Device and method for testing integrity of cement sheath of shale oil in-situ conversion well

Abstract

The invention discloses a shale oil in-situ conversion well cement sheath integrity testing device and method. The device comprises an original scale shaft structure experiment testing unit; the original-scale shaft structure experiment testing unit comprises a pressure loading system, a heating system and a shaft experiment device; wherein the pressure loading system comprises a loading pressure head, a base ring, a base and pressure equipment; the heating system comprises an electric heating rod; the shaft experiment device comprises a cement sheath, a sleeve and a simulated stratum, a loading pressure head in the pressure loading system is arranged at the top of the shaft structure, a base ring is arranged at the bottom of the shaft structure, and a base is arranged at the lower part of the base ring; an electric heating rod in the heating system is arranged in the center of the sleeve, a cement sheath is arranged outside the sleeve, and a simulated stratum is arranged outside the cement sheath.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas drilling and production engineering technology, and in particular to a testing device and method for the integrity of cement sheath in situ conversion wells of shale oil. Background Art

[0002] my country's shale oil resources are very rich, but most of the shale oil resources are relatively low in maturity, and it is necessary to convert the medium and low maturity shale oil in situ. The research on the mechanism of in-situ conversion technology mainly draws on the theoretical research in the field of in-situ conversion of oil shale and heavy oil upgrading and exploitation, and mainly examines the mechanism of conversion of heavy heavy oil, asphalt, kerogen and other solid organic matter in the reservoir into light oil and gas during continuous artificial heating. In the process of in-situ heating and exploitation of shale oil, the ultra-high temperature (350℃-650℃) and high pressure (40MPa) of shale oil in-situ conversion wells have a great influence on the mechanical properties of cement sheath and oil casing, resulting in complex working conditions downhole, which poses a more severe challenge to the stability and integrity of the wellbore.

[0003] Relevant data show that with the increase in the scale of heating mining, the probability of casing change, leakage, and seal failure in the wellbore is on the rise, and the wellbore integrity damage rate in some blocks has reached 30%. The integrity of the wellbore is mainly due to the failure of the seal and cementation of the cement ring under high temperature and high pressure, which causes leakage and slippage in the wellbore, resulting in a large amount of economic losses.

[0004] Therefore, it is necessary to test and evaluate the isolation capacity and bonding strength of the cement sheath of the wellbore under in-situ conversion conditions. How to test and evaluate the key parameters of the integrity of the cement sheath under the coupling of multiple factors under high temperature and high pressure acidic gas corrosion conditions is an urgent problem to be solved. Summary of the invention

[0005] The present application provides a testing device and method for the integrity of the cement ring of a shale oil in-situ conversion well. The designed experimental device is used to simulate the downhole temperature, pressure, and acidic corrosive gas conditions of the shale oil in-situ conversion well to test the sealing integrity and bonding surface integrity of the cement ring, so as to efficiently test and evaluate the integrity of the cement ring of the shale oil in-situ heating well under the influence of multiple factors.

[0006] In a first aspect, the present application provides a testing device for cement sheath integrity in a shale oil in-situ conversion well, the device comprising: an original-scale wellbore structure experimental testing unit; the original-scale wellbore structure experimental testing unit comprises: a pressure loading system, a heating system and a wellbore experimental device;

[0007] Wherein, the pressure loading system comprises a loading pressure head, a base ring and a pressure pump;

[0008] The heating system comprises an electric heating rod;

[0009] The wellbore experimental device comprises: a cement ring, a casing, and a simulated formation;

[0010] The loading pressure head in the pressure loading system is arranged at the top of the wellbore structure, and the base ring is arranged at the bottom of the wellbore structure;

[0011] In the heating system, an electric heating rod is arranged at the center of the casing, a cement ring is arranged outside the casing, and a simulated stratum is arranged outside the cement ring.

[0012] In a second aspect, an embodiment of the present invention provides a method for testing the integrity of a cement sheath in a shale oil in-situ conversion well, the method comprising:

[0013] Pre-completing the first wellbore experimental device and the second wellbore experimental device;

[0014] Connecting the pressure pump to the first wellbore experimental device and sealing the first wellbore experimental device;

[0015] The sealed wellbore test device is pressurized by a pressure pump to measure the cement sheath isolation strength at room temperature;

[0016] After measuring the cement sheath isolation strength at room temperature, a loading pressure head is placed on the first wellbore experimental device, and the load of the loading pressure head is changed to determine the bonding strength of the cement sheath at room temperature;

[0017] Connecting the pressure pump to the second wellbore experimental device and sealing the second wellbore experimental device;

[0018] The electric heating rod in the heating system is placed in the casing of the second wellbore experimental device and connected to the pressure pump. After the heating rod reaches a predetermined temperature, the heated second wellbore experimental device is pressurized by the pressure pump to measure the cement sheath isolation strength at the predetermined temperature.

[0019] After the cement sheath isolation strength at a predetermined temperature is measured, a loading pressure head is placed on the second wellbore experimental device, and the load amount of the loading pressure head is changed to determine the bonding strength of the cement sheath at different temperatures.

[0020] Compared with the related art, the present application provides a testing device and method for cement ring integrity in shale oil in-situ conversion wells, the testing device includes an original scale wellbore structure experimental testing unit; the original scale wellbore structure experimental testing unit includes: a pressure loading system, a temperature heating system, a pressure acquisition system and a wellbore experimental device; wherein the pressure loading system includes a loading pressure head, a base ring and a pressurizing device; the temperature heating system includes an electric heating rod; the wellbore experimental device includes: a cement ring, a casing and a simulated formation; the loading pressure head in the pressure loading system is arranged at the top of the wellbore structure, and the base ring is arranged at the bottom of the wellbore structure. The electric heating rod in the temperature heating system is arranged at the center of the casing, the casing is arranged outside the cement ring, and the simulated formation is arranged outside the cement ring. An experimental device for evaluating the integrity of the cement ring implemented in the present application can be used to simulate the downhole temperature, pressure and acidic corrosive gas conditions of the shale oil in-situ conversion well to test the sealing integrity and cementing surface integrity of the cement ring, so as to efficiently test and evaluate the integrity of the cement ring under the influence of multiple factors of the shale oil in-situ heating well.

[0021] Other features and advantages of the present application will be described in the following description, and partly become apparent from the description, or be understood by implementing the present application. Other advantages of the present application can be realized and obtained by the schemes described in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are used to provide an understanding of the technical solution of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present application and do not constitute a limitation on the technical solution of the present application.

[0023] Figure 1 This is a schematic diagram of an original-scale wellbore structure experimental test unit according to an embodiment of the present application;

[0024] Figure 2 A schematic diagram of a cement ring core simulation test unit in an exemplary embodiment;

[0025] Figure 3 It is a schematic diagram of the structure of a cement ring core simulation test unit in an exemplary embodiment. DETAILED DESCRIPTION

[0026] The present application describes multiple embodiments, but the description is exemplary rather than restrictive, and it is obvious to those skilled in the art that there may be more embodiments and implementations within the scope of the embodiments described in the present application. Although many possible feature combinations are shown in the drawings and discussed in the specific embodiments, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with any other feature or element in any other embodiment, or may replace any other feature or element in any other embodiment.

[0027] The present application includes and contemplates combinations of features and elements known to those of ordinary skill in the art. The embodiments, features and elements disclosed in the present application may also be combined with any conventional features or elements to form a unique invention scheme defined by the claims. Any features or elements of any embodiment may also be combined with features or elements from other invention schemes to form another unique invention scheme defined by the claims. Therefore, it should be understood that any feature shown and / or discussed in the present application may be implemented individually or in any appropriate combination. Therefore, except for the limitations made according to the attached claims and their equivalents, the embodiments are not subject to other restrictions. In addition, various modifications and changes may be made within the scope of protection of the attached claims.

[0028] In addition, when describing representative embodiments, the specification may have presented the method and / or process as a specific sequence of steps. However, to the extent that the method or process does not rely on the specific order of the steps described herein, the method or process should not be limited to the steps of the specific order described. As will be understood by those of ordinary skill in the art, other sequences of steps are also possible. Therefore, the specific sequence of the steps set forth in the specification should not be interpreted as a limitation to the claims. In addition, the claims for the method and / or process should not be limited to the steps of performing them in the order written, and those skilled in the art can easily understand that these sequences can be changed and still remain within the spirit and scope of the embodiments of the present application.

[0029] The embodiment of the present invention provides a testing device and method for the integrity of cement sheath in shale oil in-situ conversion wells, wherein the testing device comprises an original-scale wellbore structure experimental testing unit; the original-scale wellbore structure experimental testing unit comprises: a pressure loading system, a temperature heating system, a pressure acquisition system and a wellbore experimental device; Figure 1 The schematic diagram of the original scale wellbore structure test unit is shown, 1 is the loading head, 2 is the simulated formation, 3 is the cement ring, 4 is the casing, 5 is the electric heating rod, 6 is the base ring, 7 is the base and 8 is the pressure equipment

[0030] Wherein, the pressure loading system comprises a loading pressure head 1, a base ring 6 and a pressure device 8;

[0031] The heating system comprises an electric heating rod 5;

[0032] The wellbore experimental device comprises: a cement ring 3, a casing 4, and a simulated formation 2;

[0033] The loading pressure head in the pressure loading system is arranged at the top of the wellbore structure, and the base ring is arranged at the bottom of the wellbore structure.

[0034] In the temperature heating system, an electric heating rod is arranged at the center of the casing, a cement ring is arranged outside the casing, and a simulated stratum is arranged outside the cement ring.

[0035] In an exemplary embodiment, the full-scale wellbore structure experimental test unit further includes: a pressure acquisition system; the pressure acquisition system includes: a pressure sensor, a three-way valve and a pipeline

[0036] The pressure collection system is used to collect the pressure of the cement sheath.

[0037] In an exemplary embodiment, the pressure loading system is used to pressurize the cement sheath in the wellbore structure;

[0038] The heating system is used to heat the cement sheath and simulated formation in the wellbore structure;

[0039] The wellbore experimental device is used to simulate the real wellbore structure in the formation to be tested.

[0040] In an exemplary embodiment, the device further comprises: a cement ring core simulation test unit; Figure 2 As shown, the cement ring core simulation test unit includes: a pressure system 200, a pressure acquisition system 210, a heating system 220 and a corrosion simulation system 230;

[0041] The pressure system includes a pressure pump and a confining pressure device;

[0042] The pressure collection system includes: a pressure sensor, a pressure gauge and a water pool;

[0043] The heating system comprises: a heating box;

[0044] The corrosion simulation system: CO2 gas cylinder and liquid injector;

[0045] The CO2 gas cylinder, pressure gauge, injector and pressure pump are connected to the confining pressure device through a six-way valve. The cement ring core is clamped inside the confining pressure device through a clamping device, and the clamping device is connected to the water pool. A heating box is arranged outside the confining pressure device.

[0046] In an exemplary embodiment, the pressure generating system is used to pressurize the cement sheath core;

[0047] Pressure acquisition system, used to collect the pressure of cement sheath core;

[0048] A heating system for heating the cement sheath core;

[0049] The corrosion simulation system is used to inject corrosive fluid into the cement sheath core to simulate the corroded cement sheath.

[0050] The testing device for cement sheath integrity in shale oil in-situ conversion wells implemented in this embodiment has the following technical effects:

[0051] This testing device can realize the cement ring integrity experiment of shale oil in-situ conversion wells with multi-factor coupling effects. Specifically, this testing device can be used to test the cement ring sealing integrity and bonding surface integrity by simulating the downhole temperature, pressure, and acidic corrosive gas conditions of the in-situ conversion well.

[0052] In a second aspect, an embodiment of the present invention provides a method for testing the integrity of a cement sheath in a shale oil in-situ conversion well, the method comprising steps S300-S360;

[0053] S300: Preliminarily completing a first wellbore experimental device and a second wellbore experimental device;

[0054] S310: Connecting the pressure pump to the first wellbore experimental device, and sealing the first wellbore experimental device;

[0055] S320: pressurizing the sealed wellbore test device through a pressure pump to measure the cement sheath sealing strength at room temperature;

[0056] S330: after measuring the cement sheath isolation strength at room temperature, placing a loading pressure head on the first wellbore experimental device, and changing the load of the loading pressure head to determine the bonding strength of the cement sheath at room temperature;

[0057] S340: connecting the pressure pump to the second wellbore experimental device, and sealing the second wellbore experimental device;

[0058] S350: placing an electric heating rod in the heating system in the casing of the second wellbore experimental device and connecting it to a pressure pump, and after the heating rod reaches a predetermined temperature, pressurizing the heated second wellbore experimental device through the pressure pump to measure the cement sheath isolation strength at the predetermined temperature;

[0059] S360: After measuring the cement sheath isolation strength at a predetermined temperature, a loading pressure head is placed on a second wellbore experimental device, and the load amount of the loading pressure head is changed to determine the bonding strength of the cement sheath at different temperatures.

[0060] In an exemplary embodiment, the third wellbore experimental device and the fourth wellbore experimental device are completed in advance;

[0061] The following operations are performed on the third wellbore experimental device and the fourth wellbore experimental device respectively:

[0062] A sealing top plate is placed on the top of the simulated formation of the wellbore experimental device for sealing, and a configured corrosive fluid is injected into the cement ring of the wellbore experimental device to obtain a third wellbore experimental device under corrosive conditions and a fourth wellbore experimental device under corrosive conditions.

[0063] In an exemplary embodiment, after obtaining the third wellbore experimental device under corrosion conditions and the fourth wellbore experimental device under corrosion conditions, the method further includes:

[0064] Connecting the pressure pump to the third wellbore experimental device and sealing the third wellbore experimental device;

[0065] Pressurize the sealed wellbore test device to test the cement sheath sealing strength under normal temperature and corrosion conditions;

[0066] After measuring the cement sheath isolation strength under normal temperature and corrosion conditions, the loading pressure head is placed on the third wellbore experimental device, and the load amount of the loading pressure head is changed to determine the bonding strength of the cement sheath under normal temperature and corrosion conditions.

[0067] In an exemplary embodiment, after obtaining the cement sheaths of the third wellbore test device and the fourth wellbore test device under corrosion conditions, the method further includes:

[0068] Connecting the pressure pump to the fourth wellbore experimental device, placing the electric heating rod in the heating system in the casing of the fourth wellbore experimental device, and sealing the fourth wellbore experimental device;

[0069] The sealed fourth wellbore experimental device was heated to test the cement sheath isolation strength under different temperatures and corrosion conditions;

[0070] After measuring the cement sheath sealing strength under different temperatures and corrosion conditions, the loading pressure head is placed on the fourth wellbore experimental device, and the load amount of the loading pressure head is changed to determine the bonding strength of the cement sheath under different temperatures and corrosion conditions.

[0071] In an exemplary embodiment, a cement sheath stress model under multi-factor conditions is established:

[0072] Based on the casing-cement sheath-formation model, combined with the coupling conditions of multiple factors, Hooke's law, volume strain caused by thermal stress and pore pressure, the constitutive equation of cement sheath is established as follows:

[0073]

[0074] In the formula, σ ij is the cement sheath stress tensor, G is the shear elastic modulus, μ is the Poisson's ratio, △T is the temperature change, δ ij is the Kronecker symbol, θ is the volume strain, ε ij is the strain tensor, p is the pressure inside the pipe, α is the Biot coefficient of the cement sheath, and ω is the thermoelastic effective stress coefficient of the cement sheath.

[0075] To judge the failure of cement ring seal, the cement ring material is simplified to an ideal elastic-plastic material, and the Mohr-Coulomb criterion is used to describe the plastic behavior of the material:

[0076]

[0077] σ1, σ2, and σ3 are the axial stresses obtained from the triaxial test, in MPa; is the internal friction angle of rock and soil, in degrees; C is the cohesion of cement sheath, in MPa. The decrease in cement sheath strength caused by acidic gas corrosion can be expressed by the changes in the internal friction angle and cohesion of cement paste.

[0078] The sealing performance of cement sheath is mainly composed of three microscopic forces: capillary pressure in cement stone, fluid flow resistance in cement stone, and hydrostatic pressure of free water in cement stone.

[0079] Analyze the stress of the fluid in the pores of the cement sheath. Assuming the pressure difference between the upper and lower ends of the cement sheath is P1-P2, the hydrostatic pressure of free water is G, the fluid flow resistance is f, and the interface capillary pressure is Pc, the flow pressure difference expression is:

[0080]

[0081] The ultimate dynamic shear stress of the fluid is τ0, the average void radius is r, the density of water is ρ, and the length of the cement segment is y. PC is related to factors such as the fluid interfacial tension, the pore diameter, and the wetting angle.

[0082] The compressive stress on the cement sheath in the radial direction increases, and it is subjected to additional shear stress in the tangential direction. Since the tensile strength of the cement sheath is much smaller than its compressive strength, the cement sheath fails mainly in the form of tangential tensile failure.

[0083] P1S 环 ≤μ(P2+P3)S 胶

[0084] P1 is the cement sheath shear force, P2 and P3 are the external squeeze loads of the formation and casing, and μ is the friction coefficient of the cementing surface. When the cement sheath shear stress is greater than the friction force of the cementing surface, the cementing interface slips and the cement sheath is sheared and damaged. At the macro level, the integrity failure of the cement sheath can be judged based on the isolation capacity and cementing strength as evaluation indicators.

[0085] Based on the above analysis, experimental tests were carried out according to orthogonal experimental design. The experimental orthogonal factors included temperature, pressure, corrosion conditions, load, and cementing cement. The experimental evaluation indicators were cement sheath plugging ability and cement sheath bonding strength.

[0086] For the full-scale wellbore structure experimental test unit, the following experimental steps can be performed according to the orthogonal experiment:

[0087] S400: prefabricate a first wellbore experimental device, a second wellbore experimental device, a third wellbore experimental device, and a fourth wellbore experimental device;

[0088] S410: Connecting the pressure pump to the first wellbore experimental device, and sealing the first wellbore experimental device;

[0089] S420: pressurizing the sealed wellbore test device through a pressure pump to measure the cement sheath sealing strength at room temperature;

[0090] S430: placing the electric heating rod in the heating system in the casing of the second wellbore experimental device and connecting it to the pressure pump;

[0091] S440: After the heating rod reaches a predetermined temperature, the heated second wellbore experimental device is pressurized by a pressure pump to measure the cement sheath isolation strength at the predetermined temperature;

[0092] S450: placing a loading pressure head on the third wellbore experimental device, and determining the bonding strength of the cement sheath at room temperature by changing the load of the loading pressure head;

[0093] S460: placing a loading pressure head on the fourth wellbore experimental device, setting the electric heating rod in the heating system in the casing of the fourth wellbore experimental device, and determining the bonding strength of the cement sheath at different temperatures by changing the load amount of the loading pressure head for the heated fourth wellbore experimental device.

[0094] In an exemplary embodiment, the method for testing the integrity of the cement sheath in a shale oil in-situ conversion well further includes testing the sealing strength of the cement sheath under corrosive conditions, as follows:

[0095] Step 11, pre-completing the fifth wellbore experimental device;

[0096] Step 12: Place the sealing top plate on the top of the simulated formation of the wellbore experimental device for sealing, and inject the configured corrosive fluid into the cement ring of the wellbore experimental device to obtain the cement ring of the fifth wellbore experimental device under corrosive conditions.

[0097] Step 13, connecting the pressure pump to the fifth wellbore experimental device, and sealing the fifth wellbore experimental device;

[0098] Step 14: pressurize the sealed wellbore experimental device to test the cement sheath sealing strength under normal temperature and corrosion conditions;

[0099] Step 15: After measuring the cement sheath isolation strength at room temperature, the fifth wellbore experimental device is heated, and the cement sheath isolation strength under a predetermined temperature and corrosion condition is tested.

[0100] In an exemplary embodiment, the test method for the integrity of the cement sheath in the shale oil in-situ conversion well further includes testing the bonding strength of the cement sheath under corrosive conditions, as follows:

[0101] Step 21, pre-completing the sixth wellbore experimental device;

[0102] Step 22: Place the sealing top plate on the top of the simulated formation of the wellbore experimental device for sealing, and inject the configured corrosive fluid into the cement ring of the wellbore experimental device to obtain the cement ring of the sixth wellbore experimental device under corrosive conditions.

[0103] Step 23, placing a loading pressure head on the sixth wellbore experimental device, and determining the bonding strength of the cement sheath under normal temperature and corrosion conditions by changing the load of the loading pressure head;

[0104] Step 24, setting the electric heating rod in the heating system in the casing of the sixth wellbore experimental device, and determining the bonding strength of the cement sheath under the predetermined temperature and corrosion conditions of the heated sixth wellbore experimental device by changing the load amount of the loading pressure head.

[0105] In an exemplary embodiment, the cement sheath bonding strength calculation formula is

[0106] S=F / πDH

[0107] Where: S is the interface bonding strength, in MPa, F is the maximum pressure when the interface is damaged, in N, D is the diameter of the simulated casing, in mm, and H is the length of the contact part between the simulated casing and cement, in mm.

[0108] In an exemplary embodiment, based on the original scale wellbore structure experimental test unit, the integrity failure judgment experiment of the cement sheath can be realized at the macro level, where the two evaluation indicators are mainly based on the isolation capacity and the cementing strength. At the micro level, the cement sheath core simulation test unit is used to test the integrity failure judgment experiment of the cement sheath, where the evaluation indicator is mainly based on the isolation capacity.

[0109] Specifically, the process of testing the integrity of the cement sheath using the cement sheath core simulation test unit is as follows:

[0110] The first step is to load the core into the holder, connect the six-way valve and the pressure pump to the cement ring core experimental device and the holder confining pressure device to test the sealing capacity of the cement ring core;

[0111] Step 2: Place the holder in the heating system. After heating to the test temperature, connect the six-way valve and the pressure pump to the experimental device and the holder confining pressure device to test the sealing capacity of the cement ring core at the predetermined temperature.

[0112] The third step is to test the isolation capacity of the wellbore, open the valves of the injector and the corrosive gas (such as CO2 cylinder), control the contact between the corrosive fluid and the cement ring core, reconnect the pipeline, and use the pressure pump to increase the pressure to test the isolation capacity of the cement ring core under corrosive conditions.

[0113] Furthermore, the wellbore is placed in a high-temperature heating box to apply a temperature load. After heating to a certain temperature, the pipeline is reconnected and a pressure pump is used to increase the pressure to test the sealing capacity of the wellbore cement ring core at a predetermined temperature.

[0114] After testing the wellbore isolation capacity, open the injector and corrosive gas valve to control the contact between the corrosive fluid and the cement ring core, reconnect the pipeline, and use the pressure pump to increase the pressure to test the isolation capacity of the wellbore cement ring core under the predetermined temperature and corrosive conditions.

[0115] The cement sheath isolation capacity test is carried out through the cement sheath core simulation test unit, which can be correlated with the cement sheath isolation capacity test results obtained by the macroscopic original scale wellbore structure experimental test unit to mutually verify the rationality of the experimental parameters.

[0116] Example 1

[0117] This example demonstrates the full-scale wellbore structure experimental testing method, including the following steps:

[0118] Step 1: Prepare multiple wellbore experimental devices according to experimental requirements;

[0119] In this step, a shale oil in-situ conversion well is selected, and a wellbore experimental device of an original-scale simulated wellbore test unit is manufactured according to the actual parameters of the well;

[0120] Specific size parameters include:

[0121] Inner pipe string: 127 (5in) casing, 500mm long, 9.19mm thick, welded and sealed at both ends, closed plate;

[0122] Outer pipe string: inner diameter 152.4-200.03 (170) mm, length 500 mm;

[0123] End cover fastening bolt: M12*1.75;

[0124] Pressure test hole M10*1.5;

[0125] Eyelet hole M14*2;

[0126] A is the pressure test hole;

[0127] C is the eyelet hole.

[0128] Step 2: Place the casing in the simulated formation model, pour the cement slurry prepared as required into the annulus between the formation and the wellbore, seal the bottom to ensure the quality of the experimental cementing, and maintain it for 7 days under certain temperature conditions.

[0129] In this step, cement slurry adopts cement slurry specially used for thermal recovery wells.

[0130] Step 3, measuring the cement sheath sealing strength at room temperature;

[0131] The first wellbore experimental device was sealed, and the pressure was gradually increased at a rate of 0.05 MPa / s to observe the pressure changes in the wellbore. The pressure acquisition system in the wellbore was used to record the pressure change characteristics, and the cement sheath sealing strength at room temperature was measured.

[0132] Step 4, testing the cement sheath sealing strength at a predetermined temperature;

[0133] To test the effect of high temperature conditions on the sealing capacity of the cement sheath, the second wellbore experimental device was placed in a high-temperature heating box to apply a temperature load, and the cement sheath sealing strength at different temperatures was tested repeatedly according to step 3.

[0134] Step 5, measuring the bonding strength of the cement sheath at room temperature;

[0135] Here, the third wellbore test device that has not been tested can be used, or the first wellbore test device can be used to test the cement sheath isolation strength at room temperature before conducting the test in this step. Take the third wellbore test device that has not been tested as an example:

[0136] First, the third wellbore test device is placed on a pressure testing machine, which can be set to a loading rate of 5KN / s.

[0137] Then, the pressure head is loaded onto the cement sheath of the third wellbore experimental device, and the load is gradually increased until the load curve changes suddenly (suddenly decreases). The pressure load at this time is the cement sheath bond failure load. Compared with the material properties of the casing and cementing cement slurry, the material properties of the simulated formation and cementing cement slurry are less different, and the first interface is more easily damaged.

[0138] Finally, the test load of the cement sheath bonding strength at room temperature was recorded, as shown in Table 1, and the data parameters such as the cement sheath bonding area were measured, and the cement sheath bonding strength was obtained by calculation.

[0139] The calculation formula of cement sheath bond strength is:

[0140] S=F / πDH

[0141] Where: S is the interface bonding strength, in MPa, F is the maximum pressure when the interface is damaged, in N, D is the diameter of the simulated casing, in mm, and H is the length of the contact part between the simulated casing and cement, in mm.

[0142] Step 6, measuring the bonding strength of the cement ring at high temperature;

[0143] Here, the fourth wellbore test device that has not been tested can be used, or the second wellbore test device can be used to test the cement sheath isolation strength at high temperature before conducting the test in this step. Take the fourth wellbore test device that has not been tested as an example:

[0144] Place the fourth wellbore experimental device on the pressure testing machine, turn on the pressure testing machine and set the loading rate to 5KN / s.

[0145] The pressure head is loaded onto the cement sheath of the fourth wellbore experimental device, and the load is gradually increased until the load curve changes suddenly (suddenly decreases). The pressure load at this time is the cement sheath bond failure load. The test loads of the cement sheath bond strength at different temperatures are recorded, as shown in Table 1. The cement sheath bond area and other data parameters are measured, and the cement sheath bond strength is obtained by calculation.

[0146] Table 1

[0147]

[0148] Step 7: Test the sealing capacity and bonding strength of cement sheath under corrosive conditions

[0149] Step 71, place the sealing top plate on the top of the casing formation of the fifth wellbore experimental device and the sixth wellbore experimental device to seal, inject the configured corrosive medium into the top space, maintain the designed temperature and pressure conditions, and after 7 days of corrosion, obtain the wellbore under corrosive conditions.

[0150] Step 72, repeat steps 3, 4, 5, and 6 to test the sealing ability and bonding strength of the cement ring under corrosion conditions.

[0151] Example 2

[0152] This example demonstrates the method of testing the sealing capacity of cement ring by core simulation of cement ring. The cement ring core simulation test unit is used. The specific experimental structure is as follows: Figure 3 As shown, connect the experimental equipment. The specific experimental process is as follows:

[0153] Step 1: prepare the corresponding cementing slurry system according to relevant requirements;

[0154] Step 2: Pour cement slurry into the core mold, cure it under certain temperature conditions for 7 days, and then use a core drill to take the core. The core size is 25mm inner diameter and 8-10cm high.

[0155] Step 3: Load the core into the holder, connect the six-way valve and the pressure pump pipeline to the holder and the confining pressure generating device, drain the water and observe the pool device, etc.

[0156] Step 4: Gradually increase the pressure at a rate of 0.05 MPa / s to observe the changes in bubbles in the pool, and record the pressure change characteristics and the characteristics of the bubbles in the pool.

[0157] In this step, the core isolation capacity of the cement sheath can be quantitatively determined based on the amount and speed of bubble generation.

[0158] Step 5: Place the wellbore in a high-temperature heating box to apply temperature load. After heating to the test temperature, reconnect the pipeline and repeat the test of the wellbore isolation capacity according to steps 3 and 4.

[0159] Step 6: Open the valves of the injector and the corrosive gas (such as CO2) cylinder to control the contact between the corrosive fluid and the cement sheath core, then repeat steps 3 and 4, record the test load, as shown in Table 2, and measure the cement sheath isolation capacity.

[0160] Table 2

[0161]

[0162]

[0163] In this embodiment, the experimental test is carried out according to the orthogonal experimental design, and the experimental orthogonal factors include temperature, pressure, corrosion conditions, load, and cementing cement. The experimental evaluation indicators are the cement sheath plugging ability and cement sheath bonding strength. By testing the cement sheath sealing performance and bonding strength under different temperature, pressure and other conditions, it can be obtained:

[0164] 1. The sealing capacity and bonding strength of cement sheath gradually decrease with the increase of temperature and pressure. Temperature factor is the main influencing factor. When the temperature exceeds 350℃, the wellbore integrity performance decreases significantly.

[0165] 2. The sealing capacity of cement ring gradually decreases with the increase of acid gas corrosion concentration, and the increase in temperature will aggravate the degree of corrosion.

[0166] 3. The use of special cement slurry for thermal recovery wells can improve the cement sheath sealing strength under high temperature conditions.

[0167] It will be appreciated by those skilled in the art that all or some of the steps, systems, and functional modules / units in the methods disclosed above may be implemented as software, firmware, hardware, and appropriate combinations thereof. In hardware implementations, the division between the functional modules / units mentioned in the above description does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed by several physical components in cooperation. Some or all components may be implemented as software executed by a processor, such as a digital signal processor or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit. Such software may be distributed on a computer-readable medium, which may include a computer storage medium (or non-transitory medium) and a communication medium (or temporary medium). As known to those skilled in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, it is well known to those of ordinary skill in the art that communication media typically contain computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

Claims

1. A testing device for cement sheath integrity in shale oil in-situ conversion wells, characterized in that: The device comprises: an original-scale wellbore structure experimental test unit; the original-scale wellbore structure experimental test unit comprises: a pressure loading system, a heating system and a wellbore experimental device; Wherein, the pressure loading system comprises a loading pressure head, a base ring, a base and a pressure device; The heating system comprises an electric heating rod; The wellbore experimental device comprises: a cement ring, a casing, and a simulated formation; The loading pressure head in the pressure loading system is arranged at the top of the wellbore structure, the base ring is arranged at the bottom of the wellbore structure, and the base is arranged at the lower part of the base ring; In the heating system, an electric heating rod is arranged at the center of the casing, a cement ring is arranged outside the casing, and a simulated stratum is arranged outside the cement ring.

2. The testing device for cement sheath integrity in shale oil in-situ conversion wells according to claim 1, characterized in that: The full-scale wellbore structure experimental test unit also includes: a pressure acquisition system; The pressure acquisition system is used to acquire the pressure value of the cement sheath.

3. The testing device for cement sheath integrity in shale oil in-situ conversion wells according to claim 1, characterized in that: The pressure loading system is used to pressurize the cement sheath in the wellbore structure; The heating system is used to heat the cement sheath and simulated formation in the wellbore structure; The wellbore experimental device is used to simulate the real wellbore structure in the formation to be tested.

4. The testing device for cement sheath integrity in shale oil in-situ conversion wells according to claim 1, characterized in that: The device also includes: a cement ring core simulation test unit; The cement ring core simulation test unit includes: a pressure system, a pressure acquisition system, a heating system and a corrosion simulation system; The pressure system includes a pressure pump and a confining pressure device; The pressure acquisition system comprises: a pressure sensor; The heating system comprises: a heating box; The corrosion simulation system: CO2 gas cylinder and liquid injector; The CO2 gas cylinder, pressure gauge, injector and pressure pump are connected to the confining pressure device through a six-way valve. The cement ring core is clamped inside the confining pressure device through a clamping device, and the clamping device is connected to the water pool. A heating box is arranged outside the confining pressure device.

5. The testing device for cement sheath integrity in shale oil in-situ conversion wells according to claim 1, characterized in that: The pressure system is used to pressurize the cement sheath core; The pressure acquisition system is used to acquire the pressure of the cement sheath core; The heating system is used to heat the cement ring core; The corrosion simulation system is used to inject corrosive fluid into the cement ring core to simulate the corroded cement ring.

6. A method for testing the integrity of cement sheath in shale oil in-situ conversion wells, characterized in that: The method comprises: Pre-completing the first wellbore experimental device and the second wellbore experimental device; Connecting the pressure pump to the first wellbore experimental device and sealing the first wellbore experimental device; The sealed wellbore test device is pressurized by a pressure pump to measure the cement sheath isolation strength at room temperature; After measuring the cement sheath isolation strength at room temperature, a loading pressure head is placed on the first wellbore experimental device, and the load of the loading pressure head is changed to determine the bonding strength of the cement sheath at room temperature; Connecting the pressure pump to the second wellbore experimental device and sealing the second wellbore experimental device; The electric heating rod in the heating system is placed in the casing of the second wellbore experimental device and connected to the pressure pump. After the heating rod reaches a predetermined temperature, the heated second wellbore experimental device is pressurized by the pressure pump to measure the cement sheath isolation strength at the predetermined temperature. After the cement sheath isolation strength at a predetermined temperature is measured, a loading pressure head is placed on the second wellbore experimental device, and the load amount of the loading pressure head is changed to determine the bonding strength of the cement sheath at different temperatures.

7. The method for testing the integrity of cement sheath in shale oil in-situ conversion wells according to claim 6, characterized in that: The bonding strength of the cement sheath is: S=F / πDH Where: S is the interface bonding strength, F is the maximum pressure when the interface is damaged, D is the diameter of the casing in the wellbore test device, and H is the length of the contact part between the casing and cement in the wellbore test device.

8. The method for testing the integrity of cement sheath in shale oil in-situ conversion wells according to claim 6, characterized in that: The method also includes: The third wellbore experimental device and the fourth wellbore experimental device are completed in advance; The following operations are performed on the third wellbore experimental device and the fourth wellbore experimental device respectively: A sealing top plate is placed on the top of the simulated formation of the wellbore experimental device for sealing, and a configured corrosive fluid is injected into the cement ring of the wellbore experimental device to obtain a third wellbore experimental device under corrosive conditions and a fourth wellbore experimental device under corrosive conditions.

9. The method for testing the integrity of cement sheath in shale oil in-situ conversion wells according to claim 8, characterized in that: After obtaining the third wellbore experimental device under corrosion conditions and the fourth wellbore experimental device under corrosion conditions, the method further includes: Connecting the pressure pump to the third wellbore experimental device and sealing the third wellbore experimental device; Pressurize the sealed third wellbore test device to test the cement sheath isolation strength under normal temperature and corrosion conditions; After measuring the cement sheath isolation strength under normal temperature and corrosion conditions, the loading pressure head is placed on the third wellbore experimental device, and the load of the loading pressure head is changed to determine the bonding strength of the cement sheath under normal temperature and corrosion conditions.

10. The method for testing the integrity of cement sheath in shale oil in-situ conversion wells according to claim 8, characterized in that: After obtaining the third wellbore experimental device under corrosion conditions and the fourth wellbore experimental device under corrosion conditions, the method further includes: Connecting the pressure pump to the fourth wellbore experimental device, placing the electric heating rod in the heating system in the casing of the fourth wellbore experimental device, and sealing the fourth wellbore experimental device; The sealed fourth wellbore experimental device was heated to test the cement sheath isolation strength under different temperatures and corrosion conditions; After measuring the sealing strength of the cement sheath under different temperatures and corrosion conditions, the loading pressure head is placed on the fourth wellbore experimental device, and the load of the loading pressure head is changed to determine the bonding strength of the cement sheath under different temperatures and corrosion conditions.

11. The method for testing the integrity of cement sheath in shale oil in-situ conversion wells according to claim 6, characterized in that: The method also includes: Place the core into the holder, connect the six-way valve and pressure pump to the experimental device and the holder confining pressure device, and test the sealing capacity of the cement sheath core; The clamp is placed in the heating system. After heating to a certain temperature, the six-way valve and the pressure pump are connected to the experimental device and the clamp confining pressure device to test the sealing capacity of the cement ring core at a predetermined temperature. After testing the wellbore isolation capacity, open the injector and corrosive gas valve to test the core isolation capacity of the cement ring under corrosive conditions.

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