Oil-based drilling fluid flocculant and preparation method thereof

Abstract

The invention discloses an oil-based drilling fluid flocculant and a preparation method thereof. The flocculant comprises the following steps: step 1: adding divinylbenzene and hexadecyldimethylallyl ammonium chloride to an octadecyl acrylate solution and fully mixing; step 2: adding an initiator, condensing and refluxing under a protective atmosphere, and stirring for reaction; after the reaction is completed, filtering and drying to obtain the flocculant; the molar ratio of the octadecyl acrylate, divinylbenzene and hexadecyldimethylallyl ammonium chloride is 15-60:5-20:5-20; the quaternary ammonium group in the flocculant obtained by the invention has strong adsorption capacity and can adsorb cuttings dispersed in the oil-based drilling fluid, while providing conditions for the flocculant to selectively flocculate; the main chain atoms of the flocculant are soluble in oil and have good dispersibility, so that the flocculant has a good flocculation effect in the drilling fluid.

Description

Technical Field

[0001] The present invention relates to the technical field of flocculants, and in particular to an oil-based drilling fluid flocculant and a preparation method thereof. Background Art

[0002] In recent years, my country's oil and gas exploration technology has continuously advanced into deeper regions, and the formation conditions encountered during drilling have become increasingly complex. Water-based drilling fluids are no longer able to meet these requirements. Oil-based drilling fluids offer superior wellbore stability, inhibition, lubricity, temperature resistance, and contamination resistance compared to water-based fluids. They are the preferred choice for high-difficulty wells such as unconventional oil and gas wells, complex well structures, deep and ultra-deep water wells, high-temperature and high-pressure deep wells, and ultra-deep wells.

[0003] Due to factors such as the high cost of oil-based drilling fluids, they are typically recycled. However, prolonged drilling operations can increase the concentration of cuttings in the fluid, leading to increased viscosity. This can lead to slower drilling times, excessive pressure during tripping, deteriorating lubricity, increased fluid loss, and, in severe cases, wellbore instability. Currently, the primary method for reducing cuttings in oil-based drilling fluids is through solids control equipment. However, this method only removes larger cuttings and has little effect on micro- and nano-sized cuttings. Flocculants can aggregate and enlarge micro- and nano-sized cuttings, reaching the particle size required by solids control equipment for removal.

[0004] For example, publication number CN109652026A discloses a "method for preparing a flocculant flow pattern regulator for oil-based drilling fluid," comprising the following steps: (1) adding nano-activated carbon to a beaker equipped with a stirrer and a thermometer; (2) adding a low-viscosity synthetic base oil to the reactor of step (1) and stirring at 50°C to 90°C for 3 to 6 hours; (3) adding an emulsifier to the reactor of step (1) and stirring for 3 to 6 hours; (4) adding a wetting agent to the reactor of step (1) and stirring for 3 to 5 hours. The resulting suspension is a flocculant flow pattern regulator for oil-based drilling fluid. This method can reduce the content of finely dispersed particles in oil-based drilling fluid, but the flocculation effect is average.

[0005] For example, publication number CN113292731A discloses a "method for preparing a flocculant for removing rock cuttings from oil-based drilling fluids," comprising the following steps: (1) a hydrophilic monomer, a cationic monomer, and glycidyl methacrylate are subjected to a first polymerization reaction in the presence of a first solvent and a first initiator to prepare a prepolymer A; (2) an oil-soluble monomer, acrylamide, and 2-mercaptoethylamine hydrochloride are subjected to a second polymerization reaction in the presence of a dispersant, a second solvent, and a second initiator to prepare a prepolymer B; and (3) prepolymers A and B are subjected to a graft polymerization reaction to prepare a flocculant. This method has a cumbersome synthesis process and a relatively limited flocculation effect. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the present invention provides an oil-based drilling fluid flocculant and a preparation method thereof.

[0007] The technical solution adopted in the present invention is:

[0008] A method for preparing an oil-based drilling fluid flocculant comprises the following steps:

[0009] Step 1: Add divinylbenzene and hexadecyldimethylallyl ammonium chloride to the octadecyl acrylate solution and mix thoroughly;

[0010] Step 2: Add initiator, condense and reflux under protective atmosphere, stir and react; after the reaction is completed, filter and dry to obtain flocculant;

[0011] The molar ratio of octadecyl acrylate, divinylbenzene and hexadecyldimethylallyl ammonium chloride is 15-60:5-20:5-20.

[0012] Furthermore, the cationic monomer is one of hexadecyldimethylallyl ammonium chloride, dimethylallyldipropyl ammonium chloride and methacryloyloxyethyltrimethylammonium chloride.

[0013] Furthermore, the initiator is any one of potassium persulfate, ammonium persulfate, azobisisobutyl cyanide, potassium persulfate and sodium sulfite, ammonium persulfate and sodium bisulfite; wherein potassium persulfate and sodium sulfite are mixed in any proportion, and ammonium persulfate and sodium bisulfite are mixed in any proportion.

[0014] Furthermore, the mass ratio of the initiator to the monomer is 0.5 to 3:100, and the mass of the monomer is the total amount of octadecyl acrylate, divinylbenzene, and hexadecyldimethylallylammonium chloride.

[0015] Furthermore, in step 1, the solvent of the octadecyl acrylate solution is anhydrous ethanol, and the octadecyl acrylate and anhydrous ethanol are ultrasonically treated for 20 minutes to fully dissolve them.

[0016] Furthermore, in step 2, after adding the initiator, argon is passed through for 30 minutes, the temperature is raised to 50-65° C., and the mixture is condensed and refluxed.

[0017] Furthermore, in step 2, the stirring speed is 300-800 rpm, and the stirring reaction is carried out for 4-12 hours.

[0018] Furthermore, in step 2, the mixture is washed with anhydrous ethanol for three times and then dried at 60° C. for 12 hours.

[0019] The invention discloses an oil-based drilling fluid flocculant, which is obtained by polymerization reaction of octadecyl acrylate, divinylbenzene and hexadecyl dimethyl allyl ammonium chloride under the initiation of an initiator.

[0020] The beneficial effects of the present invention are:

[0021] (1) The preparation method of the present invention is simple to operate, has little pollution, is relatively environmentally friendly, and has low requirements for production equipment;

[0022] (2) The main chain atoms of the flocculant obtained by the present invention are soluble in oil and have good dispersibility, so that it has a good flocculation effect in the drilling fluid;

[0023] (3) The quaternary ammonium groups in the flocculant obtained by the present invention have strong adsorption properties and can adsorb cuttings dispersed in the oil-based drilling fluid, while providing conditions for the flocculant to selectively flocculate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the infrared spectrum of the flocculant obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] A method for preparing an oil-based drilling fluid flocculant comprises the following steps:

[0027] Step 1: Add divinylbenzene and a cationic monomer to the octadecyl acrylate solution and mix thoroughly; the cationic monomer is one of hexadecyldimethylallyl ammonium chloride, dimethylallyldipropyl ammonium chloride and methacryloyloxyethyltrimethylammonium chloride.

[0028] First, place octadecyl acrylate in a beaker and add anhydrous ethanol. Ultrasonicate for 20 minutes to fully dissolve it to obtain an octadecyl acrylate solution. The optimal mass ratio of octadecyl acrylate to anhydrous ethanol is 16:120. Add divinylbenzene and a cationic monomer to the octadecyl acrylate solution, stir thoroughly, and transfer to a three-necked flask.

[0029] The molar ratio of octadecyl acrylate, divinylbenzene and cationic monomer is 15-60:5-20:5-20.

[0030] Step 2: Add initiator, pass argon for 30 minutes, heat to 50-65°C, condense and reflux with high-speed stirring for 4-12 hours, and the stirring speed is 300-800 rpm.

[0031] The initiator is one of potassium persulfate, ammonium persulfate, azobisisobutyl cyanide, potassium persulfate and sodium sulfite, ammonium persulfate and sodium bisulfite, wherein the total mass ratio of the monomers to the mass of the initiator is 100:0.5-3.

[0032] After the reaction is completed, the product in the three-necked flask is vacuum filtered for excess liquid, the filtered white solid is repeatedly washed 3 times with ethanol, and placed in a vacuum oven at 60°C for 12 hours. The drying requirement is that the ethanol content in the flocculant is less than 5%, and a flocculant is obtained.

[0033] Example 1

[0034] A method for preparing an oil-based drilling fluid flocculant comprises the following steps:

[0035] Step 1: Place 16.7 g of octadecyl acrylate in a beaker, add 120 g of anhydrous ethanol, and sonicate for 20 minutes to fully dissolve it to obtain an octadecyl acrylate solution;

[0036] 2.8 g of divinylbenzene and 10.3 g of hexadecyldimethylallylammonium chloride were added to the octadecyl acrylate solution, and the mixture was stirred thoroughly and then transferred to a three-necked flask.

[0037] Step 2: Add 0.45g of azobisisobutyronitrile (ABI) as an oil-soluble initiator at 25°C, flow argon for 30 minutes to eliminate oxygen from the system, and heat to 65°C in a water bath. Stir at 300 rpm for 12 hours, and vacuum filter to obtain a white oil-based drilling fluid flocculant. The flocculant is washed three times with ethanol and dried in a vacuum oven at 60°C for 12 hours, with the ethanol content in the flocculant being less than 5%.

[0038] Figure 1 The infrared spectrum of the flocculant obtained in this example shows that the copolymer has an SDCD structure. -1 and 2851cm -1 The stretching vibration peaks of -CH3 and -CH2 are 1731cm -1 The characteristic peak of carbonyl C=O is at 1467 cm -1 The characteristic peak of disubstituted benzene ring is 1377cm -1 The characteristic absorption peak of -CH2 connected to nitrogen cation is 1269cm -1 The COC contraction vibration peak is at 700-1000 cm -1 There is no strong absorption peak between them, indicating that the double bonds are basically polymerized.

[0039] Example 2

[0040] A method for preparing an oil-based drilling fluid flocculant comprises the following steps:

[0041] Step 1: Place 16.7 g of octadecyl acrylate in a beaker, add 120 g of anhydrous ethanol, and sonicate for 20 minutes to fully dissolve it to obtain an octadecyl acrylate solution;

[0042] 2.8 g of divinylbenzene and 10.3 g of dimethylallyldipropylammonium chloride were added to the octadecyl acrylate solution, and the mixture was stirred thoroughly and then transferred to a three-necked flask.

[0043] Step 2: Add 0.45g of azobisisobutyronitrile (ABI) as an oil-soluble initiator at 25°C, flow argon for 30 minutes to eliminate oxygen from the system, and heat to 65°C in a water bath. Stir at 600 rpm for 6 hours, and vacuum filter to obtain a white oil-based drilling fluid flocculant. The flocculant is washed three times with ethanol and dried in a vacuum oven at 60°C for 12 hours, with the ethanol content in the flocculant being less than 5%.

[0044] Example 3

[0045] A method for preparing an oil-based drilling fluid flocculant comprises the following steps:

[0046] Step 1: Place 16.7 g of octadecyl acrylate in a beaker, add 120 g of anhydrous ethanol, and sonicate for 20 minutes to fully dissolve it to obtain an octadecyl acrylate solution;

[0047] 2.8 g of divinylbenzene and 10.3 g of methacryloyloxyethyltrimethylammonium chloride were added to the octadecyl acrylate solution, and the mixture was fully stirred and then transferred to a three-necked flask.

[0048] Step 2: Add 0.45g of azobisisobutyronitrile (ABI) as an oil-soluble initiator at 25°C, flow argon for 30 minutes to eliminate oxygen from the system, and heat to 65°C in a water bath. Stir at 800 rpm for 4 hours, and vacuum filter to obtain a white oil-based drilling fluid flocculant. The flocculant is washed three times with ethanol and dried in a vacuum oven at 60°C for 12 hours, with the ethanol content in the flocculant being less than 5%.

[0049] Example 4

[0050] The preparation method of this embodiment is the same as that of Example 1, except that the mass of hexadecyldimethylallylammonium chloride is 20 g.

[0051] Example 5

[0052] The preparation method of this embodiment is the same as that of embodiment 1, except that the temperature in step 2 is 50°C.

[0053] Example 6

[0054] The preparation method of this embodiment is the same as that of Example 1, except that the mass of divinylbenzene is 8.93 g.

[0055] Example 7

[0056] The preparation method of this embodiment is the same as that of Example 1, except that the mass of divinylbenzene is 0.56 g.

[0057] Comparative Example 1

[0058] The preparation method of this embodiment is the same as that of embodiment 1, except that octadecyl acrylate is replaced by methyl methacrylate.

[0059] Comparative Example 2

[0060] The preparation method of this embodiment is the same as that of Example 1, except that hexadecyldimethylallyl ammonium chloride is not added.

[0061] The flocculants prepared in Examples 1 to 5 and Comparative Examples 1 to 2 were used to treat oil-based drilling fluids to evaluate the performance of the flocculants.

[0062] The plastic viscosity (mPa·s), shear force (Pa), and initial and final shear force (Pa) of the drilling fluid were measured using a six-speed viscometer according to the method specified in GB / T16783.2-2012.

[0063] The median solid particle size of the drilling fluid was tested using Zeta PALS190Plus (Brookhaven, USA).

[0064] The density of the drilling fluid, the low-density solid content, and the barite solid content in the drilling fluid are measured according to the method specified in GB / T16783.2-2012. Unless otherwise specified, the low-density solid content and the barite solid content refer to the volume content.

[0065] The manufacturer of the six-speed viscometer is Qingdao Tongchun Petroleum Instrument Co., Ltd., model number is ZNN-D6B;

[0066] The manufacturer of the low-speed mixer is Qingdao Tongchun Petroleum Instrument Co., Ltd., model D90;

[0067] Preparation of spent drilling fluid samples:

[0068] Add 315mL of 5# white oil to the slurry cup, and add 2% organic soil, 3% primary emulsifier, 0.5% auxiliary emulsifier, and 35mL of brine (25% CaCl2) in sequence under continuous stirring, and stir at 12000r / min for 20min. Then add 3% CaO, 1% wetting agent, and appropriate amount of barite in sequence, and stir at 12000r / min for 40min. Add rock cuttings (kaolin) to the base slurry and continue high-speed stirring for 20min. Heat at 150℃ for 16h. The density of the oil-based drilling fluid is 1.5g / cm 3 , the rock fragments content is 10% and the barite content is 28%.

[0069] The flocculated solid phase components and density test methods after adding flocculants to drilling fluid are as follows:

[0070] Waste oil-based drilling fluid was poured into an enamel cup and stirred at low speed while the obtained organic drilling fluid flocculant was added. The fluid was stirred at low speed for 20 minutes to fully disperse it. The fluid was allowed to rest for 15 minutes before being poured through a 200-mesh sieve and vibrated to remove the solid phase from the waste drilling fluid. The solid phase on the sieve surface was then extracted using a Soxhlet extractor with cyclohexane at 120°C for 24 hours and then dried at 80°C to obtain a flocculated solid phase. The test results are shown in Table 1.

[0071] Table 1. Density and solid content of waste oil-based drilling fluid after flocculation and screening

[0072]

[0073]

[0074] As can be seen from Table 1, after adding the flocculant to the waste oil-based drilling fluid sample for treatment, the content of the inferior solid phase in the flocculated solid phase obtained is greater than 50 wt.%. It can be seen that the flocculant provided by the present invention has a good selective flocculation effect on the inferior solid phase in the oil-based drilling fluid, while the flocculation effect on barite is relatively weak, so that the oil-based drilling fluid after flocculation treatment can maintain good performance.

[0075] In Examples 1 to 5 of the present invention, more than 10 wt.% of barite can still be detected in the flocculated solid phase. This is because during the screening process of the flocculated drilling fluid, drilling fluid is inevitably adsorbed on the surface of the flocculated solid phase. After washing with cyclohexane, the solid phase (including barite) in the adsorbed drilling fluid remains in the flocculated solid phase.

[0076] The flocculant obtained in Comparative Example 1, due to the short hydrocarbon carbon chain of methyl methacrylate, has poor solubility in waste oil-based drilling fluid. After addition, it interacts with the aqueous phase, significantly increasing viscosity and preventing the waste oil-based drilling fluid from being sieved. Therefore, oil-based drilling fluid flocculants cannot be used to recycle waste oil-based drilling fluid.

[0077] The flocculant obtained in Comparative Example 2 lacked hexadecyldimethylallylammonium chloride, resulting in a product lacking cations, significantly weakening its adsorption effect on rock debris. Consequently, the rock debris content in the solid phase after screening was low. Furthermore, its flocculation effect on barite was also weak, resulting in essentially no flocculation effect. The resulting recovered liquid failed to meet applicable standards in terms of density and solids content.

[0078] The flocculants obtained in Examples 1 to 5 of the present invention were used to evaluate the slurry matching performance of the recovered liquid phase after flocculation and screening of waste oil-based drilling fluid.

[0079] 2.5 wt % of the flocculants prepared in Examples 1 to 5 of the present invention and Comparative Examples 1 to 2 were added to 300 mL of an oil-based drilling fluid sample (serving as a base slurry), respectively. The sample was stirred at 100 r / min for 20 minutes using a low-speed stirrer to flocculate the oil-based drilling fluid. The sample was allowed to stand for 15 minutes and then screened with a 200-mesh sieve to obtain a flocculated drilling fluid. The rheological parameters (apparent viscosity, plastic viscosity, dynamic shear force) of the treated drilling fluid, as well as the median solid phase particle size after the addition of the flocculant, are shown in Table 2.

[0080] Table 2. Performance evaluation of waste oil-based drilling fluid after flocculation and screening

[0081]

[0082]

[0083] As can be seen from the table, after the flocculant obtained by the present invention was added to the waste oil-based drilling fluid sample for treatment, the median solid phase particle size of the drilling fluid was significantly increased from 10μm to more than 60μm. Among them, the median solid phase particle size of the drilling fluid in Examples 1, 4, and 5 was increased to more than 80μm after flocculation treatment. As can be seen from Table 2, the flocculant provided by the present invention has a significant flocculation effect on micro-nano-level fine rock cuttings in the waste oil-based drilling fluid sample, thereby significantly increasing the median solid phase particle size of the drilling fluid. The hydrocarbon carbon chain of methyl methacrylate used in the comparative example is relatively short, and its solubility in the waste oil-based drilling fluid is poor. It cannot produce a flocculation effect with the rock cuttings in the system. However, since it will combine with water to make the system viscous, causing some rock cuttings to agglomerate together, the median particle size is slightly larger than the sample slurry. In Comparative Example 2, since hexadecyldimethylallyl ammonium chloride was not added, there was no flocculation effect on the rock cuttings, so the median particle size is very close to that of the sample.

[0084] In terms of drilling fluid rheology, after adding the flocculant provided by the present invention to waste oil-based drilling fluid samples for flocculation treatment, the flocculated solid phase was removed. The apparent viscosity, plastic viscosity, and dynamic shear force of Examples 1-5 all decreased, significantly improving the performance of the treated waste oil-based drilling fluid. The oil-based drilling fluid flocculant prepared by the present invention can significantly reduce the amount of oil-based waste after recycling and treatment, and reduce the cost of oil-based drilling fluid preparation by recycling waste oil-based drilling fluid, facilitating the large-scale and cost-effective application of oil-based drilling fluid technology.

Claims

1. A method for preparing an oil-based drilling fluid flocculant, characterized in that: The following steps are involved: Step 1: Add divinylbenzene and cationic monomer to the octadecyl acrylate solution and mix thoroughly; the cationic monomer is hexadecyl dimethyl allyl ammonium chloride; Step 2: Add initiator, condense and reflux under protective atmosphere, stir and react; after the reaction is completed, filter and dry to obtain flocculant; The molar ratio of octadecyl acrylate, divinylbenzene and cationic monomer is 15-60:5-20:5-20.

2. The method for preparing an oil-based drilling fluid flocculant according to claim 1, wherein: The initiator is any one of potassium persulfate, ammonium persulfate, azobisisobutyronitrile, potassium persulfate and sodium sulfite, ammonium persulfate and sodium bisulfite; wherein potassium persulfate and sodium sulfite are mixed in any proportion, and ammonium persulfate and sodium bisulfite are mixed in any proportion.

3. The method for preparing an oil-based drilling fluid flocculant according to claim 1, wherein: The mass ratio of the initiator to the monomer is 0.5 to 3:100, and the mass of the monomer is the total amount of octadecyl acrylate, divinylbenzene, and hexadecyldimethylallyl ammonium chloride.

4. The method for preparing an oil-based drilling fluid flocculant according to claim 1, wherein: In the step 1, the solvent of the octadecyl acrylate solution is anhydrous ethanol, and the octadecyl acrylate and the anhydrous ethanol are ultrasonically treated for 20 minutes to fully dissolve them.

5. The method for preparing an oil-based drilling fluid flocculant according to claim 1, wherein: In the step 2, after adding the initiator, argon was passed through for 30 minutes, the temperature was raised to 50-65° C., and the mixture was condensed and refluxed.

6. The method for preparing an oil-based drilling fluid flocculant according to claim 1, characterized in that: In step 2, the stirring speed is 300-800 rpm, and the stirring reaction is carried out for 4-12 hours.

7. The method for preparing an oil-based drilling fluid flocculant according to claim 1, characterized in that: In step 2, the product was washed with anhydrous ethanol for three times and then dried at 60° C. for 12 h.

8. The oil-based drilling fluid flocculant obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The oil-based drilling fluid flocculant is obtained by polymerization reaction of octadecyl acrylate, divinylbenzene and hexadecyl dimethyl allyl ammonium chloride under the initiation of an initiator.

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