lowered through the bore hole to take a position with its longitudinal axis parallel to the axis of the bore hole adjacent the positions of the casing as it moves through the bore hole, a gyroscope having a spin axis, a suspension for said gyroscope mounted in said casing and including a Cardan ring said suspension including means mounting said Cardan ring in said casing for pivotal movement about an axis extending in the direction of the longitudinal axis of said casing, said suspension including means mounting said gyroscope for pivotal movement about a tilt axis perpendicular to said spin axis and to the pivotal axis of the Cardan ring, means for maintaining the spin axis of said gyroscope in a plane normal to the longitudinal axis of said casing, said means comprising a pair of sectors symmetrically disposed with respect to a plane passing through the longitudinal axis of the casing, a contact point responsive to movement of the spin axis with respect to said casing axis, a servomotor having a shaft, means for connecting said servomotor shaft to said Cardan ring to apply a turning force to said Cardan ring about its pivotal axis, said contact point adapted to cornplete circuits to said servomotor through said sectors to energize said servomotor to precess said gyroscope about the tilt axis.

2. Apparatus as in claim 1 including additional means for applying a torque about the tilt axis of said gyroscope as a function of the cosine of latitude whereby to process the gyroscope about its azimuth axis to correct 10 for errors in terrestrial direction which would otherwise be introduced by the rotation of the earth on its axis.

3. Apparatus as in claim l including additional means for applying a torque about the tilt axis of said gyroscope as a function of the cosine of latitude whereby to precess the gyroscope about its azimuth axis to correct for errors in terrestrial direction which would otherwise be introduced by the rotation of the earth on its axis, said last named means comprising a weight, means for carrying said weight for movement toward and away from the tilt axis of said gyroscope and means for moving said weight.

4. Apparatus as in claim l including a housing for said gyroscope, a guide member mounted on the housing and a lweight carried yby said guide member for movement therealong, said weight providing means for adjusting the center of gravity of said gyroscope and housing to a point where it coincides with the horizontal plane passing through the tilt axis.

5. Apparatus for surveying bore holes comprising in combination an elongated casing adapted to be lowered through the bore hole to take a position with its longitudinal axis parallel to the axis of the bore hole adjacent to the position of the casing at all positions of said casing as it is being moved through the bore hole, a gyroscope having a spin axis, a suspension for said gyroscope mounted in said casing andpincluding a Cardan ring said isuspension including means mounting said Cardan ring for pivotal movement about an axis -extending in the direction of the longitudinal axis of the casing, said suspenpension including means mounting said gyroscope in said Cardan ring for pivotal movement about a tilt axis perpendicular to said spin axis and to the pivotal axis of the ACardan ring, a servomotor having a shaft, means connecting said vservomotor shaft to the Cardan ring to apply a turning force to said Cardan ring about its pivotal axis and contact means responsive to movement of the spin axis with respect to the longitudinal axis of said casing to start said servomotor, said servomotor rotat- V ing the Cardan ring to maintain the spin axis normal to the bore hole axis.

6. Apparatus for surveying bore holes as in claim 5 including a housing for said gyroscope and wherein said contact means includes a pair of conducting sectors fixed on said Cardan ring, a contact arm pivotally mounted on said Cardan ring and a parallel motion connection between said contact arm and said gyroscope housing, said contact arm resting in its normal position between said sectors when the spin axis is normal to the bore hole axis, said parallel motion connection moving said contact arm to contact one of said segments when the spin axis moves relative to the bore hole axis.

7. Apparatus for surveying bore holes as in claim 5 including a housing for said gyroscope and wherein said contact means includes a pair of conducting sectorsrixed to said Cardan ring, a contact arm pivotally mounted on said Cardan ring and a parallel motion connection between said contact arm andsad gyroscope housing, said servomotor including a pair of oppositely Wound windings, said pair of sectors 'being connected to respective windings.

8. Apparatus for surveying bore holes as in claim 5 including means for applying a torque about the tilt axis of said gyroscope as a function of the cosine of the latitude of the bore hole location. t

References Cited in the tile of this patent UNITED STATES PATENTS 1,311,768 Gray et al. July 29, 1919 1,959,141 Sperry May l5, 1934 2,220,055 Fischel et al Oct. 29, 1940 2,381,438 Curry Aug. 7, 1945 2,462,541 Norden Feb. 22, 1949 FOREIGN PATENTS 132,688 Sweden -..n -7---" Aug. 14, 19,51

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