Self-adaptive temporary plugging agent for plugging irregular holes, and preparation method therefor and use thereof

Abstract

The present invention relates to the field of exploitation of petroleum and natural gas. Disclosed are a self-adaptive temporary plugging agent for plugging irregular holes, and a preparation method therefor and the use thereof. The temporary plugging agent comprises a flexible material and a tough material layer coated outside the flexible material, wherein the tough material layer is made of a polyurea, and the tough material layer has a thickness of greater than or equal to 0.5 mm. The temporary plugging agent provided in the present invention has a double-layer structure that is soft inside and tough outside, wherein the inner layer is made of a flexible material and can be easily deformed, the outer layer is made of a tough material, the bottom hole pressure is within the compressive strength thereof, and the coating layer of the tough material can sufficiently deform along with the inner layer flexible material without damage.

Description

Adaptive temporary plugging agent for plugging irregular holes, preparation method and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent application No. 202311743727.4, filed on December 18, 2023, entitled “Adaptive temporary plugging agent for plugging irregular holes, preparation method and application thereof”, the contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to the field of oil and natural gas exploitation, and in particular to an adaptive temporary plugging agent for plugging irregular holes, a preparation method and an application thereof. Background Art

[0004] Staged horizontal well stimulation is a key technology for developing unconventional reservoirs. To significantly increase the volume of reservoir stimulation and expand the contact area between artificial fractures and the reservoir, multi-cluster perforation is often employed in horizontal well stimulation. This involves placing multiple perforation sections within the same stimulation interval. The goal is to fully open each section through measures such as increased displacement, thereby increasing the single-well production of tight oil and gas wells. However, extensive field fracturing practice has shown that the degree of perforation cluster opening is limited by heterogeneous formation lithology and stress, as well as the influence of natural fractures. Nearly 40% of all perforation clusters fail to achieve effective stimulation, resulting in a high degree of uneven fracture expansion within multiple clusters. Therefore, improving the perforation opening degree within multiple clusters is crucial for ensuring fracturing effectiveness.

[0005] Temporary plugging technology, a key technique for increasing the degree of intra-segment multi-cluster pressure opening, relies on inserting temporary plugging balls into the blastholes within the bridge plug segmented fracturing section. Based on the effective pressure-bearing capacity of the temporary plugging balls, the net pressure during operation is increased to open new clusters, thereby achieving the goal of diverting flow within the fractures and achieving uniform transformation of reservoirs with different physical properties and geostresses. However, during fracturing, high-volume sand-carrying fluids can rapidly grind the blastholes, causing varying degrees of expansion and irregular deformation. Effectively plugging these enlarged irregular perforations, limiting the flow to a small number of perforation clusters and severing the connection between the wellbore and the fault at the source, requires the selection of appropriate temporary plugging materials.

[0006] At present, conventional materials such as knot temporary plugging agents with specific shapes (CN202210704007.6, CN202210392629.X), high-strength granular temporary plugging agents (CN202211626967.1), fiber temporary plugging agents (CN202211401903.1), and temporary plugging balls (CN202111238455.3, CN202110188758.2) have limited temporary plugging capabilities and are difficult to effectively block irregular perforations.

[0007] Based on this, an adaptive temporary plugging agent that is easily deformable, can withstand strong pressure and can be degraded is developed. After entering the position of the hole that needs to be plugged, it can deform according to the shape of the hole under the action of fluid pressure, thereby achieving the purpose of adaptive plugging of different hole shapes; it is of great significance to ensure the efficiency of temporary plugging and fracturing of horizontal wells.

[0008] Summary of the Invention

[0009] The purpose of the present invention is to overcome the problem in the prior art that multiple clusters of perforations in horizontal wells cannot be effectively sealed, resulting in the inability to uniformly initiate and expand multiple clusters of hydraulic fractures. An adaptive temporary plugging agent and its preparation method and application are provided. The temporary plugging agent has the characteristics of easy deformation and strong pressure resistance. During the fracturing process, it can adaptively deform according to the irregular perforations under the action of fluid pressure and effectively plug them.

[0010] In order to achieve the above-mentioned object, the first aspect of the present invention provides a temporary plugging agent, wherein the temporary plugging agent comprises a flexible material and a tough material layer coated on the outside of the flexible material; wherein the tough material layer is made of polyurea, and the thickness of the tough material layer is greater than or equal to 0.5 mm.

[0011] A second aspect of the present invention provides a method for preparing a temporary plugging agent, wherein the preparation method comprises: placing a flexible material in a mold with a cavity, centering the flexible material in the cavity, then mixing an isocyanate semi-prepolymer and an amino compound-containing material, injecting the mixture into the cavity, and curing; the amount of the isocyanate semi-prepolymer and the amino compound-containing material is such that after curing, the thickness of the polyurea layer coated on the outer surface of the flexible material is greater than or equal to 0.5 mm.

[0012] A third aspect of the present invention provides a temporary plugging agent prepared by the preparation method provided by the present invention.

[0013] A fourth aspect of the present invention provides an application of the temporary plugging agent provided by the present invention in multi-cluster temporary plugging fracturing of a horizontal well.

[0014] Through the above technical solution, the beneficial effects of the present invention are:

[0015] To address the problem of multi-cluster hydraulic fractures not being able to initiate and propagate evenly due to the inability to effectively seal multiple perforations in horizontal wells, the temporary plugging agent provided by the present invention has a double-layer structure with a flexible inner layer and a tough outer layer. The inner layer is made of a flexible material that can easily deform, while the outer layer is a tough material, polyurea. As long as the bottomhole pressure is within its compressive strength, the tough material coating can deform sufficiently with the inner flexible material without breaking. After being set in an irregular perforation, it deforms under the action of fluid pressure, filling the irregular spaces formed by the sand-carrying fluid, effectively sealing the irregular perforation and improving the plugging efficiency. Compared with traditional temporary plugging materials such as temporary plugging balls or knotted temporary plugging agents, the temporary plugging efficiency is higher.

[0016] In addition, in a preferred embodiment of the present invention, by selecting appropriate raw materials and methods for preparing the tough material (polyurea) layer, the tough material layer wrapped on the outer surface of the flexible material can withstand a temperature of 100-120°C. During the fracturing process, when the room temperature fracturing fluid is continuously injected into the formation from the wellbore, the temperature in the wellbore is much lower than the formation temperature, and also lower than the temperature resistance of the tough material layer outside the flexible material, thereby not affecting the performance of the temporary plugging agent. After the fracturing is completed, the temperature in the wellbore gradually increases to the same temperature as the formation. After exceeding the maximum temperature resistance of the tough material layer, the tough material layer gradually deteriorates, softens, and decomposes, and the temporary plugging agent can be smoothly degraded in the later stage. In addition, through the calculation formula of the equivalent hole diameter and the change of the characteristic pressure before and after temporary plugging on the construction pressure curve, the size of the required adaptive temporary plugging agent and the temporary plugging effect can be accurately obtained, which greatly improves the construction effect of hydraulic fracturing and increases the production of a single well. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1a is a cross-sectional view of a spherical temporary plugging agent in a preferred embodiment of the present invention.

[0018] FIG1 b is a cross-sectional view of an ellipsoidal temporary plugging agent in a preferred embodiment of the present invention.

[0019] FIG1c is a cross-sectional view of a hexahedral temporary plugging agent in a preferred embodiment of the present invention.

[0020] FIG2 is a graph showing the fracturing fluid flow rate and the operating pressure when the pump is stopped by step-down fracturing fluid flow rate.

[0021] FIG3 is a construction pressure curve diagram before and after temporary plugging.

[0022] 4a and 4b are schematic diagrams of circular holes with regular original shapes.

[0023] 4c and 4e are schematic diagrams of the shapes of the irregular holes formed after abrasion.

[0024] FIG. 4 d is a schematic diagram showing the shape of the tadpole-shaped holes formed after abrasion.

[0025] FIG4f is a schematic diagram of the shape of the pot-belly eyelets formed after abrasion.

[0026] Explanation of the accompanying figures 1-flexible material 2-tough material layer 3-fracturing fluid displacement 4-operation pressure 5-instantaneous operation pressure increase after temporary plugging agent is set 6-effective temporary plugging time 7-sand concentration 8-increase in operation pressure of the same displacement before and after temporary plugging DETAILED DESCRIPTION

[0027] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0028] A first aspect of the present invention provides a temporary plugging agent, wherein the temporary plugging agent comprises a flexible material and a tough material layer coated on the flexible material; wherein the tough material layer is made of polyurea, and the thickness of the tough material layer is greater than or equal to 0.5 mm.

[0029] According to the present invention, the thickness of the tough material layer is preferably 1-3 mm. If the thickness is too thin, the tough material layer will have low compressive, tensile, and tear strengths, as well as low elongation at break, making it prone to breakage under high pressure. If the thickness is too thick, the tough material layer will have excessively high compressive, tensile, and tear strengths, making it difficult to deform under high pressure, hindering effective sealing of irregular hole edges.

[0030] According to the present invention, preferably, the weight average molecular weight of the polyurea is 30,000-100,000 g / mol.

[0031] In a preferred embodiment, the tough material layer has a compressive strength greater than or equal to 80 MPa, a tensile strength greater than or equal to 29 MPa, an elongation at break greater than or equal to 380%, and a tear strength greater than or equal to 90 MPa.

[0032] Currently, shale oil and gas extraction is conducted at a depth of 3,000-4,500 meters, with a bottomhole pressure approaching 100 MPa and a well temperature of around 130-150°C. When the performance of the tough material layer meets the requirements of compressive strength greater than or equal to 80 MPa, tensile strength greater than or equal to 29 MPa, elongation at break greater than or equal to 380%, and tear strength greater than or equal to 90 MPa, the temporary plugging agent can meet the requirements of being easily deformable and pressure-bearing under high temperature and high pressure conditions. The temporary plugging agent provided by the present invention has a double-layer structure with a flexible inner layer and a tough outer layer. The inner layer is made of a flexible material that can be easily deformed, and the outer layer is made of a tough material. When the bottomhole pressure is within its compressive strength, the tough material layer can deform sufficiently with the inner flexible material without being damaged.

[0033] Furthermore, the tough material layer has a compressive strength of 90-110 MPa, a tensile strength of 30-50 MPa, an elongation at break of 400-500%, and a tear strength of 100-120 MPa.

[0034] Preferably, the tough material layer has a temperature tolerance of 100-120°C. During the fracturing process, as ambient temperature fracturing fluid is continuously injected into the formation from the wellbore, the temperature inside the wellbore is much lower than the formation temperature and also lower than the temperature resistance of the tough material layer outside the flexible material, thus not affecting the performance of the temporary plugging agent. After fracturing is completed, the temperature inside the wellbore gradually increases to the same temperature as the formation (the formation temperature is 130-150°C). After exceeding the maximum temperature resistance of the tough material layer, the tough material layer gradually deteriorates, softens, and decomposes. The tough material layer's temperature tolerance is 30-40°C lower than the formation temperature, allowing the temporary plugging agent to be successfully degraded at a later stage.

[0035] According to the present invention, preferably, the flexible material is selected from paraffin wax and / or soft silicone. Paraffin wax and / or soft silicone, as flexible materials, can be easily deformed in a high temperature and high pressure environment and are suitable for effectively blocking irregular shaped holes.

[0036] According to the present invention, preferably, the melting point of the paraffin wax is 20-40°C, and / or the hardness of the soft silicone rubber is less than or equal to 20A. The hardness refers to the Shore A hardness. Paraffin wax with a melting point within this range can melt into a liquid state in a high-temperature environment, allowing it to deform in any direction, thereby effectively sealing irregularly shaped holes. Soft silicone rubber with a hardness within this range can easily deform in a high-temperature and high-pressure environment, thus effectively sealing irregularly shaped holes.

[0037] According to the present invention, preferably, the flexible material is spherical in shape.

[0038] According to the present invention, preferably, the diameter of the flexible material is 9-48 mm. A diameter within this range of the flexible material can effectively seal regular holes in the field. If the diameter is too small, smaller than the eroded perforations, it will enter the formation along with the fracturing fluid through the perforations during the fracturing process, making it difficult to effectively seal the hole. If the diameter is too large, on the one hand, it will affect its migration in long horizontal wellbores, making it difficult to effectively move to the hole to be sealed. On the other hand, it will be difficult to effectively seal the hole to be sealed, and it will easily fall off when the pressure or displacement fluctuates.

[0039] In the present invention, in order to be suitable for plugging perforations of different shapes, the temporary plugging agent can be in various shapes. The thickness of the tough material layer is defined as the thickness of the thinnest part of the tough material layer.

[0040] According to the present invention, the temporary plugging agent is preferably shaped like a sphere, ellipsoid, or dodecahedron. Temporary plugging agents of varying shapes are suitable for plugging perforations of varying shapes. Spherical and ellipsoidal temporary plugging agents are suitable for plugging regularly shaped perforations, while dodecahedron-shaped temporary plugging agents are suitable for plugging irregularly shaped perforations. Examples of regularly shaped perforations include those shown in Figures 4a and 4b; examples of irregularly shaped perforations include the irregularly shaped perforations shown in Figures 4c and 4e, the tadpole-shaped perforation shown in Figure 4d, and the pot-bellied perforation shown in Figure 4f.

[0041] According to a specific embodiment of the present invention, cross-sectional views of a spherical temporary plugging agent, an ellipsoidal temporary plugging agent, and a regular dodecahedron temporary plugging agent are shown in Figures 1a, 1b, and 1c, respectively. The temporary plugging agent comprises a flexible material 1 and a tough material layer 2 coated on the flexible material.

[0042] Generally, the initial perforation hole diameter is 9-11mm. During the fracturing process, as the sand-carrying fluid enters, the hole is continuously polished by the sand-carrying fluid, the hole shape becomes irregular, and the hole diameter becomes larger. In order to select the appropriate size of temporary plugging agent during the fracturing process, before the temporary plugging operation, it is necessary to calculate the expanded hole diameter. The method for calculating the hole diameter change is as follows:

[0043] In formula (1)-formula (3), P perf is the friction resistance of the perforation hole, in MPa; k perf is the hole friction coefficient, dimensionless; q is the fracturing fluid displacement, unit is m 3 / min; γ is the friction index; α is the friction coefficient, which is generally taken as 2.2326×10 -4 ; ρ is the density of fracturing fluid, unit is kg / m 3 ;n p is the number of effective opening holes; d p is the diameter after erosion, in m; η is the hole expansion coefficient, 300 kg / m 3 When the sand concentration is less than 1.0×10 -13 m 2 ·s / kg; V d is the pore flow coefficient, which is generally taken as 0.95; c is the average proppant concentration, in kg / m 3 ; t is the sand adding time, unit is min; d o is the initial perforation hole diameter, in m.

[0044] Using formula (1), calculate the hole friction coefficient P perf. The specific method is that when the pump is about to be stopped to release the temporary plugging agent during fracturing, the pump is stopped by step-by-step reduction of the fracturing fluid displacement to obtain stable construction pressure values ​​at different fracturing fluid displacements. The changes in fracturing fluid displacement 3 and construction pressure 4 are shown in Figure 2. It can be seen from Figure 2 that by step-by-step reduction of the displacement, a corresponding stable pressure value can be obtained under different displacement conditions. The perforation friction resistance and friction resistance index are fitted as unknown parameters, so that these two parameters can be obtained. In order to accurately obtain the friction coefficient, it is necessary to obtain 4-6 groups of different fracturing fluid displacements and corresponding pressure data when step-by-step reduction of the fracturing fluid displacement.

[0045] Using formulas (2) and (3), the hole diameter d after erosion is calculated p The friction resistance of the perforation hole is calculated by formula (1). The remaining two eroded diameters d in formulas (2) and (3) are p and the number of effective opening holes n p By solving the two unknowns together, we can get the hole diameter after erosion.

[0046] The hole diameter calculated theoretically above is the equivalent hole diameter. In reality, hole diameters are irregular. To ensure the adaptive temporary plugging agent securely sets, the selected size is 1.2-1.5 times the theoretically calculated hole diameter. Once securely set, the temporary plugging agent deforms under the action of fluid pressure, thereby sealing any irregular spaces and improving sealing efficiency.

[0047] According to the data statistics of the shape of the perforated holes during the fracturing process and the diameter of the holes after erosion, preferably, the diameter of the temporary plugging agent in the shape of a sphere is 11-50 mm; or, the short axis length of the temporary plugging agent in the shape of an ellipsoid is 11-50 mm, the middle axis length is the same as the short axis length, and the long axis length is 1.5-2 times the short axis length; or, the distance from the outer surface to the center of the temporary plugging agent in the shape of a regular dodecahedron is 11-50 mm.

[0048] A second aspect of the present invention provides a method for preparing a temporary plugging agent, comprising: placing a flexible material in a mold with a cavity, centered within the cavity; then mixing an isocyanate semi-prepolymer and an amino compound-containing material, injecting the mixture into the cavity, and curing the mixture; the isocyanate semi-prepolymer and the amino compound-containing material are used in such amounts that, after curing, the thickness of the polyurea layer coated on the outer surface of the flexible material is greater than or equal to 0.5 mm. Thus, the temporary plugging agent having the polyurea layer coated on the outer surface of the flexible material is obtained.

[0049] In order to make the tough material layer have more suitable compressive strength, tensile strength, tear strength and elongation at break, thereby further preventing the tough material layer from breaking under high pressure and making it easier to deform, preferably, the amount of the isocyanate semi-prepolymer and the amino compound-containing material is such that after the curing, the thickness of the polyurea layer coated on the outer surface of the flexible material is 1-3 mm.

[0050] According to a preferred embodiment of the present invention, the shape of the cavity in the mold is spherical, ellipsoidal or regular dodecahedron. In a preferred case, the diameter of the spherical cavity is 11-50mm, which is used to prepare a temporary plugging agent material with a spherical shape; the short axis length of the ellipsoidal cavity is 11-50mm, the middle axis length is the same as the short axis length, and the long axis length is 1.5-2 times the short axis length, which is used to prepare a temporary plugging agent material with an ellipsoidal shape; the distance from the surface to the center of the regular dodecahedron cavity is 11-50mm, which is used to prepare a temporary plugging agent material with a regular dodecahedron shape. In order to ensure that the flexible material is centered in the mold cavity, a thin steel needle or thin wire can be used for pre-fixation. After pouring and curing, the temporary plugging agent obtained is taken out after being wrapped with a polyurea coating.

[0051] In order to make the tough material layer have more suitable compressive strength, tensile strength, tear strength and elongation at break, thereby effectively preventing the tough material layer from breaking under high pressure, preventing the performance of the temporary plugging agent from being affected during fracturing, and increasing the effective temporary plugging time of the temporary plugging agent, while also ensuring that the temporary plugging agent is easily deformed; and further improving the degradation effect of the temporary plugging agent after fracturing is completed, preferably, the isocyanate semi-prepolymer is prepared from composition A; the composition A comprises the following components in parts by weight: 60-70 parts of isocyanate, 10-15 parts of polyether polyol, 5-10 parts of polysiloxane polyol and 5-10 parts of viscosity reducer;

[0052] And / or, the amino compound-containing material is prepared from composition B; the composition B comprises the following components in parts by weight: 50-60 parts of amino-terminated polyether, 10-20 parts of diamine chain extender, 20-40 parts of bis-sec-butylaminodiphenylmethane and 1-5 parts of defoaming agent.

[0053] The present invention has no particular limitation on the type of isocyanate, and conventional isocyanates used for synthesizing polyurea in the art can be used, preferably diphenylmethane diisocyanate.

[0054] The present invention has no particular limitation on the type of polyether polyol, and conventional polyether polyols for synthesizing polyurea in the art can be used, preferably one or more selected from polyoxypropylene diol, polyoxypropylene triol, polytetramethylene glycol diol and polytetramethylene glycol triol.

[0055] The present invention has no particular limitation on the type of polysiloxane polyol, and conventional polysiloxane polyols for synthesizing polyurea in the art can be used, preferably polysiloxane diol.

[0056] The present invention has no particular limitation on the type of viscosity reducer, which may be a conventional viscosity reducer used in preparing polyurea, preferably one or more selected from dibutyl phthalate, dioctyl phthalate, propyl carbonate and ethyl carbonate.

[0057] The present invention has no particular limitation on the type of amino-terminated polyether, and conventional amino-terminated polyethers used for synthesizing polyurea in the art can be used, preferably amino-terminated polyoxypropylene ether.

[0058] The present invention has no particular limitation on the type of diamine chain extender. Conventional diamine chain extenders for synthesizing polyurea in the art can be used, preferably one or more selected from diethyltoluenediamine (DETDA, abbreviated as E100), dimethylthiotoluenediamine (DMTDA, abbreviated as E300) and N,N'-dialkylmethyldiamine (DBMDA).

[0059] The present invention has no particular limitation on the type of the defoaming agent, which may be a conventional defoaming agent used in the preparation of polyurea, preferably a silicone defoaming agent.

[0060] According to the present invention, preferably, the method for preparing the isocyanate semi-prepolymer comprises: reacting the uniformly mixed composition A at 65-85° C. for 2-3 hours to obtain the isocyanate semi-prepolymer. Preferably, the water content of the isocyanate semi-prepolymer is ≤0.05 wt%.

[0061] And / or, the preparation method of the amino compound-containing material comprises: vacuum dehydrating the uniformly mixed composition B at 30-50° C. for 2-4 hours to obtain the amino compound-containing material. Preferably, the moisture content of the amino compound-containing material is ≤0.05 wt%.

[0062] In the present invention, the semi-prepolymer of isocyanate and the material containing the amino compound can be obtained commercially or homemade.

[0063] According to the present invention, preferably, the isocyanate semi-prepolymer and the amino compound-containing material are mixed in a weight ratio of 1:(1-1.5).

[0064] According to the present invention, preferably, the curing temperature is 15-35° C. and the curing time is 5-10 minutes.

[0065] According to the present invention, preferably, the flexible material is selected from paraffin and / or soft silicone.

[0066] In the preparation method of the temporary plugging agent in the second aspect of the present invention, the type, shape and size of the flexible material are the same as the type, shape and size of the flexible material in the temporary plugging agent described in the first aspect of the present invention. To avoid repetition, the present invention will not be further described in this second aspect, and those skilled in the art should not understand it as limiting the present invention.

[0067] A third aspect of the present invention provides a temporary plugging agent prepared by the preparation method provided by the present invention.

[0068] The fourth aspect of the present invention provides an application of the temporary plugging agent provided by the present invention in multi-cluster temporary plugging fracturing of horizontal wells. The application method includes: adding the temporary plugging agent into the fracturing section of the bridge plug segment, and after the temporary plugging agent is sealed at the irregular hole, the temporary plugging agent undergoes adaptive deformation under the action of fluid pressure, filling the irregular space formed by the sand-carrying fluid grinding, thereby achieving effective sealing of the irregular hole.

[0069] In order to evaluate whether the adaptive temporary plugging agent is effective, it is necessary to evaluate the temporary plugging effect of the temporary plugging agent. The temporary plugging effect evaluation method is explained according to Figure 3. The main method is to compare the instantaneous construction pressure increase 5 after the temporary plugging agent is sealed at the hole, and the increase 8 of the extension pressure at the same displacement construction before and after temporary plugging. The increase in the instantaneous increase indicates that the plugging has been carried out; the increase in the extension pressure under the same displacement conditions indicates that a long-lasting and effective plugging has been carried out, and there is no failure of temporary plugging due to falling off or entering the formation. The sand concentration 7 represents the mass of the proppant contained in the unit volume of fracturing fluid, and the unit is kg / m 3 ; Effective temporary plugging time 6 represents the time during which the extension pressure is higher than the extension pressure before temporary plugging under the same displacement construction conditions after temporary plugging.

[0070] The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples, unless otherwise specified, all methods are conventional; and all reagents and materials used, unless otherwise specified, can be obtained from commercial sources.

[0071] An isocyanate semi-prepolymer (Material A) was prepared by reacting a uniformly mixed composition A in an insulated kettle at 70°C for 2 hours. The moisture content of Material A was 0.05 wt%. Composition A consisted, by weight, of 65 parts of isocyanate (diphenylmethane diisocyanate), 15 parts of a polyether polyol (polyoxypropylene glycol, weight-average molecular weight 2500 g / mol), 10 parts of a polysiloxane polyol (polysiloxane diol, weight-average molecular weight 3400 g / mol), and 10 parts of a viscosity reducer (dibutyl phthalate).

[0072] The amino compound-containing material (Material B) was prepared by vacuum dehydrating Composition B, which had been uniformly stirred in a high-speed disperser, in a reactor at 40°C for 3 hours. The moisture content of Material B was 0.05 wt%. Composition B consisted, by weight, of 60 parts of amino-terminated polyether (amino-terminated polyoxypropylene ether, weight-average molecular weight 4000 g / mol), 10 parts of a diamine chain extender (diethyltoluenediamine), 25 parts of bis-sec-butylaminodiphenylmethane, and 5 parts of a defoaming agent (organic silicone).

[0073] During hydraulic fracturing operations at an oilfield, the pressure increase after plugging, the extended pressure change before and after plugging at the same displacement, and the effective temporary plugging time are obtained based on the changing characteristics of the pressure curves before and after temporary plugging as shown in Figure 3.

[0074] The compressive strength is measured according to the method specified in Q / SY 02020-2017 "Indoor Determination Method of Basic Rock Mechanics Parameters in Drilling and Completion Engineering".

[0075] The tensile strength is measured in accordance with the method specified in GB / T 528-2009 “Rubber, vulcanized or thermoplastic. Determination of tensile stress-strain properties”.

[0076] The elongation at break is determined in accordance with the method specified in GB / T 528-2009 “Rubber, vulcanized or thermoplastic. Determination of tensile stress-strain properties”.

[0077] The tear strength is measured in accordance with the method specified in GB-T 529-2008 “Vulcanized rubber or thermoplastic rubber — Determination of tear strength”.

[0078] The tolerance temperature refers to the test sample being left to stand at a constant temperature for 3 hours. After the standing treatment, the compressive strength of the sample is measured to be reduced by 15-20% (compared with before the standing treatment), the tensile strength is reduced by 8-10% (compared with before the standing treatment), the elongation at break is reduced by 18-20% (compared with before the standing treatment), and the tear strength is reduced by 10-12% (compared with before the standing treatment). The highest standing treatment temperature that meets the above-mentioned index reduction range after the standing treatment is defined as the tolerance temperature.

[0079] The following examples are used to illustrate the preparation of temporary plugging agents. The amounts of the components in the compositions involved are in parts by weight.

[0080] Example 1

[0081] S1. Fix a spherical paraffin wax with a melting point of 30°C and a diameter of 20 mm in a mold with a cavity diameter of 24 mm and a spherical shape, so that the spherical paraffin wax is centered in the mold cavity;

[0082] S2. The semi-prepolymer of isocyanate and the material containing the amino compound are mixed in a weight ratio of 1:1.3, and the mixture is immediately injected into the gap of the mold cavity with the spherical paraffin fixed thereon, so that the mixture fills the pores of the cavity, and is cured at a temperature of 20°C for 7 minutes, so that the cured polyurea is coated on the surface of the spherical paraffin to form a temporary plugging agent with a polyurea layer wrapped on the outer surface of the spherical paraffin. The temporary plugging agent is taken out after demoulding to obtain a spherical temporary plugging agent with a diameter of 24 mm and a polyurea layer thickness of 2 mm.

[0083] The weight-average molecular weight of polyurea is 35,000 g / mol; the compressive strength of the polyurea layer is 105 MPa, the tensile strength is 35 MPa, the elongation at break is 410%, the tear strength is 105 MPa, and the temperature resistance is 105°C.

[0084] Example 2

[0085] S1. Fix a spherical soft silicone rubber with a hardness of 20A and a diameter of 9 mm in a mold with an ellipsoidal cavity shape, a short axis length and a middle axis length of 11 mm, and a long axis length of 16.5 mm, so that the spherical soft silicone rubber is centered in the mold cavity;

[0086] S2. Mix the semi-prepolymer of isocyanate and the material containing the amino compound in a weight ratio of 1:1, and then immediately inject the mixture into the gap of the mold cavity fixed with the spherical soft silicone, so that the mixture fills the pores of the cavity, and cure at a temperature of 15°C for 5 minutes, so that the cured polyurea is coated on the surface of the spherical soft silicone to form a temporary plugging agent with a polyurea layer wrapped on the outer surface of the spherical soft silicone. After demolding, the temporary plugging agent is taken out to obtain an ellipsoidal temporary plugging agent with a short axis length and a middle axis length of 11 mm, a long axis length of 16.5 mm, and a thickness of 1 mm at the thinnest part of the polyurea layer.

[0087] The weight-average molecular weight of polyurea is 34,000 g / mol; the compressive strength of the polyurea layer is 108 MPa, the tensile strength is 34 MPa, the elongation at break is 405%, the tear strength is 103 MPa, and the temperature resistance is 102°C.

[0088] Example 3

[0089] S1. Fix a spherical soft silicone rubber with a hardness of 10A and a diameter of 18 mm in a mold with a cavity shaped like a regular dodecahedron and a distance from the cavity surface to the center of 11 mm, so that the spherical soft silicone rubber is centered in the mold cavity;

[0090] S2. The semi-prepolymer of isocyanate and the material containing the amino compound are mixed in a weight ratio of 1:1.5, and the mixture is immediately injected into the gap of the mold cavity fixed with the spherical soft silicone rubber, so that the mixture fills the pores of the cavity, and is cured at a temperature of 35° C. for 10 minutes, so that the cured polyurea is coated on the surface of the spherical soft silicone rubber to form a temporary plugging agent with a polyurea layer wrapped on the outer surface of the spherical soft silicone rubber. The temporary plugging agent is removed after demolding to obtain a regular dodecahedron temporary plugging agent with a distance from the outer surface to the center of 11 mm and a thickness of 2 mm at the thinnest part of the polyurea layer.

[0091] The weight-average molecular weight of polyurea is 38,000 g / mol; the compressive strength of the polyurea layer is 104 MPa, the tensile strength is 38 MPa, the elongation at break is 415%, the tear strength is 105 MPa, and the temperature resistance is 110°C.

[0092] Example 4

[0093] The spherical temporary blocking agent was prepared according to the method of Example 1, except that spherical temporary blocking agents of different sizes were prepared. Specifically, the preparation method of the temporary blocking agent is as follows:

[0094] S1. Fix a spherical paraffin wax with a melting point of 30°C and a diameter of 36 mm in a mold with a cavity diameter of 40 mm and a spherical shape, so that the spherical paraffin wax is centered in the mold cavity;

[0095] S2 is the same as S2 in Example 1, and a spherical temporary plugging agent with a diameter of 40 mm and a polyurea layer thickness of 2 mm is obtained.

[0096] The weight-average molecular weight of polyurea is 35,000 g / mol; the compressive strength of the polyurea layer is 105 MPa, the tensile strength is 35 MPa, the elongation at break is 410%, the tear strength is 105 MPa, and the temperature resistance is 105°C.

[0097] Example 5

[0098] The spherical temporary blocking agent was prepared according to the method of Example 1, except that spherical temporary blocking agents of different sizes were prepared. Specifically, the preparation method of the temporary blocking agent is as follows:

[0099] S1. Fix a spherical paraffin wax with a melting point of 30°C and a diameter of 17 mm in a mold with a cavity diameter of 21 mm and a spherical shape, so that the spherical paraffin wax is centered in the mold cavity;

[0100] S2 is the same as S2 in Example 1, and a spherical temporary plugging agent with a diameter of 21 mm and a polyurea layer thickness of 2 mm is obtained.

[0101] The weight-average molecular weight of polyurea is 35,000 g / mol; the compressive strength of the polyurea layer is 105 MPa, the tensile strength is 35 MPa, the elongation at break is 410%, the tear strength is 105 MPa, and the temperature resistance is 105°C.

[0102] Example 6

[0103] The ellipsoidal temporary plugging agent was prepared according to the method of Example 2, except that the ellipsoidal temporary plugging agents of different sizes were prepared. Specifically, the preparation method of the temporary plugging agent is as follows:

[0104] S1. Fix a spherical soft silicone rubber with a hardness of 20A and a diameter of 58 mm in a mold with an ellipsoidal cavity shape, a short axis length and a middle axis length of 60 mm, and a long axis length of 90 mm, so that the spherical soft silicone rubber is centered in the mold cavity;

[0105] S2 is the same as S2 in Example 2, and the obtained temporary plugging agent has a minor axis length and a middle axis length of 60 mm, a major axis length of 90 mm, and a thickness of 1 mm at the thinnest part of the polyurea layer.

[0106] The weight-average molecular weight of polyurea is 34,000 g / mol; the compressive strength of the polyurea layer is 84 MPa, the tensile strength is 108 MPa, the elongation at break is 403%, the tear strength is 101 MPa, and the temperature resistance is 103°C.

[0107] Example 7

[0108] The ellipsoidal temporary plugging agent was prepared according to the method of Example 2, except that the ellipsoidal temporary plugging agents of different sizes were prepared. Specifically, the preparation method of the temporary plugging agent is as follows:

[0109] S1. Fix a spherical soft silicone rubber with a hardness of 20A and a diameter of 6 mm in a mold with an ellipsoidal cavity shape, a short axis length and a middle axis length of 8 mm, and a long axis length of 12 mm, so that the spherical soft silicone rubber is centered in the mold cavity;

[0110] S2 is the same as S2 in Example 2, and the obtained temporary plugging agent has a minor axis length and a middle axis length of 8 mm, a major axis length of 12 mm, and a thickness of 1 mm at the thinnest part of the polyurea layer.

[0111] The weight-average molecular weight of polyurea is 34,000 g / mol; the compressive strength of the polyurea layer is 118 MPa, the tensile strength is 109 MPa, the elongation at break is 410%, the tear strength is 104 MPa, and the temperature resistance is 104°C.

[0112] Example 8

[0113] A spherical temporary plugging agent was prepared according to the method of Example 1, except that a paraffin wax with a different melting point was used. The spherical paraffin wax with a melting point of 50°C and a diameter of 20 mm was replaced with the spherical paraffin wax with a melting point of 30°C and a diameter of 20 mm. A spherical temporary plugging agent was obtained.

[0114] Example 9

[0115] An ellipsoidal temporary plugging agent was prepared according to the method of Example 2, except that different soft silica gels of different hardness were used. The spherical soft silica gel with a hardness of 25A and a diameter of 9mm was replaced with the spherical soft silica gel with a hardness of 20A and a diameter of 9mm. This produced an ellipsoidal temporary plugging agent.

[0116] Example 10

[0117] A spherical temporary plugging agent was prepared according to the method of Example 1, except that a different flexible material was selected. The spherical paraffin wax with a melting point of 30°C and a diameter of 20 mm was replaced with a foam plastic with a diameter of 20 mm. The spherical temporary plugging agent was obtained.

[0118] Example 11

[0119] The spherical temporary plugging agent was prepared according to the method of Example 1, except that the thickness of the polyurea layer of the spherical temporary plugging agent was different. Specifically, the preparation method of the temporary plugging agent is as follows:

[0120] S1. Fix a spherical paraffin wax with a melting point of 30°C and a diameter of 14 mm in a mold with a cavity diameter of 24 mm and a spherical shape, so that the spherical paraffin wax is centered in the mold cavity;

[0121] S2 is the same as S2 in Example 1, and a spherical temporary plugging agent with a diameter of 24 mm and a polyurea layer thickness of 5 mm is obtained.

[0122] The weight-average molecular weight of polyurea is 35,000 g / mol; the compressive strength of the polyurea layer is 125 MPa, the tensile strength is 38 MPa, the elongation at break is 420%, the tear strength is 112 MPa, and the temperature resistance is 104°C.

[0123] Example 12

[0124] The spherical temporary plugging agent was prepared according to the method of Example 1, except that the thickness of the polyurea layer of the spherical temporary plugging agent was different. Specifically, the preparation method of the temporary plugging agent is as follows:

[0125] S1. Fix a spherical paraffin wax with a melting point of 30°C and a diameter of 23 mm in a mold with a cavity diameter of 24 mm and a spherical shape, so that the spherical paraffin wax is centered in the mold cavity;

[0126] S2 is the same as S2 in Example 1, and a spherical temporary plugging agent with a diameter of 24 mm and a polyurea layer thickness of 0.5 mm is obtained.

[0127] The weight-average molecular weight of polyurea is 35,000 g / mol; the compressive strength of the polyurea layer is 82 MPa, the tensile strength is 29 MPa, the elongation at break is 380%, the tear strength is 90 MPa, and the temperature resistance is 102°C.

[0128] Example 13

[0129] A spherical temporary plugging agent was prepared according to the method of Example 1, except that the raw materials used in preparing the polyurea layer were different. Specifically, Material A was prepared by reacting a uniformly mixed composition A in an insulated kettle at 70°C for 2 hours. The moisture content of Material A was 0.05 wt%. Composition A consisted of 75 parts of an isocyanate (diphenylmethane diisocyanate), 10 parts of a polyether polyol (polyoxypropylene glycol with a weight-average molecular weight of 2500 g / mol), 7.5 parts of a polysiloxane polyol (polysiloxane glycol with a weight-average molecular weight of 3400 g / mol), and 7.5 parts of a viscosity reducer (dibutyl phthalate). Material B was prepared by vacuum dehydrating Composition B, which had been uniformly stirred in a high-speed disperser, in a reactor at 40°C for 3 hours. The moisture content of Material B was 0.05 wt%. Composition B consisted of 45 parts of amino-terminated polyether (amino-terminated polyoxypropylene ether, weight-average molecular weight 4000 g / mol), 15 parts of a diamine chain extender (diethyltoluenediamine), 30 parts of bis-sec-butylaminodiphenylmethane, and 10 parts of a defoaming agent (organic silicone). A spherical temporary plugging agent was prepared.

[0130] The weight-average molecular weight of polyurea is 10,000 g / mol; the compressive strength of the polyurea layer is 85 MPa, the tensile strength is 60 MPa, the elongation at break is 520%, the tear strength is 130 MPa, and the temperature resistance is 90°C.

[0131] Comparative Example 1

[0132] A spherical temporary plugging agent was prepared according to the method of Example 1, except that the toughness material layer was made of a different material. Specifically, a spherical paraffin wax with a melting point of 30°C and a diameter of 20 mm was coated with a 2 mm thick layer of a water-soluble polymer material (chitosan, weight-average molecular weight 60,000 g / mol). This produced a spherical temporary plugging agent.

[0133] The chitosan layer has a compressive strength of 60 MPa, a tensile strength of 60 MPa, an elongation at break of 13%, a tear strength of 12 MPa, and a temperature resistance of 1000°C.

[0134] Comparative Example 2

[0135] A spherical temporary plugging agent was prepared according to the method of Example 1, except that the temporary plugging agent did not contain a flexible material, but only a spherical polyurea temporary plugging agent. Specifically, step S1 was omitted, and a mixture of an isocyanate semi-prepolymer and an amino compound-containing material was directly injected into the mold cavity, allowing the mixture to fill the cavity. The mixture was then cured to form a spherical polyurea temporary plugging agent. After demolding, the temporary plugging agent was removed, resulting in a spherical temporary plugging agent with a diameter of 24 mm.

[0136] The weight-average molecular weight of polyurea is 35,000 g / mol; the compressive strength of the spherical polyurea temporary plugging agent is 130 MPa, the tensile strength is 39 MPa, the elongation at break is 402%, the tear strength is 110 MPa, and the temperature resistance is 102°C.

[0137] Comparative Example 3

[0138] A spherical temporary plugging agent was prepared according to the method of Example 1, except that the temporary plugging agent was not prepared as a double-layer structure. Instead, melted paraffin wax was directly mixed with an isocyanate semi-prepolymer and an amino compound-containing material and then cured. Specifically, melted paraffin wax with a melting point of 30°C and an equal weight to a spherical paraffin wax with a diameter of 20 mm, the isocyanate semi-prepolymer, and the amino compound-containing material were mixed and injected into the mold cavity for curing, resulting in a spherical temporary plugging agent with a diameter of 24 mm.

[0139] Test Case

[0140] The spherical temporary plugging agents prepared in Examples 1, 4, 5, 8, 10-13 and Comparative Examples 1-3 were set in circular holes with a theoretical size of 20 mm. The ellipsoidal temporary plugging agents prepared in Examples 2, 6, 7, and 9 were set in elliptical holes with a theoretical size of 9 mm. The hexahedral temporary plugging agent prepared in Example 3 was set in a 16 mm irregularly shaped hole. The instantaneous increase in application pressure and the change in extension pressure before and after temporary plugging at the same displacement were measured. The results are shown in Table 1.

[0141] Table 1

[0142] It can be seen from the results of Table 1 that the temporary plugging agent of the present invention of Examples 1-13 is used to seal the hole. The pressure increase after the temporary plugging agent is sealed and the extension pressure increase before and after the temporary plugging are both high, and the effective temporary plugging time is long. Comparative Example 1 uses chitosan as the toughness material layer, the temporary plugging agent prepared in Comparative Example 2 does not contain a flexible material and is only a spherical polyurea temporary plugging agent, and the temporary plugging agent of Comparative Example 3 is not prepared into a double-layer structure, but directly solidifies after the melted paraffin is mixed with a semi-prepolymer of isocyanate and a material containing an amino compound. Compared with Examples 1-13, the pressure increase after the temporary plugging agent is sealed and the extension pressure increase before and after the temporary plugging are significantly reduced during the same displacement construction, and the effective temporary plugging time is significantly shortened. This shows that the temporary plugging agent of the present invention can effectively block blastholes of different shapes and is not easy to fall off during the blocking process.

[0143] In addition, Examples 4 and 5, respectively, increased and decreased the size of the spherical temporary plugging agent. Compared with Example 1, Example 4, after increasing the size of the temporary plugging agent, showed an increase in the pressure increase after the temporary plugging agent was set and the increase in the extended pressure before and after the temporary plugging at the same displacement. However, due to the easy detachment during pressure or displacement fluctuations, the effective temporary plugging time was reduced. Compared with Example 1, after decreasing the size of the temporary plugging agent, the pressure increase after the temporary plugging agent was set and the increase in the extended pressure before and after the temporary plugging at the same displacement were reduced as the fracturing fluid passed through the perforations and entered the formation during the fracturing process, and the effective temporary plugging time was also reduced. Examples 6 and 7, respectively, increased and decreased the size of the ellipsoidal temporary plugging agent. Compared with Example 2, the temporary plugging agent prepared in Example 6 showed an increase in the pressure increase after setting and the increase in the extended pressure before and after the temporary plugging at the same displacement, but the effective temporary plugging time was reduced. The temporary plugging agent prepared in Example 7 showed a decrease in the pressure increase after setting and the increase in the extended pressure before and after the temporary plugging at the same displacement, and the effective temporary plugging time was also reduced. In Example 8, paraffin wax with a higher melting point was used as the internal flexible material for the temporary plugging agent, while in Example 10, foam plastic was used as the internal flexible material for the temporary plugging agent. In Examples 11 and 12, the thickness of the polyurea layer was increased and decreased, respectively. In Example 13, the composition of the raw materials used to prepare the polyurea was modified. Compared with Example 1, the temporary plugging agents prepared using Examples 8 and 10-13 showed a lower pressure increase after setting the hole and a lower pressure increase during the same displacement before and after temporary plugging, and their effective temporary plugging time was also shortened. In Example 9, spherical soft silica gel with a higher hardness was used as the internal flexible material for the ellipsoidal temporary plugging agent. Compared with Example 2, the temporary plugging agent prepared using Example 9 showed a lower pressure increase after setting the hole and a lower pressure increase during the same displacement before and after temporary plugging, and their effective temporary plugging time was also shortened. This demonstrates that when the temporary plugging agent size, the type and performance parameters of the internal flexible material, the thickness of the polyurea layer, and the composition of the raw materials used to prepare the polyurea meet optimal conditions, the temporary plugging agent can further enhance its effectiveness in plugging holes of different shapes and further increase its effective temporary plugging time.

[0144] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A temporary plugging agent, characterized in that: The temporary plugging agent comprises a flexible material and a tough material layer coated on the outside of the flexible material; wherein the tough material layer is made of polyurea, and the thickness of the tough material layer is greater than or equal to 0.5 mm.

2. The temporary plugging agent according to claim 1, characterized in that: The thickness of the tough material layer is 1-3 mm; And / or, the weight average molecular weight of the polyurea is 30,000-100,000 g / mol.

3. The temporary plugging agent according to claim 1 or 2, characterized in that: The tough material layer has a compressive strength greater than or equal to 80 MPa, a tensile strength greater than or equal to 29 MPa, an elongation at break greater than or equal to 380%, and a tear strength greater than or equal to 90 MPa.

4. The temporary plugging agent according to claim 3, characterized in that: The tough material layer has a compressive strength of 90-110 MPa, a tensile strength of 30-50 MPa, a breaking elongation of 400-500%, and a tear strength of 100-120 MPa.

5. The temporary plugging agent according to claim 3, characterized in that: The tough material layer has a tolerable temperature of 100-120°C.

6. The temporary plugging agent according to claim 4, characterized in that: The tough material layer has a tolerable temperature of 100-120°C.

7. The temporary plugging agent according to claim 1 or 2, characterized in that: The flexible material is selected from paraffin and / or soft silicone.

8. The temporary plugging agent according to claim 7, characterized in that: The melting point of the paraffin wax is 20-40° C., and / or the hardness of the soft silica gel is less than or equal to 20A.

9. The temporary plugging agent according to claim 7, characterized in that: The flexible material is spherical in shape.

10. The temporary plugging agent according to claim 9, characterized in that: The diameter of the flexible material is 9-48 mm.

11. The temporary plugging agent according to claim 1 or 2, characterized in that: The temporary plugging agent is in the shape of a sphere, an ellipsoid or a regular dodecahedron.

12. The temporary plugging agent according to claim 11, characterized in that: The diameter of the temporary plugging agent in the shape of a sphere is 11-50 mm; or, the short axis length of the temporary plugging agent in the shape of an ellipsoid is 11-50 mm, the middle axis length is the same as the short axis length, and the long axis length is 1.5-2 times the short axis length; or, the distance from the outer surface to the center of the temporary plugging agent in the shape of a regular dodecahedron is 11-50 mm.

13. A method for preparing a temporary plugging agent, characterized in that: The preparation method comprises: placing a flexible material in a mold with a cavity so that the flexible material is centered in the cavity, then mixing a semi-prepolymer of isocyanate and a material containing an amino compound, injecting the mixture into the cavity and curing the mixture; the amounts of the semi-prepolymer of isocyanate and the material containing an amino compound are such that after curing, the thickness of the polyurea layer coated on the outer surface of the flexible material is greater than or equal to 0.5 mm.

14. The preparation method according to claim 13, characterized in that: The shape of the cavity is spherical, ellipsoidal or regular dodecahedron.

15. The preparation method according to claim 13 or 14, characterized in that: The amounts of the isocyanate semi-prepolymer and the amino compound-containing material are such that after curing, the thickness of the polyurea layer coated on the outer surface of the flexible material is 1-3 mm.

16. The preparation method according to claim 13 or 14, characterized in that: The semi-prepolymer of isocyanate is prepared from composition A; the composition A comprises the following components in parts by weight: 60-70 parts of isocyanate, 10-15 parts of polyether polyol, 5-10 parts of polysiloxane polyol and 5-10 parts of viscosity reducer; And / or, the amino compound-containing material is prepared from composition B; the composition B comprises the following components in parts by weight: 50-60 parts of amino-terminated polyether, 10-20 parts of diamine chain extender, 20-40 parts of bis-sec-butylaminodiphenylmethane and 1-5 parts of defoamer.

17. The preparation method according to any one of claims 7 to 9, characterized in that: The semi-prepolymer of isocyanate and the material containing amino compound are mixed in a weight ratio of 1:(1-1.5); And / or, the curing temperature is 15-35°C and the curing time is 5-10min; And / or, the flexible material is selected from paraffin and / or soft silicone.

18. A temporary plugging agent obtained by the preparation method according to any one of claims 13 to 17.

19. Use of the temporary plugging agent according to any one of claims 1 to 12 and 18 in multi-cluster temporary plugging fracturing of horizontal wells.

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