Plugging agent for refracturing as well as preparation method and application thereof

Abstract

The invention provides a plugging agent for refracturing as well as a preparation method and application of the plugging agent. The plugging agent for refracturing comprises the following components: 3%-4% of an inducer, 10%-14% of vegetable gum latex, 3%-4% of a terminator, 7%-10% of a stabilizer, 1%-2% of a cross-linking agent, 2%-3% of acrylamide and 66%-71% of water, wherein the vegetable gum latex is polymerized under the action of the inducer and then mixed with other components, and the plugging agent for refracturing is obtained. The plugging agent for refracturing can form high-strength plugging at a pressure difference position, the residual plugging agent still keeps low viscosity, and the plugging agent has good fluidity.

Description

Technical Field

[0001] The invention belongs to the field of oil field exploration and development, and specifically relates to a plugging agent for repeated fracturing and a preparation method and application thereof. Background Art

[0002] Some oil fields have typical characteristics of low pressure, low permeability and low production. When the oil wells were first put into production, conventional sand fracturing was used, with sand fractures as important near-wellbore seepage channels. After a long period of production, the crude oil around the original fractures has been basically produced. Due to low permeability and low formation pressure, it is difficult to produce crude oil on the side of the fractures. The remaining oil is enriched on the side of the original fractures, forming a batch of low-yield, low-efficiency and low-production oil wells, which seriously affect the development benefits of the oil fields. Repeated transformation of old wells has become an important means to treat low-yield and low-efficiency wells. Conventional repeated fracturing technology extends the length of the fractures, which is easy to communicate with the water injection front, and the risk of water breakthrough is high. It is difficult to realize the mobilization of lateral residual oil, and the measures have poor oil-increasing effects. Plugging fracturing has gradually become the main means of repeated transformation because it can inhibit the extension of the fracture length and increase the net pressure inside the seal. However, at present, plugging fracturing still has problems such as unsatisfactory plugging effect, difficulty in plugging pressure control, and high construction risk. In order to improve the effect of repeated transformation and plugging fracturing of old wells, it is urgent to develop new plugging agents and their plugging methods to control the length of cracks, increase the net pressure in the cracks, open lateral microcracks, achieve the purpose of steering fracturing, and improve development effects. Summary of the invention

[0003] In order to solve the above problems, the purpose of the present invention is to provide a plugging agent for repeated fracturing and its preparation method and application, wherein the plugging agent for repeated fracturing can form a high-strength plugging at the pressure difference, and the remaining plugging agent still maintains low viscosity and has good fluidity.

[0004] In order to achieve the above-mentioned purpose, the present invention provides a plugging agent for repeated fracturing, which, based on the mass of the plugging agent for repeated fracturing as 100%, comprises: 3%-4% inducer, 10%-14% plant rubber latex (calculated based on the total mass of the plant rubber latex), 3%-4% terminator, 7%-10% stabilizer, 1%-2% cross-linking agent, 2%-3% acrylamide, and 66%-71% water; wherein the plant rubber latex is polymerized under the action of the inducer and then mixed with other components to obtain the plugging agent for repeated fracturing.

[0005] According to a specific embodiment of the present invention, preferably, the plant gum latex is an emulsion comprising one or more of guar gum, carrageenan, xanthan gum and agar, and the concentration of the emulsion is preferably 20-30wt%. Guar gum, carrageenan, xanthan gum and agar are all macromolecular compounds, and their chemical structures contain abundant hydroxyl (-OH) functional groups, which can react with other compound aqueous solutions to form hydrogen bonds under certain conditions.

[0006] According to a specific embodiment of the present invention, preferably, the inducer includes one or a combination of two or more of ammonium persulfate, potassium persulfate, tert-butyl hydroperoxide, and benzoyl peroxide. Ammonium persulfate and potassium persulfate are inorganic peroxides, tert-butyl hydroperoxide and benzoyl peroxide are organic peroxides, and these four inducers undergo covalent bond homolysis under the action of heat or light to generate two free radicals, which can initiate a polymerization reaction of chemical monomers. Structural formula of ammonium persulfate: Potassium persulfate structural formula: Tert-Butyl Hydroperoxide Structural Formula: Benzoyl peroxide structure:

[0007] According to a specific embodiment of the present invention, preferably, the terminator includes one or a combination of two or more of hydroquinone, catechol, and resorcinol. Hydroquinone, catechol, and resorcinol are aromatic polyhydroxy compounds. These three substances can react with initiating free radicals and propagating free radicals to make the polymerizing monomer lose its reaction activity, terminate the polymerization reaction, and obtain a polymer with uniform molecular weight and stable molecular structure. Hydroquinone structural formula: Catechol structural formula: Resorcinol structure:

[0008] According to a specific embodiment of the present invention, preferably, the stabilizer comprises one or a combination of two or more of montmorillonite, kaolin, diatomaceous earth and bentonite. Montmorillonite, kaolin, diatomaceous earth and bentonite are all inorganic minerals, which can slow down the reaction and maintain chemical balance as stabilizers.

[0009] According to a specific embodiment of the present invention, preferably, the crosslinking agent includes N,N-methylenebisacrylamide and / or divinylbenzene. N,N-methylenebisacrylamide or divinylbenzene are both unsaturated double bond compounds, which are fed together with the monomers to generate chemical bonds between linear molecules during the polymerization reaction, so that the linear molecules are connected to each other to form a network structure, thereby improving the strength of the polymer material. N,N-methylenebisacrylamide structural formula: Divinylbenzene structure:

[0010] The present invention also provides a method for preparing the above-mentioned plugging agent for repeated fracturing, which comprises the following steps:

[0011] (1) Preparation of plant gum particles: dissolving the inducer in water to obtain an inducer solution, adding the inducer solution to the plant gum latex, stirring and reacting at 40-60° C. until the latex becomes clear, and obtaining solidified plant gum particles;

[0012] (2) Emulsifying the plant gum particles: dissolving a terminator in water to obtain a terminator solution, adding the solidified plant gum particles to the terminator solution, and emulsifying the solidified plant gum particles to obtain a plant gum particle emulsion;

[0013] (3) Preparation of plugging agent for repeated fracturing: dissolving a stabilizer, a cross-linking agent and acrylamide in water to form a mixed solution, adding the mixed solution to the plant gum particle emulsion obtained in step (2) for emulsification to obtain the plugging agent for repeated fracturing.

[0014] According to a specific embodiment of the present invention, preferably, in step (1), the stirring reaction time is 1-2h.

[0015] According to a specific embodiment of the present invention, preferably, the emulsification conditions in step (2) and step (3) are: the emulsification time is 30-60 min; the emulsification speed is 12000-15000 rpm, preferably 15000 rpm.

[0016] According to a specific embodiment of the present invention, preferably, based on the mass of the plugging agent for repeated fracturing being 100%, in step (1), the amount of water used is 10%-14%; in step (2), the amount of water used is 20%-24%; in step (3), the amount of water used is 28%-41%.

[0017] According to a specific embodiment of the present invention, the above preparation method comprises the following specific steps:

[0018] (1) Preparation of plant gum particles: dissolving 3%-4% of an inducer in 10%-14% of water to obtain an inducer solution, adding the inducer solution to 10%-14% of plant gum latex, stirring at 40-60° C. for 1-2 hours, stirring until the liquid is clear, inducing polymerization of the plant gum latex, and obtaining solidified plant gum particles;

[0019] (2) Emulsification of plant gum particles: dissolving 3%-4% of the terminator in 20%-24% of water, and adding the solidified plant gum particles into the terminator solution to terminate the polymerization between the monomers, and emulsifying the mixed solution of the plant gum particles and the terminator to obtain a uniform emulsion;

[0020] (3) Preparation of plugging agent for repeated fracturing: 7%-10% of stabilizer, 1%-2% of cross-linking agent and 2%-3% of acrylamide are dissolved in 28%-41% of water to form a mixed solution, and the prepared mixed solution is added to the emulsion prepared in step (2), and emulsified using an emulsifier to obtain the final plugging agent for repeated fracturing (high-strength curing plugging agent for the ends of old well cracks). Under a certain temperature, the plugging agent, through the action of the cross-linking agent and the inducing agent, induces the functional groups between the monomers to cross-link through hydrogen bonds, van der Waals forces, electrostatic interactions, etc. (for example, acrylamides are cross-linked to form polyacrylamide through cross-linking agents, and plant gums and acrylamide are cross-linked through hydrogen bonds, etc.), forming a network structure, thereby obtaining a high-strength cured plugging gel at the pressure difference.

[0021] The present invention also provides the use of the plugging agent for repeated fracturing in repeated fracturing to create new seams or water plugging fracturing operations in oil fields.

[0022] According to a specific embodiment of the present invention, preferably, the plugging agent for repeated fracturing is injected into the oil well for 3-8 hours to form a high-strength plugging at the end of the fracture at a temperature of 50-70°C.

[0023] The present invention has the following beneficial effects:

[0024] 1. The high strength of the resin plugging agent and the low viscosity of the water-based emulsion plugging agent are combined to produce an emulsion plugging agent that is responsive to the pressure difference. It can form a high-strength plugging at the pressure difference, and the remaining plugging agent still maintains low viscosity and has good fluidity, which improves the adaptability to complex downhole conditions and has low construction risks;

[0025] 2. By changing the composition and ratio of the product, the viscosity, usage strength and curing time of the product can be adjusted to meet the requirements of different well depths, different transformation processes and mineralization for product performance. DETAILED DESCRIPTION

[0026] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention. The following percentages are calculated based on the mass of the obtained plugging agent for repeated fracturing as 100% unless otherwise specified.

[0027] The following examples use a servo material multifunctional high and low temperature control testing machine to test the use strength: the sample is made into a cylinder with a height of 30 mm and a diameter of 22 mm. After curing at 60°C for 6 hours, the servo material multifunctional high and low temperature control testing machine is used to compress the sample at a compression rate of 5 mm / min until the gel breaks, and the maximum strength is read.

[0028] Curing time: Place the prepared prepolymer liquid (plugging agent for repeated fracturing) in a 50-70℃ heating box and observe the curing status every hour. When half of the sample has cured, observe it every ten minutes until it is completely cured and record the final curing time.

[0029] Example 1

[0030] This embodiment provides a plugging agent for repeated fracturing, which is prepared by the following steps:

[0031] (1) dissolving 3% ammonium persulfate in 10% water to obtain an ammonium persulfate solution; adding the prepared ammonium persulfate solution to 10% guar gum latex (concentration of 20 wt%), stirring at 40° C. for 1.5 h until the liquid becomes clear, and obtaining solidified guar gum particles;

[0032] (2) dissolving 3% hydroquinone in 20% water; adding the solidified guar gum particles to the prepared hydroquinone solution, and emulsifying the hydroquinone solution with the guar gum particles using an emulsifier at a rotation speed of 15000 rpm for 30 minutes to obtain an emulsion;

[0033] (3) Dissolving 10% montmorillonite, 1% N,N-methylenebisacrylamide and 2% acrylamide in 41% water; adding the prepared mixed solution to the emulsion prepared in step (2), and emulsifying for 30 minutes using an emulsifier at a rotation speed of 15000 rpm to obtain the plugging agent for repeated fracturing.

[0034] The prepared plugging agent for repeated fracturing has a viscosity of 28 mPa·s, a curing time of 6 hours, and a service strength of ≥40 MPa.

[0035] Example 2

[0036] This embodiment provides a plugging agent for repeated fracturing, which is prepared by the following steps:

[0037] (1) dissolving 4% ammonium persulfate in 14% water to obtain an ammonium persulfate solution; adding the prepared ammonium persulfate solution to 14% guar gum latex (concentration of 20 wt%), stirring at 40° C. for 1.5 h until the liquid becomes clear, and obtaining solidified guar gum particles;

[0038] (2) dissolving 4% hydroquinone in 24% water; adding the solidified guar gum particles to the prepared hydroquinone solution, and emulsifying the hydroquinone solution with the guar gum particles using an emulsifier at a rotation speed of 15000 rpm for 30 minutes to obtain an emulsion;

[0039] (3) Dissolving 7% montmorillonite, 2% N,N-methylenebisacrylamide and 3% acrylamide in 28% water; adding the prepared mixed solution to the emulsion prepared in step (2), and emulsifying for 30 minutes using an emulsifier at a rotation speed of 15000 rpm to obtain the plugging agent for repeated fracturing.

[0040] The prepared plugging agent for repeated fracturing has a viscosity of 20 mPa·s, a curing time of 6 hours, and a service strength of ≥40 MPa.

[0041] Example 3

[0042] This embodiment provides a plugging agent for repeated fracturing, which is prepared by the following steps:

[0043] (1) dissolving 3% ammonium persulfate in 13% water to obtain an ammonium persulfate solution; adding the prepared ammonium persulfate solution to 13% guar gum latex (concentration of 20 wt%), stirring at 40° C. for 1.5 h until the liquid becomes clear, and obtaining solidified guar gum particles;

[0044] (2) dissolving 3% hydroquinone in 23% water; adding the solidified guar gum particles to the prepared hydroquinone solution, and emulsifying the hydroquinone solution with the guar gum particles using an emulsifier at a rotation speed of 15000 rpm for 30 minutes to obtain an emulsion;

[0045] (3) 8% montmorillonite, 1% N,N-methylenebisacrylamide and 3% acrylamide are dissolved in 33% water; the prepared mixed solution is added to the emulsion prepared in step (2), and emulsified at a speed of 15000 rpm for 30 minutes using an emulsifier to obtain the plugging agent for repeated fracturing.

[0046] The prepared plugging agent for repeated fracturing has a viscosity of 25 mPa·s, a curing time of 6 hours, and a service strength of ≥40 MPa.

[0047] Example 4

[0048] This embodiment provides a plugging agent for repeated fracturing, which is prepared by the following steps:

[0049] (1) dissolving 3% ammonium persulfate in 10% water to obtain an ammonium persulfate solution; adding the prepared ammonium persulfate solution to 12% carrageenan latex (concentration of 20 wt%), stirring at 40° C. for 1.5 h until the liquid becomes clear, and obtaining solidified carrageenan particles;

[0050] (2) dissolving 3% hydroquinone in 20% water; adding the solidified carrageenan particles to the prepared hydroquinone solution, and emulsifying the hydroquinone solution with the carrageenan particles using an emulsifier at a rotation speed of 15000 rpm for 30 minutes to obtain an emulsion;

[0051] (3) Dissolving 8% kaolin, 1% N,N-methylenebisacrylamide and 2% acrylamide in 41% water; adding the prepared mixed solution to the emulsion prepared in step (2), and emulsifying for 30 minutes using an emulsifier at a rotation speed of 15000 rpm to obtain the plugging agent for repeated fracturing.

[0052] The prepared plugging agent for repeated fracturing has a viscosity of 25 mPa·s, a curing time of 6 hours, and a service strength of ≥40 MPa.

[0053] Example 5

[0054] This embodiment provides a plugging agent for repeated fracturing, which is prepared by the following steps:

[0055] (1) dissolving 3% ammonium persulfate in 10% water to obtain an ammonium persulfate solution; adding the prepared ammonium persulfate solution to 12% xanthan gum latex (concentration of 20 wt%), stirring at 40° C. for 1.5 h until the liquid becomes clear, and obtaining solidified xanthan gum particles;

[0056] (2) dissolving 3% hydroquinone in 20% water; adding the solidified xanthan gum particles to the prepared hydroquinone solution, and emulsifying the hydroquinone solution with the xanthan gum particles using an emulsifier at a rotation speed of 15000 rpm for 30 minutes to obtain an emulsion;

[0057] (3) 8% bentonite, 1% N,N-methylenebisacrylamide and 2% acrylamide are dissolved in 41% water; the prepared mixed solution is added to the emulsion prepared in step (2), and emulsified at a speed of 15000 rpm for 30 minutes using an emulsifier to obtain the plugging agent for repeated fracturing. The obtained plugging agent for repeated fracturing has a viscosity of 25 mPa·s, a curing time of 6 hours, and a service strength of ≥40 MPa.

[0058] Comparative Example 1

[0059] This comparative example provides a plugging agent for fracturing, which is prepared by the following steps:

[0060] 3% ammonium persulfate is dissolved in 10% water to obtain an ammonium persulfate solution; the prepared ammonium persulfate solution, 5% montmorillonite, 1% N,N-methylenebisacrylamide and 10% acrylamide are dissolved in 71% water, stirred evenly, and a plugging agent for fracturing is obtained.

[0061] The prepared plugging agent for fracturing has a viscosity of 20 mPa·s, a curing time of 6 hours, and a service strength of ≤10 MPa.

[0062] Comparative Example 2

[0063] This comparative example provides a plugging agent for fracturing, which is prepared by the following steps:

[0064] 3% ammonium persulfate is dissolved in 10% water to obtain an ammonium persulfate solution; the prepared ammonium persulfate solution, 5% kaolin, 1% N,N-methylenebisacrylamide and 10% acrylamide are dissolved in 71% water, stirred evenly, and a plugging agent for fracturing is obtained.

[0065] The prepared plugging agent for fracturing has a viscosity of 20 mPa·s, a curing time of 6 hours, and a service strength of ≤10 MPa.

[0066] In summary, the viscosity of the final plugging agent for repeated fracturing is 20-28mPa·s, and the compressive strength, that is, the working strength is ≥40MPa. It has the characteristics of high mechanical strength and low working viscosity (good fluidity along the cracks in the well).

[0067] The plugging agent for repeated fracturing prepared in Example 1 was used in an oilfield fracturing device at a speed of 0.5 m 3 / min speed is injected into the oil well, and solidifies for 3-8h at 50-70℃ in the formation to form a plug. The plugging agent for repeated fracturing is a white liquid. After being poured into the sand layer, it immediately produces a pressure-holding effect, and the pressure-holding is stable at about 9.5. After drying at 70 degrees, a very thick polymer dense layer is formed. The high-strength solidified plugging agent forms a tough connection at the pressure difference downhole, forming a high-strength plugging, which prevents the old fracture from opening during repeated fracturing and realizes the opening of new lateral fractures.

Claims

1. A plugging agent for repeated fracturing, which, based on the mass of the plugging agent for repeated fracturing being 100%, comprises: Inducer 3%-4%, plant rubber latex 10%-14%, terminator 3%-4%, stabilizer 7%-10%, cross-linking agent 1%-2%, acrylamide 2%-3%, water 66%-71%; in, The plant rubber latex is polymerized under the action of an inducer and then mixed with other components to obtain the plugging agent for repeated fracturing.

2. The plugging agent for repeated fracturing according to claim 1, wherein: The plant gum latex is an emulsion comprising one or a combination of two or more of guar gum, carrageenan, xanthan gum and agar; Preferably, the concentration of the plant rubber latex is 20-30wt%.

3. The plugging agent for repeated fracturing according to claim 1, wherein: The inducer includes one or a combination of two or more of ammonium persulfate, potassium persulfate, tert-butyl hydroperoxide, and benzoyl peroxide.

4. The plugging agent for repeated fracturing according to claim 1, wherein: The terminator includes one or a combination of two or more of hydroquinone, catechol and resorcinol.

5. The plugging agent for repeated fracturing according to claim 1, wherein: The stabilizer includes one or a combination of two or more of montmorillonite, kaolin, diatomaceous earth and bentonite.

6. The plugging agent for repeated fracturing according to claim 1, wherein: The crosslinking agent includes N,N-methylenebisacrylamide and / or divinylbenzene.

7. The method for preparing the plugging agent for repeated fracturing according to any one of claims 1 to 6, comprising the following steps: (1) Preparation of plant gum particles: dissolving the inducer in water to obtain an inducer solution, adding the inducer solution to the plant gum latex, stirring and reacting at 40-60° C. until the latex becomes clear, and obtaining solidified plant gum particles; (2) Emulsifying the plant gum particles: dissolving a terminator in water to obtain a terminator solution, adding the solidified plant gum particles to the terminator solution, and emulsifying the solidified plant gum particles to obtain a plant gum particle emulsion; (3) Preparation of plugging agent for repeated fracturing: dissolving a stabilizer, a cross-linking agent and acrylamide in water to form a mixed solution, adding the mixed solution to the plant gum particle emulsion obtained in step (2) for emulsification to obtain the plugging agent for repeated fracturing.

8. The preparation method according to claim 7, wherein: In step (1), the stirring reaction time is 1-2h; Preferably, the emulsification conditions in step (2) and step (3) are: emulsification time is 30-60 min; emulsification speed is 12000-15000 rpm; Preferably, based on the mass of the plugging agent for repeated fracturing being 100%, in step (1), the amount of water used is 10%-14%; in step (2), the amount of water used is 20%-24%; in step (3), the amount of water used is 28%-41%.

9. Use of the plugging agent for repeated fracturing according to any one of claims 1 to 6 in repeated fracturing to create new fractures or water plugging fracturing operations in oil fields.

10. The use according to claim 9, wherein: The plugging agent for repeated fracturing is injected into the oil well for 3-8 hours, and forms a high-strength plugging at the end of the crack at a temperature of 50-70°C.