Test evaluation method for simulating casing damage caused by hydration heat release of shaft cement

Abstract

The invention belongs to the technical field of petroleum engineering, and relates to a test evaluation method for simulating casing damage caused by hydration heat release of shaft cement, which comprises the following steps: acquiring an initial temperature and a maximum temperature of a whole well section in a well cementation process, an initial axial load extreme value of a casing string and an annular trap pressure extreme value of a casing; a composite load working condition casing-cement sheath system deformation process simulation device is adopted to heat a casing to an initial temperature, and axial pressure is applied to the casing to an initial axial load extreme value of a casing string; heating is conducted again, and in the heating process, if the temperature is increased to the maximum temperature, the annulus entrapment pressure does not reach the extreme value of the annulus entrapment pressure, and heating is stopped at the moment; and if the temperature does not reach the maximum temperature, the annulus trap pressure reaches the extreme value of the annulus trap pressure in advance, and heating is stopped at the moment. The change process of the axial force and the annulus entrapment pressure value is recorded, the deformation degree of the casing pipe is quantified, the underground stress condition of the full-size casing pipe under the actual working condition can be simulated, and technical support is provided for workover treatment.

Description

Technical Field

[0001] This invention belongs to the field of petroleum engineering technology, specifically relating to an experimental evaluation method for casing damage caused by simulating the heat release during cement hydration in wellbore. Background Technology

[0002] In recent years, with the development of high-temperature and high-pressure wells, the impact of temperature on casing performance has attracted increasing attention. Studies have shown that compared with performance at room temperature, at 200℃, the decrease in tensile strength of casing is within 5%, and the decrease in yield strength is within 10%; at 350℃, the decrease in tensile strength is within 8%, and the decrease in yield strength is within 20%. As the yield strength decreases, the load-bearing capacity of the casing inevitably changes; if it is still designed based on the rated strength, the safety factor will decrease. The thermal strength of oilfield casing materials includes instantaneous high-temperature performance, long-term high-temperature performance, and high-temperature mechanical fatigue strength.

[0003] Currently, there is considerable research on the impact of high formation temperatures on casing performance, but research on the impact of short-term, instantaneous high temperatures caused by cement hydration on casing performance is limited. During cementing, after the cement slurry is in place, the cement hydration releases a large amount of heat instantaneously. In cases of poor cementing quality, some trapped spaces exist in the annulus. The temperature rise causes the annular fluid between the sealed casing layers to expand, creating annular trapping pressure. Under exothermic conditions, localized high pressure forms in the trapped spaces, altering the stress on the casing. Simultaneously, the casing strength is low, inevitably leading to casing problems. However, there are currently no relevant experimental evaluation methods for simulating casing damage caused by the exothermic reaction of wellbore cement hydration; existing technologies cannot simulate this. Summary of the Invention

[0004] The purpose of this invention is to provide a test evaluation method for simulating casing damage caused by the exothermic reaction of cement hydration in wellbore, which solves the problem that the annular pressure caused by the high temperature generated during cement hydration during cementing affects the stress on the casing, a problem that cannot be simulated by existing technologies.

[0005] This invention is achieved through the following technical solution:

[0006] A test evaluation method for simulating casing damage caused by exothermic cement hydration in wellbore includes the following steps:

[0007] Obtain the initial and maximum temperatures throughout the entire well section during the cementing process;

[0008] Obtain the extreme value of the initial axial load of the casing string;

[0009] Obtain the extreme value of the annular closed pressure of the casing;

[0010] The composite load condition casing-cement ring system deformation process simulation device was designed to first heat the casing to the initial temperature, and then apply axial pressure to the casing to the extreme value of the initial axial load of the casing string.

[0011] Then, the temperature is increased. During the heating process, the axial force and annular closure pressure of the casing continuously increase. The changes in the values ​​of axial force and annular closure pressure are recorded to quantify the degree of casing deformation.

[0012] During the heating process, if the annular pressure does not reach the maximum annular pressure limit when the temperature reaches the maximum, the heating should be stopped; if the annular pressure reaches the maximum annular pressure limit before the temperature reaches the maximum, the heating should be stopped.

[0013] Furthermore, the cementing process includes the cement injection process, the cement hydration heat release process, and the temperature drop process after cement hydration.

[0014] Furthermore, based on transient heat transfer theory and experimental numerical calculations of cement hydration heat release, the transient temperature field change of the wellbore during the staged cementing process was calculated, and the initial temperature and maximum temperature of the entire well section during the cementing process were obtained.

[0015] Based on the axial force calculation method of the casing string mechanics, the extreme value of the initial axial load of the casing string is obtained;

[0016] Based on the PVT state equation and elastoplastic mechanics theory, the extreme value of the annular closure pressure of the casing is obtained.

[0017] Furthermore, the device for simulating the deformation process of the casing-cement ring system under composite load conditions includes a temperature control console, a hydraulic control console, an axial force control console, a hydraulic mechanism, a connecting frame, and an outer pipe for simulating the annular closed space;

[0018] The hydraulic mechanism includes a hydraulic cylinder and a hydraulic rod; the hydraulic cylinder is connected to the axial force control console.

[0019] The end of the hydraulic rod is fixedly connected to one end of the sleeve, and the other end of the sleeve is fixedly connected to the connecting frame;

[0020] The outer tube is installed outside the casing to form a closed space, which is filled with closed liquid.

[0021] The outer pipe is connected to the hydraulic control console;

[0022] A heating tape is wrapped around the outside of the sleeve and in an area staggered from the outer sleeve. The heating tape is connected to the temperature control console.

[0023] Furthermore, the connecting frame includes a base, and a first baffle and a second baffle connected to the base;

[0024] The hydraulic cylinder is mounted on the first baffle, and the hydraulic rod passes through the first baffle and connects to the connecting piece.

[0025] The second baffle serves as the fixed connection side of the sleeve. The sleeve is connected to the second baffle via an adapter. The adapter has a pre-fabricated liquid channel inside the sleeve that communicates with the sleeve. The liquid channel inside the sleeve is connected to the hydraulic control console, and a valve is installed on the liquid channel.

[0026] Furthermore, the two ends of the sleeve are respectively connected to a first connector and a second connector;

[0027] The hydraulic rod is threaded to one end of the sleeve via a first connector, and the other end of the sleeve is threaded to the adapter via a second connector.

[0028] The second connector has a pre-formed liquid channel inside the casing that communicates with the casing.

[0029] Furthermore, the outer tube is set on the base; the circumferential seal between the outer tube and the sleeve is achieved by welding.

[0030] Furthermore, the hydraulic control console is connected to a liquid storage tank.

[0031] Furthermore, a closed liquid flow channel is prefabricated on the outer pipe, and the hydraulic control console controls the liquid to enter the closed space through the closed liquid flow channel.

[0032] Furthermore, water is used as the confining liquid.

[0033] Compared with the prior art, the present invention has the following beneficial technical effects:

[0034] This invention discloses an experimental evaluation method for casing damage caused by the exothermic reaction of cement hydration in wellbore. It is the first to propose combining several parameters—the initial and maximum temperatures of the maximum temperature variation range throughout the wellbore during cementing, the extreme initial axial load of the casing string, and the extreme annular closure pressure of the casing—into a simulation experiment of casing damage caused by the exothermic reaction of cement hydration. This method more closely reflects the actual stress conditions of the casing during cement hydration. While there is considerable research on the exothermic reaction of cement hydration, the evaluation of the impact of this closure pressure on casing strength remains lacking. Based on theoretical calculations combined with laboratory experiments, this invention provides an evaluation method for the influence of cement hydration on casing strength and designs a dedicated simulation device that can simulate the stress conditions of a full-size casing downhole under actual working conditions. This fills a gap in related domestic fields and provides technical support for well workover operations. During the heating process, if the temperature reaches its maximum value first, it means that the temperature tolerance value of the casing has been reached. If the annular closure pressure reaches the annular closure pressure extreme value in advance, it means that the pressure extreme value of the casing has been reached. In either case, the temperature should not be increased further, otherwise the casing will be damaged or deformed.

[0035] Furthermore, the present invention designs a dedicated simulation device, including a temperature control console, a hydraulic control console, an axial force control console, and an outer tube for simulating a confined space. The outer tube is sleeved outside the casing and is connected to the three control consoles at both ends of the casing through designed connectors. The control consoles control the heating of the casing and apply axial force to the initial extreme value of the axial load of the casing string, which can simulate the stress of a full-size casing downhole under actual working conditions.

[0036] Furthermore, water is used as the trapping liquid. Since the unsealed sections of the annulus all use water-based mixtures, using water as the trapping medium in the laboratory is more in line with reality. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the device for simulating the deformation process of the sleeve-cement ring system under composite load conditions according to the present invention.

[0038] The components are as follows: 1. Liquid storage tank; 2. First connecting piece; 3. Casing; 4. Adapter; 5. Second connecting piece; 6. Heating belt; 7. Outer pipe; 8. Enclosed space; 9. Enclosed liquid flow channel; 10. Circumferential weld of outer pipe; 11. First baffle; 12. Hydraulic cylinder; 13. Hydraulic rod; 14. Axial force transmission line; 15. Axial force control console; 16. Second baffle; 17. Rotary bearing; 18. Base; 19. Liquid channel inside the casing; 20. Enclosed liquid pressure control pipeline; 21. Liquid pressure control pipeline inside the casing; 22. Hydraulic control console; 23. Temperature control console; 24. Temperature control line. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0040] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0041] This invention establishes a test evaluation method for simulating casing damage caused by the exothermic reaction of wellbore cement hydration through a combination of theoretical and laboratory experiments. By theoretically calculating the real-time changes in the temperature and pressure field of the entire wellbore during service, the load spectrum variation of the casing string under different operating conditions is clarified. Then, a laboratory composite load condition casing-cement sheath test system is constructed. The specific test technical scheme is as follows:

[0042] (1) Based on the actual well conditions on site, and based on the transient heat transfer theory and the experimental values ​​of cement hydration heat release, the wellbore temperature and pressure field of the entire well section of the cementing process, consisting of the cement injection process, the cement hydration heat release process and the temperature drop process after cement hydration, was simulated. The transient temperature field change of the wellbore during the staged cementing process was calculated, and the initial temperature and maximum temperature of the entire well section of the cementing process were obtained.

[0043] (2) Based on the tubing mechanics theory, calculate the load simulation of the entire well section of the casing string and determine the extreme value of the initial axial load Fmax of the casing string;

[0044] (3) Based on the PVT state equation and the elastoplastic mechanics theory, the extreme value of the annular closure pressure ΔP of the casing is obtained;

[0045] (4) Design a simulation device for the deformation process of the sleeve-cement ring system under composite load conditions, such as Figure 1 As shown;

[0046] (5) The casing 3 was first heated to the initial temperature using the composite load condition casing-cement ring system deformation process simulation device, and axial pressure was applied to the casing 3 to the extreme value of the initial axial load of the casing column.

[0047] Then, the temperature is increased. During the heating process, the axial force and annular closure pressure of the casing 3 continuously increase. The changes in the values ​​of axial force and annular closure pressure are recorded to quantify the degree of deformation of the casing 3.

[0048] During the heating process, if the annular pressure does not reach the maximum annular pressure limit when the temperature reaches the maximum, the heating should be stopped; if the annular pressure reaches the maximum annular pressure limit before the temperature reaches the maximum, the heating should be stopped.

[0049] If the temperature reaches its maximum value first, it means that the temperature tolerance value of the casing 3 has been reached. If the annular closure pressure reaches the annular closure pressure extreme value in advance, it means that the pressure extreme value of the casing 3 has been reached. In either case, the temperature should not be increased further, otherwise the casing 3 will be damaged or deformed.

[0050] like Figure 1 As shown, the device for simulating the deformation process of the casing-cement ring system under composite load conditions includes a temperature control console 23, a hydraulic control console 22, an axial force control console 15, a hydraulic mechanism, a connecting frame, and an outer pipe 7 for simulating the annular closed space 8.

[0051] The hydraulic mechanism includes a hydraulic cylinder 12 and a hydraulic rod 13; the hydraulic cylinder 12 is connected to the axial force control console 15;

[0052] The end of the hydraulic rod 13 is fixedly connected to one end of the sleeve 3, and the other end of the sleeve 3 is fixedly connected to the connecting frame;

[0053] The outer tube 7 is fitted outside the sleeve 3, and the outer tube 7 is filled with a closed liquid;

[0054] Both the outer pipe 7 and the sleeve 3 are connected to the hydraulic control console 22;

[0055] A heating strip 6 is wrapped around the outside of the sleeve 3 and in a region offset from the outer sleeve 7. The heating strip 6 is connected to the temperature control console 23.

[0056] Specifically, the hydraulic cylinder 12 is connected to the axial force control console 15 via the axial force transmission line 14;

[0057] The heating element 6 is connected to the temperature control console 23 via the temperature control circuit 24;

[0058] A closed liquid flow channel 9 is provided on one side of the outer pipe 7. The closed liquid flow channel 9 is connected to the hydraulic control console 22 through the closed liquid pressure control pipeline 20.

[0059] Specifically, the connecting frame designed in this invention includes a base 18, and a first baffle 11 and a second baffle 16 connected to the base 18. The first baffle 11 and the second baffle 16 are disposed on both sides of the sleeve 3, and the outer tube 7 is disposed on the base 18.

[0060] Hydraulic cylinder 12 is connected to first baffle 11, hydraulic rod 13 passes through first baffle 11 and is connected to first connector 2, first connector 2 is welded to left side of sleeve 3; second baffle 16 is fixed end, second connector 5 is welded to right side of sleeve 3, second connector 5 is connected to second baffle 16 through adapter 4; mounting hole is opened on second baffle 16, rotating bearing 17 is installed in mounting hole, one end of adapter 4 is rotatably connected to rotating bearing 17.

[0061] More preferably, the second connector 5 and the adapter 4 are pre-fabricated with a casing liquid channel 19 for introducing liquid into the casing. The casing liquid channel 19 is connected to the hydraulic control console 22 via a casing liquid pressure control pipeline 21, and a valve is provided on the casing liquid channel 19. This part is an extension design of this device, and if it is necessary to apply internal pressure to the casing 3 later, the casing liquid channel 19 can be opened.

[0062] Specifically, in order to ensure good sealing performance at the connection between the outer tube 7 and the sleeve 3, a welding method is used to seal the circumferential contact between the outer tube 7 and the sleeve 3, forming an outer tube circumferential weld 10.

[0063] The first connector 2 and the second connector 5 are pre-threaded with external threads, and the hydraulic rod 13 and the adapter 4 are pre-threaded with internal threads, so that the parts are threadedly connected, which facilitates installation and disassembly.

[0064] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0065] (1) Assume that the outer diameter of casing 3 is 244.5 mm, the wall thickness is 11.99 mm, the steel grade is P110, the drilling depth is 5500 m, the depth of the test focus is 5200 m, and the drilling fluid density is 1.25 g / cm³. 3 Based on the actual well structure, well trajectory, drilling fluid properties, cement slurry properties, and other basic parameters, the initial temperature of the point of interest was calculated to be 80℃, the maximum temperature to be 140℃, and the maximum temperature variation to be 60℃.

[0066] (2) The initial axial compressive force of the test was calculated to be 898 kN;

[0067] (3) The calculated closed pressure of the test annulus was 43.15 MPa;

[0068] (4) The length of the sleeve 3 used in the experiment is 3.8m. Other parameters are the same as those described in (1). Before the experiment, the sleeve 3 should be measured in detail.

[0069] (5) First, thread the sleeve 3 to the adapter 4, then connect the hydraulic rod 13 to the sleeve 3, connect the heating belt 6, connect the two ends of the axial force transmission line 14 to the hydraulic cylinder 12 and the axial force control console 15 respectively, connect the two ends of the temperature control line 24 to the heating belt 6 and the temperature control console 23 respectively, connect one end of the closed liquid pressure control pipeline 20 to the hydraulic control console 22, and connect the other end to the closed liquid flow channel 9 respectively, and connect the other end of the hydraulic control console 22 to the liquid storage tank 1. Before the test, the entire composite load condition sleeve-cement ring system deformation process simulation device was pressure tested and inspected to ensure the safety and reliability of the equipment;

[0070] (6) First, heat the sleeve 3 to 80°C through the temperature control console 23, then apply an axial load of 898KN to the sleeve 3 through the axial force control console 15, and continue to heat the sleeve 3 to 140°C through the temperature control console 23. During the heating process, the axial force and annular closure pressure continuously increase, and record the values ​​of axial force and annular closure pressure.

[0071] (7) After the composite load is applied, observe whether the sleeve 3 has obvious deformation or failure. If there is failure / deformation, stop the test, remove the sleeve 3, and perform detailed data measurement to quantify the degree of deformation of the sleeve 3. If there is no failure, continue to increase the annular closure pressure until the sleeve 3 fails due to external extrusion. Record the test pressure value and capture the stress-strain data of the sleeve 3 during the deformation process.

[0072] (8) According to the deformation obtained from the test, the temperature change (80℃→140℃) under the cement hydration heat release condition at the point of concern caused the increase of the axial force of the sleeve 3 column (-898kN→-1918kN) and the increase of the annular pressure (2.8MPa→43.15MPa), resulting in non-uniform deformation of the sleeve 3 under the combined load of external extrusion and compression axial force.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A test evaluation method for simulating casing damage due to wellbore cement exotherm, characterized by, The process comprises the following steps: obtaining initial temperature and maximum temperature of the whole well section in the cementing process; obtaining the initial axial load extreme value of the casing string; obtaining the annular trapping pressure extreme value of the casing (3); using the designed casing-cement sheath system deformation process simulation device under the composite load working condition to firstly heat the casing (3) to the initial temperature, and apply axial pressure to the casing (3) until the initial axial load extreme value of the casing string is reached; then, heating is performed again, in the process of heating, the axial force and the annular trapping pressure of the casing (3) are continuously increased, the change process of the axial force and the annular trapping pressure is recorded, and the deformation degree of the casing (3) is quantified; in the process of heating, if the annular trapping pressure does not reach the annular trapping pressure extreme value when the temperature reaches the maximum temperature, the heating is stopped at this time; if the annular trapping pressure reaches the annular trapping pressure extreme value before the temperature reaches the maximum temperature, the heating is stopped at this time.

2. The method of claim 1, wherein the method further comprises: The cementing process comprises a cement injection process, a cement hydration heat release process and a cement hydration temperature drop process.

3. The method of claim 1, wherein the method further comprises: Based on the transient heat transfer theory and the numerical calculation of the cement hydration heat release experiment, the transient temperature field change of the wellbore in the staged cementing process is obtained, and the initial temperature and the maximum temperature of the whole well section in the cementing process are obtained; Based on the axial force calculation method of pipe string mechanics, the initial axial load extreme value of the casing string is obtained; According to the PVT state equation and the elastic-plastic mechanics theory, the annular trapping pressure extreme value of the casing (3) is obtained.

4. The method of claim 1, wherein the method further comprises: The casing-cement sheath system deformation process simulation device under the composite load working condition comprises a temperature control console (23), a hydraulic control console (22), an axial force control console (15), a hydraulic mechanism, a connecting frame and a peripheral pipe (7) for simulating an annular trapping space (8); The hydraulic mechanism comprises a hydraulic cylinder (12) and a hydraulic rod (13); the hydraulic cylinder (12) is connected with the axial force control console (15); The end of the hydraulic rod (13) is fixedly connected with one end of the casing (3), and the other end of the casing (3) is fixedly connected on the connecting frame; The peripheral pipe (7) is sleeved outside the casing (3) to form the trapping space (8), and the trapping space (8) is filled with trapping liquid; The peripheral pipe (7) is connected with the hydraulic control console (22); A heating belt (6) is wound outside the casing (3) and staggered with the peripheral pipe (7), and the heating belt (6) is connected with the temperature control console (23).

5. The method of claim 4, wherein the method further comprises: The connecting frame comprises a base (18), and a first baffle (11) and a second baffle (16) connected on the base (18); The hydraulic cylinder (12) is installed on the first baffle (11), and the hydraulic rod (13) is connected with the connecting piece through the first baffle (11); The second baffle (16) is used as a fixed connection side of the casing (3), the casing (3) is connected with the second baffle (16) through an adapter (4), a casing inner liquid channel (19) in communication with the casing (3) is preformed in the adapter (4), the casing inner liquid channel (19) is connected with the hydraulic control console (22), and a valve is installed on the liquid channel.

6. The method of claim 5, wherein the method further comprises: The two ends of the casing (3) are respectively connected with a first connecting piece (2) and a second connecting piece (5). The hydraulic rod (13) is threadedly connected with one end of the sleeve pipe (3) through the first connecting piece (2), and the other end of the sleeve pipe (3) is threadedly connected with the adapter (4) through the second connecting piece (5). The sleeve pipe inner liquid channel (19) in communication with the sleeve pipe (3) is preformed in the second connecting piece (5).

7. The method of claim 5, wherein the method further comprises: The peripheral pipe (7) is arranged on the base (18); the contact ring of the peripheral pipe (7) with the sleeve pipe (3) is sealed by welding.

8. The method of claim 4, wherein the method further comprises: The hydraulic console (22) is connected with the liquid storage tank (1).

9. The method of claim 4, wherein the method further comprises: The peripheral pipe (7) is preformed with the liquid flow channel (9), and the hydraulic console (22) controls the liquid to enter the enclosed space (8) through the liquid flow channel (9).

10. The method of claim 4, wherein the method further comprises: The enclosed liquid is water.

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