MXPA01008087A - Aphron-containing oil base fluids and method of drilling a well therewith - Google Patents

Abstract

Aphron-containing oil based well drilling and servicing fluids are disclosed which seal microfractutres and the like during drilling and well servicing operations, thus decreasing the volume of fluid lost to the formations contacted by the fluids. The fluids comprise an oleaginous liquid as the continuous phase, a viscosifier which imparts a low shear rate viscosity to the fluids of at least 10,000 centipoise, an aphron-generating surfactant, and aphrons. The fluids are used in a conventional method of drilling an oil and/or gas well or in conventional methods of servicing or treating such wells, such as in completion, workover, sand control, and frac pack operations, and as spotting fluids to released stuck pipes or tools in a wellbore.

Description

OIL BASED FLUIDS CONTAINING APHRON AND A WELL DRILLING METHOD WITH THEM The patent application is in part a continuation of the U.S. patent application. with Series No. 08 / 800,727 International Application P.C.T. No. PCT / US98 / 02566 filed on 02/1098, for each of the priorities claimed in this document. Background of the Invention Described in co-pending patent application with Serial No. 08 / 800,727 filed on 02/13/97, incorporated herein by reference, and the co-pending PCT patent application with No of Series PCT / US98 / 02566 filed on 02/10/98, incorporated herein by reference, aqueous well service and drilling fluids having a high viscosity of low average cutting (hereinafter referred to frequently as "LSRV" and containing aphrons (that is, microbubbles of a gas) Preferential fluids have aphrons, generated by imbibition air, contacted by fluids and creating aphrons due to low pressure and cavitation, which occurs when moving fluid removes the drill bit, however, inert gases such as nitrogen and carbon dioxide can be incorporated into fluids instead of relying on imbibition air or can be generated in-situ by component Reagents such as carbonates and acids. In addition, the aphrons can be generated on the surface of the well and incorporated into the fluid or the aphrons can be created on the surface in the fluid. This invention relates to service fluids and drilling of aphron containing wells, wherein the fluids have a continuous phase of oleaginous liquid. Recently, horizontal wells drilled and finished in unconsolidated sand reserves have become possible, due to new technology and methods of completion. Wells of this type require sand control, for example, as gravel packs with long open holes or the installation of mechanical sand exclusion devices (slotted shims, pre-packed screens, etc.). Wells with horizontal techniques have been successfully completed, producing intervals as long as 1800 feet (550 m), and these sand control methods are used more. In general, the wells are drilled with conventional drilling muds in the upper part of the productivity zone and the casing is configured. Then the cement is drilled into the casing shoe and the shoe is tested. The drilling mud is then replaced with a "low potential damage drilling fluid" which usually consists of polymers, viscosity improvers and particles to build a hardened agglomerate. The particles are usually graduated salt (NaCl) or calcium carbonate graduated (CaC02). These compounds are used because they are soluble in low saturated brines or hydrochloric acid. After the open hole interval has been drilled to a total depth, the gravel pack screen or sand exclusion device is placed in an open hole range. To do this it is necessary to circulate the drilling fluid from the open hole, so that the well can be packed in gravel or the sand exclusion position can be tested. The displacement of the drilling fluid is necessary with a solid-free finishing brine. There is always a concern about the physical erosion of the hardened agglomerate with the finishing fluid. That is, the hardened agglomerate must be sufficiently durable and stable to allow completion or other operation to be carried out and to protect the wellbore during the entire operation.

The drilling of microfractured shales, bag and microfractured carbonate and dolomite formations requires a drilling fluid that seals these formations, preventing the loss of gross amounts of fluids for the formations. Ideal drilling mud or drilling fluid will mechanically seal all porous openings, microfractures, and the like exposed to the well drilling, will remain intact during the completion operations, after which they will be easily removed through the production of oil or gas. Problems arise in the design of these fluids or sludge because the production zones vary in pressure, permeability, porosity and formation configuration. It would be desirable if the fluids could be created, which would prevent the loss of expensive finishing fluids for the formations and effectively protect the original permeable formation during various finishing operations such as gravel packing or wellbore reconditioning. Applications have been found for oil slurries and inverted emulsion drilling fluids (oil base) where the use of water-based fluids would result in damage to the formation through which drilling progresses. For example, it is known that certain types of shale will rise and collapse if water-based drilling fluids are used. Since oil-based drilling fluids do not result in any swelling of the shale, their use circumvents the lifting problem. The inverted emulsion sludge basically contains an oil medium, such as a hydrocarbon liquid as the continuous phase, water as the dispersed phase, various emulsifying agents, wetting agents, weight agents and viscosifiers, such as amine-treated muds. One of the disadvantages of oil-based sludge is its tendency to promote lost circulation during drilling compared to water-based muds of the same density.

SUMMARY OF THE INVENTION We have now determined that oil-based fluids (sludge) containing aphrons significantly decrease the problems of lost circulation when used to drill a well. Said oil-base fluids comprise a continuous oil phase, one or more viscosifiers which impart a low average viscosity of high fluid cut of at least 10,000 centipoise, one or more aphron generation surfactants, and aphrons. Therefore, it is an objective of the invention to incorporate aphrons in the drilling of wells with oil base and service fluids to improve the performance of these. Another object of the invention is to prepare the drilling of oil-based wells and service fluids having a low average cutting viscosity of at least approx. 10,000 centipoises and containing aphrons in these. Another object of the invention is to provide a well drilling method wherein the novel drilling fluid of this invention is used as the re-circulating drilling fluid. These and other objects of the invention will be apparent to those skilled in the art when they read the specifications and claims of this document. While the invention is susceptible to various modifications and alternative forms, the specific characterizations thereof will hereafter be described in detail and shown by examples. However, it should be understood that it is not intended to limit the invention to the particular forms described, but on the contrary, the invention is made to cover all modifications and alternatives that fall within the spirit and vision of the invention as expressed in the appended claims.

The compositions may comprise, consist essentially of, or consist of the materials cited. The method may comprise, consist essentially of, or consist of, the cited steps with the materials cited. Preferred Characterizations of the Invention In its broader aspects, the present invention is directed to the incorporation of aphrons in the service fluids and drilling of oil-based wells (hereinafter sometimes referred to as "OBWDAS" fluids). The OBWDAS fluid can be any type of fluid known in the art as those marked by well-known well companies such as: Barold (INVERMUL ™, PETROFREE ™, ENVIROMUL ™, BAROID 100 ™, etc.); Baker Hughes (CARBO-MUL ™, CARBO-DRILL ™, CARBO-TEC ™, CARBO-FAST ™, SYN-TEQ ™ etc.); M-l (NOVADRILL ™, NOVAPLUS ™, NOVALITE ™, etc.); Dowell Schfumberger (OLIRADRILL ™, etc.); and others. According to this invention, the LSRV of the OBWDAS fluid is first increased to at least 10,000 cp, preferably at least 20,000 cp, and better to at least approx. 40,000 cp when incorporating a compatible viscosifier in it. Thereafter, an aphron generation surfactant is incorporated into the fluid, and aphrons generated there. The OBWDAS fluids of this invention comprise a continuous oil phase, a viscosity solubilized or dispersed therein to increase the LSR of the fluid at least 10,000 cp, preferably at least 20,000 cp, and better yet at least 40,000 cp, a surfactant generating aphron, and aphrons. Optionally OBWDAS fluids may contain water as a dispersion phase, various emulsifying agents, humidifying agents, weight agents, fluid loss control agents, water soluble salts, and the like as is known in the art. The base oil phase can be organic, a liquid insoluble in water that can be viscosified to the desired degree. Exemplary oleaginous liquids known in the art include petroleum oils or petroleum fractions thereof, vegetable oils and various synthetic organic liquids such as unsaturated hydrocarbon oligomers, carboxylic acid esters, phosphoric acid esters, ethers, poiyalkylene glycols, diglyces, acetates, and similar. The oleaginous liquid can be viscosified with various materials such as organophilic clays, colloidal fumed silicas, resins, polymers, dimer acids, fatty amines salts of anionic polysaccharides, fatty acid salts of cationic polysaccharides, dispersible oil-soluble latex products and mixtures of these as it is known in art. Organophilic clays that are useful as viscosifiers to increase the LSRV of the oleaginous fluids of this invention are well known in the art. They comprise reaction products or organic onium compounds with clays of natural or synthetic occurrence. The clay portion of the organophilic clay gelling agents are crystalline, complex inorganic silicas, the exact composition of which can not be defined precisely since they vary greatly from one natural source to another. However, these clays can be described as complex, inorganic silicas, such as aluminum silicas and magnesium silicas, which contain, in addition to complex silica lattice, varying amounts of cation-exchangeable ions, such as calcium, magnesium and sodium . The hydrophilic clays which are preferred in this invention are smectite water swelling clays, such as montmorillonite clay, hectorite, saponite and in particular Wyoming bentonite containing interchangeable sodium ions. The attapulgite clay and saponite clay can also be used as a clay portion of the organophilic clay. The clays can be used in the impure form as such or can be purified by centrifugation of an aqueous paste of this clay.

The organic onium compounds which reacted with the smectite clays are preferably acidic salts of first, second and third amines, preferably of fourth ammonium compounds. The onium compounds must contain at least one alkyl, alkylene or alkylidene radical having at least ten carbon atoms, preferably approx. from 16 to 22 carbon atoms. Typical fourth ammonium compounds are dimethyl dehydrogenated tallow ammonium chloride, trimethyl hydrogenated tallow ammonium chloride, octadecyl benzyl dimethyl ammonium chloride and dioctodecyl benzyl methyl ammonium chloride. A typical acid salt of an amine is the acid salt of cocoamine.

Other organic onium compounds, such as organic phosphonium compounds, can be used. The modified organic clays and their preparations are described in more detail in the U.S. Pat. Nos. 2,531,427; 2,531,812; 2,966,506; 3,926,849; 4,287,086; 4,105,578, all are incorporated herein by reference. Preferential organophilic clays for use in the drilling fluids of the present invention are bimethylhydrogenated tallow ammonium benionite, bimethylbenzyl hydrogenated tallow ammonium bentonite, and methylbenzyl dehydrogenated tallow ammonium bentonite. Shumate et al. U.S. Patent No. 5,021,170, incorporated herein by reference, discloses that a sulfonated, ethylene / propylene / 5-phenyl-2-norborene terpolymer (EPDM polymer) and an organophilic clay viscosifier that synergistically increases the viscosity and fluid suspension characteristics of perforated inverted emulsion, in particular said fluids having a hydrocarbon of low aromatic content as the oil-liquid phase. The EPDM polymer is generally described in U.S. Patent No. 4,442,011, incorporated herein by reference. Basically, EPDM polymers have about 5 to approx. 30 milliequivalents of the sulfonate group per 100 grams of the sulfonated polymer, wherein the sulphonated group is neutralized with a metal cation or an amine or ammonium counterion. The EPDM polymers have about 0.5 to approx. 20% by weight of phenyl norborene, or preferably about 1 to approx. 10%, better still around 2 to approx. 8% Preferred polymers contain about 10 to approx. 80% by weight of ethylene and around 1 to approx. 10% by weight of 5-phenyl-2-norborene monomer, the balance of the polymer being propylene. Preferably, the multimeter contains from about 30 to approx. 70% by weight of ethylene, for example, 50 weight percent, and 2 to approx. 8% phenyl-2-norborene monomer, for example, 5.0 weight percent. A typical ethylene / propylene / 5-pheny terpolymer. 2-norborene has a viscosity Mooney (ML, 1 + 8, 212 ° F) of approx. 16 and has an ethylen content of approx. 50 percent by weight and a content of 5-phenyl-2-no.bo.ene of approx. 5 percent weight. The terpolymers have a number average molecular weight (Mp), as measured by the Gel Impregnation Chromatograph (GPC), of approx. 5,000 to approx. 300,000, better yet of approx. 10,000 to approx. 80,000. The Mooney viscosity of the terpolymer is approx. 5 to approx. 90, preferably of approx. 10 to approx. 80, better still around 15 to approx. 50. The gel agent comprising the terpolymer and the clay will generally be present in the drilling fluid in an amount of approx. 0.5 pounds to approx. 10 pounds per 42 gallons of barrel (ppb) of fluid. Oehler et al. U.S. Patent No. 4,816,551, incorporated herein by reference, discloses that certain amide resins provide more cutting dilution fluids with improved thixotropy in fluids containing an organophilic clay viscosifier, particularly in mineral oils of low viscosity. The amide resins are the reaction products of a dimerized or trimerized fatty acid, a dialkanolamine, and a dialkylene polyamine. The dibasic acids can be dimerized fatty acids, commercial products prepared by dimerization of unsaturated fatty acids containing at least 8, preferably approx. 10 or more to approx. 18 carbon atoms, including 9-dodecanoic (cis), 9-tetradodecanoic (cis), octadecatetranoic acids and the like. The tyl molecule would contain two carboxyl groups and approx. 36 carbon atoms in a branched chain configuration. The dibasic trimerized fatty acid can be used, which is also a commercial material and is prepared in a similar manner, containing about 54 carbon atoms, if at least one of the carboxyl groups is blocked or becomes inactive upon becoming the form of an ester group, a salt or the like, that is, the trimerized fatty acid as used in this invention is a dibasic acid. The mixtures of dimerized acids and trimerized acids can be used. Dialkanolamines include hydroxyalkylamines, for example, materials wherein the alkanol groups contain from 1 to 6 carbon atoms, preferably from 2 to 4 carbon atoms; including for example amine dietanol, di-n-propanol amine, di-iso-propanol amine, dibutapol amine, dipentanolamine, dihezanol amine and the like and combinations thereof. Diethyl amines and dipopanol amines are preferred. Alkyl hydroxyalkyl amines including ethylhydroxyethyl amine, propyl-oxyethyl amine, butylidene oxypropyl amine, and the like can also be used. Polyalkylene polyamides include materials where the alkylene groups contain approx. 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms: "poly" refers to an integer of approx. 2 to 20 and at least 3 nitrogen atoms. These materials can be represented by the general formula HHHR "" - N - (R'-N) x-R'-NR "wherein R 'is a group of alkylennes containing from 1 to 6 carbon atoms, R" " is hydrogen or a group of alkyls containing from 1 to 6 carbon atoms, an x is an integer from 1 to 20. Tyl useful materials include diethylene triamine, tetramethylene triethylene, tetramethylene pentamine, polyamine HH, polyamine HPA and the like. Preferably they are the triamine dethylene and tetramine triethylene The products can be represented by the general formula HO - R "- N - R" - Y HO - R "- N - R ,, - and HO - R" - N - R "- YC = OC = OC = ORRRC = OC = OC = OR" "- N (R * - N) x R '- N -R" "where R is an alkylene group containing 20, preferably approx. . 30 to 54 carbon atoms; R 'is an alkyl group containing 1 to 6 carbon atoms, R "is an alkylene group containing 1 to 6 carbon atoms, R" is an alkyl group containing 1 to 6 carbon atoms , R "" is a direct bridge, covalent bond, between N and Y or is a hydrogen or alkyl, adical containing 1 to 6 carbon atoms, Y is hydrogen or hydroxy, and x is an integer from 1 to 20. Cooperman et al. U.S. Patent No. 5,710,110, incorporated herein by reference, describes that from 0.01 to approx. 5% by weight of certain reaction products of amine additives in combination with one or more rheologically-active clay based materials provide ampr-position properties for the oil and investment oil emulsion based on drilling fluids. These rheologically-based clay-based materials include organoclays, smectite clays including Wyoming bentonite, beneficiated sodium and calcium bentonite and nectorite, and attapulgite clay. The organoclays and the method for making them are described, for example, in U.S. Pat. Nos. 5,075,033, 5,130,028 and 5,151, 155. The clays of the smectite type are cation-exchangeable clays described in detail and by the chemical formula in the U.S. Pat. No. 5,350,562. Bentonite, a particular clay useful for this invention, is described in detail in Carr. Industrial Minerals and Rocks, 6th Edition (1994) in a chapter entitled Bentonite, authors Drs. Elzea and Murria of Indiana University. Attapulgite clays are well-known natural clays that have a cation exchange capacity but a smaller amount than smectite-type clays such as bentonite and hectorite. The additive reaction products of amine comprise one or more reaction products of one or more polyalkoxylated aliphatic amino compounds having a chemical structure represented by the following formula: R (CH 2 CHO) x H R - NR wherein Ri is a group of alkyls of Straight chain derived from fatty sources having 12 to 18 carbon atoms, R is selected from the group consisting of hydrogen, methyl and ethyl, both x and y are at least 1, and the sum of x + y is from 2 to 15 and one or more organic compounds selected from the group consisting of anhydrides, italic anhydrides and mixtures thereof. An increase in anti-position properties is achieved from this combination of mixtures within broad ranges of amines to rheologically active clay. Alternative ways of preparing a drilling fluid according to this invention are to add said interchangeable cation exchange-based clay material to the drilling fluid separately from the aforementioned amine reaction products, to add the amine additive to the drilling fluid when the fluid is being used to drill through domains containing rheologically active clays, or to add only the amine if the drilling fluid already contains said clay-based materials. Exemplary polymers useful as viscosifiers in the fluid of this invention are determined in the following references. Peiffer et al. U.S. Statutory Invention Record No. H837, incorporated herein by reference, discloses the use of a water insoluble hydrocarbon soluble polymer complex formed from a sulfonated polymer (anionic) and an insoluble vinyl pyridine polymer (cationic) as a viscosifier for oil-based drilling mud. Peiffer et al. U.S. Patent No. 4,978,461, incorporated herein by reference, discloses the use of a thermoplastic terpolymer of a styrene / styrene p-methylstyrene sulfonate / neutralized metal as viscosifying agents for oil-based drilling muds. Patel et al. U.S. Patent No. 4,740,319, incorporated herein by reference, describes the use of lattices comprising a polymer which is the reaction product of a first monomer selected from the group consisting of styrene, butadiene, isoprene and mixtures thereof and a second monomer functional group containing a radical selected from a group consisting of amides, amines, sufonates, carboxylic acids, dicarboxylic acids and combinations thereof, provided that at least one of the functional monomers is a nitrogen containing a material selected from a group consisting of amides and amines. Turner et al. U.S. Patent No. 4,425,461, incorporated herein by reference, discloses the use of a mixture of an insoluble neutralized sulfonated thermoplastic polymer and an insoluble neutralized sulfonated elastomeric polymer as viscosification agents for oil-base drilling muds. Commercially available polymers include HYBILD ™ 201 (BP Chemicals), HYVIS ™ (Unocal), and others. The aphron generation surfactant for use in the location fluids of this invention must be compatible with the base liquid and the viscosifier therein such that the LSRV of the fluid can be maintained. The surfactant may also have one or more stabilizers incorporated therein, such as alkylalcohols, fatty alkanolamides, and alkyl betaines. In general, the alkyl chain will contain from approx. 10 to 18 carbon atoms. The aphron generation surfactant can be anionic, nonionic, or cationic depending on the compatibility with the viscosifier. The fluorosurfactants include, but are not limited to, (i) fluorinated telomeres, (ii) amphoteric fluorosurfactants, (iii) polydurinated amine oxide, (iv) ethylthio polyacrylamides, (v) perfluoroalkyl ethylthiopolyacrylamides, (vi) 1-propanaminium derivatives , 2-hydroxy-N2N9N-trimethyl-3-gamma-omega-perfluoro- (C6-C20-alkyl) thio, chloride, (vii) sodium fluoroalkyl sulfonate and (viii) sodium salts of 1-propanesulfonic acid, 2- metH-, 2-. { [1-oxo-3 [gamma, -omega, perfluoro-C 16 -C 26 -alkyl] thio} propyl} Not me} derivative. A particularly preferred fluorosurfactant is a blend of fluoroalfat polymeric esters sold by 3M Company under the brand FLUORAD ™ FC 740.

D'Arrigo U.S. Patent No. 4,684,479, incorporated herein by reference, discloses mixtures of surfactants containing (a) a member selected from a group consisting of glycerol mopoethers of saturated carboxylic acids containing from ca. 10 to approx. 18 carbon atoms; (b) a sterol-aromatic acid ester; (c) a member selected from the group consisting of sterols, terpenes, bile acids and alkali metal salts and bile acids; (d) a member selected from the group consisting of esters of allfatic acids containing from 1 to approx. 18 carbon atoms; sterol esters of sugar acids; esters of sugar acids and alcohols containing from approx. 10 to approx. 18 carbon atoms; sugar acids; saponins; and (e) a member selected from the group consisting of glycerol, glycerol di- or triestres of aliphatic acids containing ca. 10 to approx. 18 carbon atoms and aliphatic alcohols containing approx. 10 to approx. 18 carbon atoms; said components are present in said mixture in a weight radius a.b: c: d: e of 2-4: 0.5-1.5: 0.5-1.5: 0-1.5: 0- • 1.5. The incorporation of aphrons in a water-base well service and drilling fluid is described in the U.S. patent application. Serial No. 08 / 800,727 filed on 02/13/97, and PCT International Application No. PCT US98 / 02566 filed on 02/10/98, each incorporated herein by reference. As indicated, in its broader aspects, the present invention is directed to the incorporation of aphrons in service fluids and drilling of oil-base wells. The base fluid may be a fluid known in the art as exemplified by the patents and fluids determined above, or it may be a freshly prepared fluid having the desired characteristics. Location fluids containing stable aphrons are obtained by increasing the viscosity of low cut-off average (LSRV) of the fluid to at least 10,000 centipoise, preferably at least 20,000 centipoise and better still to at least 40,000 centipoise. Since the stability of the aphrons is improved as the LSRV increases, an LSRV of several thousand is desirable. We have discovered that those viscosifiers that provide the high LSRV required of the present invention have the unique property of delaying the collagescence of the aphrons for extremely long periods of time. The aphrons are obtained by incorporating (1) a surfactant to generate aphron in the fluid and subsequently generating the aphrons in the fluid or (2) generating the aphrons in a liquid compatible with the fluid and mixing the fluid containing aphron with the fluid . Felix Sebba's book entitled "Bilíquidas Foams and Foams - Aphrons", John Wiley & Sons, 1987, incorporated herein by reference, is an excellent source in the preparation and properties of aphrons, ie microbubbles, in aqueous systems. An aphron is composed of a nucleus that is usually spherical of an internal phase, usually a gas, encapsulated in a thin layer. This layer contains surfactant molecules placed in such a way that they produce an effective barrier against fusion with adjacent aphrons. The aphrons can be generated by means known in the art. In addition to the methods described by Felix Sebba in his book referred to above, methods are described in Michelsen et al. U.S. Patent No. 5,314,644, incorporated herein by reference, Ion et al. U.S. Patent No. 5,397,001, incorporated herein by reference, Kolaini U.S. Patent No. 5,783,118, incorporated herein by reference, Wheatley et al. U.S. Patent No. 5,352,436, incorporated herein by reference and U.S. Patents No. 4,162,970; 4,112,025; 4,717,515; 4,304,740, each incorporated herein by reference The aprons will be produced by pressure drop and cavitation as the fluid is pumped through the drill bit. The gas used to create the aphrons can be any gas that is not appreciably soluble in the oil phase of the fluid. So the gas can be air, nitrogen, carbon dioxide and the like, including air encapsulated in the fluid during mixing. None of the above examples describe the use of aphrons (or microbubbles) in systems under high pressures as in the present use. It is well known that the hydrostatic pressure of the fluid in a hole increases as the depth increases. Therefore, although the size of the microbubbles is compressed, it is believed that the high LSRV prevents fusion of the aphrons. In this regard, the aphrons may be larger than the surface of the well, as long as they are individual bubbles, since they will decrease in size to the aphron size range of less than 100 micrometers as they are pumped into the hole. The fluid may contain more than one liquid as a liquid dispersed or emulsified in the oleaginous base liquid in which it is relatively insoluble, such as dispersions or emulsions of water in oil, and the like, where the "water" phase is a liquid. The aqueous liquid can be fresh water, salt water or a brine containing soluble salts such as sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium bromide, potassium bromide, calcium bromide, zinc bromide, sodium format, potassium format, calcium format and mixtures of these. The brine may contain one or more soluble salts at any desired concentration up to saturation. Certainly, super saturated brines can be used where it is not desired or requires a fluid free of solids.

The concentration of aphron generation surfactant or mixtures of surfactants required is generally from 1 ppb to approx. 20ppb, preferably of approx. 1 ppb to approx. 15 ppb. An indication of the volume of aphrons generated can be obtained by determining the density reduction that occurs when the aphrons are generated in the fluid. Foaming of the fluid, which is undesirable, can occur if the concentration of aphron-generating surfactant is excessive. We have determined that the concentration of surfactant can be increased, without any adverse effect on the fluid, as the LSRV increases. Thus, the concentration of aphron generation surfactant, which can be determined by routine testing, is the amount required to generate sufficient aphrons to provide the desired density reduction but which is preferably insufficient to create a foam long-lasting on the surface of the fluid. The concentration of aphrons in the fluid is preferably from approx. 5% by volume to approx. 20%, even better from approx. 5% to approx. 15% by volume. The density of the fluids can be adjusted, as required, by adding weight materials or soluble salts to the fluids as is well known in the art. Preferably the weight material is added to the fluid before the generation or incorporation of aphrons into it, thereby adjusting the final density of the fluid containing aphrons to the desired density by the concentration of aphrons in it. As indicated, the concentration of aphrons in the fluid should be less than % by volume in atmospheric pressure. However, to the circulation of the fluid in a hole, it is believed that the volume of the aphrons decreases as the hydrostatic pressure of the fluid increases. Certainly the aphrons can be compressed in size to almost no volume depending on the depth of the hole. The density measured under pressure must be very close to the density of the fluid without any aphron. However, the aphrons do not disappear. They are still present, and additional aphrons will be generated on the face of the bit due to pressure drop and cavitation. The aphrons are extremely small, have a very high surface area and are highly energized. As soon as the fluid comes out of the drill and begins to support the annulus, a fall in pressure begins to occur and the aphrons will begin to expand. As the fluid moves up the hole and encounters a loss of formation, the aphrons seep into the porous grooves, microfractures, or other types of loss zones. These loss zones are areas where pressure drop occurs. The aphrons in these loss zones then expand and aggregate and therefore seal the zones of loss. The "% aphrons per volume" in these micro environments is very variable and will depend on the specific pressure and pressure drop within the loss zones. So it is believed that the density of the micro environment is completely different than the density of the fluid in the hole. The density reduction at atmospheric pressure that occurs at 20% by volume drag of a gas in the fluids of the invention is sufficient to provide the amount of aphrons needed in the borehole while allowing the fluid to recirculate without causing pumping problems. Additionally, the fluid may contain other functional materials known in the art as emulsifiers, wetting agents and the like. Without being limited to this, it is believed that the aphrons present in the fluid effectively seal the formation during drilling or well service operations preventing from this blunt the excessive loss of fluid in the formations being drilled or serviced.

The fluids of this invention can be used in conventional service and drilling operations as they are conducted in the art. So when drilling an oil and / or gas well the fluid flows from the surface to the bottom of the drilling pipe, pipe in coils, or the like through the drill bit and into the annulus between the drill pipe and the sides of the hole and back to the surface. The aphrons in the fluid seal the surface of the hole preventing the loss of excessive amounts of fluid for the formations being drilled. It is preferable that the aphron-containing fluid of the present invention be used in a drilling process wherein the drill bit is a drill bit assisted by injection of cavitation liquid. Drill bits assisted by exemplary cavitation liquid injection are determined in Johnson, Jr. et al. U.S. Patent No. 4,262,757, incorporated herein by reference and Johnson, Jr. et al. U.S. Patent No. 4,391,339, incorporated herein by reference. Preferably the cavitation injection nozzle in the drill bit assisted by cavitation liquid injection includes a pin received in a central position which decreases the pressure of the drilling fluid so that the cavitation bubbles are formed in the fluid. See for example Henshaw U.S. Patent No. 5,086,974, incorporated herein by reference, and Hensahw U.S. Patent No. 5,217,163, incorporated herein by reference. Similarly, the fluids of the invention can be found in well service operations such as completion operations, reconditioning operations, sand control operations, frac pack operations, and the like. The fluids can be used as locating fluids to free pipes and tools stuck in the hardened agglomerate on the sides of a hole by differential glue.

The following examples are presented to demonstrate the invention but should not be perceived as limiting the vision of the invention. The aphron generation surfactants are evaluated as follows: STEOL ™ CS-460, sodium laureth sulfate which is 60% active; and FLUORAD ™ FC-740, a mixture of fluorinated aliphatic polymeric esters. The abbreviations used in the table or this specification are presented as follows: cp = centipoise; g = grams; bbl = 42 gallons of barrel; ppg = pounds per gallon, ppb = pounds per barrel; psi = pounds per square inch; rpm = revolutions per minute, STI = cutting dilution index which is the radius of the Brookfield viscosity at 0.5 rpm and the Brookfield viscosity at 100 rpm, a measure of the degree of dilution of a fluid cut, vol. = volume; LSRV = average cut viscosity under a Brookfield Viscosimetre at 0.5 rpm. EXAMPLE 1 8.0 grams of CARBO-GEL ™ organophilic hectorite was dispersed in 300 g (1 bbl equivalent) of diesel oil with 1 g of propylene carbonate dispersant to form a viscous paste. 2.0g of STEOL ™ CS-460 surfactant was added while mixing in a high speed mixer (cut). Aphrons were incorporated into the viscous fluid from the apex in the mixer. Example 2 The ejmpk) 1 was repeated except for the fact that 11.0 g of CARBO-GEL ™ was used. The fluids of Examples 1-2 were evaluated for the Brookfield viscosity at 0.5 rpm, which is a measure of the LSRV, and the Brookfield viscosity at 100 rpm. The radius of the viscosity at 0.5 rpm at the viscosity at 100 rpm is a measure of the cut-off characteristics of the fluids. The density of the fluids was also measured and used to calculate the aphrons concentration in the fluids using the equation: (Calculated Density - Real Density) (100) - (Calculated Density). The data obtained are determined in Table A.

Table A Calculated Aphrons Viscosity Brookfield. cp Density Density Vol. Example 0.5 rpm 100 rpm STI __a PPQ% 1 47,000 369 127 5.58 7.40 24.6 2 111,000 912 122 6.51 7.47 12.9 Example 3 A barrel equivalent (350 cubic centimeters) of an inverted oil emulsion drilling fluid of 12.57 ppg having an 80/20 diesel / water oil radius and containing 5.5 ppb CARBO-GEL ™, 1 ppb of carbonate of propylene, 5 ppb of CARBO-TEC ™ L, 8 ppb of CARBO-MUL ™, 3 ppb of lime, and 229 ppb of barite, where the aqueous inner phase is 30% by weight of calcium chloride solution, placed in a high-cut laboratory Osterizer mixer and mixed for 5 minutes after adding 2 ppb of FLUORAD ™ FC-740 fluorocarbon surfactant (non-ionic fluoroaliphatic polymeric esters) to these. Then Brookfield viscosity and density were measured. This fluid, which contained approx. 9.7% of aphrons, then passed through a Gaulln ™ APV homogenizer at 100 psi and the density and viscosities were determined again.

The data obtained are determined in Table B.

Table B Viscosity fluid Brookfield, cp Density Aphrons Homoqinized 0.3 rpm 0.5 rpm 100 rpm STI ppq Vol.% No 23,000 15,200 215 71 11.43 9.7 Yes 74,000 48,200 490 98 11.52 7.5 EXAMPLE 4 8.0 grams of CARBO-GEL ™ organo-clay viscosifier was dispersed in 295 g (-1 bbi equivalents) of MENTOR ™ mineral oil with 1 g of propylene carbonate to form a viscous paste, then 1 g of CAB-O- was added. SIL ™ TS-720 hydrophobic silica followed by 1 g of STEOL ™ CS-460, and thereafter 0.55 g of FLUORAD ™ FC-740 Fluoripated surfactant This fluid was evaluated as previously done The data is given in the table C. Table C Calculated Aphrons Brookfield Viscosity cp Density Density Vol 0.5 rpm 100 rpm STI ppq _____% 100,000 900 111 6.07 7.02 13.5 Example 5 The wells are drilled in the well-known rotary process wherein a drilling fluid having a composition of the fluids determined in Example 1, Example 2, Example 3, and Example 4 are continually re-circulated within the borehole. The aphrons in the fluids seal the porous and microfractured formations contactad by the fluid preventing the excessive loss of fluid in the formations. Thereafter the fluids are used to conduct well service operations in the wells.

Claims (11)

1. CHAPTER CLAIMING Having described the invention, it is considered as a novelty and, therefore, the content is claimed in the following: CLAIMS 1. A well drilling and service fluid comprising an oil liquid as the continuous liquid phase having one or more viscosifiers incorporated therein such that the fluid has a low cut average viscosity as measured with The Brookfield Viscometer at 0.5 rpm of at least approx. 10,000 centiposes, at least one aphron and aphrons generation surfactant.
2. 2. The fluid of Claim 1 wherein the concentration of aphrons is such that the fluid has the desired density.
3. 3. The fluid of Claim 1 which contains an aqueous phase does not continue.
4. 4. The fluid of Claim 1 containing from approx. 5% by volume to approx. 20% by volume of aphrons.
5. 5. The fluid of Claim 2 which contains an aqueous phase does not continue.
6. 6. The fluid of Claim 2 containing from ca. 5% to approx. 20% by volume of aphrons
7. 7. The fluid of Claim 1, 2, 3, 4, 5, or 6 wherein the viscosity of low cut average is at least ca. 40,000 centipoise.
8. 8. A method of drilling a well wherein the fluid of Claim 1, 2, 3, 4, 5, or 6 is circulated within the borehole.
9. The method of Claim 8 wherein the fluid has a low cut average viscosity of at least ca. 40,000 centipoise.
10. 10. A method of conducting well service operations in a borehole comprising the use of the fluid of Claim 1, 2, 3,4, 5, or 6 as the borehole fluid. The method of Claim 10 wherein the fluid has a low cut average viscosity of at least approx. 40,000 centipoises.