NO152051B - HYDROXYALUMINUM SUSTAINED MIXTURE WHICH PROVIDES LEAD-FREE, Aqueous Systems A COMBINATION OF PSEUDOPLASTICITY AND LIQUID LOSS CONTROL, AND APPLICATION OF THE SAME - Google Patents

Description

The present invention relates to a hydroxyaluminum-containing mixture which gives clay-free, aqueous systems a combination of pseudoplasticity and fluid loss control when it disperses

es in water, and its use in drilling fluid that is circulated when drilling a borehole in underground formations using conventional borehole drilling equipment. Specifically, by-

the present invention relates to the formation of an improved water-based, clay-free drilling fluid containing the pre-

horizontal mixture and an improved method for drilling holes in underground formations using this drill-

liquid.

In normal well drilling operations where a well is drilled at a

rotary method, the wellbore is normally filled with a drill

liquid or sludge that is circulated in this. Drilling fluids are normally pumped down through the drill shaft to the rotating rig, circulated around the drill bit and returned to the surface through the circular passage between the drill stem and the well wall. These drilling fluids have several functions such as lubricating the drill stem and cutting, cooling the cutting, guiding the cuttings from the cutting up through the borehole to the surface where the cuttings can be separated and taken care of and providing a hydrostatic head against the walls of the well, which provides a press against the walls of the hole.

A primary requirement for a satisfactory drilling fluid is that it

have the ability to circulate and flow easily, i.e. have low visco-

site under the high cutting conditions present around the drill bit and at the same time have and maintain sufficient visco-

site to effectively transport the shears to the surface.

A typical liquid mixture contains various reagents for

to give the fluid the necessary properties during different stages of the drilling operation. The drilling fluid must therefore be able to inhibit the amount of fluid, normally water, that is lost in the porous areas through which the borehole passes. Loss of fluid causes the formation and build-up of a cake deposit which, after a certain period of time, can cause jamming of the drill pipe and clogging of

the drilling operation. The liquid must therefore be such that you get mini-mill losses in the porous areas. Reagents which provide such properties are conventionally called "water loss control agents". The drilling fluid must therefore be able: to provide the above-described water loss and pseudoplastic properties under varying composition and environmental conditions found during the drilling operation due to the fact that the borehole passes through different areas such as shale, clay, etc., and the chips from these materials are dispersed in the liquid media. The drilling fluid components should be essentially stable in the presence of various calcium compounds and sodium chloride that may be present in the fluid from the soil areas it comes into contact with and/or due to brine with calcium or sodium salts used in the formation of drilling fluids.

It is desired that the drilling fluid components are stable and functional

at a higher temperature. It is also known that as the drill increases in depth, the temperature encountered is considerably above that of the earth's surface. Furthermore, heat is generated through frictional forces on the drill bit. It is therefore desired that the components used for the formation of drilling fluids are stable at varying higher temperature conditions.

A large selection of drilling fluids have been used, including

in

water-based liquids, hydrocarbon-based liquids, air and other gases, fog, foam and the like. Since large volumes of drilling fluid are required to provide a coolant for the rotating bit and a means to transport the drilling particles, most conventional fluids in use have been based on water. Water alone is a Newtonian fluid and therefore does not have the necessary ability to efficiently transport the drilled particles from the borehole to the surface, nor does it have the ability to prevent loss of fluid into the adjacent porous areas.

It is a widespread and accepted theory that the viscosities which are suitable for giving the fluid particle-carrying ability can be achieved when the drilling fluid has pseudoplastic properties. For example, the drilling fluid must have low capacity during the high shear rates found at the drill bit, and likewise have the ability to increase viscosity (and therefore particle carrying capacity) during the decreasing shear rates found in the upward movement through the annular body.

In order to achieve the necessary pseudoplastic properties, it has often been desired to use clay or colloidal clay bodies such as betonite. Consequently, the drilling fluids are often called "muds". The use of clay-based drilling fluids has provided means that primarily meet the two basic requirements for drilling fluids, i.e. cooling and particle removal. However, the clay-based drilling fluids are very unstable when they come into contact with various salts found in drilled soil formations.

Materials that have increased in use to give the drilling mixtures rheological properties are xanthan gums as described in US patent no. 3,198,268, 2,208,526, 3,251,147, 3,243,000, 3,307,016, 3,319,715 and 3,988,246. These materials have been found to yield aqueous solutions such as drilling fluids with pseudoplastic properties under varying low shear rates. However, whether these materials are used alone or in combination with other additives, the problem is that they break down irreversibly at higher temperatures which are often found during conventional drilling operations and therefore require continuous supplementation of the material. The high price of xanthan gums and the rapid heat breaking rate limit their use to special operations.

Previous use of hydroxides or hydrated metal oxides of amphoteric metals in well drilling fluids has resulted in properties that are clearly different from the properties required for a drilling fluid that is described here. For example, US Patent Nos. 3,614,985 and 3,815,681 describe a method of plugging an underground reservoir by permeating its pores with a solution containing an amphoteric metal salt and a pH increasing reactant to induce precipitation in the pores. US Patent No. 3,603,399 describes a method of treating a water sensitive formation by permeating its pores with a hydroxy aluminum solution which is a clear and relatively non-viscous solution. In each of these previous well treatment processes, it has been important that the solution has relatively low viscosity and high filter loss to ensure that the solution penetrates into the matrix or pores of the reservoir. In a drilling fluid, on the other hand, it is important that the fluid can have a high viscosity over the largest area of use (the annular area of the drill stem), have a low viscosity around the drill bit and have the ability not to penetrate the formation and thereby leave a filter cake throughout the borehole. US Patent No. 3,860,070 describes a well completion or fracturing fluid containing an amphoteric metal salt and a base, in a ratio which makes the final solution strongly acidic to provide a thickened fluid suitable as a fracturing fluid. Such fluids cannot be used satisfactorily in a drilling operation because of their corrosive nature to the metal drilling equipment. None of the various well treatment fluids described in the above-mentioned publications would be suitable for their intended purpose if they contained a fluid loss agent.

The viscosity of a drilling fluid has been relied upon with little success as a means of fluid loss control, particularly during drilling

in and through porous substrates. To improve control, various agents have been added. In US Patent No. 3,032. 4 98, for example, it is described; a cyanoethylated starch as a water loss control agent when used in combination with a clay-based slurry. US Patent 3,988,246 describes an esterified or etherified starch as a water loss control agent compatible with a xanthan gum based drilling mud. Other starches have been used in clay-free sludge under limiting temperature conditions as starches are known to be temperature sensitive.

There is a general need for a mixture which can give aqueous mixtures such as drilling fluid mixtures both pseudoplastic and water loss controlling properties. The mixture should be stable under varying conditions and the temperatures normally encountered during drilling operations, and must be easy to manufacture cheaply to make the drilling operation economical.

The mixture according to the present invention consists of:

(a) a hydroxy-containing aluminum component formed by mixing in an aqueous medium and with vigorous stirring a water-soluble basic component selected from the group consisting of an alkali metal aluminate, alkali metal hydroxide, ammonium hydroxide and mixtures thereof with a water-soluble acidic component selected from an inorganic acid, aluminum chloride, aluminum sulfate, aluminum nitrate, hydrates and mixtures thereof, in that one of, or both, the basic and acidic components is an aluminum-containing compound, the acidic and basic components are reacted in such a ratio that the resulting product gives an aqueous medium a pH from 8 to 10, 3, in combination with (b) a reaction product formed in an aqueous acidic medium with a pH below approx. 5.5 between polyvinyl alcohol with a weight average molecular weight of at least 20,000 and an amount of an aldehyde-containing or aldehyde-releasing component that is 1 to 200% of the stoichiometric, the amount of component (a) in relation to the amount of component (b) being sufficient to directly form an aqueous system with 0.5-10% by weight of component (a) and 0.3-5% by weight of component (b) based on the water in which the mixture is to be dispersed.

The present mixture provides improved plastic and water loss control properties which cannot be attributed to the individual components alone, and which are stable at higher temperature and conditions normally found during borehole drilling operations.

The present mixture must be described in connection with use as a component in a drilling fluid.

The hydroxy-containing aluminum reagents which have been found useful as a component in the mixture according to the present invention are reagents which are mainly water insoluble, i.e. agents which exist in suspension or dispersion in aqueous systems. Furthermore, the present hydroxy-containing aluminum reagents can be characterized in that they have an X-ray diffraction spectrum that contains a substantially characteristic diffraction peak at 6.3 + 0.2 angstroms or are characterized by the X-ray diffraction spectrum as amorphous, i.e. essentially without any X-ray diffraction spectrum in the area from 1.5 to 17 angstroms. The spectrum was recorded using standard methods using the K-a doublet of copper as a radiation source.

The basic agents useful for the formation of the hydroxy-containing aluminum component can be a water-soluble basic material selected from an alkali metal aluminate, alkali metal hydroxide or ammonium hydroxide or mixtures thereof. Any alkali metal can be used such as sodium, potassium and the like, sodium being preferred. The acidic agent that can be used to form the hydroxy-containing aluminum component can be a water-soluble acidic material selected from inorganic acids such as hydrochloric acid, sulfuric acid or nitric acid and the like, or an aluminum salt selected from aluminum chloride, aluminum nitrate or aluminum sulfate, hydrates or mixtures of these acidic remedies. At least one and preferably both of the acidic and basic agents must be an aluminum-containing agent. For example, the hydroxy-containing aluminum component can be formed from an alkali metal aluminate such as sodium aluminate and aluminum chloride hexahydrate in an aqueous system. The sodium aluminate is mixed with the aluminum chloride hexahydrates in an aqueous phase with rapid stirring. The aluminates which are useful will normally have an alkali metal oxide to alumina molar ratio of from 1:1 to 2:1. These materials are commercially available. The desired solutions of one or both components can be prepared and then mixed together under rapid stirring to form the hydroxy-containing aluminum agent.

The acidic and basic precursor media can be present in concentrations from 5 to 25% by weight based on the water present. The concentration may vary outside this range, but should not be such as to prevent thorough mixing, preferably under rapid agitation, of the agents during the formation of the hydroxy-containing aluminum component. The acidic and basic agents can be mixed using conventional equipment that can give the aqueous medium strong agitation. The ratio of acidic and basic components should be such that a final pH of 8-10.3 and preferably 8.3-9.7 is obtained. The resulting aluminum component has hydroxyl groups as an essential part of its composition.

The polyvinyl alcohol reaction product found useful in the formation of the mixture according to the present invention is formed by contacting polyvinyl alcohol and a compound containing or giving an aldehyde. The polyvinyl alcohols that can be used in the formation of the present reaction product have an average molecular weight of at least approx. 20,000 and preferably the average molecular weight should be from 90,000 to 200,000. Conventional polyvinyl alcohol is the hydrolysed product of polyvinyl acetate. The hydrolysis should be at least approx. 75% complete and preferably from 80 to 95% complete to form a useful polyvinyl alcohol reactant. The polyvinyl alcohol reactant, which is formed from the hydrolysis of polyvinyl acetate or the like, can be reacted in an aqueous medium with an aldehyde-containing or releasing reactant. Suitable aldehyde-containing reactants are, for example, formaldehyde, acetaldehyde or polyaldehydes such as glyoxal, paraformaldehyde and the like. Other useful aldehyde reactants are aldehyde-releasing agents such as melamine-formaldehyde monomer products and derivatives such as tri and hexa (methylol) melamine and tri and hexa (Q-^-C 4 alkoxymethyl) melamine. Such materials can be formed by known conventional methods. The alkyl blocked derivatives are commercially available, are stable to self-polymerization and are therefore preferred. Among all the aldehyde reactants, the preferred reactants are paraformaldehyde and formaldehyde. The present polyvinyl alcohol reaction product found suitable in the present mixture to provide the combined desired properties can be formed by reacting a polyvinyl alcohol as described above with from at least approx. 1 and preferably from 1 to 200 and preferably 2 to 50% stoichiometric of an aldehyde reactant based on the hydroxyl content of polyvinyl alcohol the hole. The stoichiometry is defined as the reaction of 2 OH groups with an aldehyde group to form an acetal. Excess aldehyde can be used. The particular amount of aldehyde reactant will depend on the solubility of the reactant in the aqueous reaction medium, its reactivity and similar properties which will be apparent to those skilled in the art. The reaction product should be dispersible in water. The reaction to form the polyvinyl alcohol reaction product can be carried out in an aqueous medium which should be acidic, i.e. have a pH of 5.5 or less and preferably from 2 to 4.5 and which can contain other components such as alkali metal sulphates in from 1% up to saturation , to assist the formation of the polymer product. The reaction can be carried out at room temperature or at a higher temperature, such as from 50°C to 100°C. The solid product can be isolated by usual methods such as salting out the product with a suitable acid such as for example sulphate, carbonate or phosphate salts, decantation, filtration and drying.

Blends of the present hydroxy aluminum component and the polyvinyl alcohol/aldehyde reaction product have unexpectedly been found to have a combination of desirable properties, namely, pseudoplasticity and water loss control, which cannot be achieved by separate use of the materials or cannot be attributed to the combination of the properties of each agent when used separately.

Amphoteric metal hydroxides formed in various ways and from various materials are known to form a gelatinous mass in aqueous systems. Aqueous amphoteric metal hydroxide gels have been found to be useful for various purposes such as coatings, adhesives and the like as well as in specific well treatment mixtures such as fracturing or completion fluids. Such gels and mixtures are used under conditions clearly different from those required here and have no water loss control properties. Although the hydroxy-containing aluminum components described here have now unexpectedly been found when used alone to give aqueous systems a certain degree of pseudoplasticity, they do not provide aqueous systems with water loss control.

The present described polyvinyl alcohol/aldehyde reaction products do not exhibit, when used alone, and do not provide aqueous systems with water loss control or pseudoplasticity like water-based clay-free drilling fluids.

It has now been unexpectedly found that when polyvinyl alcohol (the aldehyde reaction product) is combined with the hydroxy-containing aluminum component, one unexpectedly achieves equivalent or better pseudoplastic properties and an exceptionally high degree of water loss control that cannot be attributed to each individual component. Furthermore, the present blend is unique

because other trivalent metal hydroxides and the present polyvinyl alcohol/aldehyde do not have the desired properties.

The aqueous system containing the present composition should have an alkaline pH of from 8 (preferably 8.3) to 10.3.

At these alkaline pH conditions, the desired properties are achieved. Adjustment of pH can be carried out with any water-soluble inorganic base or acid such as alkali metal hydroxide or carbonate, alkaline earth metal hydroxide or a hydrohalic acid, sulfuric acid, nitric acid or sodium bicarbonate.

The aqueous system should be mixed to the necessary extent so that the components of the mixture are essentially evenly distributed therein. Furthermore, the hydroxyaluminium-containing aqueous medium or preferably the system containing the resulting mixture can have the combined described properties enhanced by the system being mixed at high shear rates of approx. 20,000 second ^ or higher over shorter periods of time such as from 5 to 60 minutes by circulating the aqueous system through a tube of small internal diameter at high speed.

The aqueous medium in which the above-described hydroxyl-containing aluminum component is formed can be used directly to form the water-based drilling fluids according to the present invention. The aqueous medium may be diluted with a sufficient amount of water to provide a system with from 0.5 to 10% and preferably from 1.5 to 3.5% by weight based on the weight of the water of the resulting hydroxyaluminum compound of assumed molecular formula AIO (OH) for the hydroxyaluminum compound. The best concentration can easily be determined in conventional ways by the mud engineer based on consideration of the concentration and nature of other materials, which may also be present in the drilling fluid.

The polyvinyl alcohol/aldehyde reaction product may be used in any effective amount as in combination below

the amount of aluminum component present provides the resulting aqueous system with water loss control. Normally from 0.3 to 5% by weight and preferably from 0.75 to 2% by weight polyvinyl alcohol/reaction product is used based on the weight of the water in the resulting aqueous system. The existing concentration can be easily determined in the usual way, taking into account the polymer's

nature, i.e. molecular weight, hydroxyl content, aldehyde reactant etc, as well as the nature and concentration of the other materials in the aqueous system.

The above-described composition is capable of providing a clay-free aqueous system (the term "clay-free" as used herein means without clay that makes the drilling fluid viscous as an essential component of the fluid and not other materials), such as a water-based drilling fluid (the term "fluid " or "system" herein means water-based systems containing the present composition) with non-Newtonian pseudoplasticity, i.e. the viscosity of the resulting fluid varies inversely with respect to the shear rate to which the fluid is subjected. The shear stress's dependence on the shear rate can be defined by the legal relationship

where T means the shear stress the aqueous system of the drilling fluid is subjected to in units such as dyne/cm 2 j % is the shear rate in units of reciprocal time such as sec, .: K is a constant for the value of the shear stress of the particular aqueous system at a shear rate of 1 sec ; and n is a number greater than 0. When n=l, the system is Newtonian; if n is less than 1, the system is pseudoplastic, and if n is greater than 1, the system is dilatant. It has unexpectedly been found that fluid containing the present described mixture exhibits shear stress (f) properties at different shear rates (if) in the range from 10 to 400 seconds, i.e. in the range normally found in the annulus-body region of the borehole so that n in the statutory relationship has a value less than approx. 0.4. Such systems therefore have non-Newtonian, pseudoplastic properties to an exceptionally high and desirable degree.

The above described mixture is unexpectedly found to give a

high degree of fluid loss control. This means that the liquid is able to influence the porosity of the adjacent surroundings so that liquid loss to the porous surroundings is prevented. System fluid loss can be determined according to the American Petroleum Institute's procedure API No. RP-13B. After initial outbreak, the desired water loss control achieved with the present invention is less than approx. 20 ml per 30 minutes and, less than approx. 15 ml per 30 minutes.

It has further unexpectedly been found that the present mixture is very temperature stable, stable against calcium and sodium salts and various other conditions, which are desired for a liquid used in rotary drilling of boreholes and the like. The drilling fluids containing the present composition have unexpectedly been found to be very stable with respect to rheological and water loss properties under various adverse conditions. Such fluids have been found to be stable after being exposed to higher temperatures for longer periods of time, to high shear rates as found in the drill cutting area, they were found to be stable in the presence of various corrosive elements such as calcium chloride and sodium chloride which may be present in such fluids .

The great degree and breadth of stability until now achieved

drilling fluid in combination with its ability to provide non-Newtonian, pseudo-plastic properties under various low shear rates from 10 to 400 sec.1 and higher, as found in the annular area between the drill stem and the borehole

walls help to increase the drilling efficiency, i.e. the speed of the drilling of the borehole.

The drilling fluid mixture according to the present invention may contain other conventional drilling fluid additives such as weighting agents such as crushed oyster shells, barite and the like, thinning agents such as ferrochromium ligno-sulfonate and the like, loss circulating agents such as ground walnut shells, cotton seed necks and the like, pH adjusting agents such as MgO, sodium carbonate, sodium bicarbonate and similar, as well as other conventional additives.

The term "water-based" as used here in the description of the present invention generally includes . drilling fluid that is on a liquid base containing essentially fresh water or salt water. However, it must be understood that sometimes certain small amounts of other liquids may be emulsified or mixed with the water-based liquid. For example, drilling fluids can sometimes contain small amounts of oil, emulsified or mixed with the drilling fluid, where the oil either comes from an oil formation being drilled into, or under certain circumstances, oil can be added on purpose.

The present water-based, clay-free drilling fluids containing the present composition described above and having a pH in the range of 8 to 10.3 have been found to be stable to temperature, the presence of sodium and calcium salts, and the presence of conventional drilling fluid additives. Other viscosity and water loss controllers do not need to be present. Furthermore, the available drilling fluids are essentially non-corrosive and non-destructive to the metal equipment normally used in drilling operations.

The present composition can be used with conventional downhole drilling equipment in ways known per se to effectively drill holes in subterranean formations. The pseudo-plastic and water loss control properties of the drilling fluids containing this mixture enable effective removal of the cuttings from the area at and around the drill bit which enables more efficient drilling of the formation when the drilling fluid is circulated during hole drilling.

The following examples are intended to be illustrative only and not

limit the present invention beyond what is stated in the attached claims. All parts and percentages are parts by weight unless otherwise stated. The units for K in shear stress-2

the law is dyn/cm .

EXAMPLE I

Formation of polyvinyl alcohol/aldehyde (PVA/A) products

A. 5.625 parts of a commercially purchased polyvinyl alcohol with

an average molecular weight= 125,000 and 87% hydrolyzed (Gelvatol 20-90) was dissolved in 94.375 parts of water. The pH of the solution was adjusted to 5.0 with dilute hydrochloric acid. 1.013 parts of paraformaldehyde (50% stoichiometric) was added to the solution which was then heated to 60°C with stirring and held at that temperature for 30 minutes. The solution was allowed to cool and the pH was adjusted to 9.5 with 10% sodium hydroxide solution.

B. A second polyvinyl alcohol/aldehyde product was formed by first dissolving 11.25 parts of the commercial polyvinyl alcohol described above in 88.75 parts of water and then adjusting the pH of the solution to 3.0 with dilute HCl. 3.83 parts of paraformaldehyde (100% stoichiometric) was added and the mixture was stirred and heated to 85°C and held at this temperature for 60 minutes. After cooling, the solution was diluted with an equal part of water and the pH of the solution was adjusted to 9.5 with 10% sodium hydroxide solution.

EXAMPLE TEN

Formation of hydroxy-containing aluminum component

15.3 parts of commercial sodium aluminate (Na 2 OAl 2 O 3 ' 3H 2 O) powder was mixed with 12.2 parts of commercial aluminum chloride hexahydrate powder. The mixture was added to 350 parts water and mixed at high speed with a Hamilton Beach model 936-2 mixer for 20 minutes. The aqueous dispersion was allowed to settle for 16 hours and then mixed again at high speed for 5 minutes. The pH of the resulting dispersion was 8.5 and was adjusted to 9.5 with dilute NaOH.

In the following, the hydroxy-containing component concentrations will be determined based on the formula AlO(OH), although the present component may be in other forms.

EXAMPLE III

For comparative reasons, aqueous samples of hydroxy-containing aluminum and of polyvinyl alcohol/aldehyde reaction products were respectively examined with regard to rheology and water loss control.

An aqueous system containing 3% hydroxy aluminum product (prepared according to Example II above) and having a pH of 9.5 was analyzed rheologically by standard methods with a Haake Rotovisco RV-1 rotary rheometer at various shear rates from 8 to 800 sec. and 25°C. The measured values for n and K were 0.28 and 3.0, respectively, according to the legal relationship T=K ( cf )n where ^ means the shear stress the aqueous system is exposed to in dyn per cm 2 ;y • is the shear rate in reciprocal time so. as sec-. 1;

K is a constant with a shear stress value of one

-1 2

cutting speed a sec. and with units dyn/cm,

and n is a numerical value from 0 to 1. Pseudoplastic systems have a value for n of less than approx. 0.4. The liquid loss control of the material was measured using American Petroleum Institute (API) method RP 13B at 6.8 atmospheres at 25°C. A fluid loss control value of greater than 200 ml per 30 minutes. The product gave good pseudoplasticity, but gave essentially no fluid loss control.

The polyvinyl alcohol/paraformaldehyde products of Example I were diluted with water to give aqueous systems with i.5% PVA/A. Rheology and fluid loss control were measured in the same manner by the same method as described for the hydroxy aluminum compound above. The materials were found to be Newtonian (n=1, K=<0.1), and produced a fluid loss greater than 200 ml/30 minutes. The PVA/A reaction products do not provide pseudoplasticity or fluid loss control.

EXAMPLE IV

This example illustrates that aqueous systems containing a mixture of the hydroxy-containing aluminum compound and the polyvinyl alcohol-paraformaldehyde reaction product provide both good rheology and good fluid loss control and are stable even when exposed to higher temperatures over longer periods of time.

Four parts of the hydroxy-containing aluminum product that is.

prepared in the manner described in example II was mixed with 1 part polyvinyl alcohol-paraformaldehyde product (PVA/A) prepared in the same manner as described in example I

(B). The resulting aqueous mixture contained a uniform mixture of 2.4% hydroxy aluminum product [symbolized by AIO(OH)] and 1.5% PVA/A product. A sample (Sample 1) was taken of the mixture to determine its rheology and liquid loss control at 25°C by the methods described in Example III. Another sample (Sample 2) of the mixture was placed in a container under a ^-atmosphere, sealed and exposed to 122°C for 16 hours with constant stirring and then allowed to cool to room temperature. Rheology and liquid loss control of the heat-treated mixture was measured. Finally, a third sample (Sample 3) of the mixture was subjected to high temperature 122°C/ 16 hours and then subjected to high shear forces by circulating the sample mixture through a capillary tube (internal diameter = 0.07 85 cm) for 30 minutes which gave an approximately calculated shear rate of 25,000 sec.<1>. Rheology and fluid loss control of this sample was measured. A summary of the results is given in Table I below.

The fluid loss determined according to API method RP 13B gives a total fluid loss (TFL in ml/30 minutes) which is the cumulative value of the initial burst (Sp in ml) and the corrected fluid loss (CFL in ml/30 minutes). The breakout is obtained by plotting cumulative volume on the y-axis and the square root of time on the x-axis and then extrapolating the straight line back to the y-axis. The intercept is the breakout volume value. The corrected fluid loss is obtained by subtracting the burst value from the total fluid loss volume. The corrected fluid loss value is the amount of loss the fluid would be expected to experience over an extended period of time.

EXAMPLE V

The procedures described in Example IV above were

repeated except that the mixtures formed further contained the addition of 3.5% salt (NaCl) to simulate a salt system or 2.85% Glen.Rose clay shale to simulate stone chips. The results are set out in Table II below and show that neither salt nor stone chips negatively affect the rheology and fluid loss control properties of aqueous systems with hydroxy-containing aluminum and PVA/A mixtures.

EXAMPLE VI

An aqueous system was prepared according to the methods described in Example IV except that the PVA/A reaction product was prepared as described in Example I(A). Portions of the resulting system were made into an aqueous system without additives, with a combination of CaCl^ and NaCl to determine the effect of the presence of calcium and of salt, and with baryte, a common weighting agent for drilling fluid. Rheology and liquid loss control for each mixture was measured in the manner described in Example IV. Results are given in Table III and show good combined properties achieved in each case.

EXAMPLE VII

Polyvinyl alcohol paraformaldehyde products were prepared, transferred into dried products and reconstituted with water to determine their activity when used in combination with a hydroxy aluminum component.

A. A polyvinyl alcohol-paraformaldehyde reaction product was formed in the manner described in Example I(a), except that the polyvinyl alcohol was dispersed in a 6% sodium sulfate-water solution to give a 16.7% concentration of polymer. After the reaction and pH adjustment, the product was filtered and air dried at 50°C for 16 hours. The dried product was redispersed in water by simple mixing and gave an aqueous solution with the same PVA/A product concentration of 5.63%

as in Example I(A). This solution was mixed in a ratio of 1:4 with an aqueous dispersion of hydroxy-containing aluminum component prepared in the same manner as described in Example II above. Aqueous systems containing the mixed ingredients were investigated for rheology and fluid loss control. The results are set out in Table IV below and show that excellent efficacy is achieved.

B. The procedure described in the above section was repeated with the exceptions that the concentration of sodium sulfate was increased from 6 to 16% and the original polyvinyl alcohol concentration was increased from 16.7 to 25%. The product was easily dried to a voluminous white powder that was easy to redisperse. The rheology and fluid loss control results given in Table IV below show excellent performance.

EXAMPLE VIII

Aqueous systems of polyvinyl alcohol-paraformaldehyde reaction product and of hydroxy-containing aluminum component were prepared in the same way as described in examples I(A) and II respectively. A 4:1 mixture of the respective systems was prepared and then heated at 122°C for 16 hours with constant stirring. Conventional diluents were added to portions of the resulting mixture. Rheology and liquid loss control tests were performed as described in Example IV above. The results set forth in Table V below show that reduction in viscosity can be achieved (reduction in value of K) without any adverse effect on pseudoplasticity (n) or fluid loss control.

EXAMPLE IX

A polyvinyl alcohol-aldehyde reaction product was prepared in the same manner as described in Example I(A) with the exception that an equal weight amount of formaldehyde was used instead of paraformaldehyde.

The resulting solution of PVA/A reaction product was mixed with an aqueous dispersion of the hydroxy-containing aluminum component from Example II in the same manner as described in Example IV and the properties of the resulting aqueous system determined by the methods described in Example IV. The results (Table VI) show that the effect in terms of rheology and fluid loss control was equivalent to the effect obtained with paraformaldehyde reaction product.

EXAMPLE X

A polyvinyl alcohol reaction product was formed in the same manner as described in Example I(A) except that 0.15 parts of hexamethoxymethylmelamine (HMMM) was used as the aldehyde releasing reagent instead of paraformaldehyde, the pH of the original solution was adjusted to 3.0, the reaction temperature was 9 0°C and the reaction time 1 hour. The resulting product was mixed with an aqueous dispersion of hydroxy-containing aluminum component of the type and in the manner described in Example IV. Rheology and fluid loss control of the resulting system was tested as described in Example IV. The results are set out in Table VII below.

EXAMPLE XI

Commercially available polyvinyl alcohols of different molecular weights were used to prepare the PVA/aldehyde reaction product according to the method of Example I(A). The resulting aqueous systems each containing the reaction products were tested for rheology and fluid loss control and found to be Newtonian and greater than 200 mL/

30 minutes respectively. Each of the systems was combined as described in Example IV with dispersions of a hydroxy-containing aluminum component prepared as in Example II and in certain cases by the addition of NaCl and tested again. The results are set out in Table VIII below.

EXAMPLE XII

Aqueous systems of PVA/A reaction product prepared according to Example I(A) and of hydroxy-containing aluminum component prepared according to Example II were mixed in different ratios from 1.4:1 to 2.2:1. The resulting blend compositions were tested for rheology and fluid loss control in the manner described in Example IV. The results are listed in Table IX below.

EXAMPLE XIII

PVA/A reaction product was formed according to Example VII B above to a dry product with 12% moisture content. The dried PVA/A and the dried AlO(OH) component formed according to Example II were reconstituted in water to a concentration of 2.4% AlO(OH) and 1.3% PVA/A (dry basis) . The resulting system was tested for rheology and fluid loss control as described in Example IV. The results which

are set forth in Table X below show that aqueous systems containing the combination of such ingredients exhibit excellent rheological and fluid loss control properties.

EXAMPLE XIV

Mixtures are formed with PVA/A—reaction product from example I

(A) and with hydroxy aluminum constituents formed from the following ingredients: 1. 227.6 parts 19.1% aqueous solution of commercial sodium aluminate with 416 parts IN HC1. pH becomes 9.6. 7 Parts of the resulting product diluted with 3 parts water gives 3.5% AIO(OH). 2. 238 parts of a 34.7% aqueous solution of A12(S04)3 16H2° with 102 parts of a 30.5% solution of NaOH. pH=9.5. Solution diluted with 18.5 parts water.

All the mixes show a good combination of rheological and fluid loss control properties.

EXAMPLE XV

The procedures described in Example IV above were repeated with the exception that the pH of the resulting samples was adjusted to various values from 8.5 to 11.5. The PVA/PF product was formed as described in Example I(B) except at 60°C and with the addition of 16% sodium sulfate. The final pH adjustment was in all cases made by adding 1 part solid sodium carbonate to 99 parts of the aqueous mixture. (The concentration of A10(OH)=2.3%; of PVA/'PF=1.6%) and then adjustment to the desired pH value with a 10% sodium hydroxide solution (for pH values above 10.5) or with a 1% HCl solution (for pH values below 10.5). Certain samples listed below contained 0.5% ground limestone to simulate stone chips. The results given in Table XI below show that the desired properties are achieved at different pH values within the range from 8 to 11.5.

EXAMPLE XVI

A polyvinyl alcohol reaction product was formed in the same manner as described in Example I(A) except that the pH was adjusted to 3.0 with dilute sulfuric acid and the aldehyde reactant was formaldehyde used at 5% of stoichiometric amount. The material formed was mixed with an aqueous dispersion of hydroxyaluminum component formed in the manner described in Example II. The pH of the system was adjusted to 9.5 and contained 1.6% polyvinyl alcohol — reaction product and 2.4

% aluminum content. 0.5% ground limestone was added. The resulting system was tested for fluid loss control and rheology according to the procedure of Example IV. The material was pseudoplastic and had a TFL of 10.4, a burst of 2.3 and a CFL of 8.1. The sample was exposed to a higher temperature of 122°C for 16 hours under a nitrogen atmosphere and stirring. The sample was cooled and the liquid loss properties were found to be TFL of 12.6, burst of 4.3 and CFL of 8.3. The cake was 0.15 cm thick.

Claims (7)

1. Hydroxyaluminous composition which provides clay-free aqueous systems with a combination of pseudoplasticity and fluid loss control when dispersed in water, characterized in that it consists of: (a) a hydroxyaluminous component formed by mixing in an aqueous medium and under vigorous stirring a water-soluble basic component selected from the group consisting of an alkali metal aluminate, alkali metal hydroxide, ammonium hydroxide and mixtures thereof with a water-soluble acidic component selected from an inorganic acid, aluminum chloride, aluminum sulfate, aluminum nitrate, hydrates and mixtures thereof, one of, or both, the basic and acidic constituents are an aluminum-containing compound, the acidic and basic components are reacted in such a ratio that the resulting product gives an aqueous medium a pH of from 8 to 10.3, in combination with (b) a reaction product formed in an aqueous acidic medium with a pH below approx. 5.5 between polyvinyl alcohol with a weight average molecular weight of at least 20,000 and an amount of an aldehyde-containing or aldehyde-releasing component that is 1 to 200% of the stoichiometric, the amount of component (a) in relation to the amount of component (b) being sufficient to directly form an aqueous system with 0.5-10% by weight of component (a) and 0.3-5% by weight of component (b) based on the water in which the mixture is to be dispersed. 2. Mixture according to claim 1, characterized in that component (a) is formed from an alkali metal aluminate with an acidic reagent selected from the group consisting of an inorganic acid, aluminum chloride and aluminum nitrate, their hydrates and component (b) is formed with an aldehyde reagent in an amount from 1 to 200% of the stoichiometric and in an aqueous medium with a pH of less than about 5.5. 3. Mixture according to claim 2, characterized in that component (a) is formed from an alkali metal hydroxide or ammonium hydroxide and an aluminum compound selected from the group consisting of aluminum chloride, aluminum nitrate and aluminum sulfate, hydrates or mixtures thereof and component (b) is formed with an aldehyde component in a amount from 2 to 50% of the stoichiometric and in an aqueous medium with a pH from 2 to 4.5. 4. Mixture according to claim 1, characterized in that the polyvinyl alcohol has a weight average molecular weight of from 90,000 to 200,000 and is at least 75% hydrolysed. 5. Mixture according to claim 4, characterized in that the aldehyde component is paraformaldehyde or formaldehyde and the polyvinyl alcohol is from 80 to 95% hydrolysed. 6. Mixture according to claim 4, characterized in that the aldehyde component is a trialkoxymethylmelamine and the polyvinyl alcohol is from 80 to 95% hydrolysed. 7. Use of a mixture according to claims 1-6 in drilling fluid which is circulated when drilling a borehole in underground formations using conventional borehole drilling equipment.