NO822414L - AROUND BROWN FLUIDS. - Google Patents

Description

The present invention relates to a method and a composition for increasing the viscosity and reducing fluid loss in aqueous systems used as well treatment fluids.

Aqueous media, especially those containing oil field brines, are usually used as well treatment fluids such as drilling fluids, overhaul fluids, completion fluids, packing fluids, well treatment fluids, treatment fluids for underground formations, spacing fluids, hole plugging fluids, etc. Such well treatment fluids must if they are to be efficient and economically beneficial, exhibit low fluid losses. It is known to add certain hydrophilic polymeric materials to the well operating fluid for fluid loss control. It is e.g. known to use starch and cellulose products, e.g. corn starch and potato starch derivatives, as additives to well operating fluids, e.g. saline solutions, for fluid loss regulation.

Viscosity increase of aqueous well operating fluids, e.g. salt solutions are also required in many applications. Here too, starch and cellulose derivatives have been used to achieve such an increase in viscosity.

Examples of prior art that describe various additives to well operating fluids for viscosity increase and/or fluid loss control are US patent no.

3 6 25 889 which mentions a well completion fluid consisting of

of aqueous calcium chloride, carboxymethyl cellulose (CMC), and xanthan gum (XC polymer)., and US Patent No. 3,953,336 which describes blends of XC polymer with various cellulose derivatives such as hydroxymethyl cellulose, carboxymethyl cellulose, etc.

It is therefore an object of the present invention to provide a new composition for synergistically increasing the viscosity and regulating the fluid loss in aqueous well operating fluids.

, A further object of the invention is to provide a new composition which is suitable for synergistically increasing the viscosity and lowering the fluid loss in aqueous salt solutions used as well operating fluids.

Another purpose of the invention is to provide an improved method for reducing the fluid loss of an aqueous well operating fluid.

The above-mentioned and other purposes of the invention will be apparent from the description given below.

According to an embodiment of the present invention, there is provided a method for reducing the fluid loss in an aqueous well operating fluid, comprising adding and dispersing in the well operating fluid an effective amount of a cross-linked hydroxyethyl starch (HES)' and an effective amount of a material selected from the class consisting of carboxymethyl cellulose ether>- XC polymer and mixtures thereof.

Another embodiment of the invention is provided

a composition suitable for increasing the viscosity and reducing fluid loss in an aqueous medium, comprising an effective amount of a cross-linked hydroxyethyl starch and an effective amount of a material selected from the class consisting of carboxyalkyl cellulose ethers, XC polymer and mixtures thereof.

In yet another embodiment of the present invention, there is provided a well operating fluid comprising an aqueous medium, an effective amount of a cross-linked hydroxyethyl starch and an effective amount of a material selected from the class consisting of carboxyalkyl cellulose ethers, XC polymers and mixtures thereof.

One of the polymeric components (polymer A) in the new compositions according to the invention includes a material selected from the class consisting of carboxyalkyl cellulose ethers where the alkyl group has 1-3 carbon atoms such as carboxymethyl cellulose (CMC), carboxyethyl cellulose (CEC), etc.; xanthan gum (xanthomonas polysaccharide gum biopolymer) Known as XC polymer; and mixtures thereof. The term polymer component shall include one or more of the carboxyalkyl cellulose ethers with or without XC polymer. Of the above-mentioned polymers, the preferred polymers are XC polymer and carboxymethyl cellulose.

The XC polymers useful in the present invention, depending on the method of preparation of the well operating fluids, may either be in the form of a dry powder, substantially untreated, or may be an "activated" XC polymer. The term "activated" used refers to an XC polymer that will substantially hydrate or solubilize in a salt solution having a density greater than about 1.70 kg/liter without the need for mixing, such as by rolling, at elevated temperatures . Examples of such activated XC polymers are set forth in US Patent Application No. 146,286, which is hereby incorporated. As described in the aforementioned patent application, XC polymers that have been activated will be solubilized in salt solutions without the necessity for rolling or other forms of mixing at elevated temperatures. Any XC polymer that will solubilize in a salt solution having a density above about 1.70 kg/liter at room temperature, can generally be considered an "activated" XC polymer. However, it should be understood that the present invention is not limited to the use of such activated XC polymers. Depending on the mixing ratio and composition of the aqueous well operating fluid, unactivated XC polymers or such polymers in dry powder form are compatible with the aqueous well operating fluids used in the present invention. The term "compatible" used means that the XC polymer can be solvated or solubilized in a given aqueous solution using mixing techniques such as rolling at elevated temperatures. An incompatible system is thus one in which the XC polymer will not dissolve in the salt solution, regardless of the mixing conditions used.

The second polymeric component (polymer B) in the compositions according to the present invention is a cross-linked HES. Such hydroxyethyl starches are produced by introducing non-ionic hydroxyethyl side groups into the polymer chain in the starch followed by well-known cross-linking techniques such as e.g. those described in US Patents 2,500,950, 2,929,811;

2 989 521 and 3 014 901, which are hereby included. The cross-linked hydroxyethyl starches useful herein

invention are generally those in which the degree of substitution (DS)

in the hydroxyethyl side chain is from approx. 0.15 to approx. 0.8, preferably from approx. 0.25 to approx. 0.6. A particularly suitable cross-linked hydroxyethyl starch is known as "BORAMYL CR", which is a cross-linked potato starch derivative. "BORAMYL CR", which is a coarse flaky white material, has a bulk density (kg/m 3 ) of approximately 325 and a DS value of approximately 0.4.

The cross-linked HES can be used either in the form of

a dry powder or in flake form, substantially untreated, or may be "activated" starch where the term "activated" has the same meaning as used above in connection with the mention of activated XC polymers. Procedures for activating the cross-linked HES are described in US Patent Application No. 119,805 filed February 8, 1980, hereby incorporated. It should be understood that the present invention is not limited to the use of activated HES. Namely, it is a feature of the present invention that all the polymer components can be used in dry form for the production of well operating fluids which exhibit excellent rheological properties and low fluid loss. In certain salt solutions, however, activation or pre-solvation of the XC polymers and/or the hydroxyethyl starch may be desirable in order to reduce mixing times and load at mixing conditions.

The polymer composition according to the invention which can be used to reduce fluid loss and increase the viscosity of aqueous well operating fluids comprises an effective amount of cross-linked HES (polymer B) and an effective amount of XC polymer, a carboxyalkyl cellulose ether (CACE) polymer or mixtures thereof (polymer A) . It has been found that when either XC polymer, a CACE polymer or a mixture thereof is added to aqueous well operating fluids together with HES, depending on the nature of the fluid, a synergistic increase in viscosity and/or fluid loss control is achieved. The particular amount of each of the polymer components present in the additive composition will vary depending on the nature and composition of the aqueous well operating fluid with which the additive is to be mixed. The polymer composition according to the invention will usually contain a weight ratio for HES (polymer B). to XC polymer, CACE polymer or mixtures thereof (polymer A), from approx. 10 to 90 to approx. 90 to 10, preferably from approx. 33 to 67 to approx. 75 to 25. The polymeric composition according to the invention can either be in the form of a dry mixture of HES material and either the XC polymer, the CACE polymer or mixtures thereof or, if desired, it can be in the form of solvated or activated forms of the polymers . Thus, e.g. The HES and XC polymer be activated and the activated solutions mixed together to provide the new polymeric compositions described here.

The new well operating fluid according to the invention comprises an aqueous medium and an effective amount of a cross-linked hydroxyethyl starch and an effective amount of XC polymer, CACE polymers or mixtures thereof. The relative amounts of HES and the other polymer component (polymer A) which are mixed with the aqueous medium are such that a synergistic reduction in fluid loss to the aqueous medium is provided. Here too, the exact amount of each of the polymeric components will depend on the nature of the aqueous well operating fluid.

However, the weight ratio of HES material to the other polymer component in the well operating fluid will usually be from approx. 10 to 90 to approx. 90 to 10, more preferably from approx. 33 to 67 to approx. 75 to 25.

The well operating fluids will generally contain the polymer components in amounts from approx. 1.4 3 to approx. 28.53 kg/m<3>hydroxyethyl starch (polymer B) and from approx. 0.71 to approx. 14.27 kg/m 3 of the second polymeric component (polymer A).

The aqueous medium used in the well operating fluids according to the invention can vary from fresh water to heavy salt solutions that have a density of over 2.28 kg/m 3. In general, well operating fluids such as e.g. those used in completion and overhaul operations, prepared from aqueous media containing soluble salts such as e.g. a soluble salt of an alkali metal, alkaline earth metal, a group Ib metal, a group Ib metal, as well as water-soluble salts of ammonia and other cations. The polymeric compositions are particularly useful in the preparation of heavy salt solutions with low fluid losses, i.e. aqueous solutions of soluble salts of polyvalent ions, e.g.

Zn and Ca.

The preferred heavy salt solutions which are useful in forming the well operating fluids of the invention,

are those that have a density of over approx. 1.32 kg/l, especially those with a density above 1.80 kg/l. Such heavy salt solutions include aqueous solutions of salts selected from the group consisting of calcium chloride, calcium bromide, zinc chloride, zinc bromide and mixtures thereof.

If desired, "bridging" agents can be added to the well operating fluids to help control fluid loss. Somewhat lower filtrates are obtained with the use of such means.

However, it is a distinct and unexpected feature of the invention that a "bridging" agent is not necessary to achieve low fluid loss values in aqueous salt solutions. By using the present invention, it is thus possible to obtain clear salt solutions which have low fluid loss characteristics and low rheological characteristics.

To more fully illustrate the present invention, the following examples are given. Unless otherwise stated, all measurements of physical properties were made according to the test methods specified in STANDARD PROCEDURE FOR TESTING DRILLING MUD API RP 13B, 7th edition, April 1978. The cross-linked hydroxyethyl starch used was unless otherwise stated "BORAMYL CR ".

Example 1.

To show the synergistic effect on viscosity

and fluid loss obtained by mixing HES and XC polymer, 2.85 kg/m 3 XC polymer at either levels of 0 or 17.12 kg/m<3> of "BORAMYL CR" was added to an aqueous 10 wt -% Na Cl solution and mixed for 25 min. on a "multimixer". Then the samples were rolled or rolled at 65.6°C, cooled to 23.3°C

and stirred for 5 min. and API rheology and fluid loss determined. The data obtained which are set out in Table I below show that

""BORAMYL CR" mixed with the XC polymer synergistically decreased the fluid loss in the sodium chloride aqueous solution and increased the viscosity.

Example 2.

The procedure in Example 1 was followed with the exception that carboxymethyl cellulose (CMCl) was used instead of XC polymer. The results shown in Table IT clearly show that the combination of cross-linked hydroxyethyl starch and the CMC polymer gives synergistic results both with respect to

fluid loss and viscosity.

With regard to the data stated in tables I and II, it should be pointed out that the cross-linked HES material gives significantly better results than iJcke cross-linked material.

Example 3.

To test the effectiveness of the polymeric compositions of the invention on weighted drilling fluids, various amounts of "BORAMYL CR" and XC polymer were added to a 1.44 kg/liter sodium chloride solution weighted with "BAROID" (a baryte weighting material). "BORAMYL CR" was first added to the sodium chloride solution and mixed with a "multimixer" for 10 min. This was followed by addition of the XC polymer and mixing continued for 10 min. after which "BAROID" was added and further mixing continued in said "multimixer" for a further 10 min. Measurements of API rheology and fluid loss were obtained on the thus produced drilling fluid. The fluid was roller treated for 16 hours at 65.6°C and the rheological and fluid loss properties tested. The samples were then cooled and stirred for 5 min. and the properties determined anew.

The obtained data given in Table III below show that the XC polymer combined with "BORAMYL CR", synergistically reduces the fluid loss and increases the viscosity of weighted drilling fluids. It was also noted that there was essentially no sedimentation of the weight material.

Example 4.

To investigate the effectiveness of the present polymeric compositions with a view to viscosity increase and fluid loss control in heavy salt solutions, e.g. salt solutions containing calcium chloride, various amounts of HES and XC polymer were added to an aqueous 5% calcium chloride solution and mixed for 20 min. in a "multimixer" and the API rheological properties were determined (initial properties). The samples were then roller-treated for 16 hours at 65.6°C, tested in a hot state and not stirred. The samples were cooled, stirred for 5 min. in a "multimixer" and API rheology and fluid loss determined. The data obtained shown in Table IV show that when "BORAMYL CR" and XC polymers are combined, they will synergistically reduce the fluid loss in the aqueous calcium chloride solution and increase the viscosity. Example 5. The procedure of Example 4 was followed with the exception that after the addition of the polymeric material to the calcium chloride solution, the equivalent of 71.33.'/kg/m Glen Rose shale was added and the compositions mixed for 5 min. After this, the equivalent of 570.6 kg/m<3>"BAROID" was added to the compositions and mixing in the "multimixer" was continued for a further 5 min. The initial properties of the samples were then determined. The samples were rolled for 16 hours at 65.6°C and tested in a hot state and not stirred.

The samples were then cooled, mixed for a further 5 min. in a "multimixer", and the API rheological and fluid loss properties determined. The data set forth in Table V below show that even in the presence of a weight material and a shale material as would be the case in drilling, there is synergistic increase in viscosity and control of fluid loss using a mixture of "BORAMYL CR" and XC polymer. In addition to this, sedimentation of solids is much lower in the case where a mixture of the polymers is used.

Example 6.

To investigate the effectiveness of the polymeric compositions of the present invention on weighted drilling fluids using heavy salt solutions, various amounts of "BORAMYL CR" and XC polymer were added to a 5% calcium chloride solution weighted with the equivalent of 570.66 kg/m<3> by "BAROID". "BORAMYL CR" was first added to the calcium chloride solution and mixed with a "multimixer"

for 10 min. This was followed by addition of the XC polymer and mixing was continued for 10 min. after which "BAROID" was added and further mixing in the "multimixer" was continued for a further 5 min. Measurements for API rheology (initial properties) were obtained for the thus produced drilling fluid. The fluid was then roller treated for 16 hours at 65.6°C and the rheological properties of the hot, unstirred drilling fluid obtained. The samples were then cooled and stirred for 5 min. and the properties for rheology and fluid loss again determined. The obtained data given in Table VI below show that the XC polymer when combined with "BORAMYL.CR" synergistically reduces the fluid loss and increases the viscosity of the weighted drilling fluids. It should also be pointed out that when "BORAMYL CR" and XC polymer are combined there is essentially no sedimentation of "BAROID" weight material.

Example 7.

The procedure of Example 4 was followed using different amounts of "BORAMYL CR" and XC polymer. The data set forth in Table VII clearly demonstrate the synergistic effect on viscosity and fluid loss control using a mixture of "BORAMYL CR" and XC polymers.

Example 8.

The procedure in Example 6 was followed with the exception that different amounts of XC polymer were used and the equivalent of 570.66 kg/m 3 "BAROID" was added to the samples after addition of the polymers, the samples being mixed for 5 min. in a "multimixer". The samples were then rolled for 16 hours at 65.6°C and the API rheology determined (initial properties). The samples were then cooled, mixed for 5 min. in a "multimixer" and the API rheology and fluid loss properties were determined. The data set forth in Table VIII below again demonstrate the dramatic synergistic effect achieved on viscosity and fluid loss control using a blend of the polymers. As also appears from the data in Table VIII, no sedimentation of the weight material, "BAROID", occurred when using a mixture of the polymers.

It should be pointed out, with regard to the data set out in Tables I and II, that the cross-linked HES material gives significantly better results than non-cross-linked material.

Claims (26)

1. Method for reducing fluid loss in aqueous well operating fluids, characterized by dispersing in said fluid an effective amount of a cross-linked hydroxyethyl starch and an effective amount of a polymer component selected from the class consisting of carboxyalkyl cellulose ethers where the alkyl group has 1-3 carbon atoms, xanthan gum and mixtures thereof, the relative amounts of said hydroxyethyl starch and said polymeric component being such that the fluid loss in said aqueous fluid is reduced synergistically. 2. Method according to claim 1, characterized in that the aqueous fluid comprises an aqueous solution of at least one water-soluble salt of a polyvalent metal ion. 3. Method according to claim 1, characterized in that the aqueous medium has a density of over . about. 1.40 kg/litre. 4. Method according to claim 2, characterized in that the water-soluble salt is selected from the group consisting of calcium chloride, calcium bromide, zinc chloride, zinc bromide and mixtures thereof. 5. Method according to claim 2, characterized in that the density of the aqueous salt solution is from approx. 1.44 kg/litre to 2.30 kg/litre. 6. Method according to claim 1, characterized in that the weight ratio of the hydroxyethyl starch to the polymeric component is from approx. 10 ten 90 to approx. 90 to 10. 7. Method according to claim 6, characterized in that the weight ratio is from approx. 33 to 67 tii approx. 75 to 25. 8. Method according to claim 1, characterized in that the hydroxyethyl starch is activated before it is dispersed in the aqueous fluid. 9. Method according to claim 8, characterized in that the polymeric component comprises carboxymethyl cellulose which has been activated before dispersion in the aqueous fluid. 10. Method according to claim 8, characterized in that the polymeric component comprises xanthan gum. 11. Composition for increasing the viscosity and reducing the fluid loss in aqueous well operating fluids, characterized in that it comprises a mixture of an effective cross-linked hydroxyethyl starch and an effective amount of a polymeric component selected from the class consisting of carboxyalkyl dellulose ethers where the alkyl group has 1-3 carbon atoms , xanthan gum and mixtures thereof, the relative amounts of hydroxyethyl starch and polymeric components being such that the fluid loss from the aqueous fluid is reduced synergistically. 12. Composition according to claim 11, characterized in that the weight ratio of hydroxyethyl starch to polymer component is from approx. 10 to 90 to approx. 90 to 10. 13. Composition according to claim 12, characterized in that said ratio is from approx. 3 3 to 67 to approx. 75 to 25. 14. Composition according to claim 11, characterized in that said hydroxyethyl starch is activated. 15. Composition according to claim 14, characterized in that the polymeric component comprises carboxymethyl cellulose which is activated before it is dispersed in the aqueous fluid. 16. Composition according to claim 14, characterized in that the polymeric component comprises xanthan gum. 17. Well operating fluid, characterized in that it comprises an aqueous medium; and an effective amount of a cross-linked hydroxyethyl starch and an effective amount of a polymeric component selected from the class consisting of carboxyalkyl cellulose ethers wherein the alkyl group has a 1-3 carbon atom, xanthan gum. and mixtures thereof, the relative amounts of said hydroxyethyl starch and said polymeric component being such that the fluid loss in the aqueous medium is reduced synergistically. 18. Composition according to claim 17, characterized in that the aqueous medium comprises a solution of at least one water-soluble salt. one polyvalent metal ion. 19. Composition according to claim 17, characterized in that the aqueous medium has a density of over approx. 1.40 kg/litre. 20. Composition according to claim 18, characterized in that the water-soluble salt is selected from the group consisting of calcium chloride, calcium bromide, zinc chloride, zinc bromide and mixtures thereof. 21. Composition according to claim 18, characterized in that the density of the aqueous medium is from approx. 1.44 to 2.30 kg/litre. 22. Composition according to claim 17, characterized in that the hydroxyethyl starch is activated. 23. Composition according to claim 22, characterized in that the polymeric component is activated carboxymethyl cellulose. 24. Composition according to claim 22, characterized in that the polymeric component comprises xanthan gum. 25. Composition according to claim 17, characterized in that the weight ratio of hydroxyethyl starch to polymer component is from approx. 10 to 9 0 to approx. 90 to 10. 26. Composition according to claim 25, characterized in that the said ratio is from approx. 33 to 6 7 to approx. 75 to 25.