Formulations of self-weighted and weighted fluids and their use

Abstract

The present invention relates to formulations of self-weighted and weighted stimulation fluids, such as acids or chelators, for the stimulation of oil wells by gravity positioning. Abstract figure: 0

Description

Title of the invention: Formulations of self-weighted and weighted fluids and their use. Technical field of the invention

[0001] The present invention relates to the field of oil well stimulation, more specifically to the field of Drilling and Well Completion, and refers to formulations of self-weighted and weighted stimulation fluids, acids or chelators, in order to improve the stimulation of oil wells by gravity positioning. Previous art

[0002] Since the beginning of the development of the pre-salt carbonate fields in the Santos Basin, several optimizations have been implemented in well configurations and the technological processes involved in their construction. Currently, the most common well completion configuration consists of selective cavitation in 2 or 3 distinct zones.

[0003] Concurrently with these innovations, the reservoir stimulation activity has implemented several unusual solutions, both in terms of equipment and chemicals used, with the development of weighted acid systems, a technique hitherto unexplored by service companies or other operators and which is the subject of this patent application.

[0004] After drilling is completed, or even after perforation, wells do not normally have sufficient injection capacity to perform acid treatment, because the drilling fluid intentionally damages the pores of the formation, which is necessary to safely complete well construction. To allow the injection of acid treatment into carbonate formations, it was common to use blasting equipment inside the well, called a "coiled intervention tube," particularly in the initial phase of acid treatment. This equipment was positioned inside the well, an insulating plug located at the end of the production / injection pipe was removed, and the acid treatment was injected at the base of the lower zone.This step aimed to promote the improvement of the tank's injectivity, thus enabling subsequent massive acid treatment (main treatment) by direct injection through the production column at high flow rates (bull heading), after the installation of the final tank completion equipment, including the wet Christmas tree (WCT).

[0005] Among the disadvantages of using coiled intervention tubes, one can mention the time required for their implementation, which has a financial impact on construction wells, in addition to involving operational and safety risks. An alternative was therefore proposed for the positioning of stimulation fluids to promote the creation of initial injectivity without the need for a coiled intervention tube, utilizing the completion equipment's own ground chain and employing low-reactivity, low-corrosive acid systems. This new step began to be carried out earlier than usual, before the well was equipped with the wet Christmas tree (WCT), giving rise to what is known as "early stimulation".

[0006] Concurrently, the use of weak acids and chelating agents was introduced to create zones with moderate injectivities, sufficient only to initiate the main acid treatment, thus avoiding the need for injections exceeding reservoir fracture pressures or the induction of very high losses in the formation. These precautions became necessary because early stimulation takes place without all safety equipment being permanently installed in the well, and therefore a very high level of fluid losses in the formation is undesirable.

[0007] This new form of acid placement, using working rope, had the disadvantage of not being able to reach the bottom of the lower well zone, as was the case when using coiled intervention tubing. This limitation raised concerns about a possible loss of acid treatment quality in the lower interval, which could negatively impact the accumulated production in the well. An alternative was therefore sought to allow for injectivity to be created also at the bottom of the lower well zone, avoiding the use of coiled intervention tubing. This led to the use of weighted acids, aiming to achieve "gravitational placement" at the bottom of the lower reservoir by percolating the acid through the fluid present in the well, which has a lower density.

[0008] To address potential cases of poor injectivity in the lower wellbore, it has been proposed to use weighted EDTA so that it can settle and reach the bottom of the reservoir. Studies on EDTA formulations and other weighted acid systems have been initiated.

[0009] Fluid weighting is a concept widely used in other areas of well construction, such as drilling, cementing and reconditioning, where various solids such as barite, bentonite, limestone or soluble salts are commonly used for this purpose; however, this concept has only rarely or almost never been used in acid stimulation of oil wells.

[0010] The use of weighting agents in acid stimulation activities is nascent worldwide, with pre-salt treatments being an exception, due to their use for EDTA positioning. Several other weighted formulations are currently being tested for field applications in the various phases of acid treatments.

[0011] Gravitational positioning, as an auxiliary stimulation technique, uses weighted acid fluids to reach greater depths from the injection point. It offers a significant advantage: a novel approach that is less dependent on formation characteristics (porosity and permeability) and the effects of chemical or physical deflectors. This allows access to areas of lower permeability where treatment encounters difficulties and / or uncertainties, as it is a purely physical phenomenon occurring within the wellbore rather than through the formation's porous matrix. This does not mean abandoning deflectors or solutions already in use, but rather that this is a complementary technique designed to enhance and correlate the observed effects with the deflection occurring within the formation.

[0012] It should be noted that the use of fluids saturated or supersaturated with sodium chloride or ammonium chloride has already been carried out, with the aim of achieving a diversion effect, but not to promote an increase in the density of the fluid of interest. Since 2015, Petrobras has begun using chelating agents and weighted acetic acid in isolated stages of operations, such as injectivity generation; however, they are not yet predominant in the main acid processing.

[0013] Figure 1 schematically illustrates the evolution of the stimulation process as previously mentioned. Figure 1A shows the creation of injectivity using a coiled intervention tube, reaching the base of the lower reservoir, to allow for the primary treatment of this area and its subsequent use in treating all other intervals. 15% hydrochloric acid was used preferentially, with 10% acetic acid reserved for high-temperature wells. This sequence required significant operating time, in addition to involving increased risks related to tool blockage and the resulting fishing. A study of our database shows that the average duration of the stimulation operations was approximately five drilling days.Cases of operational problems were reported, such as a lack of coiled intervention tubing equipment, waiting for favorable weather conditions for operations, equipment failures, leaks, accidents, and blockages of cabling equipment and the coiled intervention tubing itself—all events that negatively impacted the construction of several wells. Table 1 details the average times for each stage of completion and stimulation, based on these assumptions.

[0014] From 2015 onwards, not only to avoid the use of coiled intervention tubing equipment, but also to improve the quality of acidification in the upper well zones, the use of an ethylenediaminetetraacetic acid (EDTA) solution began in an earlier step than that usually used for stimulation. This positioning began to be carried out by column-end circulation, with return to the surface via the annulus of the upper well zones, before the placement of the plugs, thus allowing better distribution of the main acid treatment in this area. However, some doubts began to emerge concerning the injectivity conditions of the lower interval, as well as a possible detriment to the distribution of the treatment in this region ([Fig.[l] B), given that the circulation point of EDTA was close to the base of the upper interval, i.e. above the lower interval.

[0015] The sequence of operational steps and the respective completion and stimulation times of a typical pre-salt well, before the modifications described, are presented in detail in Table 1 below:

[0016] Table 1: Mean operational times of the completion and stimulation step with FT and acidification in the post-WCT phase [Tables 1] Identification Task Name Average Time (hours) 1 Navigation 10 2 Pre-stimulation Steps 15.5 3 Pre-stimulation Steps 79 4 Pre-stimulation Steps 94 5 Pre-stimulation Steps 23.5 6 Pre-stimulation Steps 119 7 Pre-stimulation Steps 72.5 8 Pre-stimulation Steps 74 9 Pre-stimulation Steps 8 10 Pre-stimulation Steps 16 11 Pre-stimulation Steps 68 12 Pre-stimulation Steps 25 13 Pre-stimulation Steps 37.5 14 Pre-stimulation steps 5 15 Pre-stimulation steps 2 16 Pre-stimulation steps 6 17 Pre-stimulation steps 25.5 18 Pre-stimulation steps 14 19 WCT setup 25 20 Chemical treatment - Loss zone 54 21 Direct injection into lower zone 10 22 Chemical treatment - Direct injection into upper zone 6 23 Evidence of injection into upper zone 5 24 Evidence of injection into lower zone 10 25 Post-stimulation steps 13 26 Post-stimulation steps 32 27 End of well completion 0 total Completion activities IC 8½11 (21.59 cm). PAB installation, well re-entry, lower cavitation completion installation, CI installation, TH installation, WCT installation, acidification and mini-TI in both zones. 923.5 h

[0017] According to the sequence shown in Table 1, the average time required to complete a typical pre-salt well would be approximately 923.5 hours, or 38.5 days. It can be seen that these times are strongly influenced by the need to use coiled intervention tubing equipment to stimulate the well (70 hours) and by the installation of the WCT (12 to 15 days) with the drilling rig, and it was only after the WCT installation that the main stimulation was carried out with a stimulation boat connected to the drilling rig. Eliminating the need to use coiled tubes reduced the duration of acidification operations to approximately 24 hours and completely eliminated the WCT installation time from the scope of completion devices, once this equipment began to be installed by a smaller vessel, a boat called a SESV (Submarine Equipment Support Vessel), which is specifically dedicated to this function at Petrobras..

[0018] Document US2021324260 discloses mixtures of chelating acids for stimulating underground formation, methods of using mixtures of acids Chelating agents and hydrocarbon wells containing chelating acid mixtures are discussed in this document. It proposes adding chelating agents (including EDTA) to acid mixtures (e.g., HCl and HF) for well stimulation to reduce the risk of scale precipitation. The presence of the chelating agent can also decrease the reaction rate of the acid mixture with the formation mineralogy, allowing the chelating acid mixture to penetrate more deeply into fractures and the formation's porous network.

[0019] Document WO2008139164, for its part, refers to methods for treating a portion of the matrix of an underground formation in a pre-existing fracture or perforation, in order to increase permeability and production. The method includes, among other steps, the formation or supply of a treatment fluid comprising: (i) water; (ii) a chelating agent capable of forming a heterocyclic ring containing a metal ion bonded to at least two non-metal ions; and (iii) a viscosity-increasing agent. Although the chelating agent may be EDTA, the treatment fluid uses a polymer viscosity-increasing agent which, consequently, does not include or anticipate the increase in the density of the composition by the addition of salts, as described in the present invention.

[0020] Documents US2017044884 and US2020079989 describe the application of the chelating function of EDTA in other fluids applicable to the different stages of the life cycle of an oil well. Description of the invention

[0021] The present invention aims to provide formulations of self-weighted and weighted fluids, such as EDTA and citric acid, for the stimulation of oil wells by gravity positioning. Brief description of the figures

[0022] [Fig.1] Fig.1 shows the evolution of the well construction and stimulation model, where IA) refers to blasting at the base with a coiled intervention tube; IB) refers to the circulation of EDTA through the base of the upper well zone; IC) refers to the circulation of weighted EDTA at the base of the upper well interval.

[0023] [Fig.2] Fig.2 corresponds to the illustrative image of the percolation of a weighted fluid over a fluid of lower density, in which the colors indicate the variation of concentrations after a certain time.

[0024] [Fig. 3] Figure 3 shows the results of a CFD computer simulation of the concentration profile at the base of the lower perforation after positioning of 0.1 M EDTA, as a function of elapsed time. The test was carried out after modeling the simulator with verification of the mesh, flow regimes, and flow rates. injection, EDTA concentrations, viscosities and two turbulence models.

[0025] [Fig.4] Figure [Fig.4] shows the density gradient of citric acid solutions in three different solvents, namely industrial water, sodium chloride and calcium chloride. The variation in density was measured as a function of the molarity of citric acid in each of them. Detailed description of the invention

[0026] The present invention relates to self-weighted and weighted fluid formulations, such as EDTA and citric acid as active ingredients, for the stimulation of oil wells by gravity positioning. These formulations are described below:

[0027] A self-weighted fluid formulation, characterized in that it comprises: - 0.1 to 3.7 mol / L of a self-weighting acid / agent, preferably citric acid; - Solvent qs, preferably industrial waters; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion inhibitor; - 0 to 10% v / v of a wettability inverter, preferably butyl glycol.

[0028] Weighted citric acid formulations

[0029] Table 2: Citric acid solution in industrial water (self-weighted) [Tables2] Product Concentration Function Density (g / cm³) pH Citric acid 0.1 to 3.7 molar Acid and self-weighting agent 1.005 to 1.279 2.2 to 0.36 Industrial waters 1s qs Solvent N / AN / A Corrosion inhibitor 0.3% (v / v) Corrosion inhibitor N / AN / A Emulsifier 0.3% (v / v) Emulsifier N / AN / A Butyl glycol 0 to 10% (v / v) Wettability inverter N / AN / A

[0030] The density and pH values ​​refer to the binary mixture of citric acid in industrial water only, without the addition of any other additives. It is assumed that variations due to the addition of these elements do not result in significant changes in the densities of interest.

[0031] A weighted fluid formulation, characterized in that it comprises: - 0.1 to 3.63 mol / L of an acid, preferably citric acid; - Weighting agent qs, preferably saturated NaCl brine; - Diluent qs, preferably industrial water; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion inhibitor; - 0 to 10% v / v of a wettability inverter, preferably butyl glycol.

[0032] Table 3: Citric acid solution in a saturated sodium chloride brine [Tables3] Product Concentration Function Density (g / cm³) pH Citric acid 0.1 to 3.63 mol Acid 1.2 to 1.366 0.58 to -0.86 Brine NaCl (saturated) qs Self-weighting agent 1.19 N / A Industrial waters 1s qs Diluent N / AN / A Corrosion inhibitor 0.3% (v / v) Corrosion inhibitor N / AN / A Emulsifier 0.3% (v / v) Emulsifier N / AN / A Butyl glycol 0 to 10% (v / v) Wettability inverter N / AN / A

[0033] The density and pH values ​​refer to the binary mixture of citric acid in a saturated sodium chloride solution (NaCl brine) only, without the addition of any other additives. It is assumed that variations due to the addition of these elements do not result in significant changes in the densities of interest.

[0034] Industrial water can be used to obtain solutions with densities lower than the maximum indicated, depending on operational needs.

[0035] A weighted fluid formulation, characterized in that it comprises: - 0.1 to 3.39 mol / L of an acid, preferably citric acid; - Weighting agent qs, preferably saturated CaC12 brine; - Diluent qs, preferably industrial water; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion inhibitor; - 0 to 10% v / v of a wettability inverter, preferably butyl glycol.

[0036] Table 4: Citric acid solution in a saturated calcium chloride brine [Tables4] Product Concentration Function Density (g / cm³) pH Citric acid 0.1 to 3.39 mol Acid 1.39 to 1.466 -1.5 to -2.0 Brine CaCl₂ (saturated) qs Self-weighting agent N / AN / A Industrial waters 1s qs Diluent N / AN / A Corrosion inhibitor 0.3% (v / v) Corrosion inhibitor N / AN / A Emulsifier 0.3% (v / v) Emulsifier N / AN / A Butyl glycol 0 to 10% (v / v) Wettability inverter N / AN / A

[0037] The density and pH values ​​refer to the binary mixture of citric acid in a saturated calcium chloride solution (CaCl2 brine) only, without the addition of any other additives. It is assumed that variations due to the addition of these elements do not result in significant changes in the densities of interest.

[0038] Industrial water can be used to obtain solutions with densities lower than the maximum indicated, depending on operational needs.

[0039] A self-weighted fluid formulation, characterized in that it comprises: - 0.1 to 1.35 mol / L of a chelator / self-weighting agent, preferably EDTA; - Solvent qs, preferably industrial waters; - pH adjusters qs, preferably HCl 32% and NaOH; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion inhibitor.

[0040] Self-weighted EDTA formulations

[0041] Table 5: EDTA solution in industrial water (self-weighted) [Tables 5] Product Concentration Function Density (g / cm3) pH EDTA 0.1 to 1.35 mol Chelating agent and self-weighting agent 1.005 to 1.279 4 to 12 Industrial waters 1 s qs Solvent N / A / A HCl 32% qs pH adjustment N / A 5 to 12 NaOH qs pH adjustment N / A 5 to 12 Corrosion inhibitor 0.3% (v / v) Corrosion inhibitor N / AN / A Emulsifier 0.3% (v / v) Emulsifier N / AN / A

[0042] The density and pH values ​​refer to the binary mixture of EDTA in industrial water only, without the addition of any other additives. It is assumed that the variations due to the addition of these elements do not result in significant changes in the densities of interest.

[0043] The most commonly used EDTA concentration in pre-salting operations is around 0.35 M, with a final density of 8.6 ppg or 1.03 g / cm3 obtained when prepared exclusively with industrial water.

[0044] Formulation of weighted EDTA in a saturated sodium chloride brine

[0045] A weighted fluid formulation, characterized in that it comprises: - 0.1 to 1.35 mol / L of a chelator / self-weighting agent, preferably EDTA; - Solvent qs, preferably saturated NaCl brine; - pH adjusters qs, preferably HCl 32% and NaOH; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion inhibitor.

[0046] Table 6: EDTA solution in a saturated sodium chloride brine [Tableauxô] Product Concentration Function Density (g / cm³) pH EDTA 0.1 to 1.35 mol Chelating agent and self-weighting agent 1.005 to 1.279 4 to 12 Brine NaCl (saturated) qs Solvent 1.19 N / A HCl 32% qs pH adjustment N / A 5 to 12 NaOH qs pH adjustment N / A 5 to 12 Corrosion inhibitor 0.3% (v / v) Corrosion inhibitor N / A / A Emulsifier 0.3% (v / v) Emulsifier N / A / A

[0047] The density and pH values ​​refer to the binary mixture of EDTA in a saturated sodium chloride solution (NaCl brine) only, without the addition of any other additives. It is assumed that variations due to the addition of these elements do not result in significant changes in the densities of interest.

[0048] The most commonly used EDTA concentration in pre-salting operations is around 0.35 M, with a final density of 10.2 ppg or 1.22 g / cm³ obtained when prepared from saturated sodium chloride brine. Technological Aspects of the Invention

[0049] In order to properly plan and successfully use chelation systems and weighted weak acids, it is imperative that the "segregation / sedimentation" occur within normal timeframes, i.e., a few hours, to optimize the treatment of the lower interval. There was some doubt about the possibility of percolation of a miscible fluid through another of lower density, i.e., the sedimentation of the acid system by the fluid filling the well. Extensive discussions took place regarding the nature of the phenomena that would occur, such as the diffusivity and dilution of the chemical species in contact, the predominant flow regime, the contact area, the well geometry, viscosity, and pressure losses, until the feasibility of the proposed technique was concluded.

[0050] In order to objectively clarify these issues, computational fluid dynamics (CFD) modeling studies were initiated. Figure 2 illustrates the percolation phenomenon; the simulation shows that the EDTA concentration at the base of the zone increases over time, while at the top it decreases as expected, demonstrating that the developed CFD model is suitable for the present invention.

[0051] The initial objective was to determine the time required for a fluid weighted at 1 (lb / gal) (0.12 g / cm³) above the well fluid to migrate over a 100-meter interval. After developing the algorithm, the first hypothetical case of interest was simulated, by analogy with the conditions normally encountered in operations. It was then considered to position 100 bbl (15.9 m³) of EDTA with a density of 1 lb / gal (1 ppg ~ 0.12 g / cm³) above the fluid system present in the well, which should allow it to travel a height of 100 m. The result obtained was a time of approximately 50 minutes to reach the base of the interval, a very encouraging result, since operational times are significantly longer.

[0052] A second series of simulations was performed with the developed CFD model, considering a density difference of 0.4 ppg (Lb / gal) (0.05 g / cm³) and a height to be overcome of 100 m. Figure 3 graphically presents the results of this simulation, and after 4 hours, the concentration in the base is equivalent to 0.05 M, or 50% of the initial concentration of the EDTA used (pumping concentration), thus for a density difference of 0.4 Lb / gal (0.05 g / cm³). This result corroborates the use of the gravity positioning technique for well stimulation.

[0053] However, it should be noted that, due to limitations in material availability and solubility, it is difficult in practice to obtain density differences on the order of 1 ppg (0.12 g / cm³), particularly in fields that still retain the original reservoir pressure, normally close to 9.9 to 10 ppg (1.19 to 1.20 g / cm³). Weighting achieved solely by adding EDTA, or in combination with the base brine of the completion fluid used, requires several tons of EDTA and concentrations on the order of 40%, making it difficult to implement. A new simulation was therefore carried out considering a density difference on the order of 0.4 ppg (0.05 g / cm³). In this way, the result obtained was a migration time of 4 hours, which is also a timescale compatible with field operations, definitively making the technique viable.

[0054] In parallel, several tests were carried out to determine the properties of EDTA solutions and their mechanism of action, such as the attack on test plugs, compatibility tests with different brines, optimal pH, viscosity, maximum concentrations without precipitation, and many others. It was found that it is possible to obtain EDTA solutions exceeding 10 ppg (1.20 g / cm³) using only EDTA in industrial water in a stable form. The main drawback of systems using EDTA lies in their low solubility at acidic pH. Consequently, EDTA can be used to balance the solution itself when combined with salts such as sodium chloride, but it is not suitable for use in combination with other acids.

[0055] In the investigation of weak acids, citric acid was evaluated as a replacement for acetic acid. It acts as a (limited) chelator and has the advantage of being more soluble when the pH decreases; citric acid can be considered as a weighting agent for other acids and combined with other salts to enhance the weighting.

[0056] The laboratory tests presented in Table 7 showed a solubility of 127 g / 100 ml in distilled water (industrial water), with a slight reduction in solubility in saturated medium in sodium chloride (125 g / 100 ml) and, to a lesser extent, in calcium chloride brine (107 g / 100 ml), highlighting that no incompatibility with calcium was observed, with the formation of an insoluble citrate.

[0057] Table 7: Solubility of citric acid in different media [Tables 7] Solvent % W / MM (mol / L) Solubility (g / 100 ml) Density pH Industrial waters 41.55 3.7 127.86 1.28 0.36 NaCl brine 41.10 3.63 125.59 1.37 -0.86 CaCl2 brine 39.49 3.39 107.67 1.47 -2

[0058] Thus, it is possible to verify a substantial increase in density, ranging from 1.28 g / cm³ for industrial water to 1.47 g / cm³, using CaCl₂ brine as the base fluid. Figure 4 illustrates the weight variation in each medium tested, with the variation being greater in distilled water.

[0059] As part of a field test (Table 8), a small-scale test was carried out in a typical pre-salt well, a WAG (Water Alternate Gas) injection well, with an intelligent realization of 2 zones, where the lower zone corresponds to an interval of 329 meters, with less good permoporous conditions than those of the upper zone (length of 53 meters), in which it was estimated that it would be very difficult to stimulate the interval.

[0060] Table 8: Field tests using acid system weighting [Tables8] Lower Zone Fluid Zone Weight (lb / g) (x 0.1198 g / cm³) Volume (bbl) (x 0.159 m³) Maximum Flow Rate (bbl / min) (x 0.159 m³ / min) Time (min) I Acetic Acid 10% 9.8 263 5 53 I POL Diverter 2.5% 8.5 85 5 30 I Acetic Acid 10% 9.8 263 5 53 I POL Diverter 2.5% 8.5 85 5 17 I Acetic Acid 10% 9.8 345 5 69 I POL Diverter 2.5% 8.5 85 5 17 I Acetic Acid 10% 9.9 345 10 35 I Acid Citric acid 20% (1 molar) 10.1 50 10 5 I Hydrochloric acid 15% 8.5 167 25 7 I POL deflector 2.5% 8.5 171 25 7 I Hydrochloric acid 15% 8.9 335 25 13 I Emulsified hydrochloric acid 15% 8.5 546 25 22 I Hydrochloric acid 15% 8.9 335 25 13 I POL deflector 2.5% 8.5 171 25 7 I Hydrochloric acid 15% 8.9 335 25 13 I POL deflector 2.5% 8.5 256 25 10 I Hydrochloric acid 15% 8.9 502 25 20 I FSAL Na+ 8.5 550 25 0 4890 391

[0061] The weight of the fluid used for the workover was 9.4 lb / gal (1.13 g / cm³). Therefore, acetic acid cushions in brine were prepared to obtain a final weight of 9.8 lb / gal (1.17 g / cm³). During the treatment, citric acid was used in a sodium chloride brine weighing 10 lb / gal (1.20 g / cm³). The sequence was designed to perform a progressive treatment (from weakest to strongest acid) using the concept of gravitational segregation, increasing the density of the solutions during the treatment. It was not possible to weigh the hydrochloric acid cushions during the test due to ongoing laboratory tests and the availability of citric acid in the drilling rig.

[0062] A good result was obtained, demonstrating the viability of gravitational segregation, thanks to the feasibility of the technique, which shows great potential for field applications. Both zones were stimulated and showed good injectivities at the end of the treatment, with selectivity between the zones preserved. Table 9 summarizes the data obtained.

[0063] Table 9: Results obtained after treatment [Tables 9] Interval Zone Interval (extension) 1120min (m3 / d) / (kgf / cm2) RD Kh (mD.m) Upper S 5252.7 to 5305.7 m (53.0 m) 43.7 0.81 7120 Lower I 5337.6 to 5667.0 m (32 9.4 m) 107.9 0.52 8170

[0064] Considering that the technology developed in this invention is pioneering, its use offers several advantages; for example, cost reduction may be due to the possibility of using the technique to replace mechanical equipment Fluid positioning, such as valves, coiled tubing, or scrubbing tubing, is another advantage. A further benefit is the ability to improve treatment diversion, leading to increased productivity and improved well recovery.

[0065] The use of weighted acid fluids was originally intended to stimulate oil wells in pre-salt carbonate formations and can be extended to other types of horizontal, directional or vertical completions of sandstone and carbonate wells.

Claims

Claims

1. A self-weighting fluid formulation, characterized in that it comprises: - 0.1 to 3.7 mol / L of a self-weighting acid / agent, preferably citric acid; - Solvent qs, preferably industrial water; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion preventer; - 0 to 10% v / v of a wettability inverter, preferably butyl glycol.

2. A self-weighting fluid formulation according to claim 1, characterized in that the binary mixture of citric acid in industrial water has a density of 1.005 to 1.279 g / cm3, and a pH value of 2.2 to 0.

36.

3. A weighted fluid formulation, characterized in that it comprises: - 0.1 to 3.63 mol / L of an acid, preferably citric acid; - Weighting agent qs, preferably saturated NaCl brine; - Diluent qs, preferably industrial water; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion preventer; - 0 to 10% v / v of a wettability reverser, preferably butyl glycol.

4. A self-weighting fluid formulation according to claim 3, characterized in that the binary mixture of citric acid in the saturated sodium chloride solution has a density of 1.2 to 1.366 g / cm3, and a pH value of 0.58 to -0.

86.

5. A weighted fluid formulation according to claim 3, characterized in that the saturated sodium chloride brine has a density of 1.19 g / cm3.

6. A weighted fluid formulation, characterized in that it comprises: - 0.1 to 3.39 mol / L of an acid, preferably citric acid; - Weighting agent qs, preferably saturated CaCl2 brine; - Diluent qs, preferably industrial water; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion preventer; - 0 to 10% v / v of a wettability inhibitor, preferably butyl glycol.

7. A weighted fluid formulation according to claim 6, characterized in that the binary mixture of citric acid in the saturated calcium chloride solution has a density of 1.39 to 1.466 g / cm3, and a pH value of -1.5 to -2.

0.

8. A self-weighting fluid formulation, characterized in that it comprises: - 0.1 to 1.35 mol / L of a chelator / self-weighting agent, preferably EDTA; - Solvent qs, preferably industrial water; - pH adjusters qs, preferably 32% HCl and NaOH; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion preventer;

9. A self-weighting fluid formulation according to claim 8, characterized in that the binary mixture of EDTA in industrial water has a density of 1.005 to 1.279 g / cm3, and a pH value of 4 to 12.

10. A self-weighting fluid formulation according to claim 8, characterized in that the total density is 1.03 g / cm3 when prepared with industrial water only.

11. A weighted fluid formulation, characterized in that it comprises: - 0.1 to 1.35 mol / L of a chelator / self-weighting agent, preferably EDTA; - Solvent qs, preferably saturated NaCl brine; - pH adjusters qs, preferably 32% HCl and NaOH; - 0.3% v / v of a corrosion inhibitor; - 0.3% v / v of an emulsion preventer;

12. A weighted fluid formulation according to claim 11, characterized in that the binary mixture of EDTA in the saturated sodium chloride solution has a density of 1.005 to 1.279 g / cm3, and a pH value of 4 to 12.

13. A weighted fluid formulation according to claim 11, characterized in that the saturated sodium chloride brine has a density of 1.19 g / cm3.

14. A weighted fluid formulation according to claim 11, characterized in that the total density is 1.22 g / cm3 when prepared from saturated sodium chloride brine.

15. Use of the formulations defined in any one of claims 1 to 14, characterized in that it involves stimulating oil wells by gravitational positioning.

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