Self-adaptive temporary plugging agent for plugging irregular eyelets as well as preparation method and application of self-adaptive temporary plugging agent

Abstract

The invention relates to the field of petroleum and natural gas extraction, and discloses a self-adaptive temporary plugging agent for plugging irregular holes and a preparation method and application thereof. The temporary plugging agent comprises a flexible material and a ductile material layer wrapping the flexible material. Wherein the tough material layer is made of polyurea, and the thickness of the tough material layer is larger than or equal to 0.5 mm. The temporary plugging agent is of a double-layer structure which is soft inside and tough outside, the inner layer is made of a flexible material and can deform easily, the outer layer is made of a tough material, the bottom hole pressure is within the compressive strength of the temporary plugging agent, and a tough material wrapping layer can deform sufficiently along with the flexible material of the inner layer and cannot be damaged.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas exploitation, and particularly to an adaptive temporary plugging agent for plugging irregular holes, a preparation method thereof, and an application thereof. Background Art

[0002] The horizontal well staged stimulation technology is a key technology for unconventional reservoir development. In order to greatly increase the reservoir stimulation volume and the contact area between artificial fractures and the reservoir, multi-cluster perforation methods are often used in horizontal well stimulation, that is, multiple perforation sections are arranged within the same stimulation interval, in order to fully open each perforation section by measures such as increasing the displacement, thereby increasing the single-well production of tight oil and gas wells. However, a large number of on-site fracturing practices have shown that due to the influence of non-uniform formation lithology and stress as well as natural fractures, the opening degree of perforation clusters is limited, and nearly 40% of the clusters in all perforation clusters are not effectively stimulated, and the non-uniform expansion degree of multi-cluster fractures is high. Therefore, how to improve the opening degree of multi-cluster perforation holes is of great significance for ensuring the fracturing effect.

[0003] As a key technology to improve the opening degree of multi-clusters within a section, the basic principle of the temporary plugging technology is to put temporary plugging balls into the perforation holes to plug the perforation holes within the fracturing section segmented by bridge plugs. On the basis of the effective pressure bearing of the temporary plugging balls, the construction net pressure is increased to open new clusters, so as to achieve the purpose of fracture diversion within the section, and then realize the uniform stimulation of reservoirs with different physical properties / formation stresses. However, during the fracturing construction process, the sand-carrying fluid will quickly polish the perforation holes at high displacement, resulting in different degrees of enlargement and irregular deformation of the perforation holes. For such enlarged irregular holes, how to effectively plug them, limit the fluid from concentrating into a few perforation clusters, and cut off the connection channel between the wellbore and the fault at the source requires the selection of appropriate temporary plugging materials.

[0004] At present, materials such as conventional knot-shaped temporary plugging agents with specific shapes (CN202210704007.6, CN202210392629.X), high-strength particle temporary plugging agents (CN202211626967.1), fiber temporary plugging agents (CN202211401903.1), temporary plugging balls (CN202111238455.3, CN202110188758.2), etc. have limited temporary plugging ability and are difficult to effectively plug irregular perforation holes.

[0005] Based on this, developing an adaptive temporary plugging agent that is easy to deform, can bear high pressure, and can be degraded, after entering the position of the hole to be plugged, under the action of fluid pressure, it can deform according to the hole shape to achieve the purpose of adaptive plugging of different hole shapes; it is of great significance for ensuring the efficiency of horizontal well temporary plugging fracturing. Summary of the Invention

[0006] The object of the present invention is to overcome the problem in the prior art that the multi-cluster perforation holes in horizontal wells cannot be effectively plugged, resulting in non-uniform initiation and propagation of multi-cluster hydraulic fractures. The present invention provides an adaptive temporary plugging agent, a preparation method and an application thereof. The temporary plugging agent is characterized by being easily deformable and having high bearing pressure, and can adaptively deform according to irregular holes under the action of fluid pressure during the fracturing process to achieve effective plugging.

[0007] To achieve the above 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 outside the flexible material; wherein the material of the tough material layer is polyurea, and the thickness of the tough material layer is greater than or equal to 0.5 mm.

[0008] The second aspect of the present invention provides a preparation method of a temporary plugging agent, wherein the preparation method comprises: placing the flexible material in a mold with a cavity, making the flexible material centered in the cavity, then mixing a semi-prepolymer of isocyanate and a material containing an amino compound and injecting the mixture into the cavity for curing; the amounts of the semi-prepolymer of isocyanate and the material containing an amino compound are such that after the 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.

[0009] The third aspect of the present invention provides a temporary plugging agent prepared by the preparation method provided by the present invention.

[0010] 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.

[0011] Through the above technical solutions, the beneficial effects of the present invention are as follows:

[0012] Aiming at the problem that the multi-cluster perforation holes in horizontal wells cannot be effectively plugged, resulting in non-uniform initiation and propagation of multi-cluster hydraulic fractures, 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 uses a flexible material that can be easily deformed, and the outer layer is a tough material, polyurea. When the bottom hole pressure is within its compressive strength, the tough material coating layer can undergo sufficient deformation along with the inner flexible material without being damaged. After being seated at the irregular holes, it deforms under the action of fluid pressure to fill the irregular space formed by the sand-carrying fluid for grinding, realizing effective plugging of the irregular gun holes, improving the plugging efficiency. Compared with traditional temporary plugging materials such as temporary plugging balls or knot temporary plugging agents, the temporary plugging efficiency is higher.

[0013] In addition, in the preferred embodiment of the present invention, by selecting appropriate raw materials and methods for preparing the tough material (polyurea) layer, the temperature resistance of the tough material layer wrapped on the outer surface of the flexible material is 100 - 120 °C. During the fracturing process, when the normal temperature fracturing fluid is continuously injected from the wellbore into the formation, 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, thus 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 later. 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 self-adaptive temporary plugging agent and the temporary plugging effect can be accurately obtained, greatly improving the construction effect of hydraulic fracturing and increasing the single well production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1a is a cross-sectional view of a spherical temporary plugging agent in a preferred embodiment of the present invention;

[0015] Figure 1b is a cross-sectional view of an ellipsoidal temporary plugging agent in a preferred embodiment of the present invention;

[0016] Figure 1c is a cross-sectional view of a hexahedral temporary plugging agent in a preferred embodiment of the present invention;

[0017] Figure 2 is a curve graph of the fracturing fluid displacement and construction pressure when the pump is stopped by adopting the method of stepwise reducing the fracturing fluid displacement;

[0018] Figure 3 is a construction pressure curve graph before and after temporary plugging;

[0019] Figure 4a and Figure 4b is a schematic diagram of a circular hole with a regular original shape;

[0020] Figure 4c and Figure 4e is a schematic diagram of the shape of an irregular hole formed after abrasion;

[0021] Figure 4d is a schematic diagram of the shape of a tadpole-shaped hole formed after abrasion;

[0022] Figure 4f is a schematic diagram of the shape of a big-bellied hole formed after abrasion.

[0023] DESCRIPTION OF THE REFERENCE NUMERALS

[0024] 1 Flexible material 2 Tough material layer 3 Fracturing fluid displacement 4 Construction pressure

[0025] 5 Instant construction pressure increase after the temporary plugging agent is set 6 Effective temporary plugging time

[0026] 7 Sand concentration 8 Construction pressure increase at the same displacement before and after temporary plugging Detailed implementation manners

[0027] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

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

[0029] According to the present invention, preferably, the thickness of the tough material layer is 1 - 3 mm. If the thickness is too small, the compressive strength, tensile strength and tear strength of the tough material layer are relatively low, and the elongation at break is also relatively low, and it is easy to break under high pressure; if the thickness is too large, the compressive strength, tensile strength and tear strength of the tough material layer are too high, and it is difficult to deform under high pressure, which is not conducive to effectively sealing the edges of irregular holes.

[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 case, the compressive strength of the tough material layer is greater than or equal to 80 MPa, the tensile strength is greater than or equal to 29 MPa, the elongation at break is greater than or equal to 380%, and the tear strength is greater than or equal to 90 MPa.

[0032] Currently, the shale oil and gas exploitation depth is 3000 - 4500 m, the bottom hole pressure is close to 100 MPa, and the well temperature is about 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 easy deformation 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 uses a flexible material that can easily deform, and the outer layer is a tough material. When the bottom hole pressure is within its compressive strength, the tough material layer can undergo sufficient deformation with the flexible material in the inner layer without being damaged.

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

[0034] In a preferred case, the temperature resistance of the ductile material layer is 100 - 120 °C. During the fracturing process, when the normal-temperature fracturing fluid is continuously injected from the wellbore into the formation, the temperature in the wellbore is much lower than the formation temperature and also lower than the temperature resistance of the ductile material layer outside the flexible material, thus 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 (the formation temperature is 130 - 150 °C). After exceeding the maximum temperature resistance of the ductile material layer, the ductile material layer gradually deteriorates, softens, and decomposes. The temperature resistance of the ductile material layer is 30 - 40 °C lower than the formation temperature, and the temporary plugging agent can be degraded smoothly in the later stage.

[0035] According to the present invention, preferably, the flexible material is selected from paraffin wax and / or soft silicone rubber. Paraffin wax and / or soft silicone rubber as the flexible material can easily deform in a high-temperature and high-pressure environment to adapt to the effective plugging of irregularly shaped holes.

[0036] According to the present invention, preferably, the melting point of the paraffin wax is 20 - 40 °C, and / or,

[0037] the hardness of the soft silicone rubber is less than or equal to 20A. The hardness refers to the Shore A hardness. The melting point of the paraffin wax meets this range and can melt into a liquid state in a high-temperature environment, enabling it to deform in any direction to adapt to the effective plugging of irregularly shaped holes; the hardness of the soft silicone rubber meets this range and can easily deform in a high-temperature and high-pressure environment to adapt to the effective plugging of irregularly shaped holes.

[0038] According to the present invention, preferably, the shape of the flexible material is spherical.

[0039] According to the present invention, preferably, the diameter of the flexible material is 9 - 48 mm. The diameter of the flexible material meets this range and can meet the effective plugging of regular holes on-site. If the size is too small, when it is smaller than the abraded perforation holes, it will enter the formation along with the fracturing fluid during the fracturing process and it is difficult to effectively play a sealing role; if the size is too large, on the one hand, it will affect its migration in the long horizontal wellbore and it is difficult to effectively move to the holes that need to be plugged, and on the other hand, it is difficult to effectively set at the holes that need to be plugged and is easily detached when the pressure or displacement fluctuates.

[0040] In the present invention, in order to be suitable for plugging perforation holes of different shapes, the temporary plugging agent can be in various shapes. The thickness of the ductile material layer is defined as the thickness at the thinnest part of the ductile material layer.

[0041] According to the present invention, preferably, the temporary plugging agent is spherical, ellipsoidal or regular dodecahedron in shape. Temporary plugging agents with different external shapes are suitable for plugging perforation holes of different shapes. Among them, spherical and ellipsoidal temporary plugging agents are suitable for plugging holes with regular shapes, and regular dodecahedron temporary plugging agents are suitable for plugging holes with irregular shapes. Examples of holes with regular shapes are Figure 4a and Figure 4b the holes shown in the shape; examples of holes with irregular shapes are Figure 4c and Figure 4e the special-shaped holes shown in the figure, Figure 4d the tadpole-shaped holes shown in the figure, and Figure 4f the big-bellied holes shown in the figure.

[0042] According to a specific embodiment of the present invention, the cross-sectional views of the spherical temporary plugging agent, ellipsoidal temporary plugging agent and regular dodecahedron temporary plugging agent are respectively as shown in Figure 1a , Figure 1b and Figure 1c shown. The temporary plugging agent includes a flexible material 1 and a tough material layer 2 coated outside the flexible material.

[0043] Generally, the diameter of the initial perforation hole is 9 - 11 mm. During the fracturing process, as the sand-carrying fluid enters, the hole is continuously polished by the sand-carrying fluid, the shape of the hole becomes irregular, and the hole diameter becomes larger. In order to select a temporary plugging agent with a suitable size, during the fracturing process, before the temporary plugging operation, it is necessary to calculate the diameter of the enlarged hole. The method for calculating the change in the hole diameter is as follows:

[0044] P perf = k perf q γ , formula (1);

[0045]

[0046]

[0047] In formulas (1)-(3), P perf is the friction of the perforation hole, with the unit of MPa; k perf is the hole friction coefficient, dimensionless; q is the displacement of the fracturing fluid, with the unit of m 3 / min; γ is the friction index; α is the friction coefficient, generally taking 2.2326×10 -4 ; ρ is the density of the fracturing fluid, with the unit of kg / m 3 ; n p is the number of effectively opened holes; d p is the diameter after erosion, with the unit of m; η is the hole diameter expansion coefficient. When the sand concentration is within 300 kg / m 3 , generally taking the value of 1.0×10 -13 m 2·s / kg; C d is the hole 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.

[0048] Using formula (1), calculate the hole friction coefficient P perf The specific method is that when the pump is stopped and the temporary plugging agent is put in during fracturing, the pump is stopped by stepping down the fracturing fluid displacement to obtain the stable construction pressure value at different fracturing fluid displacements. The changes of fracturing fluid displacement 3 and construction pressure 4 are shown in the figure. Figure 2 As shown. Figure 2 It can be seen that by stepping down the displacement, a corresponding stable pressure value can be obtained under different displacement conditions. The perforation friction and friction index are fitted as unknown parameters, so that these two parameters can be obtained. In order to accurately obtain the friction coefficient, when stepping down the fracturing fluid displacement, it is necessary to obtain 4-6 groups of different fracturing fluid displacements and corresponding pressure data.

[0049] 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.

[0050] The hole diameter obtained by theoretical calculation is the equivalent hole diameter. In fact, the hole diameter is irregular. In order to ensure that the adaptive temporary plugging agent can be firmly sealed, the selected size is 1.2-1.5 times the hole diameter obtained by theoretical calculation. After being firmly sealed, the temporary plugging agent deforms under the action of fluid pressure, thereby plugging other irregular spaces and improving the plugging efficiency.

[0051] 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.

[0052] The second aspect of the present invention provides a method for preparing a temporary plugging agent. The preparation method includes: placing a flexible material in a mold with a cavity, making the flexible material centered in the cavity, then mixing a semi-prepolymer of isocyanate and a material containing an amino compound and injecting the mixture into the cavity for curing; the amounts of the semi-prepolymer of isocyanate and the material containing an amino compound are such that after the 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. The temporary plugging agent with a polyurea layer coated on the outer surface of the flexible material is obtained.

[0053] In order to make the toughness material layer have more suitable compressive strength, tensile strength, tear strength and elongation at break, so as to further avoid the toughness material layer from breaking under high pressure, and at the same time be more easily deformed. Preferably, the amounts of the semi-prepolymer of isocyanate and the material containing an amino compound are such that after the curing, the thickness of the polyurea layer coated on the outer surface of the flexible material is 1 - 3 mm.

[0054] According to a preferred embodiment of the present invention, the shape of the cavity in the mold is spherical, ellipsoidal or dodecahedron. In a preferred case, the diameter of the spherical cavity is 11 - 50 mm, which is used to prepare a temporary plugging agent material in the shape of a sphere; the short axis length of the ellipsoidal cavity 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, which is used to prepare a temporary plugging agent material in the shape of an ellipsoid; the distance from the surface to the center of the dodecahedron cavity is 11 - 50 mm, which is used to prepare a temporary plugging agent material in the shape of a dodecahedron. To ensure that the flexible material is centered in the mold cavity, fine steel needles or thin lines can be used for pre-fixing, and after pouring and curing, the obtained temporary plugging agent is taken out after being wrapped by a polyurea coating layer.

[0055] In order to make the toughness material layer have more suitable compressive strength, tensile strength, tear strength and elongation at break, so as to both effectively avoid the toughness material layer from breaking under high pressure, avoid the performance of the temporary plugging agent from being affected during the fracturing process, improve the effective temporary plugging time of the temporary plugging agent, and at the same time ensure that the temporary plugging agent is easily deformed; and further improve the degradation effect of the temporary plugging agent after the fracturing is completed. Preferably, the semi-prepolymer of isocyanate is prepared from composition A; composition A includes 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;

[0056] and / or, the material containing an amino compound is prepared from composition B; composition B includes 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-butylamino)diphenylmethane and 1 - 5 parts of defoamer.

[0057] The present invention has no particular limitation on the type of isocyanate, and the isocyanates conventionally used in the art for synthesizing polyureas can be used, preferably diphenylmethane diisocyanate. The present invention has no particular limitation on the type of polyether polyol, and the polyether polyols conventionally used in the art for synthesizing polyureas can be used, preferably one or more selected from polypropylene glycol, polypropylene triol, polytetrahydrofuran diol, and polytetrahydrofuran triol. The present invention has no particular limitation on the type of polysiloxane polyol, and the polysiloxane polyols conventionally used in the art for synthesizing polyureas can be used, preferably polysiloxane diol. The present invention has no particular limitation on the type of viscosity reducer, and the viscosity reducers conventionally used for preparing polyureas can be used, preferably one or more selected from dibutyl phthalate, dioctyl phthalate, propyl carbonate, and ethyl carbonate. The present invention has no particular limitation on the type of amino-terminated polyether, and the amino-terminated polyethers conventionally used in the art for synthesizing polyureas can be used, preferably amino-terminated polypropylene oxide ether. The present invention has no particular limitation on the type of diamine chain extender, and the diamine chain extenders conventionally used in the art for synthesizing polyureas can be used, preferably one or more selected from diethyltoluenediamine (DETDA, abbreviated as E100), dimethylthiotoluenediamine (DMTDA, abbreviated as E300), and N,N'-dialkylmethylenediamine (DBMDA). The present invention has no particular limitation on the type of defoamer, and the defoamers conventionally used for preparing polyureas can be used, preferably silicone defoamers.

[0058] According to the present invention, preferably, the method for preparing the semi-prepolymer of the isocyanate includes: reacting the uniformly mixed composition A at 65 - 85°C for 2 - 3 h to obtain the semi-prepolymer of the isocyanate. In a preferred case, the water content of the semi-prepolymer of the isocyanate is ≤ 0.05 wt%.

[0059] And / or, the method for preparing the material containing an amino compound includes: vacuum dehydrating the uniformly mixed composition B at 30 - 50°C for 2 - 4 h to obtain the material containing an amino compound. In a preferred case, the water content of the material containing an amino compound is ≤ 0.05 wt%.

[0060] In the present invention, the semi-prepolymer of the isocyanate and the material containing an amino compound can be either commercially obtained or self-prepared.

[0061] According to the present invention, preferably, the semi-prepolymer of the isocyanate and the material containing an amino compound are mixed in a weight ratio of 1:(1 - 1.5).

[0062] According to the present invention, preferably, the curing temperature is 15 - 35°C and the time is 5 - 10 min.

[0063] According to the present invention, preferably, the flexible material is selected from paraffin and / or soft silica gel.

[0064] 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 those 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 elaborate on this in the second aspect, and those skilled in the art should not understand it as a limitation to the present invention.

[0065] The third aspect of the present invention provides a temporary plugging agent prepared by the preparation method provided by the present invention.

[0066] 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 method of the application includes: putting the temporary plugging agent into the fracturing section segmented by the bridge plug. After the temporary plugging agent is seated at the irregular holes, the temporary plugging agent undergoes self-adaptive deformation under the action of fluid pressure to fill the irregular space formed by the abrasive action of the proppant-carrying fluid, so as to achieve effective plugging of the irregular holes.

[0067] In order to evaluate whether the self-adaptive temporary plugging agent is effectively temporarily plugged, it is necessary to evaluate the temporary plugging effect of the temporary plugging agent. According to Figure 3 The method for evaluating the temporary plugging effect will be described. The main method is to compare the construction pressure increase of 5 at the moment after the temporary plugging agent is seated at the hole, and the increase of the extension pressure during construction at the same displacement before and after temporary plugging of 8. An increase in the instantaneous increase indicates that plugging has been carried out; an increase in the extension pressure under the condition of the same displacement indicates that persistent effective plugging has been carried out, and there is no failure after temporary plugging due to falling off or entering the formation. The sand concentration 7 represents the mass of the proppant contained in the fracturing fluid per unit volume, and the unit is kg / m 3 ; The effective temporary plugging time 6 represents the time when, under the condition of construction at the same displacement after temporary plugging, the extension pressure is higher than the extension pressure before temporary plugging at the same displacement.

[0068] 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 are conventional methods; the reagents and materials used, unless otherwise specified, can be obtained from commercial channels.

[0069] The semi-prepolymer of isocyanate (Material A) is obtained by reacting the uniformly mixed Composition A in a heat preservation kettle at 70 °C for 2 h. The water content of Material A is 0.05 wt%. The composition of Composition A is as follows by weight: 65 parts of isocyanate (diphenylmethane diisocyanate), 15 parts of polyether polyol (polypropylene oxide diol, weight average molecular weight of 2500 g / mol), 10 parts of polysiloxane polyol (polysiloxane diol, weight average molecular weight of 3400 g / mol), and 10 parts of viscosity reducer (dibutyl phthalate).

[0070] The material containing amino compounds (Material B) is obtained by vacuum dehydrating the uniformly stirred Composition B in a high-speed disperser for 3 hours in a reaction kettle at 40°C. The water content of Material B is 0.05 wt%. The composition of Composition B is as follows by weight: 60 parts of terminal amino polyether (terminal amino polypropylene oxide ether, with a weight average molecular weight of 4000 g / mol), 10 parts of diamine chain extender (diethyl toluene diamine), 25 parts of bis(sec-butylamino) diphenyl methane, and 5 parts of defoamer (silicone).

[0071] During the hydraulic fracturing construction in the oilfield site, according to Figure 3 the change characteristics of the pressure curves before and after temporary plugging shown, the pressure increase after plugging, the change in extension pressure during construction at the same displacement before and after plugging, and the effective temporary plugging time are obtained.

[0072] The compressive strength, tensile strength, elongation at break, tear strength, and temperature resistance are measured according to the standards formulated by the International Society for Rock Mechanics (ISRM) and the American Society for Testing and Materials (ASTM).

[0073] The following examples are used to illustrate the preparation of the temporary plugging agent. Among the compositions involved, the component dosages are in parts by weight.

[0074] Example 1

[0075] S1. Fix the spherical paraffin with a melting point of 30°C and a diameter of 20 mm in a mold with a spherical cavity diameter of 24 mm, so that the spherical paraffin is centered in the mold cavity;

[0076] S2. Mix the semi-prepolymer of isocyanate and the material containing amino compounds at a weight ratio of 1:1.3, and then immediately inject the mixed liquid into the voids of the mold cavity with the fixed spherical paraffin, so that the mixed liquid fills the pores of the cavity. Cure at a temperature of 20°C for 7 minutes, so that the cured polyurea coats the surface of the spherical paraffin, forming a temporary plugging agent with a polyurea layer wrapped around the outer surface of the spherical paraffin. After demolding, take out the temporary plugging agent to obtain a spherical temporary plugging agent with a diameter of 24 mm and a polyurea layer thickness of 2 mm.

[0077] The weight average molecular weight of the 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.

[0078] Example 2

[0079] S1. Fix the spherical soft silicone with a hardness of 20A and a diameter of 9 mm in a mold with an ellipsoidal cavity shape, where the short axis and the middle axis of the cavity are 11 mm long and the long axis is 16.5 mm long, so that the spherical soft silicone is centered in the mold cavity;

[0080] S2. Mix the semi-prepolymer of isocyanate and the material containing amino compound in a weight ratio of 1:1, and then immediately inject the mixed solution into the void of the mold cavity fixed with spherical soft silica gel, so that the mixed solution fills the pores of the cavity. Cure at a temperature of 15°C for 5 minutes, so that the cured polyurea is coated on the surface of the spherical soft silica gel, forming a temporary plugging agent with a polyurea layer wrapped on the outer surface of the spherical soft silica gel. After demolding, take out the temporary plugging agent to obtain an ellipsoidal temporary plugging agent with a minor axis length and a middle axis length of 11 mm, a major axis length of 16.5 mm, and the thickness of the thinnest part of the polyurea layer being 1 mm.

[0081] The weight-average molecular weight of the 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.

[0082] Example 3

[0083] S1. Fix a spherical soft silica gel with a hardness of 10A and a diameter of 18 mm in a mold with a cavity shape of a regular dodecahedron and the distance from the surface of the cavity to the center being 11 mm, so that the spherical soft silica gel is centered in the mold cavity;

[0084] S2. Mix the semi-prepolymer of isocyanate and the material containing amino compound in a weight ratio of 1:1.5, and then immediately inject the mixed solution into the void of the mold cavity fixed with spherical soft silica gel, so that the mixed solution fills the pores of the cavity. Cure at a temperature of 35°C for 10 minutes, so that the cured polyurea is coated on the surface of the spherical soft silica gel, forming a temporary plugging agent with a polyurea layer wrapped on the outer surface of the spherical soft silica gel. After demolding, take out the temporary plugging agent to obtain a regular dodecahedron temporary plugging agent with the distance from the outer surface to the center being 11 mm and the thickness of the thinnest part of the polyurea layer being 2 mm.

[0085] The weight-average molecular weight of the 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.

[0086] Example 4

[0087] Prepare the spherical temporary plugging agent according to the method of Example 1, except that spherical temporary plugging agents with different sizes are prepared. Specifically, the preparation method of the temporary plugging agent is as follows:

[0088] S1. Fix a spherical paraffin 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 cavity shape of a sphere, so that the spherical paraffin is centered in the mold cavity;

[0089] 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.

[0090] The weight-average molecular weight of the 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.

[0091] Example 5

[0092] The spherical temporary plugging agent is prepared according to the method of Example 1, except that spherical temporary plugging agents with different sizes are prepared. Specifically, the preparation method of the temporary plugging agent is as follows:

[0093] S1. Fix the spherical paraffin 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 cavity shape, so that the spherical paraffin is centered in the mold cavity;

[0094] 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.

[0095] The weight-average molecular weight of the 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.

[0096] Example 6

[0097] The ellipsoidal temporary plugging agent is prepared according to the method of Example 2, except that ellipsoidal temporary plugging agents with different sizes are prepared. Specifically, the preparation method of the temporary plugging agent is as follows:

[0098] S1. Fix the spherical soft silica gel with a hardness of 20A and a diameter of 58 mm in a mold with an ellipsoidal cavity shape, where the short axis length and the middle axis length of the cavity are 60 mm and the long axis length is 90 mm, so that the spherical soft silica gel is centered in the mold cavity;

[0099] S2 is the same as S2 in Example 2, and an ellipsoidal temporary plugging agent with a short axis length and a middle axis length of 60 mm, a long axis length of 90 mm, and a minimum thickness of the polyurea layer of 1 mm is prepared.

[0100] The weight-average molecular weight of the 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.

[0101] Example 7

[0102] Prepare the ellipsoidal temporary plugging agent according to the method of Example 2, except that ellipsoidal temporary plugging agents with different sizes are prepared. Specifically, the preparation method of the temporary plugging agent is as follows:

[0103] S1. Fix the spherical soft silicone with a hardness of 20A and a diameter of 6 mm in a mold with an ellipsoidal cavity shape, where the short-axis length and the middle-axis length of the cavity are 8 mm and the long-axis length is 12 mm, so that the spherical soft silicone is centered in the mold cavity;

[0104] S2 is the same as S2 in Example 2 to obtain an ellipsoidal temporary plugging agent with a short-axis length and a middle-axis length of 8 mm, a long-axis length of 12 mm, and the thickness of the thinnest part of the polyurea layer being 1 mm.

[0105] The weight-average molecular weight of the 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.

[0106] Example 8

[0107] Prepare the spherical temporary plugging agent according to the method of Example 1, except that paraffin wax with different melting points is selected. Replace "spherical paraffin wax with a melting point of 30 °C and a diameter of 20 mm" with "spherical paraffin wax with a melting point of 50 °C and a diameter of 20 mm". Obtain the spherical temporary plugging agent.

[0108] Example 9

[0109] Prepare the ellipsoidal temporary plugging agent according to the method of Example 2, except that soft silicone with different hardnesses is selected. Replace "spherical soft silicone with a hardness of 20A and a diameter of 9 mm" with "spherical soft silicone with a hardness of 25A and a diameter of 9 mm". Obtain the ellipsoidal temporary plugging agent.

[0110] Example 10

[0111] Prepare the spherical temporary plugging agent according to the method of Example 1, except that different flexible materials are selected. Replace "spherical paraffin wax with a melting point of 30 °C and a diameter of 20 mm" with "foam plastic with a diameter of 20 mm". Obtain the spherical temporary plugging agent.

[0112] Example 11

[0113] Prepare the spherical temporary plugging agent according to the method of Example 1, except that the thickness of the polyurea layer of the spherical temporary plugging agent is different. Specifically, the preparation method of the temporary plugging agent is as follows:

[0114] S1. Fix the 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 cavity shape, so that the spherical paraffin wax is centered in the mold cavity;

[0115] 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.

[0116] The weight-average molecular weight of the 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.

[0117] Example 12

[0118] The spherical temporary plugging agent is prepared according to the method of Example 1, except that the thickness of the polyurea layer of the spherical temporary plugging agent is different. Specifically, the preparation method of the temporary plugging agent is as follows:

[0119] S1. Fix the spherical paraffin 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 cavity shape, so that the spherical paraffin is centered in the mold cavity;

[0120] 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.

[0121] The weight-average molecular weight of the 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.

[0122] Example 13

[0123] The spherical temporary plugging agent is prepared according to the method of Example 1, except that the raw materials for preparing the polyurea layer are different. Specifically, Material A is obtained by reacting the uniformly mixed Composition A in a heat preservation kettle at 70 °C for 2 h, and the water content of Material A is 0.05 wt%; the composition of Composition A is: 75 parts of isocyanate (diphenylmethane diisocyanate), 10 parts of polyether polyol (polyoxypropylene diol with a weight-average molecular weight of 2500 g / mol), 7.5 parts of polysiloxane polyol (polysiloxane diol with a weight-average molecular weight of 3400 g / mol), and 7.5 parts of viscosity reducer (dibutyl phthalate). Material B is obtained by vacuum dehydrating the uniformly stirred Composition B in a reaction kettle at 40 °C for 3 hours, and the water content of Material B is 0.05 wt%; the composition of Composition B is: 45 parts of amino-terminated polyether (amino-terminated polyoxypropylene ether with a weight-average molecular weight of 4000 g / mol), 15 parts of diamine chain extender (diethyltoluenediamine), 30 parts of bis(sec-butylamino)diphenylmethane, and 10 parts of defoamer (silicone). A spherical temporary plugging agent is prepared.

[0124] The weight-average molecular weight of the 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.

[0125] Comparative Example 1

[0126] The spherical temporary plugging agent was prepared according to the method of Example 1, except that the material of the tough material layer in the temporary plugging agent was different. Specifically, a water-soluble polymer material (chitosan, weight-average molecular weight 60,000 g / mol) with a thickness of 2 mm was wrapped on the outer surface of a spherical paraffin with a melting point of 30 °C and a diameter of 20 mm. The spherical temporary plugging agent was obtained.

[0127] The compressive strength of the chitosan layer is 60 MPa, the tensile strength is 60 MPa, the elongation at break is 13%, the tear strength is 12 MPa, and the temperature resistance is 1000 °C.

[0128] Comparative Example 2

[0129] The 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 and was only a spherical polyurea temporary plugging agent. Specifically, the S1 step was not carried out, and the mixed solution of the semi-prepolymer of isocyanate and the material containing amino compounds was directly injected into the mold cavity to fill the cavity with the mixed solution, and then cured to form a spherical polyurea temporary plugging agent. After demolding, the temporary plugging agent was taken out to obtain a spherical temporary plugging agent with a diameter of 24 mm.

[0130] The weight-average molecular weight of the 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.

[0131] Comparative Example 3

[0132] The spherical temporary plugging agent was prepared according to the method of Example 1, except that the temporary plugging agent was not prepared into a double-layer structure, but the melted paraffin was directly mixed with the semi-prepolymer of isocyanate and the material containing amino compounds and then cured. Specifically, the melted paraffin with the same weight as the spherical paraffin with a melting point of 30 °C and a diameter of 20 mm, the semi-prepolymer of isocyanate and the material containing amino compounds were mixed and then injected into the mold cavity for curing to obtain a spherical temporary plugging agent with a diameter of 24 mm.

[0133] Test Example

[0134] The spherical temporary plugging agents prepared in Examples 1, 4, 5, 8, 10 - 13 and Comparative Examples 1 - 3 were set in place at the orifice with a circular shape and a theoretically calculated size of 20 mm; the ellipsoidal temporary plugging agents prepared in Examples 2, 6, 7, 9 were set in place at the orifice with an elliptical shape and a theoretically calculated size of 9 mm; the hexahedral temporary plugging agent prepared in Example 3 was set in place at the irregular orifice with a theoretically calculated size of 16 mm. The instantaneous construction pressure increase and the change in the extension pressure during construction at the same displacement before and after temporary plugging were measured. The results are shown in Table 1.

[0135] Table 1

[0136]

[0137] It can be seen from the results in Table 1 that when the temporary plugging agents of the present invention in Examples 1 - 13 were set in place at the orifice, the pressure increase after the temporary plugging agent was set in place and the extension pressure increase during construction at the same displacement before and after temporary plugging were both relatively high, and the effective temporary plugging time was relatively long. In Comparative Example 1, chitosan was used as the toughening material layer. In the temporary plugging agent prepared in Comparative Example 2, there was no flexible material, and it was only a spherical polyurea temporary plugging agent. In Comparative Example 3, the temporary plugging agent was not prepared into a double-layer structure, but the melted paraffin was directly mixed with the semi-prepolymer of isocyanate and the material containing amino compounds and then cured. Compared with Examples 1 - 13, the pressure increase after the temporary plugging agent was set in place and the extension pressure increase during construction at the same displacement before and after temporary plugging were significantly reduced, and the effective temporary plugging time was significantly shortened. It shows that the temporary plugging agent of the present invention can effectively plug the blast holes of different shapes and is not easy to fall off during the plugging process.

[0138] In addition, in Example 4 and Example 5, the sizes of the spherical temporary plugging agents were increased and decreased respectively. Compared with Example 1, after the size of the temporary plugging agent was increased in Example 4, although the pressure increase after the temporary plugging agent was set and the extension pressure increase during construction at the same displacement before and after temporary plugging increased, due to easy detachment during pressure or displacement fluctuations, the effective temporary plugging time decreased; after the size of the temporary plugging agent was decreased in Example 5, compared with Example 1, during the fracturing process, as the fracturing fluid passed through the perforation holes and entered the formation, the pressure increase after the temporary plugging agent was set and the extension pressure increase during construction at the same displacement before and after temporary plugging decreased, and the effective temporary plugging time also decreased. In Example 6 and Example 7, the sizes of the ellipsoidal temporary plugging agents were increased and decreased respectively. Compared with Example 2, although the pressure increase after the temporary plugging agent prepared in Example 6 was set and the extension pressure increase during construction at the same displacement before and after temporary plugging increased, the effective temporary plugging time decreased; the pressure increase after the temporary plugging agent prepared in Example 7 was set and the extension pressure increase during construction at the same displacement before and after temporary plugging decreased, and the effective temporary plugging time also decreased. In Example 8, paraffin with a relatively high melting point was used as the flexible material inside the temporary plugging agent, in Example 10, foam plastic was used as the flexible material inside the temporary plugging agent, in Example 11 and Example 12, the thicknesses of the polyurea layer were increased and decreased respectively, and in Example 13, the composition of the raw materials for preparing polyurea was changed. Compared with Example 1, the pressure increase after the temporary plugging agents prepared in Example 8 and Examples 10 - 13 sealed the holes and the extension pressure increase during construction at the same displacement before and after temporary plugging both decreased, and the effective temporary plugging times also all decreased. In Example 9, spherical soft silica gel with a relatively high hardness was used as the flexible material inside the ellipsoidal temporary plugging agent. Compared with Example 2, the pressure increase after the temporary plugging agent prepared in Example 9 sealed the holes and the extension pressure increase during construction at the same displacement before and after temporary plugging decreased, and the effective temporary plugging time also decreased. This shows that when the size of the temporary plugging agent, the types and performance parameters of the flexible materials inside the temporary plugging agent, the thickness of the polyurea layer, and the composition of the raw materials for preparing polyurea meet the preferred conditions, the effect of the temporary plugging agent in plugging holes of different shapes can be further improved, and the effective temporary plugging time of the temporary plugging agent can be further increased.

[0139] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A temporary plugging agent, characterized in that, The temporary plugging agent includes a flexible material and a tough material layer coated outside the flexible material; wherein, the material of the tough material layer is 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; Preferably, 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 compressive strength of the tough material layer is greater than or equal to 80 MPa, the tensile strength is greater than or equal to 29 MPa, the elongation at break is greater than or equal to 380%, and the tear strength is greater than or equal to 90 MPa; Preferably, the compressive strength of the tough material layer is 90-110 MPa, the tensile strength is 30-50 MPa, the elongation at break is 400-500%, and the tear strength is 100-120 MPa; Preferably, the temperature resistance of the tough material layer is 100-120 °C.

4. The temporary plugging agent according to any one of claims 1 - 3, characterized in that, The flexible material is selected from paraffin and / or soft silica gel; Preferably, the melting point of the paraffin is 20-40 °C, and / or the hardness of the soft silica gel is less than or equal to 20A; Preferably, the shape of the flexible material is spherical; Preferably, the diameter of the flexible material is 9-48 mm.

5. The temporary plugging agent according to any one of claims 1 - 4, characterized in that, The shape of the temporary plugging agent is spherical, ellipsoidal or regular dodecahedron.

6. The temporary plugging agent according to claim 5, characterized in that, The diameter of the temporary plugging agent with a spherical shape is 11-50 mm; or, the minor axis length of the temporary plugging agent with an ellipsoidal shape is 11-50 mm, the middle axis length is the same as the minor axis length, and the major axis length is 1.5-2 times the minor axis length; or, the distance from the outer surface to the center of the temporary plugging agent with a regular dodecahedron shape is 11-50 mm.

7. A preparation method of a temporary plugging agent, characterized in that, The preparation method includes: placing the flexible material in a mold with a cavity, making the flexible material centered in the cavity, then mixing a semi-prepolymer of isocyanate and a material containing an amino compound and injecting them into the cavity for curing; the amounts of the semi-prepolymer of isocyanate and the material containing an amino compound are such that after the 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; Preferably, the shape of the cavity is spherical, ellipsoidal or regular dodecahedron.

8. The preparation method according to claim 7, characterized in that, The amounts of the semi-prepolymer of isocyanate and the material containing an amino compound are such that after the curing, the thickness of the polyurea layer coated on the outer surface of the flexible material is 1-3 mm.

9. The preparation method according to claim 7 or 8, characterized in that, The semi-prepolymer of isocyanate is prepared from composition A; composition A includes 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 material containing an amino compound is prepared from composition B; composition B includes 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-butylamino)diphenylmethane and 1-5 parts of defoamer.

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

11. A temporary plugging agent prepared by the preparation method according to any one of claims 7 - 10.

12. An application of the temporary plugging agent according to any one of claims 1 - 6, 11 in multi - cluster temporary plugging fracturing of horizontal wells.

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