A test system and method for testing shale gas extraction casing damage

Abstract

The present application provides a kind of for testing shale gas exploitation casing damage test system, comprising: test box device, it includes test box body and the simulation rock mass being arranged in the test box, and simulation casing is arranged in the simulation rock mass;Counterforce frame, the counterforce frame includes frame main body and the displacement mechanism being arranged in the top of frame main body, the test box device is placed in the frame main body;And for loading the loading device of simulation rock mass, the loading device is connected with the displacement mechanism;Wherein, the test system can simulate different working conditions, to carry out simulation test in corresponding working condition, to carry out simulation test in corresponding working condition.The present application also provides a kind of for testing shale gas exploitation casing damage test method.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of casing testing, and particularly relates to a test system and method for testing a shale gas exploitation casing. BACKGROUND

[0002] As a clean energy resource, shale gas is an important transitional fuel for China to develop a low-carbon economy, and it is of great significance to realize efficient exploitation of shale gas. Casing damage has become a common problem in shale gas exploitation at home and abroad, and the casing damage rate has a rising trend year by year. Casing damage can cause problems such as the inability to smoothly lower the bridge plug during fracturing, the inability to smoothly drill the bridge plug with the coiled tubing, and even the forced abandonment of fracturing operations in some well sections, which seriously affects the improvement of the single well production of shale gas horizontal wells.

[0003] During shale gas exploitation, fracturing fluid can penetrate through hydraulic fractures, micro annular fractures, and axial fractures formed along the wellbore, enter the nearby fault zone, and activate the fault to induce earthquakes, thereby causing casing damage, which is the main reason for casing damage. There are many types of casing damage, among which axial shrinkage is mainly caused by the increase of axial tension due to the increase of external surrounding rock pressure, squashing deformation is caused by the extrusion of casing by uneven external force, bending deformation is mainly caused by the increase of local one-way force, and shear deformation is mainly caused by the sharp increase of local shear stress. In addition, casing deformation often occurs in multiple places, and the types of deformation are often a combination of multiple forms.

[0004] In actual engineering, shale gas exploitation can affect the surrounding geological environment, and the surrounding geological environment in turn can affect the stability and deformation characteristics of the casing. These problems involve multi-field and multi-phase coupling, and it is often difficult to analyze them through theory and numerical methods, so it is necessary to rely on actual engineering for detailed research through indoor simulation tests. However, there is currently no integrated physical simulation test system that can comprehensively consider the conditions of hydraulic fracturing, fault slip, and casing shear.

[0005] Therefore, there is an urgent need for a multifunctional simulation test system and method for testing shale gas exploitation casings to truly reflect the actual engineering situation and more deeply study the casing damage problems in shale gas exploitation. SUMMARY

[0006] In view of the above technical problems, the present application aims to provide a test system and method for testing shale gas exploitation casing damage, which can truly simulate various conditions in shale gas exploitation, thereby realizing independent and coupled conditions of hydraulic fracturing, fault slip, and casing shear.

[0007] To this end, according to a first aspect of the present application, there is provided a test system for testing damage of a shale gas exploitation casing, comprising: a test box device comprising a test box body and a simulated rock mass arranged in the test box, and a simulated casing arranged in the simulated rock mass; a counterforce frame comprising a frame body and a displacement mechanism arranged at a top of the frame body, the test box device being placed in the frame body; and a loading device for loading the simulated rock mass, the loading device being connected with the displacement mechanism; wherein the test system is capable of simulating different working conditions so as to perform simulated tests under corresponding working conditions.

[0008] In one embodiment, the test box body comprises a bottom plate and a plurality of side plates, at least one of the plurality of side plates being provided with an observation window.

[0009] In one embodiment, the simulated rock mass is configured according to a predetermined similarity ratio and using materials similar to parameters of a prototype rock mass.

[0010] In one embodiment, the simulated casing is provided with a plurality of perforation holes, and the simulated casing is capable of injecting fracturing fluid through the perforation holes.

[0011] By adjusting the number and spatial distribution of the perforation holes, different hydraulic fracturing working conditions can be simulated.

[0012] In one embodiment, a plurality of partitions extending in an axial direction are arranged inside the simulated casing to form sub-zones.

[0013] By injecting fracturing fluid with different pressures into different partition sub-zones, the influence of local stress difference on deformation of the simulated casing can be simulated, and by adjusting the number and distribution angle of the partitions, casing damage at different positions can be simulated.

[0014] In one embodiment, the frame body comprises a frame base and a frame column fixedly connected with the frame base, and the displacement mechanism is arranged at a position close to an upper end of the frame column.

[0015] In one embodiment, the displacement mechanism comprises a pair of longitudinal beams fixedly connected with the frame body, a plurality of cross beams arranged above the longitudinal beams, and a plurality of sliders adapted to be mounted on the cross beams, the cross beams being capable of sliding along the longitudinal beams, and the sliders being capable of sliding along the cross beams.

[0016] In one embodiment, the cross beam is provided with a through sliding groove extending in an axial direction of the cross beam, and the slider is configured to comprise a slider body and a connecting portion fixedly arranged at a lower end of the slider body, the connecting portion extending to a lower end of the cross beam through the through sliding groove.

[0017] In one embodiment, a first guide rail is arranged on the cross beam, and a second guide rail is arranged on the longitudinal beam.

[0018] In one embodiment, the loading device comprises a plurality of servo actuators, a fixed base fixed at the upper and lower ends of the servo actuators, and a loading distribution plate,

[0019] The upper end of the servo actuator is fixedly connected with the corresponding slider through the fixed base, and the servo actuator can be in contact with the simulated rock mass through the loading distribution plate, so as to exert a load on the simulated rock mass.

[0020] According to a second aspect of the present application, a test method for testing damage of a shale gas exploitation casing is provided, comprising the following steps:

[0021] Step one: providing a test system according to the above;

[0022] Step two: making different simulated casings and simulated rock masses according to predetermined parameters, and the simulated rock mass is formed by pouring a cement ring in the test box through a mold;

[0023] Step three: simulating different working conditions through the simulated test system, and performing simulated tests under corresponding working conditions;

[0024] Wherein, independent and coupled tests under hydraulic fracturing working conditions, fault shear slip working conditions and casing shear working conditions can be performed through the simulated test system.

[0025] In one embodiment, in step two, the simulated casing is fixed in the test box and its two ends are sealed, and the simulated rock mass is formed by pouring a cement ring around the simulated casing through a mold.

[0026] In one embodiment, a pressure sensor is pre-embedded in the simulated rock mass, and the change of the stress field in the simulated rock mass can be measured through the pressure sensor.

[0027] In one embodiment, in step two, the simulated rock mass is formed by pre-embedding a plug inside it to simulate a fault.

[0028] In one embodiment, in step three, a hydraulic fracturing test is performed by injecting a pressurized fracturing fluid into the simulated casing through a pressure pump to simulate the hydraulic fracturing working condition.

[0029] In one embodiment, in step three, a fault shear slip test is performed by gradually applying vertical pressure to the top of the simulated rock mass through the loading device to simulate the fault shear slip phenomenon.

[0030] In one embodiment, in step three, the loading device is used to apply vertical pressure on the top of the simulated rock mass in steps until the simulated casing shearing failure occurs, so as to simulate the casing shearing failure condition and carry out the casing damage test.

[0031] Compared with the prior art, the present application has the following advantages:

[0032] The test system and method for testing shale gas exploitation casing damage according to the present application can simulate different conditions and carry out simulation tests under corresponding conditions, can truly simulate various conditions in shale gas exploitation, can realize independent and coupled effects of hydraulic fracturing, fault slip and casing shearing conditions, and can study different casing deformation and damage modes such as extrusion, bending and shearing and the interaction mechanism between the formation and the casing, so as to guide the actual casing design and deformation and damage diagnosis of shale gas exploitation engineering. The test system can provide an integrated solution for simulating complex conditions in actual shale gas exploitation engineering, and the utilization rate of the test system is high. The loading device can be moved arbitrarily and can be replaced by different loading devices through the connecting transmission plate arranged on the cross beam, and the cross beam can be additionally provided according to the loading range to realize multi-region synchronous loading. The model rock mass can be selected according to the actual engineering, and the working condition adaptability of the test system is strong. In addition, the test system adopts modular design, and each functional module is relatively independent, which is very convenient for future maintenance and function expansion. BRIEF DESCRIPTION OF DRAWINGS

[0033] The present application will be described below with reference to the accompanying drawings.

[0034] Figures 1 to 3 The structure of the test system for testing shale gas exploitation casing damage according to the present application is schematically shown.

[0035] Figure 4 The structure of the loading device is schematically shown.

[0036] Figure 5 is a schematic view of the hydraulic fracturing test condition.

[0037] Figure 6 is a schematic view of the fault slip test condition.

[0038] Figure 7 is a schematic view of the non-penetrating fault under the fault slip test condition.

[0039] Figure 8 is a schematic view of the penetrating fault under the fault slip test condition.

[0040] Figure 9 The lateral cross-sectional view of the simulated casing is schematically shown.

[0041] In this application, all drawings are schematic and are used only to illustrate the principles of the invention, and are not drawn to scale. Detailed Implementation

[0042] The invention will now be described with reference to the accompanying drawings.

[0043] In this application, it should be noted that... Figure 1 The direction along the X-axis is defined as "lateral", the direction along the Y-axis is defined as "longitudinal", and the direction along the Z-axis is defined as "vertical".

[0044] It should also be noted that the directional terms or qualifiers such as "up" and "down" used in this application are all specific to the referenced appendix. Figure 1 In other words, they are not used to define the absolute position of the components involved, but can vary depending on the specific circumstances.

[0045] Figures 1 to 3 The structure of a test system 100 for testing casing damage in shale gas extraction according to the present invention is shown schematically. Figure 1 As shown, the test system 100 includes a test chamber device 1, a reaction frame 2, and a loading device 3. The test chamber device 1 includes a test chamber body 101 and a simulated rock mass 102 arranged within the test chamber 101, as well as a simulated sleeve 103 disposed within the simulated rock mass 102. The reaction frame 2 includes a frame body 200 and a displacement mechanism 210 disposed on top of the frame body 200. The test chamber device 1 is placed inside the frame body 200. The loading device 3 is used to load the simulated rock mass 103, and the loading device 3 is connected to the displacement mechanism 210.

[0046] The test system 100 for testing casing damage in shale gas extraction according to the present invention can simulate different working conditions, thereby conducting simulation tests under corresponding working conditions. It can realistically simulate various conditions in shale gas extraction, realizing the independent and coupled effects of hydraulic fracturing, fault slip, and casing shear conditions. This allows for the study of different casing deformation and failure modes such as flattening, bending, and shearing, as well as the interaction mechanism between the formation and the casing, guiding the actual casing design and deformation and failure diagnosis in shale gas extraction engineering. The test system 100 can simulate the following working conditions: hydraulic fracturing test, fault shear slip test, casing shear test, hydraulic fracturing and fault shear slip dual-condition coupled test, fault shear slip and casing shear dual-condition coupled test, and hydraulic fracturing, fault shear slip, and casing shear three-condition coupled test.

[0047] According to the present invention, such as Figure 2As shown, the test box 101 comprises a bottom plate 1015 and a plurality of side plates, at least one of which is provided with an observation window. The observation window is made of organic glass, through which the surface deformation of the simulated rock mass 102 can be observed.

[0048] In one embodiment, the test box 101 is configured as an open-ended cuboid cavity structure, and the side plates of the test box 101 include a front box panel 1011, a back box panel opposite to the front box panel 1011, and two box side plates 1013 and 1014.

[0049] According to the present application, the simulated rock mass 102 is configured according to a predetermined similarity ratio and similar materials to the parameters of the prototype rock mass. The simulated casing 103 is manufactured according to the similarity ratio and the parameters of the prototype casing, and a plurality of perforation holes 1031 can be provided on the simulated casing 103 by drilling.

[0050] In this embodiment, the simulated casing 103 can inject fracturing fluid through the perforation holes 1031, and by adjusting the number and spatial distribution of the perforation holes 1031, different hydraulic fracturing conditions can be simulated. Inside the simulated casing 103, a plurality of axial partitions 1032 can be provided to form partitions, and by injecting fracturing fluid with different pressures into different partition areas, the influence of local stress difference on the deformation of the simulated casing 103 can be simulated. By adjusting the number and distribution angle of the partitions 1032, the damage of the casing at different positions can be simulated.

[0051] As shown in the figure, Figure 3 The frame body 200 comprises a frame base 201 and a frame column 202 fixedly connected with the frame base 201, and the frame column 202 is perpendicular to the frame base 201. Adjacent frame columns 202 are connected by connecting rods, which are horizontally arranged and located at the upper middle part of the frame base 201. This is conducive to ensuring the stability of the frame body 200.

[0052] The displacement mechanism 210 is arranged on the frame column 202 and located at the upper end of the frame column 202. As shown in the figure, Figure 3 The displacement mechanism 210 comprises a pair of longitudinal beams 204 fixedly connected with the frame columns 202 in the frame body 200, a plurality of cross beams 203 arranged on the longitudinal beams 204, and a plurality of sliding blocks 205 adapted to be installed on the cross beams 203. The cross beams 203 can slide along the longitudinal beams 204, and the sliding blocks 205 can slide along the cross beams 203. Therefore, the sliding blocks 205 can move in the entire horizontal plane.

[0053] In one embodiment, a through slot extending along the axial direction of the cross beam 203 is provided on the cross beam 203. The slider 205 is configured in a T shape, including a slider body and a connecting portion fixed to the lower end of the slider body. The connecting portion extends through the through slot to the lower end of the cross beam 203, and the lower end surface of the slider body is on the upper end surface of the cross beam 203.

[0054] A first guide rail 2031 extending along the cross beam direction is provided on the upper end surface of the cross beam 203, and a second guide rail 2041 extending along the longitudinal beam direction is provided on the upper end surface of the longitudinal beam 204. The lower end surface of the cross beam 203 is adapted to the second guide rail 2041, so that the cross beam 203 can move along the second guide rail 2041. The lower end surface of the slider body of the slider 205 is adapted to the first guide rail 2031, so that the slider 205 can move along the first guide rail 2031.

[0055] The displacement mechanism 210 in the counter-force frame 2 can realize the horizontal movement of the slider 205 along the first guide rail 2031 and the second guide rail 2041 through a control system (not shown). By changing the number and position of the cross beams 203, different positions of loading can be realized.

[0056] According to the present application, as shown in Figure 1 and Figure 4 The loading device 3 is arranged between the displacement mechanism 210 and the simulated rock mass 102. The loading device 3 includes a plurality of servo actuators 301, a fixed base 302 fixed to the upper and lower ends of each servo actuator, and a loading distribution plate 304. The upper end of the servo actuator 301 is fixedly connected to the lower end surface of the corresponding slider 205 through the fixed base 302. The fixed base 302 can be fixedly connected to the slider 205, for example, by fixed bolts 303. The servo actuator 301 can be in contact with the simulated rock mass 102 through the loading distribution plate 304, thereby applying a load to the simulated rock mass 102. A uniform load can be applied to the simulated rock mass 102 through the loading distribution plate 304. By changing the number and position of the servo actuators 301 and the shape of the loading distribution plate 304, different forms and areas of loading can be realized.

[0057] According to the present application, a test method for testing damage of a shale gas exploitation casing is also provided, comprising the following steps: firstly, providing the test system 100 according to the present application. Then, different simulated casings 102 and simulated rock masses 103 are made according to predetermined parameters. The simulated rock mass 102 is formed by pouring a cement ring in the test box 101 through a mold. Then, different working conditions are simulated through the simulated test system 100, and the simulated tests under corresponding working conditions are carried out. Through the simulated test system 100, independent and coupled tests under hydraulic fracturing working condition, fault shear slip working condition and casing shear working condition can be carried out, including hydraulic fracturing test, fault shear slip test, casing shear test, hydraulic fracturing and fault shear slip double-working-condition coupled test, fault shear slip and casing shear double-working-condition coupled test, and hydraulic fracturing, fault shear slip and casing shear triple-working-condition coupled test.

[0058] The test method for testing damage of a shale gas exploitation casing according to the present application is described below by taking simulated tests under specific working conditions as examples.

[0059] The working mode of the hydraulic fracturing test is as follows:

[0060] Firstly, a hole is drilled on the simulated casing 103 at a specified position to set a perforation hole 1031, both ends of the simulated casing 103 are fixed on the side plates of the test box 101, and a seal is formed between both ends of the simulated casing 103 and the test box 101. Cement is poured in the test box 101 by using a mold, and a cement ring is poured around the simulated casing 103. The simulated rock mass 102 is poured in the test box 101 to a specified height. After the simulated rock mass 102 reaches the strength requirement, the pressure pump is used to inject pressurized fracturing fluid into the simulated casing 103, and the change of the fracturing fluid reading is observed to study the influence of hydraulic fracturing.

[0061] In the present embodiment, during the process of pouring the cement ring to prepare the simulated rock mass 102, a pressure sensor (not shown) is pre-embedded, and the change of the stress field in the simulated rock mass 102 can be measured through the pressure sensor. The influence of hydraulic fracturing on the surface deformation of the rock mass can be obtained by using the digital photography method through the plexiglass observation window. In the fracturing test, different hydraulic fracturing working conditions can be simulated by changing the number and spatial distribution of the perforation holes 1031.

[0062] The working mode of the fault shear slip test is as follows:

[0063] The both ends of the test box 101 are opened and sealed, and the simulated rock mass 102 is poured. During the pouring process, steel inserts of different shapes, sizes and thicknesses are arranged in different areas. After the simulated rock mass 102 is cured to a certain extent, the inserts are pulled out to preform a non-penetrating fault 1041 (see Figure 7), the upper and lower blocks of the simulated rock mass can be poured and the interface between the rock masses can be roughened or filled with different materials to simulate real faults with different geometric sizes and mechanical parameters. The loading device 3 is used to apply vertical pressure on the top of the rock mass to simulate different fault shear slip phenomena. The displacement change of the fault is obtained by using a digital camera through the lateral plexiglass observation window. Thus, the fault shear slip phenomenon is simulated, and the fault shear slip test is performed.

[0064] The working mode of the casing damage test is as follows:

[0065] First, the two ends of the simulated casing 103 are sealed, and holes are drilled on the simulated casing 103 at designated positions to set perforation holes 1031. The simulated casing 103 is fixed to the two ends of the test box 101, and the two ends of the simulated casing 103 are sealed with the test box 101. The mold is used to pour cement in the test box 101, and the cement ring is poured around the simulated casing 103. During the pouring process, steel inserts of different shapes, sizes and thicknesses are arranged in different areas to pre-set the through fault plane 1042. The loading device 3 is used to apply vertical load on the fault to shear the casing until the casing is damaged. By changing the fault occurrence and the position relative to the simulated casing 103, different casing shear damage working conditions can be simulated, and the casing damage test can be performed.

[0066] In this embodiment, the inside of the simulated casing 103 can be divided into partitions by the partition 1032. The influence of local stress difference on the deformation of the simulated casing 103 is simulated by injecting fracturing fluid with different pressures into different partitions. By changing the number and distribution angle of the partition 1032, the simulation of casing damage at different positions can be realized.

[0067] The working mode of the hydraulic fracturing and fault shear slip double working condition coupling test is as follows:

[0068] First, the two ends of the simulation casing 103 are sealed, and holes are drilled on the simulation casing 103 at designated positions to set perforation holes 1031, the simulation casing 103 is fixed at the two ends of the test box 101, and a seal is formed between the two ends of the simulation casing 103 and the test box 101. The mold is used to cast cement in the test box 101, and a cement ring is cast around the simulation casing 103. During the casting process, steel inserts of different shapes, sizes and thicknesses are arranged in different areas, and the non-penetrating fault 1041 is precast after the simulation rock mass 102 is cured to a certain extent. After the simulation rock mass 102 reaches the strength requirement, the pressure pump is used to inject pressurized fracturing fluid into the simulation casing 103, and the influence of hydraulic fracturing is studied by observing the change of fracturing fluid reading. The change of rock mass stress field can be obtained through the pre-embedded pressure sensor, and the displacement field of the fault in the hydraulic fracturing process can be obtained by using the digital photography method through the organic glass observation window. Different hydraulic fracturing conditions can be simulated by changing the number and spatial distribution of the perforation holes 1031.

[0069] The working mode of the fault shear slip and casing shear double-working condition coupling test is as follows:

[0070] First, the two ends of the simulation casing 103 are sealed, and holes are drilled on the simulation casing 103 at designated positions to set perforation holes 1031, the simulation casing 103 is fixed at the two ends of the test box 101, and a seal is formed between the two ends of the simulation casing 103 and the test box 101. The mold is used to cast cement in the test box 101, and a cement ring is cast around the simulation casing 103. During the casting process, steel inserts of different shapes, sizes and thicknesses are arranged in different areas, and the non-penetrating fault 1041 is precast after the simulation rock mass 102 is cured to a certain extent. After the simulation rock mass 102 reaches the strength requirement, the pressure pump is used to inject pressurized fracturing fluid into the simulation casing 103, and the influence of hydraulic fracturing is studied by observing the change of fracturing fluid reading. The change of rock mass stress field can be obtained through the pre-embedded pressure sensor, and the displacement field of the fault in the hydraulic fracturing process can be obtained by using the digital photography method through the organic glass observation window. Different hydraulic fracturing conditions can be simulated by changing the number and spatial distribution of the perforation holes 1031.

[0071] The working mode of the fault shear slip and casing shear double-working condition coupling test is as follows:

[0072] First, the two ends of the simulation casing 103 are sealed, and holes are drilled on the simulation casing 103 at designated positions to set perforation holes 1031, the simulation casing 103 is fixed at the two ends of the test box 101, and a seal is formed between the two ends of the simulation casing 103 and the test box 101. Cement is poured in the test box 101 using a mold, and a cement ring is poured around the simulation casing 103. During pouring, steel inserts of different shapes, sizes and thicknesses are arranged in different areas, and the non-penetrating fault 1041 is precast after the simulation rock mass is cured to a certain extent. After the simulation rock mass 102 reaches the strength requirement, the pressure pump is used to inject the pressurized fracturing fluid into the simulation casing 103, the influence of hydraulic fracturing is studied by observing the reading change of the fracturing fluid, the change of the rock mass stress field can be obtained through the pre-embedded pressure sensor, and the displacement field of the fault in the hydraulic fracturing process can be obtained by using the digital photography method through the organic glass observation window. After the simulation rock mass 102 reaches the strength requirement, the vertical pressure is applied on the top of the rock disc through the loading device 3 to simulate different fault shear slip phenomena, and the displacement change of the fault is obtained by using the digital photography method through the lateral organic glass observation window. The number and spatial distribution of the perforation holes 1031 can be changed to simulate different hydraulic fracturing conditions.

[0073] The test system 100 and the method for testing damage of a shale gas exploitation casing according to the present application can simulate different working conditions, so that the simulation test under the corresponding working condition can be carried out, the various conditions in the shale gas exploitation can be truly simulated, the independent and coupling effects of the hydraulic fracturing, the fault slip and the casing shear working condition can be realized, so that different casing deformation and damage modes such as extrusion, bending and shear and the interaction mechanism between the formation and the casing are studied, which is used for guiding the casing design and deformation and damage diagnosis in the shale gas exploitation engineering. An integrated solution for simulating the complex working condition in the actual shale gas exploitation engineering is provided, and the utilization rate of the test system is high. The loading device 3 can be arbitrarily moved, different loading devices can be replaced through the connecting transmission plate arranged on the cross beam 203, and multiple regions can be loaded synchronously by adding the cross beam 203 according to the loading range, the model rock mass 102 can be selected according to the actual engineering, and the working condition adaptability of the test system 100 is strong. In addition, the test system 100 adopts a modular design, and each functional module is relatively independent, which is very convenient for future maintenance and function expansion.

[0074] In the description of the present application, it should be understood that the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0075] In addition, in this application, unless otherwise clearly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0076] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In this specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0077] Finally, it should be noted that the above only describes the preferred embodiments of the present application and does not constitute any limitation on the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or replace some technical features with equivalent ones. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A test system for testing damage of shale gas exploitation casing, comprising: a test box device (1) comprising a test box body (101) and a simulated rock mass (102) arranged in the test box body, and a simulated casing (103) arranged in the simulated rock mass, the simulated casing being provided with a plurality of perforation holes (1031) through which the casing can be injected with fracturing fluid, different hydraulic fracturing conditions can be simulated by adjusting the number and spatial distribution of the perforation holes, a plurality of axially extending partitions (1032) are arranged in the interior of the simulated casing to form sub-zones, the influence of local stress difference on deformation of the simulated casing can be simulated by injecting fracturing fluid with different pressures into different partition sub-zones, and casing damage at different positions can be simulated by adjusting the number and distribution angle of the partitions; a counterforce frame (2) comprising a frame body (200) and a displacement mechanism (210) arranged on the top of the frame body, the test box device being placed in the frame body; and a loading device (3) for loading the simulated rock mass, the loading device being connected with the displacement mechanism; wherein the test system can simulate different conditions to perform simulated tests under corresponding conditions. The test box body comprises a bottom plate and a plurality of side plates, at least one of the plurality of side plates being provided with an observation window.

2. The test system of claim 1, wherein, The simulated rock mass is configured according to a predetermined similarity ratio and using materials similar to parameters of a prototype rock mass.

3. The test system of claim 1 or 2, wherein, The frame body comprises a frame base (201) and a frame column (202) fixedly connected with the frame base, and the displacement mechanism is arranged at a position close to the upper end of the frame column.

4. The test system of claim 1, wherein, The displacement mechanism comprises a pair of longitudinal beams (204) fixedly connected with the frame body, a plurality of cross beams (203) arranged on the longitudinal beams, and a plurality of sliders (205) adapted to be mounted on the cross beams, the cross beams being capable of sliding along the longitudinal beams, and the sliders being capable of sliding along the cross beams.

5. The test system of claim 1 or 4, wherein, The cross beam is provided with a through sliding groove extending in the axial direction of the cross beam, and the slider is configured to comprise a slider body and a connecting portion fixedly connected with the lower end of the slider body, the connecting portion extending through the through sliding groove to the lower end of the cross beam.

6. The test system of claim 5, wherein, The cross beam is provided with a first guide rail (2031), and the longitudinal beam is provided with a second guide rail (2041).

7. The test system of claim 5, wherein, The loading device comprises a plurality of servo actuators (301), a fixed base (302) fixedly connected with the upper and lower ends of the servo actuators, and a loading distribution plate (304), 8. The test system of claim 5, wherein, the upper end of the servo actuator being fixedly connected with the corresponding slider through the fixed base, and the servo actuator being capable of contacting the simulated rock mass through the loading distribution plate to apply a load to the simulated rock mass.

9. A test method for testing damage of shale gas exploitation casing, comprising the following steps: Step 1: providing the test system according to any one of claims 1 to 8; Step 2: making different simulated casings and simulated rock masses according to predetermined parameters, and the simulated rock mass being formed by pouring a cement ring in the test box body through a mold. ​ Step three: simulate different working conditions by the test system and carry out simulation test under corresponding working conditions; wherein Through the test system, independent and coupled tests under hydraulic fracturing working condition, fault shear slip working condition and casing shear working condition can be carried out.

10. The test method of claim 9, wherein, In step two, the simulation casing is fixed in the test box body and its two ends are sealed, and the simulation rock mass is formed by pouring cement ring around the simulation casing through a mold.

11. The test method of claim 10, wherein, A pressure sensor is pre-embedded in the simulation rock mass, and the change of stress field in the simulation rock mass can be measured through the pressure sensor.

12. The test method according to claim 9 or 10, characterized in that, In step two, the simulation rock mass is formed by pre-embedding a plug in its interior.

13. The test method of claim 10, wherein, In step three, the hydraulic fracturing test is carried out by injecting pressurized fracturing fluid into the simulation casing through a pressure pump to simulate the hydraulic fracturing working condition.

14. The test method of claim 12, wherein, In step three, the fault shear slip test is carried out by gradually applying vertical pressure on the top of the simulation rock mass through the loading device to simulate the fault shear slip phenomenon.

15. The test method of claim 12, wherein, In step three, the casing damage test is carried out by gradually applying vertical pressure on the top of the simulation rock mass through the loading device until the simulation casing is sheared and damaged to simulate the casing shear damage working condition.

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