GB1574797A - Well drilling muds and methods - Google Patents

Description

(54) WELL DRILLING MUDS AND METHODS (71) I, JERRY RAYBORN, a citizen of the United States of America, of 3633 Inwood Avenue, New Orleans, Louisiana 70114, United States of America, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: When drilling, a well drilling mud is circulated down the well, for instance to remove the chips or cuttings which are produced by the rotating dril bit from the well bore. The mud is generally circulated down the well from the surface of the well through the drill string and out through openings in the drill bit such that the mud is then circulated upwardly in the annulus between the side of the well bore and the rotating drill string. A drilling mud is a mixture of water, clays and various treating agents which control the physical or rheological properties of the mud in the well bore.

One of the objectives of the mud is to reduce friction or provide a lubricating medium for the drill bit and the drill pipe to work in while drilling the well bore. It is already known to formulate the mud with the particular purpose of reducing friction.

Thus the mud is often formulated with the particular purpose of lubricating adjacent surfaces so as to enable them to move more easily over one another. Materials which have been proposed to improve lubrication include water, diesel oil, vegetable oil, detergents, bentonite clays, alcohols, gilsonite, asphaltic materials, cellulose materials, polymers, dextrose materials, glycerins and amines. Typically a drilling mud is a mixture of water, clays, detergents, filtration reducing agents and various other products.

In addition to effecting lubrication the mud may serve other purposes. For instance it may provide a medium to control or regulate the density of the drilling fluid so as to form a cake on the sides of the well bore to prevent geological pressures or openings from occurring in the sides of the bore.

Because of the wide variety of purposes for which drilling mud is used a wide variety of drilling muds and mud additives have been proposed. In particular various proposals have been made to include particulate materials in drilling muds. For example in U.S. Patent Specification No. 2,943, 679 it is proposed that angular hard particles, such as crushed walnut shells, should be included for reducing the frictional drag on a drilling string. In U.S. Patent Specification No.

3,216,933 it is proposed that hard particulate material should be included in drilling fluid to prevent sticking of the drill pipe.

The examples given of such materials are steel shot, aluminium shot, sand, walnut shells, plastic and the like. Steel and aluminium shot have relatively high specific gravities and will tend to settle out in muds of normal weight. This can be particularly troublesome when circulation ceases for one reason or another because there is then the possibility that the shot will settle out of the mud in the drill string into the bit. In certain cases, this can result in plugging of the bit.

In both these patents the particulate materials are described as being "ground" and will therefore necessarily be of irregular shape. In U.S. Patent Specifications Nos.

3,700,050 and 3,827,978 it is proposed to include particles of plastics or glass which are hollow, and which therefore have very low density. In U.S. Patent Specification No. 3,878,141 it is proposed to include particles which should be from 44 to 850 microns in diameter and which are made by crushing or grinding larger objects, for the purpose of providing a bridge in the filter cake.

A drilling mud according to the invention contains beads of a plastics material substantially all of which are substantially spherical, have a particle size of 10 to 100 mesh, are insoluble in oil and water and are capable of withstanding temperatures and forces applied during drilling an oil well without being melted or crushed. In the invention, while drilling a well, a drilling mud is so circulated down the well as to form a layer between moving parts and, for some or all of the drilling operation, a mud is used containing beads of a plastics material substantially all of which are substantially spherical, have a particle size of 10 to 100 mesh, are insoluble in oil and water and are capable of withstanding temperatures and forces applied during drilling the well without being melted or crushed.

The beads must naturally be insoluble in the hydrocarbon that is likely to pass up through the well and in the water of the mud and must be capable of withstanding the forces applied during drilling, since it is necessary that they should not be crushed to any significant extent during use. They must be solid and must be stable at the bottom hole temperatures which range up to, for example, 250"F. They must be chemically and physically inert to the well fluids. It is particularly preferred that they should have a specific gravity within the range 1.1 to 1.5, most preferably 1.2 to 1.4. If the specific gravity is above 1.5 they may tend to settle out, particularly in a ligher weight drilling mud if circulation ceases. Also they may tend to settle out in mud pits. If the specific gravity is too low they may tend to float in the mud. Specific gravity of about 1.2 is generally best.

The particle size of the beads is from 10 to 100 mesh (Tyler standard screen size) and most preferably 40 to 60 mesh. Usually the mud has to pass through a shale shaker and the maximum size of the bead should be such that the beads will pass through the shaker.

The beads may be of any plastics material that imparts to the beads the necessary physical and chemical properties. Particularly preferred are beads of a copolymer of divinylbenzene and styrene. For instance the beads may be polystyrene crosslinked with, for instance, 6 to 10%, preferably 8 to 10%, divinylbenzene or other diethylenic crosslinking agent.

As a result of including the defined beads the mud offers a significant reduction in friction. Thus it seems that the substantially spherical beads tend to act as ball bearings when two metal surfaces rub against each other, for instance a drill pipe against a casing or against a hard shale, and the ball bearing effect created by the beads thus reduces the friction. Examination of returned mud cake particles under magnification has shown that the beads appear to be partially imbedded in the surface of the mud cake leaving exposed a semi-spherical surface for contact with the drill string. Observation of this type of filter cake would lead one to believe that there exists many hundreds of these tiny protuberances of beads for each foot of bore hole. Examination of "gumbo" shale returns has revealed the cuttings to be partially coated with beads.

This suggests that the beads tend to prevent such shale from balling up bits and stabilisers.

It is naturally desirable that the beads should be as spherical as possible in order to give the best ball bearing effect. However naturally some beads can be non-spherical provided this does not unduly detract from the friction reducing effect of the spherical beads.

The invention is of particular value in reducing torque during drilling. In a preferred method a well is drilled by rotating a drill string to cut a bore hole into the earth, circulating a conventional drilling mud, i.e.

a mud not containing the said plastic beads, down through the drill string and thence up through the annulus between the drill string and the wall of the hole and observing the torque required to rotate the drill string.

When the torque rises to a predetermined level further drilling is then conducted with a drilling mud containing the said plastic beads. Thus sufficient plastic beads may be added to the mud being pumped down the bore hole to reduce the torque.

The amount of beads that have to be added to achieve significant reduction in torque will depend upon prevailing conditions but will generally be at least 1.5% by volume (4 pounds per barrel). Greater amounts may give greater reduction in torque. For instance it is often desirable to add up to, say, 10 pounds per barrel. In a particular method amounts such as 10 pounds per barrel are added to reduce the torque rapidly and then lowered torque can be maintained by continuing drilling using a mud containing 4 pounds per barrel. Since the beads tend to concentrate in the mud cake it may be that the concentration of beads in the cake will be higher than the concentration added to the mud. Thus there are indications that torque reduction depends primarily upon the concentration of beads in the cake and that effective torque reduction is only achieved when the concentration has built up to an amount of 30 pounds per barrel, but that concentrations above about 40 pounds per barrel may not result in any further decrease in torque.

In addition to reducing torque in a bore hole in which it has increased undesirably the inclusion of the said beads in the drilling mud reduces drill pipe and casing wear especially in high angle directional wells.

The beads create a layer or sheath between the metal surfaces so as to reduce friction.

They also reduce drag, wear of the bit, and can reduce balling of the stabiliser.

As an indication of the reduction in friction that can be achieved one directional well was being drilled with a downhole turbo-drill, and, in normal operation, it took two days to make fifteen feet of hole.

However, when four pounds per barrel of these plastic beads were added, the drilling rate increased to 15 feet per hour.

In like manner it has been found that the addition of the plastic beads is useful in improving wireline operations which must be performed downhole, such as well logging, by enabling the logging tool to slide on the surfaces, provided by the various plastic spheres. Further, the addition of these spheres reduces "wireline drag" both in cased well bores and open well bores.

The use of the beads in a well bore may be further aided with other mud lubricants, such as vegetable oil, such that the beads are suspended in vegetable oil and circulated in the well bore mixed with the drilling mud.

The following are Examples.

Example 1 A well was drilled that was a 37 directional well having several offsets or doglegs.

The well was a 97/s" hole being drilled at 11,200 feet with 4,000 feet of 103/4" surface casing set and using a conventional mud.

The measured total depth of the well was to be 13,400 feet and the torque had already reached 850 amps on a conventional torque gauge. The torque was such that the operator was barely turning or rotating the drill pipe. Plastic beads were added to the mud which was pumped through the drill pipe and reaching the casing whereupon the torque immediately dropped to 600-650 amps and the rotary speed increased 20 revolutions per minute. The well was drilled the remaining 2,000 feet to completion using the plastic beads.

The beads used in this Example, and in the following Examples, were all spherical beads having a smooth surface and formed of a copolymer of divinylbenzene and styrene and having a mesh size of from 10 to 100.

Example 2 A well was being drilled with 13,000 feet of casing set and it was found that the torque and drag were so severe that further drilling was unsatisfactory with the conventional mud then being used. Prior to the invention an oil-based mud would have had to have been used. However the system was "slug" treated with 5% by volume of the drilling mud with the plastic beads and 300 barrels of mud. As soon as the bead laden mud reached the annulus of the well bore, the torque began to drop and the penetration rate of the drilling string increased by 50%.

The well was treated to completion at 18,000 feet with the subject beads and upon completion, the mud system contained 13/4% by volume of the beads in relation to the drilling mud.

Example 3 A well was being drilled in South Louisiana with an excessive torque problem relative to rotation of the drill string downhole. This was a directional well which demanded a high rotary revolution per minute (rpm) in order to maintain the direction desired. The torque was being indicated as 650-750 amps on the torque gauge with 180 rpm rotary speed. The depth of the well at that time was 8,000 feet and the casing was set for 3,300 feet. The plastic beads were added at 11/2% by volume of the mud system and the torque dropped immediately to 550-600 amps. In this well, excessive "balling" or build up of shales and clays on the stabilisers and drill collars was also eliminated by the plastic beads and the well was successfully completed.

Example 4 A well was being drilled in South Louisiana, with extreme torque and drag problems relative to the drill string and drill bit. In this instance, the rotary table would actually stop turning while in high gear. In addition, the drill pipe rubbers would also have to be replaced after each "trip" with the drill bit. An "intermediate" string of casing was set to 9,000 feet to attempt to help to eliminate the torque problem. The drilling operator went in the hole with 41/4" drill pipe and could not turn the pipe. The operator pulled out of the hole and replaced the 41/4" pipe with 31/2" pipe but the torque was 750 amps and was twisting the drill pipe and the possibility of twisting the drill in two existed. Diesel, graphite and other popular torque reducers had been added with no improvement or with no reduction of torque and drag on the drill string. The plastic beads were added at 2% per volume of the drilling mud and the torque dropped to 600-625 amps as indicated on the torque indicator and the well was drilled to completion.

WHAT I CLAIM IS: 1. A drilling mud containing beads of plastics material substantially all of which are substantially spherical, have a particle size of 10 to 100 mesh, are insoluble in oil and water, and are capable of withstanding temperatures and forces applied during drilling an oil well without being melted or crushed.

2. A mud according to claim 1 in which the plastics material is cross-linked polys

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. the metal surfaces so as to reduce friction. They also reduce drag, wear of the bit, and can reduce balling of the stabiliser. As an indication of the reduction in friction that can be achieved one directional well was being drilled with a downhole turbo-drill, and, in normal operation, it took two days to make fifteen feet of hole. However, when four pounds per barrel of these plastic beads were added, the drilling rate increased to 15 feet per hour. In like manner it has been found that the addition of the plastic beads is useful in improving wireline operations which must be performed downhole, such as well logging, by enabling the logging tool to slide on the surfaces, provided by the various plastic spheres. Further, the addition of these spheres reduces "wireline drag" both in cased well bores and open well bores. The use of the beads in a well bore may be further aided with other mud lubricants, such as vegetable oil, such that the beads are suspended in vegetable oil and circulated in the well bore mixed with the drilling mud. The following are Examples. Example 1 A well was drilled that was a 37 directional well having several offsets or doglegs. The well was a 97/s" hole being drilled at 11,200 feet with 4,000 feet of 103/4" surface casing set and using a conventional mud. The measured total depth of the well was to be 13,400 feet and the torque had already reached 850 amps on a conventional torque gauge. The torque was such that the operator was barely turning or rotating the drill pipe. Plastic beads were added to the mud which was pumped through the drill pipe and reaching the casing whereupon the torque immediately dropped to 600-650 amps and the rotary speed increased 20 revolutions per minute. The well was drilled the remaining 2,000 feet to completion using the plastic beads. The beads used in this Example, and in the following Examples, were all spherical beads having a smooth surface and formed of a copolymer of divinylbenzene and styrene and having a mesh size of from 10 to 100. Example 2 A well was being drilled with 13,000 feet of casing set and it was found that the torque and drag were so severe that further drilling was unsatisfactory with the conventional mud then being used. Prior to the invention an oil-based mud would have had to have been used. However the system was "slug" treated with 5% by volume of the drilling mud with the plastic beads and 300 barrels of mud. As soon as the bead laden mud reached the annulus of the well bore, the torque began to drop and the penetration rate of the drilling string increased by 50%. The well was treated to completion at 18,000 feet with the subject beads and upon completion, the mud system contained 13/4% by volume of the beads in relation to the drilling mud. Example 3 A well was being drilled in South Louisiana with an excessive torque problem relative to rotation of the drill string downhole. This was a directional well which demanded a high rotary revolution per minute (rpm) in order to maintain the direction desired. The torque was being indicated as 650-750 amps on the torque gauge with 180 rpm rotary speed. The depth of the well at that time was 8,000 feet and the casing was set for 3,300 feet. The plastic beads were added at 11/2% by volume of the mud system and the torque dropped immediately to 550-600 amps. In this well, excessive "balling" or build up of shales and clays on the stabilisers and drill collars was also eliminated by the plastic beads and the well was successfully completed. Example 4 A well was being drilled in South Louisiana, with extreme torque and drag problems relative to the drill string and drill bit. In this instance, the rotary table would actually stop turning while in high gear. In addition, the drill pipe rubbers would also have to be replaced after each "trip" with the drill bit. An "intermediate" string of casing was set to 9,000 feet to attempt to help to eliminate the torque problem. The drilling operator went in the hole with 41/4" drill pipe and could not turn the pipe. The operator pulled out of the hole and replaced the 41/4" pipe with 31/2" pipe but the torque was 750 amps and was twisting the drill pipe and the possibility of twisting the drill in two existed. Diesel, graphite and other popular torque reducers had been added with no improvement or with no reduction of torque and drag on the drill string. The plastic beads were added at 2% per volume of the drilling mud and the torque dropped to 600-625 amps as indicated on the torque indicator and the well was drilled to completion. WHAT I CLAIM IS:

1. A drilling mud containing beads of plastics material substantially all of which are substantially spherical, have a particle size of 10 to 100 mesh, are insoluble in oil and water, and are capable of withstanding temperatures and forces applied during drilling an oil well without being melted or crushed.

2. A mud according to claim 1 in which the plastics material is cross-linked polys

tyrene.

3. A mud according to claim 2 in which the plastics material is a copolymer of styrene and divinylbenzene.

4. A mud according to any preceding claim containing at least 1.5% by volume of the beads.

5. A mud according to any preceding claim in which the beads have a specific gravity of from 1.1 to 1.5.

6. A mud according to any preceding claim in which the beads have a particle size of 40 to 60 mesh.

7. A mud according to any preceding claim containing from 4 to 10 pounds per barrel of the beads.

8. A mud according to claim 1 substantially as herein described with reference to any of the Examples.

9. A method of drilling a bore hole comprising so circulating a drilling mud down the bore hole as to form a layer between moving parts and in which, for some or all of the drilling operation, a mud is used which contains beads of plastics material substantially all of which are substantially spherical, have a particle size of 10 to 100 mesh, are insoluble in oil and water, and are capable of withstanding the temperatures and forces applied during drilling the bore hole without being melted or crushed.

10. A method of drilling a bore hole comprising rotating a drill string to cut the bore hole into the earth, circulating a drilling mud down through the drill string and thence up through the annulus between the drill string and the wall of the hole, observing the torque required to rotate the drill string and, when the torque rises to a predetermined level, using a mud containing beads of plastics material substantially all of which are substantially spherical, have a particle size of 10 to 100 mesh, are insoluble in oil and water, and are capable of withstanding the temperatures and forces applied during drilling the bore hole without being melted or crushed.

11. A method according to claim 9 or claim 10 in which the plastics material is cross-linked polystyrene.

12. A method according to claim 11 in which the plastics material is a copolymer of styrene with divinylbenzene.

13. A method according to any of claims 9 to 12 in which the mud containing the beads contains at least 1.5% by volume of the beads.

14. A method according to any of claims 9 to 13 in which the beads have a specific gravity of from 1.1 to 1.5.

15. A method according to any of claims 9 to 14 in which the beads have a particle size of 40 to 60 mesh.

16. A method according to any of claims 9 to 15 in which the mud containing the beads contains from 4 to 10 pounds of the beads per barrel.

17. A method according to claim 9 or claim 10 substantially as herein described with reference to any of the Examples.