Filtrate reducer for drilling fluid, preparation method of filtrate reducer and drilling fluid

Abstract

The invention relates to a fluid loss additive for a drilling fluid, a preparation method of the fluid loss additive and the drilling fluid. The fluid loss additive for the drilling fluid comprises starch, an alkenyl amide monomer, an alkenyl phosphate monomer, an olefine acid monomer and an alkenyl monomer with a cyclic group on a side base. According to the filtrate reducer for the drilling fluid, provided by the invention, the starch is modified by selecting specific monomers, and the high temperature resistance, the calcium resistance and the salt resistance of the starch filtrate reducer are improved by utilizing the synergistic promotion effect of multiple monomers, so that the usability of the starch filtrate reducer is improved, the high temperature resistance of the filtrate reducer for the drilling fluid can reach 200 DEG C and is obviously improved compared with the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum extraction, and in particular to a fluid loss reducer for drilling fluid, a preparation method thereof, and drilling fluid. Background Art

[0002] At present, oil and gas exploration and development are gradually developing towards deep formations, offshore and environmentally sensitive formations. Environmental protection and temperature resistance issues are becoming more and more prominent. Controlling the pollution of drilling fluid to the environment from the source, developing environmentally friendly and temperature-resistant green drilling fluid treatment agents, and achieving "green" drilling are effective ways to solve environmental problems. As one of the important treatment agents for water-based drilling fluids, fluid loss reducers play an important role in ensuring safe, fast and efficient drilling.

[0003] As a natural resource, starch is abundant, inexpensive, non-toxic, easy to degrade, and has good environmental adaptability. It is an important oilfield chemical. Its modified fluid loss reducer products are mostly non-toxic, environmentally friendly, low-cost, widely available, and highly resistant to salt and calcium. However, starch-based fluid loss reducers have poor temperature resistance, generally resistant to temperatures not exceeding 130°C, and a few starch-based fluid loss reducers have a temperature resistance of up to 140°C, which greatly limits their promotion and application.

[0004] In order to improve the performance of starch-based fluid loss reducers, starch is usually modified in the prior art to improve its performance. For example, CN102899005A discloses a high temperature, salt and calcium resistant fluid loss reducer for drilling fluid and its preparation method. The fluid loss reducer is made of the following raw materials in parts by mass, based on 100 parts of raw materials: 50-80 parts of starch, 8-20 parts of phosphate, 1-8 parts of urea, 1-10 parts of polyethylene glycol, 1-3 parts of sodium sulfite, and the rest is water; it is prepared by the following method: according to the ratio, phosphate, urea, polyethylene glycol, and sodium bisulfite are dissolved in water to form a mixed solution, the mixed solution is sprayed on the starch, stirred evenly, placed in a constant temperature drying oven, and reacted at 130℃-180℃ for 4-10h. However, its temperature resistance is also around 150℃, and its performance is still poor.

[0005] In summary, the starch-based fluid loss reducers used in the prior art still have the problems of poor high temperature performance, calcium resistance and salt resistance. Summary of the invention

[0006] In view of the problems existing in the prior art, the object of the present invention is to provide a fluid loss reducer for drilling fluid and a preparation method thereof, and drilling fluid, so as to solve the problems that starch-based fluid loss reducers still have poor high temperature performance, calcium resistance and salt resistance.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a fluid loss reducer for drilling fluid, wherein the fluid loss reducer for drilling fluid comprises starch, alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers and alkenyl monomers with side groups having cyclic groups.

[0009] The drilling fluid reducer provided by the present invention selects specific monomers to modify starch, and utilizes the synergistic promotion effect between multiple monomers to achieve the improvement of the high temperature resistance, calcium resistance and salt resistance of the starch-based fluid loss reducer, which is beneficial to improving the usability of the starch-based fluid loss reducer. Among them, the high temperature resistance of the obtained drilling fluid fluid loss reducer can reach 200°C, which is significantly improved compared with the prior art.

[0010] As a preferred technical solution of the present invention, the mass ratio of starch, alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers and alkenyl monomers with side groups having cyclic groups in the drilling fluid loss reducer is (10-50):(1-10):(1-10):(1-20):(1-10).

[0011] As a preferred technical solution of the present invention, the vinyl amide monomer includes one or a combination of at least two of acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dipropylacrylamide, N-isopropylacrylamide, N-hydroxymethylacrylamide, N,N-diisopropylacrylamide, N,N-dibutylacrylamide, N-vinylacetamide or N-vinylmethylacetamide.

[0012] Preferably, the alkenyl phosphate monomers include dimethyl vinyl phosphate and / or diethyl vinyl phosphate.

[0013] Preferably, the olefinic acid monomers include olefinic sulfonic acid monomers and / or acrylic acid monomers.

[0014] Preferably, the acrylic monomer includes one or a combination of at least two of acrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, methacrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, sodium 2-acrylamide-2-methylpropane sulfonate, allyl sulfonic acid, acryloxybutyl sulfonic acid, 2-acryloxy-2-methylpropane sulfonic acid or 2-acrylamidododecyl sulfonic acid.

[0015] Preferably, the olefinic monomer having a cyclic group on the side group includes one or a combination of at least two of N-vinyl pyrrolidone, N-vinyl caprolactam, vinyl cyclopentane, N-benzyl-3-pyrrolidone or (R)-4-benzyl-2-oxazolidinone.

[0016] In a second aspect, the present invention provides a method for preparing the fluid loss reducer for drilling fluid as described in the first aspect, the preparation method comprising:

[0017] The starch and the cross-linking agent are cross-linked according to the formula to obtain an intermediate product;

[0018] The intermediate product, the monomer mixture and the initiator are mixed and then subjected to polymerization reaction to obtain a fluid loss reducer for drilling fluid.

[0019] As a preferred technical solution of the present invention, the mass ratio of the starch to the cross-linking agent is 100:(0.5-5).

[0020] Preferably, the cross-linking agent comprises an organic acid and / or an inorganic acid.

[0021] As a preferred technical solution of the present invention, the temperature of the cross-linking treatment is 20-55°C.

[0022] Preferably, the cross-linking treatment time is 1.5-3h.

[0023] Preferably, the pH value of the intermediate product is 9-10.

[0024] As a preferred technical solution of the present invention, the monomer mixture is obtained by mixing alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers, alkenyl monomers with side groups having cyclic groups, and a solvent;

[0025] Preferably, the pH value of the monomer mixture is 6.5-7.5.

[0026] As a preferred technical solution of the present invention, the added amount of the initiator is 0.1-1% by mass of the monomer mixture.

[0027] Preferably, the initiator comprises one or a combination of at least two of ammonium persulfate, potassium persulfate, benzoyl peroxide, azobisisobutyronitrile or azobisisoheptanenitrile.

[0028] As a preferred technical solution of the present invention, the polymerization reaction is carried out under a protective atmosphere.

[0029] Preferably, the polymerization temperature is 50-80°C.

[0030] Preferably, the polymerization reaction time is 3-5h.

[0031] In a third aspect, the present invention provides a drilling fluid, wherein the drilling fluid comprises the fluid loss reducer for drilling fluid as described in the first aspect.

[0032] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0033] (1) The fluid loss reducer provided by the present invention cross-links and modifies starch to enhance the hydrogen bonds that maintain the structure of starch granules, thereby enhancing the toughness and hydrophobicity of the granules. At the same time, by introducing functional groups and utilizing the synergistic effect between the groups, the temperature resistance, salt resistance and calcium resistance of starch are improved.

[0034] (2) The filtrate reducer for drilling fluid provided by the present invention is environmentally friendly, has a temperature resistance of up to 200°C, and has good salt and calcium resistance, and is suitable for drilling operations in deep or ultra-deep wells, shale gas horizontal wells, and environmentally sensitive areas. DETAILED DESCRIPTION

[0035] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0036] The present embodiment provides a fluid loss reducer for drilling fluid, which includes starch, alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers, and alkenyl monomers with cyclic groups on the side groups.

[0037] Specifically, the mass ratio of the starch, alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers and alkenyl monomers with side groups having cyclic groups in the drilling fluid loss reducer is (10-50):(1-10):(1-10):(1-20):(1-10), for example, it can be 10:1:1:1:1, 20:1:1:1:1, 30:1:1:1:1, 40:1:1:1:1, 50:1:1:1:1, 1:1:1:1:1, 1:1:1:2:1 or 5:1:1:2:1, but is not limited to the listed range, and other values ​​not listed within the range also meet the requirements.

[0038] In the present invention, the starch includes cereal starch, potato starch, bean starch and other commonly used starches in the art, and one or a combination of at least two can be selected.

[0039] Specifically, the vinyl amide monomer includes one or a combination of at least two of acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dipropylacrylamide, N-isopropylacrylamide, N-hydroxymethylacrylamide, N,N-diisopropylacrylamide, N,N-dibutylacrylamide, N-vinylacetamide or N-vinylmethylacetamide.

[0040] Exemplarily, the combination of alkenyl amide monomers is a combination of acrylamide and N,N-dimethylacrylamide, a combination of N,N-diethylacrylamide and N,N-dipropylacrylamide, a combination of N-isopropylacrylamide and N-hydroxymethylacrylamide, a combination of N,N-diisopropylacrylamide and N,N-dibutylacrylamide, a combination of N-vinylacetamide and N-vinylmethylacetamide, and the like.

[0041] Specifically, the alkenyl phosphate monomers include vinyl dimethyl phosphate and / or vinyl diethyl phosphate.

[0042] Specifically, the olefinic acid monomers include olefinic sulfonic acid monomers and / or acrylic acid monomers.

[0043] Specifically, the acrylic monomer includes one or a combination of at least two of acrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, methacrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, sodium 2-acrylamide-2-methylpropane sulfonate, allyl sulfonic acid, acryloxybutyl sulfonic acid, 2-acryloxy-2-methylpropane sulfonic acid or 2-acrylamidododecyl sulfonic acid.

[0044] Illustratively, the combination of the acrylic acid monomers is a combination of acrylic acid and hydroxyethyl acrylate, a combination of hydroxyethyl methacrylate and methacrylic acid, a combination of 2-acrylamide-2-methylpropane sulfonic acid and sodium 2-acrylamide-2-methylpropane sulfonate, a combination of allyl sulfonic acid and acryloxybutyl sulfonic acid, a combination of 2-acryloxy-2-methylpropane sulfonic acid and 2-acrylamidododecyl sulfonic acid, and the like.

[0045] Specifically, the olefinic monomer having a cyclic group on the side group includes one or a combination of at least two of N-vinyl pyrrolidone, N-vinyl caprolactam, vinyl cyclopentane, N-benzyl-3-pyrrolidone or (R)-4-benzyl-2-oxazolidinone.

[0046] Illustratively, the combination of olefinic monomers having side groups with cyclic groups is a combination of N-vinyl pyrrolidone and N-vinyl caprolactam, a combination of vinyl cyclopentane and N-benzyl-3-pyrrolidone, and a combination of N-vinyl pyrrolidone and (R)-4-benzyl-2-oxazolidinone.

[0047] Furthermore, this embodiment provides a method for preparing the aforementioned fluid loss reducer for drilling fluid, the preparation method comprising:

[0048] The starch and the cross-linking agent are cross-linked according to the formula to obtain an intermediate product;

[0049] The intermediate product, the monomer mixture and the initiator are mixed and then subjected to polymerization reaction to obtain a fluid loss reducer for drilling fluid.

[0050] Specifically, the mass ratio of starch to cross-linking agent is 100:(0.5-5), for example, it can be 100:0.5, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, 100:3.5, 100:4, 100:4.5 or 100:5, etc., but is not limited to the listed range, and other unlisted values ​​within the range also meet the requirements.

[0051] Preferably, the cross-linking agent comprises an organic acid and / or an inorganic acid.

[0052] In the present invention, the organic acid includes lactic acid, acetic acid, malic acid, acetic anhydride and the like.

[0053] In the present invention, the inorganic acid includes phosphoric acid, nitric acid, sulfuric acid, and may also be anhydrides of the corresponding inorganic acids.

[0054] Furthermore, the cross-linking agent used in the present invention can also be selected from phosphorus oxychloride, sodium trimetaphosphate or sodium hexametaphosphate and other commonly used cross-linking agents in the art.

[0055] Specifically, the temperature of the cross-linking treatment is 20-55°C, for example, it can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C or 55°C, but is not limited to the listed range, and other unlisted values ​​within the range also meet the requirements.

[0056] Preferably, the cross-linking treatment time is 1.5-3 h, for example, 1.5 h, 2 h, 2.5 h or 3 h, but is not limited to the listed range, and other values ​​not listed within the range also meet the requirements.

[0057] Preferably, the pH value of the intermediate product is 9-10, for example, 9, 9.2, 9.4, 9.6, 9.8 or 10, etc., but is not limited to the listed range, and other values ​​not listed within the range also meet the requirements.

[0058] In the present invention, the pH value of the intermediate product is adjusted by alkali or a strong base or weak acid salt, such as sodium hydroxide, sodium carbonate or sodium bicarbonate.

[0059] Specifically, the monomer mixture is obtained by mixing alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers, alkenyl monomers with side groups having cyclic groups, and a solvent.

[0060] Preferably, the pH value of the monomer mixture is 6.5-7.5, for example, 6.5, 6.6, 6.8, 7, 7.2, 7.4 or 7.5, but is not limited to the listed range, and other values ​​not listed within the range also meet the requirements.

[0061] Specifically, the amount of the initiator added is 0.1-1% by mass of the monomer mixture, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc., but is not limited to the listed range, and other values ​​not listed within the range also meet the requirements.

[0062] Preferably, the initiator comprises one or a combination of at least two of ammonium persulfate, potassium persulfate, benzoyl peroxide, azobisisobutyronitrile or azobisisoheptanenitrile.

[0063] Specifically, the polymerization reaction is carried out under a protective atmosphere.

[0064] In the present invention, the protective atmosphere includes nitrogen, helium, neon, argon and other gases that do not affect the polymerization reaction.

[0065] Preferably, the polymerization reaction temperature is 50-80°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed range, and other values ​​not listed within the range also meet the requirements.

[0066] Preferably, the polymerization reaction time is 3-5 h, for example, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, but is not limited to the listed range, and other values ​​not listed within the range also meet the requirements.

[0067] In the present invention, after the polymerization reaction is completed, washing, drying, baking, crushing and other processes are carried out according to the use requirements to obtain a fluid loss reducer that meets the requirements.

[0068] Furthermore, this embodiment also provides a drilling fluid, which includes the aforementioned fluid loss reducer for drilling fluid.

[0069] In the present invention, the added amount of the drilling fluid fluid loss reducer in the drilling fluid is 1-5% of the total mass of the base slurry.

[0070] In order to further illustrate the high efficiency performance of the drilling fluid fluid loss reducer provided by the present invention, the following specific examples are provided for illustration, as follows:

[0071] Example 1

[0072] This embodiment provides a fluid loss reducer for drilling fluid, which is prepared by the following steps:

[0073] 25 g of potato starch was added to a reactor containing 150 mL of distilled water, and after being fully mixed, 0.3 g of a cross-linking agent (lactic acid and sodium trimetaphosphate, mass ratio of 1:1) was added, the pH value was adjusted to 10 with sodium carbonate, the starch milk was heated to 50° C., and reacted for 1.5 h to obtain an intermediate product;

[0074] 5 g of acrylamide, 5 g of acrylic acid, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 10 g of vinyl dimethyl phosphate and 6 g of N-vinyl pyrrolidone were dissolved in 100 mL of distilled water, and the pH value was adjusted to 7 with sodium hydroxide to obtain a monomer mixture;

[0075] The intermediate product was added to the monomer mixture, the temperature was raised to 60°C under nitrogen protection, 0.15 g of ammonium persulfate was slowly added, the reaction was continued for 4 h, and then the mixture was washed twice with ethanol and distilled water respectively, dried to constant weight in a vacuum drying oven at 20°C, and crushed to obtain a filtrate reducer for drilling fluid.

[0076] Example 2

[0077] This embodiment provides a fluid loss reducer for drilling fluid, which is prepared by the following steps:

[0078] 20 g of potato starch was added to a reactor containing 80 mL of distilled water, and after thorough mixing, 0.8 g of lactic acid and acetic anhydride were added, the pH value was adjusted to 9 with sodium carbonate, the starch milk was heated to 30°C, and reacted for 3 h to obtain an intermediate product;

[0079] 8 g of acrylamide, 6 g of methacrylic acid, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 12 g of vinyl dimethyl phosphate and 8 g of N-vinyl pyrrolidone were dissolved in 120 mL of distilled water, and the pH value was adjusted to 7 with sodium hydroxide to obtain a monomer mixture.

[0080] The intermediate product was added to the monomer mixture, the temperature was raised to 65°C under nitrogen protection, 0.2 g of potassium persulfate was slowly added, the reaction was continued for 3.5 h, and then the mixture was washed twice with ethanol and distilled water respectively, dried to constant weight at 20°C in a vacuum drying oven, and crushed to obtain a fluid loss reducer for drilling fluid.

[0081] Example 3

[0082] This embodiment provides a fluid loss reducer for drilling fluid, which is prepared by the following steps:

[0083] 20 g corn starch was added into a reactor containing 100 mL distilled water, 0.3 g sodium trimetaphosphate and 0.1 g lactic acid were added after thorough mixing, the pH value was adjusted to 10 with sodium carbonate, the starch milk was heated to 50°C, and the reaction was carried out for 2 h to obtain an intermediate product;

[0084] 6 g of acrylamide, 6 g of acrylic acid, 12 g of 2-acrylamido-2-methylpropanesulfonic acid, 10 g of diethyl vinyl phosphate and 5 g of N-benzyl-3-pyrrolidone were dissolved in 100 mL of distilled water, and the pH value was adjusted to 7 with sodium hydroxide to obtain a monomer mixture;

[0085] The intermediate product was added to the monomer mixture, the temperature was raised to 70°C under nitrogen protection, 0.16 g of ammonium persulfate was slowly added, the reaction was continued for 3.5 h, and then the mixture was washed twice with ethanol and distilled water respectively, dried to constant weight in a vacuum drying oven at 20°C, and crushed to obtain a fluid loss reducer for drilling fluid.

[0086] Example 4

[0087] The only difference from Example 1 is that the starch is directly reacted with the monomer mixture.

[0088] Example 5

[0089] The only difference from Example 1 is that the cross-linking agent is an equal amount of lactic acid.

[0090] Example 6

[0091] The only difference from Example 1 is that no acrylamide is added, that is, no vinylamide monomer is contained.

[0092] Example 7

[0093] The only difference from Example 1 is that no vinyl dimethyl phosphate is added, that is, no olefinic phosphate monomer is contained.

[0094] Example 8

[0095] The only difference from Example 1 is that no N-vinyl pyrrolidone is added, that is, no olefin monomer having a side cyclic group is contained.

[0096] Example 9

[0097] The only difference from Example 1 is that acrylamide is replaced by an equal amount of acryloyloxybutylsulfonic acid.

[0098] Example 10

[0099] The only difference from Example 1 is that the vinyl dimethyl phosphate is replaced by an equal amount of dimethyl diallyl ammonium chloride.

[0100] The drilling fluid obtained in the above Examples 1-10 was tested for temperature resistance, salt resistance and calcium resistance using a fluid loss reducer, specifically according to the ZB / TE13004-90 drilling fluid test procedure, including the following:

[0101] (1) Test in fresh water slurry

[0102] Fresh water-based slurry: Add 400 mL of tap water to a high-stirring cup, add 16.0 g of Huai'an bentonite and 0.8 g of Na2CO3 in a quantitative manner while stirring continuously, stir for 20 minutes, stop at least twice to scrape off the bentonite adhering to the container wall, and cure in a sealed container for 24 hours.

[0103] Fluid loss reducer + fresh water drilling fluid system: quantitatively weigh the high temperature resistant fluid loss reducer prepared in Examples 1-10, add it to the above fresh water base slurry, stir it thoroughly and then cure it in a sealed container for 24 hours.

[0104] The freshwater base slurry and the filtrate reducer + freshwater drilling fluid system were stirred at high speed for 5 minutes and then placed in a high-temperature aging tank. They were heated at 200°C for 16 hours. The filtrate loss of the drilling fluid was measured using a normal temperature medium-pressure filtrate loss meter and a high temperature and high-pressure filtrate loss meter. The results are shown in Table 1.

[0105] Table 1

[0106] Test subjects API filtration loss at room temperature / mL High temperature and high pressure filtration loss / mL Fresh water base slurry 72.0 Full leak Fresh water base slurry + 2% Example 1 10.8 25.8 Fresh water base slurry + 2% Example 2 9.8 26.5 Fresh water base slurry + 2.5% Example 2 8.6 22.8 Fresh water base slurry + 2.5% Example 3 9.0 25.5 Fresh water base slurry + 2% Example 4 13.5 30.5 Fresh water base slurry + 2% Example 5 14.5 31.3 Fresh water base slurry + 2% Example 6 16.8 32.3 Fresh water base slurry + 2% Example 7 16.4 33.7 Fresh water base slurry + 2% Example 8 17.6 36.8 Fresh water base slurry + 2% Example 9 16.4 34.8 Fresh water base slurry + 2% Example 10 15.6 35.4

[0107] (2) Test in saturated salt water slurry

[0108] Saturated salt water slurry: Add 400 mL of tap water to a high stirring cup, add sodium chloride quantitatively to saturation under constant stirring, and then add 16.0 g of Huai'an bentonite and 0.8 g of Na2CO3. Stir for 20 minutes, stop at least twice to scrape off the bentonite adhering to the container wall, and cure in a sealed container for 24 hours.

[0109] Fluid loss reducer + saturated brine drilling fluid system: quantitatively weigh the high temperature resistant fluid loss reducer prepared in Example 1-11, add it to the saturated brine base slurry, stir it thoroughly and then cure it in a sealed container for 24 hours.

[0110] The saturated salt water base slurry and the fluid loss reducer + saturated salt water drilling fluid system were stirred at high speed for 5 minutes and then loaded into a high temperature aging tank, heated at 200°C for 16 hours, and the drilling fluid loss was measured using a normal temperature medium pressure filter loss meter and a high temperature and high pressure filter loss meter. The results are shown in Table 2.

[0111] Table 2

[0112] Test subjects API filtration loss / mL High temperature and high pressure filtration loss / mL Saturated salt water slurry Full leak Full leak Saturated salt water base slurry + 3% Example 1 10.8 27.6 Saturated salt water base slurry + 3.5% Example 2 8.2 24.8 Saturated salt water base slurry + 3.5% Example 3 8.8 25.2 Saturated salt water base slurry + 3% Example 4 16.7 35.6 Saturated salt water base slurry + 3% Example 5 15.6 34.8 Saturated salt water base slurry + 3% Example 6 18.5 36.4 Saturated salt water base slurry + 3% Example 7 17.3 37.2 Saturated salt water base slurry + 3% Example 8 15.3 33.5 Saturated salt water base slurry + 3% Example 9 16.8 34.8 Saturated salt water base slurry + 3% Example 10 17.9 35.8

[0113] (3) Test in calcium-based slurry

[0114] Calcium-based slurry: Add 400 mL of tap water to a high-stirring cup, add 1 g of calcium chloride, 16.0 g of Huai'an bentonite and 0.8 g of Na2CO3 while stirring continuously. Stir for 20 minutes, stopping at least twice to scrape off the bentonite adhering to the container wall, and cure in a sealed container for 24 hours.

[0115] Fluid loss reducer-calcium-containing drilling fluid system: Weigh the high-temperature resistant fluid loss reducer prepared in Example 1-11, add it to the above calcium-containing base slurry, stir it thoroughly, and then cure it in a sealed container for 24 hours.

[0116] The calcium-containing base slurry and the filtrate reducer-calcium-containing drilling fluid system were stirred at high speed for 5 minutes and then placed in a high-temperature aging tank. They were heated at 200°C for 16 hours. The filtrate loss of the drilling fluid was measured using a normal temperature medium-pressure filtrate loss meter and a high temperature and high-pressure filtrate loss meter. The results are shown in Table 3.

[0117] Table 3

[0118] Test subjects API filtration loss / mL High temperature and high pressure filtration loss / mL Calcium-based paste Full leak Full leak Calcium-based slurry + 3% Example 1 8.4 23.8 Calcium-based slurry + 3.5% Example 2 7.0 22.2 Calcium-based slurry + 4% Example 3 6.2 21.5 Calcium-based slurry + 3% Example 4 15.3 35.1 Calcium-based slurry + 3% Example 5 17.5 33.5 Calcium-based slurry + 3% Example 6 16.8 34.2 Calcium-based slurry + 3% Example 7 17.9 32.6 Calcium-based slurry + 3% Example 8 19.7 31.8 Calcium-based slurry + 3% Example 9 18.6 36.8 Calcium-based slurry + 3% Example 10 18.9 38.4

[0119] It can be seen from the results of Table 1, Table 2 and Table 3 that in the fluid loss agent + fresh water drilling fluid system, after aging at 200°C for 16h, when the concentrations of the high temperature resistant fluid loss agent prepared in the above Examples 1-3 are added as 2.0wt% (Example 1), 2.0wt% (Example 2) and 2.5wt% (Example 3), respectively, the API filtration loss of the drilling fluid can be reduced to less than 15mL, and the high temperature and high pressure filtration loss of the drilling fluid can be reduced to less than 30.0mL. Compared with the fluid loss agent + fresh water drilling fluid system, the amount of environmentally friendly high temperature resistant fluid loss agent in the fluid loss agent + saturated salt water drilling fluid system and the fluid loss agent + calcium-containing drilling fluid system is appropriately increased, which can effectively reduce the filtration loss of the drilling fluid system. It can be shown that the temperature resistance of the high temperature resistant fluid loss agent of the present invention can reach 200°C, and it has good salt resistance and calcium resistance. Therefore, this fluid loss reducer product is suitable for use in deep wells and ultra-deep wells under high temperature, high salt or high calcium geological conditions.

[0120] Furthermore, by comparing the results of Example 1 and Examples 4-10, it can be seen that after adjusting the formula of the fluid loss reducer provided by the present invention, the performance of the obtained fluid loss reducer will be significantly reduced. For example, if the monomer in the fluid loss reducer is omitted or replaced with other monomers, the salt resistance and calcium resistance will be reduced, and the high temperature resistance will also be reduced, which is not conducive to the performance of the fluid loss reducer.

[0121] (4) Biological toxicity test

[0122] According to the permissible value of biological toxicity of oilfield chemicals and drilling fluids, if the biological toxicity test result is ≥20000 mg / L, it meets the biological toxicity requirements. The high temperature resistant fluid loss reducer prepared in Examples 1-3 was subjected to a luminescent bacteria biological toxicity test, and the results are shown in Table 4.

[0123] Table 4

[0124] Test subjects Example 1 Example 2 Example 3 <![CDATA[EC 50 / (mg / L)]]> 2250000 2030000 1860000

[0125] It can be seen from Table 4 that the EC of the high temperature resistant fluid loss reducer obtained in Examples 1-3 is 50 All of them are greater than 20000 mg / L, have no toxicity, and meet the biological toxicity requirements of the first-level sea area and the second-level sea area. Therefore, the high-temperature resistant fluid loss reducer product of the present invention is also suitable for shale gas horizontal wells and drilling operations in environmentally sensitive areas.

[0126] It is stated that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0127] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0128] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0129] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A fluid loss reducer for drilling fluid, characterized in that: The fluid loss reducer for drilling fluid comprises starch, alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers and alkenyl monomers with cyclic groups on the side groups.

2. The fluid loss reducer for drilling fluid according to claim 1, characterized in that: The mass ratio of starch, alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers and alkenyl monomers with side groups having cyclic groups in the drilling fluid loss reducer is (10-50):(1-10):(1-10):(1-20):(1-10).

3. The fluid loss reducer for drilling fluid according to claim 1 or 2, characterized in that: The vinyl amide monomers include one or a combination of at least two of acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dipropylacrylamide, N-isopropylacrylamide, N-hydroxymethylacrylamide, N,N-diisopropylacrylamide, N,N-dibutylacrylamide, N-vinylacetamide or N-vinylmethylacetamide; Preferably, the alkenyl phosphate monomers include vinyl dimethyl phosphate and / or vinyl diethyl phosphate; Preferably, the olefinic acid monomers include olefinic sulfonic acid monomers and / or acrylic acid monomers; Preferably, the acrylate monomer comprises one or a combination of at least two of acrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, methacrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, sodium 2-acrylamide-2-methylpropane sulfonate, allyl sulfonic acid, acryloxybutyl sulfonic acid, 2-acryloxy-2-methylpropane sulfonic acid or 2-acrylamidododecyl sulfonic acid; Preferably, the olefinic monomer having a cyclic group on the side group includes one or a combination of at least two of N-vinyl pyrrolidone, N-vinyl caprolactam, vinyl cyclopentane, N-benzyl-3-pyrrolidone or (R)-4-benzyl-2-oxazolidinone.

4. A method for preparing a fluid loss reducer for drilling fluid according to any one of claims 1 to 3, characterized in that: The preparation method comprises: The starch and the cross-linking agent are cross-linked according to the formula to obtain an intermediate product; The intermediate product, the monomer mixture and the initiator are mixed and then subjected to polymerization reaction to obtain a fluid loss reducer for drilling fluid.

5. The preparation method according to claim 4, characterized in that: The mass ratio of the starch to the cross-linking agent is 100:(0.5-5); Preferably, the cross-linking agent comprises an organic acid and / or an inorganic acid.

6. The preparation method according to claim 4 or 5, characterized in that: The temperature of the cross-linking treatment is 20-55°C; Preferably, the cross-linking treatment time is 1.5-3h; Preferably, the pH value of the intermediate product is 9-10.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The monomer mixture is obtained by mixing alkenyl amide monomers, alkenyl phosphate monomers, alkenyl acid monomers, alkenyl monomers with side groups having cyclic groups, and a solvent; Preferably, the pH value of the monomer mixture is 6.5-7.

5.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The amount of the initiator added is 0.1-1% of the mass of the monomer mixture; Preferably, the initiator comprises one or a combination of at least two of ammonium persulfate, potassium persulfate, benzoyl peroxide, azobisisobutyronitrile or azobisisoheptanenitrile.

9. The preparation method according to any one of claims 4 to 8, characterized in that: The polymerization reaction is carried out under a protective atmosphere; Preferably, the polymerization reaction temperature is 50-80°C; Preferably, the polymerization reaction time is 3-5h.

10. A drilling fluid, characterized in that: The drilling fluid comprises the filtrate reducer for drilling fluid as claimed in any one of claims 1 to 3.