In-situ self-generating proppant for fracturing micro-cracks in calcium-rich reservoirs and its preparation method and application

Abstract

The invention discloses an in-situ self-generating proppant for micro-cracks in a calcium-rich reservoir fracturing, and a preparation method and application thereof, and relates to the technical field of petroleum fracturing. The in-situ self-generating proppant for micro-cracks in a calcium-rich reservoir fracturing in the invention is suitable for calcium-rich reservoirs, and includes clean water, phosphate and acid, wherein, by volume fraction, the clean water is 50 to 80 parts, the phosphate is 10 to 30 parts, and the acid is 1 to 10 parts. The invention also proposes a preparation method and application thereof for in-situ self-generating proppant for micro-cracks in a calcium-rich reservoir fracturing. The invention injects a phosphate system into the formation fracturing cracks, utilizes the formation environment to perform hydrothermal synthesis in situ in the calcium-rich reservoir to generate in-situ self-generating proppant, solves the problem that the proppant is difficult to transport in the micro-cracks at the far end of the fracturing and the proppant is difficult to effectively support, realizes effective support for the cracks, improves the fracture conductivity of the rock, and lays a foundation for enhancing the efficiency and stability of the fracturing and production increase transformation of the calcium-rich reservoir.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum fracturing, and in particular to an in-situ self-generated proppant for fracturing microcracks in a calcium-rich reservoir, and a preparation method and application thereof. Background Art

[0002] Fracturing technology is an important technology for the development of oil and gas fields. It releases oil and gas by injecting high-pressure fluid into the formation to break the rock. Proppant is a key material in the fracturing process of oil and gas wells. Its main function is to support the cracks formed during the fracturing process and prevent them from closing, thereby maintaining the conductivity of the cracks and ensuring that the oil and gas can flow out smoothly.

[0003] Both hydraulic fracturing cracks and natural cracks can form complex fracture networks, which are beneficial to the development and production of oil and gas. However, the micro-cracks after fracturing reservoir transformation are easy to close, and there are problems such as difficulty in proppant transportation and poor effective support in the micro-cracks at the far end of the fracturing, which seriously limits the conductivity of the fracture network. Due to the small opening of the micro-cracks, traditional proppants (such as ceramsite, quartz sand, etc.) cannot enter the micro-cracks to form effective support, and during the production process, affected by factors such as ground stress and rock elastic recovery, the micro-cracks without effective support are easy to close, which reduces the communication ability between the fracture network and the natural fractures, seriously restricts the efficiency and stability of the fracturing production increase transformation, and causes the production of the fracturing wells to drop rapidly. Studies have shown that most of the micro-cracks after fracturing are in an unsupported state, and the volume of unsupported cracks accounts for more than 50% of the fracturing volume.

[0004] Maintaining the aperture of microcracks is one of the keys to increasing and stabilizing the production of reservoir fracturing transformation. Using microproppants to support microcracks is the most direct way to maintain the aperture of microcracks. However, microproppants are easy to agglomerate and difficult to disperse. There is a potential risk of blocking the sand diversion channel of the main fracture due to the backflow after fracturing, which makes the transportation of microproppants to remote microcracks still a big obstacle, especially for microcracks with a width of less than 150μm. In order to achieve effective support for fracturing microcracks, relevant experts proposed to generate proppants through in-situ reaction between fracturing fluid and rock and mineral, that is, in-situ self-generated proppant technology.

[0005] However, there are few applications of in-situ self-generated proppant technology at present, and the solid particles of in-situ self-generated proppants synthesized at this stage are small in size and average in strength, which cannot reach the level of existing proppants and are difficult to apply in actual fracturing operations. Summary of the invention

[0006] In order to address the deficiencies of the above-mentioned prior art, the present invention proposes an in-situ autogenous proppant for fracturing microcracks in calcium-rich reservoirs, as well as a preparation method and application thereof. By in-situ hydrothermal synthesis of inorganic proppants in calcium-rich reservoirs, the problems of difficult proppant transportation and poor effective support in the microcracks at the far end of the fracturing are effectively solved, thereby improving the efficiency and stability of fracturing and production-increasing transformation.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] An in-situ self-generated proppant for fracturing micro-cracks in a calcium-rich reservoir, suitable for calcium-rich reservoirs, comprising clean water, phosphate and acid, wherein, by volume fraction, the clean water is 50-80 parts, the phosphate is 10-30 parts, and the acid is 1-10 parts;

[0009] The phosphate is at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate;

[0010] The acid is at least one of hydrochloric acid, formic acid, acetic acid, propionic acid, butyric acid, phosphoric acid, maleic acid, tartaric acid, benzoic acid, phenylacetic acid, carbonic acid, and citric acid.

[0011] Preferably, calculated by volume, the water is 60-80 parts, the phosphate is 20-30 parts, and the acid is 3-5 parts.

[0012] A method for preparing an in-situ self-generated proppant for fracturing microcracks in a calcium-rich reservoir, which is used to prepare the above-mentioned in-situ self-generated proppant for fracturing microcracks in a calcium-rich reservoir, comprises the following steps:

[0013] Step 1, weighing phosphate, acid and clean water according to a preset ratio, adding the phosphate and acid into the clean water and stirring until the phosphate is completely dissolved, so as to prepare a fracturing fluid pre-fluid;

[0014] Step 2: injecting the fracturing fluid pre-fluid into the fractures of the calcium-rich reservoir to react for 24 hours, using the formation temperature to hydrothermally synthesize hydroxyapatite crystals, and generating in-situ autogenous proppants on the fracture surface of the calcium-rich reservoir.

[0015] Preferably, the calcium content of the core minerals in the calcareous reservoir is greater than 50%, and the formation temperature is greater than 60°C.

[0016] The invention discloses an application of an in-situ self-generated proppant for fracturing micro-cracks in a calcium-rich reservoir in a calcium-rich reservoir. The in-situ self-generated proppant for fracturing micro-cracks in a calcium-rich reservoir is used to inject the in-situ self-generated proppant for fracturing micro-cracks in a calcium-rich reservoir into the calcium-rich reservoir, and in-situ proppant particles are generated on the crack surface of the calcium-rich reservoir to support the cracks in the calcium-rich reservoir and improve the conductivity of the cracks.

[0017] Preferably, the in-situ self-generated proppant for fracturing micro-cracks in the calcium-rich reservoir is a pure liquid phase fluid.

[0018] Beneficial technical effects brought by the present invention:

[0019] (1) The present invention proposes an in-situ autogenous proppant for fracturing micro-cracks in a calcium-rich reservoir, as well as a preparation method and application thereof, which is suitable for calcium-rich reservoirs. Based on the prerequisite that calcium minerals can generate proppants in situ under a hydrothermal environment, a phosphate system is injected into the fracturing cracks of the formation, and hydroxyapatite crystals are synthesized in situ in the cracks using the formation temperature hydrothermal method as an in-situ autogenous proppant, thereby achieving effective support for the fracturing cracks. In addition, the present invention utilizes hydrothermal synthesis to synthesize proppants in situ in the calcium-rich reservoir, which makes full use of the original material in the formation minerals. The raw materials are easily available and will not cause damage to the formation.

[0020] (2) The present invention proposes an in-situ self-generated proppant for fracturing microcracks in calcium-rich reservoirs, as well as a preparation method and application thereof, which solves the problems of difficulty in transporting proppant to microcracks at the far end of fracturing and difficulty for conventional proppants to enter microcracks for support. The in-situ self-generated proppant generated by the present invention is hydroxyapatite crystal, which has a high hardness and can effectively support the cracks, improve the fracture conductivity of the rock, and is conducive to enhancing the efficiency and stability of fracturing and production increase, thus providing technical support for ensuring the development and production of calcium-rich reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a microscope image of a carbonate rock core slice.

[0022] Figure 2 This is a scanning electron microscope image of the in-situ proppant magnified 2000 times.

[0023] Figure 3 This is a scanning electron microscope image of the in-situ proppant magnified 10,000 times.

[0024] Figure 4 The schematic diagram of the in-situ autogenous proppant generated on the surface of carbonate rock fractures by the method of the present invention.

[0025] Figure 5 This is a comparison of the conductivity of core fractures before and after the reaction.

[0026] In the figure, the circled part is the in-situ proppant. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings, embodiments and comparative examples.

[0028] Example 1

[0029] This embodiment discloses an in-situ autogenous proppant for fracturing microcracks in a calcium-rich reservoir. The phosphate used is diammonium hydrogen phosphate and the acid is hydrochloric acid. According to the volume fraction, the clean water is 50 parts, the diammonium hydrogen phosphate is 10 parts, and the hydrochloric acid is 1 part. After the clean water, diammonium hydrogen phosphate and hydrochloric acid are uniformly mixed to prepare a phosphate system solution, calcium carbonate is added to the phosphate system solution and stirred evenly, and reacted at 80° C. for 24 hours. After the reaction is completed, the solid mixture of the in-situ autogenous proppant and calcium carbonate is filtered to obtain.

[0030] Since the decomposition temperature of calcium carbonate is 825°C, and the decomposition temperature of the in-situ autogenous proppant is 1200°C, the filtered solid mixture is placed in a muffle furnace at 900°C for high-temperature calcination treatment to decompose the calcium carbonate in the solid mixture into calcium oxide and carbon dioxide. After obtaining a solid mixture of calcium oxide and the proppant, an NH4Cl solution with a volume concentration of 20% is prepared, and the NH4Cl solution is added to the solid mixture of calcium oxide and the proppant and placed in a 50°C constant temperature water bath for reaction for 0.5-1h. After the reaction is completed, it is filtered, and the reaction is repeated 3-5 times until no obvious irritating odor is released or the solution pH is 7, which is considered to be completely reacted. The reacted solution is filtered and dried to obtain the in-situ autogenous proppant, thereby separating the unreacted calcium carbonate from the mixture to obtain the in-situ autogenous proppant.

[0031] Example 2

[0032] This embodiment discloses an in-situ autogenous proppant for fracturing microcracks in a calcium-rich reservoir. The phosphate used is diammonium hydrogen phosphate and the acid is formic acid. According to the volume fraction, 80 parts of clean water, 30 parts of diammonium hydrogen phosphate and 10 parts of formic acid are used. After the clean water, diammonium hydrogen phosphate and formic acid are uniformly mixed to obtain a phosphate system solution, calcium carbonate is added to the phosphate system solution and stirred evenly, and reacted at 80° C. for 24 hours. After the reaction is completed, the solid mixture of the in-situ autogenous proppant and calcium carbonate is filtered to obtain.

[0033] Since the decomposition temperature of calcium carbonate is 825°C, and the decomposition temperature of the in-situ autogenous proppant is 1200°C, the filtered solid mixture is placed in a muffle furnace at 900°C for high-temperature calcination treatment to decompose the calcium carbonate in the solid mixture into calcium oxide and carbon dioxide. After obtaining a solid mixture of calcium oxide and the proppant, an NH4Cl solution with a volume concentration of 20% is prepared, and the NH4Cl solution is added to the solid mixture of calcium oxide and the proppant and placed in a 50°C constant temperature water bath for reaction for 0.5-1h. After the reaction is completed, it is filtered, and the reaction is repeated 3-5 times until no obvious irritating odor is released or the solution pH is 7, which is considered to be completely reacted. The reacted solution is filtered and dried to obtain the in-situ autogenous proppant, thereby separating the unreacted calcium carbonate from the mixture to obtain the in-situ autogenous proppant.

[0034] Example 3

[0035] This embodiment discloses an in-situ autogenous proppant for fracturing microcracks in a calcium-rich reservoir. The phosphate used is diammonium hydrogen phosphate and the acid is propionic acid. According to the volume fraction, the water is 60 parts, the diammonium hydrogen phosphate is 20 parts, and the propionic acid is 3 parts. After the water, diammonium hydrogen phosphate and propionic acid are uniformly mixed to prepare a phosphate system solution, calcium carbonate is added to the phosphate system solution and stirred evenly, and reacted at 80° C. for 24 hours. After the reaction is completed, the solid mixture of the in-situ autogenous proppant and calcium carbonate is filtered to obtain.

[0036] Since the decomposition temperature of calcium carbonate is 825°C, and the decomposition temperature of the in-situ autogenous proppant is 1200°C, the filtered solid mixture is placed in a muffle furnace at 900°C for high-temperature calcination treatment to decompose the calcium carbonate in the solid mixture into calcium oxide and carbon dioxide. After obtaining a solid mixture of calcium oxide and the proppant, an NH4Cl solution with a volume concentration of 20% is prepared, and the NH4Cl solution is added to the solid mixture of calcium oxide and the proppant and placed in a 50°C constant temperature water bath for reaction for 0.5-1h. After the reaction is completed, it is filtered, and the reaction is repeated 3-5 times until no obvious irritating odor is released or the solution pH is 7, which is considered to be completely reacted. The reacted solution is filtered and dried to obtain the in-situ autogenous proppant, thereby separating the unreacted calcium carbonate from the mixture to obtain the in-situ autogenous proppant.

[0037] Example 4

[0038] This embodiment discloses an in-situ autogenous proppant for fracturing microcracks in a calcium-rich reservoir. The phosphate used is diammonium hydrogen phosphate and the acid is phosphoric acid. According to the volume fraction, the clean water is 80 parts, the diammonium hydrogen phosphate is 30 parts, and the phosphoric acid is 5 parts. After the clean water, diammonium hydrogen phosphate and phosphoric acid are uniformly mixed to obtain a phosphate system solution, calcium carbonate is added to the phosphate system solution and stirred evenly, and reacted at 80° C. for 24 hours. After the reaction is completed, the solid mixture of the in-situ autogenous proppant and calcium carbonate is filtered to obtain.

[0039] Since the decomposition temperature of calcium carbonate is 825°C, and the decomposition temperature of the in-situ autogenous proppant is 1200°C, the filtered solid mixture is placed in a muffle furnace at 900°C for high-temperature calcination treatment to decompose the calcium carbonate in the solid mixture into calcium oxide and carbon dioxide. After obtaining a solid mixture of calcium oxide and the proppant, an NH4Cl solution with a volume concentration of 20% is prepared, and the NH4Cl solution is added to the solid mixture of calcium oxide and the proppant and placed in a 50°C constant temperature water bath for reaction for 0.5-1h. After the reaction is completed, it is filtered, and the reaction is repeated 3-5 times until no obvious irritating odor is released or the solution pH is 7, which is considered to be completely reacted. The reacted solution is filtered and dried to obtain the in-situ autogenous proppant, thereby separating the unreacted calcium carbonate from the mixture to obtain the in-situ autogenous proppant.

[0040] Example 5

[0041] This embodiment discloses an in-situ autogenous proppant for fracturing microcracks in a calcium-rich reservoir. The phosphate used is diammonium hydrogen phosphate and the acid is acetic acid. According to the volume fraction, the water is 80 parts, the diammonium hydrogen phosphate is 20 parts, and the acetic acid is 3 parts. After the water, diammonium hydrogen phosphate and acetic acid are uniformly mixed to prepare a phosphate system solution, calcium carbonate is added to the phosphate system solution and stirred evenly, and reacted at 80° C. for 24 hours. After the reaction is completed, the solid mixture of the in-situ autogenous proppant and calcium carbonate is filtered to obtain.

[0042] Since the decomposition temperature of calcium carbonate is 825°C, and the decomposition temperature of the in-situ autogenous proppant is 1200°C, the filtered solid mixture is placed in a muffle furnace at 900°C for high-temperature calcination treatment to decompose the calcium carbonate in the solid mixture into calcium oxide and carbon dioxide. After obtaining a solid mixture of calcium oxide and the proppant, an NH4Cl solution with a volume concentration of 20% is prepared, and the NH4Cl solution is added to the solid mixture of calcium oxide and the proppant and placed in a 50°C constant temperature water bath for reaction for 0.5-1h. After the reaction is completed, it is filtered, and the reaction is repeated 3-5 times until no obvious irritating odor is released or the solution pH is 7, which is considered to be completely reacted. The reacted solution is filtered and dried to obtain the in-situ autogenous proppant, thereby separating the unreacted calcium carbonate from the mixture to obtain the in-situ autogenous proppant.

[0043] The mineral composition of the in-situ autogenous proppant was analyzed by X-ray diffraction, and the results of the mineral composition analysis were shown in Table 1. From the analysis of Table 1, it can be seen that the main component of the in-situ autogenous proppant in this embodiment is hydroxyapatite.

[0044] Table 1 Mineral composition of in-situ autogenous proppant in Example 5

[0045] .

[0046] Example 6

[0047] The phosphate in Example 5 was replaced by ammonium dihydrogen phosphate, and other raw materials and reaction conditions remained unchanged. After the reaction was completed, a mixture of in-situ autogenous proppant and calcium carbonate was obtained by filtration, and unreacted calcium carbonate was separated from the mixture to obtain the in-situ autogenous proppant.

[0048] The mineral composition of the in-situ self-generated proppant was analyzed by X-ray diffraction, and the mineral composition analysis results were obtained, as shown in Table 2. According to Table 2, the main component of the in-situ self-generated proppant in this embodiment is hydroxyapatite, and the mineral composition is similar to that of the in-situ self-generated proppant in Example 5.

[0049] Table 2 Mineral composition of in-situ autogenous proppant in Example 6

[0050] .

[0051] Example 7

[0052] The phosphate in Example 5 was replaced with trisodium phosphate, and other raw materials and reaction conditions remained unchanged. After the reaction was completed, a mixture of in-situ autogenous proppant and calcium carbonate was obtained by filtration, and unreacted calcium carbonate was separated from the mixture to obtain the in-situ autogenous proppant.

[0053] The mineral composition of the in-situ autogenous proppant was analyzed by X-ray diffraction, and the mineral composition analysis results were obtained, as shown in Table 3. According to Table 3, the hydroxyapatite content in the in-situ autogenous proppant in this embodiment is lower than that in the in-situ autogenous proppant in Example 6.

[0054] Table 3 Mineral composition of in-situ autogenous proppant in Example 7

[0055] .

[0056] Example 8

[0057] The phosphate in Example 5 was replaced by disodium hydrogen phosphate, and other raw materials and reaction conditions remained unchanged. After the reaction was completed, a mixture of in-situ autogenous proppant and calcium carbonate was obtained by filtration, and unreacted calcium carbonate was separated from the mixture to obtain the in-situ autogenous proppant.

[0058] The mineral composition of the in-situ self-generated proppant was analyzed by X-ray diffraction, and the mineral composition analysis results were obtained, as shown in Table 4. According to Table 4, the hydroxyapatite content in the in-situ self-generated proppant in this embodiment is further reduced compared with the hydroxyapatite content in the in-situ self-generated proppant in Example 7.

[0059] Table 4 Mineral composition of in-situ autogenous proppant in Example 8

[0060] .

[0061] Example 9

[0062] The phosphate in Example 5 was replaced with sodium dihydrogen phosphate, and other raw materials and reaction conditions remained unchanged. After the reaction was completed, a mixture of in-situ autogenous proppant and calcium carbonate was obtained by filtration, and unreacted calcium carbonate was separated from the mixture to obtain the in-situ autogenous proppant.

[0063] The mineral composition of the in-situ autogenous proppant was analyzed by X-ray diffraction, and the results of the mineral composition analysis were shown in Table 5. From the analysis of Table 5, it can be seen that the main component of the in-situ autogenous proppant in this embodiment is hydroxyapatite.

[0064] Table 5 Mineral composition of in-situ autogenous proppant in Example 9

[0065] .

[0066] Example 10

[0067] The carbonate core was cut into pieces to obtain carbonate core pieces, and then placed in the phosphate system solution prepared in Example 5. After reacting at 80° C. for 24 hours, the carbonate core pieces were taken out and the surface of the carbonate core pieces was observed under a microscope. The image of the carbonate core pieces under a microscope is as follows: Figure 1 As shown, through observation, it can be seen that a large number of white crystal particles are generated on the surface of the carbonate rock core piece. The circled ones in the figure are the generated white crystal particles, and the white crystal particles are hydroxyapatite products.

[0068] Furthermore, the surface of the carbonate core slice was observed using a scanning electron microscope (SEM) to obtain a scanning electron microscope image of the in-situ proppant in the carbonate core slice, such as Figure 2 and Figure 3 As shown, it can be further concluded through observation that the hydroxyapatite product generated on the surface of the carbonate rock core piece is spherical.

[0069] Embodiment 11

[0070] The phosphate system solution prepared in Example 5 was used in accordance with the provisions of "SY / T 5336-2006 Core Analysis Method" to drill a carbonate core with a calcium content of more than 90%, and an artificial fracture making device was used to make fractures in the carbonate core. The carbonate core was used to simulate a calcium-rich reservoir, and the phosphate system solution prepared in Example 5 was injected into the fractures of the carbonate core as a fracturing fluid pre-fluid. After reacting at 80° C. for 24 hours, the carbonate core was taken out and observed, and it was found that white hydroxyapatite crystals were generated on the fracture surface of the carbonate core, that is, the in-situ autogenous proppant proposed by the present invention, such as Figure 4As shown, it is verified that by injecting the phosphate system solution proposed by the present invention into the rock fractures of the calcium-rich reservoir, in-situ proppant particles can be generated on the surface of the rock fractures to achieve effective support for the rock fractures.

[0071] Example 12

[0072] In order to further verify the supporting effect of the in-situ proppant proposed in the present invention, the supporting effect of the in-situ proppant was tested in the laboratory, and the fracture conductivity under different confining pressures before and after the reaction was tested using a core displacement device. The experimental process specifically includes the following steps:

[0073] Step 1: Select a carbonate core with a calcium content of more than 90%, use an artificial slit making device to make a slit in the carbonate core as a test core, and use a vernier caliper to measure the diameter and length of the carbonate core to obtain the core size of the carbonate core.

[0074] Step 2: Install the test core in the core displacement device, place it in the rubber sleeve of the core holder, connect the pipeline, and compress the test core.

[0075] Step 3: Under room temperature, control the core displacement device to apply a confining pressure of 1 MPa to the test core, and use clean water to displace the test core. After the pressure and flow rate are stable, test the core fracture conductivity of the test core before the reaction. .

[0076] Step 4, control the core displacement device to change the confining pressure value applied to the test core, and adjust the confining pressure value to 3MPa, 5MPa, 7MPa, and 10MPa in turn, and displace the test core with clean water under each confining pressure value condition. After the pressure and flow rate are stable, the core fracture conductivity of the test core under each confining pressure condition before the reaction is tested.

[0077] Step 5, injecting the prepared phosphate system solution in Example 5 into the fractures of the test core as a fracturing fluid pre-fluid, reacting at 80° C. for 24 hours, and generating in-situ proppants on the surface of the rock fractures.

[0078] Step 6, under room temperature conditions, control the core displacement device to apply confining pressure values ​​of 1MPa, 3MPa, 5MPa, 7MPa, and 10MPa to the reacted test core in sequence, and displace the test core with clean water under each confining pressure value condition. After the pressure and flow rate are stable, the core fracture conductivity of the test core under each confining pressure condition after the reaction is tested.

[0079] In step 4 and step 6, the calculation formula for the core fracture conductivity of the test core is:

[0080] (1)

[0081] In the formula, is the conductivity of core fractures, in μm 2 cm; is the flow rate of fluid passing through the core per unit time, in units of ; is the fluid viscosity, in units of ; is the core length, in units of ; is the core diameter, in units of ; It is the pressure difference before and after the fluid passes through the core, in MPa.

[0082] In this embodiment, the core fracture conductivity under different confining pressure values ​​was tested before and after the in-situ autogenous proppant was generated. Figure 5 As shown in the figure, by comparing the core fracture conductivity of the test core before and after the in-situ self-generated proppant is generated, it can be seen that the in-situ self-generated proppant proposed in the present invention can effectively improve the core permeability and increase the conductivity of rock fractures. At the same time, from the perspective of fracture conductivity, it can be obtained that under a confining pressure value of 10MPa, the in-situ self-generated proppant proposed in the present invention can increase the fracture conductivity of the rock from 1.22158μm to 1.22158μm. 2 cm increased to 2.15754 μm 2 ·cm, that is, the in-situ autogenous proppant proposed in the present invention increases the fracture conductivity of the rock by 76.6%, thereby verifying the improvement of the fracture conductivity of the rock by the in-situ autogenous proppant in the present invention.

[0083] The average fracture conductivity under different confining pressures after the pressure and flow rate are stabilized is further compared, as shown in Table 6.

[0084] Table 6 Average fracture conductivity of the test core under different confining pressures before and after reaction

[0085] .

[0086] It can be seen from Table 6 that the in-situ self-generated proppant generated by the present invention plays a supporting role on rock fractures, and can effectively solve the problems of difficult proppant transportation, poor effective support, and easy closure of fractures in micro-cracks at the far end of fracturing.

[0087] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", "connect", and "fix" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0088] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing an in-situ self-generated proppant for fracturing microcracks in a calcium-rich reservoir, characterized in that: The following steps are involved: Step 1, weighing phosphate, acid and clean water according to a preset ratio, adding the phosphate and acid into the clean water and stirring until the phosphate is completely dissolved, so as to prepare a fracturing fluid pre-fluid; Step 2, injecting the fracturing fluid pre-fluid into the fractures of the calcium-rich reservoir with a calcium content greater than 90% and reacting at 80° C. for 24 hours, using the formation temperature to hydrothermally synthesize hydroxyapatite crystals, and generating in-situ autogenous proppants on the fracture surface of the calcium-rich reservoir; According to volume fraction, water is 50-80 parts, phosphate is 10-30 parts, and acid is 1-10 parts; The phosphate is at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate; The acid is at least one of hydrochloric acid, formic acid, acetic acid, propionic acid, butyric acid, phosphoric acid, maleic acid, tartaric acid, benzoic acid, phenylacetic acid, carbonic acid, and citric acid.

2. The method for preparing the in-situ self-generated proppant for fracturing microcracks in calcium-rich reservoirs according to claim 1, characterized in that: Calculated by volume, water is 60-80 parts, phosphate is 20-30 parts, and acid is 3-5 parts.

3. An application of an in-situ self-generated proppant for fracturing microcracks in a calcium-rich reservoir in a calcium-rich reservoir, characterized in that: The in-situ self-generated proppant for fracturing micro-cracks in the calcium-rich reservoir is prepared by the preparation method of the in-situ self-generated proppant for fracturing micro-cracks in the calcium-rich reservoir according to any one of claims 1 to 2, and the fracturing fluid pre-fluid is injected into the calcium-rich reservoir to generate in-situ proppant particles on the crack surface of the calcium-rich reservoir to support the cracks in the calcium-rich reservoir and improve the conductivity of the cracks.

Images