US3384189A

US3384189A - Drilling method and compositions therefor

Info

Publication number: US3384189A
Application number: US516400A
Authority: US
Inventors: Joseph L Pekarek; Paul W Schaub
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1965-12-27
Filing date: 1965-12-27
Publication date: 1968-05-21
Anticipated expiration: 1985-05-21

Description

May 21', 1968 J. L. PEKAREK ET AL.

A DRILLING METHOD AND CQMPQSITIONS THEREFOR Filed Dec. 27, 1965 Q %N\ 0000 v mm an vw x unh- //V YEA/T0195. JOSEPH L. PEK/I/PEK PAUL W SCH-4M5 United States Patent O 3,384,189 DRILLING METHOD AND COMPOSITION I I THEREFOR Joseph L. Pekarek and Paul. W. Schaub, Penn Hills Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa a corporation of Delaware Filed Dec. 27, 1965, Ser. No. 516,400 8 Claims. (Cl. 175- 67) ABSTRACT OF THE DISCLOSURE This invention relates to the drilling of wells and more particularly to an improved drilling process in which a stream of drilling liquid containing suspended ferrous abrasive is discharged at extremely high velocities against the bottom of a borehole to drill through hard formations.

Improvements in conventional rotary drilling processes have greatly increased rates of drilling in soft formations and formations of medium hardness. To a large extent, the improvenients have resulted from more powerful equipment which allows the application of greater bit weights to the cone or drag-type bits. One type of bit that is used widely to drill soft formations is referred to as the jet bit. It differs from the usual bit principally in directing the drilling mud against the bottom of the hole to clean the bottom of the hole rather than over the surface of the cutters to keep the cutters clean. The purpose of jet bits is to improve the removal of cuttings broken from the formation by the mechanical cutting elements of bits rather than to cut grooves in the forma tion being drilled; however, some penetration of soft formations by the stream of drilling mud may be responsible for some of the increase in drilling rate. Quick removal of the cuttings from the bottom of the hole reduces shielding of the bottom of the hole from the bit by the cuttings and reduces regrinding of cuttings. The conventional jet bits have been ineffective in increasing the rate of drilling in hard formations.

Recently, a novel hydraulic jet drilling process which is effective in increasing the rate of drilling of hard formations has been developed. In the hydraulic jet drilling process, an abrasive-laden liquid is discharged at extremely high velocities against the bottom of the hole to cut the formation being drilled and remove cuttings from the hole. In the hydraulic jet drilling process, substantially all of the penetration of the rock being drilled is accomplished by the abrasive-laden stream, and mechanical removal of rock from the bottom of the hole by cutting elements on a bit is restricted to removal of ridges which may extend upward between grooves cut by the high velocity streamJIn the hydraulic jet drilling process, the weight applied to the nozzle head, referred to for convenience as the bit, is approximately one-fourth, or less, of the weight applied in comparable conventional drilling methods. Hydraulic jet drilling in hard formations is substantially faster than drilling with conventional rock bits but is still relatively slow compared to drilling in soft formations and further increases in hydraulic jet drilling rates are desirable.

3,384,189 Patented May 21, 1968 The high velocity at which the abrasive-laclen stream passes through nozzles in the bit causes rapid erosion of the nozzle with a resultant increase in the diameterof the orifice in the nozzle. Because the rate of drilling is highly dependent upon the velocity at which the abrasiveladen stream strikes the bottom of the borehole, the reduced velocity resulting from enlargement of the nozzle orifice reduces the drilling rate and makes it necessary to replace the bit. In deep wells, a substantial part of the rig time can be used in making the round trips necessary to replace the bit. For this reason, it is important to reduce the rate of erosion of the nozzles.

' -When the high velocity stream of abrasive-laden liquid strikes the formation being drilled, the abrasive, as well as the formation, is subjected to severe stresses. When sand is used as the abrasive in the drilling, approximately one-half of the sand is broken up in a single pass through the bit into fine particles unsuited for further use. The large amounts of abrasive consumed causes the abrasive to be an important part of the .cost of the hydraulic jet drilling process. It is desirable to use an abrasive that breaks up only to a negligible extent on striking the bottom of the borehole and, hence, can be reused to reduce the abrasive requirements.

This invention resides in a method of drilling hard formations by discharging a stream of a drilling liquid laden with ferrous abrasive at an extremely high velocity against the bottom of the borehole. We have found that if the hardness of the ferrous abrasive exceeds about 55 on the Rockwell C scale, an increased rate of cutting hard formations can be attained with a reduced rate of erosion of the nozzles through which the abrasiveladen liquid is discharged against the bottom of the hole. The ferrous abrasive has a further advantage in hydraulic jet drilling processes resulting from the very low rate of break-up of the grit to sizes not effective in the hydraulic jet drilling process.

The single figure of the drawings is a diagrammatic illustration, partially in vertical section and partially expanded, of apparatus for hydraulic jet drilling of a well with a liquid having ferrous grit suspended in it.

The ferrous abrasive used in the hydraulic jet drilling process of this invention may be either cast iron par-ticlcs or steel particles readily available as commercial products used in the cleaning and treating of metal surfaces. Ferrous abrasives can be manufactured by blowing a high velocity stream of air or steam against molten cast iron or steel to separate globules of the metal. The globules are blown into water where they are chilled. The solidified particles are heat treated and graded by size. Grit is prepared by crushing shot .and then heat treating the granular particles and grading them according to size. Either angular granular particles, referred to as grit, or rounded particles, referred to as shot can be used, but the shot is preferred because faster cutting rates are obtained with shot. Ferrous abrasives having a Rockwell C hardness of at least about 55 give much higher drilling rates than sand. Ferrous abrasives of lower Rockwell C hardness have an advantage over sand of a much lower particle break-up rate, but have no advantage over sand in drilling rate. 'In some instances the softer ferrous abrasives are even slower drilling than sand.

The ferrous particles used in this invention have a size in the range of 7 to mesh. The drilling rate is faster with the particles of larger size, and it is desirable to use the largest particles that will pass through the nozzles in the drill bit without plugging the nozzles. In nozzles having a minimum orifice of As-inch di ameter, ferrous abrasive particles having a size in the range of 16 to 50 mesh are preferred. The maximum particle size of the abrasives is also limited by the ability of the high-pressure pumps to handle large particles. Particles of ferrous abrasives smaller than 40 mesh, such as 50-80 mesh, will cause drilling rates higher than can be obtained with 20 to 40 mesh sand and can be used. Because of the low rate of break-up of the ferrous abrasive particles and the effectiveness of particles as small as 80 mesh in hydraulic jet drilling processes, the ferrous abrasive can be recirculated for many cycles in the drilling operation.

The ferrous abrasive particles are suspended in a drilling liquid in a concentration of /2 to 6 percent, preferably 1 to 4 percent by volume. Higher concentrations increase the amount of abrasive in the system and the amount broken into fines without a corresponding increase in drilling rate. Lower concentrations of abrasive markedly reduce the drilling rate. The drilling liquids used to suspend the ferrous abrasive must have a relatively high gel strength and viscosity to remove the abrasive from the hole during the drilling operation and to prevent settling of the abrasive in the borehole when it is necessary to stop the circulation of the drilling liquid. A suitable drilling liquid is an invert emulsion of water and diesel oil containing 30 to 60 percent oil, with the oil in the continuous phase. A preferred drilling liquid is an invert emulsion containing 40 to 50 percent diesel oil. The emulsion can be stabilized by, for example, a sulfurized potassium soap of tall oil containing 5 percent sulfur. Other emulsifiers, such as polyhydric alcohol fatty acid esters, sulfated sperm oil soaps, and polyvalent metal soaps f rosin acids can be used. The pH of the drilling liquid is adjusted to the range of 9 to 10 by the addition of alkaline material such as caustic soda. Another suitable drilling liquid is an aqueous dispersion of bentonite containing 2 percent bentonite and 1 to 2 percent Flosal, a fibrous asbestos material, Hydraulic jet drilling with a ferrous-abrasive-laden drilling liquid is not limited to the use of any particular drilling liquid as long as the drilling liquid has adequate gel strength and viscosity to give satisfactory suspension of the abrasive particles.

For purposes of illustration, a hydraulic jet drilling process will be described in which 20 to 40 mesh particles of Indogrit, a cast iron granular material, manufactured by Industeel Company of Pittsburgh, Pa., is suspended in an invert-emulsion drilling liquid containing 50 percent diesel oil. The drilling liquid is delivered by high pressure pumps 10 through a line 12 into the drill string 14 of a drilling rig 16 suitably equipped to rotate the drill string in the borehole. The drilling liquid is pumped at a high rate downwardly through the drill pipe 14 and discharged against the bottom 18 of the borehole 20 through nozzles Aa-inch in diameter in a bit 22 at the lower end of the drill pipe. Drill pipe 14 is rotated at a rate of at least r.p.m. during the drilling. For effective drilling by the hydraulic jet drilling method, the drilling liquid must be discharged against the bottom of the borehole at an extremely high velocity of at least 500 feet per second, and preferably at least 600 feet per second, from nozzles having an outlet A-inch to 1 /2 inches from the bottom of the borehole. Control of the spacing between the bottom of the hole and the nozzle outlets is obtained by means of stand-off bars on the bottom surface of the bit. In a typical hydraulic jet drilling operation four pumps driven by motors supplying a total of about 2,000 to 2,400 horsepower pump 450 to 600 gallons per minute of the drilling liquid at a pressure of 5,000 p.s.i. to the drill pipe 14 for delivery to a bit head having a plurality of nozzles, for example, 10 to nozzles /s-inch in diameter, having outlets approximately /2-inch from the bottom of the borehole.

The drilling liquid and entrained cuttings pass upwardly through the borehole and are discharged the-refrom through line 24 and delivered to a shale shaker 4 26 in which the oversize cuttings are removed from the drilling liquid. Ferrous-grit-laden drilling liquid is delivered through line 28 to a bank of cyclone separators 30 in which abrasive particles are separated from the liquid and delivered as an underfiow through line 32. Overflow from separators 30 is delivered through line 34 to a second bank 36 of separators in which further clean-up of ferrous-grid particles from the drilling liquid is accomplished, and the ferrous-grit particles separated in separators 36 are discharged as underflow through line 38.

Overflow from separators 36 contains less than 0.2 percent particles larger than 200 mesh and is delivered into a storage tank 40. Ferrous-grit-free drilling liquid is withdrawn from tank 40 through line 42 and passed through another bank of cyclone separators 44 for removal of fine solid particles of 200 mesh size and smaller to reduce the concentration of larger than 200 mesh particles to a trace and control the density of the drilling liquid. Clean drilling liquid from the separators 44 is delivered through line 46 to the high pressure pumps 10. Abrasive from

lines

32 and 38 is mixed with the clean drilling liquid for recirculation in the well. Because of the low rate of break-up of ferrous abrasives, removal of fines from all .of the liquid circulated in the borehole is not required and drilling liquid may be delivered fiom the shale shaker directly to pumps 10 through a suitably valved bypass line 48. Make-up abrasive is added to the system at shale shaker 26 from a storage hopper 50.

The ferrous grit particles are effective in increasing the drilling rate over that which is obtained with other abrasive particles such as sand. A series of tests was made in which the abrasive-laden drilling liquid was discharged from a single nozzle onto a block of hard black granite rotated in a horizontal plane about an axis 1 /2 inches from the bit axis at a rate of about 30 r.p.m. The outlet of the nozzle was maintained /2-inch from the original rock surface during the tests. The tests were made at a nozzle inlet pressure .of 5000 p.s.i. and a drilling liquid velocity of approximately 776 feet per second. Each test was continued for a period of 20 seconds after which the depth of the cut was measured to give an indication of the drilling rate. Test runs were made on drilling liquids containing different concentrations of 20-40 mesh cast iron and steel grit and shot of different Rockwell C hardness and with sand and alumina of the same size. The results are presented in Table I.

TABLE I. Penetration of Black Granite, Inches Abrasive Concentration,

percent by Volume Run Material Rockwell G No. Hardness 1% 1%% 2% 4% 1 Cast Iron Grit 35 25 3 .4 .5 (3%) 2--. Steel Grit 42-50 .25 .28 .32 5 (5%) 3 Sand 7. 0 (M0115) 3 42 7 (3%) 4. Cast Iron Grit". 55-60 1. 5 1. 7 1.8 2. 5 5. Stool Grit. -65 1.1 1. 1. 8 2. 4 6. Cast Iron Sh 55-60 1. 8 2.05 2. 4 3. 5 7. Steel Sh0t 60435 1. 55 2. 1 2. 55 4. 3 8 A1203 9 (Mohs) 6 0. 8 1. 0 1. 4

As shown by a comparison of Runs Nos. 6 and 7 with Run No. 3, drilling rates approximately five times the drilling rate with sand can be obtained wit-h ferrous shot having a Rockwell C hardness of at least 55. Ferrous grit of Rockwell C hardness greater than 55 gave drilling rates three times the drilling rate with sand. Softer ferrous abrasives gave drilling rates actually lower than sand, as shown by Runs Nos. 1 and 2. Hardness is not the sole factor in hydraulic jet drilling. Both sand and A1 0 are harder than the iron or steel but result in slower drilling rates.

During the cutting test described above, the drilling liquid samples were caught, diluted, screened, dried, weighed, sieved, and reweighed. These data were then reduced to an average percentage of particles larger than 40 mesh broken to smaller than 40 mesh. The results of the particle break-up determinations are presented in Because of the extremely high velocities of the drilling liquid passing through the nozzles, erosion of the nozzles is an important factor in determining the feasibility of hydraulic jet drilling. A series of tests was run in which 20 to 40 mesh sand particles were pumped through a nozzle having a %-inch diameter inlet tapering down to a Aa-inch diameter orifice over a distance of 2 /2 inches and a straight section /2-inch long and Aa-inch in diameter extending from the orifice to the nozzle outlet. In the test, suspensions of 20 to 40 mesh cast iron grit and of 20 to 40 mesh sand were caused to fiow through the nozzle at rates giving a pressure drop across the nozzle of 5000 psi. or more. The nozzles were constructed of two types of tungsten carbide. The results of the tests are presented in Table III.

TABLE III.-NOZZLE WEAR TESTS [Test duration: 6 hours] said bit having a nozzle therein directed downwardly toward the bottomof the borehole, maintaining the nozzle outlet in the range of A-inch to 1 /2 inches from the bottom of the borehole of'the well, pumping a drilling liquid having /2 to 6 percent by'volume of ferrous abrasive suspended therein down the drill stem, said ferrous abrasive particles having a' Rockwell C hardness of at least about 55, discharging the drilling liquid from the bit at a velocity of at least 500 feet per second against the bottom of the hole, and circulating the liquid up the borehole around the drill string to carry cuttings from the borehole.

3. A method as set forth in claim 2 in which the abrasive particles are of a particle size in the range of 7 to SO mesh in the US. Sieve Series.

4. A method as set forth in claim 2 in which the ferrous abrasive is ferrous shot having a Rockwell C hardness of at least and a particle size in the range of 7 to 80 mesh in the US. Sieve Series.

'5. A method as set forth in claim 2 in which the ferrous abrasive is steel shot having a Rockwell C hardness of at least about 55 and a particle size in the range of 7 to 80 mesh in the US. Sieve Series.

The results presented in Table III show that nozzle wear is much lower when a ferrous abrasive, which had a Rockwell C hardness exceeding 55, is suspended in the drilling liquid than when the abrasive is sand in spite of the fact that the ferrous abrasive causes a much higher drilling rate. Because the drilling rate is a measure of the ability of the drilling liquid to cut a hard surface, it is surprising that the nozzle erosion is less when iron grit is suspended in the drilling liquid than When sand is suspended in the drilling liquid. Contrary results are obtained if tabular alumina is suspended in the drilling liquid. Although tabular alumina will give drilling rates exceeding those obtained with sand but lower than those obtained with ferrous shot, nozzle erosion is so severe that tabular alumina cannot be effectively used in hydraulic jet drilling operations.

Both cast iron and steel shot and grit having a Rockwell C hardness of at least about 55 are highly advantageous in hydraulic jet drilling operations in making possible high drilling rates through very hard rock formations. The high drilling rates can be obtained with a relatively low rate of erosion of the nozzles through which the drilling liquid is discharged against the bottom of the hole. Moreover, the low rate of break-up of the ferrous grit particles allows their repeated use, and thereby greatly reduces the cost of the abrasive required in hydraulic jet drilling.

We claim:

1. In a hydraulic jet method of drilling a well in hard formations in which a drilling liquid is discharged at a velocity of at least 500 feet per second from a nozzle against the bottom of the borehole of the well, the outlet of said nozzle being in the range of A-inch to 1 /2 inches from the bottom of the borehole, the improvement comprising suspending in the drilling liquid ferrous abrasive particles in a concentration of /2 to 6 percent by volume, said ferrous abrasive particles having a Rockwell C hardness of at least about 55.

2. A method of drilling a well in hard formations comprising rotating a bit at the bottom of a drill string,

6. A method of drilling a well in hard formations comprising rotating a drill stem having a drill bit at its lower end in the borehole of the well, pumping a drilling liquid having /2 to 6 percent by volume ferrous abrasive suspended therein down the drill stem and discharging the liquid from nozzles in the bit at a velocity of at least 500 feet per second, said ferrous abrasive particles having a Rockwell C hardness of at least about 55, the size of the abrasive particles being in the range of 7 to mesh, maintaining the outlet of the nozzles at a distance in the range of At-inch to 1 /2 inches from the bottom of the borehole, circulating the drilling liquid and cuttings upwardly through the borehole to the surface, separating cuttings and fine solid particles from the drilling liquid, and recirculating drilling liquid containing the ferrous abrasive in the well.

7. A method of drilling a well comprising rotating a bit mounted on the lower end of a drill string in the well at a rate of at least 5 r.p.m., said bit having nozzles therein adapted to direct fluids against the bottom of the borehole, maintaining the outlets of the nozzles in the bit between Mt-inch and 1 /2 inches from the bottom of the borehole, pumping a liquid having /2 to 6 percent by volume ferrous abrasive suspended therein down the drill stem and outwardly through the bit at a rate adapted to give a nozzle outlet velocity of at least 500 feet per second, said ferrous abrasive particles having a Rockwell C hardness of at least about 55, circulating the liquid and entrained cuttings upwardly through the well to the surface, removing cuttings and finely divided solids from the drilling liquid, adding ferrous abrasive to the drilling liquid to adjust the concentration of ferrous abrasive to 1 to 6 percent by volume, and recycling the thusprepared drilling liquid down the well for further drilling.

8. A drilling liquid for the hydraulic jet drilling of wells in hard formations comprising a liquid having suspended therein /2 to 6 percent by volume ferrous abrasive of a Rockwell C hardness of at least about 55.

(References on following page) References Cited UNITED STATES PATENTS Wuensch 17566 Boynton 175-67 Hays 17567 X Desbrow 175422 X Bergey 175-66 Marwil 17566 Graham 17566 X Quick 17567 Bobo 17567 Stone 17566 Buck 17566 CHARLES E. OCONNELL, Primary Examiner.

NILE C. BYERS, JR., Examiner.