US2244476A - Art of drilling deep wells - Google Patents

Description

Jun 3, 1941.

G. L. RA'cLn-FE ART OF DRILLING- DEEP WELLS Filed Dem-19, 1958'- 2 Sheets-Sheet l June 3, '1 941' G. L. RATCLIFFE 2,244,476

ART OF DRILLING DEEP WELLS Fled D60. 19, 1938- 2v Sheets-Sheet 2l Patented June 3, 1941 UNITED STATES PATENT UFFICI?.

' i :mia-47s .Y v

George4 L. Batcliil'e, Los Angeles, Calif., assignor to National Lead Company, Los Angeles, Calif., a corporation of New Jersey 4Claims.

This invention relat to the art of drilling deep wells and more .particularly vto the drilling of such wells through shaley formations.

In the procedure of drilling deep wells such as oil and gas 'wells the rotary drilling procedure is employed. In such a .procedure 1a drilling iluid is used which is introduced through the drill stem tothe bit and there issues to rise i-n the bore hole; from hence it is conducted to a settling ditch where the cuttingsare settled out, and then to a 'suction pit, :from which the iluid is again conducted into'the drill stem. In some instances the cuttings are separated from the drilling uid by screens.

'I'he drilling uid performs various flmctions such as carrying the cuttings to .the top of the well, but a particularly useful function of the drilling uid is to wall the bore hole. Accordingly, the uid should contain a wall-building component which, where or ry clay is used, `is the clay itself, including its gel-forming oomponent. In many instances a concentrated :col- .loidal clay such as bentonite is employed, as disclosed in. the Harth .a Patent No. 1,991,637, pat- `ented February 19, 1935. In some-'instances a mud weighting material-is employed, asdisclosed in the Stroud Patent No. 1,575,945, patented March 9, 1926. I.

When a drilling mud consisting of water and clay comes in contact with a bed of shale as the.

well is drilled, a certain. amount of water from the drilling mud seeps into the shale and wets it to a depth of one-fourth inch or so. The action of, the water varies on diiierent shales inasmuch as some shales chip oi in small flakes when the surface becomes wet to a depth of oneeighth or one-fourth of an inch; some shales become wet and sticky and do not slough oi and l still other sha'les disintegrate rapidly to a powdered form when they become wet'.

Applicanthas found that inthe wetted portion of shale together with any lter cake .which may have ibeen formed on the face of the shale y by the drilling mud is placed under considerable pressure, the wetted portionwill 'be consolidated by the pressure into a hard, compact, impervious mass. The higher the pressure placed upon the shale, the more compact will this'sheath upon the face of the shale become.

One of the objects od this invention is to sprovide a .process having `:for its purpose preventing of sloughing, caving or heaving ci shales ordinarily encountered in oil WeilV drilling; and in accordancerwith this invention' this is accom= plished by applying suicient pressure to the wet however, will compact shale to the point where prevents W-ater infiltration but also mechanically A strengthens the wall of the bore hole.

Another object of th-'ls invention is to provide a process in which the drilling fluid containing a. wall-building component is subjected to a pressure suilicient to compact the wallbuildingd component lon the -wall of the well.

Further objects will appear from the detailed description taken in connection with the accompanying drawingslshowing illustrative embodiments of this invention,` although it will 'be understood that this'invention is susceptible of various embodiments. y

As set forth above, some shales tend to cave or slough more readily than other shales and it is,- therefore, diicult to state exactly what pressure will be required to -produce the desired rev `sult inasmuch as obviouslyit would be necessary to compact a badly caving shale more than it would be necessary tocompact a shale which had'only a tendency to cave or slough to a slight degree when wet. Generally speaking, however, ordinary clay drilling fluids have not been able to prevent the type of heaving or sloughing to which reference has been made. The ordinary clay drilling iiuid, made up of clay land water only, would weigh say seventy-live pounds per cubic foot or would have a specic gravity of approximately A1.2. The maximum weight of iluid which can be made up out of clay and water and still be utilized in drilling, is ninety pounds or less. Such a fluid would have a speciiic gravity of 1.44. An average drilling iiuld, therefore, let us say would have a'. speciiic gravity of 1.32. If a shale Were encountered at the .bottom of a well 5,000 feet deep in which a mud uld having a specific gravity of 1.32 was being used. it would have a pressure on it, due to the weight of the mud column, of 2,864 pounds per square inch; under the same conditions, a shale encountered at a depth of 10,000 feet would haves.

hydrostatic pressure on it, due to the weight of the mud column, of 5,738 pounds persquare inch. These figures are based on. the assumption that no pressure exists inthe shale itself. Generally speaking, these pressures are not sumcient to prevent the caving or sloughing to which reference has been made. Y

Greater pressures than those mentioned above,

caving, sloughi-ng and heaving are prevented. Sometimes it is only necessary to slightly increase the pressure above this point but generally speaking, it is safer to have a substantial margin o f safety by increasing the pressure substantially above those pressures mentioned above. Applicant has found that this caving or sloughing will be prevented in the ordinary cases if the pressure 5 is raised to a point where the pressure on the shale, expressed in pounds per square inch. is 75/100 times the depth of the hole in feet. Occasi-onally this pressure is not adequate and .it

is necessary togo higher than this. In some cases it wil-l 'be advisable to have the pressure on` the shale, expressed in pounds per square inch, equivalent numerically to the depth from the surface of the ground down to the shale in feet.

In other words, in a hole 10,000 feet deep, it

. might :be necessary to have a ypressure on the shale at the bottom of the hole of 10,000 pounds per square inch in order to satisfactorily consolidate the shale and prevent heaving or caving.

Possibly, even greater pressures might have to be resorted to under certain conditions.

These increased pressures are sometimes obtained by adding weight material (consisting of .nely pulverized barytes, etc.) to the drilling mud so as to increase the weight of each unit volume of the mud thereby increasing the hydrostatic pressure. Applicant proposes to accomplish this by adding pressure to the drilling iluid over and above that due to the weight of the fluid itself so' as to increase the pressure on 30 the shale to the desired point. Applicant proposes to accomplish this in two Ways:

First: By utilizing mud pumps which are capable of circulating the mud fluid at high pressures, or

Second: By utilizing a hydraulic pump at periodical intervals to increase the pressure on the drilling fluid and thus compact the shale.` In the first embodiment of applicants :invention, if it were desired to maintain a pressure 40 of 10,000 pounds per square in ch at the bottom of the 10,000 foot hole and the pressure on the shale dueto the weight of the drilling iiuid was 5,000 pounds per square inch, applicant would utilize slush pumpsfor circulating the mud which were capable of pumping the mud at a pressure of 5,000 pounds per square inch. This 5,000 pounds per square inch added to the 5,000 pounds' per square inch due to the weight ofl the drilling mud column would' provide the required 10,000 50 pounds per square inch at the bottom of the hole after its surface became wetted. In this embodiment a suitable back pressure on the mud discharged from the hole would be retained so the desired purpose would be accomplished.

Practically all deep wells drilled today are equipped with suitable blow-out preventers which can be closed against the drill pipe in order to hold any pressure encountered during drilling. 'I'hese blow-out preventers are, customarily, only 60 used when there is danger of a well blowing but I due to high oil, gas ork water pressures encountered in drilling. In the second embodiment of my invention the well would be drilled in the ordinary manner with regular drilling fluid which could consist ofl a straight clay drilling uid or Aa clay drilling fluid weighted with barytes, iron oxide, or some other weighting material. When shale which is liabl,x to cave or sloughis encountered, it would be drilled in the ordinary manner for a given length of time or until a given amount of shale had been drilled. For example, say thirty feet of shale had been drilled, circulation ofthe mud fluid would be discontinued and a' valve placed o n the top of ,75

thel drill pipe and closed. The blow-out preventer would be closed packing ofl the space between the casing or the wall of the hole and the drill pipe. The hole would remain full of drilling mud. Pressure would then be placed upon the column of drilling mud ythrough a pipe inlet to the casing below the blow-out preventer. By means of a hydraulic pump, water or additional drilling mud could be pumped in on top of the drilling mud in the well by the hydraulic pumpl until the pressure was raised to any de- I sired point. The hydraulic pump could either be lrand operated or driven in any customary manner. Care would have to be exercised not to use any more pressure than necessary due t0 the strain on the surface casing or other casing in the Well and, of course, the pressure would have to be kept below a point at which the casing would be ruptured or the blow-out preventer cease to function. The desired pressure would be maintained for a. suitable length of time, say a period of fifteen minutes or a half hour, until the pressure had compacted the wetted portion of the shale. The pressure would then be released and drilling would be resumed in the customary manner until enough additional hole had been made to render it advisable to compact the Inewly drilled shale before proceeding further.

Experience would be the only guide as to the pressure necessary in any given case and as to the length of time it would be necessary to maintain the pressure in. order l to properly compact the newly wetted shale.

Pressure drilling methods are in use now but generally speaking they do not maintain more than 2,000 pounds excess pressure on the mud. Pressure drilling is not used at present toconsolidate the shlales but only for the purpose of 4confining oil, gas and water to their respective formations. In otherwords, the pressure drilling process is used to eliminate the necessity for weighted mud.

While the apparatus which may be used for performing theprocess may be varied, for illustrative purposes, two embodiments of apparatus which may be employed are shown in the accompanying drawings.

Figure 1 is an elevation partly in section illustrating an apparatus capable of carrying out the process embodying this invention; and v i, Figure 2 shows another form of apparatus. In the drawings, Figure 1 shows an oil-well rig of conventional rotary type, equipped to drill under continuous high pressure according to the disclosure of this invention, and Figure 2 represents the same equipped to drill under usual cfnditions with the application of intermittent high. It will be evident that a. single rig drill pipe 9; the mud owing downwardly therethrough passes through holes in the bit III, up

around the outside of the drill pipe into the flow line II, thence through a ditch I2 back into the pit 2. I3 is the casing head, I4 a blowout pre- .venter of usual design, its function being to pack off around the drill pipe, I5 a master gate valve, I6 a. rotary table for imparting rotary motion to the kelly and hence also to the bit. l1 is a draw works to operate the rotary table and operate the hoists. i

Referring to Figure 1, special features enabling the continuous high pressure method to be carried out may beseen to be as follows: The compounding of the pumps 3, i8 and I9 enables high mud pressures 'of 5,000 to 10,000 lbs. per sq. in. to be produced. is a pressuregauge indicating the pressure produced thereby. 2l is a packer around a kelly, a known and frequently used device to permit maintenance .of pressure in the bore hole by preventing the, escape of l mud from the casing. This pressure is 'also maintained by a choke 22 in the flow line. If for example the hole is being drilled lwith 6,000

vlbs/sq. in. applied mud pressure, there will be approximately this pressure differential across both kelly packer and choke. A float valve 23 is installed at the lower end of the drill string in order that new lengths of drill stem may be added while maintaining pressure in the well. During such an operation the blowout preventer is closed around the drill stem.

Referring to Figure 2, it will be seen that a three-way valve is installed at 24, in order that mud may be pumped either to the standpipe for routine drilling or through the feeder line 25 to the hydraulic booster 26, this last being a device enabling mudunder very high pressure to be pumped into the space between drill pipe and casing at point 2l, below the blowout preventer. A pressure gauge 28 indicates the applied pressure. In carrying out the process of the second method of the invention, drilling is interrupted,

the blowout preventer is closed, valve 24 is turned so that mud will be fed to the booster, a valve 29 at the foot of the standpipe is closed, andI mud is pumped into the casing at 21 under any desired high pressure, usually above 5000 lbs/sq.

in.. A float valve 30 is used here also to assist valve 24 in preventing mud issuing from the drill pipe.

It is desirable to keep both the continuous and intermittent pressures greaterrthan the prevailing rock pressures, 'as thus caving from pressure release is prevented if the.pressure is lowered below the rock pressure. Thepressure employed is preferably at about one pound per square inch' per 'foot of well depth... It has been foundA that in order to preventingress of water into heaving shale, intermittent pressure should be used for short periods of about two minutes and repeated mud through the final chokes so as to prevent clogging and undue wear of the chokes. An entirely closed mud system can also be used.

It will be seen that the invention accomplishes its objects. A process is provided in which sloughing, caving or heaving of shales ordinarily encountered in oil well drilling is not only prevented, 'but the wet shale is compacted to insure consolidation of the wetted portion into a rm, compact mass which not only. prevents water infiltration but also mechanically strengthens the wall of the bore hole. This can be accomplished in a simple and effective manner and with a minimum of equipment. It is, of course, to be understood that this invention is applicable not only to rotary drilling, but to cable tool drilling. It is also applicable Ito situations where mud weightingand mud conditioning materials are employed.

It will be understood that not only is this invention susceptible of various embodiments, but that various changes may be made in details without departing from the spirit of this invention. It is, therefore, to be understood that this invention is not to be limited to the details de.- scribed and/or shown.-

Having thus described the invention, what is claimed is:

1. In the art of drilling deep wells through shaley formations, the process comprising, em-

ploying a drilling uid and subjecting the fluid repeatedly for short intervals to a pressure sufficient to insure consolidation of the wetted portion of the shaley formation into a firm compact mass.

2. In the art of drilling deep wells through shaley formations, vthe process comprising, employinga drilling fluid and subjecting the fluid to a pressure which at any depth is substantially in excess of that generated by the weight of the column of fluid at that depth in order to insure consolidation of the wetted portion of the shaley formation into a flrm compact mass.

3. In the art of drilling deep. wells through shaley formations-with the aid of a drilling uid, the process comprising, wetting the shale 'wall 'n to a slight depth by means of Athe drilling fluid,

every half hour. Furthermore, it is desirable to r include a check valve just above the bit in the drill pipe to retain pressure in the hole when breaking the kelly or when applying pressure to the mud in the casing. Snubbers may also be necessary to force the drill pipevinto the hole against pressure or maintain it there when pressure is momentarily reduced. In the event of a high sand content in the mud issuing from the bore, it may be necessary to carry out 'aparltial desanding under pressure before passing the drillingl uid by applying thereto repeatedly for'I and compacting the drilled shale formation where it has been wetted by applying thereto uid pressure substantially in excess of the natural formation pressure whereby to consolidate said wetted portion into a rm, compact mass relatively impervious to Water.

4. In the art of drilling deep wells through shaly formationswith the aid of a drilling fluid, the process comprising, compacting the drilled shale formation where it has been wetted by the short intervals, through the agency of the drilling fluid, fluid pressure substantially in excess of the natural formation pressure whereby to consolidate said wetted portion into a rm, compact mass relatively impervious to water.

' GEORGE L. RATCLIFFE.

Images