MXPA98007400A - A process and a formulation to inhibit scale in oil field production - Google Patents

Abstract

This invention is a process and a formulation for minimising the squeezing and shut-in operations needed to inhibit scale in a production well using the precipitation squeeze method by injecting into an oil-bearing rock formation a water-miscible formulation comprising:(a) a water-miscible surfactant which is in liquid form, (b) a solution of water-soluble metal salt comprising a multivalent cation and (c) a solution of a water-miscible scale-inhibiting compound comprising an anionic component capable of forming a scale-inhibiting precipitate in situ in the presence of the cations in (b) upon injection into the rock formation, wherein the surfactant is a glycol ether and the minimum ion concentration of the scale-inhibiting compound (c) is 5000 ppm based on the total weight of the formulation.

Description

A PROCESS AND FORMULATION FOR INHIBITING PE PEPQSIT S CALCAREOUS FORMATION IN PE PETROLEUM OIL FIELD Field of the invention This invention relates in general to chemical products for petroleum fields and, in particular, to chemical products for the exploitation of deposits of oil and with its use. State of the Art Among the chemical products for oil deposits are the inhibitors of calcareous deposits, which are used in production wells to stop the appearance of calcareous deposits in the matrix of the rock formation of the deposit and / or in the production lines existing in the drilling and on the surface. The formation of calcareous deposits not only causes a restriction of the pore size in the reservoir rock formation matrix (also known as "formation damage") and therefore a reduction of the oil production rate and / or gas, but also blocking the installation of pipes and pipes during the processing on the surface. To solve this problem, the production well undergoes the so-called "temporary closure" treatment, in which an aqueous composition comprising an inhibitor of the formation of calcareous deposits is injected into the production well, generally under pressure, and "compress" in the formation and it stays there. In the compression process, the inhibitor of the formation of calcareous deposits is injected radially several meters into the production well where it is retained by adsorption and / or formation of a sparingly soluble precipitate. The inhibitor is leached slowly in the water produced over a period of time and protects the well against calcareous deposits. The "temporary closure" treatment must be carried out regularly, for example, one or more times a year, at least if it is desired to maintain high production rates, and constitutes the "unproductive time" during which no production takes place. One such method is that described in US-A-5002126 wherein a metal water-soluble surfactant salt containing a terminal metal ion is injected down the well bore into the reservoir, the surfactant is adsorbed onto the surfaces of the reservoir. reservoir and then an aqueous solution containing a calcareous deposit inhibitor, capable of reacting with the surfactant, is injected into the reservoir in order to form a metal inhibitor that dissolves slowly in the water produced by the Deposit. At the end of the year there is: a reduction of the total production corresponding to the number of unproductive times during the compression / temporary closing operation, as well as a lower production as the problem of the formation of calcareous deposits increases. However, in certain cases the calcareous deposit inhibitor is poorly retained within the reservoir rock formation matrix and short compression times are experienced. The net result €? N these cases is that of frequent interventions in the well which impacts both the productivity of the well and the profitability of the deposit. A method for mitigating this type of problems is described and claimed in the publication WO 96/22451 which is mainly related to the adsorption of the calcareous deposit inhibitor on the surface of the reservoir rock formation matrix which is susceptible to formation of calcareous deposits. In this last document, the surfactant is chosen so that the retention period of the inhibitor of calcareous deposits on the surface thus treated is prolonged, that is, the speed with which the inhibitor is dissolved by the water produced is reduced and, in consequently, the frequency with which hei intervenes in the well is also considerably reduced. Another approach to mitigate the same problem, using a technique of compression of the calcareous deposit / -closer substantially similar, consists in precipitating the inhibitor of calcareous deposits of low solubility in water on the surface susceptible to the formation of such deposits. One such method is described in US-A-4357248. According to this publication, an underground deposit is treated by injecting in it a self-reactive inhibitor solution that subsequently precipitates an inhibitor of calcareous deposits of low water solubility on the relevant surfaces of the matrix of the rock formation of the deposit. In this process, an anionic inhibitor of calcareous deposits and a multivalent cationic salt are dissolved in an alkaline aqueous liquid, to provide a solution containing both the anions inhibiting calcareous deposits and multivalent cations, which are mutually soluble at alkaline pH but which at a lower pH and at the reservoir temperature, they precipitate as a limescale inhibiting compound having an effective but relatively low water solubility. Also dissolved in the solution is at least one compound that reacts at a relatively slow rate to reduce the pH of the alkaline solution. The speed at which the pH of the solution is reduced is controlled by controlling the composition and / or concentration of the dissolved compounds in the solution to correlate the rate of pH reduction with the temperature and properties of injection capacity of the well and the reservoir. . This is what is known as the "compression by precipitation" method.

Fvm-damentp of the invention It has now been found that selecting a specific surfactant and controlling the amount of said surfactant used not only greatly improves the performance of the compression method by precipitation but, surprisingly, this improvement is much superior to the performance of the same surfactant when it is used in a compression method by adsorption of calcareous deposits. SUMMARY OF THE INVENTION Therefore, the present invention consists of a process to minimize the number of compression and temporary closure operations necessary to inhibit the formation of calcareous deposits and thus increase the production rate of an oil well using the method of compression by precipitation, whose process involves injecting, in an oil-bearing rock formation matrix, a water-miscible formulation comprising: (a) a water-miscible surfactant that is in liquid form; (b) a solution of a water soluble metal salt comprising a multivalent cation; and (c) a solution of a water-miscible lime-inhibiting compound comprising an anionic component capable of forming in situ an inhibitory precipitate of calcareous deposits in the presence of cations of (b) after injection into the matrix of rock formation; characterized in that the surfactant (a) is a glycol ether and the minimum ion concentration of the limescale inhibitor compound (c) is 5000 ppm based on the weight of the total formulation, said components (a) - (c) being introduced into the matrix of the rock formation either as a single preformed homogeneous composition, or simultaneously in parallel or sequentially in any order. Detailed Description of the Invention The glycol ether is suitably an alkyl glycol ether wherein the alkyl group can be straight or branched chain and suitably has from 3 to 6 carbon atoms, preferably from 3 to 5 carbon atoms. The glycol ether that can be used suitably is a monoalkyl ether such as, for example, n-butyltriglycol ether (also known as triethylene glycol mono-n-butyl ether). More specifically these glycol ethers include, inter alia, one or more of: Ethylene glycol monoethylether Ethylene glycol mono-n-propyl ether Ethylene glycol mono-isopropyl ether Ethylene glycol mono-n-butyl ether Ethylene glycol mono isobutyl ether Ethylene glycol mono-2-butyl ether Ethylene glycol mono-tert-butyl ether Diethylene glycol mono -n-propyl ether Diethylene glycol mono-isopropyl ether Diethylene glycol mono-n-butyl ether Diethylene glycol mono-isobutyl ether Diethylene glycol mono-2-butyl ether Diethylene glycol mono-tert-butyl ether Diethylene glycol mono-n-pentylether Diethylene glycol mono-2-methylbutyl ether Diethylene glycol mono-3-methylbutyl ether Diethylene glycol mono -2-pentylether Diethylene glycol mono-3-pentylether Diethylene glycol mono-tert-pentylether Triethylene glycol monobutyl ether (n-butyltriglycol ether) Tetraethylene glycol monobutyl ether (n-butyltetraglycol ether) and Pentaethylene glycol monobutyl ether (n-butylpentaglycol ether). The water-soluble metal salt (b) comprising multivalent cations is suitably a water-soluble salt of a Group II or Group VI metal of the Table Periodic More specifically, salts of one or more metals selected from copper, calcium, magnesium, zinc, aluminum, iron, titanium, zirconium and chromium are suitably treated.

Since the salts have to be soluble in water, they are preferably the halides, nitrates, formats and acetates of said metals. When selecting the relevant metal, however, due precautions must be taken to ensure that the conditions existing in the rock formation matrix are not such as to cause the formation of calcareous deposits by means of one of these metals. The use of calcium chloride, magnesium chloride or mixtures thereof is preferred. The solution of the water-soluble salt is suitably an aqueous solution. The water-miscible calcareous scale inhibitor compound (c) comprising an anionic component capable of forming in situ, in the presence of cations (b), a precipitate inhibitor of calcareous deposits after injection into the matrix of rock formation, can be any of those well known in the art. The precipitate formed in situ is particularly effective in stopping the formation of calcium and / or barium deposits with threshold amounts instead of stoichiometric amounts. The minimum ionic concentration (hereinafter "MIC") of the limescale inhibitor compote (c) is at least 5000 ppm based on the total weight of the formulation and suitably is at least 10,000 ppm, preferably from at least 12,000 ppm by weight. The calcareous deposit inhibiting compound (c) can be a water soluble organic molecule having at least two carboxylic acid and / or phosphonic acid and / or sulfonic acid groups, for example, 2-30 such groups. Preferably, the calcareous deposit inhibiting compound (c) is an oligomer or a polymer, or it can be a monomer having at least one hydroxyl group and / or an amino nitrogen atom, especially in a hydroxycarboxylic acid or a hydroxy acid - or amino-phosphonic or -sulfonic. Examples of compounds (c) are aliphatic phosphonic acids having 2-50 carbon atoms, such as hydroxyethyldiphosphonic acid and aminoalkylphosphonic acids, for example, polyaminoethylenephosphonates with 2-10 N atoms, for example, each carrying at least one methylene phosphonic acid group. Examples of the latter are described in EP-A-479462, the description of which is incorporated herein for reference purposes only. Other calcareous deposit inhibiting compounds are polycarboxylic acids such as lactic or tartaric acids, and polymeric anionic compounds such as polyvinylsulfonic acid and poly (meth) acrylic acids, optionally with at least some phosphonyl or phosphinyl groups such as in the phosphinyl polyacrylates. The inhibitors of calcareous deposits are suitably found, at least partially, in the form of their alkali metal salts, for example sodium salts. An illustrative list of such chemical compounds can be found in EP-A-0459171 and such compounds are included herein for reference purposes only. More specifically, examples of (c) include one or more of the polyphosphinocarboxylic acids: polyacrylic acids polymaleic acids other acids or polycarboxylic anhydrides such as, for example, maleic anhydride, itaconic acid, fumaric acid, mesaconic acid and citraconic acid, polyvinylsulfonates co- and ter-polymers of the foregoing, for example, copolymers of polyvinyl sulfonate-polyacrylic acid terpolymers of polyvinylsulfonate-polyacrylic acid-polymaleic acid copolymers of polyvinyl sulfonate-polyphosphinocarboxylic acid, poly (acid to inethylene-phosphonic) phosphonates such as, for example, aminotrimethylenephosphonic acid ethylenediamine tetramethylene phosphonic acid nitrile tri (methylene phosphonic acid) diethylene triamine penta (methylene phosphonic acid) N, N '-bis (3-aminobis (methylene phosphonic acid) propyl) ethylene diamine bis (methylene phosphonic acid) 1-hydroxyethylidene-1, diphosphonic acid organophosphate esters such as, for example, phosphate esters of polyols containing one or more 2-hydroxyethyl groups, and phosphomethylated polyamines. It has previously been said that one of the ways of controlling the formation of the precipitate of the limescale inhibitor compound, in situ, consists in controlling the pH of the solution of the compound from its original value, at whose value the compound remains in solution, up to that pH value in which a precipitate of the calcareous deposit inhibitor is generated in situ when it comes into contact with component (B). This can be achieved by various means. For example, depending on the nature of the components (a) - (b) introduced in the rock formation in order to generate a solution of them: i) if the aqueous system that surrounds the formation matrix of Rock is relatively highly acidic and therefore of a low pH value, then it may be necessary to inject, in said rock formation matrix, solutions of (b) and (c) which are relatively alkaline and also keep the dissolved components at that pH value before injection into the matrix of the rock formation. In this way, when the two solutions come into contact with each other within the matrix of the rock formation and under the prevailing conditions of pH and temperature, they deposit in situ a precipitate of the inhibitor of calcareous deposits on the surface or surfaces of the matrix of rock formation; ii) however, if the aqueous system surrounding the rock formation matrix is relatively less acidic or even alkaline and therefore of a relatively high pH value, it may be necessary to inject in said matrix the formation of rock, solutions of (b) and (c) that are relatively highly acidic and also keep the components in the dissolved state at that pH value prior to injection into the matrix of the rock formation. Thus, also in this case, when the two solutions arrive in contact with each other within the matrix of the rock formation and under the prevailing conditions of pH and temperature, they deposit in situ a precipitate of the inhibitor of calcareous deposits on the surface. the surface or surfaces of the matrix of the rock formation. When certain combinations of (b) and (c) are employed, especially when the aqueous system surrounding the rock formation matrix has a relatively less acidic or even alkaline pH, as described in (ii) above, it may be necessary to inject into the formation a solution of another compound that is heat sensitive and capable of decomposing under the thermal conditions of the rock formation matrix to generate a basic compound and thus influence the pH prevailing in the formation of rock, to facilitate the formation in situ of precipitate of the inhibitor of calcareous deposits. Examples of such heat sensitive compounds include urea and its derivatives. Therefore, and according to a specific embodiment, the present invention consists of a formulation comprising in an aqueous medium: (d) at least one surfactant comprising n-butyltriglycol ether in an amount of 1-45% p. / p of the total formulation; (e) a solution of a water soluble metal salt comprising a multivalent cation capable of generating a precipitate in situ when combined with the anion of a calcareous deposit inhibiting compound (f) under the prevailing conditions in the formation matrix of rock; and (f) a solution of a water-miscible, limescale-inhibiting compound in an amount of 1-25% w / w of the total formulation and comprising an anionic component capable of forming the calcareous deposit inhibitor in situ. in the presence of (e) after injection into the rock formation matrix, characterized in that the minimum ion concentration of the calcareous deposit inhibiting compound (f) is 5000 ppm based on the total weight of the formulation. It will be evident that when the components of the formulation are introduced simultaneously but separately, either sequentially, or as a single preformed composition, appropriate precautions should be taken when choosing the components to ensure that they do not form significant amounts of a precipitate, especially the inhibitor of calcareous deposits. In the sequential introduction of components (a), (b) and (c), the injected glycol ether (a) can "move", in most cases, at a lower rate than the calcareous deposit inhibitor constituted by the components (b) and (c). In that case, a double-tailed deployment system could be used. For example, a glycol ether plug (a) could first be injected into the formation, followed by a calcareous deposit inhibitor plug formed by components (b) and (c). The two plugs could then be flooded thoroughly near the well borehole in the usual manner in which the compression treatments of the calcareous deposits are carried out. Optionally, a seawater separator can be placed between the two plugs of the main treatment and, in this case, the flooding could be sized to achieve the mixing of the two plugs in the reservoir (assuming that the speeds are known). It is preferable that each of the components used is itself homogeneous and also miscible with water.

Thus, the surfactant is suitably present in the formulation in an amount of 1-45% by weight, preferably 5-25% by weight, more preferably 5-15% by weight. In the present invention it is possible to use by-product streams from processes for the preparation of glycol ethers containing a high proportion of glycol ethers such as, for example, n-butyltriglycol ether. One such by-product stream comprises about 75% w / w n-butyltriglycol ether, about 2.5% w / w butyl glycol ether, about 19% butyltetragli-ether and about 2% butylpentaglycol ether. The relative proportions of components (a) - (c) in the formulation can vary within wide ranges depending on whether the components are introduced into the rock formation matrix simultaneously, sequentially or as a single preformed composition, according to with the need to maintain a homogeneity before its injection into the matrix of rock formation. For example, at relatively higher concentrations of the surfactant or at relatively higher temperatures or extremely low temperatures, it is possible for a preformed formulation to lose its homogeneity as a result of the lower solubility of one or more components of the formulation under said conditions. In those cases, small amounts of a solubilizing agent such as, for example, a lower aliphatic alcohol, especially methanol or ethanol, may be added to the inhomogeneous preformed formulation, or said solubilizing agent may be used to partially replace the surfactant of the formulation to restore the homogeneity of the formulation. Thus, the homogenous preformed formulations of the present invention may contain, in addition to the glycol ether, a cosolvent such as, for example, a lower aliphatic alcohol, especially methanol or ethanol. The aqueous medium of the formulation can consist of fresh water, tap water, river water, sea water, produced water or formation water, with a total salinity of, for example, 0-250 g / 1, such as 5-50 g / 1, and may have a pH of 0.5-9. When seawater is used, the formulation can normally have a highly acidic pH, on the order of 0.1 to 1.5, if a highly acidic lime scale inhibiting compound is employed. In such cases, it may be necessary to neutralize the acidity of the formulation using an alkali metal hydroxide, especially sodium hydroxide, potassium hydroxide or lithium hydroxide, in order to ensure the homogeneity of the formulation. It has been found, for example, that the use of lithium hydroxide as a neutralizing agent, instead of the other alkali metal hydroxides, allows the use of relatively higher levels of the surfactant in the formulation when it is necessary to maintain the homogeneity of the formulation. The amount used of the limescale inhibitor compound is at least 5,000 ppm, suitably at least 10,000 ppm and is in the range of 1-25% w / w of the total formulation, suitably in the range of 5-15% w / w, preferably 6-10% w / w. Within these ranges, the amount used will depend on the nature of the chemical compound used and the purpose for which it is intended, as well as the nature of the matrix of the rock formation, and in any case will be in accordance with the fact that The components of the formulation are miscible in water and homogeneous. It is important in the formulations of the present invention that they remain clear and stable in a range of temperatures ranging from room temperature to at least about 45 ° C. However, within the ranges of concentration of the components specified above, it is possible to develop formulations that remain stable over a much wider temperature range, for example between ambient temperature and the temperature of the production well, (e.g., Approximately 90 to 150 ° C, especially around 110 ° C) into which the formulation is introduced. In the present invention, when the components of the formulation are injected under pressure in the production well or in the rock formation matrix, either as a preformed formulation either simultaneously or sequentially, the calcium deposit inhibitors precipitate in situ on the surface or surfaces of the matrix of the rock formation and are retained for relatively long periods. By using a relatively small molecule, such as a glycol ether, especially a (C3-C6) alkyl triglycol ether as a surfactant, the use of large surfactant molecules (having alkyl groups >) is avoided.C6), thereby minimizing any risk of surfactant aggregates forming which, in turn, could result in high viscosity emulsions that would cause blockages in the wells. Thus, said formulation may contain, in addition, other components such as (x) other production chemicals or (and) cosolvents which, when necessary, will cause the formulation to remain stable at relatively higher temperatures or when the surfactant is used in concentrations in the upper quartile of the specified range. However, said formulations should be substantially free of water immiscible components. The preformed homogeneous formulation of the present invention, when used, can be suitably prepared by adding the glycol ether surfactant (a) to an aqueous solution of the compounds (b) and (c) forming the calcareous deposit inhibitor, followed by gentle mixing. In the event that the material initially prepared is cloudy, it will then be necessary to make small adjustments to the relative proportions of the ingredients or to effect a change in the nature or amount of the cosolvent used or in the temperature. Its viscosity is suitably such that, at tank temperature, for example at 100 ° C, the formulations can be easily pumped to the bottom of the perforation. The preformed formulations of the present invention can be prepared by way of a concentrate of the ingredients (a), (b) and (c), which can be transported as such to the point of use, where it is mixed with the medium aqueous in the proportions suitable to achieve the desired homogeneity and in which the chemical has been dissolved. The components can be injected, suitably under pressure, into an oil bearing zone, for example the matrix of rock formation, via a well in production, for example down the core, followed by a separate liquid for Forcing the components of the formulation to pass within the oil carrier zone; The liquid can be used as a flood and can be seawater or diesel oil. The components of the formulation are then left ("temporary closure") in the oil bearing zone while the oil production is temporarily stopped. A convenient temporary closure period is 5-50 hours, for example, -30 hours. During this process, the injected components of the formulation percolate through the oil bearing zone under the injection pressure. In the period of temporary closures, the injected components of the formulation come into contact with fluids from the reservoir and form in situ a precipitate of the calcareous deposit inhibitor which is deposited on the surface or surfaces of the formation matrix. of rock. This is what constitutes the so-called "compression by precipitation" effect, whose precipitate inhibits the calcareous deposition and, in addition, is not easily leached by the production water, thus maintaining a continuous recovery of oil from such areas. After this period, oil production can be restarted. In the case where the oil production rate is initially high, so will the soluble calcium content of the water produced. In the course of time, for example several months, the rate of production can decrease and so will the content of limescale inhibitor in the production water, representing possible problems of calcareous deposit formation in rock formation, after which production can be stopped to inject into the well a new aliquot of the components of the formulation. Similar methods can be used to achieve inhibition of asphaltenes, inhibition or dispersion of waxes or sweeping of hydrogen sulphide, while for the inhibition of corrosion and inhibition of gaseous hydrates, the formulation is usually injected continuously descending through the perforation. Another feature of the formulations of the present invention is that when an inhibitor of calcareous deposits is employed, the oil and glycol ether are recovered on the surface, ie above ground level, after the aforementioned method of compression by precipitation, and after the subsequent cooling thereof, most of the glycol ether enters the aquosei phase instead of the oil phase of this composition. Thus, the glycol ether does not cause any problem in the subsequent production or refining operations, for example, problems that contribute to the formation of turbidity in the fuels as a consequence of the presence of water solubilized in the glycol ether. Furthermore, if the separated aqueous phase is discharged into the sea, the biodegradation of the dissolved glycol ether can be relatively rapid in the thermal sea layer, thereby reducing pollution to a minimum. On the other hand, the formulations of the present invention can increase the effectiveness of the limescale inhibitor in an amount of at least two times, so that less chemical product will usually be needed per year and correspondingly the unproductive time derived from it will be reduced. the application of the chemical as well as the temporary closure, thereby increasing the production rate. The process can be carried out with equal efficiency by injecting the components of the formulation sequentially into the production well. The present invention is illustrated in the following Examples. Example 1: 1.1 The precipitation compression technique was tested to inhibit the formation of calcareous deposits in a series of laboratory scale flood experiments. The general procedure was as follows: In a Hassler-type core holder, a plug of control material (3.8 cm x 15.25 cm, sampled from the sandstone of Brent Group Forties Field) was set up to simulate the formation of rock from an oil well. This testic material was miscible cleaned with a sequence of solvents including methanol, toluene and water, at room temperature. The plug of control material was then saturated with brine from the formation and the permeability to the brine was measured at room temperature. The plug was then saturated with crude oil oil (from Forties Field, North Sea) and heated to 107 ° C, leaving it at that temperature for 24 hours. At this temperature, a flood was carried out with water at low speed to reestablish the control of the reference material at the saturation of residual crude (Sor), that is, until no more crude could be extracted. The plug of control material was then cooled to room temperature. Into the plug of control material, then, two pore volumes of a 15% by weight solution of a mixture of glycol ethers (PCP 96-44 (see below in relation to the composition of the glycol ether mixture) in water were injected. The temperature of the stopper was then raised again to 107 ° C and the stopper was left at that temperature for 6 hours, then 8 pore volumes of a calcareous scale inhibitor compound plug (c) were injected at that temperature. ) mixed with the metal salt (b) in solution in seawater and the control material was left in a closed condition: temporary at that temperature for a further 12 hours After the temporary closure, the control was post-flooded with seawater. The results of the witness flood are given in a table below: Specifically, the lime scale inhibitor compound (c) used was Dequest® 2060S * (from Monsanto which consists of a solution of diethylenetriamine pent acid). ameti-lenfosfónico), dissolved in seawater. For product precipitation, the concentration of the calcareous scale inhibitor compound (c) was 12,628 ppm of active inhibitor compound and, to effect precipitation, 2000 ppm of calcium ion (b) was added as CaCl2.6H20. The calcium addition was followed by the adjustment of the pH to 4. In the case of the reference precipitation (control), the concentration of active inhibitor compound was 12,000 ppm at pH 4.5. Another test was also carried out to compare the performance of the method of the present invention (hereinafter abbreviated as "IMPROVED") with the traditionally used adsorption method. For the adsorption method, the same Dequest® 2060S lime scale inhibitor compound was used but at an active compound concentration of 12,000 ppm at pH 2, to achieve a reference adsorption. It should be noted that the lower pH value, pH 2, of the reference adsorption favors, in fact, the improved retention of the calcareous deposit inhibitor compared to the relatively higher value used in the method of the invention. The brine used in the post-flooding consisted of: Ion Composition (mg / l) Na 31275 Ca 5038 Mg 739 K 654 S04 0 Cl 60848 Sr 771 Ba 269 PCP surfactant 96-44 had the following composition: n-Butyltriglycollether 75% w / w n-Butyldiglycolether 2.5% w / w n-Butyltetraglicoleter 19.0% w / w n-Butylpentaglycolether 2.0% w / w RESULTS OF THE FLOODING OF WITNESSES TABLE 1 The improvement achieved by the process of the present invention can be summarized as a function of the minimum concentration of inhibitor as indicated below: The precipitation compression technique was tested to inhibit calcareous deposition in a series of laboratory flooding experiments at laboratory scale. The general procedure was as follows. A testigro material plug (2.54 cm x 7.62 cm, sampled from Magnus Main sandstone) was placed in a Hassler-type test holder to simulate the rock formation of an oil well. This plug was cleaned with a sequence of mild solvents including the alternate injection of toluene and methanol at room temperature to remove any hydrocarbon or polar components present in the control sample. The added brine was injected into the core at 120 ml / hour and the resulting effluent stream was sampled in 2 ml aliquots. The plug of control material was then saturated with brine from the Magnus formation at 120 ml / hour for 3 hours and the permeability to the brine was measured at room temperature. The brine of the Magnus formation was added with 50 ppm of lithium indicator to determine the Clean Pore Volume of the control sample. A graph of the normalized lithium concentration was then used to determine the effective pore volume by determining the volume of injected brine when the lithium concentration was half the normalized value, and subtracting the known dead volume from the system. The absolute liquid permeability of the control was determined by heating it to 116 ° C and then flooding the control sample at 0, 30, 60, 90 and 120 ml / hour. The slope of the graph of the pressure difference across the control against the flow velocity was used to calculate the permeability following the Darcy equation, K = A? P / Lμ. The plug was then saturated with dead oil (from Magnus Field, North Sea, filtered and degassed) by injecting the crude into the sample at 120 ml / hour for a period of 1 hour, after which it was heated to 116 ° C and left at that temperature for 24 hours. The crude permeability (a Swc) was then measured using the same procedure above. The crude oil was displaced from the control by flooding with water from the Magnus formation at the reservoir temperature (116 ° C) and at a flow rate of 120 ml / hour, then a measurement of the permeability to Sor was made using the Synthetic seawater indicated above was then injected into the plug sample of control material, two pore volumes of a 15% by weight solution of the ESP2000 compression enhancing surfactant (which consists of a mixture of glycol ethers also known as PCP-96-44, identified above.) The plug of control material was then cooled to 80 ° C for a period of at least 18 hours, then a 2.5 ml solution was injected into the core at 60 ml / hour. % by weight of the active compound Scaletreat® XL 14 FD (an active polymaleate as an inhibitor of calcareous deposit formation of TR Oil Services Ltd, Dyce, Aberdeen) in sea water The inlet lines were cleaned by water dación and bled to the face of the control with the retro-flow brine (also known as "post-flood") (formation water: sea water 50:50) before increasing the temperature to 116 ° C. The fluids existing within the control sample were then left in temporary closure for 24 hours. The inhibitor solution was added with 50 ppm of lithium indicator to allow the determination of the effective volume of liquid pores in this phase of the test. After the temporary closure, the control was post-flooded with a mixture of water from the formation: 50:50 seawater (retro-flow brine) which was injected into the control at 60 ml / hour for approximately 2400 volumes. The 50:50 brine permeability was then determined using the same procedure above. The testicle was flooded with crude oil at 120 ml / hour for 1 hour. The permeability to the crude was then determined. Once the retro-flow (post-flood) was finished, the sample was cleaned again using toluene and methanol and saturated with water from the Magnus formation. The final water permeability of the formation was then measured. After measuring the permeability, methanol was passed through the sample, before proceeding to disassemble the apparatus, remove the control sample and dry. The scanning electron microscopy (SEM) analysis was performed on the sample after the test and compared with that performed on a sample prior to the test. As a sample after the test, the face of the stopper was used upstream of the actual test sample. The pieces were disposed in standard aluminum protrusions using colloidal graphite as cement, with the recently broken faces in the highest position. The faces of the new sample were then coated with gold using a sputter coating apparatus. Photomicrographs were taken under imaging conditions by secondary electrodes (SE) and ionic retro-bombardment electrons (BSE). The identification of the phases was facilitated by the use of scattered energy x-ray analysis (EDX). The results of the witness flood are given below in a table. Specifically, the calcareous deposit inhibiting compound used was a registered formulation Scaletreat® XL 14FD (which generated an active polymaleate in situ) as follows. The solutions of the maleate and a calcium chloride of low acidity were injected into the matrix of the rock formation. Next, a thermally decomposable compound, urea, was introduced into the latter, which decomposed under the prevailing temperature conditions in the matrix of the rock formation, to generate with it a basic compound that raised the pH of the solutions and generated in situ a precipitate of the active polymaleate compound. The brines used had the ions indicated in the following table: Notes: The concentration of Fe2 + was in each case 0. Sulfamate was separated from the sea water used to prepare the 50:50 brine (formation water: seawater) and replaced with an equal molar amount of NaCl. The brines were degassed before adjusting the pH to a value of 6.1.

RESULTS OF THE FLOODING OF WITNESSES TABLE 2 The improvement achieved by the process of the present invention can be summarized as a function of the minimum concentration of inhibitor as shown below: The permeability measurements made during this work were a mean with respect to a number of flow velocities. The results are indicated in Table 2 above. The initial permeability to the brine of the clean sample was measured at 98 mD [represents mil Darcy]. This value dropped to 27 D in the saturation of residual crude oil before the application of the inhibitor, all according to what was expected. Once the retro-flow phase of the trial was completed, this value had risen to 69 mD. This rise was probably due to the separation of a small amount of crude oil from the sample during the application of the inhibitor. After the end of the test, the brine permeability of the re-clean sample was 86 mD. During the witness flood, two measurements of the permeability to the crude oil were also made. The first one, performed in the water saturation of the formation, turned out to be 30 mD. At saturation of residual crude, at the end of the test, the permeability to crude oil had dropped to 21 mD. The analysis of the permeability measurements shows that there was a small reduction in liquid permeability as a result of the work of the test. It was thought that this permeability reduction could probably be due to the calcareous deposition of barite within the test sample. This theory was supported by the SEM analysis of the sample after the trial. The calcareous deposition may have taken place during the end of the retro-flow phase of the test, since the inhibitor concentration fell below the minimum inhibitor concentration (MIC) in the calcareous deposit formation environment. Therefore, the reduction of permeability can be considered as an artifact of the test methodology, since during the application in the reservoir the performance of additional compression treatments would prevent such conditions from appearing. The test results indicate that the period of compression at high and low MIC values has doubled as a consequence of the incorporation of ESP2000 into the test procedure. By combining the compression-enhancing chemical with the limescale inhibitor by improved precipitation, based on an MIC of 10 ppm of active compound, a service period of the order of 6 times that achieved in conventional treatment was achieved only by adsorption.

Claims (34)

1. NOVELTY OF THE INVENTION Having described the present invention is considered as a novelty and, therefore, the content of the following claims is claimed as property: 1. - A process to minimize the number of compression and temporary closure operations necessary to inhibit the formation of calcareous deposits and thus increase the production rate of an oil well using the compression method by precipitation, whose process involves injecting, in an oil-bearing rock formation matrix, a water-miscible formulation comprising: (a) a water-miscible surfactant that is in liquid form; (b) a solution of a water soluble metal salt comprising a multivalent cation; and (c) a water-miscible solution of a calcareous deposit inhibiting compound comprising an anionic component capable of forming in situ a calcareous scale inhibiting precipitate in the presence of cations of (b) after injection into the matrix of the rock formation; characterized in that the surfactant (a) is a glycol ether and the minimum ion concentration of the limescale inhibitor compound (c) is 5000 ppm based on the weight of the total formulation, said components (a) - (c) being introduced into the matrix of the rock formation either as a single preformed homogeneous composition, or simultaneously in parallel or sequentially in any order.
2. 2. A process according to claim 1, characterized in that the glycol ether is an alkyl glycol ether wherein the alkyl group is straight or branched chain and has 3-6 carbon atoms.
3. 3. - A process according to any of the preceding claims, characterized in that the glycerol comprises one or more ethers selected from: Ethylene glycol monoethylether Ethylene glycol mono-n-propyl ether Ethylene glycol mono-isopropyl ether Ethylene glycol mono-n-butyl ether Ethylene glycol mono isobutyl ether Ethylene glycol mono-2 -butyl ether Ethylene glycol mono-tert-butyl ether Diethylene glycol mono-n-propyl ether Diethylene glycol mono-isopropyl ether Diethylene glycol mono-n-butyl ether Diethylene glycol mono-isobutyl ether Diethylene glycol mono-2-butyl ether Diethylene glycol mono-tert-butyl ether Diethylene glycol mono-n-pentylether Diethylene glycol mono-2 -methyl glycerol Diethylene glycol mono-3-methylbutyl ether Diethylene glycol mono-2-pentylether Diethylene glycol mono-3-pentylether Diethylene glycol mono-tert-pentylether Triethylene glycol monobutyl ether (n-butyltriglycol ether) Tetraethylene glycol monobutyl ether (n-butyltetraglycol ether) and Pentane-glycol monobutyl ether (n-butylpentaglycol ether).
4. 4. - A process according to any of the preceding claims, characterized in that the water soluble metal salt (b) comprising multivalent cations is a metal salt of Group II or Group VI of the Periodic Table.
5. 5. - A process according to any of the preceding claims, characterized in that the metal salt soluble in water (b) is a salt of one or more metals selected from copper, calcium, magnesium, zinc, aluminum, iron, titanium, zirconium and chromium .
6. 6. - A process according to any of the preceding claims, characterized in that the metal salt soluble in water (b) is chosen from the halides, nitrates, formats and acetates of metals.
7. 7. - A process according to any of the preceding claims, characterized in that the water soluble metal salt (b) is calcium chloride, magnesium chloride or mixtures thereof.
8. 8. - A process according to any of the preceding claims, characterized in that the solution of the water soluble metal salt (b) is an aqueous solution.
9. 9. - A process according to any of the preceding claims, characterized in that the water-miscible limestone-inhibiting compound (c) comprises an anionic component capable of forming in situ, in the presence of the cations of (b), a precipitate inhibitor of calcareous deposits after injection into the matrix of rock formation, is a water soluble organic molecule having at least two: (i) carboxylic acid groups and / or (ii) phosphonic acid groups and / or (iii) sulfonic acid groups.
10. 10. A process according to claim 9, characterized in that the compound (c) has 2-30 carboxylic acid and / or phosphonic acid and / or sulfonic acid groups.
11. 11. A process according to any of the preceding claims, characterized in that the limescale inhibitor compound (c) is an oligomer or a polymer, or is a monomer with at least one hydroxyl group and / or amino nitrogen atom. .
12. 12. A process according to claim 11, characterized in that the compound (c) is a hydroxycarboxylic acid, a hydroxy- or amino-phosphonic acid or a sulfonic acid.
13. 13. A process according to claim 12, characterized in that the compound (c) is selected from one or more of: polyphosphinocarboxylic acids polyacrylic acids polymaleic acids other polycarboxylic acids or anhydrides polyvinylsulfonates and co- and ter-polymers of the same polyphosphonates ( aminoethylene phosphonic acids) 1-hydroxyethylidene-1, 1-diphosphonic acid esters organophosphates and phosphomethylated polyamines.
14. 14. A process according to claim 12, characterized in that the compound (c) is selected from one or more of lactic acid, citric acid, tartaric acid, maleic anhydride, itaconic acid, fumaric acid, mesaconic acid, citraconic acid, copolymers of polyvinyl sulfonate-polyacrylic acid, terpolymers of polyvinyl sulfonate-polyacrylic acid-polymaleic acid, polyvinyl sulfonate-polyphosphincarboxylic acid copolymers, aminotrimethylene phosphonic acid, ethylenediaminetetramethylenephosphonic acid, nitrilotri- (ethylenephosphonic acid), diethylenetria in-penta (methylene phosphonic acid), N, N '-bis [3-aminobis (methylene phosphonic acid) propyl], ethylenediaminebis (methylenephosphonic acid) and phosphate esters of polyols containing one or more 2-hydroxyethyl groups.
15. 15. A process according to claim 12, characterized in that the compound (c) is an aliphatic phosphonic acid having 2-50 carbon atoms.
16. 16. A process according to claim 15, characterized in that the compound (c) is a polyaminomene-tynnphosphonate having 2-10 N atoms carrying each of the nitrogen atoms, optionally, at least one methylene phosphonic acid group.
17. 17. A process according to any of the preceding claims, characterized in that the limescale inhibitor compound (c) is found, at least partially, in the form of its alkali metal salt.
18. 18. A process according to any of the preceding claims, characterized in that the minimum ionic concentration (hereinafter "MIC") of the limescale inhibitor compound (c) is at least 10,000 ppm based on the total weight of the formulation .
19. 19. A process according to any of the preceding claims, characterized in that the pH value of the formulation is controlled so that, before its introduction into the matrix of the rock formation, the components of the formulation are in solution while, After injection into the matrix of the rock formation and under the conditions of pH and temperature prevailing or created in said matrix, the pH of the solution varies to a value in which a precipitate of the inhibitor of calcareous deposits is generated in situ when the compound (c) comes into contact with the compound (b).
20. 20. A process according to claim 19, characterized in that: a. the solution comprising the compounds (b) and (c) in the formulation is highly acidic and b. The aqueous system surrounding the rock formation matrix has a relatively less acidic pH or an alkaline pH, insufficient to allow in situ precipitation of the calcareous deposit inhibitor after the injection of the formulation into the formation matrix. of rock, with which c. a solution of another compound that is sensitive to heat and capable of decomposing under the thermal conditions of the rock formation matrix is injected into the matrix of the rock formation., in order to generate a basic compound to influence the prevailing pH in the formation of rock to facilitate the in situ formation of the precipitate of the calcareous deposit inhibitor.
21. 21. A process according to claim 20, characterized in that the heat-sensitive compound is urea or a derivative thereof.
22. 22. - A process according to any of the preceding claims, characterized in that the components (a), (b) and (c) are introduced sequentially into the matrix of the rock formation, so that in the first place a plug of glycerol (a) in the matrix of the formation, followed by a plug of components (b) and (c) formers of the calcareous deposit inhibitor, optionally placing a seawater separator between the two blocks of the main treatment.
23. 23. - A formulation comprising in an aqueous medium: (d) less a surfactant comprising n-butyltriglycol ether in an amount of 1-45% w / w of the total formulation; (e) a solution of a water soluble metal salt comprising a multivalent cation; and (f) vina solution of a water-miscible, limescale-inhibiting compound in an amount of 1-25% w / w of the total formulation and comprising an anionic component capable of forming the calcareous deposit inhibitor in situ. in the presence of the cations of (e) after injection into the rock formation matrix, characterized in that the minimum ion concentration of the calcareous deposit inhibiting compound (f) is 5000 ppm based on the total weight of the formulation.
24. 24. A formulation according to claim 23, characterized in that the surfactant (d) is present in the formulation in an amount of 1-45% by weight.
25. 25. A formulation according to claim 23, characterized in that the surfactant (d) is a by-product stream from a glycol ether preparation process, whose stream contains a high proportion of an n-alkyltriglycol ether.
26. 26. A formulation according to claim 23, characterized in that the n-alkyltriglycollether is n-butyltriglycol ether and the by-product stream comprises approximately 75% w / w of n-butyltriglycol ether, approximately 2.5% w / w of butyl diglycol ether, about 19% butyltetra-glycol ether and about 2% butylpentaglycol ether.
27. 27. A formulation according to any of claims 23 to 26, characterized in that it is a homogeneous solution optionally comprising small amounts of a solubilizing agent to maintain the homogeneity of the solution during storage and transport thereof.
28. 28. A formulation according to claim 27, characterized in that the solubilizing agent is a lower aliphatic alcohol present in an amount sufficient to maintain the homogeneity of the formulation in solution.
29. 29. A formulation according to claim 26 or 27, characterized in that the solubilizing agent is methanol or ethanol.
30. 30. - A formulation according to any of claims 23 to 29, characterized in that the aqueous medium in the formulation is derived from fresh water, tap water, river water, sea water, produced water or formation water, with a Total salinity between 0 and 250 g / liter.
31. 31. A formulation according to claim 30, characterized in that the salinity of the aqueous medium is 5-50 g / liter.
32. 32. A formulation according to any of the preceding claims, characterized in that in aqueous medium has a pH value of 0.5-9.
33. 33. A formulation according to any of claims 23 to 32, characterized in that the amount used of the limescale inhibitor compound is at least 5000 ppm and is in the range of 1-25% w / w of the total formulation .
34. 34.- A formulation according to any of the preceding claims, characterized in that the amount used of the limescale inhibitor compound is at least 5000 ppm and is in the range of 5-15% w / w of the total formulation.