High-temperature-resistant polymer for tackifying workover fluid for oil and gas wells and preparation and use methods of high-temperature-resistant polymer

Abstract

The invention relates to a high-temperature-resistant polymer for a tackifying workover fluid for an oil and gas well as well as a preparation method and a use method of the high-temperature-resistant polymer. 0.2 to 6.0 parts of an anionic monomer; 0.02 to 1.0 part of a copolymerization crosslinking monomer; 0.5 to 50.0 parts of lauryl sodium sulfate; 100 to 1000 parts of deionized water; 0.003 to 3.0 parts of an initiator; and 0.001 to 1.0 part of sodium sulfite; the copolymerized cross-linking monomer is at least one of 1, 5-diallyl naphthalene in 9, 10-diphenylethylene anthracene, 1, 4-diallyl benzene and 4, 4 '-diallyl biphenyl, and the copolymerized cross-linking monomer is at least one of 9, 10-diphenylethylene anthracene, 1, 4-diallyl benzene and 1, 5-diallyl naphthalene in 4, 4'-diallyl biphenyl. The invention provides an ultra-high-temperature-resistant polymer for a brine workover fluid and a preparation method thereof, wherein the ultra-high-temperature-resistant polymer can still keep good tackifying property, salt resistance, aging resistance, filtrate loss reduction property and sand washing and lithology carrying property in an ultra-deep well bottom temperature environment of 180 DEG C or above, and the ultra-high-temperature-resistant polymer TBG which is micro-crosslinked, grafted by biogel and good in water solubility is prepared.

Description

Technical Field

[0001] The present invention belongs to the field of oilfield exploitation, and particularly relates to a super-high temperature resistant polymer used for a viscosifying workover fluid in ultra-deep oil and gas wells, and a preparation method and a use method thereof. Background Art

[0002] With the development of oil and gas drilling and exploitation technologies in China, oil and gas exploitation has been moving towards ultra-deep layers. Therefore, during the exploitation process, a large number of ultra-deep oil and gas wells need to carry out workover operations to ensure the normal production of the oil and gas wells. The depths of these ultra-deep oil and gas wells exceed 6000 m, and even the depths of some wells reach 8000 m, and the bottom-hole temperature is as high as 180 °C or above. At present, high salinity oilfield formation water is generally used as the workover fluid at the construction site, or soluble inorganic salts or fresh water are added to the oilfield formation water to adjust the density of the brine, so as to match the formation pressure coefficient. However, due to the extremely low viscosity of the brine workover fluid, serious losses occur during the workover construction. For wells with severe losses, the loss volume in one workover can reach thousands of cubic meters. The brine has extremely weak suspension ability for cuttings, and its sand washing and cuttings carrying performance is poor. A large amount of losses not only damage the reservoir, but also make it difficult for the workover fluid to circulate in the annulus. In addition, the density of the brine is greatly affected by temperature, and it is difficult to effectively control the density of the workover fluid, which poses a hidden danger to the safety of the workover operation. Therefore, in order to ensure the safety of the workover operation, significantly reduce the loss of the workover fluid at the bottom hole, enhance the cuttings carrying ability of the workover fluid, and improve the workover efficiency, the solution viscosity of the workover fluid can be increased, and modified cellulose ethers such as sodium polyanionic cellulose and hydroxyethyl cellulose, as well as biopolymers such as commonly used xanthan gum, are added to the brine workover fluid.

[0003] The water-soluble modified cellulose ether solution has high solution viscosity and good salt resistance at temperatures below 70 °C, but it will degrade violently when the bottom-hole temperature is higher than 100 °C, and the thickening performance will be completely lost. The anti-aging performance of xanthan gum is significantly stronger than that of modified cellulose. It is used as a thickener in salt water, has good salt resistance, and obvious shear thinning and thixotropy, which is beneficial to the pumping of workover fluids and the sand washing and rock carrying at the bottom of the well. However, when the bottom-hole temperature is higher than 120 °C, xanthan gum will undergo serious thermal degradation, and the solution viscosity will drop sharply. Moreover, multivalent salts such as Ca2+, Mg2+, Fe2+, and Fe3+ at high temperatures will exacerbate the loss of solution viscosity. In the workover construction site, the water used to prepare workover fluids is generally formation water containing multivalent salts. This requires that the polymer used to thicken workover fluids for ultra-deep oil and gas wells can also resist multivalent salts when heated at ultra-high temperatures. The addition of formate or formate with a mass percentage concentration higher than 30% can improve the high-temperature thermal stability of xanthan gum brine solution to a certain extent, but at 160 °C, xanthan gum also begins to carbonize significantly, and the solution viscosity loss is serious. In addition, the use of high-concentration organic salts formate or formate significantly increases the cost of workover fluids. Even if a large amount of anti-aging additives are added, it is difficult for commonly used modified cellulose ethers and xanthan gum with good salt resistance to be used as thickeners for workover fluids in ultra-deep oil and gas wells with a bottom-hole temperature exceeding 180 °C. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a polymer resistant to ultra-high temperature for thickening workover fluids in ultra-deep oil and gas wells, and its preparation and use methods.

[0005] The technical solution of the present invention is as follows:

[0006] A polymer resistant to ultra-high temperature for thickening workover fluids in ultra-deep oil and gas wells, characterized in that the formula components include:

[0007]

[0008] 0.003 - 3.0 parts of initiator;

[0009] and 0.001 - 1.0 part of sodium sulfite;

[0010] The copolymerization cross-linking monomer is at least one of 9,10-diphenylanthracene, 1,4-diallylbenzene, 4,4'-diallylbiphenyl, and 1,5-diallylnaphthalene.

[0011] Preferably, the temperature-resistant biopolymer is dinatrol, welan gum, gellan gum, and / or scleroglucan,

[0012] Preferably, the anionic monomer is 2-acrylamido-2-methylpropanesulfonic acid and / or sodium 4-vinylbenzenesulfonate.

[0013] Preferably, the initiator is potassium persulfate.

[0014] The preparation method of the ultra-high temperature resistant polymer for the viscosifying workover fluid of ultra-deep oil and gas wells described above is characterized by including the following steps:

[0015] Add the temperature-resistant biogum and deionized water into a three-necked reaction flask, stir and then add the sodium dodecyl sulfate, add the initiators potassium persulfate and sodium sulfite, and then slowly add the anionic monomer and the copolymerization crosslinking monomer for reaction to obtain an ultra-high temperature resistant polymer with micro-crosslinking, biogum grafting and good water solubility.

[0016] Preferably, the stirring duration is 0.5 to 1 hour to fully dissolve the temperature-resistant biogum; add the initiators potassium persulfate and sodium sulfite at 40 to 80 °C.

[0017] Preferably, adjust the pH value of the solution to 5 to 8 with sodium hydroxide, and react for 6 to 24 hours under N 2 2.

[0018] The using method of the ultra-high temperature resistant polymer for the viscosifying workover fluid of ultra-deep oil and gas wells described above is characterized in that at room temperature, dissolve the polymer with a solvent into a concentrated solution, and then dilute the concentrated solution with a solvent to prepare 1000 grams of a polymer solution with a mass-volume concentration of 3 g / L to 20 g / L; then, during the stirring process, successively add 1.0 to 300 parts of an ultra-high temperature viscosity stabilizer and 0.1 to 10 parts of a bactericide, and continue to stir evenly; then add 0.1 to 10 parts of an ultra-high temperature deoxidizer and mix evenly; finally, add 0.5 to 4000 parts of a density regulator to obtain an ultra-deep oil and gas well viscosifying workover fluid with a density of 1.002 to 2.50 g / cm 3 3.

[0019] Preferably, the solvent is at least one of clear water and formation water in the oilfield, the ultra-high temperature viscosity stabilizer is at least one of trisodium nitrilotriacetate, sodium 2-hydroxypropionate, trisodium citrate, tetrasodium ethylenediaminetetraacetate, sodium propionate, potassium propionate, sodium formate, potassium formate, sodium acetate and potassium acetate, the bactericide is at least one of formaldehyde, glutaraldehyde, sodium trichlorophenate, glutaraldehyde, malondialdehyde and succinaldehyde, the ultra-high temperature deoxidizer is at least one of sodium bisulfite, potassium bisulfite, sodium sulfite, potassium sulfite, sodium borohydride, potassium borohydride, sodium dithionite, potassium dithionite, thiourea and o-xylenedithiourea, and the density regulator is at least one of sodium chloride, potassium chloride, calcium chloride, sodium bromide, potassium bromide, calcium bromide and zinc bromide.

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

[0021] The present invention provides a super high temperature resistant polymer used in brine workover fluid, which can still maintain good viscosifying property, salt tolerance, anti-aging property, filtration loss reducing property and sand washing and rock carrying property under the super deep well bottom temperature environment of 180 °C and above, and a preparation method thereof. The characteristics are that a temperature resistant biopolymer is used as a raw material, and through aqueous solution copolymerization reaction, anionic monomers are grafted onto the macromolecular chain of the temperature resistant biopolymer, and a temperature resistant crosslinking monomer is also added to the copolymerization system to prepare a slightly crosslinked, biopolymer grafted, super high temperature resistant polymer TBG with good water solubility. The temperature resistant biopolymer is at least one of diutan gum, welan gum, gellan gum and scleroglucan, the anionic monomer is at least one of 2-acrylamido-2-methylpropanesulfonic acid and sodium 4-vinylbenzenesulfonate, and the copolymerization crosslinking monomer is at least one of 9,10-distyrylanthracene, 1,4-diallylbenzene, 4,4'-diallylbiphenyl and 1,5-diallylnaphthalene.

[0022] The present invention discovers that in the preparation of super high temperature resistant water-soluble polymers, the concentration of temperature resistant biopolymer, the concentration of anionic monomer, the concentration of copolymerization crosslinking monomer, the reaction temperature, the concentration of initiator, the concentration of surfactant and the reaction pH value can significantly affect the solution properties of the obtained polymer, such as water solubility, viscosifying property, salt tolerance, anti-aging property and temperature resistance. Through the preferred components and conditions, the preparation of a super high temperature resistant polymer used in brine workover fluid, which can still maintain good viscosifying property, salt tolerance, anti-aging property and sand washing and rock carrying property under the super deep well bottom temperature environment of 180 °C and above, is realized.

[0023] In the present invention, first, the temperature resistant biopolymer is dissolved in deionized water at a certain temperature, and then potassium persulfate as an initiator is added. The anionic S 2 O 8 2- , under the action of the reducing agent Na 2 SO 3 , decomposes to generate free radicals SO 4- ·, which initiates the dehydrogenation of –OH on the molecular chain of the temperature resistant biopolymer to generate biopolymer free radicals. Then, the biopolymer free radicals initiate the copolymerization reaction of anionic monomers and crosslinking monomers, thereby grafting anionic monomer and crosslinking monomer units onto the temperature resistant biopolymer, and preparing a slightly crosslinked biopolymer grafted polymer containing –SO3 2- ions.

[0024] Although the thermal stability of the uncrosslinked temperature resistant biopolymer is stronger than that of the commonly used xanthan gum, but under the synergistic action of other additives, even when saturated potassium formate or sodium formate is added, when it is aged at a temperature above 190 °C for 16 h, the viscosity of the brine solution is severely lost. Therefore, in the present invention, the free radical micellar polymerization method is adopted to graft a temperature resistant and hydrophilic sulfonate-type anionic monomer into the temperature resistant biopolymer, and at the same time, a trace amount of copolymerization crosslinking monomer is introduced into the grafted polymer.

[0025] Compared with the unmodified high-temperature-resistant bioadhesive, the ultra-high-temperature-resistant polymer TBG contains grafted polymer chains. Moreover, due to the presence of large side groups, these grafted polymer chains are rigid, which further enhances the rigidity and extensibility of polymer TBG in saline solution, avoiding the precipitation of the polymer at ultra-high temperatures; the introduction of –SO3 2- ions, which makes the polymer more hydrophilic and avoids the dehydration of the polymer after being heated for a long time at ultra-high temperatures; the structure of the TBG molecular chain is a micro-crosslinked structure, and this micro-crosslinked structure contains an aromatic ring structure with rigidity and strong thermal stability, which also significantly enhances the rigidity of the TBG polymer chain, making its molecular chain structure stable at ultra-high temperatures, thereby significantly improving the anti-aging property, thickening property, temperature resistance, and salt resistance of TBG at ultra-high temperatures, especially significantly weakening the polyvalent salt effect and being able to resist high-concentration polyvalent metal cations such as Ca 2+ 、Mg 2+ 、Fe 3+ and Fe 2+ etc. in formation water at ultra-high temperatures.

[0026] The introduction of grafting, micro-crosslinking, salt-resistant hydrophilic groups, and crosslinking-point aromatic ring structure in the ultra-high-temperature-resistant polymer TBG, combined with the synergistic effect of various additives in the workover fluid. For example, the bactericide in the system can prevent the growth of bacteria, the ultra-high-temperature deoxidizer can remove trace oxygen in the system, avoiding the oxidative degradation and carbonization of polymer TBG at ultra-high temperatures, and the ultra-high-temperature viscosity stabilizer can complex polyvalent salts in the system, weakening the salt effect of polyvalent salts on TBG. This enables the ultra-deep oil and gas well thickening workover fluid prepared with the ultra-high-temperature-resistant polymer to still maintain good anti-aging property, thickening property, salt resistance, sand washing and rock carrying property, and filtration loss reduction property at the bottom hole temperature of 180°C - 240°C. Specific Embodiments

[0027] The present invention will be further described in detail below with reference to specific embodiments.

[0028] Example 1

[0029] Add 5.0 grams of Dingyou glue and 500 grams of deionized water into a three-neck reaction flask, stir for 1 hour to fully dissolve the high-temperature-resistant bioadhesive, then add 10.0 grams of sodium dodecyl sulfate, add 1.092 grams of initiator potassium persulfate and 0.260 grams of sodium sulfite at 60°C, and then slowly add 2.5 grams of 2-acrylamido-2-methylpropanesulfonic acid and 0.10 grams of 4,4′-diallylbiphenyl. Adjust the pH value of the solution to 7.0 with sodium hydroxide, and react for 24 hours under N 2 to prepare the micro-crosslinked, bioadhesive-grafted ultra-high-temperature-resistant polymer TBG.

[0030] At room temperature, dissolve TBG in oilfield formation water to form a concentrated solution, and then dilute the concentrated solution with formation water to prepare 1000 grams of a polymer solution with a mass-volume concentration of 8 g / L. The formation water contains 17 g / L of sodium chloride, 2.0 g / L of calcium chloride, 3.5 g / L of magnesium chloride, 45 mg / L of iron(III) chloride, and 12 mg / L of iron(II) chloride until the TBG is completely dissolved. Then, during the stirring process, successively add 3.0 grams of sodium ethylenediaminetetraacetate, 4.0 grams of nitrilotriacetic acid trisodium salt, 80 grams of potassium formate, 60 grams of sodium formate, 40 grams of sodium acetate, 0.8 grams of sodium trichlorophenate, 0.7 grams of glutaraldehyde, and continue to stir evenly. Then add 1.5 grams of sodium bisulfite, 1.0 gram of thiourea, 0.8 grams of o-xylthiourea, and mix well. Then add 5 grams of potassium chloride to adjust the density of the workover fluid. Finally, a workover fluid with a density of 1.124 g / cm 3 and can be applied to high-viscosity workover fluids for ultra-deep oil and gas wells with bottom-hole temperatures of 180 °C to 240 °C.

[0031] Example 2

[0032] Add 3.0 grams of DY gum, 2.0 grams of Welan gum, and 300 grams of deionized water to a three-necked reaction flask, stir for 1 hour to fully dissolve the temperature-resistant biopolymer, then add 15 grams of sodium dodecyl sulfate, add 1.638 grams of initiator potassium persulfate and 0.378 grams of sodium sulfite at 65 °C, then slowly add 3.50 grams of 4-vinylbenzenesulfonic acid sodium salt and 0.25 grams of 1,4-diallylbenzene, adjust the pH value of the solution to 6.0 with sodium hydroxide, and react for 8 hours under N 2 to prepare a micro-crosslinked, biopolymer-grafted ultra-high temperature-resistant polymer TBG.

[0033] At room temperature, dissolve TBG in fresh water to form a concentrated solution, and then dilute the concentrated solution with fresh water to prepare 1000 grams of a polymer solution with a mass-volume concentration of 17.0 g / L. Then, during the stirring process, successively add 4.0 grams of sodium ethylenediaminetetraacetate, 5.0 grams of 2-hydroxypropionate, 100 grams of potassium formate, 30 grams of potassium acetate, 0.6 grams of formaldehyde, 0.5 grams of malonaldehyde, and continue to stir evenly. Then add 1.0 gram of potassium borohydride, 0.8 grams of thiourea, and mix well. Then add 10 grams of sodium chloride to adjust the density of the workover fluid. Finally, a workover fluid with a density of 1.094 g / cm 3 and can be applied to high-viscosity workover fluids for ultra-deep oil and gas wells with bottom-hole temperatures of 180 °C to 240 °C.

[0034] Example 3

[0035] 1.0 g of welan gum, 4.0 g of gellan gum and 700 g of deionized water were added to a three-necked reaction flask, and stirred for 1 hour to fully dissolve the temperature-resistant biopolymer. Then 28 g of sodium dodecyl sulfate was added. At 70 °C, 1.913 g of initiator potassium persulfate and 0.452 g of sodium sulfite were added, and then 1.5 g of 2-acrylamido-2-methylpropanesulfonic acid, 2.5 g of sodium 4-vinylbenzenesulfonate and 0.40 g of 9,10-diphenylanthracene were slowly added. The pH value of the solution was adjusted to 6.0 with sodium hydroxide. Under N 2 atmosphere, the reaction was carried out for 12 hours to obtain a micro-crosslinked and biopolymer-grafted ultra-high temperature resistant polymer TBG.

[0036] At room temperature, TBG was dissolved in water to form a concentrated solution, and then the concentrated solution was diluted with water to prepare 1000 g of a polymer solution with a mass-volume concentration of 12.0 g / L. Then, during stirring, 6.0 g of trisodium nitrilotriacetate, 4.0 g of trisodium citrate, 200 g of potassium formate, 30 g of potassium propionate, 50 g of sodium acetate, 1.0 g of formaldehyde, and 0.6 g of adipic dialdehyde were successively added, and stirring was continued until homogeneous. Then 0.8 g of potassium dithionite and 1.0 g of o-xylthiourea were added and mixed thoroughly. Then 230 g of sodium chloride and 600 g of calcium bromide were added to regulate the density of the workover fluid. Finally, a workover fluid with a density of 1.603 g / cm 3 and applicable to ultra-deep oil and gas wells with bottom hole temperatures of 180 °C to 240 °C for viscosity-increasing workover fluid was obtained.

[0037] Example 4

[0038] 3.0 g of scleroglucan, 2.0 g of welan gum and 900 g of deionized water were added to a three-necked reaction flask, and stirred for 0.5 hour to fully dissolve the temperature-resistant biopolymer. Then 36 g of sodium dodecyl sulfate was added. At 75 °C, 2.680 g of initiator potassium persulfate and 0.635 g of sodium sulfite were added, and then 3.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 2.5 g of sodium 4-vinylbenzenesulfonate, 0.60 g of 1,5-diallylnaphthalene and 0.10 g of 1,4-diallylbenzene were slowly added. The pH value of the solution was adjusted to 6.0 with sodium hydroxide. Under N 2 atmosphere, the reaction was carried out for 16 hours to obtain a micro-crosslinked and biopolymer-grafted ultra-high temperature resistant polymer TBG.

[0039] At room temperature, dissolve TBG in clear water to form a concentrated solution, and then dilute the concentrated solution with clear water to prepare 1000 grams of a polymer solution with a mass-volume concentration of 8.0 g / L. Then, during stirring, successively add 8.0 grams of sodium ethylenediaminetetraacetate, 3.0 grams of sodium 2-hydroxypropionate, 60 grams of sodium formate, 40 grams of potassium acetate, 0.6 grams of glutaraldehyde, and 0.5 grams of sodium trichlorophenate, and continue stirring until evenly mixed. Then add 0.6 grams of potassium bisulfite and 0.7 grams of sodium borohydride, and mix thoroughly. Then add 10 grams of sodium chloride, 5.0 grams of calcium chloride, and 3 grams of zinc bromide to adjust the density of the workover fluid. Finally, a workover fluid with a density of 1.076 g / cm 3 and can be applied to the viscosifying workover fluid for ultra-deep oil and gas wells with bottom-hole temperatures of 180°C to 240°C.

[0040] Example 5

[0041] Add 4.0 grams of dextran, 1.0 gram of scleroglucan, and 1000 grams of deionized water to a three-necked reaction flask, stir for 1.0 hour to fully dissolve the temperature-resistant biopolymer, then add 48 grams of sodium dodecyl sulfate, add 2.893 grams of initiator potassium persulfate and 0.820 grams of sodium sulfite at 75°C, and then slowly add 2.0 grams of 2-acrylamido-2-methylpropanesulfonic acid, 3.5 grams of sodium 4-vinylbenzenesulfonate, 0.20 grams of 4,4′-diallylbiphenyl, and 0.30 grams of 1,4-diallylbenzene. Adjust the pH value of the solution to 7.5 with sodium hydroxide, and react for 24 hours under N 2 to prepare a micro-crosslinked and biopolymer-grafted ultra-high temperature-resistant polymer TBG.

[0042] At room temperature, dissolve TBG in clear water to form a concentrated solution, and then dilute the concentrated solution with clear water to prepare 1000 grams of a polymer solution with a mass-volume concentration of 5.0 g / L. Then, during stirring, successively add 3.0 grams of nitrilotriacetic acid trisodium salt, 50 grams of sodium formate, 10 grams of sodium propionate, 0.6 grams of glutaraldehyde, 0.3 grams of formaldehyde, and 0.2 grams of succinaldehyde, and continue stirring until evenly mixed. Then add 0.5 grams of o-xylthiourea and 0.4 grams of potassium dithionite, and mix thoroughly. Then add 10 grams of potassium chloride and 5 grams of sodium chloride to adjust the density of the workover fluid. Finally, a workover fluid with a density of 1.048 g / cm 3 and can be applied to the viscosifying workover fluid for ultra-deep oil and gas wells with bottom-hole temperatures of 180°C to 240°C.

[0043] Performance test:

[0044] Table 1 Effect of test temperature on the apparent viscosity of the viscosifying workover fluid for ultra-deep oil and gas wells before aging

[0045]

[0046] Note: Test shear rate: 170.3 s -1

[0047] Table 2 Influence of Different Aging Temperatures on Apparent Viscosity of Viscosity-increasing Workover Fluid for Ultra-deep Oil and Gas Wells

[0048]

[0049] Note: Test temperature: 30°C, Shear rate: 170.3 s -1 , Aging time: 16 h

[0050] Table 3 Apparent Viscosity and Rheological Parameters of Samples after Aging at 210°C for 16 h in Example 1

[0051]

[0052] Note: Test temperature: 30°C, Flow behavior index n is a dimensionless quantity, Unit of consistency coefficient K is Pa·s n 。

[0053] Analysis of Test Results:

[0054] (1) The relationship between the apparent viscosity of the viscosity-increasing workover fluid for ultra-deep oil and gas wells prepared with ultra-high temperature resistant polymers and the test temperature is shown in Table 1. Since after the test temperature exceeds 140°C, some water in the sample will volatilize during the test, thus affecting the accuracy of the test results. Therefore, the test temperature is only measured up to 140°C. When the temperature is below 100°C, the apparent viscosity of the viscosity-increasing workover fluid increases with the increase of the test temperature; when the temperature is above 100°C, the apparent viscosity gradually decreases, but within the whole temperature range, the influence of temperature on the apparent viscosity of the workover fluid prepared with ultra-high temperature resistant polymers is relatively small. The results show that the viscosity-increasing workover fluid for ultra-deep oil and gas wells prepared with ultra-high temperature resistant polymers has good temperature resistance performance.

[0055] (2) The relationship between the apparent viscosity of the viscosity-increasing workover fluid for ultra-deep oil and gas wells prepared with ultra-high temperature resistant polymers and the aging temperature is shown in Table 2. The aging time of all samples is 16 h. The viscosity-increasing workover fluid for ultra-deep oil and gas wells prepared with ultra-high temperature resistant polymers still has high viscosity and viscosity retention rate after aging at ultra-high temperatures of 230°C and 240°C for 16 h, thus enabling the polymer workover fluid to have good sand washing and rock carrying performance and filtration loss reduction performance at the ultra-high temperature bottom hole. The results show that the micro-crosslinked bio-gum grafted polymer obtained by grafting and crosslinking copolymerization of temperature-resistant bio-gum with anionic monomers and copolymer crosslinking monomers has good anti-aging performance at ultra-high temperatures, still has good viscosity-increasing performance after being heated for a long time at ultra-high temperatures, and can resist high concentrations of Fe 3+ , Fe 2+ , Ca 2+ and Mg 2+ and other polyvalent metal cations in formation water.

[0056] (3) After the ultra-deep oil and gas well viscosifying workover fluid formulated with the ultra-high temperature resistant polymer of Example 1 was aged at 210 °C for 16 h, the apparent viscosities at different shear rates are shown in Table 3. The flow behavior index n value in Table 3 is lower than 1, and the consistency coefficient K value is higher, which indicates that the ultra-high temperature resistant polymer in the workover fluid still has good pseudoplasticity and viscosifying property after being heated at ultra-high temperature for a long time. This makes the apparent viscosity of the workover fluid low during the wellbore flow at high shear rates, that is, the frictional resistance in the wellbore is low, but during the annulus flow at lower shear rates, the apparent viscosity increases significantly, which is beneficial for sand washing and rock carrying. The results show that the ultra-deep oil and gas well viscosifying workover fluid after being heated at ultra-high temperature for a long time exhibits good pseudoplastic behavior and still has good sand washing and rock carrying property at the ultra-high temperature well bottom.

[0057] The above embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Researchers in the field can make some non-essential improvements and adjustments to the present invention according to the content of the present invention, and all should fall within the protection scope of the claims of the present invention.

Claims

1. A super high temperature resistant polymer for thickening workover fluid in oil and gas wells, characterized in that the formula components include: 5.0 parts of temperature resistant biopolymer; 0.2 - 6.0 parts of anionic monomer; 0.02 - 1.0 parts of copolymerization crosslinking monomer; 0.5 - 50.0 parts of sodium dodecyl sulfate; 100 - 1000 parts of deionized water; 0.003 - 3.0 parts of initiator; and 0.001 - 1.0 parts of sodium sulfite; the copolymerization crosslinking monomer is at least one of 9,10 - diphenylanthracene, 1,4 - diallylbenzene, 4,4′ - diallylbiphenyl and 1,5 - diallylnaphthalene.

2. The polymer according to claim 1, characterized in that the temperature resistant biopolymer is diutan gum, welan gum, gellan gum and / or scleroglucan.

3. The polymer according to claim 1, characterized in that the anionic monomer is 2 - acrylamido - 2 - methylpropanesulfonic acid and / or sodium 4 - vinylbenzenesulfonate.

4. The polymer according to claim 1, characterized in that the initiator is potassium persulfate.

5. A preparation method of a super high temperature resistant polymer for thickening workover fluid in oil and gas wells according to any one of claims 1 - 4, characterized in that it includes the following steps: Add the temperature resistant biopolymer and deionized water into a three - necked reaction flask, stir and then add the sodium dodecyl sulfate, add the initiator potassium persulfate and sodium sulfite, and then slowly add the anionic monomer and copolymerization crosslinking monomer for reaction to obtain the super high temperature resistant polymer.

6. The method according to claim 5, characterized in that the stirring time is 0.5 - 1 hour to fully dissolve the temperature resistant biopolymer; add the initiator potassium persulfate and sodium sulfite at 40 - 80°C.

7. The method according to claim 5, characterized in that Adjust the pH value of the solution to 5-8 with sodium hydroxide and react for 6-24 hours while passing N 2 under.

8. A usage method of a super high temperature resistant polymer for thickening workover fluid in oil and gas wells according to any one of claims 1 - 4, characterized in that At room temperature, dissolve the polymer into a concentrated solution with a solvent, and then dilute the concentrated solution with a solvent to prepare 1000 grams of a polymer solution with a mass - volume concentration of 3 g / L - 20 g / L; then, during stirring, successively add 1.0 - 300 parts of super high temperature viscosity stabilizer and 0.1 - 10 parts of bactericide, and continue to stir evenly; then add 0.1 - 10 parts of super high temperature deoxidizer and mix evenly; finally, add 0.5 - 4000 parts of density regulator to obtain a super deep oil and gas well thickening workover fluid with a density of 1.002 - 2.50 g / cm3.

9. The method according to claim 8, characterized in that The solvent is at least one of fresh water and formation water in the oilfield. The ultra-high temperature viscosity stabilizer is at least one of trisodium nitrilotriacetate, sodium 2-hydroxypropionate, trisodium citrate, tetrasodium ethylenediaminetetraacetate, sodium propionate, potassium propionate, sodium formate, potassium formate, sodium acetate and potassium acetate. The bactericide is at least one of formaldehyde, glutaraldehyde, sodium trichlorophenate, glutaraldehyde, malondialdehyde and succinaldehyde. The ultra-high temperature deoxidizer is at least one of sodium bisulfite, potassium bisulfite, sodium sulfite, potassium sulfite, sodium borohydride, potassium borohydride, sodium dithionite, potassium dithionite, thiourea and o-xylylthiourea. The density regulator is at least one of sodium chloride, potassium chloride, calcium chloride, sodium bromide, potassium bromide, calcium bromide and zinc bromide.

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