CN114856542A - A device and method for testing the integrity of cement sheath under simulated prestress - Google Patents

Abstract

A device and a method for testing the integrity of a cement ring under the action of simulated prestress are characterized in that the device comprises a pressure-bearing cavity, an inner blind pipe, an annular space, an outer sleeve, a heating sleeve, a first screw, a second screw, a first nut, a boosting bearing, a square rod, a stress sensor, a rubber gasket, a circular plate, a gasket, a second nut, a pressure control system, a first through hole, an annular groove, a circular groove, a second through hole, a first male thread, a second male thread, a third male thread and a cement ring; the device and the method can simulate the integrity of the cement sheath under the prestress action under the real working condition, test the interface bonding strength of the cement sheath, and establish the quantitative relation between the prestress and the interface bonding strength of the cement sheath based on the interface bonding strength of the cement sheath. The invention is suitable for the technical field of petroleum and natural gas drilling and production engineering.

Description

A device and method for testing the integrity of cement sheath under simulated prestress

technical field

The patent relates to the technical field of oil and natural gas drilling and production engineering, in particular to a device and method for testing the integrity of cement sheath under the action of simulated prestress.

Background technique

China's heavy oil resources are widely distributed, accounting for about 25% to 30% of the total oil resources, while the resources of individual oil fields account for a higher proportion, and heavy oil production has become the most important part of its output. Domestic and foreign oilfields generally use steam huff and puff and steam flooding technologies in heavy oil production. The steam huff and puff technology is to inject high temperature and high pressure steam (generally 300 ℃ ~ 360 ℃, 10MPa ~ 15MPa) into the well, heat preservation and pressure for a certain period of time (called "simmering well"), and then the heavy oil is thinned and then recovered. Compared with the conventional thin oil recovery method, one of the most important problems in the development of heavy oil oilfields is that the high temperature causes the casing to generate high thermal stress and has a certain amount of elongation. At the same time, the cemented casing is sealed by the cement ring. Under the action of multiple thermal cycles, the shear bonding strength of the interface between the casing and the cement sheath fails, resulting in the casing becoming a completely free section, which intensifies the wellhead uplift.

Prestress is one of the main ways to solve wellhead uplift. Its mechanism is to apply a certain pretension force to the casing string in the well before or after cementing, and to solidify the cement slurry under the condition of applying prestress. Due to the prestressing of the casing in advance, the casing has a certain pre-elongation, which can reduce or offset the casing elongation caused by thermal stress during steam injection, and prevent the shearing and cementation failure of the casing and the cement sheath. Protecting wells and extending their life. However, the influence mechanism and influence law of prestress on the integrity of cement sheath, especially the shear bond strength of cement sheath interface, are still unclear. The main reasons are as follows: 1) In the presence of prestress, the shear bond of cement sheath interface is The strength is difficult to test; 2) There is a lack of devices and methods that can truly simulate the integrity of the cement sheath under the action of prestress.

Therefore, in view of the technical problem that it is difficult to accurately analyze the influence law of prestress on the integrity of cement sheath at present, the present invention proposes a test device and method for the integrity of cement sheath under the action of simulated prestress, which can accurately obtain the cement sheath under real working conditions. The shear bond strength of the cement sheath under different prestresses, and the relationship between the prestress and the cement sheath interface shear bond strength is quantified based on this, and the protective effect of the prestress on the integrity of the cement sheath is verified. The mechanical properties of the cementing interface, the integrity of the cement sheath and the optimal design of cementing in oil and gas wells provide a theoretical basis.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a test device and method for the integrity of cement sheath under the action of simulated prestress, while maintaining the integrity of the test device, and to solve the quantitative evaluation of the relationship between the shear bond strength of the cement sheath interface and the prestress under the action of prestress The method is simple to use and low cost.

The invention provides a cement sheath integrity testing device and method under simulated prestress, characterized in that the device includes a pressure-bearing chamber, an inner blind tube, an annulus, an outer casing, a heating jacket, a first screw, and a second screw , first nut, booster bearing, square rod, stress sensor, rubber washer, circular plate, washer, second nut, pressure control system, first through hole, ring groove, round groove, second through hole, first male Thread, second male thread, third male thread, cement ring; wherein, the circular plate includes a first through hole, a ring groove and a circular groove, which are respectively used for fixing the inner blind pipe, the outer casing and the first screw; The inner blind tube of the screw passes through the rubber washer, the first through hole and the washer in sequence, and is finally connected to the second nut through the second male thread. The pressure control system externally connected to the inner blind tube is used for loading and unloading the pressure of the pressure-bearing chamber. In order to simulate the actual downhole pressure, the rubber gasket is used to seal the annulus to avoid leakage of cement when the cement ring is maintained in the annulus. The outer casing is set in the ring groove to prevent eccentricity between the outer casing and the inner blind pipe; the heating jacket of the external temperature control system is wrapped on the outer wall of the outer casing to simulate the actual temperature in the well; After the first screw rod is connected with the square rod with the second through hole through the third male thread, the square rod is inserted into the second screw rod through the second through hole, and the first screw rod is fixed in the circular groove; The bearing is inserted outside the second screw rod and finally placed on the square rod to avoid direct contact between the square rod and the first nut; the first nut is connected with the inner blind tube welded with the second screw rod through the first male thread, Move the first nut to make the inner blind tube welded with the second screw to bear an upward pulling axial load to realize the simulation of prestress and the test of the interface shear bond strength. The stress sensor is used to detect the axial load of the inner blind tube. .

Based on a device for testing the integrity of cement sheath under simulated prestress, a method for testing the integrity of cement sheath under simulated prestress is proposed. The method mainly includes the following steps:

Step 1: Rotate the first nut to apply an upward-pulling axial load F ₁ to the inner blind tube welded with the second screw, and record the magnitude of the axial load F ₁ through the stress sensor;

Step 2: Prepare the cement slurry system according to the actual needs of the site, pour the cement slurry into the annulus, start the heating jacket to heat to the simulated temperature, start the pressure control system, load the pressure-bearing chamber to the simulated pressure, and cure to form a cement ring;

Step 3: After the maintenance is completed, according to the experimental requirements, the loading-unloading of alternating temperature/pressure is realized by controlling the heating jacket and the pressure control system;

Step 4: After unloading the pressure in the pressure-bearing chamber 1 through the pressure control system, unscrew the second nut and remove the washer;

Step 5: Rotate the first nut until the interface between the inner blind tube and the cement sheath is separated, and record the maximum axial load F ₂ in this process through the stress sensor;

Step 6: Calculate the shear bond strength of the cement sheath interface under the action of the prestress F ₁ as σ _b =F ₂ -F ₁ .

Step 7: Different axial loads F ₁ are formed by twisting the first nut, and steps 1 to 6 are repeated to obtain the quantitative relationship between the axial load F ₁ and the shear bond strength σ _b of the cement sheath interface.

The present invention has the following advantages:

The present invention can accurately obtain the size of the prestress of the inner blind pipe, and test the integrity of the cement sheath under the action of the prestress in combination with the shear bonding strength of the cement sheath interface; It can realize the loading of prestress and the test of the shear bonding strength of the cement sheath interface; the test results can provide an important theoretical basis for the cement sheath integrity and cementing engineering optimization design of heavy oil thermal recovery.

Description of drawings

Figure 1 is a schematic diagram of a cement sheath integrity testing device under the action of prestress.

Figure 2 is a schematic diagram of the cement sheath integrity testing device after prestressing.

Figure 3 is a top view of the ring.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings.

The present invention provides a cement sheath integrity testing device and method under simulated prestress, characterized in that the device comprises a pressure-bearing chamber 1, an inner blind pipe 2, an annulus 3, an outer casing 4, a heating jacket 5, a first Screw 6, second screw 7, first nut 8, booster bearing 9, square rod 10, stress sensor 11, rubber washer 12, circular plate 13, washer 14, second nut 15, pressure control system 16, first pass Hole 17 , annular groove 18 , circular groove 19 , second through hole 20 , first male thread 21 , second male thread 22 , third male thread 23 , cement ring 24 ; wherein the circular plate 13 includes the first through hole 17 , the ring groove 18 and the circular groove 19 are used to fix the inner blind pipe 2, the outer sleeve 4 and the first screw 6 respectively; the inner blind pipe 2 welded with the second screw 7 passes through the rubber gasket 12 and the first through hole 17 in turn. and the washer 14, finally connected with the second nut 15 through the second male thread 22, the pressure control system 16 externally connected to the inner dead pipe 2 is used for loading and unloading the pressure of the pressure chamber 1 to simulate the actual downhole pressure, the rubber washer 12 It is used to seal the annular space 3 to avoid leakage of cement when the annular space 3 maintains the cement ring 24. The gasket 14 is used to protect the second nut 15; The tube 4, the rubber gasket 12 and the circular plate 13 are composed. The outer sleeve 4 is set in the ring groove 18 to prevent the eccentricity between the outer sleeve 4 and the inner blind tube 2; the heating sleeve 5 of the external temperature control system is wrapped around the outer wall of the outer sleeve 4 It is used to simulate the actual downhole temperature; after the first screw 6 is connected with the square rod 10 with the second through hole 20 through the third male thread 23, the square rod 10 is inserted into the second screw through the second through hole 20 7, and fix the first screw 6 in the circular groove 19; the booster bearing 9 is inserted outside the second screw 7, and finally placed on the square rod 10 to avoid direct contact between the square rod 10 and the first nut 8; A nut 8 is connected with the inner blind tube 2 welded with the second screw rod 7 through the first male thread 21, and the inner blind tube 2 welded with the second screw rod 7 is subjected to an upward pulling shaft by screwing the first nut 8 To achieve the simulation of the prestress and the test of the interface shear bond strength, the stress sensor 11 is used to detect the axial load of the inner blind pipe 2 .

Based on a device for testing the integrity of cement sheath under simulated prestress, a method for testing the integrity of cement sheath under simulated prestress is proposed. The method mainly includes the following steps:

Step 1: Rotate the first nut 8 to apply an upward-pulling axial load F ₁ to the inner blind tube 2 welded with the second screw 7 , and record the magnitude of the axial load F ₁ through the stress sensor 11 ;

Step 2: Prepare a cement slurry system according to the actual needs of the site, pour cement slurry into the annulus 3, start the heating jacket 5 to heat to the simulated temperature, start the pressure control system 16, load the pressure-bearing chamber 1 to the simulated pressure, and cure to form a cement ring twenty four;

Step 3: After the maintenance is completed, according to the experimental requirements, the loading-unloading of alternating temperature/pressure is realized by controlling the heating jacket 5 and the pressure control system 6;

Step 4: After the pressure in the pressure-bearing chamber 1 is unloaded through the pressure control system 16, the second nut 15 is unscrewed, and the washer 14 is removed;

Step 5: Twist the first nut 8 until the interface between the inner blind pipe 2 and the cement sheath 24 is separated, and record the maximum axial load F ₂ in this process through the stress sensor 11;

Step 6: Calculate the shear bond strength of the cement sheath interface under the action of the prestress F ₁ as σ _b =F ₂ -F ₁ .

Step 7: Different axial loads F ₁ are formed by twisting the first nut 8 , and steps 1 to 6 are repeated to obtain the quantitative relationship between the axial load F ₁ and the shear bond strength σ _b of the cement sheath interface.

Claims (2)

1. A device and a method for testing integrity of a cement ring under the effect of simulated prestress are characterized by comprising a pressure-bearing chamber (1), an inner blind pipe (2), an annular space (3), an outer sleeve (4), a heating sleeve (5), a first screw (6), a second screw (7), a first nut (8), a boosting bearing (9), a square rod (10), a stress sensor (11), a rubber gasket (12), a circular plate (13), a gasket (14), a second nut (15), a pressure control system (16), a first through hole (17), a ring groove (18), a circular groove (19), a second through hole (20), a first male thread (21), a second male thread (22), a third male thread (23) and a cement ring (24); the circular plate (13) comprises a first through hole (17), a ring groove (18) and a circular groove (19) which are respectively used for fixing the inner blind pipe (2), the outer sleeve (4) and the first screw (6); the inner blind pipe (2) welded with the second screw (7) sequentially penetrates through the rubber gasket (12), the first through hole (17) and the gasket (14) and is finally connected with the second nut (15) through the second male thread (22), a pressure control system (16) externally connected with the inner blind pipe (2) is used for loading and unloading the pressure of the pressure bearing chamber (1) to simulate the actual underground pressure, the rubber gasket (12) is used for sealing the annular space (3) to avoid cement leakage when the annular space (3) is used for maintaining the cement ring (24), and the gasket (14) is used for protecting the second nut (5); the annular space (3) for curing cement to form a cement sheath (24) consists of an inner blind pipe (2), an outer sleeve (4), a rubber gasket (12) and a circular plate (13), wherein the outer sleeve (4) is seated in the annular groove (18) to prevent the outer sleeve (4) and the inner blind pipe (2) from being eccentric; a heating sleeve (5) externally connected with a temperature control system is wrapped on the outer wall of the outer sleeve (4) and used for simulating the actual underground temperature; after the first screw rod (6) is connected with the square rod (10) with the second through hole (20) through the third male thread (23), the square rod (10) is inserted out of the second screw rod (7) through the second through hole (20), and the first screw rod (6) is fixed in the circular groove (19); the boosting bearing (9) is inserted outside the second screw (7) and finally placed on the square rod (10) to avoid direct contact between the square rod (10) and the first nut (8); the first nut (8) is connected with the inner blind pipe (2) welded with the second screw (7) through the first male thread (21), the inner blind pipe (2) welded with the second screw (7) bears an axial load which is pulled upwards by screwing the first nut (8), the simulation of prestress and the test of interface cementation strength are realized, and the stress sensor (11) is used for detecting the axial load of the inner blind pipe (2).

2. The device for simulating the integrity of the cement ring under prestress according to claim 1, wherein the testing method of the device for simulating the integrity of the cement ring under prestress comprises the following steps:

the method comprises the following steps: screwing the first nut (8) to apply an upward-pulling axial load F to the inner blind pipe (2) welded with the second screw (7) ₁ And recording the axial load F by means of a stress sensor (11) ₁ The size of (d);

step two: preparing a cement paste system according to actual requirements on site, pouring cement paste into the annulus (3), starting the heating sleeve (5) to heat to a simulated temperature, starting the pressure control system (16), loading the pressure of the pressure-bearing cavity (1) to a simulated pressure, and curing to form a cement sheath (24);

step three: after the maintenance is finished, the heating sleeve (5) and the pressure control system (16) are controlled to realize the loading and unloading of the alternating temperature/pressure according to the experimental requirements;

step four: after the pressure in the pressure-bearing chamber (1) is unloaded through a pressure control system (16), a second nut (15) is unscrewed, and the gasket (14) is removed;

step five: screwing the first nut (8) until the inner blind pipe (2) is separated from the interface of the cement sheath (24), and recording the maximum axial load F in the process through the stress sensor (11) ₂ ；

Step six: calculating the prestress F ₁ The cementing strength of the cement sheath interface under the action is sigma _b ＝F ₂ -F ₁ 。

Step seven: by screwing the first nut (8) different axial loads F are formed ₁ Repeating the first step to the sixth step to obtain the axial load F ₁ Bonding strength sigma to cement sheath interface _b The quantitative relationship of (1).

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