US2444359A - Method and product for inhibiting hydrous disintegration of shale by aqueous drilling muds - Google Patents

Description

Patented June 29, 1948 METHOD AND PRODUCT FOR INHIBITING HYDROUS DISINTEGRATION OF SHALE BY AQUEOUS DRILLING MUDS Norman E. Martello, Turtle Creek, Pa., assignor to Hall Laboratories, Inc., Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application October 9, 1944,

Serial No. 557,932

13 Claims.

This invention relates to the treatment of aqueous drilling muds, and particularly to the treatment of those muds which are employed in the control of what is commonly referred to as heaving shale encountered in the drilling of oil Wells.

My invention relates to the compounding and use of drilling muds in such composition that when employed in drilling through a formation of heaving shale, the disintegration of this shale is substantially retarded. According to my invention, this may be achieved by using substantially water-insoluble alkali metal metaphosphate or mixtures of substantially water-insoluble alkali metal metaphosphates or mixtures of one or more water-insoluble alkali metal metaphosphates with certain water-soluble salts in the drilling mud.

In drilling oil wells, for example, it is customary to employ a mud or fluid which performs variouswell known functions. The mud is circulated from a pit or sump above the ground through the drill pipe, through and around the drilling bit where it picks up the chips formed by the drill, and then up the bore to screens where the chips and cuttings are removed. Other functions of these muds are to seal gas, oil, and water formations and to lubricate both the drilling tools and the drill pipe.

It has been well known for many years that there exist certain geological formations which are termed heaving shale formations or heaving shale. As stated in U. S. Patent 2,165,82el, issued to Vietti and Garrison, the terms denote shale strata which do not remain consolidated during the drilling operations. It is believed that the disintegration of this shale is due to its hydrolysis or hydration and numerous methods have been proposed to inhibit Or prevent this disintegration, In many instances the shale falls into the hole when drilling tools are removed or the shale may disintegrate and keep running or caving into the hole and the mud stream during the drilling operation itself. Some of these shales swell when hydrolyzed and may result in pinching of the drill pipe and cause it to twist off, a serious event. the consequences of which are well known to those skilled in the oil well drilling art. shales which hydrolize or hydrate, whether they swell, as bentonite, or not are referred to herein as hydrolyzable shales.

the distintegration of hydrolyzable shale.

Several theoretical proposals have been oifered for explaining the distintegration of the shale which may be controlled by mechanical methods. One such theory is that the disintegration is due to gases under high pressure which exist in the fissures of the shale strata while another theory is that this type of shale is under considerable stress which is relieved by the drilling of a hole through the strata, the caving of the shale thereby relieving this stress.

It is now a generally accepted fact that the aqueous phase of the drilling mud causes the distintegration of those shales which require chemical treatment for efiective control. Numerous methods have been suggested for chemically controlling heaving shale, one such method involving the incorporation in the mud of such water-soluble salts as calcium chloride, magnesium chloride, or sodium nitrate. Another methof f chemical control is disclosed in the Vietti and. Garrison patent previously referred to. This involves the incorporation of certain sodium silicates in which the molecular ratio of sodium oxide to silica falls within the range of from 1:2 up to 1:3.9.

A drilling mud employing sodium silicate to chemically control the disintegration of shale generally comprises clays, water, and from 20% to by volume of a sodium silicate. Frequently other solid materials are added to the mud for increasing the specific gravity, commonly used weightin materials being barytes, iron oxide, or the like.

It is well known that certain water-soluble polyphosphoric acid compounds in very small concentrations are extremely effective in reduc ing the viscosity of drilling muds, but these materials are not effective in chemically controlling For example, I have found that a concentration of as much as 25% of sodium phosphate glass of the Grahams salt type, based on the weight of the water used in the drilling mud does not inhibit the distintegration process. Other water-soluble phosphoric acid compounds areequally ineffective.

In my invention, I employ water-insoluble crystalline alkali-metal metaphosphates. These phosphates are generally termed water-insoluble, because they have a limiting solubility in distilled water of only a few parts per million,

whereas sodium phosphate glasses of the Grahams salt type are miscible in water in nearly all proportions. Thus water-insoluble crystalline NaPOs, commonly referred to as sodium monometaphosphate or Maddrell salt is soluble in distilled water to the extent of about 5 P. P. M., and water-insoluble KPOa, referred to in the literature as potassium monometaphosphate, is soluble in distilled water to theextent of about 40 P. P; M. In contrast with these solubilities, the phosphate glasses have practically unlimited solubilities, and solutions of 50% or greater concentration may readily be made. The phosphates I employ have a limiting solubility in pure water at ordinary temperature of less than 0.005%.

The eifectiveness of the water-insoluble crystalline alkali metal metaphosphates in controlling the viscosity of drilling fluid has been disclosed in several recently filed applications. Partridge in application Serial No. 522,974, filed February 18, 1944, which issued as U. S. Patent 2,393,560 on January 22, 1946, and which is a continuationin-part of Serial No. 465,456 filed November 13, 1942, discloses the addition of very small amounts of water-insoluble crystallin alkali metal metaphosphate in solid form directly to the drilling mud. Martello in application Serial No. 522,955, filed February 18, 1944, which issued as U. S. Patent 2,414,381 on January 14, 1947, discloses the addition of a slurry or suspension of mixtures of water-insoluble crystalline alkali metal metaphosphate to drilling mud preparations, Tjoflat in Serial No. 522,973, also filed February 18, 1944, discloses th addition of water-insoluble crystalline alkali-metal metaphosphate solubilized by any one of a number of metallic salts, both inorganic and organic in nature. It should be pointed out that in each of these applications, the phosphate addition is made for the purpose of reducing and controlling the viscosity of the drilling mud and it is the general practice to employ substantially less than 0.5% of phosphate chemical based on the total weight of the drilling mud.

I have referred to water-insoluble sodium metaphosphate and water-insoluble potassium metaphosphate by which I mean the sodium salt, often designated as Maddrell salt, and the corresponding potassium salt, which were described by R. Maddrell in Philosophical Magazine, series 3, vol; 30 (1847), page 329, and have been called salts of monometaphosphoric acid or monometaphosphates by T. Fleitmann in Poggendorfs Annalen, vol. 78 (1849), pages 360363. The waterinsoluble crystalline sodium metaphosphate may be made by heating NaHzPOr or NQJHZPZO'I to a temperature above 300 and below 500 C. and cooling either rapidly or slowly. It is advisable to heat the NaH2PO4 or NazHzPzOv to a temperature of from 400 to 450 C. in order to obtain a product which consists almost entirely of the water-insoluble crystalline sodium metaphosphate.

Water-insoluble crystalline potassium metaphosphate may be prepared by heating KI-I2PO4 to any temperature above about 300 C. and up to or above its melting point, which is slightly above800 C., and cooling either rapidly or slowly If the material is heated to a melt, it should not, however, be cooled with sufficiently extreme means to produce a readily Water-soluble glass. When temperatures in the lower part of the range. are employed, heating should be conducted. for a. suflicient time to insure that the product will consist substantially entirely of the waterinsoluble crystalline potassium metaphosphate. Methods for making the water-insoluble potassium phosphates are described by Pascal, Bull. Soc. Chim. 1924 35, 1119.

In my invention, I may employ a water-insoluble potassium monometaphosphate which is solubilized in water by a water-soluble, ionizable calcium, sodium, lithium, or ammonium compound. Typical of the: solubilizing compounds which may be used are hydroxides, carbonates, bicarbonates, sesquicarbonates, chlorides, sulfates, nitrates, silicates, orthophosphates, pyrophosphates, tripolyphosphates, metaphosphates, borates, acetates, and the salts of natural organic radicals derived from tannin and lignin. In addition, the waterinsoluble KPO3 may be solubilized by the waterinsoluble NaPOs.

If I use the water-insoluble NaPOa it may be solubilized by a water-soluble, ionizable calcium, potassiwn, lithium, or ammonium compound selected from the group of typical compounds stated above in connection with the monometaphosphate.

The mixture of the water-insoluble phosphate and the solubilizing agent may be added in the form of a slurry to the mud or the necessary amounts may be added in dry form if a dry compound is selected for solubilization. I may also add the water-insoluble KPO: or the Maddrell salt in dry form without additional solubilizing agents where the drilling mud itself contains a solubilizing material such as NaCl or KCl. '1 do not intend to limit myself to any particular methods of compounding or preparing the drilling muds employed by me in eifecting the operation of my invention.

While the materials I employ are efiective over a wide range of concentration, from about 1% to about 30% based on the weight of the water used in the mud, I have found that concentrations of from about 4% to about 10% or 20% are satisfactorily effective and economical in cost.

Uniform samples of heaving shale are not readily obtainable for laboratory experimental purposes. However, as described by Baker and Garrison in volume 34, No. 6, Transactions of- American Institute of Chemical Engineers, certain native kaolins react similarly to the hydro-- lyzable shales encountered in well drilling. I prepared small lumps of Georgia kaolin which were oven-dried at a temperature of C. for twelve hours. These were placed in large test tubes containing varying concentrations of different solutions I examined for preventing the disintegration of the clay lumps.

In each series of tests I used a blank of distilled water and also a sample consisting of two volumes of a commercial sodium silicate having a specific gravity of 50 Baum and one volume of saturated sodium chloride solution. This latter solution is used by Baker and Garrison as a standard for determining whether or not certain core samples suspected of being hydrolyzable are subject to disintegration. According to these authors, representative portions of core samples are placed in companion test tubes one containing water and the other containing the silicate-sodium chloride solution. Any cracking, swelling, or disintegration of the samples immersed in water is Warning that heaving shale has been tapped. The sample immersed in the silicate-chloride solution should not be subject to this disintegration so that I have included the mixture in each series of the tests I have conducted.

The following examples are illustrative of the various tests which I have made:

Example No. 1

[Treating agents used are equal parts of KPO; (insoluble potassium monometaphosphate) and NaPO; (insoluble sodium monometaphosphate)] Test N 0.

Type of aqueous suspension Appearance of shale after 48 hours About A. of specimen broke in fine pieces, rest broke up into large pieces. Broke up in some small and some large pieces. Less fine than pieces in Test No. 1. About same as Test No. 2.

o. Specimen uncrackcd, retained its original shape.

6 16% KPO -NaPO Specimen had small crack in edge. retained its original shape. 7 20% KPOa-NaPOa. Specimen same as in Test No. 5 except few small pieces flaked oti one side. 3 Control: Sodium Silicate Several pieces cracked off one side, some flaked off other side, rest of specimen retained its original shape.

In the above tests, Example 1, the ratio of KPOsINaPOs is 1:1.

Example No. 2 {Treating agents used are KPO; (insoluble potassium monometaphosphate) and sodium phosphate glass} Test No Type of aqueous solution Appearance of shale of tar 72 hours Control: Distilled water- Control: Sodium Silicate... Control:

2 volumes sodium silicate 1 volume saturated NaCl solution. 0.75% KPOIl 0.375% sodium phosphate glass. 1.5% KPO;

Specimen broke up in about 20 pieces. Specimen cracked clear across but retained its form. Piece cracked oil bottom edge.

Specimen broke up into about 10 pieces.

}Specimen in 1 piece. Few small pieces spelled ofi sample.

Specimen broke in about 6 pieces.

Specimen in 1 piece. Few small pieces spalled off.

1.125% sodium phosphate glass.. 7 ggg gi fi a g g: }Specimen broke into 2 large and 2 small pieces. 8 s D0 2.g7%12%d(1)um phosphate glass. 9 7.

9 Sodlum phosphate glasfL }Spec1men broke into 4 pieces. 10 d .fi ...h..t....]..... }Two lllJlgcesfi broke ofi specimen. Crack across top of specimen and some small pieces soiump ospaegass. spae o. n E 32 5; Bibi-Hail; g- 5:: Specimen in one piece. Little spalled ofi.

N own: The sodium phosphate glass used in the above tests is a phosphate glass having a molar ratio of 1:1 NaaO: 1 P105. In the above tests, Example 2, the ratio of KPO; to sodium phosphate glass is 2:1.

Example N0. 3

[Treating agents used are KPO; (insoluble potassium monometaphosphate) and N aCl] Test No Type of aqueous suspension Appearance of shale after 24 hours Control: Distilled water- Control:

2 volumes Sodium silicate 1 volume Saturated NaCl solution. 71% KPO Specimen crumbled and broke up with few large pieces on top.

About of specimen crumbled, rest split up into 3 or 4 pieces.

}Specirnen crumbled and broke up.

Specimen partly crumbled rest retained its original form.

About same as Test N0. 4.

8 7.14% KPO; Little crumbled on bottom rest split up into large pieces retaining some of its original ...31% NaCl form.

In the above tests, Example 3, the ratio of KPO :NaC1 is slightly greater than 3:1.

Example No. 4

[Treating agents used are NaP O (insoluble sodium monometaphosphate) and K2003 (potassium carbonate)] Test No. Type of aqueous suspension Appearance of shale after 24 hours Control: Distilled water Control:

2 volume sodium silicate Specimen broke into 15-20 pieces.

Specimen broke into 3 pieces. Specimen broke into 3 large, 2 small pieces, some crumbled ofi sample. Specimen broke into about 8 pieces.

Specimen broke into about 4 pieces, considerable spalled ofi bottom.

Specimen broke into 3 pieces, small amount spalled off.

Specimen broke into 3 pieces, a little crumbled oil.

Specimen broke into 4 or 5 pieces, some crumbled oft.

Specimen broke into 3 pieces, some crumbled ofi.

In the above tests, Example 4, the ratio of NaPOazK Coe is 1:2.

[Treating agents used are KPO; (insoluble potassium monometaphosphate) and sodium silicate] Type of aqueous suspension Appearance of shale after 24 hours Control: Distilled water Control:

2 volumes sodium silicate 1 volume saturated NaGl solution.

2a Control:

2 volumes sodium silicate 1 volume saturated NaCl solut n.

. Control: 2.5% sodium silicate solution.

Specimen broke in 1 large and about 10 small pieces. Specimen broke in about 10 pieces.

}Specimen broke in several large and about 6 or 7 smaller pieces.

}Spccimen broke in 5 pieces.

Specimen broke in about 6 pieces. Specimen broke in 2 large and about 6 or 7 smaller pieces; some crumbled ofi the bottom.

}Spccimcn cracked off the top. 2 pieces.

610% KP03 1.0% sodium silicat shape.

KP 0a 10a %KPO sodium silicate }Specimen in l picce.

Specimen in 1 piece.

}Specimen in 1 piece; a little crumbled ofi specimen.

}Specimen broke in 2 large and about 7 smaller pieces; some crumbled ofi bottom. }Spccimcn broke in 3 pieces; some crumbled off the top and side. }Specimen cracked in 1 place; retained its complete shape. }Specimen split in 3 pieces; a few chips spalled ed the bottom.

One-piece broke ofi specimen; some spalled ofi one side; rest of specimen in excellent Specimen in one piece.

Specimen cracked in 2 pieces.

Specimen split in 3 pieces.

: }Specimen broke in 2 pieces; some spalled oif one side.

}Specimen broke in 1 large, 2 small pieces.

In the above tests,Example 5, the ratio of KPO; to sodium silicate is 6:1.

Example N o. 6

[Treating agent used was sodium phosphate glass] Type of aqueous suspension Appearance of shale after 15 minutes Same as Test No Same as Test No Same as Test No Same as Test No Same as Test No Same as Test No Specimen crumbled and 1, except specimen crumbled into finer pieces.

. 2, except specimen crumbled into still finer pieces. 3, except specimen crumbled into 4, except finer pieces.

. 5 except finer pieces.

. 6 except specimen crumbled into pieces finer than in Test N o. 6.

broke up.

pieces finer than in Test No. 3.

NOTE: The phosphate glass used in the above tests was a sodium phosphate glass having a ratio of NazO:PgOs of about 1.1:l.

It will be observed that the sodium phosphate glass was less effective than the distilled water control, Test No. 1.

Example N0. 7

[Treating agent used was sodium silicate (N 320 SiO; ratio 1:2.00)]

Test No. Type of aqueous suspension Appearance of shale after 24 hours 1 Control: Distilled water Specimen broke into 3 large pieces, 1 small piece; small amount spalled off. 2 4.86% sodium silicate... Specimen broke into 3 pieces; some spalled off. 3 9.72% sodium silicate. Specimen broke into 4 pieces; some spalled oil. 4 14.58% sodium silicate. Specimen broke into 2 pieces; some spalled off. 5 19.44% sodium silicate.. Specimen broke into 2 pieces; some spalled off. 6 24.3% sodium silicate Specimen in one piece; some spalled ofii.

N OTE: This example is prior art.

The tests set forth in the foregoing examples show clearly the efiicacy of the water-insoluble alkali metal anetaphosphates Whether employed as mixtures of NaPOs and KPOs as in Example 1; whether employed singly but in admixture with a Water-soluble sodium salt, as mixtures of KPOs and sodium phosphate glass, as in Example 2; or as mixtures of KPOs and sodium chloride, as in Example 3; or as a mixture of water-insoluble NaPO: and an alkaline water-soluble potassium salt, such as K2CO3, as in Example 4; a mixture of KPOs (water-insoluble) and an alkaline sodium salt such as sodium silicate, as in Example 5.

It will be noticed by the comparison of Examples .5 and '7, that the mixture of KPO: and silicate is effective even though the concentration of silicate is far below the effective concentration of the silicate used either alone or with sodium chloride. See Examples 2, 3, and 4.

In the examples given, the column Appearance of shale after the stated times, merely indi-- cates the length of time during which frequent observations were made of the condition of the lumps of shale (oven-dried kaolin). After these time periods, the lumps were observed only occasionally. For instance, in the test represented by Example 1, the test specimens were preserved for a period of about two months, at the end of which time the test specimens in KPOs-NaPOz suspension were in the condition indicated after 48 hours. This was true of the specimens in Example 3 after a period of about two months. With respect to Example 1, the test specimens were removed from the KPOa- NaPOa suspensions, washed in water. Some of them were immersed in water for several days and one specimen was immersed in Water for about two weeks. These specimens did not disintegrate when given such drastic treatment.

A test corresponding to Examples 1 and 2 was made wherein the samples were heated in an oven to 110 C. for a period of four days while in a mixed suspension of K90: and NaPOs, and KPOa and sodium phosphate glass, respectively, and disintegration did not occur. The test specimens after removal from the suspension were washed in water and found to be stronger and harder to break than the original test specimens. These prolonged tests corresponding to Examples 1 and 2 indicate that the specimens in other examples herein stated and illustrating the invention, would behave similarly when subjected to similar drastic conditions.

Observation of the tests set forth in Examples 1 and 2 over periods of time longer than those noted in the time column, indicates that even though some of the test specimens cracked, hydrous disintegration of the specimens was prevented and inhibited.

Where an alkali metal water-insoluble monometaphosphate and an alkali-metal compound for solubilizing the insoluble monometaph-osphate are used to treat the mud, the ratio of the alkalimetal monometaphosphate to the alkali-metal compoiuid may vary from about 1:2 to :1.

When Water-insoluble potassium metaphosphate and sodium silicate are employed, the ratio of the potassium metaphosphate to the sodium silicate may vary from about 3:1 to about 10:1.

It is obvious that modifications and variations of the invention as hereinbefore described may be made without departing from the spirit and scope thereof.

What I claim as new and desire to secure by Letters Patent is:

1. A drilling mud having the property of inhibiting the disintegration of hydrolyzable shale comprising finely divided solids commonly used in drilling muds, water, and a mixture of waterinsoluble potassium monometaphosphate and water-insoluble sodium metaphosphate, the dry weight of said mixture in the mud being from about 1% to about 30% of the weight of the water content of the mud and the ratio of potassium monometaphosphate to the sodium monometaphosphate being about 1:1.

2. A drilling mud having the property of inhibiting the disintegration of hydrolyzable shale comprising finely divided drilling mud solids, water, and a mixture of water-insoluble potassium monometaphosphate and a water-soluble alkali metal the alkali-metal of which is other than potassium the amount of said mixture in the mud on a dry weight basis being from about 1% to about 30% of the weight of the water in the mud and the ratio of water-insoluble potassium monometaphosphate to the water-soluble compound being in the range of from about 2: 1 to 10: l.

3. A drilling mud having the property of inhibiting the disintegration of hydrolyzable shale comprising finely divided drilling mud solids, water, and a. mixture of water-insoluble potassium monometaphosphate and a water-soluble sodium phosphate, the dry weight of said mixture being from about 1% to about 30% of the weight of the water used in the mud and the ratio of water-insoluble potassium monometaphosphate to water-soluble sodium phosphat being about 2:1

4. A drilling mud having the property of preventing and inhibiting the disintegration of hydrolyzable shale comprising finely divided solids, water, and a mixture of water-insoluble potassium monometaphosphate and a water-soluble sodium compound the dry weight of said mixture being from about 1% to about 30% of the weight of the water used in the mud and the ratio of water-insoluble potassium monometaphosphate to water-soluble sodium compound being in the range of from 2:1 to 10:1.

5. In the drilling of wells with the use of a drilling mud, the method of preventing the disintegration of hydrolyzable shale which comprises circulating through the well, as the drilling proceeds through formations of shale which disintegrate on contact with water, a drilling mud comprising finely divided solids and water, and adding to said mud a mixture of water-insoluble potassium monometaphosphate and Waterinsoluble sodium metaphosphate, the dry weight of said mixture being from about 4% to about 20% of the Weight of the water content of the mud and the ratio of the potassium monometaphosphate to the sodium metaphosphate being about 1:1, said mixture being added in amount suflicient to inhibit the disintegration of said shale by the water in said mud and being substantially in excess of that amount required for reducing the viscosity of such drilling mud.

6. In the drilling of wells with the use of a drilling mud the method of preventing the disintegration of hydrolyzable shale which comprises circulating through the well, as the drilling proceeds through hydrolyzable shale formations, a drilling mud comprising finely divided solids commonly used in drilling muds and water, and adding to said mud a mixture of water-insoluble potassium monometaphosphate and a sufiicient amount of a watersoluble alkali-metal compound the alkali-metal of which is other than potassium, to exert a solubilizing effect upon the Water-insoluble potassium monometaphosphate, said mixture being added in amounts based on the weight of water in the mud sufiicient to inhibit the disintegration of said shale formation by the water in said mud and being substantially in excess of that amount required for reducing the viscosity of such a drilling mud.

7. In the drilling of wells with the use of a drilling mud the method of preventing the disintegration of hyd-rolyzable shale which comprises circulating through the well, as the drilling proceeds through hydrolyzable shale formations, a drilling mud comprising finely divided solids and water, and adding to said mud a mixture of water-insoluble potassium monometaphosphate and a sufficient amount of a watersoluble sodium phosphate to exert a solubilizing effect upon the water-insoluble potassium monometaphosphate, in amounts based on the weight of water in the mud sufiicient to protect such shale against disintegration by the water in said mud and in amount substantially in excess of that required to reduce the viscosity of such drilling mud.

8. In the drilling of wells with the use of a drilling mud the method of preventing the disintegration of hydrolyzable shale which comprises circulating through the well, as the drilling proceeds through hydrolyzable shale formations, a drilling mud comprising finely divided solids commonlyused in' drilling muds, water, and adding to the mud a mixture of water-insoluble potassium monometaphosphate and a water-soluble sodium compound the amount of said water-soluble sodium compound being sufiicient to exert a solubilizing efiect on the Water-insoluble potassium monometaphosphate and said mixture being added on the basis of weight of water in the mud and in amounts sufficient to prevent the-Water in said mud from hydrolyzing said shale and thereby checking disintegration thereof said added amounts being substantially in excess of those required to reduce the viscosity of such drilling mud.

9; The method of preventing an aqueous drilling' mud from attacking and causing disintegration of hydrolyzable shales encountered in formations through which a well is drilled, comprising adding to the mud a treating agent containing a water-insoluble alkali metal monometaphosphate, the amount of monometaphosphate added to the mud being, on a dry weight basis, from about 1% to about 30% of the weight of Water'in the mud.

10: A method according to claim 9 in which the treating agent comprises a suspension in waterof water-insoluble sodium and potassium metaphosphates wherein the relativeamounts of water-insoluble sodium-metaphosphate to waterinsolublepotassium metaphosphate are such as to effect a'solubilizing reaction between said metaphosphates, the amount of phosphates of such agent added to the mud being, on a dry weight basis, from about 1% to10% based on the weight of water in the mud.

11; A method according to claim 9 in which the treating agent comprises a suspension in water of water-insoluble sodium and potassium metaphosphate the relative amounts of Waterinsoluble sodium metaphosphate and water-insoluble potassium metaphosphatebeing such that a mutual solubilizing reaction is effected and the amount of phosphates of such agent added to the mud being, on a dry weight basis, from about 4% to 20% based on the weight of water in the mud.

12. The method of preventing an aqueous drilling mud fromattacking and causing disintegration' of hydrolyzable shales encountered in formations through which a well is drilled, which comprises adding to the mud a treating agent containing a Water-insoluble alkali metal monometaphosphate and an alkali-metal compound the alkali metal of which is dissimilar to the alkali metal of said monometaphosphate which compound acts as a solubilizing agent for the monometaphosphate when contacted with said waterinsoluble alkali-metal monometaphosphate in the presence of Water, the amount of monometaphosphate added to the mud being, on a dry weight basis, from about 1% to about 30% of the weight of water in the mud and the ratio of the monometaphosphate to the solubilizing agent being in the range of from about 10:1 to about 1:2.

13. A drilling mud for inhibiting the disintegration of hydrolyzable shale comprising finely divided solids, water, and a mixture of waterinsoluble potassium monometaphosphate and a water-soluble sodium compound, said water-soluble sodium compound being in sufficient concentration to exert a solubilizing effect on the Water-insoluble potassium monometaphosphate, the amount of said mixture being substantially in excess of that required for reducing the viscosity of such drilling mud and being at least that amount required to retard the disintegration of hydrolyzable shale, which amount may be determined by tests.

NORMAN E. MARTELLO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,292,267 Garrison Aug. 4, 1942 2,294,877 Wayne Sept. 1, 1942 2,296,716 Jelen 1 Sept, 22, 1942 2,315,995 Williams Apr, 6, 1943 2,324,124 Williams July 13, 1943 2,353,230 Garrison et al July 11, 1944 2,365,489 Partridge Dec. 19, 1944 2,379,100 Partridge June 26, 1945 OTHER REFERENCES Rudy et al., A; P, C. publication, Ser. No. 434,- 621, June 1, 1943.

Certificate of Correction Patent No. 2,444,359.

NORMAN E. MARTELLO It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 9, line 60, clalm 2, after the word metal and before the insert compound; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant G'ommz'ssz'oner of Patents.

June 29, 1948.

NORMAN E. MARTELLO It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 9, line 60, claim 2, after the word metal and before the insert compound; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 7th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

June 29, 1948.