Mixed metal hydroxides for thickening water or hydrophilic fluids

MIXED METAL HYDROXIDES FOR THICKENING WATER OR HYDROPHILIC FLUIDS

This invention concerns the thickening of water or hydrophilic fluids by use of mixed metal layered hydroxides.

There are various reasons for thickening water, aqueous solutions, hydrophilic fluids, and the like, such as for use as water-based metal working fluids, fire control fluids, oil field drilling fluids, food additives, hydraulic fluids, water-based paints or coatings, stripping solutions, and other applications wherein thickening of a liquid or solution is beneficial.

Water thickening agents, such as guar gum and polyacrylamide are not stable to high shear, hydrothermal treatment above about 250°F (121°C), oxidation, bacterial attack, and salts. To make up for some of these problems, 15 such additives as bacteriacides and antioxidants are sometimes required.

Thickening agents or viscosifying agents for aqueous materials, such as drilling fluids, which involve some form of hydrous aluminum compound are disclosed, for

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-2example, in U.S. Patents 4,240,915; 4,349,443;

4,366,070; 4,389,319; 4,428,845; 4,431,550; 4,447,341;

4,473,479; and 4,486,318. Patents disclosing other forms of aluminum compounds for the same purpose are, for example, U.S. Patents 4,240,924; 4,353,804;

4,411,800; and 4,473,480. Similar patents disclosing other types of viscosifying agents are, for example, U.S. Patents 4,255,268; 4,264,455; 4,312,765; 4,363,736; and 4,474,667.

The above patents deal with the formation of the hydrous aluminum compounds in situ. The major disadvantages to such a process are: (1) The resulting thickened fluid contains copious amounts of reaction salts. This may be undesirable in many situations.

For example, in applications such as paints, metal working fluids, or water-based hydraulic fluids, the presence of salt could cause severe corrosion problems.

In the case of oil field drilling fluids, many performance additives do not work well if salt is present.

Thus it is desirable to drill in fresh water if possible.

(2) The reactions described in the cited patents are run in situ (e.g. in the mud pit of a drilling rig); under such conditions the reaction cannot be adequately controlled and the properties of the resultant thickener may be unpredictable.

Other problems with the use of A1(OH)₃ as a gelling agent for various processes are as follows:

1. Al(OH)₃ gels are known to detrimentally change with time unless certain anions such as carbonate or citrate are present.

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-32. The rheology of A1(OH)₃ is not very constant with changing pH values. For example, a slurry of Al(0H)₃ may be very thick and uniform at pH 6 but at pH 10, which the drilling industry prefers, the slurry collapses and the A1(OH)₃ settles out of suspension. This creates significant problems since most drilling operations are run at pH values in the 10 '- range of 9 to 10.5.

A historically popular thickening agent, especially in drilling mud, has been mineral clays, such as bentonite clay, often used with other agents or densifiers, such as Fe₂0₃, BaS0₄ and others. Variations 15 from batch to batch of bentonite clay, and sensitivities to ions and temperature have resulted in erratic results and adjustment of the formulation is often required during use; this hampers the drilling operation.

Certain forms of crystalline layered mixed 20 metal hydroxides are disclosed, e.g., in U.S. Patents 4,477,367; 4,446,201; and 4,392,979; wherein various Li, Mg, Cu, Zn, Mn, Fe, Co, and Ni compounds form part of the crystal structure. Other layered compounds are disclosed, e.g., in U.S. Patents 2,395,931; 2,413,184;

3,300,577; and 3,567,472. These compounds are prepared through various reactions including coprecipitations, intercalations, acid digestions and base digestions.

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-4In the drilling of oil wells, drilling fluids or muds perform several functions:

1. They remove cuttings from the hole.

2. They cool the drill bit.

3. They provide hydrostatic pressure to balance formation pressure.

4. They control ingress of fluids into the formation and protect the formation.

In order to perform some of these functions it is necessary for the fluid to possess pseudoplastic rheology. There are several shear zones in the bore hole of a well and the fluid should have varying viscosities in these zones. In the annulus between the drill pipe and the formation, the shear rate is approximately 100 to

1000 sec . At the drill bit the shear rate is between _1 about 25,000 and 200,000 sec . In the mud pit the _1 shear rate is less than 30 sec . In order to carry drill solids at low shear rates, a fluid must have a significant viscosity. However, if the fluid has a high viscosity at the drill bit, a significant amount of energy is lost in pumping the fluid. Thus, a good drilling fluid should be shear thinning. It is very important that the fluid maintain this rheology throughout the drilling process. However, many adverse conditions that typically inhibit the performance of existing drilling fluids are, the presence of various cations (such as calcium and magnesium), fluctuating salt concentrations, high temperatures, oxidative conditions, and the presence of bacteria.

Some of the commercially accepted gelling agents that are used in water-based drilling fluids are

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-5polymers such as xanthan gum, guar gum and polyacrylamides.

Non-polymer gelling agents are typically clays such as bentonite and attapulgite. Each of these gelling agents has its own limitations. The polymers typically have instability to various salts, they are susceptible to oxidation and bacterial attack, they break down under extensive shear, and they are thermally stable to only about 120 to 150°C. The most popular clay gelling agent is bentonite. The bentonite is severely affected by polyvalent cations and is limited to about 100°C unless certain thinners are incorporated. However, bentonite cannot be oxidized under hydrothermal conditions, and it is stable in a liquid carrier to high shear conditions.

The present invention provides a novel gelling component of a process fluid, for example, a drilling fluid, drilling mud,. frac fluid, packer fluid, completion fluid, and the like, or other thixotropic fluid, said gelling component, also referred to as a thicken20 ing agent, comprises a mixed metal layered hydroxide of the empirical formula ^Lim^Dd^T(OH)(m+2d+3+na)^Aa‘^qH2° where m is from zero to about 1;

D represents divalent metal ions;

d is from zero to about 4;

T represents trivalent metal ions;

A represents monovalent or polyvalent anions or negative-valence radicals other than

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-סthe OH״ ions ;

a is the number of ions of A;

n is the valence of A;

na is from zero to about -3; q is from zero to about 6; (m+d) is greater than zero; and (m+2d+3+na) is equal to or greater than 3.

These layered mixed metal hydroxides are preferably prepared by an instantaneous (flash) coprecipitation wherein soluble compounds, e.g., salts, of the metals are intimately mixed (using non-shearing agitation or mixing) with an alkaline material which supplies hydroxyl groups to form the mixed metal hydrous oxide crystals. While the empirical formula appears to be similar to previously disclosed compositions, a distinguishing feature of this present composition is that the crystals are essentially monolayer, or one layer of the mixed metal hydroxide per unit cell. In a liquid carrier the crystals essentially monodispersed meaning individual crystals are distinct layers of the mixed metal hydroxide. These monodispersed, monolayer crystals are believed to be novel.

In the above formula, the number of Li ions is represented by the value of m and may be from zero to about 1, preferably 0.5 to 0.75.

The D metal represents divalent metal ions and may be Mg, Ca, Ba, Sr, Mn, Fe, Co, Ni, Cu, or Zn, preferably Mg, Ca, Mn, Fe, Co, Ni, Cu, or Zn, most preferably Mg or Ca, or mixtures of these. The value of d, the number of D ions in formula (I), may be zero to about 4, preferably 1 to 3, most preferably about 1.

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-רThe amount of (m+d) is greater than zero .

The T metal may be Al, Ga, Cr or Fe, preferably Al or Fe, most preferably Al.

In the subscript (m+2d+3+na), the nais actually 5 a negative number because the anion valence, n, is negative. Addition of a negative number results in a subtraction.

The A anions may be monovalent, divalent, trivalent, or polyvalent, and may be inorganic ions 10 such as halide, sulfate, nitrate, phosphate, or carbonate, preferably halide, sulfate, phosphate or carbonate, or they may be hydroph lie organic ions such as glycolate, lignosulfate, polycarboxylate, or polyacrylate or salts thereof, such as sodium polyacrylate.

These anions often are the same as the anions which formed part of the metal compound precursors from which these novel crystals are formed.

The compound of formula (I) is substantially balanced and preferably neutral in change. Substan20 tially balanced means there is little positive or negative net change to the compound.

The liquid which is gelled by the present described novel mixed metal hydroxides may be an aqueous liquid, such as water or aqueous solution, or a hydro25 phi lie organic material such as alcohol or ketone; also a dispersion or emulsion comprising an aqueous medium which contains non-soluble ingredients (organic and/or inorganic) in dispersed form can be gelled by use of

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-8the presently described gelling agent. Whereas the present gelling agent is found useful as a thickening agent for water-based metal working fluids, fire fighting fluids, food additives, hydraulic fluids, latex paints, stripping fluids, lubricants, and others, especially where extreme pseudoplasticity is a desirable property, it is particularly useful when employed as an additive to form thixotropic fluids for use in subterranean operations, such as drilling fluids, drilling muds, fracture fluids, packer fluids, completion fluids, and the like, especially drilling fluids, whether it be for drilling oil wells, water wells, or gas wells, including drilling in the ocean floor.

The present invention also provides a process for preparing the compounds of formula I by (a) preparing a solution of predetermined quantities of compounds which provide the de.sired predetermined amounts of Li, D, T, and A ions; (b) admixing said solution with an alkaline solution which provides a source of hydroxyl ions to cause coprecipitation of such Li, D, and T metals as crystalline mixed metal compounds containing, as anions, hydroxyl ions and A ions, said crystals being monodispersed and exhibiting monolayer unit cell structures as determined by crystallographic analysis; and (c) said admixing being performed in a manner in which rapid, thorough, flash precipitation is achieved without the use of shearing agitation.

The flash precipitation technique employed, in preparing the present gelling agents, closely approx!mates steady-state reaction wherein the ratio of

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-9reactant feeds (cations/anions), and other reaction conditions (e.g. concentration, pH, temperature) are substantially constant. Such constant conditions are substantially achieved by mixing or combining a metered stream (or regularly fed portions) of the cation solution with a predetermined amount of the anion solution; the combined solutions comprise a mixture (containing reaction product as a floc), which is removed from the mixing area or zone. In this manner, each’ new portion of cation solution sees a new portion of anion solution, neither of these new portions having been involved in the mixing of the previous portions. Thus one obtains substantially constant conditions of temperature, pH, and ratio of feed reactants and obtains a more homogeneous, compositionally uniform product, each new portion of product having undergone the same orders (and rates) of reaction as any previous portion of product. By performing the reaction in this m anner the formation of flocs is maximized, so long as there is not enough shearing agitation to break up the flocs.

This steady-state reaction is in contradistinction to a non-steady reaction wherein reaction conditions (such as temperature, pH, ratio of reactants) are variable rather than constant. For instance, if one has a vessel containing a cation solution to which one slowly adds a stream (or portions) of the anion solution, the first bit of anion solution sees all the cations, the second bit sees not as many cations but sees some reaction product as well. Each subsequent bit of anion solution sees a different quanitity of cations and product; the ratio of cations/anions being united is

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-10changing throughout the procedure leading, very likely, to a non-homogeneous or non-uniform product as a result of there having been different orders of reactivity encountered, or different rates of reaction over the course of the anion addition. Here, in such a non-steady state reaction, one encounters the likelihood that some of the subsequent anions may react with some of the already formed product, giving rise to a mixture of products.

One may theorize that an absolutely constant, uniform product is prepared under absolutely constant conditions by reacting a molecule of one reactant with the requisite or stoichiometric molecular amount of the other reactant. Such absolutely constant conditions are not achievable in commercial practice, but one may substantially approach such conditions by employing substantially steady-state conditions where constant conditions are closely approached.

The temperature of the reacting mixture should, of course, be above freezing and not above boiling. Going above boiling would require a closed, pressured vessel to prevent evaporation of the liquid and this is generally unproductive, offering no additional benefit commensurate with the added expense. A temperature below about 5°C would be expected to slow down the reaction rate. An ambient temperature in the range of about 15 to 40°C may be used, but warmer temperatures up to 80°C or more may be quite beneficial, not only in keeping the beginning compounds in solution, but also in speeding the rate at which the compounds react.

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-11A mixture of the selected soluble metal compounds, especially the acid salts (e.g. chloride, nitrate, sulphate, phosphate) are dissolved in an aqueous carrier. The ratios of the metal ions in the solution are predetermined to give the ratios desired in the final product. The concentration limit of the metal compounds in the solution is governed, in part, by the saturation concentration of the least soluble of the metal compounds in the solution; any non-dissolved portions of the metal compounds may remain in the final product as a separate phase, which is not a serious problem, usually, if the concentration of such separate phase is a relatively low amount in comparison to the soluble portions, preferably not more than about 20% of the amount of soluble portions. The solution is then mixed rapidly and intimately with an alkaline source of OH״ ions while substantially avoiding shearing agitation thereby forming monodispersed crystals of layered mixed metal hydroxides. One convenient way of achieving such mixing is by flowing the diverse feed streams into a mixing tee from which the mixture flows, carrying the reaction product, including the monodispersed layered mixed metal hydroxides of formula (I) above. The mixture may then be filtered, washed with fresh water to remove extraneous soluble ions (such as Na , NH₄⁺ ions and other soluble ions) which are not part of the desired product.

The particular transmission electron microscope used in conducting crystallographic analyses of the subject' mixed metal layered hydroxides was operated at its maximum limits of detection, i.e. a resolution of about 8 angstroms. The monodispersed crystals were

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-12so thin, with respect to their diameter, that some curling of the monolayer crystals was found, making precise thickness measurements difficult, but reasonable estimates place the crystal thickness in the range of 8 to 16 angstroms for various crystals. During the drying process some agglomeration of crystals is apparent, as detected in the analysis, giving rise to partides which contain a plurality of the monolayer unit cell structures. Many flat, unagglomerated crystals are detectable in the analyses. These monolayer unit crystals are in contradistinction to 2-layer and 3-layer unit cell structures referred to in e.g., U.S. Patent 4,461,714.

One process for preparing the composition, however not exclusively the only process, is to react a solution of metal salts such as magnesium and aluminum salts (the salt concentrations are preferably less than about 2 molar and most preferably about 0.25 molar) with a source of hydroxide ion. Sodium hydroxide may be used, for instance, however, ammonium hydroxide is preferable. The concentration and the quantities of the base are at least sufficient to precipitate the mixed metal hydroxide compound. For ammonium hydroxide, the most preferable range is between 1 to 1.5 moles of OH” per mole of Cl .

The precipitation should be done with little or no shear so that the resultant flocs are not destroyed. One method of accomplishing this is to flow two streams, the salt stream and the base stream, against one another so that they impinge in a low shear, converging zone such as is found in a tee. The reaction product is then filtered and washed, producing

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-13a filtercake of approximately 10% solids. At this point if the layered mixed metal hydroxide composition has been washed carefully to reduce the dissolved salt concentration to a relatively low point, for example, about 300 ppm or less, an odd phenomenon occurs. Over a period of time, the filter cake changes from a solid waxy material to an opalescent or iridescent liquid that efficiently scatters light. If ionic material is added back to the dispersion, the viscosity increases drastically and the dispersion gels. The rate of relaxation is dependent on the free ion concentrations in the dispersion and will not occur if the concentrations are too high. The effect of various ions on the relaxation process differs. For example, the relaxation process is more tolerant of monovalent ions such as chloride ions than it is of polyvalent ions such as sulfate, carbonate, or phosphate.

If the relaxed dispersion is dried, when the solids level reaches about 20 to 25%, the material forms a solid hard translucent material that is very brittle. It can be crushed to a powder, even though it is approximately 80% water. This solid will not redisperse well in water or other hydrophilic solvents. Even if shear is applied with a Waring Blender or an ultrasonic cell disrupter, the solids cannot be made to form stable dispersions.

One fruitful method of drying the material is to add a quantity of hydroph)lie organic material such as glycerine or polyglycol to the relaxed dispersion prior to drying. The material may be dried to about 5% water, or less, and still be redispersible. If this is

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-14done the resultant dry material will spontaneously disperse in water. If a salt is then added to this dispersion, the fluid will build viscosity in the same manner as the product that has never been dried. This drying technique does not work if significant quantities of dissolved salts are present in the dispersion. In this case some dispersion may be possible, but the resultant fluid will not build viscosity.

One of the distinguishing features of the presently disclosed mixed metal hydrous oxides is the fact that upon filtration after the flash coprecipitation there remains on the filter a gel which is predominantly the liquid phase with the crystalline hydrous oxides so swollen by the liquid that they are not visible as a solid phase. One might call the gel a semi-solution or quasi-solution and it has the appearance and feel .of a semi-solid wax. This is in contradistinction to prior art hydrous oxide precipitates which are readily filtered out of liquid as a discrete: particulate solid material. Apparently, the particular crystalline morphology obtained here permits or causes the imbibing and holding of large amounts of the liquid.

The gelling agent may also be composed of either pure mixed metal hydroxide compounds or physical mixtures of the layered compounds with themselves or other hydrous oxides of the D or T metals such as, for example, hydrous alumina, hydrous magnesia, hydrous iron oxides, hydrous zinc oxide, and hydrous chromium oxides.

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-15In each of the subsequent examples, the mixed metal layered hydroxide compound was prepared by coprecipitation. The compounds were then filtered and washed to produce a substantially pure material. This purified product was then dispersed in water to build the thickened fluid.

In this disclosure, the following U.S. to metric conversion factors are appropriate: 1 gal = 3.785.liter; 1 lb. = 0.454 Kg; 1 lb/gal (U.S.) = 119.83 Kg/M³; 1 bbl = 42 gal = 159 liters; 1 Ib/bbl = 2.85 2 kg/m³; lb/ft x 47.88 = 1 Pascal; 1 lb/100 ft²=4.88 Kg/100M².

The following examples are to illustrate certain embodiments, but the invention is not limited to the particular embodiments shown.

Example 1

A 0.25 molar solution of MgCl₂-AlCl₃ was prepared. This solution then pumped through a peristaltic pump into one arm of a tee. A 2.5 molar solution, of NH4OH was pumped into a second opposite arm of the tee so that the two solutions met in the tee. The product poured out of the third arm and into a beaker. The flows of the two solutions were carefully adjusted so that the product of the coprecipitation reaction would have a pH of about 9.5. In this situation that amounts to about a 10 to 20% excess of NH₄OH. The reactor product consisted of delicate flocs of MgAl(0H)_4t7CI0.3 suspended in an aqueous solution of NH₄C1. The dispersion was then carefully poured into a Buchner Funnel with a medium paper filter. The product

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-16was filtered and washed in the filter with water to remove the excess NH₄C1. After washing the dissolved

Cl” concentration was about 300 ppm as measured by Cl specific ion electrode. The filter cake that resulted was translucent, but not optically clear.

The resultant cake was about 9% solids by weight, determined by drying at 150°C for 16 hrs. The cake had the consistency of soft candle wax. The product was analysed for Mg and Al. It was found that the Mg:Al ratio was essentially 1:1.

Electron micrographic analysis of the product showed tiny platelets with diameters of 300 to 500 angstroms. The particles were so thin that in some cases, they curled. Estimates of thicknesses of these particles are 8 to 16 angstroms. The maximum resolution on the microscope is about 8 angstroms. The theoretical thickness of one layer of crystalline MgAl(0H)₄.₇C1_O.₃ is about 7.5 angstroms. These data strongly suggest that some of the particles are one to two crystals thick. It should also be noted that in the process of preparing the sample for electron microscopy, the material was dried which apparently caused a degree of agglomeration of the crystals.

After setting undisturbed for about 16 hours, the filter cake had the consistency of petroleum jelly. After about 48 hours, the material was a thixotropic liquid. The relaxation process continued for about 5 days. At the end of this time, the product was more viscous than water but it was pourable. A small amount of NaCI was added to a sample of the liquid and it gelled almost instantaneously.

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-17A quantity of glycerine was added to the product that was equal to 17% by weight of the solids present in the dispersion. When the glycerine was added to the dispersion, the apparent viscosity decreased to about 1 centipoise. The slurry was then placed in a pan and dried in an oven for 16 hours. On large scale, more efficient drying equipment would be utilized, such as spray dryers or shelf dryers. The product from the oven was a brittle solid that could be easily crushed. It was 95% solids by weight, including the glycerine. When the solid material was placed in water, it spontaneously dispersed in less than 5 minutes. Phosphate ions in the form of NaH₂PO₄ were added to the dispersion and it increased in viscosity in the same way that it did before drying.

Example 2

In a similar manner, a solution of magnesium and aluminum chlorides which had a composition of 4 magnesiums per 1 aluminum was reacted with NH₄0H. The concentration of Mg₃.₂A1(OH)₈,₄C1! was about 1 molar. The product was filtered and washed immediately. After about 24 hours, the filter cake had relaxed to a very thin fluid. The solids content of the fluid was about 10% and the bulk analysis of the solids indicated that the Mg:Al ratio was 3.2:1.

Transmission electron microscopy was performed on the material and it was found that the product is made up of platelets having an average diameter of 500 angstroms (±100 angstroms). Some of the crystals are lying on edge so that it is possible to estimate the crystallite thickness. It appears that

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-18there are crystals that are only about 10 angstroms thick. This suggests that the material is essentially monodispersed. The literature (Crystal Structures of Some Double Hydroxide Minerals Taylor, H.F.W., Mineralogical Magazine, Volume 39, Number 304, Dec. 1973) teaches that known magnesium aluminum hydroxide compounds having Mg:Al ratios as high as 4:1 are in the hydrotalcite class of compounds. The crystal structure data that has been accumulated in the literature indicates.that there are basically two types of hydrotalcite, one having a c-axis spacing of about 24 angstroms and another having a c-axis spacing of about 15 angstroms. Since the data revealed here indicates that many of the crystals prepared in this example are thinner in the c direction than hydrotalcite, then the crystal structure data indicate that the material must have a crystal structure that is different than hydrotalcite.

Example 3

One part of aqueous solution containing 23.8% by weight of MgCl₂-AlCl₃ is diluted with 4 parts of deionized water and sufficient MgSO₄ is added to provide a calculated ratio for Mg:Al of 4:1. The solution, at room temperature, is rapidly and thoroughly mixed, without any substantial shearing forces, with a stoichiometric quantity of NH₄0H, thus providing an instantaneous or flash coprecipitation of Mg₃.₂A1(OH)_84־C1!. The reaction mixture is filtered, leaving a semi-solid waxy gel on the filter which contains about 6% by wt. of the coprecipitate. The gel is washed on the filter, with additional quantities of deionized water to substantially _2 remove extraneous material such as nh₄0h, so₄ , and Cl^-. However, the final Cl^- concentration was greater than 0.02 molar. The filter cake is diluted with

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-19deionized water to make a 2.5% dispersion which, measured with a Brookfield viscometer, is found to be about 556 times as viscous as water at low shear rates and is thixotrophic. Enough BaS0₄ was added to the aqueous slurry to raise the density to about 10 lb/gal. The BaSO₄ suspended well and did not settle out over a period of 6 months.

Example 4 . A similar experiment was performed in which the Mg:Al ratio was 1:4. The product was washed until the Cl” content was less than 110 ppm. Upon the addition of salt, this material was capable of building viscosity and supporting BaS0₄ in suspension for extended periods of time.

Example A (for comparison)

MgSO_{47 ־}H₂Q was dissolved in enough water to make a 0.25 molar solution. This was then reacted with KOH to make Mg(0H)₂ in a reaction tee. The product was filtered and washed to essentially nil Cl concentration. This fluid was then dispersed in water and found to be thixotropic. BaSO₄ was then dispersed in the slurry and it was allowed to stand undisturbed for 6 months; the BaSO₄ was mostly settled out of the dispersion.

Example B (for comparison)

A 1-molar solution of A1₂(SO₄)₃ was prepared and precipitated with NH₄0H. The resultant product was thoroughly washed and reslurried to make a 2.5% dispersion. BaSO₄ was added to test the suspension characteristics of the slurry. The slurry was allowed to sit undisturbed for 6 months; the BaSO₄ was mostly settled out of the dispersion.

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-20Example 5

A 0.25 molar solution of MgCl₂*AlCl₃ was prepared. This solution was reacted with NH₄0H to precipitate a material having a Mg:Al ratio of 1:1. The product was filtered and washed to a point that the Cl” concentration in the cake was 2800 ppm. The product was then dispersed in water forming a thixotropic slurry. It was then weighted to 9.5 Ib/gal. with BaS0₄and allowed to set for 6 months; there was very little settling. There was a syneresis effect in which the top 10% of the fluid was clear water, but there was only about a 10% density gradient through the remaining other 90% of the fluid.

Example 6

100 ml. of 1 molar MgCl₂־AlCl₃ solution was diluted with 200 ml of deionized water and 14.7 grams of CaCl₂ were addedThe resulting aqueous salt solution was then flash precipitated with NH₄0H at a reaction pH of 10. The slurry was filtered and washed. The resulting product was then dispersed in water and weighted as described in previous examples. This slurry was also thixotropic.

Example 7

A fairly large quantity of flash precipitated MgAl(OH)₄.₇C1_O.₃ was prepared and washed. The following tests were then performed on fluids containing the gelling agent.

1. Rheology data

2. Shear stability

3. Time dependence

4. pH dependence

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5.

6.

7.

8.

9.

10.

KC1 dependence

CaCl₂ dependence

Filtration data

Weighted fluids

Thermal stability

Na₂SO₃ stability

Rheology Data

The rheology data that is illustrated here was obtained using a Fann 35 rotary viscometer. Unless otherwise stated all of the data were obtained at 46°C. Table 1 is a comparison of plastic viscosity, yield point and 10 sec and 10 min gel strengths for 7 Ib/bbl MgAl(0H)_4>7C10.3, 15 Ib/bbl Aquagel, (a beneficiated sodium bentonite marketed by Baroid), and 20 Ib/bbl Aquagel. The most notable differences are in the plastic viscosities and gel strengths. In the case of the MgAl(0H)_{4 7 ־}C1_O .3. the plastic viscosity is very low, being about one eighth of the value of the yield point. In the case of the Aquagel samples, the plastic viscosity is greater than the yield point. The gel strengths of the MgAl(OH)₄.₇C1_O.3 are nearly equal while those of the Aquagel fluids are significantly different. These data indicate that the MgAl(OH)₄.₇C1_O.₃ fluid gels vary rapidly and does not continue to build gel strength. Such a fluid is said to produce fragile gels. The Aquagel fluids gel more slowly and continue to build over a longer period of time forming progressive gels. Fragile gels are more desirable for the drilling of oil wells because the fluid will not become so strongly gelled that it cannot be easily broken.

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<td colspan="5"> TABLE 1 RHEOLOGY DATA</td>

<td rowspan="2"> Agent/ Concentration</td><td rowspan="2"> Plastic Viscosity (cp)</td><td rowspan="2"> Yield Point (lb/100 ft.²)</td><td colspan="2"> Gel strengths</td>

<td> 10 sec (lb/100</td><td> 10 min ft.*)</td>

<td> MgAl(OH)₄.₇Cl₀.3 7 Ib/bbl</td><td> 2.5</td><td> 21</td><td> 9.5</td><td> 11.0</td>

<td> Aquagel* 15 Ib/bbl</td><td> 7.8</td><td> 4.5</td><td> 1.8</td><td> 2.</td>

<td> Aquagel* 20 Ib/bbl</td><td> 15</td><td> 14.5</td><td> 3.0</td><td> 8.5</td>

*Aquagel is used here for comparison.

Table 2 tabulates shear stress and shear rate data for a 7 Ib/bbl slurry prepared with MgAl(0H)_4t7C1_O.₃. These data were generated using a capillary viscometer. The fluid is extremely shear thinning from about 1 _1 -¹sec to about 25,000 sec where it becomes newtonian. This is typical of all water based drilling fluids.

The viscosity of this fluid at low shear rates is about 600 cp but, at the drill bit, the viscosity is only about 4.5 cp.

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־22-23-

<td></td><td colspan="3"> TABLE 2 CAPILLARY VISCOMETRY DATA</td>

<td> Shear Rate</td><td> Shear</td><td> Stress</td><td> Viscosity</td>

<td rowspan="2"> (sec-¹) 10.35</td><td> (kg/100 m²)</td><td> (lb/100 ft.²)</td><td> (cp)</td>

<td> 59.08</td><td> 12.10</td><td> 597.40</td>

<td> 20.60</td><td> 80.56</td><td> 16.50</td><td> 409.30</td>

<td> 40.95</td><td> 92.28</td><td> 18.90</td><td> 235.85</td>

<td> 102.80</td><td> 114.25</td><td> 23.40</td><td> 116.32</td>

<td> 204.48</td><td> 130.36</td><td> 26.70</td><td> 66.72</td>

<td> 393.00</td><td> 152.14</td><td> 31.16</td><td> 40.52</td>

<td> 666.75</td><td> 179.67</td><td> 36.80</td><td> 28.20</td>

<td> 981.00</td><td> 190.71</td><td> 39.06</td><td> 20.35</td>

<td> 1257-.50</td><td> 227.03</td><td> 46.50</td><td> 18.90</td>

<td> 1720.00</td><td> 230.74</td><td> 47.26</td><td> 14.04</td>

<td> 2527.60</td><td> 292.95</td><td> 60.00</td><td> 12.13</td>

<td> 6551.60</td><td> 394.50</td><td> 80.80</td><td> 6.30</td>

<td> 13694.20</td><td> 687.93</td><td> 140.90</td><td> 5.26</td>

<td> 25552.40</td><td> 1098.55</td><td> 225.00</td><td> 4.50</td>

<td> 61743.30</td><td> 2735.62</td><td> 560.30</td><td> 4.64</td>

<td> 87019.00</td><td> 3961.11</td><td> 811.30</td><td> 4.76</td>

Shear Stability Data

Table 3 tabulates plastic viscosity, yield point, and gel strengths versus time of shear, in a Waring Blender. Except for some change in the first few minutes, the viscosity parameters remain fairly constant. The capillary viscometry data also indicate that the MgAl(OH)₄.₇Cl_o.3 fluids are shear stable since they were passed through the capillary viscometer three times and no observable shear degradation occurred.

TABLE 3 SHEAR STABILITY DATA

Gel-strengths Shear Time Plastic Yield Point 10 sec 10 min (min) Viscosity(cp) (lb/100 ft.²) (lb/100 ft.²)

0.0 3.0 15.0 13.015.0

10.0 2.0 8.0 8.07.0

35.0 2.0 8.0 8.08.0

75.0 2.5 11.0 9.010.0

33,596-F

-24Time Dependence Data

Table 4 lists the plastic viscosity, yield point and gel strengths for a 7 Ib/bbl. MgAl(OH)₄.₇C1_O.₃slurry over a period of 2.5 days. These data indicate 5 that there is some change in yield point over the first several days. However, the change is not considered to be significant. The fluids from these tests were also allowed to set for 3 months and the rheology was again measured on them. There were virtually no changes in 10 the fluids.

<td></td><td></td><td></td><td> TABLE 4</td><td></td><td></td>

<td></td><td></td><td> TIME</td><td> DEPENDENCE DATA</td><td></td><td></td>

<td></td><td></td><td></td><td rowspan="2"> Yield Point</td><td colspan="2"> Gel-strengths</td>

<td></td><td> Time</td><td> Plastic</td><td> 10 sec 10</td><td> min</td>

<td rowspan="2"> 15</td><td> days _</td><td colspan="2"> Viscosity(cp) (lb/100 ft.²</td><td> ) (lb/100</td><td> ft.⁵)</td>

<td> 0.0</td><td> 5.0</td><td> 5.5</td><td> 3.0</td><td> 6.0</td>

<td></td><td> 0.3</td><td> 5.-0</td><td> 7.0</td><td> 3.5</td><td> 6.0</td>

<td></td><td> 1.0</td><td> 5.0</td><td> 7.0</td><td> 3.5</td><td> 5.8</td>

<td></td><td> 2.0</td><td> 5.0</td><td> 6.2</td><td> 3.5</td><td> 5.8</td>

<td> 20</td><td> 2.5</td><td> 5.0</td><td> 6.0</td><td> 3.5</td><td> 5.5</td>

<td></td><td> pH Effects</td><td></td><td></td><td></td><td></td>

<td></td><td></td><td colspan="2"> Table 5 lists plastic viscosity,</td><td> yield point,</td><td></td>

and gel strengths versus pH. Below about pH 6 the yield point drops off drastically. It is flat to about pH 11. Above that point, it increases very rapidly. These results are good since the drilling operations are run from pH about 9.5 to about 10.5.

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-25TABLE 5 pH EFFECTS ON FRESH WATER SYSTEMS

Gel-strengths

<td></td><td> Plastic</td><td> Yield Point</td><td> 10 sec 10</td><td> min</td>

<td> PH</td><td> Viscosity (cp)</td><td> (lb/100 ft.²)</td><td> (lb/100</td><td> ft.^k</td>

<td> 4.5</td><td> 3.0</td><td> 2.5</td><td> 2.5</td><td> 5.0</td>

<td> 7.0</td><td> 3.0</td><td> 22.0</td><td> 7.0</td><td> 7.0</td>

<td> 10.5</td><td> 3.0</td><td> 25.0</td><td> 20.0</td><td> 21.0</td>

<td> 12.0</td><td> 3.0</td><td> 55.0</td><td> 12.0</td><td> 12.0</td>

<td> -</td><td> Table 6 tabulates</td><td colspan="2"> rheology parameters for a</td><td></td>

<td colspan="2"> fluid composed of 35% CaCl₂</td><td colspan="2"> and about 6 Ib/bbl of</td><td></td>

MgAl(OH)4₁₇Cl_o.3 at pH 6 and pH 8.5. There is basically no change in rheology.

TABLE 6 pH

Gel-strengths Plastic Yield Point 10 sec 10 min pH Viscosity (cp) (lb/100 ft.²) (lb/100 ft.²)

6.0 8.5 14 6.5 8.5

8.5 8.0 14 8.0 10 *CaCl₂ concentration = 35%, Fluid weight = 11 Ib/gal.

KC1 and CaCl₃ Stability Data

KC1 is often added in varying quantities .to water-based drilling fluids for shale stabilization. Table 7 is a listing of the various rheological properties against KC1 concentration from 0% to 27%. The experiment was performed by starting with an aqueous dispersion of MgAl(0H)₄.₇C1_O.3 and adding quantities of KC1 to the slurry. Increasing KC1 concentrations had very little effect on the overall rheology of the fluid. A similar

33,596-F

-26experiment was performed with CaCl_2׳ Table 8, where a drop in yield point is observed between 0.25% and 27.7%.

There is also an increase in plastic viscosity.

However, these changes are not of great magnitude.

These data are important because they indicate that fluctations in commonly encountered salts will not have a detrimental effect on the properties of aqueous dispersions of MgAl(0H)₄₇־C1_O.3.

TABLE 7

<td rowspan="2"> Concentration KC1</td><td colspan="2"> KC1 STABILITY DATA*</td><td colspan="2"> Gel-strengths</td>

<td> Plastic</td><td> Yield Point</td><td> 10 sec</td><td> 10 min</td>

<td> (Wt. percent)</td><td> Viscosity (cp)</td><td> (lb/100 ft.²)</td><td colspan="2"> (lb/100 ft.²</td>

<td> 0.00</td><td> 4.5</td><td> 11.0</td><td> 7.5</td><td> 8.0</td>

<td> 0.25</td><td> 3.2</td><td> 8.5</td><td> 9.0</td><td> 7.5</td>

<td> 0.50</td><td> 3.2</td><td> 9.0</td><td> 6.0</td><td> 5.5</td>

<td> 1.00</td><td> 3.0</td><td> 10.0</td><td> 5.5</td><td> 5.5</td>

<td> 3.00</td><td> 2._5</td><td> 12.0</td><td> 5.5</td><td> 5.0</td>

<td> 10.0</td><td> 3.5</td><td> 10.0</td><td> 6.5</td><td> 5.5</td>

<td> 27.0 *MgAl(OH)₄.₇Cl</td><td colspan="2"> 3.2 11.0 ₀3_־ concentration = 7 Ib/bbl.</td><td> 6.5</td><td> 5.5</td>

TABLE 8 CaCl? STABILITY DATA

Concentration Gel-strengths

CaCl₂ Plastic Yield Point 10 sec 10 min (wt. Viscosity(cp) (lb/100 ft.²) (lb/100 ft.²)

<td> 0.35</td><td> 2.5</td><td> 21.0</td><td> 9.5</td><td> 11.0</td>

<td> 27.7</td><td> 6.5</td><td> 15.0</td><td> 8.5</td><td> 8.5</td>

<td> 35.0</td><td> 8.0</td><td> 15.0</td><td> 8.0</td><td> 10.0</td>

Filtration Data

Aqueous dispersions of MgAl(0H)_47־C1_O.3 exhibit very high A.P.I. fluid loss values. Thus, it is generally

33,596-F

-27desirable to add fluid loss control agents to a drilling fluid built around mixed metal layered hydroxides. However, it has been found that the addition of commercially available fluid loss control agents such as starch, polyacrylates, carboxymethyl cellulose, and the like provide adequate fluid loss control (less than 10 cm³ loss in 30 min.

using an A.P.I. fluid loss cell). The quantities required to give adequate control are roughly the amounts suggested by the manufacturers of the agents. Some of these data are listed in Table 9. As would be expected, the presence of drill solids such as shales is also beneficial to fluid loss control. More than one fluid loss agent may be used in a drilling fluid.

TABLE 9

FILTRATION

Fluid loss control agents

Hydroxyethylcarboxymethy1cellulose

Hydroxyethylcarboxymethylcellulose (low viscosity)

Cornstarch

Sodium polyacrylate *7 Ib/bbl MgAl(0H)_{4 7}C1_O 3

Concentration to produce 12cm³ or less API fluid loss (Ib/bbl)

1.5

2.0

6.0

2.0 and 10 Ib/bbl bentonite (simulated drill solids)

Weighted Fluids

Table 10 lists rheology data for 9.5 and 15 Ib/bbl fluids weighted with BaS0₄. One unexpected result is that the plastic viscosity remains very low while there is a high yield point. This runs contrary to current theories concerning viscosities of aqueous dispersions.

33,596-F

«י

It is typically thought that as weighting material is added to an aqueous dispersion, the plastic viscosity must increase drastically. One possible explanation is that the MgAl(0H)₄.₇C1_O.₃ may be acting as a lubricant in the system. The potential outcome of such a property is that higher penetration rates may be achieved with weighted fluids than are currently possible.

TABLE 10

WEIGHTED FLUIDS DATA

Gel-strengths Mud Weight Plastic Yield Point 10 sec 10 min (Ib/gal.) Viscosity (cp) (lb/100 ft.²) (lb/100 ft.²)

9.5 3.0 24.5 11.0 15.0

15.0 4.0 32.0 14.0 14.0

Thermal Stability Data

Table 11 illustrates shear stress versus shear rate curves for an 8 Ib/bbl fluid before and after static thermal treatment at 400°F (204°C) for 20 hours. The result of the test is that the rheological properties, measured at 115°F (46°C) were basically unchanged.

TABLE 11

THERMAL STABILITY DATA*

<td> Thermal Conditioning</td><td> Plastic Viscosity (cp)</td><td> Yield Point (lb/100 ft.²)</td><td> Gel-strengths 10 sec 10 min (lb/100 ft.²)</td>

<td> 46°C/24 hrs.</td><td> 2.5</td><td> 21.0</td><td> 9.5 11.0</td>

<td> 204°C/24 hrs.</td><td> 2.5</td><td> 20.0</td><td> 8.6 10.0</td>

*7 lb/bbl slurry in 3% NaCl.

Na_?S0^ Stability

Na₂SO₃ is commonly added to aqueous drilling fluids in order to control corrosion by scavenging oxygen. Table 12 shows the effect of adding 1500 ppm of Na₂SO₃ to

33,596-F

-29an aqueous dispersion of MgAl(OH)_47־C1_O,₃. The effect is that the viscosity is generally increased. Typical levels of

Na₂SO₃ are about 100 to 200 ppm.

TABLE 12

STABILITY TO Na_?SO_q*

Na2SO₃ Gel-strengths

Concentration Plastic Yield Point 10 sec 10 min (ppm.)Viscosity(cP) (lb/100 ft.²) (lb/100 ft.²)

0.0 2.0 23.0 8.0 8.0

1500.0 4.0 32.0 8.0 8.0 *9 Ib/bbl. MgAl(0H)₄.₇C1_O.3.

Example 8

A very pure, low salt concentration, monodispersed mixed metal layered hydroxide of the formula MgAl(0H)₄.₇C1_O.3 at a concentration of 7 Ibs/bbl of aqueous solution was mixed with various weight ratios of NaH₂PO₄«H₂O and the viscosity properties at various shear rates (RPM of agitation) were obtained. These data and other rheological properties are shown in Table 13. All tests were made at ambient temperatures in the range of about 74-78°F (about 23-26°C).

The addition of P0₄ ions increases the viscosity significantly. Similar, but less pronounced, results are obtained with other salts, such as NaCl, Na₂CO₃, CaCl₂, and the like.

33,596-F

-30TABLE 13

Ratio of NaH₇P0₄‘H_?0/MgAl(0H)4 ₇C1q 3

<td></td><td> Test״______________ 600 rpm</td><td> 0.0 5</td><td> 0.1 27.5</td><td> 0.2 28.5</td><td> 0.3 27</td><td> 0.4 27</td><td> 0.5 25</td><td> 0.6 24.5</td><td> 0.7 21</td><td> 0.8 20</td>

<td> 5</td><td> 300 rpm</td><td> 3</td><td> 23</td><td> 24</td><td> 22.5</td><td> 23</td><td> 21.5</td><td> 20.5</td><td> 18</td><td> 16</td>

<td></td><td> 200 rpm</td><td> 2</td><td> 19</td><td> 20</td><td> 19.5</td><td> 20</td><td> 19.5</td><td> 18</td><td> 15.5</td><td> 14</td>

<td></td><td> 100 rpm</td><td> 1</td><td> 15.5</td><td> 16.5</td><td> 16</td><td> 17</td><td> 17.5</td><td> 15</td><td> 13.5</td><td> 12</td>

<td></td><td> 6 rpm</td><td> -</td><td> 10</td><td> 10.5</td><td> 10</td><td> 11.5</td><td> 12.5</td><td> 11</td><td> 10.5</td><td> 9</td>

<td></td><td> 3 rpm</td><td> -</td><td> 8.5</td><td> 7.5</td><td> 6</td><td> 7</td><td> 7.5</td><td> 7</td><td> 8</td><td> 7.5</td>

<td> 10</td><td> Plastic Viscosity, cp 2</td><td> 2</td><td> 4.5</td><td> 4.5</td><td> 4.5</td><td> 4</td><td> 3.5</td><td> 4</td><td> 3</td><td> 4</td>

<td></td><td> Yield Pt.,lb/100ft</td><td> 1</td><td> 18.5</td><td> 19.5</td><td> 18</td><td> 19</td><td> 18</td><td> 16.5</td><td> 15</td><td> 12</td>

<td></td><td> 2 10-sec. gel,lb/100ft 2</td><td> 0</td><td> 7</td><td> 6.5</td><td> 5.5</td><td> 6.5</td><td> 6.5</td><td> 6.5</td><td> 6</td><td> 5.5</td>

<td></td><td> 10-min. gel,lb/100ft *All measurements made</td><td colspan="5"> 0 6.5 5.0 4.5 5 using a Fann viscometer</td><td> 6</td><td> 5.5</td><td> 5.5</td><td> 5.5</td>

33,596-F

-31Example 9

A solution of 11.2g of MgCl₂ and 32.7g of FeCl₃ in 300 ml of deionized H₂0 is reacted with a stoichiometric amount of NH₄0H in a manner whereby rapid, thorough mixing, without using shearing agitation, is achieved; this provides a flash precipitation of a compound conforming essentially to the approximate formula Mg!.₇Fe(OH)₆Cl_o.₄ after filtering and washing.

A 2.5% solids in water slurry exhibits thixotropic rheology.

Example 10

In similar manner to Example 9, an aqueous solution of 31.7g A1C1₃«6H₂O, 16.96g CaCl₂’2H₂O and 500 ml of H₂O is reacted with ΝΗ₃.Η₂Ο. The slurried product, CaAl(0H)₄.₅C1_O5י exhibits thixotropic rheology.

Example 11

In similar‘manner to Example 9, three samples are prepared in which aliquots of an aqueous 23.8% MgCl₂«AlCl₃ solution are mixed, respectively, with CaCl₂, BaCl₂, and ZnCl₂. These solutions are flash precipitated by reaction with NH₄0H to prepare, correspondingly MgCa₀,₃A1(OH)₆C1₀MgBa₀.₃A1(OH)_eCl_o.₄, and Mg₀.₃Zn_03־A1(OH)₆C1_o.₄. The precipitates are filtered, washed, and diluted to about 2.5% solids; each so-formed dispersion demonstrates thixotropic rheology.

Example 12

In a similar manner to Example 9, 0.125 moles of LiCl and 0.25 moles of A1C1₃ are dissolved in deionized H₂0. The resultant solution is reacted with 0.88 moles of NH₄0H with little or no agitation. The

33,596-F

-32product, L1_{0 5}A1(OH)_{3 5}, is filtered and washed. A ’ * 3 diluted sample, 6 Ib/bbl (17.12 Kg/M ), exhibits pseudoplastic rheology and, upon dispersion therein of BaS0₄, retains the BaSO₄ in suspension for extending periods of time.

Example 13

A sample of MgAl(0H)₄.₇C1₀.₃ prepared by flash precipitation was diluted to 7 Ib/bbl (2% wt on a MgAl(0H)_{4 7}Cl_03־ basis) and 1.5 Ib/bbl of NaH₂P0₄*H₂0 (0.4% wt on a NaH₂PO₄*H₂O basis) was added with mixing. The fluid immediately became thick. The fluid was allowed to sit for 4 days and a series of diluted fluids were prepared having the following concentration; 1 Ib/bbl, 2 Ib/bbl, 3 Ib/bbl, 4 Ib/bbl, 5 Ib/bbl, and 6 Ib/bbl fluid. The following Table 14 contains plastic viscosity and yield point data for the fluids.

<td></td><td> ־ TABLE 14</td><td></td>

<td> Concentration</td><td> Yield</td><td> Plastic</td>

<td> In the Mixture</td><td> Point</td><td> Viscosity</td>

<td> (Ib/bbl)</td><td> (lb/100 ft²)</td><td> (cp)</td>

<td> 1</td><td> 1</td><td> 1</td>

<td> 2</td><td> 2</td><td> 1</td>

<td> 3</td><td> 9</td><td> 2</td>

<td> 4</td><td> 14</td><td> 2</td>

<td> 5</td><td> 18</td><td> 2</td>

<td> 6</td><td> 22</td><td> 3</td>

<td> 7</td><td> 28</td><td> 3</td>

<td> Example 14</td><td></td><td></td>

Quantities of 120.7 g of A1C1_36־ H₂O, and 101.7 g of MgCl₂’6H₂O, were dissolved in 4 liters of deionized water. 20 g of NaOH pellets were dissolved in 2 liters of deionized water. These two stock solutions were pumped against one

33,596-F

-33another in a tee. The resultant flocs were collected, filtered and washed. The resultant product was used to prepare a 7 lb/bbl MgAl(OH)₄._sC10 s fluid in water. The fluid was thickened with NaH₂PO₄. The fluid was very thixotropic and capable of supporting BaSO₄ and drill solids.

Examples 15

A solution containing 0.5 molar MgCl₂ and 0.25 molar A1C1₃ was prepared in deionized water. This solution was pumped into a tee against an appropriate volume of 0.5 molar NH₄OH. The reaction product pH was 9.5. The product was filtered and washed and the composition was checked. It was found that the approximate composition was Mg!.₈!A1(OH)₅.₈₈C1_O.₇₄•2.2 H₂O. The product was used to prepare a 7 lb/bbl fluid containing NaH₂PO₄. The fluid was thixotropic and was capable of supporting BaSO₄ and drill solids.

Example 16

In a manner similar to Example 15, a solution containing 0.75 molar MgCl₂ and 0.25 molar A1C1₃ was prepared in deionized water. This solution was pumped into a tee against an appropriate volume of 0.5 molar NH₄0H. The reaction product pH was 9.5. The product was filtered and washed and the composition was checked. It was found that the approximate composition was Mg₂.₅₈A1(OH)₇.1₄C1!.01.2H₂O. The product was used to prepare a 7 lb/bbl fluid containing NaH₂PO₄. The fluid was thixotropic and was capable of supporting BaS0₄ and drill solids.

33,596-F

-34Example 17

In a manner similar to Example 15, a solution containing 1.5 molar MgCl₂ and 0.25 molar A1C1₃ was prepared in deionized water. This solution was pumped into a tee against an appropriate volume of 0.5 molar NH₄OH. The reaction product pH was 9.5. The product was filtered and washed and the composition was checked. It was found that the approximate composition was M93.76A1(OH)9_5־C1!,022H₂O. The product was used to prepare a 7 lb/bbl fluid containing NaH₂PO₄. The fluid was thixotropic and was capable of supporting BaS0₄ and drill solids.

Example 18

Monolayer Li₀.₅Mg₀.7₅A1(OH)₄._SC1_O.4 is prepared by mixing together 500 ml of 1 molar LiCl, 750 ml of 1 molar MgCl₂ and 1 liter of 1 molar A1C1₃, then flash precipitating the monolayer crystals by conveying a stream of the solution with a stream of NH₄0H, the precipitate being a floc. After filtering and washing, a waxy-like filter cake is obtained which is about 4.23% solids by weight. The cake is diluted to 2% in water (i.e. about 71bs/bbl) and tested with viscosifiers added, each in the amount of about 0.5 lb/bbl, as shown in Table 16 below.

<td rowspan="2"> Viscosifier</td><td colspan="2"> TABLE 16</td>

<td> Plastic Viscosity ___L22J___</td><td> Yield Point (lb/100 ft²)</td>

<td> None (control)</td><td> 4.0</td><td> 7.0</td>

<td> NaH₂PO₄</td><td> 6.5</td><td> 15.5</td>

<td> NaHCO₃</td><td> 4.0</td><td> 7.0</td>

<td> Al₂S0₄'9H₂0</td><td> 4.5</td><td> 7.0</td>

33,596-F

-35Miscellaneous Properties

Due to the chemical composition it is essentially impossible to oxidize MgAl(0H)₄.₇C1_O.3. This is of great interest to the oil industry since it is not 5 possible to totally eliminate oxygen and heat in drilling operations.

MgAl(OH)_4>7Cl₀.3 is also uneffected by typical bacteria. Samples of formulated fluids have been stored with periodic exposure to the air for about 6 10 months and no bacterial colonies have been observed.

MgAl(0H)₄.₇C1_O.3 is also totally soluble in mineral acids. This is of great importance since it is often desirable to acidize formations after a well is drilled.