Temperature-resistant and salt-resistant zwitterionic nanoplugging agent and preparation and application thereof

Abstract

The application belongs to the technical field of petroleum engineering, and particularly relates to a temperature-resistant and salt-resistant zwitterionic nano plugging agent and a preparation and application thereof. The plugging agent is composed of cationic monomers, anionic monomers, neutral monomers, an initiator and modified nano SiO2. The cationic monomers are (3-acrylamidopropyl) trimethylammonium chloride and / or dimethyldiallylammonium chloride; the anionic monomers are 2-acrylamido-2-methylpropanesulfonic acid; the neutral monomers are N-vinylpyrrolidone; and the initiator is azobisdimethylamidino hydrochloride. In the application, a carbon-carbon double bond is connected to the surface of SiO2 nanoparticles by using KH570, and then a variety of monomers are mixed to initiate a free radical chain polymerization reaction on the surface of SiO2 particles under the action of the initiator, so as to obtain the plugging agent. The plugging agent has good high-temperature resistance and salt resistance, and is suitable for formation pore and fracture plugging in extreme environments, and can effectively prevent wellbore instability.

Description

Technical Field

[0001] This invention belongs to the field of petroleum engineering technology, specifically relating to a temperature- and salt-resistant zwitterionic nano-blocking agent and its preparation and application. Background Technology

[0002] Wellbore instability, such as wellbore collapse, is a common and complex downhole problem, particularly severe in the drilling of deep wells and shale wells. A major cause of wellbore instability is the prevalence of micro / nano fractures in the formation. When water-based drilling fluids are used to drill into such formations, the drilling fluid filtrate seeps into the formation along these fractures, causing changes in formation pore pressure and rock strength, leading to wellbore collapse and spalling. Therefore, effectively sealing these formation fractures is crucial.

[0003] Currently, to effectively seal formation micro / nano fractures, asphalt-based, polymeric alcohol-based, nano-latex-based, and polymer-modified nanoparticles are commonly added to drilling fluids to seal formation pore throats and fractures, reduce pore pressure transmission and mud cake permeability, prevent drilling fluid filtrate from invading the formation, and improve the effective strength of the surrounding rock formations. However, these methods have the following drawbacks: asphalt-based plugging agents have poor environmental performance; polymeric alcohol-based plugging agents have poor temperature resistance and sealing strength; nano-latex-based plugging agents have poor foaming and / or temperature resistance and storage stability; and polymer-modified nanoparticles have poor salt resistance or temperature and salt resistance. To improve the temperature and salt resistance of plugging agents, some researchers have attempted to use high-density anionic polymers to modify nanoparticles. For example, Xie Gang et al. modified nano-silicon nitride with high-density anionic polymers to obtain a high-strength salt-resistant plugging agent; Ma Lan et al. obtained a temperature- and salt-resistant plugging agent by introducing a high-density potassium methyl methacrylate sulfonate polymer onto the surface of graphene oxide. Grafting high-density anionic polymers onto the surface of nanoparticles can improve their salt resistance, but this method is "acceptable" and its salt resistance is limited.

[0004] The invention patent with publication number CN107501456A discloses a method for preparing a cationic plugging agent for drilling fluid. The plugging agent is prepared by emulsion polymerization using styrene, butyl acrylate, and dimethyl diallyl ammonium chloride as raw materials. However, the plugging agent is cationic and is not resistant to calcium salts. Summary of the Invention

[0005] In view of this, in order to overcome the problems of poor temperature and salt resistance of existing plugging agents, and to overcome the problems of easy thermal degradation in high temperature environment and easy flocculation and sedimentation in high salt environment, which leads to poor plugging effect and plugging failure, one of the objectives of this invention is to provide an amphoteric polymer modified nanoparticle plugging agent suitable for extreme environments such as high temperature, high sodium salt content, and high calcium salt content.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A temperature- and salt-resistant amphoteric nano-blocking agent, wherein the blocking agent is an amphoteric blocking agent; the blocking agent is composed of a cationic monomer, an anionic monomer, a neutral monomer, an initiator, and modified nano-SiO2; the cationic monomer is (3-acrylamidopropyl)trimethylammonium chloride (AAPTAC) and / or dimethyldiallylammonium chloride (DMDAAC); the anionic monomer is 2-acrylamido-2-methylpropanesulfonic acid (AMPS); the neutral monomer is N-vinylpyrrolidone (NVP); the molar ratio of the cationic monomer, anionic monomer, and neutral monomer is 5:1:1 to 1:1:5.

[0008] The plugging agent of this invention exhibits anti-polyelectrolyte effect solution behavior, and is not "passively resistant to salt" but "actively responsive to salt." The grafted polymer chains are more extended in the salt environment, enabling the plugging agent of this invention to be stably dispersed in high-concentration salt environments. The presence of silicon-based particle cores gives the plugging agent of this invention good high-temperature resistance. Furthermore, through particle size matching optimization, the particle size range of the plugging agent of this invention is more suitable for sealing formation fractures, thereby more effectively ensuring wellbore stability.

[0009] Furthermore, the structural formula of the AAPTAC is shown in Formula II, and the structural formula of the DMDAAC is shown in Formula III.

[0010] , ;

[0011] Furthermore, the extreme environments include high temperature, high sodium content, and high calcium content environments.

[0012] Furthermore, the initiator is azobisisobutyramidine hydrochloride (AIBA).

[0013] Furthermore, the modified nano-SiO2 is SiO2@KH570.

[0014] Preferably, the molar ratio of the cationic monomer, anionic monomer, and neutral monomer is 1:1:1.

[0015] Furthermore, the molecular structure of the plugging agent is shown in Formula I;

[0016] ;

[0017] Where R1 is or Degree of polymerization a:b:c = 5:1:1 ~ 1:1:5.

[0018] The second objective of this invention is to provide a method for preparing a temperature- and salt-resistant zwitterionic nano-blocking agent.

[0019] To achieve the above objectives, the present invention adopts the following technical solution:

[0020] The preparation method of the plugging agent includes the following steps:

[0021] S1: Modified SiO2 was prepared by using KH570 to attach carbon-carbon double bonds to the surface of SiO2 nanoparticles.

[0022] S2: The modified nano-SiO2 obtained in S1 is mixed with the cationic monomer, the anionic monomer and the neutral monomer, ultrasonically dispersed and then the initiator is added to carry out a free radical chain polymerization reaction to obtain the blocking agent.

[0023] Furthermore, the particle size range of the nano-SiO2 particle raw material is 20~100nm, of which silicon-based particles with a particle size of 20nm account for ≥75%.

[0024] Furthermore, the optimal total concentration of the anionic monomer, cationic monomer, and neutral monomer in the blocking agent is 25 w / w.

[0025] Preferably, the molar ratio of the anionic monomer, the cationic monomer, and the neutral monomer is 1:1:1.

[0026] Furthermore, the amount of initiator added is 0.15~0.35 w / w of the total mass of the monomers.

[0027] Preferably, the optimal amount of the initiator is 0.2 w / w.

[0028] Furthermore, the amount of modified SiO2 added is 2.5~5.5 w / w of the total mass of the monomer.

[0029] Preferably, the optimal amount of the initiator is 5 w / w.

[0030] Furthermore, the polymerization reaction takes 1 to 5 hours and the reaction temperature is 45 to 65°C.

[0031] Preferably, the polymerization reaction takes 4-5 hours and the reaction temperature is 56-65°C. Most preferably, the polymerization reaction takes 4 hours and the reaction temperature is 56°C.

[0032] Further, S1 specifically involves: ① taking 100 mL of a mixture of anhydrous ethanol / deionized water and placing it in a beaker, adding 5 g of SiO2 particles, and ultrasonically dispersing for 15 min; ② taking 100 mL of the mixture of anhydrous ethanol / deionized water and adding KH570 silane coupling agent (5 v / v%), adjusting the pH of the solution to 4 with hydrochloric acid, stirring for 2 h, and carrying out a hydrolysis reaction; ③ mixing the solutions obtained in steps ① and ② together and stirring at 60 °C for 3 h; centrifuging, washing three times with anhydrous ethanol, and placing the obtained precipitate in a 60 °C oven for vacuum drying for 4 h to obtain the modified SiO2.

[0033] Furthermore, in the anhydrous ethanol / deionized water mixed solution, the volume ratio of anhydrous ethanol to deionized water is 9:1.

[0034] Further, S2 specifically involves: dissolving the anionic monomer in deionized water, adjusting the pH to neutral with NaOH solution (1 mol / L); adding the neutral monomer and cationic monomer sequentially under stirring, followed by adding the modified SiO2 prepared in S1 under stirring; ultrasonically dispersing for 25 min after the nanoparticles are completely dissolved; transferring the above mixture into a three-necked flask, purging with nitrogen for 30 min, heating to 45-65°C, adding the initiator, and polymerizing for 1-5 h to obtain a gel-like product, washing 3-4 times with anhydrous ethanol, shearing and granulating, and drying at 75°C for 24 h to obtain the blocking agent.

[0035] The third objective of this invention is to provide a drilling fluid.

[0036] To achieve the above objectives, the present invention adopts the following technical solution:

[0037] Drilling fluid containing the plugging agent described in Purpose 1.

[0038] The fourth objective of this invention is to provide a method for sealing formation micro / nanopores and fissures using the aforementioned sealing agent and / or drilling fluid. Adding the sealing agent of this invention to the drilling fluid can effectively seal formation micro / nanopore throats and fissures, reduce pore pressure transmission and mud cake permeability, prevent drilling fluid filtrate from invading the formation, and improve the effective strength of the rock strata surrounding the wellbore.

[0039] To achieve the above objectives, the present invention adopts the following technical solution:

[0040] A method for sealing formation fractures using the plugging agent and / or the drilling fluid, wherein the plugging agent is added to the drilling fluid and / or the drilling fluid is used directly for drilling.

[0041] The fifth objective of this invention is to provide an application of the plugging agent described in objective one in improving the plugging performance of drilling fluid.

[0042] The plugging agent can be used to seal formation micro / nanopore throats and fissures, reduce pore pressure transmission and mud cake permeability, prevent drilling fluid filtrate from invading the formation, and improve the effective strength of the rock formations surrounding the wellbore.

[0043] Furthermore, the sealing performance includes temperature resistance and salt resistance.

[0044] The sixth objective of this invention is to provide an application of the plugging agent described in objective one in improving the rheological properties and filtration performance of drilling fluids under high temperature and high salinity conditions.

[0045] The seventh objective of this invention is to provide an application of the plugging agent and / or the drilling fluid in sealing formation micro / nanopores and fractures and maintaining wellbore stability.

[0046] The beneficial effects of this invention are as follows:

[0047] 1. Compared with previously reported plugging agents, the plugging agent of this invention is not "passively salt-resistant" but "actively salt-responsive". The grafted polymer chains are more extended in the salt environment, which makes the plugging agent of this invention stably dispersed for a long time in extreme environments such as high temperature, high sodium content, and high calcium content, so as to better exert the micro / nano plugging effect and ensure well wall stability.

[0048] 2. Through extensive experiments, this invention optimizes the selection of monomers, the exploration of the molar ratio between monomers, the amount of modified SiO2, time, temperature, and other conditions, and finally obtains the optimal preparation conditions for the plugging agent of this invention. The plugging agent prepared by this method has better plugging performance, better high-temperature resistance, and better nitrate performance. Attached Figure Description

[0049] Figure 1 This is a graph showing the long-term dispersion stability results, where... Figure 1 Figure A shows the dispersion stability test results of unmodified SiO2 after standing for 0 hours. Figure 1 Figure B shows the dispersion stability test results of unmodified SiO2 after standing for 30 minutes; Figure 1 Figure C shows the dispersion stability test results of the plugging agent SiO2-g-PNST of this invention after standing for 0 hours; Figure 1 Figure D shows the dispersion stability test results of the plugging agent SiO2-g-PNST of this invention after standing for 10 days;

[0050] Figure 2 This is a particle size distribution diagram of unmodified SiO2;

[0051] Figure 3 This is a particle size distribution diagram of the plugging agent SiO2-g-PNST of the present invention;

[0052] Figure 4 This is a schematic diagram of the filter cake. Detailed Implementation

[0053] The technical solution of the present invention will be described more clearly and completely below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0054] Example 1. Preparation method of plugging agent

[0055] (1) SiO2 particles were modified with KH570 to attach carbon-carbon double bonds to the surface of the SiO2 particles. Specific steps: Anhydrous ethanol and deionized water were mixed at a volume ratio of 9:1. 100 mL of the anhydrous ethanol / deionized water mixture was placed in a beaker, and 5 g of SiO2 particles were added. The mixture was ultrasonically dispersed for 15 min. Another 100 mL of the anhydrous ethanol / deionized water mixture was then added, along with KH570 silane coupling agent (5 v / v%). The pH of the solution was adjusted to 4 with hydrochloric acid, and the mixture was stirred for 2 h to carry out the hydrolysis reaction. The two solutions were then mixed together and stirred at 60 °C for 3 h. The mixture was centrifuged, washed three times with anhydrous ethanol, and the resulting precipitate was vacuum dried in a 60 °C oven for 4 h to obtain SiO2@KH570, thus attaching carbon-carbon double bonds to the surface of the SiO2 particles.

[0056] (2) Surface-initiated free radical chain polymerization reaction. Specific steps: Dissolve the anionic monomer in deionized water, and adjust the pH to neutral with NaOH solution (1 mol / L). Under stirring, add the neutral monomer and cationic monomer in sequence, and continue to add SiO2@KH570 particles under stirring. After the nanoparticles are completely dissolved, ultrasonically disperse for 25 min. Transfer the above mixture to a three-necked flask, purge with nitrogen for 30 min, raise the temperature to 45~65℃, add the initiator, and after polymerization reaction for 1~5 h, obtain a gel-like product. Wash with anhydrous ethanol 3-4 times, shear and granulate, and dry at 75℃ for 24 h to obtain the blocking agent SiO2-g-PNST of this invention.

[0057] Example 2

[0058] The partial synthesis scheme of the plugging agent SiO2-g-PNST of the present invention is shown in Table 2, and it is prepared by the preparation method of Example 1.

[0059] Table 1. Preferred synthesis scheme of the plugging agent SiO2-g-PNST of the present invention

[0060]

[0061] Example 3. Performance evaluation of the plugging agent

[0062] Taking the plugging agent prepared by Scheme 1# as an example, the performance of the plugging agent of the present invention is evaluated.

[0063] 1) Dispersion performance evaluation

[0064] a. Macro-level observation of dispersion

[0065] Saturated sodium chloride brine and 11 wt% calcium chloride brine were prepared, and the pH was adjusted to 8.5-9 using NaCO3. Unmodified silicon-based nanoparticles and SiO2-g-PNAS were dispersed in saturated sodium chloride brine and 11 wt% calcium chloride brine, respectively, at a concentration of 10 mg / mL. The sedimentation of the particles was observed after prolonged standing. The unmodified silicon-based nanoparticle suspension was ultrasonically dispersed for 5 min, while the unmodified suspension was stirred at low speed for 5 min. The resulting suspensions were diluted and the particle size distribution was measured.

[0066] The results are as follows Figure 1 As shown, the unmodified SiO2 particle dispersion exhibited aggregation within half an hour despite ultrasonic treatment, with the aggregation being particularly pronounced in brine. The SiO2-g-PNST particle dispersion, though not ultrasonically treated, maintained dispersion stability for an extended period, showing no significant aggregation even after standing for over a week in saturated sodium chloride brine and high-concentration calcium chloride brine.

[0067] b. Microparticle size analysis

[0068] like Figures 2-3 As shown, the unmodified particles become very large in salt water, D 50 The particle size is close to 10 μm, indicating that the unmodified SiO2 particles exhibit significant agglomeration. In contrast, the modified particles maintain a smaller particle size range in salt water. 50 The particle size decreased to below approximately 200 nm, indicating that SiO2-g-PNST exhibits stable nano / submicron particle size dispersion in salt water.

[0069] 2) Evaluation of mud cake permeability and rheological properties

[0070] a. Drilling fluid-based slurry preparation:

[0071] Add 4% bentonite to deionized water, adjust the pH to 8.5-9 using anhydrous Na2CO3, stir well, and cure in a sealed container for 24 hours to obtain a freshwater-based slurry.

[0072] Take 300 mL of freshwater-based slurry and add 35% NaCl or 11% CaCl2, stir at high speed for 20-30 min to obtain saturated sodium chloride brine-based slurry or high-concentration calcium brine-based slurry, as the control group. Add SiO2-g-PNST to the above brine-based slurry as the test group.

[0073] b. Measurement method for the reduction rate of permeability of high-temperature and high-pressure mud cake:

[0074] 350 mL of each of the above drilling fluid-based slurries was taken and subjected to a high-temperature, high-pressure filtration loss experiment using a nanofiltration membrane (pore size 220 nm). The test conditions were: 160℃, 3.5 MPa, and 30 min. After the test began, the relationship between filtrate volume and time was recorded, with a point recorded every 5 minutes. A straight line was plotted, and the slope was calculated as the filtration loss rate Q. After the experiment, the filter cake thickness L and the total filtrate volume were recorded. The filter cake permeability K (Equation 1) and the filter cake permeability reduction rate were obtained according to the filter cake permeability calculation formula. (Equation 2).

[0075] (Equation 1)

[0076] In Equation 1, Q — filtration rate (cm) 3 / s);

[0077] μ — Filtrate viscosity (cP);

[0078] L — filter cake thickness (cm);

[0079] A — Cross-section of the filtrate (cm) 2 );

[0080] ΔP—Inner pressure of the tank (3.5MPa).

[0081] (Equation 2)

[0082] In Equation 2, K0 is the filter cake permeability of the blank group (without sealing agent).

[0083] K' — Filter cake permeability of the experimental group (with sealing agent).

[0084] c. Drilling fluid rheological testing methods

[0085] Take 350 mL of each of the above base slurries, age them at 160℃ for 16 h, stir at high speed for 10 min, and then use a ZNN-D6 type rotational viscometer with six speeds to measure the viscosity values ​​of the base slurries at 300 r / min and 600 r / min, and record them as φ300 and φ600. Calculate the apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP) of the base slurry system according to the following formulas.

[0086] AV = φ600 / 2;

[0087] PV = φ600 - φ300;

[0088] YP=0.511(φ300-PV).

[0089] The results are shown in Tables 2 and 3. Figure 4 As shown in Table 3, the addition of the plugging agent SiO2-g-PNST of the present invention can effectively improve the high-temperature viscosity of the base slurry, which is beneficial for drilling fluid to carry and suspend cuttings and reduce filtration loss; and as shown in Table 2, Figure 4 It can be seen that, compared with the blank, the addition of the sealing agent of this invention can significantly improve the sealing performance of saturated sodium chloride brine-based slurry and high-concentration calcium brine-based slurry, making the filter cake dense and thin.

[0090] Table 2. Performance of the plugging agent prepared according to the synthesis scheme corresponding to Example 2

[0091]

[0092] Table 3. Rheological properties

[0093]

Claims

1. A temperature- and salt-resistant zwitterionic nano-blocking agent, characterized in that, The blocking agent is composed of a cationic monomer, anionic monomer, neutral monomer, initiator, and modified nano-SiO2; the cationic monomer is (3-acrylamidopropyl)trimethylammonium chloride and / or dimethyldiallylammonium chloride; the anionic monomer is 2-acrylamido-2-methylpropanesulfonic acid; the neutral monomer is N-vinylpyrrolidone; the molar ratio of the cationic monomer, anionic monomer, and neutral monomer is 1:1:1; The plugging agent is prepared using the following method: S1: Modified SiO2 was prepared by using KH570 to attach carbon-carbon double bonds to the surface of SiO2 nanoparticles. S2: The modified nano-SiO2 obtained in S1 is mixed with the cationic monomer, the anionic monomer and the neutral monomer, and after ultrasonic dispersion, the initiator is added to carry out a free radical chain polymerization reaction to obtain the temperature-resistant and salt-resistant zwitterionic nano-blocking agent.

2. The sealing agent according to claim 1, characterized in that, The initiator is azobisisobutyramidine hydrochloride.

3. The method for preparing the plugging agent according to any one of claims 1-2, characterized in that, Includes the following steps: S1: Modified SiO2 was prepared by using KH570 to attach carbon-carbon double bonds to the surface of SiO2 nanoparticles. S2: The modified nano-SiO2 obtained in S1 is mixed with the cationic monomer, the anionic monomer and the neutral monomer, ultrasonically dispersed and then the initiator is added to carry out a free radical chain polymerization reaction to obtain the blocking agent; The molar ratio of the anionic monomer, the cationic monomer, and the neutral monomer is 1:1:

1.

4. The preparation method according to claim 3, characterized in that, The particle size range of the SiO2 nanoparticle raw material is 20~100nm, and the proportion of SiO2 nanoparticles with a particle size of 20nm is ≥75%.

5. The preparation method according to claim 3, characterized in that, The total concentration of the anionic monomer, cationic monomer, and neutral monomer is 25 w / w; the amount of modified nano-SiO2 added is 2.5~5.5 w / w of the total monomer mass; and the amount of the initiator added is 0.15~0.35 w / w of the total monomer mass.

6. The preparation method according to claim 3, characterized in that, The polymerization reaction takes 4-5 hours and is carried out at a temperature of 56-65°C.

7. Drilling fluid, characterized in that, The drilling fluid contains the plugging agent according to any one of claims 1-2.

8. A method for sealing formation nano / micro pores using the plugging agent of claim 1 and / or the drilling fluid of claim 7, characterized in that, Drilling is performed by adding the plugging agent of claim 1 to the drilling fluid and / or by directly using the drilling fluid of claim 7.

9. The application of the plugging agent according to claim 1 in improving the plugging performance of drilling fluid.

10. The application of the plugging agent according to claim 1 in improving the rheological properties and filtration properties of drilling fluid under high temperature and high salinity conditions.

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