MX2007006193A - Emulsifier-free wellbore fluid. - Google Patents

Abstract

A wellbore fluid is described having a continuous non-aqueous phase and inorganicparticles wherein said particles are coated with essentially permanently adsorbedamphiphilic molecules causing a lipophilic behavior of said particles underoperating conditions.

Description

FREE OF EMULSIFIERS DRILLING FLUID FIELD OF THE INVENTION This invention concerns drilling fluids comprising a continuous non-aqueous liquid phase having inorganic powder particles dispersed therein.

BACKGROUND OF THE INVENTION The drilling fluids of this invention are for use in the construction or repair of oil, gas, injection, water or geothermal wells. Accordingly, the term "drilling fluids" encompasses sounding fluids ("slurries"), termination fluids, re-operation fluids, consolidation fluids, and fluids used in corrective treatments. The main function of the particles dispersed in the drilling fluid is to inse the density of the fluid, although inorganic powders are contemplated that serve for other functions in drilling fluids such as bridging solids that are used to seal pores or fractures in formations rocky underground The terms "oil-based fluid" or "oil-based slurries" are used herein to refer to any of the drilling fluids with a non-liquid phase.

Aqueous Drilling muds are used to transport rock cuttings out of the drilling and to the surface. Other functions of the drilling muds are to cool and lubricate the drills, to protect against the ejection of a well, to counteract the pressure of the formation in the bottom of the drilling, to keep the drilling stable and to prevent the loss of fluids in the drilled formations. Both sludge, water based and oil based are used as drilling mud. Water-based sludge is generally cheaper and less toxic than oil-based sludge, but it has many operational sales, particularly for drilling wells at high angles, long range and high pressure / high temperature. As in a growing number of jurisdictions the disposition of drill debris is strictly regulated, the advantages of water-based sludge have slowly desed. However, conventional sludge with oil base (OBMs) also suffer from numerous undesirable characteristics. The oil can be retained on the drilling debris, which has environmental implications. In addition, the presence of emulsifiers and Other oily wetting agents which are essential components of conventional OBMs can alter the wettability of deposit formations thereby reducing their oil permeability. Oily moistening agents are added to conventional OBMs to emulsify the aqueous phase in the oil phase and ensure that all solids in the slurry are moistened by the oil. Oily-based drilling fluids are, almost without exception, formulated using comparatively low molecular weight emulsifiers and oily wetting agents. Typically a brine phase is dispersed in the continuous oil phase as a water / oil emulsion ("W / 0") using emulsifiers such as oleic acid or wood pulp oil fatty acids, usually in the form of its soaps. calcium. Alternatively W / 0 emulsifiers which are commonly used include amidoamines or imidazolines manufactured by the condensation of fatty acids such as those mentioned above with a polyalkyleneamine such as triethylenetetraamine or tetraethylenepentamine. The alkylamidoamines or alkylimidazolines can additionally be reacted with, for example, maleic anhydride, in order to introduce the carboxylic acid functionality into these molecules Additional oily moisturizing agents such as lecithin or calcium soap of dodecylbenzenesulfonic acid are also used. A water / oil (W / O) emulsifier is also normally added when an oil-based drilling fluid is formulated without a dispersed brine phase to combat inadvertent contamination of the fluid by water such as an underground brine flow. The emulsifier can, however, damaging the deposit, for example most of the perforated formations are naturally wetted by water but when contacted with the emulsifier present in OBMs they can be easily changed to wetted by oil. The ability to remove such emulsifiers would allow detritus and perforated deposit formations to use OBMs to remain in their moist state in natural water. This would lead to both lower oil retention and smaller reductions in permeability. Unfortunately, it is important that the penetrating agent of the drilling fluid remains moist in oil. This is especially true for the surface of barite particles such as barium sulfate powder which is normally used to increase the density of the drilling fluid. Agents moistened by oil - must be added to disperse the weighed agent in the oil and prevent the particles from being wetted again in water. If the weighing agent becomes wet in water, the particles will agglutinate and form lumps together causing rapid fluid separation and a potentially dangerous head and density loss. The U.S. Patent No. 5,376,629 discloses oil-free drilling fluids free of emulsifier or oily wetting agents, the sludges comprising a ballast having a siloxane or silane coating thereon. The objectives were similar to some of those of the present invention. For example, avoiding the conversion of moistened in water to moistened in oil of the rocky surfaces of the production formation leads to the maintenance of the optimum permeability to the oil. The basic principle of 5,376,629 is to coat a hydrophobic layer of a silane or siloxane on particles of ballast, the layer which is then mobilized by the polymerization and cross-linking of the silane or siloxane carried by hydrolysis by any moisture present and / or by a heating step. The preferred weaning people were barite. This type of hydrophobic barite suffers from several disadvantages: - The polysiloxane layer on the surface of the barite could be dislodged by exposing the drilling fluid to high shear coefficients as found in mud pumps or when the fluid passes to the barite. through the auger nozzles. In contrast to their chemisorption on hydroxyl mineral surfaces such as silica, silanes adsorb more strongly on non-hydroxylated surfaces such as barium sulfate. Barite has a low energy surface with no tendency to form covalent bonds of type X-O-Si where X is the surface of the solid substrate. Accordingly, the siloxane layer wetted by oil polymerized around each particle was not strongly adsorbed and could be "disintegrated" by interparticle collisions at high shear rates. This allowed the partial wetting by water of the barite with consequent instability of the suspension. - Silanes and siloxanes are relatively expensive. - It could be dangerous during the formation of the polysiloxane coating due to hydrochloric acid or methanol liberated from chlorosilanes or methoxysilanes (respectively). The silane coating of the particles required a manufacturing process consisting of the addition of the silane to a dry mixture of the powder in air at high shear rates, and a heating step at 120 ° C to crosslink the silane coating. The U.S. Patent No. 6,017,854 describes an attempt to formulate simplified nonaqueous drilling fluids where viscosity / suspension ability properties and fluid loss control are obtained from a polystyrene-polyolefin-polystyrene block copolymer that has not been further functionalized to contain polar adsorbent groups. An example of such missing functional groups is the dicarboxylic acid group that could have been introduced by grafting this polymer with maleic anhydride. The oil-based fluids described in this patent do not contain an additive that is designed to maintain the ballast in an oil wetting condition. In fact, the agent weights in a condition of wetted in oil. In fact, the importance of wetting with oil of the bulking agent is not appreciated. In Example 1 of the patent, the drilling fluid contains simplified drilling fluids containing only oil, a non-polar block copolymer of styrene-ethylene / butylene-styrene designated for stimulation, barite powder and REV DUST (a mineral powder) a to stimulate the perforated solids. If this formulation were to be used in a well, there could be some serious wetting preparation with water of the solid particles. A certain amount of contamination is almost inevitable in any corrective or drilling operation. This could wet the barite in water causing potentially dangerous agglutination and separation of the particles. The U.S. Patent No. 4,776,966 discloses the use of certain block or graft copolymers in oil-based drilling fluids as emulsifying agents for brine in oil. The advantages of amphiphilic block copolymers as agents for dispersing matter in the form of solid particles in the oil-based drilling fluid are not mentioned or appreciated. The dispersing agent claimed by means of this patent is a surfactant that contains a chain hydrocarbon having 30 to 500 carbon atoms as the hydrophobic coent, and a polar coent (which is not a polymeric block) that absorbs on the surface of the solid in the form of particles. In view of the foregoing, the invention is directed towards solving many problems exacerbated by mobile emulsifiers and relatively low molecular weight oily wetting agents which are present in conventional non-aqueous drilling fluids, particularly oil-based sludges (OBM). These problems include: - Oily humectants of a production formation can be caused by emulsifiers and oily moisturizing agents (hereinafter "surfactants") dissolved in the filtrate of the mud that permeates the permeable rock such as limestone or sandstone. A change from wettability to wet in oil results in the reduction in the permeability of the rock to the oil and thus reduced production quantities. - Sometimes the emulsification of the water of the formation induced by surfactants with the filtrate can cause an "emulsion block" that restricts the production. - Oily moistening of the wall and tubing Steel drilling, induced by surfactants frequently results in poor bonding of the cement pumped into the annulus between the casing and the perforation wall. -Detritus of soundings produced in an auger often consist of shale moistened with water. Surfactants moistened in oil cause penetration of the oil into the porous shale, especially along planes of weakness. Surfactants thus tend to disperse the detritus into particles sufficiently small that they can not be easily removed. This dispersion induced by surfactants leads to the accumulation of "low gravity solids" (LGS) and high viscosity. The remedy with only OBS is to dilute the sludge with the oil leading to the undesirable generation of extra fluid volume. The LGS increase presents difficulties that inhibit the multiple reuse of the OBM. - An OBM is sometimes contaminated by amounts of water or brine, usually as a result of a groundwater flow. This can happen when the drilling operation is being performed sub-balanced and there is a need to separate the fluid produced from the drilling fluid, in a fluid with conventional oil base, mobile surfactants attempt to incorporate a large fraction of the volume of contaminated water into the oil phase as emulsified droplets, resulting in a high viscosity sludge or sludge. It is difficult to separate the phases for re-use or disposal. Again, oil dilution and undesirable volume increase is required to restore fluid properties. - Because conventional OBM surfactants are mobile and can be relocated onto new surfaces (such as a stream of emulsified water in the mud), the ballasting agent (usually pulverized barite) can lose some of its surfactant layers of oily humectants and turn them into moistened in water This is a difficult and dangerous situation because the barite moistened with water quickly agglomerates and separates from the fluid. This can result in a loss of hydrostatic pressure at the bottom of the borehole and an ejection of the well or collapse of the borehole. - In conventional OBM the surfactants have a harmful slimming effect on the viscosity and gels conferred by the addition of organically modified clays. This effect is especially obvious after exposure to high temperatures when the viscosity at low shear rates and resistance of the gel can disappear substantially. This can result in potentially dangerous sedimentation of the ballasting agent. - The mobility of surfactants of OBM allows the division to some degree in water, the fluid is discharged (for example as adherent contamination or detritus) in a body of water such as the sea. Surfactants are usually very toxic towards marine flora and fauna, and are an important contributor to the poor acute toxicity that results from conventional oil-based fluids towards test organisms such as Skeletonema costatum, a seaweed. It is very difficult to remove oil-based drilling fluid adhering to rock debris after they are separated using a shaker screen. The oily moisturizing surfactants cause not only adhesion of the fluid to the debris surface but also the inhibition of detritus of porous rock in oil. Attempts to use detritus washing techniques to reduce the discharge of oil to the environment have not been successful, for the above reasons. It has often been necessary to resort to costly and potentially dangerous high temperature distillation techniques to clean detritus so as to adapt them for disposal.

It is believed that surfactants, and quicklime required activation, many of them contribute strongly to human skin irritation frequently associated with OBM. Clearly, there is a real need to solve these problems that are largely caused by the mobility of the used surfactants.

SUMMARY OF THE INVENTION In general terms, the present invention provides a drilling fluid having a continuous non-aqueous phase and inorganic particles wherein said particles are coated with an immobilized adsorbed layer giving the particle a lipophilic character. This invention concerns drilling fluids comprising a continuous non-aqueous liquid phase which has dispersed therein inorganic powder particles which are coated with an immobilized lipophilic adsorbed layer, which is resistant to friction, desorption and dissolution, particularly for a prolonged period of use in drilling operations such as drilling, completion, placement of consolidation fluids, repair of wells or corrective treatments.

The oily moistening components of the immobile moistened oily moistening layer on the dispersed inorganic powder particles can not be significantly relocated to adsorb onto other surfaces such as debris (or perforated solids in the form of smaller particles), the producing formation or tubular steel objects. , and can be divided into a watercourse and for that reason they adsorb on marine flora and fauna. In this way the drilling fluids of this invention overcome or minimize the problems associated with conventional emulsifiers and oily wetting agents. Thus, problems of formation damage caused by changes in wettability or emulsion blockage, poor cement bond, dispersion of drilling solids induced by surfactants, inability to separate water contamination, poor rheological properties and high temperature stability , toxicity to drinking water or marine species, difficulty in washing detritus, and skin irritation can all be overcome or minimized by the drilling fluids of this invention. The main function of coated particles dispersed in the drilling fluid is to increase the density of the fluid, although it is contemplated that similarly coated inorganic powders serving for other functions in drilling fluids such as bridging solids that are employed to seal the entrances to pores or fractures in underground rock formations. These inorganic particles preferably have a diameter representing the average particle weight of less than about 10 microns, preferably less than about 5 microns, and preferably less than 3 or 2 microns. Preferably the drilling fluid is substantially free of mobile emulsifiers or oily moisturizing agents that are capable of migrating through the oil phase to stabilize water droplets or fresh wetted oil surfaces such as recently exposed rock formations. The placement of the oily wettable layer on the particles is achieved by using molecules or polymers that can be characterized as being amphiphilic. The amphiphilic coating agent thus has at least one, preferably two or more polar sections and one or more lipophilic sections. The sections as defined in the present are parts or groups in the molecule or polymer that provide functionality. In particular, the polar section is sections, more preferably terminal sections, of the molecule that includes a polarized linkage. The polar section or sections effect the adsorption of the coating on the surface of the particle. The lipophilic sections that can be defined as the coating or envelope around the particle thus determining the character of their interactions with the surrounding chemical medium. The lipophilic sections are preferably hydrocarbylic in nature, ie they have a carbon backbone. The immobilized adsorbed layer can be a monolayer. In preferred embodiments of the invention, the immobilization is effected using two possible methods: 1. The oily moistening agent is an amphiphilic block copolymer having lipophilic block and alternating hydrophilic blocks containing polar functional adsorbent groups such as carboxylate groupings, ester sulfates, sulfonates, ester sulfonates, ester phosphates, phosphonates and polyoxyethylene. Strong adsorption and occlusion of the polar block (s) they allow the placement and immobilization of the oily wettable layer to occur spontaneously and concurrently. 2. The oily moistening agent is a molecule comprising at least one polar absorbent group selected by its strong adsorption on the inorganic powder in question, at least one lipophilic group that is predominantly hydrocarbyl, and at least one reactive group capable of forming chemical bonds in at least one contiguous molecule. The oily moistening coating adsorbed around each particle is immobilized in a separate step by cross-linking between adjacent molecules via the action of a suitable cross-linking agent, catalyst, or a source of energy or radiation. A combination of these two variants is possible where the amphiphilic block copolymer also comprises reactive groups that are capable of forming crosslinks in one or more adsorbed block copolymer molecules. The process of adsorption and immobilization is not based predominantly on the establishment of a non-polar covalent chemical bond between the substrate or the surface of the particle and the amphiphilic agent. Accordingly, it is different in character from links based in silane or siloxane. Preferably, the adsorption process of the present invention is a surfactant or ligand adsorption based predominantly on electrostatic interactions, dentate bonding, or, in rare cases, on hydrogen bonds between the surface of the particle and the amphiphilic molecule. Preferably the polar group carrying out the immobilization is directly linked to a carbon atom and in turn is preferably linked to the rest of the amphiphilic molecule through additional carbon-carbon bonds. The oily wettable coating is applied to the surfaces of the inorganic particles, either during or after any crushing that may be required. The coating can be placed on the surface of the inorganic particles either in a dry powder process, or in a process where the particles are suspended in a liquid. The liquid can be aqueous, or a non-aqueous liquid that is compatible with non-aqueous liquids that are suitable as the base fluid of the drilling fluid. In the variant of a coating process carried out in an aqueous phase, after adsorbing and immobilizing the coating, the water must be removed of the product before use. When the inorganic particles are coated with a hydrophobic layer they tend to flocculate because of the hydrophobic attraction between the particles. This facilitates the separation of the coated material by filtration. The wet filter cake can then be dried and milled to give a dry powder product. An advantage of dry powder products is that they can be added to any non-aqueous base fluid that is suitable for the drilling fluid, facilitating a wide selection of base fluids without any non-aqueous fluid contamination. The choice of base fluid is usually made to comply with local environmental restrictions, melting point and flash point properties to match the expected conditions, and hydrolytic or thermal stability of the base fluid for high temperature applications. In the variant of the invention where a quantity of non-crosslinked or non-adsorbed oily wetting agent remains in the coated product, it can be easily removed using adsorbent materials that are selected by their affinity for the wetting agent. For example, free fatty acids or polymers carboxylates can be easily removed using macroporous basic magnesium oxide granules suspended with the product. After a period of exposure the granules can be easily removed together with the oily excess wetting agent by, for example, sieving. The immobilized and adsorbed layer on the particles remains intact. This process could be carried out either before or during use in a drilling fluid. In the variant of a crosslinkable oily wettable coating, a crosslinkable oily wettable agent, hereinafter also referred to as CLOWA, is adsorbed on the surface of the mineral particles. Having formed an oily wettable layer tightly packed on the surface, crosslinking of the CLOWA molecules is caused by the introduction of a suitable crosslinking agent, catalyst, or energy source or radiation. The hydrophobic coating becomes not only a continuous crosslinked layer, but also remains strongly adsorbed on the particles via the polar anchor groups. In this way resistance to friction, desorption and dissolution is achieved desired. Oily crosslinkable wetting agents comprise at least one hydrophobic alkyl, aryl or alkyl aryl hydrocarbon group that retains at least 4 carbon atoms, at least one polar group capable of strong adsorption on the inorganic particles, and at least one group capable of forming bonds Chemicals in at least one contiguous CLOWA molecule via the action of a suitable crosslinking agent, catalyst or a source of energy or radiation. In nonaqueous fluids, by virtue of the amphiphilic nature of the CLOWA, any excess not adsorbed will combine to form opposite miscels, the polar groups that are concentrated in this core of the miscelas surrounded by an envelope of hydrophobic portions. These CLOWA micelles can by themselves be crosslinked by the action of the crosslinking agent, catalyst, or a suitable energy or radiation source. The molecules of CLOWA thus become "fixed" in the micelle with the polar groups hidden. Accordingly, they can not easily be relocated to adsorb onto new surfaces and the advantages of this invention can be maintained. Similarly if an inverted emulsion of a Disperse aqueous phase is formed using a CLOWA as the emulsifier before crosslinking, the CLOWA film adsorbed around the emulsion droplets can also be immobilized during the crosslinking step. This allows the use of an inverted emulsion while maintaining a fluid that is substantially free of active and unbonded surfactants. In any case, for reasons of economy, the amount of excess CLOWA can be minimized by ascertaining by means of simple tests the minimum dose required for the efficient coating of the particles for the materials in question. Any remaining non-adsorbed / non-crosslinked CLOWA excess should be quickly removed by adsorption on new surfaces during drilling fluid applications. For example, during drilling, fresh mineral surfaces such as detritus or drilling solids should adsorb the excess CLOWA without, however, depleting the crosslinked layer on the surfaces of inorganic material by weight. This immobilized layer shows very little tendency to desorber by virtue of its nature of multiple links and its multiple anchor points.

The advantages of not having movable or free wetting agents / emulsifiers can thus be realized. Optionally, specific adsorbents can be employed to "remove" any "free" CLOWA either before application in the drilling fluid or during use. Free amphiphilic block copolymers according to the first variant of the invention can be removed when necessary using similar methods. Therefore, it is an advantage of the present invention to provide a drilling fluid that is either inherently or with minimal modification or treatment, free of emulsifiers or free dispersants so that only a very limited amount of harmful emulsifiers or dispersants are present in the fluid in its place of application. It was contemplated that the lipophilic mineral particles of this invention will have foreign applications those of drilling fluids. These and other features of the invention, preferred embodiments and variants of this possible applications and sales will be appreciated and understood by the experts in the field from the following figures and detailed description.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic illustration of a chemical system in accordance with a first example of the invention; Figure 2 is a schematic illustration of a chemical system in accordance with a second example of the invention; and Figure 3 illustrates a chemical structure suitable for the purpose of the present invention.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLES A range of different chemical species may be used for the purpose of this invention. Compounds that can be led to a spontaneous formation of an elastic coating as contemplated in the first variant of the invention as described above are termed amphiphilic block copolymers. Chemistries including crosslinking are further described below in the section "Crosslinkable oily humectants" together with suitable crosslinkers. An additional section describes potential compositions for drilling fluids followed by examples of the foregoing. The term "molecular weight" when used herein means the weight representing the average molecular weight. Copolymers in Amphiphilic Block In the following description of the hydrophilic and lipophilic blocks the use of the term "block" in the singular does not imply that a plurality of said blocks can not be present, and vice versa. Suitable amphiphilic block copolymers can be diblock or tri-block or larger. In the example of Figure 1, a particle 10 surrounded by amphiphilic block copolymers 11 is shown with the schematic structure L-H with L denoting the amphiphilic blocks and H the hydrophilic blocks. The triblock of hydrophilic blocks H shown are selected so that they adsorb strongly and spontaneously on the inorganic particle 10. In its absorbed state the lipophilic tails L of amphiphilic block copolymers 11 give the particle a lipophilic character. Preferably the lipophilic block is predominantly of hydrocarbon nature. But not all hydrophobic blocks are suitable lipophilic blocks. For example, alkylene oxide hydrophobes such as polypropylene oxide are insufficiently lipophilic and do not confer the desired properties to the drilling fluids. Therefore products of the well-known large range of EO / PO block copolymers are not suitable. Although segments of the polydimethylsiloxane, hydrophobic block are not preferred, and are not as lipophilic as the hydrocarbon segments. Typically, suitable hydrophobic blocks have a molecular weight in the range from 400 to 40,000, preferably from 1,000 to 20,000. They could comprise polymers of ethylene, propylene, butadiene, isoprene, styrene, alpha olefins, or any random copolymer of the aforementioned monomers. Homopolymers or copolymers of vinyl esters or amide monomers having a hydrocarbyl group of at least 4 carbon atoms (such as lauryl methacrylate and N-dodecyl acrylamide) are also suitable. Optionally, the copolymer block also contains reactive groups that can form crosslinks with adsorbed contiguous block copolymer molecules.

As shown in Figure 1, the hydrophilic block comprises any hydrophilic polymeric segment having sufficient polar anchor groups H to strongly adsorb on the inorganic particles 10. The nature of the anchor groups H should be selected by their strong adsorption on the substrate concerned. For example polymers formed of monomers possessing carboxylate, ester sulfate, sulfonate, ester phosphate, phosphonate and polyoxyethylene sulfate adsorbents on barium sulfate particles by virtue of their coordination with barium atoms on the surface of the particle. Amino- or quaternary ammonium anchor groups are better suited for, for example, silica particles. The hydrophilic block can be polyethylene oxide having a molecular weight of at least about 260 and a higher molecular weight limit consistent with the Hydrophobic-Lipophilic Balance (HLB, Hydrophobic-Lipophilic Balance) of block copolymer that is less than about 12, and preferably less than about 10. Thus, for a polyethylene-block-poly (ethylene oxide) di-block copolymer having an ethylene block of 10,000 molecular weight, an HLB of about 10 or less it is obtained if the molecular weight of the polyethylene oxide block is restricted to a maximum of 10,000. The HLB system or classification of nonionic surfactants or dispersants is a semi-empirical method to predict what type of surfactant properties will provide a molecular structure. It was introduced by William C. Griffith in 1949 and 1954. The HLB system is based on the concept that some molecules have hydrophilic groups, other molecules have lipophilic groups, and some have both. Percentages by weight of each type of group on a molecule or in a mixture predicts what behavior the molecular structure will exhibit. The HLB is calculated by forming the percentage of molecular weight of the hydrophilic portion of the molecule and dividing by this percentage by a scale factor to preserve the range of small HLB numbers. Using 5 as the scale factor the range of workable surfactants becomes 0.5 to 19.5 Water-in-oil emulsifiers have low HLB numbers, typically around 4. Solubilizing agents have high HLB numbers. Oil-in-water emulsifiers have high HLB numbers. Preferably, when the inorganic particles barium sulfate the hydrophilic block comprises carboxylate or sulfonate groups. For example, blocks of polyacrylic acid or poly (styrene sulfonic acid (or their neutralized salts) can be used.) Again the molecular weight of the hydrophilic block is restricted such that the HLB of the copolymer is less than about 12, preferably less than about 10. Amphiphilic block copolymers can be difficult and expensive to synthesize Polar groups of grafting over a preformed nonpolar block copolymer can be more convenient and cheaper, for example, commercial styrene-ethylene tri-block copolymers butylene-styrene (SEBS), styrene-isoprene-styrene (SIS), and styrene-butadiene-styrene (SBS) can be grafted with maleic anhydride (MA), then after hydrolysis a plurality of dicarboxylic acid groups are introduced which are very effective anchoring groups for barium sulfate.The degree of grafting is restricted so that the HLB of the product does not exceed e 12, and preferably does not exceed 10. In the case of SIS and SBS grafted onto MA, after adsorption of the block copolymer onto the substrate, the residual double bond of the polyisoprene chains or contiguous polybutadiene will be in close proximity. This allows them to be cross-linked by, for example, a free radical process. The strength and resistance to desorption of the adsorbed layer can thus be further improved. Alternatively certain groups in a preformed non-polar block copolymer can be chemically modified to become polar groups. For example, some of the styrene groups in ESBS can be easily sulfonated by leaving the random copolymer ethylene / butylene block untouched. The degree of sulfonation is restricted so that the HLB of the product is less than 12, preferably less than 10. Crosslinkable Oily Moisturizing Agents In the example of Figure 2, a particle 20 is shown surrounded by oily crosslinkable wetting agents 21 with the schematic structure LXH, with L denoting the lipophilic sections, H the polar anchor group and X a crosslinkable group of the agent. The hydrophilic groups H shown are chosen to adsorb strongly and spontaneously on the organic particle 20. In its absorbed state the lipophilic tails L of amphiphilic block copolymers 21 give the particle a lipophilic character.

To obtain a crosslinked oily wettable coating, an oily crosslinkable wetting agent (CLOWA) is first adsorbed onto the surface of the inorganic particles. Then the adsorbed layer is crosslinked via the action of a crosslinking agent, catalyst, or a suitable source of energy or radiation. On Section X- The L-crosslinked lipophilic coating around each particle can be viewed as an outstanding hydrocarbon chain lattice that is either anchored to the particle in many locations or cross-linked in many locations. The oily wetting agent is therefore not able to desorb, nor surfaces freshly moistened in oil, nor water added to the emulsifier. The crosslinkable oily wetting agent comprises at least one lipophilic alkyl, aryl, or alkylaryl group having at least 4, and preferably at least 8 carbon atoms, and at least one polar group capable of strong adsorption on the organic particles. For example, strong adsorption on barium sulfate is provided by carboxylate, ester phosphate, phosphonate, ester sulfate, sulfonate and polyoxyethylene groups. Other groups may be more suitable for others minerals such as silica whereby the anchor groups containing an amine or o-quaternary ammonium group are more effective. The CLOWA additionally comprises at least one group capable of forming crosslinks for one or more CLOWA molecules adsorbed in contiguity via the action of a suitable crosslinking agent, catalyst, or source of energy or radiation. These crosslinkable groups can be vinyl, allyl or other unsaturated groups capable of forming crosslinks via, for example, a free radical process. They can be polyunsaturated groups present in the hydrocarbyl chain of a fatty acid such as linoleic acid capable of forming crosslinks during an air insufflation process. The crosslinkable groups can be amino groups capable of crosslinking with an aldehyde linking agent such as glutaraldehyde, or with an amide-forming crosslinking agent such as a polyanhydride, or with an epoxy-possessing molecule to provide epoxide crosslinking. In an inversion of the above, the crosslinkable groups on the CLOWA can be aldehyde, anhydride, or epoxy groups, which will react with the appropriate crosslinking agents, preferably agents polyfunctional crosslinkers. The hydroxide groups on CLOWA can be cross-linked using low molecular weight silanes such as trimethoxypropyl silane, or with ester titanate and zirconate, or using isocyanate-containing crosslinking agents that form urethane linkages. In the case of a CLOWA possessing a simple crosslinkable group it was preferred to use a polyfunctional crosslinking agent in order to achieve sufficiently long bonding of the CLOWA molecules to achieve effective immobilization of the adsorbed layer. Linoleic acid and linolenic acid, including its ammonium or metal salts of the fatty acid have been adsorbed on, for example, the surface of a barium sulfate particle, the salient hydrophobic tails and the multiple double bonds will be in close proximity, The linkage of double bonds can be broken approximately by introducing a compound that generates a free radical or a Lewis acid catalyst, or preferably by blowing air into a suspension of the coated particles, optionally in the presence of a transition metal catalyst. such as a cobalt compound.

Other possible crosslinking methods for fatty acids include sulfur curing and other vulcanization processes (sulfur monochloride). A preferred polyunsaturated fatty acid is a dehydrated castor oil fatty acid. It is commercially available in more than 90% purity for immobilized coatings by air insufflation. Sedico ™ 5981 (ex Unigema) contains over 90% linoleic acid and over 60% is conjugated linolenic acid (which is more reactive). A small proportion of this material consists of non-crosslinkable fatty acids. After the coating is "cured" by air insufflation the non-crosslinkable free fatty acids can be adsorbed (for example) onto basic magnesium oxide granules. These can then be removed (along with the free fatty acids) by sieving. Other suitable CLOWAs include the maleinized polybutadiene and methacrylated polybutadiene products available, for example, from Sartomer (part of Atofina) as RICON ™ resins. This consists of a liquid polybutadiene of relatively low molecular weight. (approximately 1,000 to 10,000) that has a number (between approximately 1 and 10) of anhydride groups maleic or methacrylate grafted onto the chain. The methacrylate, maleic anhydride (or dicarboxylic acid of maleic anhydride hydrolysis) groups strongly adsorb on many mineral surfaces, and are especially suitable for barium sulfate. The hydrophobic loops and tails of the polybutadiene chain contain a number (about 10 to 100) of vinyl groups some of which will be in close proximity to vinyl groups on contiguous molecules after adsorption on the particles. The neighboring vinyl groups can then be crosslinked, for example by means of peroxide curing agents, optionally in combination with a reactive co-monomer such as divinyl benzene or trimethylolpropane trimethacrylate. Somewhat similar polyunsaturated maleinized polymers are available from Kuraray Co. Ltd as LIR-403 ™ and LIR-410 ™. These are liquid isoprene rubbers that have been grafted with maleic anhydride. In LIR-410 MA groups are partially esterified with methanol. The molecular weight is reported in the region of 25,000. It was found that Ricon 131 MA17 ™ and LIR-403 ™ are effective dispersants for barium sulfate powder in mineral oil, especially after the maleic anhydride groups are opened in the ring by hydrolysis to give dicarboxylic acid anchor groups. The wet layer in adsorbed oil can be cross-linked and immobilized by heating in the presence of a peroxide such as dicumyl peroxide or dibenzoyl peroxide. The normal function of these resins in conjunction with mineral fillers is to provide bonds between the filler and a continuous elastomer phase. The functional groups adsorb onto the filler, while the vinyl groups can be crosslinked with the elastomer, thus providing improved properties to the finished article. You found, the resin as used herein is part of a persistent hydrophobic coating that is not formally bonded to the continuous phase. Using certain suitable crosslinking agents it was surprisingly found that a relatively conventional particular class of oil-based fluid additives can be used as a crosslinkable oily wetting agent. An exemplary type of additive is manufactured by condensation of two moles of a fatty acid such as Fatty Acid Pulp Oil.

Wood (TOFA) with a polyethyleneamine such as triethylenetetraamine or tetraethylenepentamine. The diamine thus produced contains two or three residual secondary amine groups. The maleic anhydride is added to introduce the carboxylate molecule the property of good adsorption on barite. The molecule thus produced will adsorb to deposit a wet layer in oil on barite particles and disperse them in oil very effectively. After adsorption residual secondary amine groups residing in polar head groups are available for further reaction with, for example, polyfunctional crosslinking agents such as glutaraldehyde, polyanhydrides, ester titanate such as TYZOR ™ TnBT (tetra-n- butyl), tetraalkyl zirconates, titanium and xirconium chelates, and low molecular weight silanes such as trimethoxypropyl silane. Polyfunctional crosslinking agents are preferred since they will promote a more extensive network of bound oily moistening molecules. A low molecular weight silane can be used at low concentration as a crosslinking agent for a CLOWA having at least one group capable of reacting with said low molecular weight silane crosslinking agent. This contrasts with US Pat. No. 5,376,629 in which the ballasting agent is coated with a hydrophobic layer that is completely a silane or siloxane that has been polymerized or cured by heat treatment. The present invention overcomes all the disadvantages of US 5,376,629 of high price, acid or flammable emissions during manufacture, and (especially) the relative fragility of the hydrophobic coating. The coating provided in the present invention is more robust due to the multiple anchoring sites on the surface of the particle where the anchor groups are selected for their strong adsorption on the inorganic substance in question. Generally the quality of the dispersion is an oil phase (which exhibits minimal particle-to-particle interactions) is better when the exposed groups protrude from the particle are predominantly hydrocarbon in nature and therefore similar to the oil phase itself. Although hydrophobic, the polysiloxane coating of 5,376,629 is not as lipophilic as the oily wettable coating of the present invention.

The CLOWA can be added to the particles organic during or after any crushing is required. Intense mixing is desirable to promote the optimal distribution and adsorption of CLOWA. The coating may be on dry powder, or by mixing the CLOWA in an aqueous suspension of the inorganic particles. Alternatively, the process is carried out in a suspension in an oil-based liquid that is compatible with the non-aqueous liquid which is the fluid base of the drilling fluid. Aqueous or dry processes are preferred if an oil-soluble reactive co-monomer is used because it ensures that the co-monomer (which itself can not be strongly adsorbed) is present at high concentration in the adsorbed layer before crosslinking. In the case of a coating process carried out in an aqueous phase, after adsorbing and immobilizing the coating, the water must be removed from the product before use. When the organic particles are coated with the hydrophobic flocculant layer. This facilitates the separation of the coated material by filtration. The wet filter cake can then be dried and milled to give a dry powder product. It will be obvious to those skilled in the art that there is an immense number of potential combinations of groups crosslinkable and crosslinking agents or processes. It is believed that the drilling fluids of this invention are new to any combination of crosslinking groups, crosslinking agents, or crosslinking processes. The oily, amphiphilic, strongly adsorbed wetting agents possessing hydrocarbyl groups of this invention differ from the hydrophobicizing silane or siloxane materials disclosed in US 5,376,629. Drilling Fluids of this Invention Drilling fluids such as drilling fluids with advantageous properties can be formulated using the coated inorganic powder as a weighing agent, bridging agent, or agent for fluid loss control. The non-aqueous phase of the drilling fluid can be any oleoaginous liquid with suitable physical, safety and environmental properties as are well known to those in the field of construction and well repair. For example they could be selected from mineral oils, certain esters, n-alkanes, olefins, polyalphaolefins, and diesel oil. The material selected to be a pulverized weighed agent suitable for coating according to to this invention can be any suitable inorganic compound or element that is of sufficient density for the purpose. Suitable materials include barium sulfate (barite), calcium carbonate, magnesium carbonate, dolomite, ilmenite, synthetic manganese tetroxide (Mn30- - synthetic hausmanite), synthetic or natural hematite or other iron, powdered iron or stainless steel minerals, olivine, siderite, strontium carbonate, strontium sulfate, titanium dioxide, or any mixture thereof. A preferred embodiment of this invention uses inorganic particles having a particle size much smaller than the usual particles. For example, a product whose particles have a diameter that represents the average particle weight is preferred.

(D50) of less than 2 microns, as discussed in PCT / EP97 / 03802. This results in a product that is more resistant to friction by the force of interparticle collisions than one based on conventional Barite Api with a D50 of about 25 microns. The use of fine sieves or more intense centrifugation is also allowed to remove the sounding solids even more efficiently, without the substantial co-removal of the weighing agent that could take place with sizes of much larger, conventional particles. After the manufacture of the lipophilic coated powder, a simple test can show how successful the immobilization of the oily wettable layer is. A suspension of the coated lipophilic powder dispersed in mineral oil can be mixed at high shear rate with water without emulsification signal or aqueous wetting of the barite. The dispersion of barite in oil and substantially clear water quickly separates as two distinct liquid phases after the mixing has ceased. In contrast, conventional OBM barite dispersions form viscous gelatinous emulsions which are very difficult to separate when mixed at high shear with water. Using the coated ballast material in an oil-based fluid, there is no need to add additional emulsifiers or wetting agents. A fluid that is substantially free of water can be easily formulated. Any contamination of the fluid by ground or surface water will not be very emulsified in the fluid, in contrast to the residues that are generated by conventional oil-based sludge contaminated by a high concentration of dispersed water, Therefore the contamination can be easily removed from the fluids of this invention, for example by centrifugation. The drilling fluid is usually more dense than water, so it can be recovered by centrifugation as the sub-flow or bottom phase while the water is removed as the overflow or top phase. An alternative means of removing water is now made possible by the absence of mobile emulsifiers. In said drilling fluids that have been viscosified by organically modified clays, water contamination can be physically emulsified separately by the structure of the gel. There may be sufficient structure in the fluid to make centrifugal separation more difficult. However, the simple addition and mixing of sufficient bentonite as untreated, aqueous clay will "find" the contamination of the water causing it to gel and agglutinate. The lumps occluded with gelatinized water are easy to remove by sedimentation or screening. When no free wetting or emulsifying agent is present, debris from rocks such as shale moistened in water remains moist in water. This results in dispersion induced in the phase oily detritus in finely divided drilling solids. Solids are removed more efficiently by screening and centrifugation because they remain larger, if any, tend to clump together through polar attractions. Another benefit is that oily residues adhere less to the detritus, if any, the oil penetrates the debris (in contrast to oil inhibition induced by conventional wetting agents and emulsifiers). Therefore, the detritus purification efficiency by means of processes such as washing or centrifugation is improved. Accordingly, the fluids are well adapted for use in an environmentally sound manner. Because contamination by water or solids is more easily removed, fluids can be reused many times. Effluents difficult to treat such as oily mixtures are avoided. Decreasing amounts of drilling fluids (oily) are associated with the detritus that needs disposal and the disposal is facilitated. Other benefits of avoiding mobile oily moistening agents or emulsifiers include improved bonding of cement to rocks and steel tubulars, and avoiding production losses caused by a change in wettability of the productive rock formation, or caused by emulsion blocks. In conventional OBMs, the behavior of organoclays is adversely effected by mobile tenso-assets that have anionic functional groups. They tend to deflocculate the structure formed by the clay lamellae, especially after exposure to high temperatures. The fluids of this invention are preferably free of said conventional additives, and the immobilized oily moistening agents can not be relocated to deflocculate the organarcilla. Accordingly, the rheological profile is greatly improved compared to conventional OBM of similar properties in another way. Generally the viscosity at low shear coefficient is much higher and the Plastic Viscosity at higher shear coefficient is lower. These improvements contribute to improved wellbore cleanup, ballast material suspension and reduced Equivalent Circulating Density (reduced frequency of open fractures and fluid lost in the formation). The viscous properties are much more stable for the effects of exposure to high temperatures. Examples and Experimental Procedures Dose Curve Procedure A suspension based on 277 g of barite in 217 g of oil by shear was prepared in a Silverson mixer at high shear (7000 rpm). The dispersant was titrated into the mixture, typically in increments of 0.25 ml. After each addition the sample was sheared for 5 to 10 minutes, until the retro suspension visibly thinned. Usually during the dispersant addition a sample must go from extremely viscous, to the consistency of double cream, to appear very "thin" while shearing but still have a visible gel (like simple cream in appearance) that does not have a gel visible in total. After this final stage the rheology of the suspension was measured. Sample Preparation-Procedure A base suspension was prepared using 217 g of Clairsol 350M HF base oil and 277 g of Microbar 4C Barite. The dispersant was added in the amount determined in the dose curve procedure and the mixture was sheared at 5000 rpm using a Silverson mixer for 20 minutes. The crosslinking agent (where required) was then added and the mixture was sheared for 5 minutes at 2000 rpm. If necessary, then a catalyst and mixed at 2000 rpm for 1 minute. The samples were then thermally compacted in pressurized cells at 100 ° C for 16 hours before testing (Other curing temperatures were sometimes used when indicated). Emulsion Test To ensure that the dispersion contained little or no free dispersant and there was no desorption of the barite dispersant over time, a test emulsion was made. 10 ml of water was placed in a glass bottle and shaken to ensure that the glass surface was moistened with the water; then 10 ml of the sample suspension was placed in the bottle and shaken vigorously for 30 seconds. A sample passes the test if the aqueous phase and the suspension are easily separated, there is no visual increase in viscosity, and the virio remains moistened with water. Contrarily the sample fails the test if the phases are emulsified forming a gel and the glass is moistened with the oil-based suspension. If the sample initially passes progressively, more aggressive shaking is applied to determine if the coating moistened in oil on the particles is susceptible to gradual disintegration or desorption.

The emulsion test can be considered as a test of the stability and elasticity of the coating. Examples Using Surfactant Polymers Containing Maleic Anhydride (MA) Ricon resins as per order of Sartomer Company, Inc. 502 Thomas Jones Way Exton, PA 19341 are polybutadienes grafted with anhydride of molecular weight of about 5000. It is thought that the fingerprints of moisture on the barite ring opened the anhydride to produce carboxylic acid groups, which in turn act as anchors for the dispersant as shown in Figure 3. Additional classes of maleic anhydride copolymers identified as good dispersants at dosing 1 - 4 ppb are: • polyethylenes grafted with maleic anhydride • poly (maleic anhydride co-alpha-olefins) • polyisoprene grafted with maleic anhydride Typical rheology data for 12 ppg suspensions are given in Table 1.

Table 1. Barite Suspension Reology MA adducts.

It should be noted that the values of the plastic viscosity (PV) and the yield strength (YP) of the base suspension are 116 and 51. The alpha-olefin derivatives are crosslinkable using commercial crosslinking agents Epikures 3055, 3115, which are oligomeric polyamides formed from a polyamide and a dimeric acid (as used in the present dimeric acid is a term for the dimerization product of oleic or linoleic acid using a clay catalyst) as the MA groups are capable of reacting with amine functions to give amide or imide linkages. Samples of these compounds pass the previous emulsion after the barite is kiln dried to remove residual moisture. The adducts of maleic anhydride-polyisoprene (PI / MA) are crosslinkable using high temperatures (130-160 ° C) and peroxides with a higher decomposition temperature. Dicumyl peroxide is a more effective crosslinker than benzoyl peroxide. Examples Using Surfactant Polymers Containing Polyunsaturated Fatty Acids Triglyceride drying oils such as flaxseed oil, soybean oil, and Aleuritis cordata Stend oil (tung oil) are produced in large quantities and are relatively inexpensive. The products useful in this invention are polyunsaturated fatty acids with low levels of monounsaturated and saturated fatty acids. These inert, non-reactive components can be removed by adsorption using an agent to scavenge free fatty acids in a non-surfactant form. The purification through adsorption by means of polyvalent metal hydroxides, or addition of quicklime are possible mechanisms. The examples tested are 99% pure linoleic acid commercially available through for example Sigma, and a dehydrated castor oil Prifac 5981 commercially available from Unigema, Prifac 5981 is known as being > 90% polyunsaturated Using the barite suspension Microbar 4C in Clairsol mineral oil described above, it was found that both of these two materials were good dispersants that reduce the viscosity efficiently as shown in Table 2.

Table 2. Typical Results for Polyunsaturated Fatty Acids Curing was achieved by air insufflation-air bubbling slowly through the suspension for 24 hours, using cobalt acetyl acetonate (an oleo-soluble cobalt complex) as a catalyst. The addition of an antioxidant; 0.5 ppb of 2,6,6-di-t-butyl-4-dimethylaminoethyl) phenol to the suspension after 24 hours prevents excessive curing and adhesion of the suspension. Saturated fatty acids and unreacted residual material can be removed using desiccant MgO beads as an absorbent. After mixing the suspension containing the MgO beads overnight, the beads (together with the adjacent fatty acids) were removed from the suspension by screening. The "clean" suspension then passes the emulsion test.

Examples Using Surfactant Polymers Containing Carboxylated Amidoamine A commercially available carboxylated amidoamine dispersant available as EMUL RT (Trademark of MI Drilling Fluids, has at least one dicarboxylic acid group available for adsorption on the surface of barite, and up to three amine groups (-NH) which are potentially reactive sites for crosslinking. The crosslinking is carried out using formaldehyde, the which is known to react with amine functions. Alternatively, larger difunctional aldehydes, glutaraldehyde and diglycidyl ether of Bisphenol A, can be used as crosslinking agents. Table 3 summarizes some of the properties obtained using the same base suspension Microbar 4C / Clairsol, dispersed with 2.5 ppb of Emul RT. Table 3. Typical Results for Fluids with Emul RT Emul RT is known to be a good oily humectant and emulsifying agent, hence its good dispersing quality. But the base suspension fails the emulsion test. Partially successful emulsion tests can be achieved using dialdehydes, particularly glutaraldehyde Examples Using Surfactant Polymers Containing Copolymers in the Amphiphilic Block The styrene- (ethylene, butylene) -styrene (SEBS) maleinized multi-block copolymer used in this example is commercially available as FG 1901 from Kraton Polymers. This block copolymer was dissolved at 100 ° C in Xylene, then sheared while still hot in 217 g of Clairsol base oil with 277 g of Microbar 4C Barite at 5000 rpm in the Silverson mixer for 10 minutes. To complete the coating and dispersion, the sample was thermally compacted at 150 ° C for 48 hours. Another product included as an example is a solvent-soluble AB block copolymer based on polyacrylate containing long alkyl chains marketed as Nuosperse FX 9086 from Elementis. Table 4 summarizes some of the properties obtained.

Table 4. Typical Results for Block Copolymers The advantage of this type of system is that no crosslinking step is necessary. The emulsion test is passed directly after dispersion.

Claims (21)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty, and therefore the content of the following is claimed as property: CLAIMS 1. - A drilling fluid having a non-harassing continuous phase and inorganic particles characterized in that said particles are coated with an immobile layer of essentially amphiphilic molecules permanently adsorbed via at least one polar section and having at least one section that causes a behavior lipophilic of said particles under operating conditions. 2. The drilling fluid according to claim 1, characterized in that the polar group that performs the immobilization is directly linked to a carbon atom which in turn is linked to the remains of the amphiphilic molecule through carbon bonds. additional carbon. 3. The drilling fluid according to claim 1, characterized in that the section causing a lipophilic behavior is based on hydrocarbyl. 4.- The drilling fluid in accordance with the claim 3, characterized in that the amphiphilic molecules comprise at least one lipophilic section that includes an alkyl, aryl, or arylalkyl group. 5. The drilling fluid according to claim 1, characterized in that the at least one polar section is selected from a group consisting of carboxylate, ester phosphate, phosphonate, ester sulfate, sulfonate groups that adsorb onto alkaline mineral substrates particles in the form of particles, amine groups including primary, secondary and tertiary amines, quaternary ammonium groups that adsorb onto acid substrates in the form of hydroxyl-possessing particles, and polyoxyethylene groups. 6. The drilling fluid according to claim 1, characterized in that the amphiphilic molecules are block copolymers with at least one hydrophilic block containing polar groups and at least one lipophilic block. 7. The drilling fluid according to claim 6, characterized in that the lipophilic block comprises lipophilic hydrocarbyl blocks. 8. The drilling fluid according to claim 6, characterized in that the lipophilic block comprises a lipophilic hydrocarbyl block which has a molecular weight in the range of 400 to 40,000. 9. The drilling fluid according to claim 6, characterized in that the hydrophilic block of the amphiphilic block copolymer is a polymer of a vinyl monomer having acid selected from a group consisting of acrylic acid, maleic acid (or anhydride) , methacrylic acid, itaconic acid, vinylsulphonic acid, vinyl sulfuric acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and vinyl ester phosphate or hydrophilic salts of said polymers of an acid-bearing vinyl monomer. 10. The drilling fluid according to claim 6, characterized in that the hydrophilic block the amphiphilic block copolymer comprises at least one segment of polyethylene oxide. 11. The drilling fluid according to claim 6, characterized in that the hydrophilic block of the amphiphilic block copolymer comprises a non-polar polymeric group with at least one polar grafted hydrophilic group. 12. The drilling fluid according to claim 1, characterized in that the molecules amphiphiles comprise at least one reactive group capable of forming chemical bonds in at least one contiguous amphiphilic molecule. 13. The drilling fluid according to claim 12, characterized in that the particles are coated with amphiphilic molecules in a cross-linked state. 14. The drilling fluid according to claim 1, characterized in that the hydrophobic-lipophilic balance of the amphiphilic molecules is less than 12. 15. The drilling fluid according to claim 6., characterized in that the hydrophobic-lipophilic balance of the amphiphilic block copolymer is less than 12. 16. The drilling fluid according to claim 1, characterized in that the concentration of free oily moisturizing agents or emulsifiers in the fluid is less than 1 percent by weight determined by analysis of the oil obtained from the filtration of a sample of the drilling fluid. 17. The drilling fluid according to claim 1, characterized in that the particles have a diameter that represents the average weight of particle of less than about 10 microns. 18. The drilling fluid according to claim 1, characterized in that the inorganic particles are selected from a group consisting of barium sulfate (barite), calcium carbonate, magnesium carbonate, dolomite, ilmenite, synthetic manganese tetroxide. (Mn304-synthetic haumanite), natural or synthetic hematite. Or other iron, stainless iron or stainless steel minerals, olivide, siderite, strontium carbonate, strontium sulfate, titanium dioxide, and any mixture thereof. 19. The drilling fluid according to claim 1, characterized in that the continuous non-aqueous phase comprises one or more liquids selected from a group consisting of mineral oils, esters, n-alkanes, olefins, polyalphaolefins, and diesel oil or a mixture of them. . 20. The drilling fluid according to claim 1, characterized in that it comprises one or more viscosity imparters or one or more fluid loss control agents, or a mixture thereof. 21. - The drilling fluid according to claim 1, further characterized in that it comprises a dispersed aqueous phase.