A self-breaking gelatinous valve, its preparation method and application

Abstract

The application belongs to the technical field of underbalanced drilling and discloses a self-degradable gel valve, a preparation method and application thereof. The self-degradable gel valve comprises the following mass percentages of raw materials: 8-15% of monomers, 1-2% of degradable cross-linking agents, 0.01-0.015% of initiators, 0.2-0.5% of dispersants and 82.485-90.79% of water. The degradable cross-linking agent is a reaction product obtained by reacting anhydrous strong acid, poly(ethylene glycol) methacrylate and methoxylated benzaldehyde. The self-degradable gel valve is in a liquid state before gelation, is easy to pump, has good gelation performance, stable strength, can replace a casing valve, seals the bottom pressure of a well and has more suitable gelation time and gel breaking time and wider adaptability. After the operation is completed, the self-degradable gel valve can be self-catalyzed to gradually hydrolyze the self-prepared degradable cross-linking agent, and mechanical gel breaking or external gel breaking agents are not needed.

Description

Technical Field

[0001] This invention belongs to the field of underbalanced drilling technology, specifically relating to a self-breaking gel valve, its preparation method, and its application in pressure control during underbalanced drilling. Background Technology

[0002] With the in-depth research and widespread application of underbalanced drilling technology, the requirements for this technology are becoming increasingly stringent both domestically and internationally. How to achieve full-process underbalanced drilling operations has gradually become a research hotspot. The core of full-process underbalanced drilling technology lies in pressure control. Currently, commonly used pressure control technologies include downhole casing valve technology and gel valve technology. Downhole casing valve technology is costly and has a low safety factor; while gel valve technology is low-cost, has good well isolation effect, and can effectively replace casing valves to achieve full-process underbalanced drilling.

[0003] Gel valve technology refers to the injection of a high-viscosity gel fluid into the wellbore. Under certain pressure and temperature downhole, the gel fluid gels, forming a gel slug that seals the wellbore. The gel slug possesses both strength and pressure resistance, enabling isolation during operations; it also exhibits adhesion and resilience, forming a static seal with the casing and a dynamic seal with the drilled / completed tubing string. The gel's viscosity enables it to withstand pressure differentials and remain stationary in the wellbore (valve fixation); its solid mechanical properties isolate and seal oil and gas in the wellbore (valve sealing); its viscoelasticity allows for smooth tubing penetration and its own recovery (valve opening and closing); and its ruptureable nature allows for rupture and return to the surface after operations (valve release). Currently, commonly used gel valves are gels formed from polymers and crosslinking agents. After operations are completed, a large amount of rupture agent is required, which increases the complexity of the construction process. Furthermore, insufficient contact between the breaker and the gel valve leads to incomplete gel breaking and difficulty in return. Third, most breaker agents are strong oxidants, which can cause corrosion to the tubing string. For example, Chinese patent application CN112480888A discloses a downhole gel valve and its preparation method. After construction, this method requires injecting ammonium persulfate solution into the well for gel breaking, which is cumbersome, complex, and cannot achieve self-degradation. Chinese patent application CN113185656A discloses a temperature-responsive self-degrading temporary plugging agent and well workover method, which can gel at 55-85℃ with a gel breaking time of 72-95 hours. However, as the temperature increases, the gel forming time gradually increases while the gel breaking time decreases, failing to meet the requirements of long-term downhole operations. Summary of the Invention

[0004] The purpose of this invention is to provide a self-degrading gel valve, its preparation method, and its application in underbalanced drilling pressure control. The self-degrading gel valve provided by this invention is liquid before gelation, with low viscosity, good fluidity, easy pumping, good gelation performance, and stable strength. It can replace casing valves to seal bottom hole pressure and has more suitable gelation and degelation times, making it more adaptable. After operation, the gel valve can gradually hydrolyze the self-made degradable crosslinking agent through autocatalysis, leading to the breakage of crosslinking points and the degradation of low-viscosity linear polymers in a three-dimensional network structure, without the need for mechanical degelation or the addition of external degelating agents.

[0005] One objective of this invention is to provide a self-breaking gel valve, comprising the following raw materials by weight percentage: 8%-15% of alkenyl monomer, 1%-2% of degradable crosslinking agent, 0.01%-0.015% of initiator, 0.2%-0.5% of dispersant, and 82.485%-90.79% of water;

[0006] The degradable crosslinking agent is derived from the reaction product obtained by reacting anhydrous strong acid, poly(ethylene glycol) methacrylate as shown in formula (1), and methoxylated benzaldehyde as shown in formula (2).

[0007]

[0008] In formula (2), the position indicated by 1 and / or the position indicated by 2 is replaced by a methoxy group.

[0009] In a preferred embodiment of the present invention, the self-breaking gel valve comprises the following raw materials by mass percentage: 10%-13% of alkenyl monomer, 1.5%-2% of degradable crosslinking agent, 0.012%-0.014% of initiator, 0.35%-0.45% of dispersant, and 84.536%-88.138% of water.

[0010] According to the present invention, the methoxylated benzaldehyde is selected from 4-methoxybenzaldehyde and / or 3-methoxybenzaldehyde, more preferably 4-methoxybenzaldehyde.

[0011] In a preferred embodiment of the present invention, the number average molecular weight of the poly(ethylene glycol) segments in the poly(ethylene glycol) methacrylate is 200-600; preferably, the number average molecular weight of the poly(ethylene glycol) segments in the poly(ethylene glycol) methacrylate is at least one of 200, 300, 400, and 600, more preferably at least one of 200 and 300; most preferably 200.

[0012] In this invention, "poly(ethylene glycol)" is also "polyethylene glycol", for example, a poly(ethylene glycol) segment is also a polyethylene glycol segment.

[0013] According to the present invention, the anhydrous strong acid acts as a catalyst to catalyze the reaction between poly(ethylene glycol) methacrylate and methoxylated benzaldehyde. Many types of anhydrous strong acid can be selected; in a preferred embodiment of the present invention, the anhydrous strong acid is selected from at least one of p-toluenesulfonic acid and trifluoromethanesulfonic acid.

[0014] In a more preferred embodiment of the present invention, the degradable crosslinking agent has the structural formula shown in formula (3):

[0015]

[0016] According to the present invention, the preparation method of the biodegradable crosslinking agent includes, but is not limited to, the preparation method of the present invention. Preferably, the preparation method of the biodegradable crosslinking agent includes the following steps: mixing anhydrous strong acid, poly(ethylene glycol) methacrylate, methoxylated benzaldehyde, and anhydrous tetrahydrofuran, and carrying out a crosslinking reaction; preferably, after the crosslinking reaction, the method further includes filtration, removal of solvent by vacuum distillation, and purification by silica gel column chromatography to obtain the biodegradable crosslinking agent.

[0017] According to the present invention, the mass ratio of anhydrous strong acid, poly(ethylene glycol) methacrylate, and methoxylated benzaldehyde can be selected within a wide range. In a more preferred embodiment of the present invention, the mass ratio of anhydrous strong acid, poly(ethylene glycol) methacrylate, and methoxylated benzaldehyde is 1:(15-25):(4-10), preferably 1:(15-20):(5-8).

[0018] According to the present invention, the conditions of the crosslinking reaction can be selected within a wide range. In a more preferred embodiment of the present invention, the temperature of the crosslinking reaction is 0-10°C, preferably 0-5°C; and / or, the time of the crosslinking reaction is 5-7h, preferably 5.5-6h.

[0019] According to the present invention, the mass ratio of the poly(ethylene glycol) methacrylate to anhydrous tetrahydrofuran can be selected within a wide range. In a more preferred embodiment of the present invention, the mass ratio of the poly(ethylene glycol) methacrylate to anhydrous tetrahydrofuran is (2-3):1.

[0020] As an example, the preferred method for preparing the biodegradable crosslinking agent RJ-2 includes the following steps:

[0021] p-Toluenesulfonic acid monohydrate, poly(ethylene glycol) (Mn = 200) methacrylate, 4-methoxybenzaldehyde, and anhydrous tetrahydrofuran were mixed and subjected to cross-linking reaction in sequence. The mixture was then filtered, the solvent was removed by vacuum distillation, and the mixture was purified by silica gel column chromatography to obtain the degradable cross-linking agent RJ-2.

[0022] In the above technical solution, the preferred mass ratio of p-toluenesulfonic acid monohydrate, poly(ethylene glycol) methacrylate, and 4-methoxybenzaldehyde is 1:18:7; the preferred mass ratio of poly(ethylene glycol) methacrylate and anhydrous tetrahydrofuran is 18:8; the preferred temperature of the crosslinking reaction is 0-10℃, more preferably 0-5℃; the preferred time of the crosslinking reaction is 5-7h, more preferably 5.5-6h; the preferred eluent for purification by silica gel column chromatography is ethyl acetate:hexane = 1:9; the preferred vacuum distillation temperature is 40-55℃, more preferably 45-50℃. The present invention does not specifically limit the filtration process; any filtration process well known in the art can be used.

[0023] The preparation of crosslinking agent RJ-2 includes, but is not limited to, the methods described in the embodiments of this invention. The specific preparation method of crosslinking agent RJ-2 is as follows: 1.0 g of p-toluenesulfonic acid monohydrate is dissolved in a round-bottom flask containing anhydrous tetrahydrofuran. Then, an appropriate amount of molecular sieve is added, followed by 18.0 g of poly(ethylene glycol) methacrylate and 7.0 g of 4-methoxybenzaldehyde, which are mixed thoroughly. The round-bottom flask is then placed in ice water and reacted for several hours. The molecular sieve is removed by filtration, and the solvent is removed by vacuum distillation. After solvent removal, the clear liquid residue is purified by silica gel column chromatography to obtain crosslinking agent RJ-2.

[0024] In this invention, the crosslinking agent can crosslink linear alkenyl monomers to form a three-dimensional network structure, thereby enhancing the strength and adhesion of the gel valve.

[0025] In a preferred embodiment of the present invention, the alkenyl monomer is selected from one or more of acrylamide, methyl methacrylate, hydroxyethyl methacrylate, ethyl acrylate, and vinyl acetate.

[0026] According to the present invention, the initiator can be selected from a wide range. In a preferred embodiment of the present invention, the initiator is selected from one or more of ammonium persulfate, potassium persulfate, sodium persulfate, ammonium persulfate / sodium bisulfite and azobisisobutyramidine hydrochloride.

[0027] According to the present invention, the dispersant can be selected from a wide range of options. In a preferred embodiment of the present invention, the dispersant is selected from one or more of sodium dodecylbenzenesulfonate, dodecylphenol polyoxyethylene ether, Tween 40, Tween 60 and Tween 80.

[0028] According to the present invention, the self-degrading gel valve is capable of self-degrading and gel breaking. Preferably, the self-degrading time is 4-12 days, more preferably 5-10 days, and even more preferably 7-8 days.

[0029] According to the present invention, the time for the raw material to gel in the self-breaking gel valve is 1-5 hours, preferably 1-4 hours, and more preferably 2-3 hours.

[0030] In a preferred embodiment of the present invention, the self-destructive gel valve is prepared by the following method: mixing the raw materials including the alkenyl monomer, degradable crosslinking agent, initiator, dispersant and water to obtain the self-destructive gel valve base liquid, and then gelling to obtain the self-destructive gel valve.

[0031] Preferably, the gelation time is 1-5 hours, more preferably 1-4 hours, and even more preferably 2-3 hours.

[0032] The self-breaking gel valve of this invention exhibits excellent overall performance in terms of gel formation and self-breaking time. Within the gel formation time range, the raw materials for the self-breaking gel valve can be transported downhole, allowing sufficient time for material transport and facilitating operation. If the gel formation time is too short, gel may form during transport or before reaching the target sealing area, which is inconvenient and fails to achieve the desired sealing effect. Conversely, if the gel formation time is too long, construction efficiency will be too low. The self-breaking time of the self-breaking gel valve of this invention is more conducive to construction. A suitable drilling pressure control time for underbalanced drilling is reserved before self-breaking begins. If the self-breaking time is too short, the sealing time may be insufficient before breaking, failing to achieve the pressure control effect during construction. Conversely, if the self-breaking time is too long, construction efficiency will also be too low. More preferably, the time for the raw material to gel in the self-breaking gel valve is 1-5 hours, preferably 1-4 hours, and more preferably 2-3 hours; the time for self-breaking is 4-12 days, preferably 5-10 days, and more preferably 7-8 days.

[0033] This invention, by changing the type of monomer, the amount of monomer added, and the type of crosslinking agent, can alter the autocatalytic degradation rate of the gel valve to achieve control over the gelation time and degradation time within the range of 60-80℃. The gel valve self-destructs after maintaining high strength (above 15MPa) for a period of time, better meeting the needs of construction in strata at 60-80℃. It solves the problems of complex construction procedures and potential corrosion from de-corrosion agents in existing gel valve systems, enabling safe operation and causing no pollution to the underground environment.

[0034] According to the present invention, preferably, the breakthrough pressure of the self-breaking gel valve of the present invention is above 15MPa, and it has high pressure resistance.

[0035] According to the present invention, the self-degradation time of the self-degradable gel valve, i.e., the self-degradation time, refers to the time from when the self-degradable gel valve forms its own gel until the start of self-degradation. Before the start of degradation, the strength of the self-degradable gel valve remains stable.

[0036] According to the present invention, the self-degrading gel valve generally completes its self-degradation within 1-2 hours after it begins to degrade.

[0037] As mentioned above, the self-breaking time refers to the time when the freezing valve begins to break the glue, and the breakthrough pressure starts to decrease when the freezing valve begins to break the glue.

[0038] The second aspect of the present invention is to provide a method for preparing the self-destructive gel valve described in the first aspect, comprising mixing raw materials including the alkenyl monomer, a biodegradable crosslinking agent, an initiator, a dispersant, and water to obtain a self-destructive gel valve base liquid, and then gelling it to obtain the self-destructive gel valve; preferably,

[0039] The gelation time is 1-5 hours, preferably 1-4 hours, more preferably 2-3 hours; and / or, the gelation temperature is 60-80℃.

[0040] Unless otherwise specified, the present invention does not have special requirements on the source of the raw materials used in the preparation, and commercially available products well known to those skilled in the art can be used.

[0041] The self-breaking gel valve provided by the present invention comprises 8%-15% by mass of an alkenyl monomer, preferably 10%-13%.

[0042] In this invention, the alkenyl monomer is preferably one or more of acrylamide, methyl methacrylate, hydroxyethyl methacrylate, ethyl acrylate, and vinyl acetate, more preferably acrylamide. When there are multiple monomers, this invention does not have a special limitation on the ratio of different types of monomers, and any ratio is acceptable.

[0043] The present invention preferably achieves controllable adjustment of the gelation and self-breaking rate of the gel valve by adjusting the type and amount of monomers. It does not require the addition of external breaking agents or catalysts, and the self-breaking can be achieved by degradation through self-catalytic crosslinking agents, thus reducing construction steps.

[0044] The self-breaking gel valve provided by the present invention comprises an initiator with a mass percentage of 0.01%-0.015%, preferably 0.012%-0.014%.

[0045] In this invention, the initiator is preferably one or more of ammonium persulfate, potassium persulfate, sodium persulfate, ammonium persulfate / sodium bisulfite, and azobisisobutyramidine hydrochloride, more preferably ammonium persulfate. When multiple initiators are used, this invention does not have a special limitation on the ratio of different types of initiators, and any ratio is acceptable.

[0046] The self-breaking gel valve provided by the present invention comprises 1%-2% by mass of a biodegradable crosslinking agent, preferably 1.5%-2%.

[0047] The biodegradable crosslinking agent in this invention has been described in detail in the section on the self-breaking gel valve in the first aspect, and will not be repeated here.

[0048] The self-breaking gel valve provided by the present invention comprises a dispersant of 0.2%-0.5% by mass, preferably 0.35%-0.45%, for example 0.4%.

[0049] In this invention, the dispersant is preferably one or more of sodium dodecylbenzenesulfonate, dodecylphenol polyoxyethylene ether, Tween 40, Tween 60, and Tween 80, more preferably sodium dodecylbenzenesulfonate. When multiple dispersants are used, this invention does not have a special limitation on the ratio of different types of dispersants, and any ratio is acceptable.

[0050] In this invention, the crosslinking agent RJ-2 is oil-soluble and poorly soluble in water. After adding the dispersant, the crosslinking agent can be uniformly dispersed in water, so that the gelation reaction can proceed smoothly and the resulting gel valve has a uniform texture.

[0051] The self-breaking gel valve provided by this invention includes a residual water.

[0052] In this invention, an alkenyl monomer, an initiator, a biodegradable crosslinking agent, a dispersant, and water are mixed. The mixing is preferably carried out under stirring conditions. This invention does not have any special limitations on the stirring time and power; the materials can be mixed evenly according to the actual situation.

[0053] A third aspect of the present invention is to provide a method for controlling drilling pressure, comprising the following steps:

[0054] According to the preparation raw materials and proportions of the self-breaking gel valve, the preparation raw materials including the alkenyl monomer, degradable crosslinking agent, initiator, dispersant and water are mixed to obtain the self-breaking gel valve base liquid;

[0055] The self-breaking gel valve base fluid is transported downhole. The self-breaking gel valve base fluid gels at the reservoir temperature to form a self-breaking gel valve, that is, the base fluid gels at the reservoir temperature to seal the reservoir section.

[0056] When the self-degrading gel valve reaches its self-degrading gel breaking time, the self-degrading gel valve begins to self-degrade, and the resulting gel breaking liquid is discharged back to the ground. That is, construction is carried out during the time when the self-degrading gel valve has not yet started to break. After the construction is completed, the self-degrading gel valve self-catalyzes the gel breaking, and the resulting gel breaking liquid is discharged back to the ground.

[0057] The self-breaking gel valve is the self-breaking gel valve described in the first aspect or the self-breaking gel valve prepared by the preparation method described in the second aspect.

[0058] In a preferred embodiment of the present invention, the temperature of the reservoir section is 60-80°C; and / or the gelation time is 1-5 hours, preferably 1-4 hours, and more preferably 2-3 hours.

[0059] In a preferred embodiment of the present invention, the self-breaking gel valve begins to break down in 4-12 days, preferably 5-10 days, and more preferably 7-8 days.

[0060] The fourth aspect of the present invention is to provide an application of the self-breaking gel valve described in the first aspect, or the self-breaking gel valve prepared by the preparation method described in the second aspect, or the drilling pressure control method described in the third aspect, in the field of underbalanced drilling technology.

[0061] The self-breaking gel raw material of this invention has a low viscosity base liquid before gelation, making it easy to pump. After being pumped into the formation, the monomers undergo free radical polymerization to form a gel with a certain strength, and this strength can be maintained for a period of time. Over time, the polymer gradually hydrolyzes under formation conditions to produce acidic substances. The self-made crosslinking agent hydrolyzes under acidic conditions, causing the crosslinking points to break. The three-dimensional network structure of the gel collapses, transforming into linear small molecules, which facilitates its return to the surface.

[0062] As mentioned above, the self-destructive gel valve provided by this invention forms a gel under the influence of formation temperature (60-80℃, i.e., downhole temperature) and maintains its strength and viscosity for a period of time (before the self-destruction begins). After gelling, the self-destructive gel valve is a viscoelastic solid with a three-dimensional network structure. As time goes by, when the self-degradation gel breaking time of the self-destructive gel valve is reached, the gel valve gradually hydrolyzes the degradable crosslinking agent through autocatalysis, causing the crosslinking points to break and the three-dimensional network structure to degrade into a small molecule linear structure, thus realizing the self-destruction of the gel valve. This invention, by changing the type and dosage of monomers and the type of crosslinking agent, can alter the autocatalytic degradation rate of the gel valve, thereby controlling the gelation and degradation times within the 60-80℃ range (gelation time is 1-5 hours, preferably 1-4 hours, more preferably 2-3 hours; self-breaking time is 4-12 days, preferably 5-10 days, more preferably 7-8 days). This allows for the selection of different self-breaking gel valve formulations based on varying construction conditions and schedule requirements, meeting construction needs and offering wider adaptability. The gel valve of this invention self-breaks after maintaining high strength (above 15 MPa) for a period, eliminating the need for mechanical breaking, external breaking agents, or degradation catalysts. This better meets the needs of 60-80℃ geological formation construction, solving the problems of complex construction procedures and potential corrosion from breaking agents in existing gel valve systems. It enables safe operation and causes no pollution to the underground environment.

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof. Attached Figure Description

[0064] Figure 1 This is a structural diagram of a preferred biodegradable crosslinking agent. Detailed Implementation

[0065] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0066] Detection method:

[0067] 1. Method for detecting adhesive breakage time:

[0068] Visual inspection method. When evaluating, invert the reagent bottle; the time when the colloid can flow is the gel breaking time of the gel valve.

[0069] 2. Test method for the pressure-bearing performance of self-breaking gel valves:

[0070] The pressure-bearing performance of the self-breaking gel valve was tested using a multifunctional core displacement device and a nitrogen reverse displacement experiment. First, a certain amount of gel valve base liquid was prepared. Then, the prepared base liquid was injected into the core using a horizontal pump. The core was then placed in a constant-temperature oven to react and gel. The pressure-bearing performance of the self-breaking gel valve was tested using nitrogen reverse displacement, and the maximum reading on the pressure gauge was taken as the breakthrough pressure of the self-breaking gel valve.

[0071] Unless otherwise specified, the devices and raw materials used in the following embodiments are all commercially available products.

[0072] Example 1

[0073] In a 250 mL round-bottom flask, dissolve 1.0 g of p-toluenesulfonic acid monohydrate in anhydrous tetrahydrofuran, then add 1 g of molecular sieve (spherical). A molecular sieve (3mm-5mm) was used, followed by the addition of 18g of poly(ethylene glycol) methacrylate (polyethylene glycol Mn: 200) and 7g of 4-methoxybenzaldehyde, which were mixed thoroughly. The round-bottom flask was placed in ice water and the mixture was stirred for 6 hours. The molecular sieve was removed by filtration, and the solvent was removed by vacuum distillation. After solvent removal, the clear liquid residue was purified by silica gel column chromatography to obtain the crosslinking agent RJ-2.

[0074] 10g of acrylamide (methyl methacrylate / vinyl acetate), 0.012g of ammonium persulfate, 1.5g of crosslinking agent RJ-2, and 0.4g of sodium dodecylbenzenesulfonate were added sequentially to a 150mL reagent bottle. Then, distilled water was added to prepare a 100mL mixed solution. The reagent bottle was placed in an 80℃ constant temperature water bath for a period of time (i.e., gelation time, see Table 1). Three groups of self-breaking gel valve products were obtained according to different monomer types. The experimental results are shown in Table 1.

[0075] Table 1. Effect of monomer type on gelation time and breakage time of gel valve

[0076] serial number Monomer type gelation time / h Time to break down adhesive / day 1 Acrylamide 3 7 2 Methyl methacrylate 3.5 8 3 Vinyl acetate 4 10

[0077] As can be seen from Table 1, the monomer type affects the gelation and breaking time of the gel valve. In practical applications, the autocatalytic rate can be adjusted by changing the monomer type to control the gelation and breaking time of the gel valve.

[0078] Example 2

[0079] In a 250 mL round-bottom flask, dissolve 1.0 g of p-toluenesulfonic acid monohydrate in anhydrous tetrahydrofuran, then add 1 g of molecular sieve (spherical). Molecular sieves (3mm-5mm) were used, followed by the addition of 20g of poly(ethylene glycol) methacrylate (polyethylene glycol Mn: 300) and 5g of 4-methoxybenzaldehyde, which were mixed thoroughly. The round-bottom flask was placed in ice water and the mixture was stirred for 6 hours. The molecular sieves were removed by filtration, and the solvent was removed by vacuum distillation. After solvent removal, the clear liquid residue was purified by silica gel column chromatography to obtain the crosslinking agent RJ-3.

[0080] In a 250 mL round-bottom flask, dissolve 1.0 g of p-toluenesulfonic acid monohydrate in anhydrous tetrahydrofuran, then add 1 g of molecular sieve (spherical). A molecular sieve (3mm-5mm) was used, followed by the addition of 25g of poly(ethylene glycol) methacrylate (polyethylene glycol Mn: 600) and 5g of 4-methoxybenzaldehyde, which were mixed thoroughly. The round-bottom flask was placed in ice water and the mixture was stirred for 6 hours. The molecular sieve was removed by filtration, and the solvent was removed by vacuum distillation. After solvent removal, the clear liquid residue was purified by silica gel column chromatography to obtain the crosslinking agent RJ-6.

[0081] 10g acrylamide, 0.012g ammonium persulfate, 1.5g crosslinking agent (RJ-2, RJ-3), and 0.4g sodium dodecylbenzenesulfonate were added sequentially to a 150mL reagent bottle. Then, distilled water was added to prepare a 100mL mixed solution. The reagent bottle was placed in an 80℃ constant temperature water bath for a period of time (i.e., gelation time, see Table 2) to obtain two groups of self-breaking gel valve products. The experimental results are shown in Table 2.

[0082] Table 2. Effect of crosslinking agent molecular weight on gelation time and breakage time of gel valve.

[0083] serial number Crosslinking agent type gelation time / h Time to break down adhesive / day 1 RJ-2 3 7 2 RJ-3 2.5 5

[0084] As can be seen from Table 2, the molecular weight of the crosslinking agent affects the gelation and breaking time of the gel valve. The larger the molecular weight of the crosslinking agent, the shorter the breaking time of the gel valve.

[0085] Example 3

[0086] 9g (12g / 15g) of acrylamide, 0.01g of ammonium persulfate, 1.5g of crosslinking agent RJ-2, and 0.5g of sodium dodecylbenzenesulfonate were added sequentially to a 150mL reagent bottle. Then, distilled water was added to prepare a 100mL mixed solution. The reagent bottle was placed in an 80℃ constant temperature water bath for a period of time (i.e., gelation time, see Table 3) to obtain 3 groups of self-breaking gel valve products. The experimental results are shown in Table 3.

[0087] Table 3. Effects of monomer dosage on gelation time and breakage time of gel valve.

[0088] serial number Monomer dosage / g gelation time / h Time to break down adhesive / day 1 9 5 9 2 12 3 8 3 15 2.5 7

[0089] As shown in Table 3, the monomer dosage also affects the gelation and breaking time of the gel valve. The higher the monomer dosage, the shorter the gelation and breaking time of the gel valve. This self-breaking gel valve's degradation time can be adjusted by controlling the monomer dosage. In practical applications, the breaking time of the gel valve can be controlled according to the actual construction conditions on site, demonstrating strong adaptability.

[0090] Example 4

[0091] 15g acrylamide, 0.015g ammonium persulfate, 2g crosslinking agent RJ-2, and 0.5g sodium dodecylbenzenesulfonate were added sequentially to a 150mL reagent bottle. Then, distilled water was added to prepare a 100mL mixed solution. The reagent bottle was placed in an 80℃ (60℃ / 70℃) constant temperature water bath for a period of time (i.e., gelation time, see Table 4) to obtain 3 groups of self-breaking gel valve products. The experimental results are shown in Table 4.

[0092] Table 4. Effects of temperature on gelation time and breakage time of gel valve

[0093] serial number Temperature / °C gelation time / h Time to break down adhesive / day 1 60 5 12 2 70 4 9 3 80 2 7

[0094] As can be seen from Table 4, the higher the temperature, the shorter the gelation time and the breaking time of the gel valve.

[0095] Example 5

[0096] Add 12g acrylamide, 0.01g ammonium persulfate, 2g crosslinking agent RJ-2, and 0.5g sodium dodecylbenzenesulfonate sequentially to a 150mL reagent bottle, then add distilled water to prepare a 100mL mixed solution. Inject 1PV of the prepared mixed solution into a core sample with a permeability of 2100mD using a horizontal flow pump, and place it in an 80℃ constant temperature oven to react for 3 hours to form a gel.

[0097] The pressure resistance of the self-breaking gel valve was tested using nitrogen reverse displacement. Experimental results showed that the breakthrough pressure of the gel valve reached 15.1 MPa, indicating that the self-breaking gel valve has strong pressure resistance and is highly adaptable to formations with pressures below 15.1 MPa. Verification showed that the breakthrough pressure of the self-breaking gel valve remained stable for 9 days. After 9 days, the breakthrough pressure began to decrease, indicating the start of gel breaking. Within 1-2 hours, the self-breaking gel valve completely broke down into liquid.

[0098] The breakthrough pressure of the self-breaking gel valves obtained in other embodiments is greater than 15 MPa.

[0099] Comparative Example 1

[0100] 10g acrylamide, 0.015g ammonium persulfate, 1g crosslinking agent (RJ-2, RJ-6), and 0.5g sodium dodecylbenzenesulfonate were added sequentially to a 150mL reagent bottle. Then, distilled water was added to prepare a 100mL mixed solution. The reagent bottle was placed in an 80℃ constant temperature water bath for a period of time (i.e., gelation time, see Table 5) to obtain two groups of self-breaking gel valve products. The experimental results are shown in Table 5.

[0101] 10g of acrylamide, 0.015g of ammonium persulfate, and 1g of crosslinking agent (polyethylene glycol diacrylate, with Mn of 200 in the polyethylene glycol segment) were added sequentially to a 150mL reagent bottle. Then, distilled water was added to prepare a 100mL mixed solution. The reagent bottle was placed in an 80℃ constant temperature water bath for a period of time (i.e., gelation time, see Table 5) to obtain a group of self-breaking gel valve products. The experimental results are shown in Table 5.

[0102] Note: Among the above self-breaking gel valve products, the self-breaking gel valve products corresponding to crosslinking agents RJ-2 and RJ-6 are examples, while the self-breaking gel valve products corresponding to polyethylene glycol diacrylate are comparative examples (i.e., the main subject of comparative example 1). For a more intuitive description, these three sets of products are discussed together.

[0103] Table 5. Effects of crosslinking agent type on gelation time and breakage time of gel valve.

[0104] serial number Crosslinking agent type gelation time / h Time to break down adhesive / day 1 RJ-2 4.5 6 2 RJ-6 3.5 4 3 Polyethylene glycol diacrylate 1.5 2

[0105] Comparative Example 2

[0106] The gel valve base solution was prepared according to the following formula (by mass percentage): (5%, 20%) monomer (acrylamide) + 1% biodegradable crosslinking agent RJ-2 + 0.01% initiator (ammonium persulfate) + 0.2% dispersant (sodium dodecylbenzenesulfonate) + balance water. The base solution was then placed in an 80℃ constant temperature water bath to gel. The experimental results are shown in Table 6.

[0107] Table 6

[0108] serial number Monomer dosage / % gelation time / h Time to break down adhesive / day 1 5 5.5 13 2 20 1 4

[0109] Comparative Example 3

[0110] The gel valve base solution was prepared according to the following formula: by mass percentage, 8% monomer (acrylamide) + (0.5%, 3%) biodegradable crosslinking agent RJ-2 + 0.01% initiator (ammonium persulfate) + 0.2% dispersant (sodium dodecylbenzenesulfonate) + balance water. The base solution was then placed in an 80℃ constant temperature water bath to gel. The experimental results are shown in Table 7.

[0111] Table 7

[0112] serial number Degradable crosslinking agent dosage / % gelation time / h Time to break down adhesive / day 1 0.5 4 3 2 3 1.5 20

[0113] The gel breaking time in these two sets of experiments was either too fast or too slow, which did not meet the requirements for on-site construction.

[0114] Comparative Example 4

[0115] The gel valve base solution was prepared according to the following formula: by mass percentage, 8% monomer (acrylamide) + 1% biodegradable crosslinking agent RJ-2 + (0.005%, 0.02%) initiator (ammonium persulfate) + 0.2% dispersant (sodium dodecylbenzenesulfonate) + the balance being water. The base solution was then placed in an 80℃ constant temperature water bath to gel. The experimental results are shown in Table 8.

[0116] Table 8

[0117] serial number Initiator dosage / % gelation time / h Time to break down adhesive / day 1 0.005 6 6 2 0.02 0.5 6

[0118] The gelation time in these two sets of experiments was either too fast or too slow, which did not meet the requirements for on-site construction.

[0119] Comparative Example 5

[0120] The gel valve base solution was prepared according to the following formula: by mass percentage, 8% monomer (acrylamide) + 1% biodegradable crosslinking agent RJ-2 + 0.01% initiator (ammonium persulfate), (0.1% and 0.6%) dispersant (sodium dodecylbenzenesulfonate) + the balance being water. The base solution was then placed in an 80℃ constant temperature water bath to gel. The experimental results are shown in Table 9.

[0121] Table 9

[0122]

[0123]

[0124] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

[0125] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0126] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0127] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0128] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0129] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0130] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be obviously unreasonable.

Claims

1. A self-breaking gel valve, comprising the following raw materials by weight percentage: 8%-15% alkenyl monomer, 1%-2% biodegradable crosslinking agent, 0.01%-0.015% initiator, 0.35%-0.5% dispersant, 82.485%-90.79% water, the sum of the above components is 100%; in, The biodegradable crosslinking agent is derived from the reaction product obtained by reacting anhydrous strong acid, poly(ethylene glycol) methacrylate as shown in formula (1), and methoxylated benzaldehyde as shown in formula (2); the preparation method of the biodegradable crosslinking agent includes the following steps: Anhydrous strong acid, poly(ethylene glycol) methacrylate, methoxylated benzaldehyde, and anhydrous tetrahydrofuran are mixed and subjected to a cross-linking reaction at a temperature of 0-10℃. Equation (1); Formula (2), in which the position indicated by 1 and / or the position indicated by 2 is replaced by a methoxy group; The number-average molecular weight of the poly(ethylene glycol) segments in poly(ethylene glycol) methacrylate is 200-600; The alkenyl monomer is selected from one or more of acrylamide, methyl methacrylate, hydroxyethyl methacrylate, ethyl acrylate, and vinyl acetate.

2. The self-breaking gel valve according to claim 1, characterized in that... The preparation raw materials include the following mass percentages: 10%-13% alkenyl monomer, 1.5%-2% biodegradable crosslinking agent, 0.012%-0.014% initiator, 0.35%-0.45% dispersant, and 84.536%-88.138% water.

3. The self-breaking gel valve according to claim 1, characterized in that: The number-average molecular weight of the poly(ethylene glycol) segments in poly(ethylene glycol) methacrylate is at least one of 200, 300, 400, and 600; And / or, the anhydrous strong acid is selected from at least one of p-toluenesulfonic acid and trifluoromethanesulfonic acid.

4. The self-breaking gel valve according to claim 1, characterized in that: The number-average molecular weight of the poly(ethylene glycol) segments in the poly(ethylene glycol) methacrylate is at least one of 200 and 300.

5. The self-breaking gel valve according to claim 1, characterized in that... The preparation method of the biodegradable crosslinking agent includes the following steps: Anhydrous strong acid, poly(ethylene glycol) methacrylate, methoxylated benzaldehyde, and anhydrous tetrahydrofuran are mixed and subjected to a crosslinking reaction. After the crosslinking reaction, the solvent is removed by filtration and vacuum distillation, and purified by silica gel column chromatography to obtain the degradable crosslinking agent.

6. The self-breaking gel valve according to claim 1, characterized in that... The mass ratio of anhydrous strong acid, poly(ethylene glycol) methacrylate, and methoxylated benzaldehyde is 1:(15-25):(4-10); and / or, The crosslinking reaction is carried out at a temperature of 0-5°C; and / or, the crosslinking reaction is carried out for a time of 5-7 hours; and / or, The mass ratio of the poly(ethylene glycol) methacrylate to anhydrous tetrahydrofuran is (2-3):

1.

7. The self-breaking gel valve according to claim 1, characterized in that... The mass ratio of anhydrous strong acid, poly(ethylene glycol) methacrylate, and methoxylated benzaldehyde is 1:(15-20):(5-8); and / or, The cross-linking reaction takes 5.5-6 hours.

8. The self-breaking gel valve according to claim 1, characterized in that: The initiator is selected from one or more of ammonium persulfate, potassium persulfate, sodium persulfate, ammonium persulfate / sodium bisulfite, and azobisisobutyramidine hydrochloride; and / or, The dispersant is selected from one or more of sodium dodecylbenzenesulfonate, dodecylphenol polyoxyethylene ether, Tween 40, Tween 60 and Tween 80.

9. The self-breaking gel valve according to any one of claims 1-8, characterized in that: The self-degrading gel valve is capable of self-degrading and breaking down gels.

10. The self-breaking gel valve according to any one of claims 1-8, characterized in that: The self-degrading gel valve is capable of self-degrading and breaking down gels, with a self-degradation time of 4-12 days.

11. The self-breaking gel valve according to any one of claims 1-8, characterized in that: The self-degrading gel valve is capable of self-degrading and breaking down gels, with a self-degradation time of 5-10 days.

12. The self-breaking gel valve according to any one of claims 1-8, characterized in that: The self-degrading gel valve is capable of self-degrading and breaking down gels, with a self-degradation time of 7-8 days.

13. The self-breaking gel valve according to any one of claims 1-8, characterized in that: The self-destructible gel valve is prepared by the following method: mixing the raw materials including the alkenyl monomer, biodegradable crosslinking agent, initiator, dispersant and water to obtain the self-destructible gel valve base liquid, and then gelling to obtain the self-destructible gel valve.

14. The self-breaking gel valve according to claim 13, characterized in that: The gelation time is 1-5 hours.

15. The self-breaking gel valve according to claim 13, characterized in that: The gelation time is 1-4 hours.

16. The self-breaking gel valve according to claim 13, characterized in that: The gelation time is 2-3 hours.

17. A method for preparing a self-destructive gel valve according to any one of claims 1-16, comprising mixing the raw materials including the alkenyl monomer, the biodegradable crosslinking agent, the initiator, the dispersant and water to obtain a self-destructive gel valve base liquid, and then gelling to obtain the self-destructive gel valve.

18. The method for preparing the self-breaking gel valve according to claim 17, characterized in that: The gelation time is 1-5 hours; and / or the gelation temperature is 60-80℃.

19. The method for preparing the self-breaking gel valve according to claim 17, characterized in that: The gelation time is 1-4 hours.

20. The method for preparing the self-breaking gel valve according to claim 17, characterized in that: The gelation time is 2-3 hours.

21. A method for controlling pressure during drilling, comprising the following steps: According to the preparation raw materials and proportions of the self-breaking gel valve, the preparation raw materials including the alkenyl monomer, degradable crosslinking agent, initiator, dispersant and water are mixed to obtain the self-breaking gel valve base liquid; The self-destructible gel valve base liquid is transported downhole, and the self-destructible gel valve base liquid gels at the reservoir temperature to form a self-destructible gel valve. When the self-degrading gel valve reaches its self-degrading gel breaking time, the self-degrading gel valve begins to break the gel, and the resulting gel breaking liquid is discharged back to the ground. The self-breaking gel valve is the self-breaking gel valve according to any one of claims 1-16 or the self-breaking gel valve prepared by the preparation method according to any one of claims 17-20.

22. The drilling pressure control method according to claim 21, characterized in that: The reservoir section temperature is 60-80℃; and / or, the gelation time is 1-5 hours; and / or, The self-breaking gel valve begins to break down in 4-12 days.

23. The drilling pressure control method according to claim 21, characterized in that: The gelation time is 1-4 hours; and / or, The self-breaking gel valve begins to break down in 5-10 days.

24. The drilling pressure control method according to claim 21, characterized in that: The gelation time is 2-3 hours; and / or, The self-breaking gel valve begins to break down in 7-8 days.

25. The application of the self-breaking gel valve according to any one of claims 1-16, or the self-breaking gel valve prepared by the preparation method according to any one of claims 17-20, or the drilling pressure control method according to any one of claims 21-24, in the field of underbalanced drilling technology.

Images