US2474329A - Drilling fluid for heaving shale - Google Patents

Description

UNITED STATES PATENT OFFICE 2,474,329 DRILLING FLUID FOR HEAVING SHALE Richard A. Salathiel, Houston, Tex., assignor, by mesne assignments, to Standard Oil Development Company, Elizabeth, N. J a corporation of Delaware No Drawing. Application January 13, 1948, Serial No. 2,139

4 Claims. (Cl. 2528.5)

This invention relates to a drilling fluid which disintegrates continuously to such an extent as to will effect a minimum of disintegration of heavin rf re w h r llin p on ing shale. The rates of disintegration of sloughing and In the rotary drilling of oil and gas wells fluid heaving shales may be decreased when using conis pumped down the drill stem to the drill at the Ventional drilling muds by adding materials which Working face in the bottom of the bore. Th reduce the rate of filtration loss and improve annular space between the drill stem and the ties from shale disintegration are encountered borehole walls. In some areas, as for example 1.0 occasionally and serious hole enlargement in shale cessfully by the ordinary rotary drilling methods drilling fluids, the methods heretofore practiced when using common mud fluids. These shales have not been entirely satisfacto Not the least have a tendency to disintegrate by swelling or of the disadvantages of such methods is the high cracking or both so that the walls of the hole are cost of materials required in their practice.

unstable and material sloughs into the hole or It is an object of this invention to P d t moves into the hole by swelling. The caving or drilling fluid for the drilling of boreholes into cracking caused by the presence of seams or thin the disintegration thereof.

layers of readily hydratable and swellable ma- In accordance with the present invention the terial closely interbedded with harder and less disintegration of heaving shale is prevented by readily hydratable shale materials. In many employing a drilling fluid consisting of water, Cases n the pa t filling 0 h bo eho e, 0 parts clay, alkali metal hydroxide, salt, and materials of it, have resulted in stuck drill pipe and abanfor promoting the efiectiveness of the hydroxide donment of further eiforts to make additional in preventing disintegration of shale. Instead of hole. It is common in drilling shale sections addin the alkali metal hydroxide, salt and a mawh ch d no w ll or slou h v re y enough to terial for promoting the effectiveness of the hystop drilling operations or even to cause extreme droxide t a mixture of water and clay, th

difliculty to observe extensive enlargements of the materials may be added to ordinary drilling mud borehole or even the formation of subterranean provided the drilling mud contains a suitable cavities. In these cases although the materials amount of clay to give a fluid having the desired which swell, slough or cave into the hole are reyield point and Viscosity after the above moved by the arming fluid the enlarged holes and tioned constituents have been added. Finely dicavities which are formed interfere to various devided material Such as barytes, iron oxide, and grees with operations involved in drilling and the like may be used to supplement the c1 ay in completing the well. When such enlargements formingthe drilling mud and (.mvmes are formed the rate of.flow of h Anumber of different materials may be used for mud s greatly reduced and the carrying ca promoting the effectiveness of the alkali metal thereof is diminished. To increase the rate of hydroxide employed and I have found that the pumps having a large excess capacity must alkali metal salts of weak inorganic acids are 2: 0 5 2 5 3 512232 32 2 3 22 65 2 8? 2 particularly suitable. Of these sodium carbonate ment are required in order to obtain a proper 15 9 y an efiectlve Promoter but 15 also sealing 2"? l With? $23??? 1333; fj i oiumsupiean lSOlmpO a a tcg23553 3; a i g a i s lie li y grgtigif 3f been found to give t d esults for promoting the h l adjacent th borehole by water contained effectiveness of alkali metal hydroxide in the drillin the ordinary drilling mud. Thus, a heaving ing of v n shale f rma ions. 0f g,ou1 s the shale may be defined as oneiwhich in ontact potassium OI lithium salts Of weak 11'101' amc aCldS with the usual water base drilling fluids swells or may be employed although they are somewhat more expensive than the corresponding sodium salt.

It is known that when shales are immersed in suitably strong solutions of alkali metal hydroxides they do not swell. Tests made by placing samples of shales in solutions of sodium hydroxide showed that when substantially less than the optimum concentration of sodium hydroxide was used, swelling and sloughing still occurred and little advantage was gained. It was also observed that when substantially more than the optimum concentration of sodium hydroxide was used swelling did not occur but cracking was observed which weakened some of the shales. Shale samples differed among themselves in the optimum concentration of sodium hydroxide solutions required for their preservation. These optimum concentrations for the different shale samples tested varied within the limits of and 30% by weight of sodium hydroxide. It was further observed that the amount of sodium hydroxide required to preserve a particular shale could be decreased by adding sodium chloride, a much less expensive material, to the solution. With concentrations of sodium hydroxide and sodium chloride above the optimum, as with the sodium hydroxide solutions, cracking of some of the shales occurred. It was still further observed that the addition of small amounts of certain salts to the caustic alkali solutions or to the solutions of sodium chloride and caustic alkali, of more than sufficient concentration to prevent swelling, served to prevent cracking of the shales and thus adapted the solutions to preserving a wider range of shale types. For example, I have found that a fluid consisting of 70.3 weight percent water, 8.25 weight percent sodium hydroxide, 4.15 Weight percent sodium carbonate, and 17.3 weight percent sodium chloride is substantially equivalent to a weight percent solution of sodium hydroxide from the standpoint of preventing the swelling of clay and shale samples and superior to such a solution from the standpoint of cracking of some of the shale samples. Thus, the use of a material such as sodium carbonate greatly reduces the cracking of shales contacted by alkali hydroxide solutions. It has further been found that the use of sodium carbonate makes any given caustic-brine solution effective over a wider range of shale types than is the case when no such promoter material is used.

It is to be understood that the amount of material for promoting the effectiveness of the hydroxide to be employed in the drilling fluid may vary within a substantial range depending largely on the character of the shale encountered. The minimum concentration of the electrolytes which will be effective in any particular case may be determined by experimentation, that is, by obtaining a sample of the shale through which drilling is to be accomplished and observing its rate or degree of disintegration by the action of water-containing various concentrations of the materials. When optimum amounts are incorporated in the drilling mud, the rate of disintegration of the shale sample will be negligible. In general, the amount of alkali metal hydroxide may be varied from about 6% to about 15% by weight of the total fluid, and when such concentrations are utilized, the amount of the material for promoting the eifectiveness of the alkali metal hydroxide may vary from about 1% to about 10% based on the total fluid, the preferable range of the latter being from about 2% to about 6%.

The concentration of the alkali metal hydroxide required will generally increase as the drier shales are encountered in deep, high temperature formations. Salt is added to the fluid in quantities sufficient to substantially saturate the fluid after the alkali meta1 hydroxide and the promoter material have been dissolved therein.

Although any alkali metal hydroxide may be employed, it is preferable to use sodium hydroxand cheapness. Although any of the previously mentioned materials for promoting the effectiveness of the hydroxide may be employed, I prefer to use sodium carbonate not only because it is slightly superior but also because of its ready availability. Either commercia1 salt or pure sodium chloride may A solution representative of those effective in preserving a wide variety of shales contains 70.3 weight percent water, 8.25 weight percent sodium hydroxide, 4.15 weight percent sodium carbonate and 17.3 weight percent sodium chloride. This solution at about 75 F. has a specific gravity of 1.25 and a viscosity of about 4.7 centipoises. While clays do not disperse readily into solutions of this kind, it is easily possible to prepare muds having suitable viscosity and gel properties by dispersing clay into water before adding the electrolytes to provide an aqueous phase of the desired composition. The following are examples of muds so prepared in which the aqueous phase contained 70.3 weight percent water, 8.25 weight percent sodium hydroxide, 4.15 weight percent sodium carbonate and 17.3 weight percent sodium chloride:

17 O. P. 25 C. P. S. Vis. S. Vis. Mud Mud Per cent of Fluid 93 Per cent of El Paso Clay 4 5 Per cent Wy. Bentonite Clay 1 2 The mud referred to above as having 17 centipoises viscosity (at 600 rpm Stormer) had an extrapolated yield value of 18 grams Stormer while the 25 centipoise viscosity mud had an extrapolated yield value of 24 grams Stormer. filtration rate of the 25 centipoise viscosity mud was 66 cos. in 30 minutes at pounds as tested on the standard API low pressure mud tester. Additions of small amounts of starch to muds of this type decrease the filtration rate greatly. For example, addition of 1.2% of pearl starch to a mud prepared in the same way as those described above but which contained 4% of El Paso clay as the only clay component provided a mud fluid of the following properties: Viscosity, 41 centipoises; extrapolated yield value, 23 grams Stormer; API filtration rate, 6 cos. (30 minutes at 100 pounds).

Gelation rates of the caustic-brine-promoter muds are high making it desirable to keep the yield values of such mud fluids as low as possible while holding the desired solids in suspension. By so doing, gas or air cutting of the mud are avoided and at the same time sand and cuttings may easily be separated from the mud at the surface.

It will be apparent from the above data that drilling fluids having desirable viscosities and yield values may be prepared from clay with water containing sodium hydroxide, brine, and sodium carbonate. Viscosity and yield value may, of

course, be controlled by controlling the amount for promoting of clay in the drilling fluid. These Values will be influenced by the type of clay used and normally it will be desirable to use the clay produced from the borehole. In general, the clay content of the fluid will not be less than 2% nor exceed about although in some instances it will be understood that the clay content may be somewhat less or somewhat greater than these values.

It will be further understood that in the practice of my invention other materials may also be added to form the drilling mud. For example, if a heavily Weighted mud is required it may be necessary to add weightin materials such as barytes, iron oxide and the like. In addition, treating agents such as sodium-hexametaphosphate, tannin, and the like, may also be included in the drilling fluid.

The nature and objects of the present invention having been thus described, what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. A drilling fluid for preventing the hydrous disintegration of shales comprising clay, water, 6 to sodium hydroxide by weight based on the fluid, 1 to 10% by weight based on the fluid of an alkali metal salt of a weak inorganic acid the efiectiveness of the sodium hyhydroxide is an alkali metal sulphite.

4. A composition in accordance with claim 1 in acid for promoting the efiectiveness of the sodium phosphate. RICHARD A. SALATHIEL.

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

UNITED STATES PATENTS Number Name Date 2,044,758 Cross et al June 16, 1936 2,073,413 Cross et a1 Mar 9, 1937 2,109,858 Cannon Mar. 1, 1938 2,191,312 Cannon Feb. 20, 1940