Non-acidic scale remover for removing iron sulfide scale from wellbores and methods of making

Abstract

The application discloses a non-acid scale dissolver for removing iron sulfide scale in a wellbore, which comprises the following components in mass ratio: a main agent, hexaazacyclic compound, 20-40%; an auxiliary agent, organic phosphonate, 15-35%; a penetrating agent, non-ionic surfactant, 1-5%; and water, the rest. The application also discloses a preparation method of the non-acid scale dissolver, which comprises mixing and stirring the raw materials and adjusting the pH value to obtain the non-acid scale dissolver. The scale dissolving rate of the scale dissolver to iron sulfide reaches more than 80%, which is close to the scale dissolving efficiency of an acid scale dissolver, and the scale dissolver is neutral, which is low in corrosion to the wellbore in the plugging removal process, and overcomes the serious corrosion problem caused by the traditional acid scale dissolver in the plugging removal process.

Description

Technical Field

[0001] This invention belongs to the field of wellbore descaling technology in oil and gas field development, specifically relating to a non-acidic scale remover for removing iron sulfide scale from wellbores; it also relates to a method for preparing the non-acidic scale remover for removing iron sulfide scale from wellbores. Background Technology

[0002] During oil and gas field development, the presence of H2S causes corrosion of the wellbore, leading to both wellbore perforation and the formation of iron sulfide scale, which can block oil and gas flow channels and reduce well production. Iron sulfide exists in various crystal forms, depending on the temperature and pressure range. Pyrite and pyrite are the most common types, while other forms include pyrrhotite, chamfered iron, pyrite, and makinite. Generally, iron sulfide scale in wellbores is a mixture of these various crystal forms.

[0003] Currently, common descaling methods include mechanical descaling and chemical descaling. Mechanical descaling involves using milling or other similar cutting tools to cut the scale off the pipe surface. However, this process inevitably damages the tubing. Chemical descaling methods are more versatile and can clean scale buildup in wellbores, bends, pumps, etc. They offer good descaling results, simple operation, and lower operating costs. For iron sulfide scale, commonly used descaling agents are acidic, including hydrochloric acid (HCl), tetramethylphosphoric acid sulfate (THPS), formic acid (HCOOH), and acetic acid (CH3COOH). However, acidic systems introduce severe corrosion problems during descaling. Therefore, a non-acidic descaling system needs to be developed. Chelating agents are commonly used in non-acidic systems. Chelating agents are a better technology, offering high descaling efficiency and extremely low corrosivity to wellbore materials, while maintaining wellbore integrity during the descaling process. Summary of the Invention

[0004] The purpose of this invention is to provide a non-acidic scale remover for removing iron sulfide scale from wellbores, overcoming the serious corrosion problems caused by traditional acidic scale removal systems during the scale removal process.

[0005] Another objective of this invention is to provide a method for preparing a non-acidic scale remover for removing iron sulfide scale from wellbores.

[0006] The first technical solution adopted in this invention is a non-acidic scale remover for removing iron sulfide scale from wellbore, comprising the following composition in the following mass ratio: The main agent is a hexaazaheterocyclic compound, with a content of 20%~40%; The excipient is an organophosphonate, with a content of 15% to 35%; The penetrant is a nonionic surfactant, with a content of 1% to 5%; The rest is water.

[0007] The invention is further characterized in that, The hexaazaheterocyclic compound is any one of the hexaazaheterocyclic sodium hexaacetate, hexaazaheterocyclic sodium hexaphosphonate, and hexaazaheterocyclic methyl hexaacetate.

[0008] The organophosphate is any one of the following: sodium hydroxyethylidene diphosphonate (HEDP•2Na), pentasodium diethylenetriaminepentamethylidene phosphonate (DTPMP•Na5), or tetrasodium 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA•Na4). The nonionic surfactant is either fatty alcohol polyoxyethylene ether (AEO) or alkylphenol polyoxyethylene ether (APEO).

[0009] The structural formula of the hexa-nitrogen heterocyclic compound is:

[0010] In the structural formula, R can be any one of amino-NH2, alkylamino-NHR, dialkylamino-NR2, hydroxy-OH, amide-NHCOR, or alkoxy-OR.

[0011] The second technical solution adopted in this invention is: a method for preparing a non-acidic scale remover for removing iron sulfide scale from wellbore, the specific operation steps of which are as follows: Step 1: Add a hexaazaheterocyclic compound to the reaction vessel; Step 2: Add organophosphonate to the reaction vessel; Step 3: Continue adding nonionic surfactants into the reactor. Step 4: Add water to the reactor and stir for 25-35 minutes. Then add pH adjuster to adjust the pH to 7-8 and continue stirring for 30 minutes to obtain a non-acidic scale solvent.

[0012] The mass percentages of hexaazaheterocyclic compounds, organophosphonates, and nonionic surfactants are 20%–40%, 15%–35%, 1%–5%, and the remainder is water.

[0013] The invention is further characterized in that, Compared with the prior art, the present invention has the following beneficial effects: This invention addresses the problem of iron sulfide scale buildup in sulfur-containing wells during production, caused by H2S corrosion of the wellbore and its inclusion in produced materials at the bottom of the well, leading to scale blockage and reduced production in oil and gas wells or water injection in injection wells. A non-acidic scale remover has been developed for removing iron sulfide scale from wellbores. This scale remover achieves a scale removal rate of over 80% for iron sulfide, approaching the efficiency of acidic scale removers. Furthermore, this scale remover is neutral, exhibiting extremely low corrosion to the wellbore during the unblocking process. It overcomes the severe corrosion problems caused by traditional acidic scale removers during unblocking. This invention can support the flow of oil and gas wells during production, thereby increasing oil and gas well production. Attached Figure Description

[0014] Figure 1 This is the 1H NMR spectrum (1H NMR) of sodium hexaazaheterocyclic hexaacetate of the present invention, which is Example 2. Figure 2 This invention relates to the hydrogen nuclear magnetic resonance (1H NMR) spectrum of sodium hexaazaheterocyclic hexaphosphonate as described in Example 3 of this invention. Figure 3 This is the 1H NMR spectrum of hexaaza-heterocyclic methyl hexaacetate in Example 4 of the present invention. Detailed Implementation

[0015] The present invention will now be described in detail with reference to specific embodiments.

[0016] Example 1 The preparation process of the non-acidic scale remover for removing iron sulfide scale from wellbore is as follows: Step 1: Add 20-40% of hexaazaheterocyclic compounds to the reactor; Step 2: Add 15-35% organophosphonate to the reaction vessel; Step 3: Add 1-3% nonionic surfactant to the reaction vessel; Step 4: Add water to the reactor and stir for 30 minutes. Then add a pH adjuster to adjust the pH to 7-8. Continue stirring for another 30 minutes to obtain a non-acidic scale solvent.

[0017] Evaluation of the scale-dissolving effect of non-acidic scale solvents: Add 1g of iron sulfide scale and 50mL of non-acidic scale remover to a 100mL aging tank, and evaluate the scale removal effect by maintaining the temperature at 90℃ and 140℃ for 48h.

[0018] Scale dissolution rate = (Weight of dissolved scale / Weight of original scale) * 100% According to the standard "SY / T 5405 Test Methods and Evaluation Indicators for Performance of Corrosion Inhibitors for Acidification", Section 5, the method and evaluation indicators for determining the static corrosion rate under normal pressure are used to evaluate the static corrosion of non-acidic scale inhibitors under normal pressure.

[0019] Example 2 The preparation process of the non-acidic scale remover for removing iron sulfide scale from wellbore is as follows: Step 1: Add 20% sodium hexaazaheterocyclic hexaacetate (SCH) to the reactor. The structural formula is as follows:

[0020] Figure 1 The peak at chemical shift 3.4 corresponds to the substitution of α-H on aliphatic C atom by N atom, proving the existence of CN bond in molecule; the peak at chemical shift 6.5~7.5 corresponds to hydrogen on benzene ring, proving the existence of benzene ring in molecule; the peak at chemical shift 7.8 corresponds to hydroxyl hydrogen, proving the existence of carboxyl hydroxyl group in molecule.

[0021] Step 2: Add 25% 2-phosphonobutane-1,2,4-tricarboxylic acid tetrasodium sodium (PBTCA•Na4) to the reaction vessel. Step 3: Add 3% fatty alcohol polyoxyethylene ether (AEO) to the reactor. Step 4: Add water to the reactor and stir for 30 minutes. Then add a pH adjuster to adjust the pH to 7-8. Continue stirring for another 30 minutes to obtain a non-acidic scale solvent.

[0022] Example 3 The preparation process of the non-acidic scale remover for removing iron sulfide scale from wellbore is as follows: Step 1: Add 20% sodium hexaazaheterocyclic sodium hexaphosphonate to the reactor. The structural formula is as follows:

[0023] Figure 2 The peak at chemical shift 3.7 corresponds to the substitution of α-H on aliphatic C atom by N atom, proving the existence of CN bond in the molecule; the peak at chemical shift 6.5~7.5 corresponds to hydrogen on benzene ring, proving the existence of benzene ring in the molecule; the peak at chemical shift 7.9 corresponds to hydroxyl hydrogen, proving the existence of hydrogen phosphate group in the molecule.

[0024] Step 2: Add 15% sodium hydroxyethylidene diphosphonate (HEDP•2Na) to the reaction vessel. Step 3: Add 1% alkylphenol polyoxyethylene ether (APEO) to the reactor. Step 4: Add water to the reactor and stir for 30 minutes. Then add pH adjuster to adjust the pH to 7-8 and continue stirring for 30 minutes to obtain a non-acidic scale solvent.

[0025] Example 4 The preparation process of the non-acidic scale remover for removing iron sulfide scale from wellbore is as follows: Step 1: Add 20% hexaazacyclic methyl hexaacetate to the reactor. The structural formula is as follows:

[0026] Figure 3 The peak at chemical shift 3.5 corresponds to the substitution of α-H on aliphatic C atom by N atom, proving the existence of CN bond in the molecule; the peaks at chemical shifts 6.5~7.5 correspond to hydrogen on benzene ring, proving the existence of benzene ring in the molecule.

[0027] Step 2: Add 15% sodium hydroxyethylidene diphosphonate (HEDP•2Na) to the reaction vessel. Step 3: Add 2% alkylphenol polyoxyethylene ether (APEO) to the reactor. Step 4: Add water to the reactor and stir for 30 minutes. Then add pH adjuster to adjust the pH to 7-8 and continue stirring for 30 minutes to obtain a non-acidic scale solvent.

[0028] Example 5 The preparation process of the non-acidic scale remover for removing iron sulfide scale from wellbore is as follows: Step 1: Add 20% of the hexaazacyclic sodium hexaacetate from Example 2 into the reactor; Step 2: Add 35% diethylenetriaminepentamethylphosphonate pentasodium (DTPMP•Na5) to the reaction vessel. Step 3: Add 2% alkylphenol polyoxyethylene ether (APEO) to the reactor. Step 4: Add water to the reactor and stir for 30 minutes. Then add pH adjuster to adjust the pH to 7-8 and continue stirring for 30 minutes to obtain a non-acidic scale solvent.

[0029] Example 6 The preparation process of the non-acidic scale remover for removing iron sulfide scale from wellbore is as follows: Step 1: Add 40% of the hexaazaheterocyclic sodium hexaacetate from Example 2 into the reactor; Step 2: Add 25% 2-phosphonobutane-1,2,4-tricarboxylic acid tetrasodium sodium (PBTCA•Na4) to the reaction vessel. Step 3: Add 1% fatty alcohol polyoxyethylene ether (AEO) to the reactor. Step 4: Add water to the reactor and stir for 30 minutes. Then add pH adjuster to adjust the pH to 7-8 and continue stirring for 30 minutes to obtain a non-acidic scale solvent.

[0030] Example 7 The preparation process of the non-acidic scale remover for removing iron sulfide scale from wellbore is as follows: Step 1: Add 20% of the hexaazacyclic sodium hexaacetate from Example 2 into the reactor; Step 2: Add 15% tetrasodium 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA•Na4) to the reactor. Step 3: Add 1% fatty alcohol polyoxyethylene ether (AEO) to the reactor. Step 4: Add water to the reactor and stir for 30 minutes. Then add pH adjuster to adjust the pH to 7-8 and continue stirring for 30 minutes to obtain a non-acidic scale solvent.

[0031] Example 8 The preparation process of the non-acidic scale remover for removing iron sulfide scale from wellbore is as follows: Step 1: Add 20% of the hexaazacyclic sodium hexaacetate from Example 2 into the reactor; Step 2: Add 25% 2-phosphonobutane-1,2,4-tricarboxylic acid tetrasodium sodium (PBTCA•Na4) to the reaction vessel. Step 3: Add 3% fatty alcohol polyoxyethylene ether (AEO) to the reactor. Step 4: Add water to the reactor and stir for 30 minutes. Then add pH adjuster to adjust the pH to 7-8 and continue stirring for 30 minutes to obtain a non-acidic scale solvent.

[0032] The evaluation results of the scale-dissolving effect and corrosion rate of the non-acidic scale solvents obtained in Examples 2-8, according to the evaluation method described in Example 1, are shown in Table 1.

[0033] Table 1

[0034] As can be seen from the table above, the non-acidic scale removers prepared in Examples 2-4 generally have good scale removal rates. The scale removal effect is best when the mass percentages of hexaazaheterocyclic compounds, organophosphonates, and nonionic surfactants are 20%~30%, 25%~35%, and 1%~2%, respectively.

[0035] The non-acidic scale remover of this invention is a novel chelating agent system that improves scale removal efficiency and rate, meeting the needs of oil and gas wells for removing iron sulfide scale blockage. Compared with traditional acidic scale remover systems, the novel chelating agent system has an extremely low corrosion rate. This composition has a good scale removal effect on iron sulfide scale, achieving an 80% scale removal effect at 140°C. Furthermore, this non-acidic scale remover is neutral and has an extremely low corrosion rate on the tubing. The non-acidic scale remover of this invention can be used in water injection wells and production wells to remove iron sulfide scale blockage, ensuring wellbore fluidity and achieving the goal of stable and increased oil and gas well production. It provides technical support for improving stable and increased oil and gas well production.

[0036] The key innovation of this invention lies in the following: the hexa-acid heterocyclic chelating agent in this non-acidic scale remover contains multiple N and O atoms, which can combine with Fe ions to form a stable, water-soluble, multidentate ligand. Therefore, it can transform insoluble ferrous sulfide scale into water-soluble compounds, thereby achieving the purpose of dissolving ferrous sulfide scale. Furthermore, the organophosphonate in this non-acidic scale remover can further combine with free iron ions in water, promoting the dissolution of ferrous sulfide. The nonionic surfactant in this non-acidic scale remover has a penetration-enhancing effect, promoting the penetration of the active ingredients for dissolving ferrous sulfide scale into the interior of the scale, thereby accelerating the dissolution and removal of ferrous sulfide scale. Therefore, this non-acidic scale remover has a good descaling effect on ferrous sulfide scale.

[0037] This non-acidic scale remover is neutral. Compared to acidic de-clogging systems, it not only significantly reduces the corrosiveness of steel pipes, but also the benzene ring and other heteroatoms such as N and O contained in the hexa-nitrogen heterocyclic chelating agent molecule can be adsorbed on the pipe surface to form a protective film, isolating the corrosive medium. Therefore, it also has a certain protective effect on the pipe surface.

[0038] To achieve the above objectives, the main technical means adopted in this invention are described clearly, completely, and accurately, and the substantive content of the invention is explained. The degree of disclosure is such that it is sufficient for a person skilled in the art to understand and implement the invention.

Claims

1. A non-acidic scale remover for removing iron sulfide scale from wellbore, characterized in that, The following composition is included in the mass ratio: The main agent is a hexaazaheterocyclic compound, with a content of 20%~40%; The excipient is an organophosphonate, with a content of 15% to 35%; The penetrant is a nonionic surfactant, with a content of 1% to 5%; The rest is water.

2. The non-acidic scale remover for removing iron sulfide scale from wellbore according to claim 1, characterized in that, The hexaazaheterocyclic compound is any one of sodium hexaacetate, sodium hexaphosphonate, and methyl hexaacetate.

3. The non-acidic scale remover for removing iron sulfide scale from wellbore according to claim 1, characterized in that, The organophosphate is any one of sodium hydroxyethylidene diphosphonate (HEDP•2Na), sodium diethylenetriaminepentamethylidene phosphonate (DTPMP•Na5), or tetrasodium 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA•Na4).

4. The non-acidic scale remover for removing iron sulfide scale from wellbores according to claim 1, characterized in that, The nonionic surfactant is either fatty alcohol polyoxyethylene ether (AEO) or alkylphenol polyoxyethylene ether (APEO).

5. The non-acidic scale remover for removing iron sulfide scale from wellbore according to claim 1, characterized in that, The structural formula of the hexa-nitrogen heterocyclic compound is: In the structural formula, R can be any one of amino-NH2, alkylamino-NHR, dialkylamino-NR2, hydroxy-OH, amide-NHCOR, or alkoxy-OR.

6. A method for preparing a non-acidic scale remover for removing iron sulfide scale from wellbore, characterized in that, The specific operating steps are as follows: Step 1: Add a hexaazaheterocyclic compound to the reaction vessel; Step 2: Add organophosphonate to the reaction vessel; Step 3: Continue adding nonionic surfactants into the reactor; Step 4: Add water to the reactor and stir for 25-35 minutes. Then add pH adjuster to adjust the pH to 7-8 and continue stirring for 30 minutes to obtain a non-acidic scale solvent.

7. The method for preparing the non-acidic scale remover for removing iron sulfide scale from wellbore according to claim 6, characterized in that, The hexaazaheterocyclic compound, organophosphonate, and nonionic surfactant account for 20%~40%, 15%~35%, 1%~5% by mass, respectively, with the remainder being water.

8. The method for preparing the non-acidic scale remover for removing iron sulfide scale from wellbore according to claim 6, characterized in that, The hexaazaheterocyclic compound is any one of the hexaazaheterocyclic sodium hexaacetate, hexaazaheterocyclic sodium hexaphosphonate, and hexaazaheterocyclic methyl hexaacetate. The organophosphate is any one of sodium hydroxyethylidene diphosphonate (HEDP•2Na), sodium diethylenetriaminepentamethylidene phosphonate (DTPMP•Na5), or tetrasodium 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA•Na4). The nonionic surfactant is either fatty alcohol polyoxyethylene ether (AEO) or alkylphenol polyoxyethylene ether (APEO).

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