A process for treating metal naphthenates-induced sludge

Abstract

A process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stable homogeneous mixture comprising steps of: a) preparing a mixture of a demulsifying agent or solubiliser and a solvent; b) preparing a mixture of hydrochloric acid and an aromatic naphtha; and c) mixing the preparation in step a) with the preparation in step b) to form a thermodynamically stable homogenous mixture.

Description

[0001] A PROCESS FOR TREATING METAL NAPHTHENATES-INDUCED SLUDGE

[0002] FIELD OF INVENTION

[0003] The present invention relates to the treatment of metal naphthenates-induced sludge which includes oilfield sludge, deposits, and mixed and / or wetted oilfield scales.

[0004] BACKGROUND OF INVENTION

[0005] Oilfields around the world in North Sea, Brunei, Malaysia, China, Congo, Angola, Indonesia, among others present problems related to treatment of metal naphthenate-induced sludge. The problem resides in the difficulty of demulsification and deposition of metal naphthenates in tubing and surface facilities.

[0006] Conventional tank bottom sludge is a tough water in oil emulsion. It typically consists of crude oil, formation water, precipitated heavy ends (waxes and asphaltenes), and inorganics such as sand, silt, scales and corrosion particles. Surfactants found in the crude oil, metal naphthenates and wetted solid particles stabilise this emulsion. Metal naphthenates play a big role in stabilising the sludge in many oilfields in Indonesia, Malaysia, North Sea, Congo, Angola, China, and Brunei.

[0007] Naphthenic acids form a fraction of the broad spectrum of carboxylic acids which create tough emulsion and metal soap scale deposition problems in the production process. Emulsion can be further stabilised by formation fines, scale, corrosion product particles having a coating of metal naphthenates. Mixing the emulsion in organic solvents like xylene and subjecting the mixture to a boiling temperature seem to dissolve the emulsion but in fact, the metal naphthenates melt but upon lowering the temperature the emulsion appears as it is. When combining with available divalent cations like calcium, magnesium and iron, the emulsion tends to deposit at metallic surface in tubing, separator, and flow lines.

[0008] The metal naphthenate deposits so formed may melt in boiling xylene but are insoluble. The tough emulsion formed by these species gets collected in the bottom of the storage tanks, thus reducing storage capacity. Initially, the emulsion may be consisting of nano- sized droplets (microemulsion) settling at the tank bottom above the water layer as thermodynamically stable lamellar and / or bicontinuous emulsion. Conventional approach in many cases where an efficient solution does not exist alludes to disposal by incineration. However, incineration is costly, presents environment hazard and generates thousands of tons of avoidable carbon dioxide.

[0009] Conventional sludge treatment is performed by manual desludging which is a tedious process. The challenge for applying any dynamic process to treat is the immobility of the sludge, removal of inorganic solids and breaking of the emulsion. In the past, various strategies relating to treatment of tank bottom sludge have been developed.

[0010] Malaysia Patent No. MY-143762-A disclosed an organic composition for treating and removing deposits formed due to naphthenic acids or due to formation of napthenates found in the crude oil production system. Accordingly, the aforementioned organic composition is a combination of a carboxylic acid, a solvent, and an additive which is selected from a group consisting of surfactants or corrosion inhibitors. Namad et al. (2008) described sludge treatment where some chemicals were added to sludge in homogeniser tank. The sludge was transferred to another tank where another chemical was added which generated heat The heated sludge was passed through a decanting centrifuge to separate oil, water and solids. Eke et al. (2019) described drivers for metal naphthenate formation and treatment strategies in their review paper. With the problems associated with acid injection, the current drive is to develop environment friendly, robust, low-dose surfactant inhibitors, for control of metal naphthenate in oilfield.

[0011] Treatment of tough emulsion and slop have been discussed in prior art European Publication No. EP1165723A1 taught demulsification using blend of diepoxide polymer, one polyol and one aromatic sulfonic acid (DDBSA) in aromatic solvent which is capable of transferring metal containing components to water. Meanwhile, Chinese Publication No. CN201610016631 disclosed a method to resolve high water containing slop oil which consists of washing the slop oil with sodium hydroxide solution followed by treatment with sulfuric acid to form a reaction with sodium naphthenate and converted into naphthenic acids. Misra et al. (2021) disclosed a microemulsion formulation for dissolution and removal of predominantly iron naphthenate particles which choke strainer at the oil export line. Keatch (2022) described the invention provides a composition and method of use for the dissolution of calcium naphthenate solids in the presence of water which comprises at least one carboxylic acid and a mutual solvent comprising ethylene glycol monobutyl ether. Misra and Singh (2011) disclosed an organic formulation for dissolution and removal of calcium and iron naphthenates deposits from oil well system.

[0012] Wetted scales are inorganic scales or formation fines coated with organic material like wax, asphaltenes or metal naphthenates. Treatment of mixed or wetted scales also refers to wetted surfaces where formation rock is coated with organic material like wax, asphaltenes or metal naphthenates presenting problem in well stimulation.

[0013] At present, studies on dynamic sludge treatment process are lacking and less than satisfactory, thus motivating the inventors of the present invention to develop a novel method in addressing and overcoming the foregoing challenges in relation to treatment of metal naphthenates-induced sludge which includes oilfield sludge, deposits, and mixed and / or wetted oilfield scales. Mixed scales are characterised by formation of deposits having interstitial layers of different material in the matrix. Here ‘different material’ is referred to species of organic and inorganic nature. The use of microemulsions in preventing or removing formation of deposits, organically or inorganically, and / or mixtures thereof existing in subterranean nature is described in US Patent Application No. 17 / 275,797.

[0014] The present invention seeks to resolve the sludge which ensures fast resolution and good oil and water quality.

[0015] SUMMARY OF THE INVENTION

[0016] In alleviating limitations in the foregoing challenges, the present invention provides a process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stable homogeneous mixture comprising steps of: a) preparing a mixture of a demulsifying agent or solubiliser and a solvent; b) preparing a mixture of hydrochloric acid and an aromatic naphtha; and c) mixing the preparation in step a) with the preparation in step b) to form a thermodynamically stable homogenous mixture.

[0017] Accordingly, the metal naphthenates-induced sludge includes oilfield sludge, deposits, and mixed and / or wetted oilfield scales. Treatment of wetted scales also extends to treatment of wetted surfaces which comes in the way of well stimulation. Other features and advantages of the present invention are readily apparent from the following detailed description with the accompanying drawings, which illustrate, by way of example, but not limiting in scope, the various embodiments of the present invention.

[0018] BRIEF DESCRIPTION OF THE DRAWING

[0019] The accompanying figure constitutes part of this specification and includes an exemplary or preferred embodiment of the present invention, which may be embodied in various forms. It should be understood, however, that the figure disclosed herein is not to be interpreted as restrictive, but rather intended as an illustrative basis for teaching a person having ordinary skill in the art of the present invention.

[0020] In the appended figure:

[0021] FIG. 1 illustrates a typical image of (a) before and (b) after sludge treatment.

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A detailed description of the present invention is described herein. The present invention is directed to a process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stable homogeneous mixture comprising steps of: a) preparing a mixture of a demulsifying agent or solubiliser and a solvent; b) preparing a mixture of hydrochloric acid and an aromatic naphtha; and c) mixing the preparation in step a) with the preparation in step b) to form a thermodynamically stable homogenous mixture.

[0024] Preferably, the demulsifying agent or solubiliser is linear alkyl benzene sulfonic acid present in a fraction of 1-20% or more appropriately 2-10%. Meanwhile, the solvent is 2- butoxyethanol in a fraction of 5-40% or more appropriately 10-30%. The solvent is butane-l-ol in a fraction of 2-20% or more appropriately 3-8%. The hydrochloric acid strength is 10-25% or more appropriately 15-20% and its fraction is 20-60% or more appropriately 30-40%. The aromatic naphtha fraction in the thermodynamically stable homogeneous mixture is 30-60% or more appropriately 30-40%.

[0025] The present invention provides a process for treating metal naphthenates-induced oilfield sludge wherein thermodynamically stable homogeneous mixture prepared is added to a metal naphthenates-induced sludge at a fraction of 5-15% or more appropriately 8-12% which was preheated at 70°C and further mixed vigorously and kept at 70°C temperature for separation of water and oil phases.

[0026] The present invention also provides a process for treating metal naphthenates-induced deposits wherein thermodynamically stable homogeneous mixture prepared was added to a sample of metal naphthenates-induced deposit in the ratio of 15:1 or more appropriately 10:1 at ambient temperature. The mixture containing metal naphthenate deposit and thermodynamically stable homogeneous mixture was observed for dissolution of the deposit

[0027] The present invention also provides a process for treating mixed scales deposit wherein thermodynamically stable homogeneous mixture prepared was added to a sample of mixed scales deposit in the ratio of 15:1 or more appropriately 10:1 at 50° C. The mixture containing mixed scales deposit and thermodynamically stable homogeneous mixture was observed for dissolution of the deposit

[0028] The present invention also provides a process for oil well stimulation wherein thermodynamically stable homogeneous mixture prepared is squeezed in oil well formation for stimulation.

[0029] A typical image of before and after sludge treatment are illustrated in FIG. 1.

[0030] In a preferred embodiment, the present invention provides a process for treating metal naphthenates-induced oilfield sludge. Firstly, a mixture of linear alkyl benzene sulfonic acid and 2-butoxyethanol or butane-l-ol is prepared. Meanwhile, a mixture of hydrochloric acid and aromatic naphtha is prepared separately. Both preparations are then mixed to form a thermodynamically stable homogenous mixture which is used to treat the oilfield sludge which has been pre-treated with heat at 70°C in a water bath for 15 minutes. The contents are mixed after 15 minutes of heating followed by keeping the tube in the water bath for the observation. The observation is carried out every 15 minutes until the sludge is fully separated.

[0031] In another preferred embodiment, the present invention provides a process for treating metal naphthenates-induced deposits. Firstly, a mixture of linear alkyl benzene sulfonic acid and butane-l-ol is prepared. Meanwhile, a mixture of hydrochloric acid and aromatic naphtha is prepared separately. Both preparations are then mixed to form a thermodynamically stable homogenous mixture which is used to treat the deposits and maintained at ambient temperature for four hours. The treated deposits are then subjected to filtration with filter paper leaving only residue and followed by washing with n-hexane. Finally, the filtered and washed residue is dried at 100°C.

[0032] In yet another preferred embodiment, the present invention provides a process for treating mixed and / or wetted oilfield scales. Firstly, a mixture of linear alkyl benzene sulfonic acid and 2-butoxyethanol is prepared. Meanwhile, a mixture of hydrochloric acid and aromatic naphtha is prepared separately. Both preparations are then mixed to form a thermodynamically stable homogenous mixture which is used to treat the mixed and / or wetted oilfield scales and maintained at ambient temperature for eight hours until the scales are fully dissolved.

[0033] The following examples further illustrate but by no means limit the scope of the present invention.

[0034] Example 1:

[0035] Method

[0036] 2g of linear alkyl benzene sulfonic acid and 8g of 2 -butoxyethanol were mixed in one test tube. Separately, 5g of 19.5% HC1 and 5g of aromatic naphtha were mixed in another test tube. Subsequently, 5.7g of mixture from the first tube was added in the second tube with mild stirring until a thermodynamically stable homogenous mixture was formed.

[0037] Next, 25g of metal naphthenate sludge was placed in a graduated tube and heated to 70°C in a water bath for 15 minutes, followed by the introduction of 2.5ml homogeneous solution in the sludge with mixing and finally placed in the water bath for 15 minutes. The process of mixing the content of the tube was again done after 15 minutes followed by placing the tube in the water bath for observation.

[0038] Results

[0039] Observation on the sludge resolution was carried out every 15 minutes. The sludge was separated fully in an hour and 45 minutes.

[0040] Example 2:

[0041] Method

[0042] 9g of linear alkyl benzene sulfonic acid and lg of butane-l-ol were mixed in one test tube. Separately, 3g of 15% HC1 and 7g of aromatic naphtha were mixed in another test tube. Subsequently, 8.7g of mixture from the first tube was added in the second tube with mild stirring until a thermodynamically stable homogenous mixture was formed. Next, 25g of metal naphthenate sludge was placed in a graduated tube and heated to 70 °C in a water bath for 15 minutes, followed by the introduction of 2ml homogeneous solution in the sludge with mixing and finally placed in the water bath for 15 minutes. The process of mixing the content of the tube was done once more after 15 minutes followed by placing the tube in the water bath for observation.

[0043] Results

[0044] Observation on the sludge resolution was carried out every 15 minutes. The sludge was separated fully in an hour and 45 minutes.

[0045] Example 3:

[0046] Method

[0047] 9g of linear alkyl benzene sulfonic acid and lg of butane-l-ol were mixed in one test tube. Separately, 3g of 15% HC1 and 7g of aromatic naphtha were mixed in another test tube. Subsequently, 8.7g of mixture from the first tube was added in the second tube with mild stirring until a thermodynamically stable homogenous mixture was formed.

[0048] Next, lg of metal naphthenate deposit placed in a test tube, followed by the introduction of 10ml homogeneous mixture. The test tube was kept at ambient temperature for four hours. Contents of the tube were filtered through a pre-weighed filter paper and washed with n-hexane. The residue was dried at 100°C and weighed.

[0049] Results

[0050] It was found that 76% of the deposit was dissolved in the solution.

[0051] Example 4:

[0052] Method

[0053] 2g of linear alkyl benzene sulfonic acid and 8 g of 2-butoxyethanol were mixed in one test tube. Separately, 5g of 19.5% HC1 and 5g of aromatic naphtha were mixed in another test tube. Subsequently, 5.7g of mixture from the first tube was added in the second tube with mild stirring until a thermodynamically stable homogenous mixture was formed.

[0054] Next, lg of mixed scales sample comprising calcite and intra-matrix wax was placed in a test tube. 10ml homogeneous mixture was added into the test tube and was kept at 50QC temperature for eight hours.

[0055] Results

[0056] It was found that the scales were fully dissolved in the solution.

[0057] Having described preferred embodiments of the present invention with reference to the accompanying figures, it is not intended that these embodiments and examples illustrate and describe all possible forms of the present invention, and that various changes and modifications may be effected therein by a person having ordinary skill in the art without departing from the scope of the present invention as defined in the appended claims.

Claims

CLAIMS1. A process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stable homogeneous mixture comprising steps of: a) preparing a mixture of a demulsifying agent or solubiliser and a solvent; b) preparing a mixture of hydrochloric acid and an aromatic naphtha; and c) mixing the preparation in step a) with the preparation in step b) to form a thermodynamically stable homogenous mixture.

2. The process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stable homogeneous mixture according to claim 1 wherein the demulsifying agent or solubiliser is linear alkyl benzene sulfonic acid present in a fraction of 1-20% or more appropriately 2-10%.

3. The process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stable homogeneous mixture according to claim 1 wherein the solvent is 2-butoxyethanol in a fraction of 5-40% or more appropriately 10-30%.

4. The process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stable homogeneous mixture according to claim 1 wherein the solvent is butane- l-ol in a fraction of 2-20% or more appropriately 3-8%.

5. The process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stable homogeneous mixture according to claim 1 wherein the hydrochloric acid strength is 10-25% or more appropriately 15-20% and its fraction is 20-60% or more appropriately 30-40%.

6. The process for treating metal naphthenates-induced oilfield sludge, metal naphthenate deposits or oilfield mixed scales by preparing a thermodynamically stablehomogeneous mixture according to claim 1 wherein the aromatic naphtha fraction in the thermodynamically stable homogeneous mixture is 30-60% or more appropriately 30-40%.

7. The process for treating metal naphthenates-induced oilfield sludge wherein thermodynamically stable homogeneous mixture prepared according to claim 1 is added to a metal naphthenate induced sludge to form a sludge-mixture at a fraction of 5-15% or more appropriately 8-12% which was preheated at 70°C.

8. The process for treating metal naphthenates-induced oilfield sludge wherein the sludge-mixture obtained in claim 7 was further mixed vigorously and kept at 70° C temperature for separation of water and oil phases.

9. A process for treating metal naphthenates-induced deposits wherein thermodynamically stable homogeneous mixture prepared according to claim 1 was added to a sample of metal naphthenates-induced deposit in the ratio of 15:1 or more appropriately 10:1 at ambient temperature.

10. The process for treating metal naphthenates-induced deposits according to claim 9 wherein mixture containing metal naphthenate deposit and thermodynamically stable homogeneous mixture was observed for dissolution of the deposit.

11. A process for treating mixed scales deposit wherein thermodynamically stable homogeneous mixture prepared according to claim 1 was added to a sample of mixed scales deposit in the ratio of 15:1 or more appropriately 10:1 at 50° C.

12. The process for treating mixed scale deposits according to claim 11 wherein mixture containing mixed scales deposit and thermodynamically stable homogeneous mixture was observed for dissolution of the deposit.

13. The process for oil well stimulation wherein thermodynamically stable homogeneous mixture prepared according to claim 1 is squeezed in oil well formation for stimulation.

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