Soilless phase reservoir protection water-based drilling fluid and preparation method and application thereof

Abstract

This invention provides a soil-free reservoir protection water-based drilling fluid, its preparation method, and its application, belonging to the field of drilling fluid technology. The drilling fluid of this invention comprises the following raw materials in parts by weight: 100 parts water, 0.2-0.4 parts a first pH adjuster, 1-3 parts an oxygen scavenger, 0.1-0.4 parts a viscosity enhancer and shearing agent, 2-4 parts a filtration loss reducer, 4-6 parts magnesium aluminum hydrotalcite, 4-6 parts micro / nano alumina, 4-6 parts ultrafine calcium carbonate, 4-6 parts a lubricant, 1-2 parts a corrosion inhibitor, and 70-660 parts an inorganic salt weighting agent. The drilling fluid of this invention exhibits excellent high-temperature resistance, good rheological properties, and excellent filtration loss reduction performance. It can be formulated into a saturated CaCl2 / saturated CaBr2 system, is free of barite and clay, has a high mud cake acid solubility, and after plugging, its permeability recovery is greater than 72%, providing good reservoir protection and possessing the potential for large-scale field application.

Description

Technical Field

[0001] This invention relates to a water-based drilling fluid for soil-free reservoir protection, its preparation method, and its application, belonging to the field of drilling fluid technology. Background Technology

[0002] Clay-free water-based drilling fluids are water-based drilling fluids that do not contain clay-based materials. They avoid the thorny problem of drilling fluid performance deterioration caused by clay failure under high temperature and high salinity conditions. Compared with clay-containing water-based drilling fluids, they also have the advantage of better reservoir protection. The development of high-performance clay-free water-based drilling fluids can provide technical support for drilling in deep, complex, and harsh formations and deep reservoirs.

[0003] Existing patent documents have disclosed various soil-free water-based drilling fluids. Chinese patent document CN109266318A discloses a soil-free water-based drilling fluid using starch microgel as a thickener and shearing enhancer, with temperature resistance up to 150℃, suitable for horizontal well drilling; however, the document does not mention the salt resistance of this drilling fluid. Chinese patent document CN109266316A discloses a soil-free water-based drilling fluid using calcium alginate microgel as a thickener and shearing enhancer, and sulfonated lignite resin and sulfonated phenolic resin as filtration loss reducers, with temperature resistance up to 160℃ and KCl resistance up to 3%. Chinese patent document CN104650827A discloses a high-temperature resistant solids-free water-based drilling fluid composed of a temperature-resistant micro-crosslinked thickener, filtration loss reducer, inorganic salts, and an oxygen scavenger, with temperature resistance up to 180℃ and NaCl saturation resistance. Chinese patent document CN104497188A discloses a filtration loss reducing plugging agent for use in alkyl glycoside-based water-based drilling fluids without soil. After adding 2% of the plugging agent, the high-temperature, high-pressure filtration loss of this water-based drilling fluid after aging at 130°C is 8.0 mL. Although the above-mentioned water-based drilling fluid without soil exhibits excellent temperature and salt resistance, its temperature resistance does not reach 190°C, and there is a lack of reports on its reservoir protection performance in the literature.

[0004] To address the aforementioned problems, this invention is proposed to provide technical support for deep drilling. Summary of the Invention

[0005] To address the technical challenges of insufficient temperature resistance and reservoir protection performance in existing soil-free water-based drilling fluids, this invention provides a soil-free reservoir protection water-based drilling fluid, its preparation method, and its applications. The drilling fluid of this invention exhibits excellent high-temperature resistance, reaching up to 190℃, and possesses good rheological properties and reduced filtration loss. This drilling fluid can be formulated into a saturated CaCl2 and saturated CaBr2 system, is free of barite and clay, has a high mud cake acid solubility, and its permeability recovery after plugging is greater than 72%, demonstrating good reservoir protection and the potential for large-scale field application.

[0006] The technical solution of the present invention is as follows:

[0007] A water-based drilling fluid for reservoir protection without soil phase comprises the following raw materials in parts by weight: 100 parts water, 0.2-0.4 parts first pH adjuster, 1-3 parts oxygen scavenger, 0.1-0.4 parts viscosity improver and shearing agent, 2-4 parts filtration loss reducer, 4-6 parts magnesium aluminum hydrotalcite, 4-6 parts micro-nano alumina, 4-6 parts ultrafine calcium carbonate, 4-6 parts lubricant, 1-2 parts corrosion inhibitor, and 70-660 parts inorganic salt weighting agent.

[0008] According to a preferred embodiment of the present invention, the first pH adjuster is sodium hydroxide or potassium hydroxide.

[0009] According to a preferred embodiment of the present invention, the oxygen scavenger is any one of sodium sulfite, sodium bisulfite, urea, or anhydrous citric acid.

[0010] According to a preferred embodiment of the present invention, the thickening and cutting agent is a zwitterionic polyacrylamide with a weight-average molecular weight of 4 million to 6 million, a cationicity of 20-30%, and an anionicity of 30%-40%; preferably, the zwitterionic polyacrylamide has a weight-average molecular weight of 6 million.

[0011] According to a preferred embodiment of the present invention, the filtration loss reducing agent is prepared from the following raw materials:

[0012] Dimethylaminopropylmethacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, docosyl methacrylate, 4-acryloylmorpholine, 4-vinylbenzoic acid, emulsifier, initiator, secondary pH adjuster, deionized water.

[0013] Preferably, the emulsifier is any one of Span 80, Tween 80, or OP-10; the mass ratio of emulsifier to deionized oil is 0.01-0.05:100, preferably 0.03:100.

[0014] Preferably, the initiator is potassium persulfate, ammonium persulfate, or 2,2'-azobis(2-methylpropylamidine) dihydrochloride; the mass ratio of the initiator to the total monomer is 0.010-0.25:47-53, preferably 0.15:47-53.

[0015] Preferably, the second pH adjuster is a NaOH aqueous solution with a concentration of 5-15 mol / L.

[0016] Preferably, the mass ratio of dimethylaminopropylmethacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 4-vinylbenzoic acid, 4-acryloylmorpholine, and docosyl methacrylate is 25:10-15:5-6:3-5:2-3; and the mass ratio of the total mass of monomers to deionized water is 47-53:100.

[0017] Preferably, the method for preparing the filtration loss reducing agent includes the following steps:

[0018] 2-Acrylamido-2-methylpropanesulfonic acid and 4-vinylbenzoic acid were added to deionized water, and the pH of the system was adjusted to 7.0 using a second pH adjuster. Dimethylaminopropylmethacrylamide and 4-acryloylmorpholine were added and dispersed thoroughly. Then, an emulsifier and dodecyl methacrylate were added and dispersed thoroughly. After heating to the reaction temperature, an initiator was added, and the mixture was reacted, dried, and pulverized to obtain the filtration loss reducer.

[0019] More preferably, the reaction temperature is 60-70℃, the reaction time is 2-6 hours, and the reaction is carried out under the protection of a protective gas and with stirring. The protective gas is nitrogen or argon.

[0020] According to a preferred embodiment of the present invention, the average particle size of the magnesium-aluminum hydrotalcite is 800-900 mesh.

[0021] According to a preferred embodiment of the present invention, the micro / nano alumina is composed of a mixture of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 1 μm to 2 μm, and the average particle size of the nano-sized alumina particles is 300 nm to 400 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 2-6:1-3.

[0022] According to a preferred embodiment of the present invention, the average particle size of the ultrafine calcium carbonate is 100 nm to 300 nm, preferably 200 nm.

[0023] According to a preferred embodiment of the present invention, the lubricant is liquid paraffin.

[0024] According to a preferred embodiment of the present invention, the corrosion inhibitor is 1H-benzotriazole.

[0025] According to a preferred embodiment of the present invention, the inorganic salt weighting agent is anhydrous calcium chloride or anhydrous calcium bromide.

[0026] The preparation method of the above-mentioned water-based drilling fluid for soil-free reservoir protection includes the following steps:

[0027] Add the first pH adjuster to water and mix thoroughly; add the oxygen scavenger and mix thoroughly; add the viscosity improver and mix thoroughly; add the filtration loss reducer and mix thoroughly; add magnesium aluminum hydrotalcite and mix thoroughly; add micro-nano alumina and mix thoroughly; add ultrafine calcium carbonate and mix thoroughly; add the lubricant and mix thoroughly; add the corrosion inhibitor and mix thoroughly; finally add the inorganic salt weighting agent and mix thoroughly to obtain a soil-free reservoir protection water-based drilling fluid.

[0028] The above-mentioned water-based drilling fluid without soil-phase reservoir protection is used in deep and / or ultra-deep oil and gas drilling. The deep layers are formations with a depth > 4500m, and the ultra-deep layers are formations with a depth > 6000m.

[0029] The technical features and beneficial effects of this invention are as follows:

[0030] (1) In this invention, high molecular weight zwitterionic polyacrylamide, polymer filtration reducer, and micro / nano particles (such as magnesium aluminum hydrotalcite, micro / nano alumina, and ultrafine calcium carbonate) synergistically regulate the rheological properties of drilling fluid. High molecular weight zwitterionic polyacrylamide and polymer filtration reducer have strong salt resistance and thickening properties. The two polymers are intertwined and linked together, and adsorbed with nanoparticles to form a tight three-dimensional network structure, enabling the drilling fluid to maintain good rheological properties under high temperature and high salt conditions.

[0031] (2) This invention uses a polymer filtration loss reducer in synergistic action with magnesium aluminum hydrotalcite, micro-nano alumina, and ultrafine calcium carbonate to control the filtration loss of drilling fluid. The magnesium aluminum hydrotalcite, micro-nano alumina, and ultrafine calcium carbonate form a rigid sealing layer, which provides an effective pressure-bearing effect; the filtration loss reducer has soft polymer chains, which can effectively fill the gaps between rigid nanoparticles, providing a flexible sealing effect, enhancing the compactness of the mud cake, and maintaining a low level of filtration loss in the drilling fluid.

[0032] (3) The drilling fluid of the present invention has excellent high temperature resistance and salt resistance, with a temperature resistance of up to 190℃. It can resist CaBr2 and CaCl2 to saturation, and has good rheological properties and excellent filtration loss reduction performance.

[0033] (4) The drilling fluid of the present invention can be configured into a saturated CaCl2 and saturated CaBr2 system, without barite and clay, with high mud cake acid solubility, and the formation permeability is restored to more than 72% after plugging, with good reservoir protection and potential for large-scale field application.

[0034] (5) The raw material composition of this invention works together as a whole to achieve the excellent effects of this invention. If the types and proportions of raw materials are not suitable, the performance of the resulting drilling fluid will be reduced. Attached Figure Description

[0035] Figure 1 Infrared spectrum of the filtration reduction agent obtained in Example 1;

[0036] Figure 2 This is a photograph of the appearance of the drilling fluid obtained in Example 1. Detailed Implementation

[0037] The specific embodiments of the present invention will be further described below. The present invention can be better understood from the following examples. However, those skilled in the art will readily understand that the specific material ratios, process conditions, and results described in the examples are for illustrative purposes only and should not, and will not, limit the present invention as described in detail in the claims. Furthermore, unless otherwise specified, all materials used in the following examples and comparative examples are commercially available, and all methods used are conventional methods in the art.

[0038] Preparation Example 1

[0039] The preparation method of filtration loss reducer A1 includes the following steps:

[0040] First, add 100g of deionized water to a clean three-necked flask, then add 15.0g of 2-acrylamido-2-methylpropanesulfonic acid and 5.0g of 4-vinylbenzoic acid. Adjust the pH of the system to 7.0 using a 10mol / L NaOH aqueous solution, and stir at 400 rpm for 5 minutes to ensure uniform monomer dispersion. Then, add 25.0g of dimethylaminopropyl methacrylamide and 5.0g of 4-acryloylmorpholine sequentially, and stir thoroughly for 10 minutes to ensure uniform monomer dispersion. Add 0.03g of emulsifier OP-10 and 3.0g of docosyl methacrylate, and stir for another 5 minutes. Transfer the three-necked flask to a water bath, heat to 65℃, add 0.15g of potassium persulfate, and continue stirring under a nitrogen atmosphere for 4 hours to obtain a gel product. Dry, cut, and pulverize the gel to obtain the filtration loss reducer A1.

[0041] The infrared spectrum of the filter loss reducer obtained in this preparation example is as follows: Figure 1 As shown. Located at 3412 cm. -1 The broad peak nearby originates from the stretching vibrations of the amide and hydroxyl groups, located at 2930 cm⁻¹. -1 The characteristic peak at 2852 cm⁻¹ originates from the antisymmetric stretching vibration of the CH bonds in the methyl and methylene groups. -1 The characteristic peak at m1722 originates from the stretching vibration of the CH bonds in the methyl and methylene groups. -1 The characteristic peak at 1660 cm⁻¹ originates from the stretching vibration of the C=O group in the ester group. -1 The characteristic peak at 1600 cm⁻¹ originates from the stretching vibrations of the C=O groups in the amide and carboxyl groups, as well as the C=O group attached to the morpholine ring. -1 1537cm -1 and 1500cm -1 The characteristic peak at 1468 cm⁻¹ originates from the skeletal vibrations of the benzene ring. -1 The characteristic peak at 1294 cm⁻¹ originates from the stretching vibration of the CN bond. -1 1181cm -1 and 1037cm-1 The characteristic peak at 1109 cm⁻¹ originates from the asymmetric and symmetric stretching vibrations of the sulfonic acid group. -1 The characteristic peak at 626 cm⁻¹ originates from the stretching vibration of the COC bond in the morpholine ring. -1 The characteristic peak at 720 cm⁻¹ originates from the stretching vibration of the CS bond. -1 The characteristic peak at the position originates from the rocking vibration of the methylene group in the docosyl chain. Infrared spectroscopy analysis results indicate that the filtration loss reducer was successfully synthesized from dimethylaminopropylmethacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, docosyl methacrylate, 4-vinylbenzoic acid, and acryloylmorpholine.

[0042] Preparation Example 2

[0043] The preparation method of filtration loss reducer A2 includes the following steps:

[0044] First, add 100g of deionized water to a clean three-necked flask, then add 10.0g of 2-acrylamido-2-methylpropanesulfonic acid and 5.0g of 4-vinylbenzoic acid. Adjust the pH of the system to 7.0 using a 10mol / L NaOH aqueous solution, and stir at 400 rpm for 5 minutes to ensure uniform monomer dispersion. Then, add 25.0g of dimethylaminopropyl methacrylamide and 5.0g of 4-acryloylmorpholine sequentially, and stir thoroughly for 10 minutes to ensure uniform monomer dispersion. Add 0.03g of emulsifier OP-10 and 2.0g of docosyl methacrylate, and stir for another 5 minutes. Transfer the three-necked flask to a water bath, heat to 65℃, add 0.15g of potassium persulfate, and continue stirring under a nitrogen atmosphere for 4 hours to obtain a gel product. Dry, cut, and pulverize the gel to obtain filtration loss reducer A2.

[0045] Preparation Example 3

[0046] The preparation method of filtration loss reducer A3 includes the following steps:

[0047] First, add 100g of deionized water to a clean three-necked flask, then add 12.0g of 2-acrylamido-2-methylpropanesulfonic acid and 6.0g of 4-vinylbenzoic acid. Adjust the pH of the system to 7.0 using a 10mol / L NaOH aqueous solution, and stir at 400 rpm for 5 minutes to ensure uniform monomer dispersion. Then, add 25.0g of dimethylaminopropylmethacrylamide and 3.0g of 4-acryloylmorpholine sequentially, and stir thoroughly for 10 minutes to ensure uniform monomer dispersion. Add 0.03g of emulsifier OP-10 and 2.5g of docosyl methacrylate, and stir for another 5 minutes. Transfer the three-necked flask to a water bath, heat to 65℃, add 0.15g of potassium persulfate, and continue stirring under a nitrogen atmosphere for 4 hours to obtain a gel product. Dry, cut, and pulverize the gel to obtain the filtration loss reducer A3.

[0048] Comparative Preparation Example 1

[0049] The method for preparing the filtration loss reducer B1 is as described in Preparation Example 1, except that 4-vinylbenzoic acid is not added; the other steps and conditions are the same as in Preparation Example 1.

[0050] Comparative Preparation Example 2

[0051] The method for preparing the filtration loss reducer B2 is as described in Preparation Example 1, except that the amount of 4-vinylbenzoic acid added is 1g; the other steps and conditions are the same as in Preparation Example 1.

[0052] Comparative preparation example 3

[0053] The method for preparing the filtration loss reducer B3 is as described in Preparation Example 1, except that docosyl methacrylate is not added; the other steps and conditions are the same as in Preparation Example 1.

[0054] Comparative preparation example 4

[0055] The method for preparing the filtration loss reducer B4 is as described in Preparation Example 1, except that the amount of dodecyl methacrylate used is 1g; the other steps and conditions are the same as in Preparation Example 1.

[0056] Comparative preparation example 5

[0057] The method for preparing the filtration loss reducer B5 is as described in Preparation Example 1, except that docosyl methacrylate is replaced with octadecyl methacrylate; the other steps and conditions are the same as in Preparation Example 1.

[0058] Example 1

[0059] A water-based drilling fluid F1 for soil-free reservoir protection comprises the following raw materials in parts by weight: 100 parts water, 0.4 parts sodium hydroxide, 1 part sodium sulfite, 0.2 parts zwitterionic polyacrylamide (weight-average molecular weight of 6 million, cationicity of 20%, anionicity of 30%), 4 parts filtration loss reducer A1 prepared by the method of Preparation Example 1, 4 parts magnesium aluminum hydrotalcite (average particle size of 800 mesh), 6 parts micro / nano alumina (composed of a mixture of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 2.0 μm, and the average particle size of the nano-sized alumina particles is 400.0 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 6:3), 6 parts ultrafine calcium carbonate (average particle size of 200 nm), 4 parts lubricant (liquid paraffin), 2 parts corrosion inhibitor (1H-benzotriazole), and 210 parts anhydrous calcium chloride as an inorganic salt weighting agent.

[0060] The preparation method of the above-mentioned soil-free reservoir protection water-based drilling fluid F1 includes the following steps: adding tap water to a clean slurry cup, adding sodium hydroxide, and stirring at a rate of 2000 rpm for 5 minutes; adding sodium sulfite and stirring at a rate of 2000 rpm for 5 minutes; slowly adding a viscosity-enhancing and shear-lifting agent and stirring at a rate of 12000 rpm for 10 minutes; slowly adding a filtration-reducing agent and stirring at a rate of 12000 rpm for 10 minutes; adding magnesium aluminum hydrotalcite and stirring at a rate of 6000 rpm for 5 minutes; adding micro / nano alumina and stirring at a rate of 6000 rpm for 5 minutes; adding ultrafine calcium carbonate and stirring at a rate of 6000 rpm for 5 minutes; adding a lubricant and stirring at a rate of 6000 rpm for 5 minutes; adding a corrosion inhibitor and stirring at a rate of 6000 rpm for 5 minutes; and finally adding an inorganic salt weighting agent and stirring at a rate of 4500 rpm for 10 minutes to obtain soil-free reservoir protection water-based drilling fluid F1.

[0061] The appearance photograph of the drilling fluid obtained in this embodiment is as follows: Figure 2 As shown.

[0062] Example 2

[0063] A water-based drilling fluid F2 for soil-free reservoir protection comprises the following raw materials in parts by weight: 100 parts water, 0.4 parts sodium hydroxide, 1 part sodium sulfite, 0.4 parts zwitterionic polyacrylamide (weight-average molecular weight of 6 million, cationicity of 20%, anionicity of 30%), 22 parts filtration loss reducer A1 prepared by the method of Preparation Example 1, 4 parts magnesium aluminum hydrotalcite (average particle size of 800 mesh), 6 parts micro / nano alumina (composed of a mixture of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 2.0 μm, and the average particle size of the nano-sized alumina particles is 400.0 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 6:3), 4 parts ultrafine calcium carbonate (average particle size of 200 nm), 6 parts lubricant (liquid paraffin), 2 parts corrosion inhibitor (1H-benzotriazole), and 210 parts anhydrous calcium chloride as an inorganic salt weighting agent.

[0064] The preparation method of the above-mentioned water-based drilling fluid F2 without soil phase reservoir protection is the same as in Example 1.

[0065] Example 3

[0066] A water-based drilling fluid F3 for soil-free reservoir protection comprises the following raw materials in parts by weight: 100 parts water, 0.4 parts sodium hydroxide, 1 part sodium sulfite, 0.2 parts zwitterionic polyacrylamide (weight-average molecular weight of 6 million, cationicity of 20%, anionicity of 30%), 4 parts filtration loss reducer A1 prepared by the method of Preparation Example 1, 6 parts magnesium aluminum hydrotalcite (average particle size of 800 mesh), 4 parts micro / nano alumina (composed of a mixture of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 2.0 μm, and the average particle size of the nano-sized alumina particles is 400.0 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 6:3), 6 parts ultrafine calcium carbonate (average particle size of 200 nm), 4 parts lubricant (liquid paraffin), 2 parts corrosion inhibitor (1H-benzotriazole), and 210 parts anhydrous calcium chloride as an inorganic salt weighting agent.

[0067] The preparation method of the above-mentioned water-based drilling fluid F3 for soil-free reservoir protection is the same as in Example 1.

[0068] Example 4

[0069] A water-based drilling fluid F4 for soil-free reservoir protection comprises the following raw materials in parts by weight: 100 parts water, 0.4 parts sodium hydroxide, 1 part sodium sulfite, 0.4 parts zwitterionic polyacrylamide (weight-average molecular weight of 6 million, cationicity of 20%, anionicity of 30%), 3 parts filtration loss reducer A1 prepared by the method of Preparation Example 1, 6 parts magnesium aluminum hydrotalcite (average particle size of 800 mesh), 6 parts micro / nano alumina (composed of a mixture of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 2.0 μm, and the average particle size of the nano-sized alumina particles is 400.0 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 6:3), 4 parts ultrafine calcium carbonate (average particle size of 200 nm), 4 parts lubricant (liquid paraffin), 2 parts corrosion inhibitor (1H-benzotriazole), and 210 parts anhydrous calcium chloride as an inorganic salt weighting agent.

[0070] The preparation method of the above-mentioned water-based drilling fluid F4 for soil-free reservoir protection is the same as in Example 1.

[0071] Example 5

[0072] A water-based drilling fluid F5 for soil-free reservoir protection comprises the following raw materials in parts by weight: 100 parts water, 0.4 parts sodium hydroxide, 1 part sodium sulfite, 0.2 parts zwitterionic polyacrylamide (weight-average molecular weight of 6 million, cationicity of 20%, anionicity of 30%), 4 parts filtration loss reducer A1 prepared by the method of Preparation Example 1, 6 parts magnesium aluminum hydrotalcite (average particle size of 800 mesh), 4 parts micro / nano alumina (composed of a mixture of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 2.0 μm, and the average particle size of the nano-sized alumina particles is 400.0 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 6:3), 4 parts ultrafine calcium carbonate (average particle size of 200 nm), 6 parts lubricant (liquid paraffin), 2 parts corrosion inhibitor (1H-benzotriazole), and 210 parts anhydrous calcium chloride as an inorganic salt weighting agent.

[0073] The preparation method of the above-mentioned water-based drilling fluid F5 for soil-free reservoir protection is the same as that in Example 1.

[0074] Example 6

[0075] A water-based drilling fluid F6 for soil-free reservoir protection comprises the following raw materials in parts by weight: 100 parts water, 0.4 parts sodium hydroxide, 1 part sodium sulfite, 0.2 parts zwitterionic polyacrylamide (weight-average molecular weight of 6 million, cationicity of 20%, anionicity of 30%), 3 parts filtration loss reducer A1 prepared by the method of Preparation Example 1, 4 parts magnesium aluminum hydrotalcite (average particle size of 800 mesh), 4 parts micro / nano alumina (composed of a mixture of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 2.0 μm, and the average particle size of the nano-sized alumina particles is 400.0 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 6:3), 6 parts ultrafine calcium carbonate (average particle size of 200 nm), 6 parts lubricant (liquid paraffin), 2 parts corrosion inhibitor (1H-benzotriazole), and 210 parts anhydrous calcium chloride as an inorganic salt weighting agent.

[0076] The preparation method of the above-mentioned water-based drilling fluid F6 for soil-free reservoir protection is the same as in Example 1.

[0077] Example 7

[0078] A water-based drilling fluid F7 for soil-free reservoir protection has the same raw material composition as in Example 1, except that the filtration loss reducer A1 prepared by the method of Example 1 is replaced by the filtration loss reducer A2 prepared by the method of Example 2; the other raw material composition is the same as in Example 1.

[0079] The preparation method of the above-mentioned water-based drilling fluid F7 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0080] Example 8

[0081] A water-based drilling fluid F8 for soil-free reservoir protection has the same raw material composition as in Example 1, except that the filtration loss reducer A1 prepared by the method of Example 1 is replaced with the filtration loss reducer A3 prepared by the method of Example 3; the other raw material compositions are the same as in Example 1.

[0082] The preparation method of the above-mentioned water-based drilling fluid F8 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0083] Example 9

[0084] A water-based drilling fluid F9 for soil-free reservoir protection has the same raw material composition as in Example 1, except that the weight-average molecular weight of the thickener and shearing agent, zwitterionic polyacrylamide, is 6 million, the cationicity is 30%, and the anionicity is 40%; the other raw material compositions are the same as in Example 1.

[0085] The preparation method of the above-mentioned water-based drilling fluid F9 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0086] Example 10

[0087] A water-based drilling fluid F without soil phase reservoir protection 10 The raw material composition is the same as in Example 1, except that: the average particle size of the micron-sized alumina particles is 1.0 μm, and the average particle size of the nano-sized alumina particles is 300.0 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 2:1; and the other raw material compositions are the same as in Example 1.

[0088] The above-mentioned water-based drilling fluid F without soil phase reservoir protection 10 The preparation method is the same as in Example 1, except that the differences are the same.

[0089] Example 11

[0090] A water-based drilling fluid F without soil phase reservoir protection 11 The raw material composition is the same as in Example 1, except that the average particle size of the magnesium aluminum hydrotalcite is 900 mesh; the other raw material compositions are the same as in Example 1.

[0091] The above-mentioned water-based drilling fluid F without soil phase reservoir protection 11 The preparation method is the same as in Example 1, except that the differences are the same.

[0092] Example 12

[0093] A water-based drilling fluid F without soil phase reservoir protection 12 The raw material composition is the same as in Example 1, except that the weight-average molecular weight of the thickening and cutting agent, zwitterionic polyacrylamide, is 4 million; the other raw material compositions are the same as in Example 1.

[0094] The above-mentioned water-based drilling fluid F without soil phase reservoir protection 12 The preparation method is the same as in Example 1, except that the differences are the same.

[0095] Example 13

[0096] A water-based drilling fluid F without soil phase reservoir protection 13 The raw materials consist of the following parts by weight: 100 parts water, 0.2 parts potassium hydroxide, 3 parts urea, 0.2 parts zwitterionic polyacrylamide (weight average molecular weight of 6 million, cationicity of 20%, anionicity of 30%), 4 parts filtration loss reducer A1 prepared by the method of Preparation Example 1, 4 parts magnesium aluminum hydrotalcite (average particle size of 800 mesh), 6 parts micro / nano alumina (composed of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 2.0 μm, and the average particle size of the nano-sized alumina particles is 400.0 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 6:3), 6 parts ultrafine calcium carbonate (average particle size of 200 nm), 4 parts lubricant (liquid paraffin), 1 part corrosion inhibitor (1H-benzotriazole), and 210 parts anhydrous calcium chloride, an inorganic salt weighting agent.

[0097] The above-mentioned water-based drilling fluid F without soil phase reservoir protection 13 The preparation method is the same as in Example 1.

[0098] Comparative Example 1

[0099] A water-based drilling fluid DF1 for soil-free reservoir protection has the same raw material composition as in Example 1, except that the filtration loss reducer A1 prepared by the method of Preparation Example 1 is replaced with the filtration loss reducer B1 prepared by the method of Comparative Preparation Example 1; the other raw material compositions are the same as in Example 1.

[0100] The preparation method of the above-mentioned water-based drilling fluid DF1 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0101] Comparative Example 2

[0102] A water-based drilling fluid DF2 for soil-free reservoir protection has the same raw material composition as in Example 1, except that the filtration loss reducer A1 prepared by the method of Preparation Example 1 is replaced with the filtration loss reducer B2 prepared by the method of Comparative Preparation Example 2; the other raw material compositions are the same as in Example 1.

[0103] The preparation method of the above-mentioned water-based drilling fluid DF2 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0104] Comparative Example 3

[0105] A water-based drilling fluid DF3 for soil-free reservoir protection has the same raw material composition as in Example 1, except that the filtration loss reducer A1 prepared by the method of Preparation Example 1 is replaced with the filtration loss reducer B3 prepared by the method of Comparative Preparation Example 3; the other raw material compositions are the same as in Example 1.

[0106] The preparation method of the above-mentioned water-based drilling fluid DF3 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0107] Comparative Example 4

[0108] A water-based drilling fluid DF4 for soil-free reservoir protection has the same raw material composition as in Example 1, except that the filtration loss reducer A1 prepared by the method of Preparation Example 1 is replaced with the filtration loss reducer B4 prepared by the method of Comparative Preparation Example 4; the other raw material compositions are the same as in Example 1.

[0109] The preparation method of the above-mentioned water-based drilling fluid DF4 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0110] Comparative Example 5

[0111] A water-based drilling fluid DF5 for soil-free reservoir protection has the same raw material composition as in Example 1, except that the filtration loss reducer A1 prepared by the method of Preparation Example 1 is replaced with the filtration loss reducer B5 prepared by the method of Comparative Preparation Example 5; the other raw material compositions are the same as in Example 1.

[0112] The preparation method of the above-mentioned water-based drilling fluid DF5 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0113] Comparative Example 6

[0114] A water-based drilling fluid DF6 for soil-free reservoir protection has the same raw material composition as in Example 1, except that it does not contain filtration loss reducer A1; the other raw material composition is the same as in Example 1.

[0115] The preparation method of the above-mentioned water-based drilling fluid DF6 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0116] Comparative Example 7

[0117] A water-based drilling fluid DF7 for soil-free reservoir protection has the same raw material composition as in Example 1, except that no thickening and shearing agent is added; the other raw material composition is the same as in Example 1.

[0118] The preparation method of the above-mentioned water-based drilling fluid DF7 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0119] Comparative Example 8

[0120] A water-based drilling fluid DF8 for soil-free reservoir protection has the same raw material composition as in Example 1, except that: the amount of magnesium aluminum hydrotalcite is 2 parts, and the amount of micro-nano alumina is 2 parts; the other raw material composition is the same as in Example 1.

[0121] The preparation method of the above-mentioned water-based drilling fluid DF8 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0122] Comparative Example 9

[0123] A water-based drilling fluid DF9 for soil-free reservoir protection has the same raw material composition as in Example 1, except that: the amount of ultrafine calcium carbonate is increased by 2 parts, and the amount of lubricant is increased by 2 parts; the other raw material composition is the same as in Example 1.

[0124] The preparation method of the above-mentioned water-based drilling fluid DF9 for soil-free reservoir protection is the same as that in Example 1, except that it is the same as above.

[0125] Comparative Example 10

[0126] A soil-free reservoir protection water-based drilling fluid DF 10 The raw material composition is the same as in Example 1, except that magnesium aluminum hydrotalcite, micro-nano alumina, and ultrafine calcium carbonate are not added; the other raw material compositions are the same as in Example 1.

[0127] The above-mentioned water-based drilling fluid DF without soil phase reservoir protection 10 The preparation method is the same as in Example 1, except that the differences are the same.

[0128] Comparative Example 11

[0129] A soil-free reservoir protection water-based drilling fluid DF 11 The raw material composition is the same as in Example 1, except that the amphoteric polyacrylamide, which is used as a thickening and cutting agent, is replaced with xanthan gum; the other raw material compositions are the same as in Example 1.

[0130] The above-mentioned water-based drilling fluid DF without soil phase reservoir protection 11 The preparation method is the same as in Example 1, except that the differences are the same.

[0131] Experimental Example 1

[0132] The drilling fluids prepared in Examples 1-13 and the comparative example were placed in a stainless steel aging tank and kept at a constant temperature of 190°C for 16 hours. After aging, they were cooled to room temperature and removed, then stirred at 6000 rpm for 20 minutes. The apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), dynamic shear force (YP, Pa), and API filtration loss (FL) of the drilling fluids before and after high-temperature aging were determined according to the petroleum and natural gas industry standard GB / T 29170-2012 "Petroleum and Natural Gas Industry - Laboratory Testing of Drilling Fluids". API and high temperature and high pressure filtration loss FLHTHP(190℃、3.5MPa) The results are shown in Tables 1 and 2.

[0133] Table 1. Drilling fluid performance testing

[0134]

[0135] Table 2. Drilling fluid performance testing

[0136]

[0137] Experimental results show that the drilling fluid of this invention exhibits good rheological and filtration loss properties both before and after aging at 190℃. In this invention, the zwitterionic polyacrylamide thickener, filtration loss reducer, and nanoparticles form a three-dimensional spatial network structure through adsorption and entanglement, forming a dense mud cake under positive pressure differential, effectively maintaining viscosity and reducing filtration loss. Increasing the cationic and anionic properties of the zwitterionic polyacrylamide strengthens the electrostatic interaction between the zwitterionic polyacrylamide and the filtration loss reducer, nanoparticles, and other treatment agents, resulting in a denser network structure, which enhances the rheological properties of the drilling fluid and reduces filtration loss. Reducing the particle size of the nanoparticles within a certain range promotes the formation of a dense mud cake and reduces filtration loss. Comparative data shows that unsuitable preparation conditions for the filtration loss reducer, unsuitable types of thickeners and thinners, unsuitable amounts of micro / nanoparticles, or the absence of a certain component all lead to a decrease in the rheological properties of the drilling fluid and an increase in filtration loss. Experimental results demonstrate that the soil-free reservoir protection water-based drilling fluid of this invention has good temperature and salt resistance.

[0138] Experimental Example 2

[0139] Example 1: The density of drilling fluid F1 is 1.41 g / cm³. 3 Based on Example 1, the dosage of the inorganic salt weighting agent was varied, specifically 70.0, 140.0, and 350.0 parts of anhydrous calcium chloride, to adjust the drilling fluid density to 1.26, 1.35, and 1.43 g / cm³, respectively. 3 We obtained soil-free calcium chloride drilling fluids with different densities.

[0140] Based on Example 1, the type and amount of inorganic salt weighting agent were varied, with inorganic salt weighting agents of 150, 300, 450, and 660 parts of anhydrous calcium bromide, respectively, to adjust the drilling fluid density to 1.36, 1.51, 1.64, and 1.75 g / cm³, respectively. 3 Calcium bromide drilling fluids without soil phase were obtained at different densities.

[0141] The drilling fluid was placed in a stainless steel aging tank and kept at a constant temperature of 190°C for 16 hours. After aging, it was cooled to room temperature and removed, then stirred at 6000 rpm for 20 minutes. The apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), dynamic shear force (YP, Pa), and API filtration loss (FL) of the drilling fluid before and after high-temperature aging were determined according to the petroleum and natural gas industry standard GB / T 29170-2012 "Petroleum and Natural Gas Industry - Laboratory Testing of Drilling Fluids". API and high temperature and high pressure filtration loss FL HTHP(190℃、3.5MPa) The results are shown in Tables 3 and 4.

[0142] Table 3. Performance of soil-free calcium chloride drilling fluid at different densities

[0143] Table 4. Performance of calcium bromide drilling fluids without soil phase at different densities

[0144] Table 3 shows that when the densities of the calcium chloride drilling fluid are 1.26, 1.35, 1.41, and 1.43 g / cm³, respectively... 3 At that time, the drilling fluid, after aging at 190 ℃, maintained good viscosity and shear strength, and FL API All less than 3.0 mL, FL HTHP(190℃、3.5MPa) All values ​​are less than 25.0 mL, indicating that the soil-free calcium chloride-based drilling fluid of this invention has good temperature and salt resistance, and can be saturated with calcium chloride, with a density reaching 1.43 g / cm³. 3 .

[0145] Table 4 shows that when the densities of calcium bromide drilling fluid are 1.36, 1.51, 1.64, and 1.75 g / cm³, the results are as follows: 3 At that time, the drilling fluid can still maintain good AV, PV, YP, and FL even after aging. API The concentrations were 2.2, 2.0, 2.4, and 2.0 mL respectively, FL HTHP The concentrations were 26.0, 25.2, 27.6, and 24.2 mL, respectively. The experimental results show that the calcium bromide drilling fluid of this invention still possesses good rheological and filtration properties under high temperature and high density conditions, and can be saturated with calcium bromide, achieving a density of up to 1.75 g / cm³. 3 .

[0146] Experimental Example 3

[0147] Acid preparation: Prepare a 10.0 wt% hydrochloric acid aqueous solution for later use. Take 3.0 ± 0.1 g (accurate to 0.01 g) of the mud cake from the drilling fluid of Experimental Example 1 after high-temperature and high-pressure filtration loss testing and add it to the acid solution. Let it stand at 25℃ for 8 hours to allow the mud cake to dissolve. Filter the solution containing mud cake residue after acid dissolution to obtain the filter residue. Dry the filter residue at 105℃ and weigh it. Calculate the mud cake acid solubility rate according to the following formula:

[0148] Sludge cake acid solubility = [(A1-A0) / A1] × 100%

[0149] In the formula:

[0150] A1 represents the mass of the mud cake before acid dissolution;

[0151] A0 represents the mass of the mud cake after acid dissolution.

[0152] Table 5. Acid solubility of mud cake

[0153]

[0154] The experimental results show that the acid solubility of the drilling fluid in the embodiments of the present invention is above 75%, indicating good acid solubility. The acidification process can effectively remove the mud cake and reduce damage to the oil and gas reservoir.

[0155] Test Example 4

[0156] Core plugging and unplugging experiments were conducted on the drilling fluid prepared in the examples.

[0157] Core plugging experiment procedure: (1) Fix the fully dried sandstone core on the core holder and install the forward displacement manifold and reverse displacement manifold. (2) Fill the slurry cup with simulated formation water, seal it, and check the remaining manifolds to ensure complete sealing. Set the confining pressure to 5MPa, the forward displacement pressure to 5MPa, and the flow rate to 2mL / min. Forwardly displace the saturated core and continue displacing for 1h to obtain the initial permeability K0 of the core. (3) Fill the slurry cup with 300mL of drilling fluid, keep the confining pressure and forward displacement pressure at 5MPa, and the flow rate at 2mL / min. Use the drilling fluid to plug the core to obtain the permeability K1 after core plugging.

[0158] Core unblocking experiment procedure: (1) Acid preparation: Prepare a 10.0wt% hydrochloric acid aqueous solution for later use. (2) Keep the confining pressure, positive displacement pressure and flow rate constant, and continuously inject the hydrochloric acid solution into the core after positive displacement and sealing for 5 hours, and measure the permeability K2 of the core after unblocking. The results are shown in Table 6.

[0159] Core permeability recovery rate is calculated using the following formula:

[0160] R = [(K2-K1) / K0] × 100%

[0161] In the formula: R is the core permeability recovery rate, %;

[0162] K0—Initial permeability of the core, mD;

[0163] K1—Permeability of the core sample after drilling fluid plugging, mD.

[0164] K2—Permeability of the core sample after acid unblocking, in mD.

[0165] Table 6. Core permeability recovery rate

[0166]

[0167] According to the experimental results in Table 6, after the high-temperature resistant, soil-free reservoir protection water-based drilling fluid of the present invention displaced the core sample, the core permeability recovery rate after acid treatment was all above 72%. This indicates that the drilling fluid mud cake can be effectively removed by the acid solution, relieving the blockage of the oil and gas reservoir by the sealing material, and also proves that the high-temperature resistant, soil-free reservoir protection water-based drilling fluid of the present invention has good reservoir protection properties.

[0168] In summary, the high-temperature resistant, soil-free reservoir protection water-based drilling fluid of this invention has a temperature resistance of up to 190℃ and exhibits good rheological and filtration properties under high-temperature and high-density conditions. It can be weighted to saturation with calcium chloride and calcium bromide, achieving a maximum density of 1.75 g / cm³. 3 The drilling fluid of this invention has an acid solubility rate of over 75% in the mud cake and a core permeability recovery rate of over 72%, exhibiting excellent reservoir protection properties and providing technical support for efficient drilling in deep, especially deep, reservoirs.

[0169] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0170] 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 describe the various possible combinations separately.

[0171] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A water-based drilling fluid for soil-free reservoir protection, characterized in that, The raw materials consist of the following parts by weight: 100 parts water, 0.2-0.4 parts primary pH adjuster, 1-3 parts oxygen scavenger, 0.1-0.4 parts thickener and shearing agent, 2-4 parts filtrate reducer, 4-6 parts magnesium aluminum hydrotalcite, 4-6 parts micro / nano alumina, 4-6 parts ultrafine calcium carbonate, 4-6 parts lubricant, 1-2 parts corrosion inhibitor, and 70-660 parts inorganic salt weighting agent. The first pH adjuster is sodium hydroxide or potassium hydroxide; The oxygen scavenger is any one of sodium sulfite, sodium bisulfite, urea, or anhydrous citric acid; The thickening and shearing agent is amphoteric polyacrylamide with a weight-average molecular weight of 4 million to 6 million, a cationic degree of 20-30%, and an anionic degree of 30%-40%. The filtration loss reducer is prepared from the following raw materials: dimethylaminopropylmethacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, docosyl methacrylate, 4-acryloylmorpholine, 4-vinylbenzoic acid, emulsifier, initiator, second pH adjuster, and deionized water; the mass ratio of dimethylaminopropylmethacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 4-vinylbenzoic acid, 4-acryloylmorpholine, and docosyl methacrylate is 25:10-15:5-6:3-5:2-3. The micro / nano alumina is composed of a mixture of micron-sized alumina particles and nano-sized alumina particles; wherein the average particle size of the micron-sized alumina particles is 1 μm to 2 μm, and the average particle size of the nano-sized alumina particles is 300 nm to 400 nm; the mass ratio of micron-sized alumina particles to nano-sized alumina particles is 2-6:1-3. The average particle size of the magnesium aluminum hydrotalcite is 800-900 mesh; the average particle size of the ultrafine calcium carbonate is 100 nm to 300 nm. The lubricant is liquid paraffin; the corrosion inhibitor is 1H-benzotriazole; and the inorganic salt weighting agent is anhydrous calcium chloride or anhydrous calcium bromide.

2. The water-based drilling fluid for soil-free reservoir protection according to claim 1, characterized in that, Filtration loss reducing agents include one or more of the following conditions: i. The emulsifier is any one of Span 80, Tween 80, or OP-10; the mass ratio of emulsifier to deionized oil is 0.01-0.05:100; ii. The initiator is potassium persulfate, ammonium persulfate, or 2,2'-azobis(2-methylpropylamidine) dihydrochloride; the ratio of initiator to total monomer mass is 0.010-0.25: 47-53; iii. The second pH adjuster is a NaOH aqueous solution with a concentration of 5-15 mol / L; iv. The mass ratio of total monomer mass to deionized water is 47-53:

100.

3. The water-based drilling fluid for soil-free reservoir protection according to claim 1, characterized in that, The preparation method of the filtration loss reducing agent includes the following steps: 2-Acrylamido-2-methylpropanesulfonic acid and 4-vinylbenzoic acid were added to deionized water, and the pH of the system was adjusted to 7.0 using a second pH adjuster. Dimethylaminopropylmethacrylamide and 4-acryloylmorpholine were added and dispersed thoroughly. Then, an emulsifier and dodecyl methacrylate were added and dispersed thoroughly. After heating to the reaction temperature, an initiator was added, and the mixture was reacted, dried, and pulverized to obtain a filtration loss reducer. The reaction temperature is 60-70℃, the reaction time is 2-6 hours, and the reaction is carried out under the protection of a protective gas and under stirring conditions; the protective gas is nitrogen or argon.

4. The method for preparing the soil-free reservoir protection water-based drilling fluid according to any one of claims 1-3, characterized in that, Including the following steps: Add the first pH adjuster to water and mix thoroughly; add the oxygen scavenger and mix thoroughly; add the viscosity improver and mix thoroughly; add the filtration loss reducer and mix thoroughly; add magnesium aluminum hydrotalcite and mix thoroughly; add micro-nano alumina and mix thoroughly; add ultrafine calcium carbonate and mix thoroughly; add the lubricant and mix thoroughly; add the corrosion inhibitor and mix thoroughly; finally add the inorganic salt weighting agent and mix thoroughly to obtain a soil-free reservoir protection water-based drilling fluid.

5. The application of the soil-free reservoir protection water-based drilling fluid as described in any one of claims 1-3 in deep and / or ultra-deep oil and gas drilling, characterized in that, The deep layer is a stratum with a depth greater than 4500m, and the ultra-deep layer is a stratum with a depth greater than 6000m.

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