Temporary plugging acid fracturing device based on true triaxial and crack monitoring method

Abstract

The invention discloses a true triaxial-based temporary plugging acid fracturing device. The true triaxial-based temporary plugging acid fracturing device is characterized in that a fracturing unit is used for fracturing a sample by utilizing triaxial stress; the multi-pump parallel liquid injection unit is used for adding fracturing fluid into the sample, and the 3D fracture reconstruction scanner is used for scanning a fracture surface and obtaining a fracture surface reconstruction diagram; the magnetic detection sensor is used for detecting the magnetic chips and obtaining a magnetic field distribution diagram. By using the multi-pump parallel liquid injection system, the liquid injection rate can be increased; in addition, the feasibility of fracture steering is verified, and old fracture plugging and new fracture steering can be clearly and visually observed through the carbonate rock true triaxial fracture internal temporary plugging acid fracturing physical simulation experiment method; meanwhile, the magnetic chips are added, so that crack propagation of temporary plugging acid fracturing is not affected, and crack initiation and propagation forms can be monitored in real time; in addition, the acid fracturing crack and the secondary crack can be accurately identified by using the 3D crack scanner, and the temporary plugging acid fracturing effect evaluation can be more effectively carried out.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploitation, and in particular to a temporary plugging acid fracturing device based on true triaxial pressure and a crack monitoring method. Background Art

[0002] As an effective means of fracturing transformation, the temporary plugging and diversion fracturing technology in fractures refers to the use of high-strength water-soluble granular temporary plugging agents once or multiple times during fracturing construction. The granular temporary plugging agents form filter cakes in the blastholes and high-permeability zones of the fractures, temporarily plugging old fractures and increasing the pressure in the wellbore. Combined with perforation technology, it promotes the opening of fractures in other locations in the horizontal production layer, and ultimately forms multiple new fractures, achieving the purpose of densely cutting the reservoir and effectively increasing the transformation volume of a single well.

[0003] "Effective plugging" and "successful diversion" are the key links to ensure the success of temporary plugging and acid fracturing construction in cracks. The current true triaxial temporary plugging and acid fracturing cracks use fluorescent powder to monitor the cracks. After the experiment, a large amount of fluorescent powder is distributed at the crack mouth and inside the crack, making it difficult to determine whether the temporary plugging material has temporarily plugged the crack, resulting in crack diversion.

[0004] Therefore, in view of the shortcomings of the existing crack monitoring method, a new crack monitoring method needs to be studied. Summary of the invention

[0005] The object of the present invention is to provide a temporary plugging acid fracturing device and a crack monitoring method based on true triaxial analysis to solve the above technical problems.

[0006] To achieve the above object, the present invention provides a temporary plugging acid fracturing device based on true triaxial, the device comprising: a fracturing unit, a multi-pump parallel injection unit, a 3D fracture reconstruction scanner and a magnetic detection sensor;

[0007] The fracturing unit is used to perform fracturing on the sample using triaxial stress; the multi-pump parallel injection unit is used to add fracturing fluid to the sample; the 3D fracture reconstruction scanner is used to scan the fracture surface and obtain a fracture surface reconstruction map; the magnetic detection sensor is used to detect magnetic chips and obtain a magnetic field distribution map;

[0008] Wherein, the fracturing fluid comprises: gel acid solution and granular powder temporary plugging agent containing magnetic chips.

[0009] Optionally, the device further comprises a loading unit for adjusting the triaxial stress.

[0010] Optionally, the loading unit includes: a stress setting operation chamber, an X-axis hydraulic cylinder, a Y-axis hydraulic cylinder and a Z-axis hydraulic cylinder.

[0011] Optionally, the fracturing unit includes: a pressure plate, a test bench, and a fracturing pipeline for conveying hydraulic oil to the stress plate.

[0012] Optionally, the multi-pump parallel injection unit includes two parallel fracturing fluid injection pipelines for respectively adding the gel acid solution and the granular powder temporary plugging agent containing magnetic chips into the sample.

[0013] Optionally, the granular powder temporary plugging agent containing magnetic chips includes: 1% 40 mesh particles, 1% 100 mesh powder and magnetic chips.

[0014] Optionally, the gel acid solution includes: 20% hydrochloric acid, 1% iron ion stabilizer and 1% corrosion inhibitor.

[0015] Optionally, the magnetic detection sensor is a three-axis fluxgate magnetometer.

[0016] Optionally, the device further comprises a temporary plugging agent preparation unit for injecting magnetic chips into the temporary plugging agent.

[0017] The present invention also provides a crack monitoring method, the method comprising:

[0018] Applying triaxial stress to the specimen using a fracturing unit;

[0019] When the pressure is stable, injecting fracturing fluid into the sample using a multi-pump parallel injection unit;

[0020] After temporary plugging and acid fracturing, the magnetic detection sensor is used to detect the magnetic chips distribution and obtain the magnetic chips distribution map;

[0021] Use a 3D crack reconstruction scanner to scan the crack surface after breaking the sample and obtain a crack surface reconstruction image;

[0022] Obtaining a crack monitoring result according to the magnetic chip distribution map and the crack surface reconstruction map;

[0023] Wherein, the fracturing fluid comprises: gel acid solution and granular powder temporary plugging agent containing magnetic chips.

[0024] Optionally, injecting fracturing fluid into the sample using a multi-pump parallel injection unit includes:

[0025] Injecting gel acid solution into the sample using the multi-pump parallel injection unit;

[0026] When the sample is broken, the multi-pump parallel injection unit is used to inject a temporary plugging agent containing magnetic chips into the sample.

[0027] Optionally, the method further includes: adjusting the triaxial stress using a loading unit.

[0028] Technical effects and advantages of the present invention:

[0029] The present invention provides a temporary plugging acid fracturing device based on true triaxial stress, the device comprising: a fracturing unit, a multi-pump parallel injection unit, a 3D fracture reconstruction scanner and a magnetic detection sensor; the fracturing unit is used to implement fracturing on a sample by using triaxial stress; the multi-pump parallel injection unit is used to add fracturing fluid to the sample, the 3D fracture reconstruction scanner is used to scan the fracture surface and obtain a fracture surface reconstruction map; the magnetic detection sensor is used to detect magnetic chips and obtain a magnetic field distribution map; wherein the fracturing fluid comprises: a gel acid solution and a granular powder temporary plugging agent containing magnetic chips.

[0030] The advantages of the present invention are as follows: (1) the use of a multi-pump parallel injection system can increase the injection rate; (2) the present invention not only verifies the feasibility of fracture redirection, but also can clearly and intuitively observe the "old fracture plugging" and "new fracture redirection" through the method of temporary plugging and acid fracturing physical simulation experiment in true triaxial fractures of carbonate rocks; (3) the disadvantage that the temporary plugging position cannot be determined due to the wide distribution of fluorescent powder is solved, magnetic chips are added to the temporary plugging agent, and the crack initiation and expansion morphology are observed according to the magnetic field distribution; (4) the addition of magnetic chips not only does not affect the crack expansion of temporary plugging and acid fracturing, but also can achieve real-time monitoring of the crack initiation and expansion morphology; (5) the use of a 3D fracture scanner can accurately identify acid fracturing fractures and secondary fractures, and more effectively evaluate the effect of temporary plugging and acid fracturing.

[0031] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of the fracture monitoring method based on true triaxial temporary plugging and acid fracturing;

[0033] Figure 2 This is a rock sample diagram;

[0034] Figure 3 It is the projection diagram of the rock sample on the XY plane;

[0035] Figure 4 Scan pictures for 3D cracks;

[0036] Figure 5 It is the X-axis magnetic anomaly profile;

[0037] Figure 6 This is the Y-axis magnetic anomaly profile. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0040] In order to solve the shortcomings of the prior art, the present invention discloses a temporary plugging acid fracturing device based on true triaxial stress, the device comprising: a fracturing unit, a multi-pump parallel injection unit, a 3D fracture reconstruction scanner and a magnetic detection sensor; the fracturing unit is used to implement fracturing on a sample using triaxial stress; the multi-pump parallel injection unit is used to add fracturing fluid to the sample, the 3D fracture reconstruction scanner is used to scan the fracture surface and obtain a fracture surface reconstruction map; the magnetic detection sensor is used to detect magnetic chips and obtain a magnetic field distribution map; wherein the fracturing fluid comprises: gel acid and a granular powder temporary plugging agent containing magnetic chips.

[0041] It should be noted that the device further includes a loading unit for adjusting the triaxial stress. The loading unit includes: a stress setting operation room, an X-axis hydraulic cylinder, a Y-axis hydraulic cylinder and a Z-axis hydraulic cylinder.

[0042] It should also be noted that the fracturing unit includes: a pressure plate, a test bench and a fracturing pipeline.

[0043] It should also be noted that the multi-pump parallel injection unit includes two parallel fracturing fluid injection pipelines, which are used to add the gel acid solution and the granular powder temporary plugging agent containing magnetic chips into the sample respectively. Specifically, the multi-pump parallel injection unit is an alternating injection unit, that is, the gel acid solution is injected into the carbonate rock sample to reduce the strength of the carbonate rock, and the granular powder temporary plugging agent containing magnetic chips is injected into the carbonate rock sample after fracture.

[0044] The temporary plugging agent containing magnetic particles and powders includes: 1% 40-mesh particles, 1% 100-mesh powder and magnetic particles; the gel acid solution includes: 20% hydrochloric acid, 1% iron ion stabilizer and 1% corrosion inhibitor.

[0045] It should also be noted that the device also includes a temporary plugging agent preparation unit for injecting magnetic chips into the temporary plugging agent.

[0046] It should also be noted that the 3D crack reconstruction scanner includes: an imaging system and a scanning system; using the scanner to perform cross-sectional scanning on the sample can reconstruct the crack surface more realistically.

[0047] It should also be noted that the magnetic detection sensor is a three-axis fluxgate magnetometer. Among them, the three-axis fluxgate magnetometer is economical, simple, reliable, durable, and can measure posture in motion. The following is the principle of magnetic detection:

[0048] (1) The transient electromagnetic method detection device consists of two parts: the transmitting coil and the receiving coil. Transmission, electromagnetic induction and reception are the three parts of its working process. First, a step current of 1 is passed through the transmitting coil and then suddenly turned off. The transmitting current instantly drops from 1 to zero. According to the electromagnetic induction theory, the sudden change of the current in the transmitting coil will generate a magnetic field around it. The magnetic field generated by the current shutdown is called the primary magnetic field. During the propagation of the primary magnetic field, when it encounters a conductive medium, it will stimulate an induced current inside it. This current can also be called a secondary current or eddy current. As the secondary current decreases over time, a new magnetic field is generated around it. This magnetic field generated by the change of the secondary current is called the secondary magnetic field. The reason for the decrease of the secondary current is that there is heat loss of the induced current in the conductive medium. The secondary magnetic field decays exponentially with the increase of time. This magnetic field is called a transient magnetic field. The induced current in the conductive medium is the main source of the secondary magnetic field. Therefore, in order to interpret the relevant physical parameters of the underground conductive medium, it is necessary to observe the secondary magnetic field through the receiving coil and analyze and process the observed data (because the secondary magnetic field contains electromagnetic information related to the medium).

[0049] This experimental device uses a three-axis fluxgate magnetometer. The high-temperature fluxgate circuit and the three-axis fluxgate probe form a three-axis fluxgate magnetometer. The three measuring coils share a Permalloy core, which is located in the center of the three measuring coils. The shared core and the three measuring coils form a three-axis fluxgate probe to measure the three components of a point in space. The three measuring coils that constitute the three measuring axes are orthogonal, and the three measuring axes are: X-axis, Y-axis and Z-axis. The three measuring axes can measure the three components of the magnetic field: X-axis component, Y-axis component and Z-axis component. At the same time, the three-axis fluxgate magnetometer can also measure the total magnetic field. In the experiment of this article, the total magnetic field of the X-axis and Y-axis is mainly measured.

[0050] (2) The electromagnetic detector probe is composed of an iron core and a coil. The induced electromotive force received by the coil is a function of the electrical parameters of each layer in the "columnar layer structure" and is also related to the "layer thickness r". When the dielectric constant is basically determined, the change law of the received signal is determined by "r". In the directional electromagnetic detection, the differential expression of Maxwell's equations is:

[0051]

[0052]

[0053] Among them: B, H, E are magnetic induction intensity, magnetic field intensity and electric field intensity respectively; J is the conduction current density; D is the electric displacement vector.

[0054] For time-harmonic signals, substituting D = εE, J = σE, and B = μH into equations 1 and 2 yields:

[0055]

[0056]

[0057] Among them, μ and σ are the magnetic permeability and electrical conductivity of the dielectric body respectively; i is the number of turns; ω is the angular velocity of the closed coil rotating in the magnetic field; ε is the absolute dielectric constant of the medium.

[0058] In each homogeneous region, the magnetic field and electric field can be regarded as the superposition of the fields generated by the magnetic source and the power source, that is:

[0059] E=E e +E m (Formula 5

[0060] H=H e +H m (Formula 6

[0061] Among them, E e E is electrostatic energy; m is the induced electrical energy; H e is the static magnetic energy; H m For induced magnetic energy.

[0062] It can be seen that only two of the three components of the magnetic field in the above equations are independent of each other, so the following equations exist:

[0063]

[0064]

[0065]

[0066] The present invention also provides a crack monitoring method using the above device, such as Figure 1 The method comprises: applying triaxial stress to the sample by using a fracturing unit; when the pressure is stable, injecting fracturing fluid into the sample by using a multi-pump parallel injection unit; after the temporary plugging acid pressure is completed, detecting the magnetic chips distribution by using a magnetic detection sensor and obtaining a magnetic chips distribution map; scanning the fracture surface after breaking the sample by using a 3D fracture reconstruction scanner and obtaining a fracture surface reconstruction map; obtaining fracture monitoring results according to the magnetic chips distribution map and the fracture surface reconstruction map; wherein the fracturing fluid comprises: gel acid and a temporary plugging agent containing granular powder containing magnetic chips.

[0067] In order to better understand this method, the crack monitoring method is introduced in detail below.

[0068] 1. Prepare the samples required for the experiment: drill a wellbore at the center of the rock sample, fill the soluble material in the pre-set open hole section and compact it; then add cementing glue, and before the cementing glue is bonded, install the simulated wellhead into the wellbore, and set the wellbore seal of the simulated wellhead; let it stand until the cementing glue is bonded, open the seal of the simulated wellhead, and inject water into the wellbore until the soluble material is completely dissolved.

[0069] 2. Start the fracturing unit to apply triaxial stress to the rock sample. After the confining pressure is stable, first use the multi-pump parallel injection unit to inject gelled acid into the rock sample through the simulated wellhead until the rock sample breaks. After the rock sample breaks, add the prepared granular powder temporary plugging agent containing magnetic chips into the rock sample. After the pressure is successfully held, the pressure drops suddenly again, and the temporary plugging acid fracturing ends.

[0070] 3. Use the electromagnetic detector probe in the magnetic detection sensor to detect the magnetic distribution of the sample. Then break along the cracks of the rock sample, and use the 3D crack reconstruction scanner to scan the crack surface to evaluate the temporary plugging and acid fracturing effect;

[0071] 4. Compare the 3D fracture surface reconstruction image with the electromagnetic distribution results.

[0072] In order to better explain the present scheme, examples are also provided below.

[0073] A method for monitoring temporary plugging and acid fracturing fractures in carbonate reservoir fractures, the specific steps are as follows:

[0074] (1) Prepare the samples required for the experiment: drill a wellbore at the center of the rock sample, fill the pre-set open hole section with soluble material and compact it; then add cementing glue, and before the cementing glue is bonded, install the simulated wellhead into the wellbore, and set the wellbore seal of the simulated wellhead; let it stand until the cementing glue is bonded, open the seal of the simulated wellhead, and inject water into the wellbore until the soluble material is completely dissolved. Figure 2 and Figure 3 shown.

[0075] (2) Preparation of fracturing fluid: The acid liquid adopts gel acid liquid, and the ratio is 20% hydrochloric acid + 1% iron ion stabilizer + 1% corrosion inhibitor; the temporary plugging agent formula is 1% 40 mesh particles + 1% 100 mesh powder + magnetic chips.

[0076] (3) The fracturing unit is started to apply triaxial stress to the rock sample. In this experiment, the triaxial stresses are set to 25 / 15 / 18 MPa, respectively; and the horizontal stress difference is 10 MPa.

[0077] (4) After the confining pressure is stabilized, a multi-pump parallel injection unit is used to inject gelled acid into the rock sample through the simulated wellhead at a rate of 30 ml / min, and the pressure is released when the injection pressure reaches half of the fracture pressure (in this process, the fracturing fluid in tank A is gelled acid, and the fracturing fluid in tank B is a temporary plugging agent. During the pumping process, the valve of tank B is first closed, and the gelled acid in tank A is injected into the sample).

[0078] (5) When the rock sample breaks, open the valve of tank B, close the valve of tank A, and inject the temporary plugging agent with magnetic chips inside tank B into the carbonate rock sample through the pipeline.

[0079] (6) After the pressure is successfully held, the pressure suddenly drops again. The temporary plugging and acid fracturing are ended. The magnetic detection sensor is used to detect the distribution of magnetic chips in the X, Y, and Z directions of the rock sample. Finally, the rock sample is opened by physical rock breaking method to observe the distribution of magnetic chips. At the same time, the 3D fracture surface of the broken rock sample is reconstructed, such as Figure 4 shown.

[0080] Experimental results: A large magnetic anomaly appears on the X-axis after 90 mm, indicating that there are a lot of magnetic chips in the crack after 90 mm, as shown in Table 1 and Figure 5 As shown in Table 2 and Figure 6 As shown, it means that the crack is temporarily blocked at 90 mm in the X direction and the temporary blocking agent continues to migrate into the crack to cause temporary blocking, which eventually causes the acid fracturing crack to deflect downward by about 30 mm.

[0081] After the measurement, the rock samples were opened using the physical rock breaking method to observe the distribution of temporary plugging agent and the crack expansion morphology. The experimental results show that the temporary plugging of the crack at about 90 mm in the crack forced the crack to turn inside, and it was concluded that adding magnetic chips to the temporary plugging agent to monitor the crack had a good effect.

[0082] Table 1 X-axis magnetic signal data table

[0083] Measuring point coordinates / mm 0 30 60 90 120 150 Magnetic signal data / nt 15.4 15.2 15.6 92.3 161.5 253.8

[0084] Table 2 Y-axis magnetic signal data table

[0085] Measuring point coordinates / mm 0 -10 -20 -30 -40 -50 Magnetic signal data / nt 15.4 15.2 15.6 32.5 36.7 39.8

[0086] On the basis of true triaxial acid fracturing physical simulation, the present invention further adopts the method of adding magnetic chips to the temporary plugging agent to perform temporary plugging acid fracturing in the fracture. The experimental results show that adding magnetic chips to the temporary plugging agent not only does not affect the temporary plugging effect, but also can monitor the fracture morphology through the magnetic field distribution. The design method of the improved temporary plugging agent can accurately determine the temporary plugging acid fracturing of the fracture mouth in the fracture and perform temporary plugging acid fracturing fracture morphology monitoring, which has guiding significance for carrying out temporary plugging acid fracturing construction of carbonate rocks in the well area.

[0087] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A temporary plugging and acid fracturing device based on true triaxial testing, characterized in that: The device comprises: a fracturing unit, a multi-pump parallel injection unit, a 3D fracture reconstruction scanner and a magnetic detection sensor; The fracturing unit is used to perform fracturing on the sample using triaxial stress; the multi-pump parallel injection unit is used to add fracturing fluid to the sample; the 3D fracture reconstruction scanner is used to scan the fracture surface and obtain a fracture surface reconstruction map; the magnetic detection sensor is used to detect magnetic chips and obtain a magnetic field distribution map; Wherein, the fracturing fluid comprises: gel acid solution and granular powder temporary plugging agent containing magnetic chips.

2. The temporary plugging and acid fracturing device based on true triaxial testing according to claim 1 is characterized in that: The device also includes a loading unit for adjusting the triaxial stress.

3. The true triaxial temporary plugging and acid fracturing device according to claim 2 is characterized in that: The loading unit comprises: a stress setting operation room, an X-axis hydraulic cylinder, a Y-axis hydraulic cylinder and a Z-axis hydraulic cylinder.

4. The temporary plugging and acid fracturing device based on true triaxial testing according to claim 1 is characterized in that: The fracturing unit comprises: a pressure plate, a test bench and a fracturing pipeline for conveying hydraulic oil to the stress plate.

5. The temporary plugging and acid fracturing device based on true triaxial testing according to claim 1 is characterized in that: The multi-pump parallel injection unit comprises two parallel fracturing fluid injection pipelines, which are used to add the gel acid solution and the granular powder temporary plugging agent containing magnetic chips into the sample respectively.

6. The true triaxial temporary plugging and acid fracturing device according to claim 1 is characterized in that: The granular powder temporary plugging agent containing magnetic chips comprises: 1% 40-mesh particles, 1% 100-mesh powder and magnetic chips.

7. The temporary plugging and acid fracturing device based on true triaxial testing according to claim 1 is characterized in that: The gel acid solution comprises: 20% hydrochloric acid, 1% iron ion stabilizer and 1% corrosion inhibitor.

8. The true triaxial temporary plugging and acid fracturing device according to claim 1 is characterized in that: The magnetic detection sensor is a three-axis fluxgate magnetometer.

9. The temporary plugging and acid fracturing device based on true triaxial testing according to claim 1 is characterized in that: The device also includes a temporary plugging agent preparation unit, which is used to inject magnetic chips into the temporary plugging agent.

10. A crack monitoring method using the device of any one of claims 1 to 9, characterized in that: The method comprises: Applying triaxial stress to the specimen using a fracturing unit; When the pressure is stable, injecting fracturing fluid into the sample using a multi-pump parallel injection unit; After temporary plugging and acid fracturing, the magnetic detection sensor is used to detect the magnetic chips distribution and obtain the magnetic chips distribution map; Use a 3D crack reconstruction scanner to scan the crack surface after breaking the sample and obtain a crack surface reconstruction image; Obtaining a crack monitoring result according to the magnetic chip distribution map and the crack surface reconstruction map; Wherein, the fracturing fluid comprises: gel acid solution and granular powder temporary plugging agent containing magnetic chips.

11. The crack monitoring method according to claim 10, characterized in that: Injecting fracturing fluid into the sample using a multi-pump parallel injection unit, comprising: Injecting gel acid solution into the sample using the multi-pump parallel injection unit; When the sample is broken, the multi-pump parallel injection unit is used to inject a temporary plugging agent containing magnetic chips into the sample.

12. The crack monitoring method according to claim 10, characterized in that: The method further includes: adjusting the triaxial stress using a loading unit.

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