High-temperature resistant, high-strength, and thixotropic gel plugging agent and its preparation method and application

Abstract

A high-temperature resistant, high-strength, and thixotropic gel plugging agent is composed of 8-20% of acrylamide monomer, 0.05-0.5% of reactive polymer, 0.1-1.0% of organic polymer cross-linker, 3.0-8.0% of resin toughening agent, 1.0-5.0% of flow pattern regulator, 0.01-0.5% of cross-linking regulator by the weight in the water. The gel solution shows a low apparent viscosity during the shear flow and is easy to be pumped into the wellbore and then into the formation leakage layer; after the pumping stops, the gel solution shows rapidly increased viscosity and strong adhesive force, and form a high-strength barrier between the wellbore and the formation, preventing the drilling fluid from further leaking.

Claims

1. A high-temperature resistant, high-strength, and thixotropic gel plugging agent, characterized in that it comprises raw materials in the following mass percent: 8-20% acrylamide monomer, 0.05-0.5% reactive polymer, 0.1-1.0% organic polymer cross-linker, 3.0-8.0% resin toughening agent, 1.0-5.0% flow pattern regulator, 0.01-0.5% cross-linking regulator, and water in the remaining percentage.

2. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 1, characterized in that it comprises raw materials in the following mass percent: 12-18% acrylamide monomer, 0.1-0.3% reactive polymer, 0.3-0.8% organic polymer cross-linker, 4.0-7.0% resin toughening agent, 2.0-4.0% flow pattern regulator, 0.05-0.2% cross-linking regulator, and water in the remaining percentage.

3. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 1, characterized in that the said reactive polymer is a polycondensatable macromolecular polymer with hydroxymethyl groups (—CH.sub.2OH) on its surface.

4. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 1, characterized in that the said reactive polymer has a viscosity-average molecular weight of 5-13 million.

5. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 1, characterized in that the organic polymer cross-linker is a polymerizable macromolecular polymer with vinyl groups (CH.sub.2═CH) on its surface.

6. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 1, characterized in that the said resin toughening agent is a combination of one or more from among phenolic resin, epoxy resin, urea resin and amino resin.

7. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 1, characterized in that the said flow pattern regulator is a combination of one or more from among aluminum-magnesium silicate, magnesium lithium silicate, Na-montmorillonite, and Li-montmorillonite.

8. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 1, characterized in that the said cross-linking regulator is a combination of one or more from among encapsulated potassium persulfate, encapsulated sodium persulfate, and encapsulated ammonium persulfate.

9. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 3, characterized in that the reactive polymer is prepared by the following steps: (1) add lipophilic emulsifier and hydrophilic emulsifier into oil phase solvent and stir them evenly; then, add hydrophobic monomer drop by drop into the above solution system and stir them evenly to get solution A; (2) add acrylamide monomer and functional cross-linker into deoxygenated and deionized water, and stir until they dissolve completely; then, add EDTA and stir until it dissolves completely to get solution B; (3) add the solution A slowly into the solution B drop by drop and stir evenly, add chain extender and initiator in order to stimulate the reaction and get microemulsion C when the temperature is increased to 40-60° C.; and (4) add precipitant into the microemulsion C to separate out solid phase materials; wash and dry the solid phase materials to get the reactive polymer.

10. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 9, characterized in that the Step (1) includes one or more of the following conditions: i. said oil-phase solvent is a combination of one or more from among cyclohexane, kerosene, and liquid paraffin; ii. said lipophilic emulsifier is a mixture of sorbitan stearate and sorbitane monooleate, the mass ratio of sorbitan stearate to sorbitane monooleate in the said mixture is 0.2-0.6:1; the mass of the said lipophilic emulsifier is 0.5-2.5% of that of the oil-phase solvent; iii. said hydrophilic emulsifier is a mixture of polyethylene sorbitan monostearate and polyoxyethylenesorbitan monooleate, the mass ratio of polyethylene sorbitan monostearate to polyoxyethylenesorbitan monooleate in the mixture is 1-4:1; the mass of the said hydrophilic emulsifier is 0.25-1.2% of that of the oil-phase solvent; and iv. said hydrophobic monomer is a combination of one or more from among styrene, α-methylstyrene, and 4-methylstyrene; the mass of the hydrophobic monomer is 5-12% of that of the oil-phase solvent.

11. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 9, characterized in that the Step (2) includes one or more of the following conditions: i. said acrylamide monomer and the deionized water have a mass ratio of 0.05-0.20:1; ii. said acrylamide monomer and the hydrophobic monomer have a mass ratio of 5-15:1; iii. said functional cross-linker is N-methylol acrylamide; the mass of the said functional cross-linker is 5-25% of that of the acrylamide monomer; and iv. mass of the EDTA is 0.03-0.2% of that of the acrylamide monomer.

12. The high-temperature resistant, high-strength, and thixotropic gel plugging agent according to claim 9, characterized in that the preparation method includes one or more of the following conditions: i. said chain extender in Step (3) is a combination of one or more from among ethanediamine, triethanolamine, trimethylolpropane, and sorbitol; the mass of the chain extender is 2-12% of that of the acrylamide monomer; ii. said initiator in Step (3) is potassium persulfate and/or ammonium persulfate, and the mass of said initiator is 0.2-2.5% of that of the acrylamide monomer; iii. said reaction time in Step (3) is 6-12 h; iv. said precipitant in Step (4) is absolute ethyl alcohol, said precipitant and the microemulsion C have a volume ratio of 0.5-1.0:1; and v. said washing in Step (4) is carried out with absolute ethyl alcohol.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is the infrared spectrogram of the organic polymer cross-linker prepared in Preparation Example 1.

(2) FIG. 2 is the infrared spectrogram of the reactive polymer prepared in Preparation Example 2.

DETAILED EMBODIMENTS

(3) The invention is further described in combination with the embodiments as follows, but is not limited to that. All raw materials used in the embodiments are conventional raw materials available on the market; unless otherwise specified, the said methods can all be implemented with the existing technologies.

(4) The organic polymer cross-linker and the reactive polymer used in the embodiments and the comparative examples are respectively prepared with the following methods as described in Preparation Example 1 and Preparation Example 2.

Preparation Example 1

(5) A preparation method of the organic polymer cross-linker, including the following steps:

(6) (1) Dissolve 6 g acrylamide monomer in 5 mL deoxygenated and deionized water to get the solution D1, and dissolve 0.06 g ammonium persulfate in 2 mL deoxygenated and deionized water to get the solution D2;

(7) (2) Stir 6 g lipophilic emulsifier mixture of Span60/Span80 (the mass ratio of Span60 and Span80 is 0.4:1), 14 g hydrophilic emulsifier mixture of Tween60/Tween80 (the mass ratio of Tween60 and Tween80 is 2:1) and 63 mL cyclohexane evenly to get the solution E;

(8) (3) Dropwise add the solution D1 and solution D2 successively and slowly into the solution E and stir evenly; place the above solution system still at 60° C. for 6 h and then add 2 g N-methylol acrylamide to get the microemulsion F; adjust the pH value of the microemulsion F to 5.5 with the hydrochloric acid solution with a mass fraction of 10% to get the microemulsion I;

(9) (4) Add 70 mL absolute ethyl alcohol into the microemulsion I to separate out the solid-phase materials which then will be washed with absolute ethyl alcohol and dried to get the organic polymer cross-linker.

(10) Conduct an infrared spectrum test for the prepared organic polymer cross-linker with an infrared spectrometer. The infrared spectrogram is as shown in FIG. 1, from which it can be seen that the C═C double bond vibration peak appears at around 1605 cm.sup.−1, which proves the existence of vinyl groups.

Preparation Example 2

(11) A preparation method of the reactive polymer, including the following steps:

(12) (1) Stir 0.12 g lipophilic emulsifier mixture of Span60/Span80 (the mass ratio of Span60 and Span80 is 0.4:1), 0.06 g hydrophilic emulsifier mixture of Tween60/Tween80 (the mass ratio of Tween60 and Tween80 is 2:1) and 7.1 g cyclohexane evenly; dropwise add 0.7 g α-methylstyrene slowly into the mixture system and stir evenly to get the solution A;

(13) (2) Add 7 g acrylamide monomer and 0.8 g N-methylol acrylamide into 55 g deoxygenated and deionized water and stir until they dissolve completely; then, add 0.005 g EDTA and stir until it dissolves completely to get the solution B;

(14) (3) Dropwise add the solution A slowly into the solution B with a dropping funnel and stir evenly; after the temperature rises to 50° C., add 0.35 g ethanediamine and 0.08 g ammonium persulfate successively and keep stirring to get the microemulsion C after reaction for 8 h.

(15) (4) Add 50 mL absolute ethyl alcohol into the microemulsion C to separate out the solid-phase materials which then will be washed with absolute ethyl alcohol and dried to get the reactive polymer.

(16) Conduct an infrared spectrum test for the prepared reactive polymer with an infrared spectrometer. The infrared spectrogram is as shown in FIG. 2, from which it can be seen that the NH—H vibration peak and shear vibration peak of the amide appear at around the 3196 cm.sup.−1 and 1610 cm.sup.−1 respectively, which proves the existence of —CONH.sub.2 groups in combination with the peaks appearing at around 1665 cm.sup.−1 and 1416 cm.sup.−1.

Embodiment 1

(17) A high-temperature resistant, high-strength, and thixotropic gel plugging agent, which is composed of raw materials in the following mass percent: 18% acrylamide monomer, 0.8% organic polymer cross-linker, 0.3% reactive polymer, 7.0% urea resin, 4.0% lithium bentonite, 0.2% encapsulated ammonium persulfate, and water in the remaining percentage.

(18) The said high-temperature resistant, high-strength, and thixotropic gel plugging agent is prepared in the following steps:

(19) (a) Add the acrylamide monomer, organic polymer cross-linker, and reactive polymer successively into the water and stir at the speed of 250 rpm until they dissolve completely to get the mixed solution G;

(20) (b) Add the resin toughening agent into the said mixed solution G and stir at the speed of 250 rpm until it disperses evenly to get the mixed solution H;

(21) (c) Add the flow pattern regulator into the said mixed solution H and stir at the speed of 400 rpm until it disperses evenly to get the mixed solution J;

(22) (d) Add the cross-linking regulator into the said mixed solution J and stir at the speed of 250 rpm until it dissolves completely to get the mixed solution K;

(23) (e) Keep the mixed solution K standing after sealing and solidify it at 150° C. for 8 h to get the high-temperature resistant, high-strength, and thixotropic gel plugging agent I.sub.1.

Embodiment 2

(24) A high-temperature resistant, high-strength, and thixotropic gel plugging agent, which is composed of raw materials in the following mass percent: 15% acrylamide monomer, 0.55% organic polymer cross-linker, 0.2% reactive polymer, 5.5% urea resin, 3.0% lithium bentonite, 0.1% encapsulated ammonium persulfate, and water in the remaining percentage.

(25) The said high-temperature resistant, high-strength, and thixotropic gel plugging agent is prepared according to the method in Embodiment 1, and the high-temperature resistant, high-strength, and thixotropic gel plugging agent I.sub.2 is obtained.

Embodiment 3

(26) A high-temperature resistant, high-strength, and thixotropic gel plugging agent, which is composed of raw materials in the following mass percent: 12% acrylamide monomer, 0.3% organic polymer cross-linker, 0.1% reactive polymer, 4.0% urea resin, 2.0% lithium bentonite, 0.05% of encapsulated ammonium persulfate, and water in the remaining percentage.

(27) The said high-temperature resistant, high-strength, and thixotropic gel plugging agent is prepared according to the method in Embodiment 1, and the high-temperature resistant, high-strength, and thixotropic gel plugging agent I.sub.3 is obtained.

Embodiment 4

(28) A high-temperature resistant, high-strength, and thixotropic gel plugging agent, which is composed of raw materials in the following mass percent: 8% acrylamide monomer, 0.1% organic polymer cross-linker, 0.05% reactive polymer, 3.0% urea resin, 1.0% lithium bentonite, 0.01% encapsulated ammonium persulfate, and water in the remaining percentage.

(29) The said high-temperature resistant, high-strength, and thixotropic gel plugging agent is prepared according to the method in Embodiment 1, and the high-temperature resistant, high-strength, and thixotropic gel plugging agent 14 is obtained.

Comparative Example 1

(30) A gel plugging agent as described in Embodiment 1 provided however that the content of the acrylamide monomer is 5%.

(31) The said gel plugging agent is prepared according to the method in Embodiment 1, and the gel plugging agent II.sub.1 is obtained.

Comparative Example 2

(32) A gel plugging agent as described in Embodiment 1 provided however that no organic polymer cross-linker is added.

(33) The said gel plugging agent is prepared according to the method in Embodiment 1, and the gel plugging agent II.sub.2 is obtained.

Comparative Example 3

(34) A gel plugging agent as described in Embodiment 1 provided however that no reactive polymer is added.

(35) The said gel plugging agent is prepared according to the method in Embodiment 1, and the gel plugging agent II.sub.3 is obtained.

Comparative Example 4

(36) A gel plugging agent as described in Embodiment 1 provided however that no urea resin is added.

(37) The said gel plugging agent is prepared according to the method in Embodiment 1, and the gel plugging agent II.sub.4 is obtained.

Comparative Example 5

(38) A gel plugging agent as described in Embodiment 1 provided however that no lithium bentonite is added.

(39) The said gel plugging agent is prepared according to the method in Embodiment 1, and the gel plugging agent II.sub.5 is obtained.

Test Example

(40) Test the gel plugging agents prepared in Embodiments 1-3 and Comparative Examples 1-5 for their thixotropy, mechanical performance, migration-filling effect, and plugging effect.

(41) Testing method for the thixotropy of the gel plugging agent solution: Use a HAAKE RS6000 rotational rheometer to test the apparent viscosity of the gel plugging agent solution before solidifying at different shear rates (1.0-1000 l/s). The shear rate first increases from low to high and then decreases by the original values. In this test, compared to the initial apparent viscosity (at the shear rate of 1.0 l/s), when the shear rate is reduced again to 1.0 l/s after high-speed shearing (100-1000 l/s), the closer the gel solution's apparent viscosity to the initial value, the better the thixotropy turns out to be. The results are shown in Table 1.

(42) Testing method for the mechanical performance of the gel plugging agent after solidifying: Use a universal electronic tensile testing machine to test the tension-resistance mechanical performance of the gel plugging agent after gelatinization. In this test, the greater the fracture stress of the gel is, the higher the tensile strength of the gel after solidifying turns out to be. To be specific, the tension rate of the universal electronic tensile testing machine shall be 1 mm/s. The results are as shown in Table 2.

(43) Testing method for the migration-filling effect of the gel plugging agent solution in a vertical fracture: Use a 50 cm long, 30 cm high and 5 mm wide visible fracture as a model to test the migration-filling effect of the gel plugging agent solution in vertical fractures. The specific testing method is as follows: Add 1000 mL dyed gel plugging agent solution into an intermediate container, and use a large-displacement constant-flux pump to inject water into the intermediate container at the speed of 10 mL/min; inject the gel solution into the vertically placed visual fracture model with the help of a piston; divide the fracture space equally into the upper and the lower parts by height, and take the total injection volume reaching half of the fracture space volume as a benchmark to observe in time and measure the distribution of the gel solution in the vertical fracture space based on the dyed area. Taking the ratio of the gel injection amount in the upper and lower parts of the fracture as a reference, the closer the ratio is to 1, the more even the distribution of gel solution is in the vertical fracture and the better the filling effect is, so that its filling effect in fractures can be evaluated. The test results are as shown in Table 2.

(44) Testing method for the plugging effect of the gel plugging agent: Test the plugging effect of the gel plugging agent in fractures with a high-temperature and high-pressure leakage plugging testing device. Use a 10 cm long and 3.0 mm wide steel fracture model to simulate a leakage layer. The specific testing method is as follows: pour 500 mL gel plugging agent solution (added with the cross-linking regulator) into the dehydration cylinder of the leakage plugging device; place a movable piston from its upper part and then seal the cylinder by tightening its cover; after the solution solidifies for 8 h, pressurize the cylinder by injecting drilling fluid into it with a large displacement constant-flux pump, and record in time the pressure at the inlet end of the fracture model. Take the maximum pressure when the drilling fluid leaks from the outlet end of the fracture model as the maximum plugging pressure of the gel, and the testing temperature is 150° C. The test results are as shown in Table 2.

(45) TABLE-US-00001 TABLE 1 Thixotropy testing data of the gel plugging agent solution before solidifying Shear rate (1/s) (first increase and then decrease) No. 1.0 10 100 1000 100 10 1.0 I.sub.1 3650 823 143 130 145 840 3600 I.sub.2 3400 785 139 125 142 795 3350 I.sub.3 3100 779 125 110 122 785 3020 II.sub.1 3550 796 142 127 141 801 3380 II.sub.2 3250 730 136 122 135 735 3090 II.sub.3 3290 716 139 124 140 712 3120 II.sub.4 3230 706 132 119 135 708 3070 II.sub.5 132 28 12 10 14 24 83

(46) TABLE-US-00002 TABLE 2 Testing data of the mechanical performance, migration-filling effect, and fracture plugging effect of the gel plugging agents after solidifying No. I.sub.1 I.sub.2 I.sub.3 II.sub.1 II.sub.2 II.sub.3 II.sub.4 II.sub.5 Maximum tensile 245 238 220 68 93 124 140 162 fracture stress/KPa Gel injection volume ratio 0.98 0.95 0.94 0.97 0.96 0.96 0.94 0.45 of the upper and lower parts of the fracture Maximum plugging 5.35 5.18 5.05 2.28 2.48 3.40 3.85 4.02 pressure of fracture/MPa

(47) As can be seen from Table 1 and Table 2, when the gel plugging agents prepared in the embodiments of the invention are in solution state before solidifying and subject to a shear rate of 1.0 l/s, the gel solution has a high apparent viscosity; when the shear rate increases to 1000 l/s, the apparent viscosity decreases. Hereafter, as the shear rate gradually decreases, the apparent viscosity starts to pick up slowly; when the shear rate decreases to 1.0 l/s, the apparent viscosity basically returns to the value when the initial shear rate is 1.0 l/s. This indicates that the gel plugging agent prepared in the invention is destroyed in structure when sheared in solution state before solidifying and its viscosity is decreased, but it can re-establish the apparent viscosity when the shearing force disappears, which proves that the gel plugging agent is not affected by the shear process and has excellent thixotropic properties. The gel plugging agents prepared in the Comparative Examples 1˜4 have no big differences before and after being sheared in solution state and have good thixotropic properties. By contrast, the gel plugging agent without flow pattern regulator in the Comparative Example 5 has a low apparent viscosity of 132 mPa.Math.s before the gel solution solidifies and when the shear rate is 1.0 l/s; when the shear rate increases to 1000 l/s, the apparent viscosity of the gel solution is 10 mPa.Math.s; when the shear rate decreases to 1.0 l/s, the apparent viscosity rises back to 83 mPa.Math.s at last, proving that the gel plugging agent prepared in the Comparative Example 5 has poor thixotropic properties.

(48) The maximum tensile fracture stress of the gel plugging agents prepared in Embodiments 1-3 in the invention are 245 KPa, 238 Kpa and 220 KPa respectively after solidifying, indicating that the gel plugging agents in the invention have excellent tension-resistance mechanical properties; the ratio of injection volume in the upper and lower parts of the fracture is 0.98, 0.95 and 0.94 respectively for the pre-solidification solution of the gel plugging agents prepared in Embodiments 1-3 in the invention, indicating that the gel plugging agents in the invention have excellent migration-filling effects and can fill up the vertical fractures evenly; also, the gel plugging agents prepared in the invention have higher maximum plugging pressure on the fracture after solidifying, indicating that they have excellent plugging effects; in Comparative Example 1, as the acrylamide monomer is in small amount, although the gel plugging agent has good migration-filling effect before solidifying, the tension-resistance mechanical performance and the plugging effect are poor; in Comparative Examples 2-4, although the solution of the prepared gel plugging agents have good migration-filling effect before solidification, but its tension-resistance mechanical performance and plugging effect are poor. In addition, as can be seen from Embodiment 1 and Comparative Example 2, the addition of the reactive polymer in the invention can greatly improve the tension-resistance mechanical performance and the plugging performance of the gel plugging agents. It can also be seen from Comparative Example 2 and Comparative Example 3 that reactive polymer can improve the tension-resistance mechanical performance and the plugging performance of the gel plugging agents better than the organic cross-linker polymer; although the gel plugging agent prepared in the Comparative Example 5 has better tensile strength and plugging capacity, its solution has poor migration-filling effect before solidification and cannot fill up the vertical fracture space evenly.

(49) As can be seen from the above data, the gel plugging agents prepared in the embodiments of the invention have excellent thixotropic performance, mechanical performance, migration-filling capacity and plugging performance, showing that the gel plugging agents prepared in the invention have advantages of high temperature resistance, high strength, and thixotropy and can be used to solve the lost circulation problem in high-temperature deep fractured leakage formations.

(50) The above content has described the preferred embodiments of the invention in detail, but the invention is not limited to that. Within the technical conceive of the present invention, a variety of simple variants can be made to the technical scheme of the present invention, including the combinations of various technical features in any other appropriate manner. These simple variants and combinations shall also be regarded as the disclosed content of the invention and shall fall within the protection scope of the invention.