US2830791A - Earth penetrating apparatus - Google Patents

Description

E. W. SMlTH EARTH PENETRATING APPARATUS April 15, 1958 2 Sheets-Sheet 1 Filed Feb. 12, 1954 w 6 4. 4 W 3 w ww w v d z w i W zw PF E. W. SMITH EARTH PENETRATING APPARATUS April 15, 1958 2 Sheets-Sheet 2 Filed Feb. 12. 1954 v INVENTOR.V w s \\mw W a v fal w im. assarsi Pafenteol Apr. 15, 1958 EARTH PENETRATENG APPLRA'EUS Edward W. hnith, l'vielrose Highlands, Application February 12, 1954, Serial No. 4839,363

2Clahns. (El. 255-4l.6)

This invention relates to earth penetrating apparatus and more particularly to dlling tools adapted for use where cable tools have custornarily heretofore been employed.

As is well known, particularly in the oil and gas well drilling art, many types of subterranean formation can satisfactorily be penetrated only by striking the formation repeatedly with weighted bits. These bits are suspended by exible cables from the end of a walking beam and are raised and lowered two to three feet by reciprocation of the beam. This method of drilling is cumbersome and slow since the frequency of impact cannot exceed about 50 strokes per minute in the initial stages of drilling and 25-30 as the depth of the hole increases. Furthermore, particularly as the hole becomes deeper, the stretch and whip of the cable cause the bit to rise and fall out of phase with the rising and falling of the walking beam so that it is quite possible for the rig to operate without making any hole at all. In any event, it is obvious that Cable tool drilling as presently practised is severely limited both in force and frequency of impact brought to bear on the area being drilled.

Vlt has long been recognized that the rate of penetration of hard formations can be increased more or less in direct proportion to the increase in force and frerguency of impact. See, for example, the articie commencing page 245 in the Oil and Gas Journal for November 16, 1953. However, prior to my invention, so far as l am aware, no satisfactory means have been devised thereby to provide forceful, rapid impacts at the bottcrn of a deep well of the size required for the practicable recovery of gas and oil.

lt is the principal object of my invention to provide a novel apparatus for impact drilling capable of delivering impacts at a frequency far greater than is producible by conventional apparatus.

lt is a further object of this invention to provide a novel impact drilling apparatus which is self-contained and is consist-ently maintained adjacent the formation being drilled.

lt is another object of this invention to provide novel means for impact drilling without raising and dropping the drllling tool assembly, thereby making unnecessary the use of heavy reciprocating surface equipment and greatly diminishing the wear on the supporting Cable.

My invention can best be understood and appreciated from the following description taken in connection with the accompanying drawings in which:

Fig. 1 is a view of the apparatus partly in cross section,

Fig. 2 is a cross sectional detail view of the mechanism for driving the bit taken between lines A--A and B-B of Pig. 1, and

Fig. 3 is a cross sectional view of another embodiment of the apparatus of rny invention.

The apparatus shown in Pig. l comprises a large mass element w and a small mass element 12 connected together by a steel red .1:4 having a high modulus elasticity. Any convenient means for securing rod 14 to the mass elements may be employed. As illustrated, the rod is threaded at each end and is screwed directly into small mass element 12 at one end and into a cap or rope socket 16 which is itself threaded and screwed onto mass element ltl, the latter being bored to accommodate the rod. Attached as by threads to the opposite or lower end of mass element 110 is a tubular member or sleeve 18 of sufficient length to enclose rod 1d completely and to encompass at least a portion of mass element 12, thereby acting as a guide for its reciprocation and as a dam to seal the interior as hereinafter discussed. At bit 20 of suitable shape is attached to mass element 12 and a cable 22 for maneuvering the apparatus in the hole is secured to rope socket 16 in conventional manner.

lt will be noted that the above arrangement then consists essentially of a mass element 12 connected by a resilient rod M to a second and much larger mass composed of the tubular section 18, mass element 10, and cap 16. The system is set in motion by exerting a motive force on mass element T12 to either stretch or compress resilient rod 1121-. Upon release of the force the red tends to resume its position of repose but overtravels in so doing because of the effect of the masses attached to its ends. lf just sulicient force is applied to element 12 to overcc'me inertia losses and is applied at the resonant frequency of the system, this element will be maintained in Vertical oscillation of selected amplitude. The rcsonant frequency of the system is, of course, determined by the characteristics and dimensions of the elements thereof, notably by the stifiness of rod 14 and the magnitude of the respective masses of elements lt) and 12 Vwith their associate accessories.

It is by means of the oscillation of mass element 12 With its Cutting tool or bit Ztl that impacts are delivered to the structure being drilled. Means for initiating and maintaining oscillation at he resonant frequency of the system is illustrated in Fig. 2. This consists of an electromagnetic element consis'ting of an annular armature 24 secured around vrcd M adjacent small mass 12 and concentric electrornagnet cr field piece 26 securcd .to the wall of sleeve E8. The opposing faces of the armature and of the poles of the magnet are parallel to and out of contact with one another and are set at an angle to the axis of motion determined according to conditions hereinafter described. Alternatively, the components of the electromagnetic element may be reversed, i. e., the armature may be secured to sleeve 18 and the magnet to rod 14.

While any convenient electromagnetic construction may be employed in the apparatus of my invention, including a series of separate units secured around rod and sleeve respectively, I have found the construction described above the most satisfactory, particnlarly when the ring elements are composed of a plurality of L-shaped laminations arranged radially in adjoining annular series. An electrical winding around magnet 26 is provided in conventional manner and occupies space 28 between armature 24 and magnet 26.

Although both elements of the electrornagnet may be secured directly to rod and sleeve respectively, it is advantageous to employ base rings 3d and 32 as mountings for ease in assembly and disassembly.

There must of course be an air gap between the poles of magnet 26 and the armature block 24 so that one eleient may move relative to the other. Then when an electric current is passed through the magnet winding in space 28 a magnetic flux will be established across the air gap. By reason of the angular arrangement of the .opposing faces of the electrornagnetic elements, rod 14 will be stretched under the influence of the magnetic attraction, causing relative motion between masses and 12.

As has already been explained, the mass element 12 has a natural period of oscillation which depends on its magnitude, the stilfness of rod E4 and the magnitude of the hacking mass. Therefore, if the frequency of the magnetic impulses applied across the airgap between the field and armature elements is made the same as the natural period of vibration of mass 12 the amplitude and force of the vibration of mass 12 may be controlled by varying the amount of current passed through the Winding.

By utilizing the mechanical resonance characteristics of the above arrangement the number of impacts given by the cutting tool to the formation can be enormously increased over what would normally be possible. As an example, if ordinary 60 cycle alternating current is passed through the winding it can be used to maintain synchronous vibratory motion of element 12 at the rate of 7200 vibrations per minute. and the stiffness of rod 14- are' so chosen as to give the arrangement a natural frequency of 7200 vibrations per minute also, very substantial impacts at this frequency will be 'delivered to the formation.

Mention has already been made of the fact that the airgap in the magnetic circuit makes an angle with the center line of rod 14 so as to give a downward component of pull to stretch rod 14 periodically. Bearing in mind that at maximum practicable flux density of 60,000 lines per s. in. the effective distance between pole and magnet cannot exceed about 0.055 in., it will be evident that the face angle of such components must largely be determined according to the extent of motion required. Thus, for an amplitude of motion of about 1A;

inch and less a face angle of about degrees from the rod axis appears to be Optimum although not critcal. So it is only necessary that the airgap not exceed 0.055 in., that the faces of pole and armature do not strike together and that the magnetic force is sufficient to cause elongation of the rod as described above.

In considering the above design it might be supposed that difiiculties Would be encountered with breakage of rod 14 due to the high frequency alternating Stress being applied to it. Actually this is not the case if a good grade of steel is used and the maximum fiber stress is not allowed to exceed about 10,000 lbs./sq. in. for suitable readily available materials of construction. This requires in effect that the length of rod 14 should be at least approximately 3000 times the desired amplitude. The above value for maximum fiber stress has been determined from experience with vibratory systems utilizing conventional steel rod of good grade. For any given stress the required minimum length of rod may readily be determined from the established formula Pl AE in which d is the defiection, P the force applied, l the length of the rod, A .the cross sectional area of the rod and E is Young's modulus of the material of the rod, e. g., million lbs./sq. in. for steel.

The natural period of vibration of such a system as has been described above is determined by the relationship where is the frequency in cycles per second, u is the stifness of rod 14 expressed in dynes per centimeter, and m and m' are respectively the masses in grams of element 12 and hacking mass 10 with its associated accessories.

It 'should also be noted that in a vibratory system such as has been outlined above both mass 12 and the backing mass (10-16-13 and a portion of rod 14-) will vibrate in opposite directions and at amplitudes which are Then if the mass of element 12 LR inversely Proportional to their masses. Therefore if the mass of the hacking mass is made say 10 times the mass of element 12 then the hacking mass will as a practical matter not be moving at all and no vibration will be applied to the supporting cable.

Under such conditions the above equation practically reduces to f l u 27.- 'm

where M is the mass of element 12 in metric units and the stiifness u is expressed as before in dynes per centimeter. It should also be remembered in computing the mass of element 12 that approximately 1A of the mass of rod 14 should be considered as forming part of the mass of element 12.

Referring again to Fiig. 1 it will be noted that element 12 is fitted with gaskets 34' of any suitable type such as the so-called O-ring gaskets which will serve to seal the interior of the unit from the entrance of liquid, and the electrical conductors needed to carry the current to the unit may well be incorporated in the cable 22.

The embodiment of the apparatus shown in Pig. 3

- functions according to the same principles as those above described except that instead of one mass being substantially stationary as for the apparatus of Fig. 1, both masses are of substantially equal mass and both have the same amplitude of motion. Thus a considerably longer tubular member 40 is secured to cap 16. Two masses 42 and 44, the latter including the bit 20, are connected by a resilient rod 156 secured at its nodal point by bracket 48 to tubular member 40. Oscillation of the system is initiated and maintained by the mechanism previously described and illustrated by Pig. 2. Gaskets 4 secured around mass 44 perform the same function as previously described, i. e., to seal the interior of the unit.

In operation, oscillation is initiated by the electromagnetic element working on rod 46 adjacent mass 44. As the rod stretches downwardly from supporting bracket 48 it also stretches upwardly to cause an opposite and equivalent motion of mass 42. At resonant frequency both masses reciprocate with an equal amplitude of travel.

It will be clear from the above description that the present inventon provides a novel and effective method and means for imparting very high frequency impacts to the formation to be drilled and that this is accomplished Without the usual raising and lowering of the cable so that this latter element is no longer the limting factor in drilling rate and the Operating life of the cable is also enhanced by the reduction in the stresses to which it is normally subjected.

A representative apparatus constructed according to this inventon may have the following dimensions and characteristics.

For a frequency of 7200 strokes per minute and 10 horsepower input, mass 12 would weigh about lbs., rod 14 would be 376 inches long and have a diameter of 1.33 inches and the total length of stroke would be 1A: inch, or 1/8 inch in each direction beyond the position of rest.

Having thus described my inventon, I claim:

l. An impact bit drilling tool comprising two masses of unequal size connected together by a resilient rod having a high modulus of elasticity, the larger of the two masses being secured to a supporting cable, and the smaller mass having a bit attached thereto being secured only to the connecting rod, a tubular housing secured to the larger mass and extending to enclose the smaller mass with a slip fit for a portion of its length and, electromagnetic and armature elements adjacent the smaller mass, one lof said elements being secured around the resilient rod and the other of said elements being concentrically secured to the inner wall of the housing, the faces of said elements being parallel to and out of contact with one another and sloping at an angle to the axis of the tool whcreby energization of the electromagnet at a frequency synchronous with the resonant frequency of the system of masses and connecting rod will cause longitudinal vibraton of the small mass at such resonant frequency. 1,047,625 French Dec. 17,

2. The apparatus of claim 1 in which the faces of the :3, 1,284,930 Roberts Nov. 12, 1918 electromagnet and armature slope at an angle of about 1,567,197 Schmidt Decv 29, 20 degrees from the axis of the tool and are spaced apart 1,966,446 Hayes July 17, no more than about 0.055 inch at their positions of maxi- 2,241,364 Hulbert May 6, mum separation. 2,672,322 Bodine Mar. 16,

References Cited in the file of this patent UNITED STATES PATENTS

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