US3498394A - Asbestos-laden drilling fluid and use thereof in hydraulic jet drilling - Google Patents

Description

March 3, 1970 R. J. GOODWIN ET AL ASBESTOS-LADEN DRILLING FLUID AND USE THEREOF IN HYDRAULIC JET DRILLING Filed March 11, 1968 may message PUMPS A36 ale/44 0V6 uau/o 34 77 54 TMENT //V VENT 0R5 ROBERT. J. GOODW/A/ W/LL/AM MEYEQ United States Patent 3,498,394 ASBESTOS-LADEN DRILLING FLUID AND USE THEREOF IN HYDRAULIC JET DRILLING Robert J. Goodwin, Oakmont, and William K. Meyer, Indiana Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Mar. 11, 1968, Ser. No. 711,932 Int. Cl. E21b 7/18 US. Cl. 17567 8 Claims ABSTRACT OF THE DISCLOSURE A drilling liquid capable of suspending ferrous abrasives and characterized by a low pressure drop on flowing through pipe. The drilling liquid comprises clay solids, asbestos fibers and ferrous abrasive particles suspended in water. To increase to an acceptable range the ability of the drilling liquid to suspend ferrous abrasive particles, the drilling liquid is sheared by passing it through a nozzle at a velocity causing a pressure drop through the nozzle of at least 4,000 psi.

This invention relates to drilling wells, and more particularly to a hydraulic jet drilling process in which a drilling liquid is discharged at high velocities against the bottom of the borehole of a well to penetrate hard formations.

Most oil and gas wells are presently drilled by a rotary drilling process in which a bit rotated at the lower end of drill pipe mechanically breaks particles from the bottom of the borehole. A drilling mud is circulated down the well through the drill pipe and up through the annulus surrounding the drill pipe to remove cuttings from the borehole. Clay solids are dispersed in the drilling mud to increase the viscosity and g l strength of the drilling mud to aid in removal of the cuttings from the hole. Another function of the drilling mud is to counteract pressures existing in underground formations and prevent flow from those formations into the borehole during the drilling operations. Weighting agents, particularly barite, are incorporated in the drilling mud to increase its density and thereby create hydrostatic pressure adequate to overcome the formation pressure. Both the barite and clay particles suspended in drilling muds are finely divided. Most of the particles will pass through a 325 mesh scre n.

The conventional rotary drilling method described in the preceding paragraph allows extremely fast drilling in soft formations, but the rate of drilling decreases rapidly as the hardness of the formation increases. The slow drilling in hard formations is aggravated by increased wear of the drill bit which makes necessary frequent interruption of the drilling for replacement of the bit.

A drilling method that has been developed in an attempt to overcome the high cost of drilling hard formations is hydraulic jet drilling. In hydraulic jet drilling, an abrasive-laden liquid is pumped down through drill pipe and is discharged at a velocity of preferably 650 feet per second or more through a plurality of nozzles in a drill bit at the bottom of drill pipe. A preferred abrasive material for use in the hydraulic jet drilling process is iron or steel grit or shot having a particle size of 10 to 80 mesh and preferably to 40 mesh. It is essential that the drilling liquid used in the hydraulic jet drilling process be capable of suspending the abrasive as well as the cuttings when circulation of the drilling liquid is interrupted while adding a joint to the drill pipe or pulling the drill pipe to replace a drill bit. The high density and large size of the ferrous abrasives make suspension of the abrasive particles in the drilling liquid difficult. A drilling 3,498,394 Patented Mar. 3, 1970 liquid of suitable suspension properties cannot be obtained merely by the addition of clay solids without increasing the viscosity and gel strength of the drilling liquid to such an extent that the pressure loss in the drill pipe precludes effective drilling by the hydraulic jet drilling method.

This invention resides in a novel hydraulic jet drilling methodand drilling liquid in whch asbestos fibers and clay solids are suspended in an aqueous liquid passed through a nozzle at a high velocity produced by a pressure drop of the order of 4,000 pounds per square inch or more across the nozzle. Ferrous abrasive particles are suspended in the resultant drilling liquid which is circulated down a well and discharged at high velocities against the bottom of the borehole to penetrate the formations being drilled. A preferred drilling liquid of this invention contains ground corn to reduce loss of whole drilling liquid or filtrate and to aid in suspension of the liquid.

The single figure of the drawing is a diagrammatic view, partially in vertical section, of apparatus for drilling by this invention.

Referring to the drawing, a well indicated generally by reference numeral 10 is illustrated with casing 12 set in the upper end of the well and with open hole 14 at the lower end of the well. Drill pipe 16 extends downwardly through the well substantially to the 'bottom 18 of the borehole. A drill bit 20 having a plurality of nozz es 22 opening through its lower end is connected to the lower end of drill pipe 16.

A kelly 24 connected to the upper end of drill pipe 16 extends through a suitable closure 26 and rotary table 28. Power is supplied to the rotary table through a shaft 30 to rotate the drill pipe 16 and the drill bit 20 secured to the lower end of the drill pipe.

Opening from the casing 12 below closure 26 is a line 32 extending to apparatus 34 indicated generally by the legend Drilling Liquid Treatment. A line 36 from the drilling liquid treatment apparatus delivers drilling liquid to high-pressure pumps 38 which recirculate the drilling liquid through a line 40 to the upper end of the kelly 24. A pair of pressure transfer cases 42 may be provided for injecting the abrasive into the high-pressure drilling liquid delivered to the upper end of kelly 24.

In the performance of the hydraulic jet drilling method of this invention, an aqueous suspension of asbestos fibers and clay solids is delivered by high-pressure pumps through line 40 into the .upper end of kelly 24. The drilling liquid passes from kelly 24 downwardly through drill pipe 16 into the drill bit 20 from which the drilling liquid is discharged through nozzles 22. The high flow rate of the drilling liquidprovided by high-pressure pumps 38 causes a pressure drop across nozzles 22 of at least 4,000 and preferably exceeding 5,000 psi. The high-velocity jets discharged from the nozzles cut the bottom 28 of the borehole, and the cuttings from the bottom of the borehole are recirculated upwardly through the annulus between the borehole wall and the drill pipe to the top of the well.

Drilling liquid discharged through line 32 is delivered to apparatus 34 in which the drilling liquid is treated before it is recirculated in the well. Ordinarily, the treatment consists of removing large-size cuttings and very fine particles and cooling the liquid before passing it to the high-pressure pumps. After one circulation of the aqueous suspension of asbestos and clay solids, the ferrous abrasive particles are introduced into the suspension to form the desired drilling liquid. The incorporation of the ferrous abrasive particles can be accomplished in the drilling liquid treatment and the abrasive-laden drilling liquid delivered to the high-press ure pumps 38.

Another method of incorporating the abrasives is to add the abrasive particles to the abrasive-free liquid discharged from the pumps 38. Such addition can be accomplished by means of the high-pressure transfer cases 42. The abrasive-laden drilling liquid is then delivered down through the drill pipe and discharged through nozzles 22 to cut the bottom of the borehole. Clay solids, asbestos fiber, ferrous abrasives and water are added to the system as required to maintain the desired volume of drilling mud of the desired composition.

In the hydraulic jet drilling method, the abrasive-laden drilling liquid is discharged from the drill bit at a high velocity against the bottom of the borehole in a plurality of jet streams that cut a major portion of the bottom of the borehole as the jet bit 20 is rotated. Because of the extremely high velocity at which the drilling liquid is discharged from the drill bit and necessity of a large number of jet streams, usually 10 to 20, to cut the entire bottom of the borehole at a high rate of penetration, the flow rate in the drill pipe and annulus is high. Unless the drilling liquid has a unique combination of strong solidssuspension characteristics and low-pressure drop, it cannot be used effectively in hydraulic jet drilling with ferrous abrasives. A clay suspension having an adequate viscosity and gel strength to suspend ferrous abrasive causes an excessive pressure drop in the drill pipe and annulus.

The asbestos fibers used in the drilling liquid of this invention are finely divided fibrous particles of chrysotile. Because of the fibrous nature of the particles, they are not accurately measured by the usual screening technique; however, particles used in the preparation of the drilling liquid should be smaller than 10 mesh. The size of the particles originally incorporated into the drilling liquid is not highly critical inasmuch as the particles are separated and broken during the hydraulic jet drilling operation. After one pass through the nozzles of the drill bit, the drilling liquid other than the abrasive particles will pass through a 100-rnesh screen. A typical particle size analysis of asbestos fibers suitable for use in this invention before addition to the drilling liquid is:

On US. Sieve Series, mesh: Percent 10 1.5

Pan

Clay solids are incorporated in the aqueous suspension of aqueous fibers as a dispersing agent aiding in dispersion of the fibers in the liquid. Because of the necessity of reducing the viscosity of the drilling liquid to maintain a low pressure loss in the drill pipe and annulus when the drilling liquid is circulated through the well, clays such as attapulgite or some native clays are preferred to high-yield clays such as bentonite.

The asbestos fibers are suspended in the drilling liquid in a concentration in the range of one to four percent by weight of the drilling liquid. The concentration of clay solids is in the range of 2 to 7 percent by weight. The ratio of asbestos fibers to clay solids is preferably in the range of 1 to 2 to 1 to 3.5.

The aqueous suspension of asbestos fiber, clay solids, and ferrous abrasives will in many instances be an adequate drilling liquid without further modification. When drilling some formations, the loss of filtrate from the drilling liquid may be excessive. To prevent excessive loss of drilling liquid, ground corn can be added to the drilling liquid in a concentration of 1 to 4 percent by weight of the drilling liquid. The severe shear to which the drilling liquid is exposed in passing through the nozzles of the drill bit apparently liberates the starch from the ground corn and eliminates the processing steps heretofore required to produce the starch used in drilling muds for conventional rotary drilling processes. In addition to reducing the filtrate loss of the drilling liquid, because of the presence of corn starch, the fibrous or lamellar particles of the ground corn help suspend the abrasive particles and aid in plugging openings in the borehole wall which might otherwise cause loss of whole drilling liquid, as distinguished from loss of only the liquid component of the drilling liquid. If ground corn is added to the drilling liquid, a starch preservative such as a phenyl mercury compound, formaldehyde, or pentachlorophenol should be added to the drilling liquid. While ground corn is a highly preferred additive because of the several beneficial effects it produces, other fluid-loss reducing additives conventionally used in drilling muds can be incorporated in the drilling liquid to reduce fluid loss.

When making up the initial drilling liquid for the hydraulic jet drilling process, the aqueous suspension of asbestos and clay solids preferably is circulated at least once through the drill bit to separate the clumps of asbestos fibers and give a drilling liquid capable of suspending the ferrous abrasive. An alternative method is to provide a suitably valved line from the outlet of the high-pressure pump to nozzles at the surface positioned to discharge the liquid into a storage tank. Thereafter, the ferrous abrasive is added in a concentration of 1 to 4 percent and preferably 1 /2 to 2 /2 percent by weight of the drilling liquid. The ferrous abrasives used in hydraulic jet drilling are commercially available abrasives widely used in cleaning metal castings. It is preferred that the abrasive particles have a Rockwell C hardness of at least about 55 and have a particle size in the range of 10 to and preferably 20 to 40 mesh. Either cast iron or steel particles are suitable and the particles can be either in the form of shot or grit.

The drilling liquid used in hydraulic jet drilling is subjected to severe shear as it passes through the nozzles in the drill bit. Many of the organic compounds, such as starches, gums, carboxymethyl cellulose, and acrylonitriles, that have been added to the drilling muds to thicken them and reduce the fluid loss of the drilling mud lose their effectiveness when subjected to the severe shear in the drill bit nozzles. In contrast, the novel drilling liquids of this invention do not possess the properties necessary to suspend ferrous abrasives until they have been subjected to severe shear such as occurs by passing through a nozzle at a velocity causing a pressure drop of 4,000 p.s.1.

To illustrate the effect of severe shearing on the properties of the drilling muds of this invention, suspensions in water of bentonite alone and in combination with chrysotile asbestos fiber were mixed according to API specifications of oil well drilling fluid materials RP-l3(b) of November 1962. The mixing was accomplished in a Hamilton-Beach mixer and was continued for 5 to 7 minutes after which the suspensions were aged about 16 hours. Samples of the bentonite-asbestos were sheared by two passes through a nozzle at a pressure drop of approximately 4,000 p.s.i. Starch was added to a sample of each of the sheared and unsheared bentonite-asbestos suspensions approximately one hour before determination of the viscosity and suspendibility of the compositions. The compositions of the different samples in percent by weight of the Water were:

Sample A: Unsheared2 /z bentonite, 1 /2% chrysotile asbestos Sample B: Sheared2 /2% bentonite, 1 /2% chrysotile asbestos Sample C: 10% bentonite Sample D: Sample A +2% starch Sample E: Sample B +2% starch The viscosities of the resulting suspensions were determined on a Fann viscometer. The suspendibility of the suspensions was determined by measuring the rate of settling of steel shot S 230 through a column of the drilling liquid and is reported in second required to settle a distance of one foot. Steel shot S 230 has an average diameter of 0.023 inch. The 30-minute filtrate was determined by the standard API test for measuring the rate of liquid loss of drilling muds. The suspendibility and viscosities are reported in Table I:

The legend No in Table I indicates that there was no measurable settling of the steel shot in the drilling liquid in a one-hour period.

An essential characteristic of the drilling liquid for a hydraulic jet drilling process is a low pressure drop when pumped at high velocities through drill pipe. Frequently, the hard formations in which the hydraulic jet drilling method is most advantageous are at substantial depths. If the pressure drop caused by high rates of flow of the drilling liquid in the drill pipe and annulus is high, the power requirements for maintaining the necessary pressure drop across, and flow through, the drill pipe become excessive.

Each of the suspensions described above was pumped through a 17-foot section of /z-inch stainless steel pipe at controlled and measured flow rates. The pressure drop in the 17-foot section of pipe was measured. The pressure drops of the different suspensions are reported in Table II:

TABLE II Sample A Rate, gal/min: AP, p.s.i. 8.3 .317

Sample B 6.25 .66

Sample C 7.69 1.75

Sample D 6.6 .32

Sample E 10.0 .76

The drilling liquid of this invention has a unique combination of properties making it valuable in jet drilling operations. A suspendibility of ferrous abrasive of at least 4 minutes per foot is essential and as high as possible is desirable. The drilling liquid of this invention suspended ferrous abrasive particles without measurable settling in a one-hour period. Only after shearing does the drilling liquid have the excellent suspendibility characteristics. The shearing does not impair the filtrate-loss characteristics of the drilling liquid. The excellent suspendability is obtained without the high viscosity and pressure drop of suspensions of bentonite alone in water. Circulating the asbestos-laden drilling liquid in the ordinary rotary drilling process in which the drilling liquid merely conveys rock particles cut mechanically by the drill bit does not impart the unique properties to the drilling liquid.

We claim:

1. A hydraulic jet method of drilling a well comprising mixing clay and asbestos fibers with water to form an aqueous suspension, circulating the suspension down the well and discharging the suspension through nozzles of a drill bit at a rate causing a pressure drop across the nozzles of at least 4,000 p.s.i., circulating the suspension up the well through the annulus around the drill pipe, mixing ferrous abrasive particles with the suspension circulated up the Well to form a drilling liquid, and recirculating the drilling liquid of clay, asbestos fibers, ferrous abrasive and water down the well for continued drilling, the concentration of the clay and asbestos being adapted to cause suspension of the abrasive particles in the drilling liquid.

2. A method as set forth in claim 1 in which the concentration of clay solids is 1 to 7 percent by weight of the water and the ratio of asbestos to clay solids is in the range from 1 to 2 to 1 to 3.5.

3. A hydraulic jet method for drilling a borehole in hard formations comprising delivering a drilling liquid through drill pipe and discharging the liquid against the hard formation from a bit at the end of the drill pipe at a rate causing a pressure drop of at least 4,000 p.s.i. through nozzles in the drill bit, said drilling liquid comprising clay, ferrous abrasives, and asbestos fibers dispersed in water to provide a drilling liquid capable of suspending the ferrous abrasive particles.

4. A drilling liquid comprising water, clay solids, chrysotile asbestos fibers, and ferrous abrasive particles sheared by passing through a nozzle at a pressure drop in the nozzle of at least 4,000 p.s.i., said drilling liquid being capable of suspending ferrous abrasive S 230 particles whereby the particles settle at a rate less than 15 feet per hour.

5. A drilling liquid as set forth in claim 4 containing ground corn disseminated therethrough.

6. A drilling liquid as set forth in claim 4 in which the concentration of clay solids is in the range of 2 to 7 percent by weight of the drilling liquid, and the concentration of the chrysotile asbestos fibers is in the range of 1 to 4 percent by weight of the drilling liquid.

7. A drilling liquid as set forth in claim 4 in which the size of the ferrous abrasive particles is in the range of 10 to mesh and the chrysotile asbestos fibers pass through a -mesh screen after a single pass through the nozzle.

8. A method of preparing drilling liquid for use in hydraulic jet drilling of a well comprising mixing clay solids and asbestos fibers with water to form a suspension, pumping the suspension down drill pipe in the well and discharging the suspension through a drill bit at the lower end of the drill pipe at a velocity causing a pressure drop of at least 4,000 psi. across nozzles in the drill bit, returning the suspension to the surface and adding ferrous abrasive particles having a size in the range of 10 to 80 mesh to the drilling liquid to maintain an abrasive concentration in the range of 1 to 4 percent.

References Cited UNITED STATES PATENTS 3,245,469 4/1966 Bertness -65 3,384,189 5/1968 Pekarek et al. 17567 STEPHEN J. NOVOSAD, Primary Examiner US. Cl. X.R. 252-85

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