Document My2k2bXKNavLx9rm7NkRGBjz

FILE NAME: Drilling Muds (DRM) DATE: 1955 Dec 13 DOC#: DRM002 DOCUMENT DESCRIPTION: US Patent - Drilling Fluid United States Patent Office ,2 727,001 Patented Dec. 13, 1955 1 2 States Letters Patent No. 2,044,758, does not undergo flocculation in the presence of salts and therefore will 2,727,001 maintain the desired viscosity of drilling muds prepared from salt water, or of muds which become contaminated DRILLING FLUID 5 by salts during the drilling. With this type of clay, how David A. Rowe, Houston, Tex., assignor to Sun Oil Com pany, Philadelphia, Pa., a corporation of New Jersey ever, it has been found that relatively large amounts of starch are required in order to reduce the water loss prop erties of the mud to a desirably low value. No Drawing. Application December 24, 1952, Serial No. 327,901 10 Claims. (Cl. 252-- 8.5) It has now been found that aqueous drilling muds pre 10 pared from the more common types of colloidal clays can be rendered suitable for use in the presence of salt by incorporating therein finely divided asbestos obtained from the mineral chrysotile. The presence of this particu lar type of asbestos in some manner not fully understood This invention relates to drilling fluid for use in the 15 prevents flocculation of the clay particles due to salt and rotary drilling of wells and more particularly to aqueous maintains the viscosity of the mixture at a desired value. drilling fluid compositions having enhanced viscosity, sta Thus, according to the invention, an improved aqueous bility, and water loss characteristics. The drilling fluid drilling mud is prepared by admixing water with a col compositions according to the invention are especially loidal clay and with finely divided asbestos derived from suitable for use in the presence of salt. 20 chrysotile. In drilling wells such as oil or gas wells, the drilling There are six different types of asbestos known com fluid which is circulated into and out of the borehole mercially, which are obtained from the following min should have certain properties so that it will perform its erals: chrysotile, amosite, anthophyllite, crocidolite, desired functions properly. One important characteristic tremolite and actmolite. (See "Asbestos, a Mineral of Un of the fluid is viscosity. It is essential that the fluid have 25 paralleled Properties" by M. S. Badollet, Transactions of sufficient viscosity to suspend the drill cuttings so that they the Canadian Institute of Mining and Metallurgy, vol. will be carried from the borehole but the viscosity should LIV, 1951, pages 151-160). The term "asbestos" is used not be so high as to render the pumping operation difficult. as a generic designation of these various types. The fibers It is generally desirable that the Stormer viscosity of the obtained from these minerals vary from soft, flexible fibers drilling fluid be at least 10 and less than 100 centipoises 30 of good spinnability to harsh, brittle fibers having poor and a more preferable range is 20-40 centipoises. The spinnability. most common drilling fluids are prepared by dispersing a< Of these various types of asbestos, only one--namely, colloidal clay such as bentonite in water, the clay being chrysotile asbestos--is suitable for preparing a drilling added in sufficient amount to impart the desired degree of mud in accordance with the present invention. While viscosity to the mixture. Weighting material, such as 35 asbestos derived from chrysotile will vary in properties barytes, iron oxide, et cetera, may also be added. dependent upon the deposit from which the chrysotile is Another desirable characteristic of the drilling fluid is obtained, nevertheless any chrysotile asbestos is effective its wall building characteristic, or the ability to form a for use in the present invention. It is preferred to employ thin mud sheath on the wall of the borehole that will pre chrysotile which yields soft, flexible fibers, as this kind is vent loss of water to the formations traversed. The cus 40 most effective in preventing or minimizing flocculation of tomary procedure for improving water loss characteristics clay particles in the presence of salt; but it has been found of aqueous drilling fluid is by adding a suitable organic that chrysotile of the kind which yields harsh, brittle colloid, such as starch or carboxymethylcellulose to the fibers is also effective although not to the same degree. mud composition until the water loss is reduced to a On the other hand, it has been found that asbestos de desirably low level. 45 rived from any of the minerals other than chrysotile is It is well known that the ordinary drilling mud com substantially ineffective in avoiding the undesirable floc prising bentonitic clay dispersed in water is unsatisfactory culating effect of salt on the clay particles. This may be for use under conditions in which the mud contains or due to the fact that chrysotile fibers are positively charged, becomes contaminated with salt. Soluble salts of sodium, whereas fibers derived from the various other minerals calcium, magnesium and the like are often encountered 50 from which asbestos is made are negatively charged. It during drilling, as when the drill penetrates a brine-con is not definitely known at present, however, whether or taining formation or a formation such as a salt dome, not the type of electric charge carried by the fibers plays salt bed, gypsum, anhydrite and the like. Also, in coastal an important role in determining the effectiveness of the regions salt water may be the only available source of asbestos. Grades of asbestos which are especially useful water for preparing the drilling mud, so that it, of neces 55 for the present purpose are obtainable, for example, from sity, will contain salt. In other instances salt is purposely chrysotile deposits in Vermont, Quebec and Ontario. added to the drilling fluid at some point in the operation The degree of effectiveness of chrysotile asbestos in and attempt is made to stabilize the mixture by addition the present invention is also dependent upon the extent of special materials in anticipation of drilling into a salt- of purification achieved during its manufacture. Com containing formation. The presence of salt in the drilling 00 mercial preparation of asbestos involves milling followed mud, generally in amount above 10,000 p. p. m. tends to by suitable separation procedures, such as washing or air cause flocculation and sedimentation of the clay particles flotation, and usually a number of different grades of from the aqueous phase. Flocculation results in a de asbestos of varying purity are produced. Some of the crease in viscosity and an increase in water loss. When products may contain a relatively high proportion of ser the salt is present in sufficiently high concentration, the 05 pentine rock dust or other impurities while others may be viscosity will become so low that the mixture will have no essentially chrysotile fibers in a high state of purity, it has utility as a drilling fluid. been found that any of the commercial chrysotile prod In order to avoid the difficulties resulting from the pres ucts containing a substantial proportion of chrysotile ence of salt, it has been general practice, heretofore, to fibers are effective for the present purpose and that the employ a special type of clay in preparing the mud com 70 effectiveness increases with increasing purity. However, position. This clay, which is a certain type of zeolite since the more highly purified products are more expen found in the Georgia-Florida area as described in United sive, it may often be more economical in practicing the 3,787,001 3 present invention to use fibers of lower purity but in in 4 The following examples are illustrative of the inven creased amount sufficient to impart the desired viscosity tion and advantages derived therefrom: and stability characteristics to tire drilling mud composi Example I tion. The asbestos incorporated in the drilling mud should 5 Four mud compositions were prepared, each of which be of a fineness such that it will pass 16 mesh (U. S. Sieve contained 315 cc. of saturated salt water and 22 g. of Series) and more preferably of a fineness such that it will dispersed clay or clay-asbestos solids. One of the com pass 50 mesh. It has been found that, as a practical mat positions had no asbestos while the others had varying ter, grinding of the more flexible forms of chrysotile as amounts of asbestos. Wyoming bentonite and Quebec bestos is facilitated by adding clay to the asbestos and 10 chrysotile asbestos ground to a fineness such that it grinding the two together. Clay in amount of at least passed 50 mesh were used in each case. The composi twenty-five (25% ) per cent by weight aids the grinding tions had the following Stor.mer viscosities: and handling of the ground product and it is preferable to use at least fifty (50% ) per cent clay. The resulting mixture of finely divided clay and asbestos can then be W e ig h t ra tio of A sbestos to C lay V iscosity, cp used conveniently as an additive for supplying to the final mud composition the desired amount of asbestos. Weight #1......................................................................................... (n o a s b e s t o s ) .- 1 ing agents may be added to the mud when required to give #2 . . . . ....... . ......................................... 5 :6 5 ...................... 14 the desired weight, and oil may be dispersed in the mix #3 - .................. . .............................. 1 0 :9 0 .................... # 4 ......................................................................................... 1 5 :8 5 .................... 26.6 38 ture if an emulsion type mud is desired. The amount of asbestos employed in preparing a drill These results show the effect of increasing the amount ing fluid according to the invention should be sufficient of asbestos in raising the viscosity to a desirable level. to maintain its viscosity substantially above that of water, Under these conditions, in order to secure a viscosity and it usually will be desirable to use an amount such of above 10, the proportion of asbestos to clay should that the Stormer viscosity of the drilling mud composition w0 be at least 4:96; and for a viscosity above 20, the pro will be within the range of 10-100 centipoises, more pref portion should be at least 8:92. erably, 20-40 centipoises. An increase in the amount of asbestos increases the viscosity of the resulting compo Example II sition, so that the amount to use in any given case will Another set of compositions was prepared in the manner depend on the viscosity desired. As a general rule, the 30 specified in Example I except that fresh water was used, ratio of asbestos to clay in the composition should be at least 2:98 on a weight basis. With most grades of with results as follows: chrysotile asbestos that are available commercially, it usually will be desirable to use an amount of asbestos such that the asbestos to clay ratio in the mud compo W eight ratio of A sbestos to C lay V iscosity, cp. sition is at least 5:95 and typically of the order of 10:90. In order to obtain the desired properties of the drill # 1 ......................................................................................... ( n o a s b e s t o s ) . . #2 .............. ,,............... ................... 5 :0 5 ....................... 15 19 ing fluid, a considerably higher asbestostclay ratio may #3 ............................................................ 1 0 :9 0 .................... 26.5 be required in some instances but it seldom will need to u ............................................................ 1 5 :8 5 ................... 30 exceed 30:70. As the clay component of the drilling fluid, any known or suitable colloidal clay having base exchange proper These results show that the addition of chrysotile as bestos to a fresh water mud increases the viscosity. ties can be used. This includes the bentonitic clays, Example HI kaolin and zeolitic clays of the Florida-Georgia type; and for the present purposes, shales may be considered as 45 Five mud compositions were prepared, each of which also included. The invention has outstanding utility contained 315 cc. of saturated salt water and 22 g. of in the preparation of a salt resistant mud from the ben dispersed clay or clay-asbestos solids. One of the com tonitic type of clays, which clays are much more widely positions had no asbestos while the others had varying available than the special zeolitic clays heretofore used amounts of asbestos. A Texas bentonite and Quebec in preparing salt water muds. However, the use of 50 chrysotile asbestos ground to a fineness such that it would finely divided asbestos of the type described in conjunc pass 50 mesh were used in each case. The compositions tion with the zeolitic clays also is advantageous in that had the following Stormer viscosities: the volume yield of mud for a given weight of total solids added to secure a mud of a given viscosity is sub stantially increased, and furthermore the requirements W eight ratio ot A sbestos to C lay V iscosity, cp. of organic colloid additives, such as starch, for securing a satisfactorily low water loss are substantially reduced. #1 ..................................................................... 1 In locations where the only available water supply is 9 .1 :9 0 .9 ............... #3......................................................................................... 1 3 .7 :8 6 .3 ............. 3 12 salt water, practice of the present invention will involve #4 ............................................................................ 1 8 .2 :8 1 .8 ............. 22 adding finely divided asbestos to the drilling mud when it 5 ...................................... .......................... 22.7:77.3............. 24 is originally prepared. In other locations the drilling These results show the effect of increasing the amount operation may be started with a conventional mud which of asbestos in raising the viscosity to a desirable level. is subsequently converted to a composition according to Under these conditions, in, order to secure a viscosity of the present invention by the addition of finely divided 65 above 10, the proportion of asbestos to clay should be at asbestos at any time this may become desirable or neces least 13:87; and if a viscosity of at least 20 is desired, the sary. This usually will be when the mud, during the proportion should be about 17:83. course of drilling, becomes sufficiently contaminated v/ith sodium chloride or other soluble salts that flocculation Example IV difficulties are likely to occur, for example, when the 70 A comparison was made between a salt water mud pre salt content of the mud increases to above 10,000 p. p. m. pared according to the present, invention and one pre Incorporation of the finely divided asbestos in the mud pared from a zeolitic clay, of the, Georgia-Florida type, will then maintain the viscosity at the desired level and specially produced commercially for salt water use. The also avoid excessive water loss with a smaller amount zeolitic clay mud contained 22 g. of clay, while the mud of organic colloid additive. 76 of the present invention contained 4 g. of chrysotile ,2 727,001 6 5 asbestos and 18 g. of Texas bentonite, the total solids of the clay particles, thereby causing the viscosity to be content of the mixes thus being the same. The asbestos considerably higher than that of the mixture to which no was a Quebec product and was ground to a fineness such asbestos was added and also preventing separation of clear that it would pass 50 mesh. Stormer viscosities of these water from the composition. compositions after five minutes of mixing and after sixty S minutes of mixing were determined to be as follows: Example VIII Two other batches of drilling mud were prepared in Z e o lite M ud A sbestosC lay M ud exactly the same manner as in the preceding example, but in this case purified asbestos samples derived from 10 two types of Arizona chrysotile were used. One of the 3 17 asbestos samples was the harsh, brittle type while the 23.5 <13 other was the soft, flexible type. In each case 2 g. of asbestos was used in admixture with 20 g. of Wyoming These results show that the asbestos-clay mixture was bentonite. Tests were made in the same manner as de more effective in improving viscosity than was the special 15 scribed in Example VII for comparison with the results Georgia-Florida zeolitic clay. therein listed. Example V The asbestos-clay mud of the preceding example was T y p e of V iscosity, g. driv in g stirred at low speed for 96 hours to determine whether 20 or not the mixture would be relatively stable over a pro A sbestos w eig h t for 10 seco n d s longed period. At the end of this time no tendency to ward flocculation was observed. H . ..................................... # 5 ............... A r i z o n a - s o f t ___ 130 (S o lid ) A m o u n t of clear w ater a t top V W in 24 hours. N o n e in 24 h o u rs. Example VI 25 These results show that the harsh type o f chrysotile is Additional comparative runs to determine water loss effective in increasing viscosity and in improving stability properties were made with a zeolitic clay mud and an of the mixture but that it is not nearly so effective as the asbestor-bentonite clay mud prepared as described in soft type. The fact that mixture # 5 was solid even Example IV, but also containing pre-gelatinized starch though it contained only 2 grams of the soft chrysotile in amounts of 2 and 4 lbs./bbl. The A. P. I. 30-minute 30 means that this form of asbestos is so effective that only water loss values of the mud compositions were deter a very small proportion need be used to secure the desired mined to be as follows: viscosity. Its effectiveness is thought to be due not only to its type (i, e. soft, flexible fibers) but also to the fact A . P . I. W ater loss, cc. that it had been highly purified. A m ount of S tarch, lbs./bbl. Z e o lite M ud 35 A sbestosC lay M ud Example IX Four other compositions were prepared for comparison 2 ........................................................- .......................................... 59 4 ............................................. ................................................ 16 10 with those of Examples VII and VUI. These were pre 7 pared and tested in the same manner as described in those These results show that the amount of starch required for effectively lowering the water loss is less for the mud prepared according to the present invention. For ex 40 examples, employing 2 g. of asbestos and 20 g. of Wyoming bentonite, but in this instance the asbestos samples were derived from other minerals as listed below. awmatpelre,lo4slsbso.fotfhsetazrecohlipteercblabyl. wmausdretoqutihreedstaomreedluevceelthaes 45 T y p e of A sbestos V iscosity, g. driving w eig h t for A m o u n t of clear w ater a t top was obtained with 2 lbs./bbl. with asbestos-containing 10 seconds mud. Example VII # 6 ............................................. 7 .............................. Three comparative batches of drilling mud were pre 50 #8 _ _ ........................................ # 9 ............................................ anthophyllite--h a rsh .. pared comprising Wyoming bentonite in saturated salt 74 M e" a fte r 24 h rs. 74 W * a fte r 3 h rs. 60 Do. 74 a fte r 24 hrs. water. The first contained no asbestos and the other two contained varying amounts of a Johns-Manville asbestos Since the comparative composition containing no asbestos designated as 6D20 (standard Canadian chrysotile as had a viscosity of 74 as shown in Example VII, it can be bestos classification), a soft flexible type of Canadian 55 seen that the types of asbestos used in mixtures # 6 -# 9 chrysotile. Each was prepared by adding to 315 cc. of were wholly ineffective in increasing viscosity even though saturated salt water 22 g. of the bentonite or bentonite- some stabilization of the mixtures against separation asbestos mixture and then mixing in a high speed Waring evidently resulted. The failure to increase viscosity is Blendor for 5 minutes. Viscosity measurements were interpreted as due to the inability of these types of asbestos then made with a Stormer viscosimeter and the values 60 to inhibit flocculation of the clay particles in the presence were expressed in terms of the number of grams of driving of salt, at least in the manner or to the extent effected by weight required to cause the spindle to rotate through a chrysotile. specified number of revolutions in 10 seconds. There It is recognized that prior disclosures have suggested the after the mixtures were allowed to stand and were ob use of asbestos, among numerous other fibrous or flaky saerravteedd atot tdheetetromp.ineRheoswultsmuwcehrecalesafrolalqouweso:us layer sep 65 mingatewrihaalst, ifsorreufseerrienddrtoilliinng tmheudarats aasn a"lgoesntt cfiorrcuplraetvioenn.t" This involves using relatively long fibers which will form G ram s in M ixture bentonite asbestos V iscosity, g. driving w eight for 10 se co n d s A m o u n t of clear w ater a t top a mat on the borehole wall adjacent to any formation that is sufficiently porous that the mud fluid as a whole would otherwise enter it and thus not be returned from 70 the well for re-use. In the present invention, however, n ...................................... 22 0 # 2 - .................................... 21.3 0.7 # 3 ...................................... 20 2 74 in 24 hrs. 120 N o n e i n 24 h rs . 190 Do. the asbestos is ground to a fineness at which it would be in capable of preventing lost circulation and at which it has a heretofore unrecognized characteristic, namely, the ability to increase viscosity of the mud composition and These results show that the asbestos inhibited flocculation 75 prevent an increase in water loss due to flocculation of the