US2684835A - Apparatus for drilling well boreholes - Google Patents

Description

y 27, 1954- I '1". v. MOORE- 2,634,835

. APPARATUS FOR DRILLING WELL BOREHOLES Filed July 26, 1950 I -i CYLIMD-QICAL.

- ELEMENT Q T Azme.

' Z PISTON HEAD 4 Poms FIQ-Q a 5 :DQIVE. BQSHIMG A Q, TOOL QJonuT E ox No'z'z-ha HyQQ Thomas V. Mo orc Unvemaor abtaorneq Patented July 27, 1954 APPARATUS FOR DRILLING WELL BOREHOLES Thomas V. Moore, Manhasset, N. Y., assignor to Standard Oil Develo ration of Delaware pment Company, a corpo- Application July 26, 1950, Serial No. 175,932

1 Claim. 1

The present invention is concerned with an improved apparatus for drilling well bore holes. The invention is particularly concerned with a novel bottom hole assembly by which it is possible to employ an improved method of exerting the necessary force on the bit during the drilling operation. In accordance with the present in vention the required force on the bit during a drilling operation is secured by utilization of the head of the drilling fluid within the drill stem. The art of drilling well bore holes into subterranean areas of the earth has been extensively developed. A wide variety of drilling bits, associated apparatus and various techniques have been utilized. However, conventional techniques for rotary drilling apply the required force to the bit by allowing the weight of the drill string to partially rest on the bit. This process while entirely satisfactory has a number of inherent difiiculties. For example, part of the drill pipe may be in compression resulting in buckling of the pipe which in instances causes the hole to deviate from the vertical. Furthermore, the stress induced due to the buckling and unbuckling oi the compressed pipe results in corrosion fatigue. To reduce this difiiculty, drill collars, which are heavy lengths of pipe, are used. These are expensive, and are subject to frequent failures. Another disadvantage is that the friction against the walls of the hole causes the drill pipe to Wind up with the result that a substantial amount of bouncing of the bit occurs on the bottom of the hole. This aggravates the wearing of the cutter hearings in rock bits. It has now been discovered that these disadvantages are overcome providing the force on the bit is secured by a method other than by allowing the weight of the drill string to partially rest on the bit. The improved method of the present inven tion is secured by utilizing a novel bit assembly wherein the force on the bit is secured by the utilization of the head of the drilling fluid in the drill stem.

The present invention may be readily understood by reference to the drawing illustrating one embodiment of the same. Figure 1 of the drawing illustrates the apparatus of the present invention attached to the lower end of a drill string disposed in the earths substrata in a well bore. Figure 2 is a cross-sectional view taken along the line II-II of Figure 1. Referring specifically to the drawing the lower end of a drill string I is shown positioned within well bore hole 8. The bit assembly of the present invention is shown attached to the end of drill string l 0. The assembly comprises a cylindrical element l which contains positioned therein a piston assembly. The piston consists of a piston head 2 which contains suitable packing elements I to prevent the flow of fluid around the piston head. A piston rod 3 extends downwardly through a drive bushing 5 and contains at the lower end thereof a tool joint box 6 which contains attached thereto a suitable bit 9. Cylinder l contains ports 4 at the lower part permitting passage of fluid from the area between the well bore hole and the cylinder, and the area between the piston rod and the inner surface of the cylinder. The pressure below the piston is thus relieved, resulting in a net downward force on the piston. Nozzles I l are shown in the bit. A crosssection of the apparatus through section IIII is illustrated by Figure 2.

While the drawing has been described utilizing a drag or fishtail bit, it is to be understood that the present invention may be also utilized when employing other bits, as for example, rock bits and the various types of jet bits.

In operation the pressure of the mud or other drilling fluid on the piston exerts a force on the bit through the piston rod or lower Kelly joint. This joint, as shown in the cross section, Figure 2, is fluted or square in order that sufiicient torque may be applied to turn the bit. This permits the entire string of drill pipe to hang in tension. The control of the weight on the bit is secured first by the size of the nozzles in the bit and second by changes in the mud velocity.

This invention is particularly valuable when used with the so-called, jet bits which have recently been developed. These jets are designed with small nozzles through which an extremely high velocity mud stream is passed. Bits of this kind have been found to drill much faster and more economically than the conventional bits. In order to obtain the optimum mud velocities when using this type of bit, a pressure differential through the nozzle of several hundred pounds is commonly employed. Bits of this kind generally employ nozzles of from to 1" in diameter. In this invention, the nozzle diameter would be used as a major factor which would determine the weight to be carried on the bit. By way of example, suppose that the inside diameter of the cylinder were 6" and that it were desired to hold a force on the bit of 20,000 lbs, the cross-sectional area of the cylinder would be approximately 28 square inches and the pressure differential across the cylinder would be approximately 700 lbs. Assume that two nozzles are Force OnBit (Thousands of Lbs.)

Nozzle Diameter (each) (For 2 Nozzles) A 1% is g G. P. M. Mud Circulated:

The 6.'.-inside diameter cylinder would probably beused'when drillingholesof a diameter ofapproximately 9 inches. For drillinglarger diameter holes, it would bepossible to use a cylinder of largerdiameter and likewise smaller holes would demand that a smaller cylinder be used. The force on the bit,'of course, for a given rate of circulation and nozzle size will be directly proportionate to the cross-sectional area of the cylinder.

The-invention. is. broadly concerned with the utilization of theheadfof the drilling fluid Within thedrillv steinto secure the required force on the bitduring a drilling operation. The invention may be used'when. employing any type of bit but is particularlylefiective with jet bits, which bitsareedesigned with relatively small nozzles in order to secure ahigh velocity mud streamthroughthe bits Fromtheabove it is apparent that the specific drilling conditions employed .whenutilizingthe present invention will be a function of various related conditions, as for example, nozzle size; density. of the mud; the-rate otrnud circulation; and the diameter of the drilling-stemused. These factors vary ap preciablydependingupon the formation being penetrated;' the diameter of well bore hole desi.red,-as well as,.upon otherdrilling conditions. With other factorsmaintained constant, simple calculations'of the force. exerted on the bit assembly may be made bynoting that the pressure on the piston is roughly proportioned to the square of .the velocity ofv themud through the nozzles and inversely proportioned to the specific weight of the. mud. The nozzles diameters are generally in the range from about to l. The diameters, however, will vary depending upon the nozzles in the bit .whichusually vary from 2 to 4 The diameter of the drill string may vary from 2 to 7" and. higher, although usually the diameter is in the range from 4 to The density. ofv themud generally is in the range from 9. to 16--lbs..per gallon, although the density may, under certain conditions, be without this range. The quantity of mud circulated is usually in the range from 200 to 1000 gallons per minute. The desired force in the bit, likewise, may vary appreciably as for example in the range from 4,000 to 40,000 lbs. and higher.

A preferred method of operating infaccordance with the present 'inventiom is that the driller lowers the drill pipe until such time as a slight reduction in the reading of the weight indicator at thesurface-indicates that the weight of the drills'tring is resting in part on the lower Kelly joint. The driller then raises the drill string a small distance "which assures the driller that the weight of thedrill pipe is not resting on the bit. The drillerthen continues to drill in normal fashion tor-such length of time as the driller might expect is required to make an amount of hole somewhat less than the maximum stroke of the lower Kelly joint. This will vary from a few minutes to an hour'ortwo depending on the hardness of the formation being drilled and the progress being made. The driller then repeats the operation and in this way it is possible to makesure the-tithe drill pipe is always hanging in tension throughout its length and that the bit is'on .the'bottom with the weight required.

Having described the invention, it is claimed:

Improved'drill bit assembly adapted to be attached to the: lower endof adrill string comprising a cylindrical. element, the upper end of which is adapted to be attached to the lower end of saididrill string; a: drive bushing located within and attached to the lower end of said cylindrical element, apiston head element within and movable withrespect to-said cylindrical element above the said drive bushing, a piston rod elementattached to said piston head element, said piston rod element extending below the lower end of said cylindrical element and through said drive bushing, aplurality'ci ports passing through said cylindrical element immediately above the drive bushing, a drill bit characterized by'containing a plurality of restricted nozzle passageways attached to the lower end: of said piston rod element, said piston rod element being characterized by being hollowandpreviding a conduit from'the area above said piston head to said nozzle'passageways.

References Cited-in thefile or" this patent UNITED STATES PATENTS Number Name Date 1,357,554 Hughes Nov. 2, 1926 1,660,033 Braswell Feb. 21, 1928 1,686,945 Abercrombie Oct. 9, 1928 1,767,350 Crowell June 24, 1930 1,844,257 Lincoln Feb. 9, 1932 1,900,932 HolleStalle Mar. 14,1933 1,905,497 Peters Apr. 25, 1933 2,300,805 Pew Nov. 3,1942

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