Device for preventing deformation of shale gas well casing and design method

Abstract

A device for preventing deformation of a shale gas well casing belongs to the field of shale gas development and is composed of a pair of semi-annular slips, and the main body structure of each semi-annular slip comprises an outer cladding layer, a metal marble and a lining layer; the outer cladding is a semicircular ring body and is divided into an upper conical ring, a lower conical ring and a semi-cylindrical ring, and the upper conical ring and the lower conical ring are the same in shape and size; half circles of craters are arranged along the inner arc surfaces of the upper conical ring and the lower conical ring, and metal marbles are embedded in the craters; the lining layer is arranged in the inner cambered surface, and holes with the same number as the craters are formed in the lining layer; the upper edge and the lower edge of the outer wrapping layer are each provided with two clamping grooves which are embedded into the edge of the lining layer and provided with an annular sealing ring, and the annular sealing rings are located on the outer side of the lining layer. A pin hole is further formed in the outer wrapping layer and used for being connected with a pin of the two semi-annular slips in an embedded mode. The device is installed at the position of a casing coupling, when the casing is subjected to the effect of abnormal external pressure, the device is excited to rotate, and the abnormal pressure acting on the outer surface of the casing is released.

Description

Technical Field

[0001] The invention belongs to the field of shale gas development, and particularly relates to a device for preventing shale gas well casing deformation and a design method. Background Art

[0002] Casing is a special steel pipe used for cementing oil and gas wells. It is used to maintain the stability of the well wall and isolate different formations, while providing a channel for oil and gas to be produced from the reservoir. The casing consists of a body and a coupling. The coupling is used to connect the casings one by one to form a casing string that is several thousand meters long. During the production of oil and gas wells and various downhole operations, the casing string is subjected to pressure from the formation and the wellbore, and the coupling often becomes a weak point in the pressure. Therefore, when the pressure inside and outside the casing is enough to deform the casing, the most serious deformation and the boundary of the deformation area are mainly located at the location of the coupling.

[0003] In the field operation of shale gas wells, especially those with a depth of more than 4,500 meters, abnormally high-pressure formations and fractured formations often show sudden changes in ground stress. At the same time, factors such as acid fracturing operations carried out from the ground to the well will also exert additional pressure on the casing, bringing the risk of local deformation of the casing. In most cases, the deformation starts from one casing collar, passes through several casings, and ends at another casing collar.

[0004] At present, combined casing is often used to prevent casing deformation. The combined casing is divided into two layers, the inner casing is the usual completion casing (steel), and the outer casing is made of high-strength fiber. The inner casing is connected by upper and lower joints, and the outer casing is sleeved on the outside of the inner casing. There is a water-absorbing expansion device (composed of expansion rubber) between the inner and outer casings. The expansion device completes the expansion process during the cementing process and becomes one with the cement ring. The expanded rubber can buffer the impact of external forces such as fracturing on the casing, and play a role in protecting the casing and preventing casing deformation. Although this measure has a certain effect, it still has the following problems: (1) After the rubber expands, the elasticity will weaken. Therefore, it is necessary to further study the properties of cement slurry and the precise control of rubber expansion coefficient to achieve better results; (2) When the casing string is subjected to external forces, the coupling position is the weakest link. The outer casing of this technology does not cover the coupling position. Summary of the invention

[0005] The purpose of the present invention is to propose a device and a design method for preventing shale gas well casing deformation. The device is installed at the location of the casing coupling. When the casing is subjected to abnormal external pressure, the device is stimulated to rotate to a certain extent, thereby releasing the abnormal pressure acting on the outer surface of the casing.

[0006] The technical solution adopted by the present invention is:

[0007] A device for preventing casing deformation of a shale gas well is composed of a pair of semi-annular slips, wherein the main structure of the semi-annular slips comprises an outer cladding, a metal marble and an inner lining; the outer cladding is integrally formed and is a semi-circular ring as a whole, and the semi-circular ring is divided into an upper cone ring, a lower cone ring, and a semi-cylindrical ring located between the upper cone ring and the lower cone ring; the upper cone ring and the lower cone ring have the same shape and size, and the center of the upper end face of the upper cone ring is not on the same vertical axis as the center of the lower end face;

[0008] A half circle of craters is arranged along the inner arc surface of the upper cone ring and the lower cone ring, and metal marbles are embedded in the craters; the inner lining layer is arranged in the inner arc surface, and the inner lining layer is provided with holes having the same number as the craters, and the diameter of the holes is smaller than the diameter of the metal marbles;

[0009] The inner lining layer is in the shape of a hollow semicircular ring as a whole, which is used to clamp the metal marbles. All the metal marbles are tightly clamped by the annular space formed by the outer layer and the inner lining layer to prevent the metal marbles from falling.

[0010] Two grooves are respectively arranged on the upper and lower edges of the outer layer, one of which is used to embed the edge of the inner lining layer, and the other is used to set an annular sealing ring, which is located outside the inner lining layer;

[0011] The outer side of the lining layer refers to the side away from the outer covering body and close to the casing coupling.

[0012] The outer cladding is also provided with pin holes for embedding pins connecting the two semi-annular slips.

[0013] Furthermore, the length of the semi-annular slip is: along the axial direction of the casing coupling, from the center of the casing coupling, extending 25 cm to 100 cm upward and downward respectively.

[0014] Furthermore, an anti-stick coating is plated on the outer surface of the outer cladding layer, and the material of the anti-stick coating is Teflon or nano anti-stick coating.

[0015] Furthermore, the density and diameter parameters of the metal marbles are determined according to the maximum stress value that can be generated, and the relationship is:

[0016]

[0017] Where, T d is the maximum stress value that the metal marble can produce in each direction, a1, b1, k1, k2 are constants, ρ1 is the density of the metal marble, and d1 is the diameter of the metal marble.

[0018] Furthermore, the density and thickness parameters of the outer cladding are determined according to the maximum stress value that can be generated, and the relationship is:

[0019]

[0020] Where, T b is the maximum stress value that the outer cladding can produce in each direction, a2, b2, k3, k4 are constants, ρ2 is the outer cladding density, and d2 is the outer cladding thickness.

[0021] Furthermore, the stress value borne by the entire device is the minimum value between the maximum stress value that can be generated by the metal marble and the maximum stress value that can be generated by the outer cladding.

[0022] Before an elastomer undergoes plastic deformation, the amount of stress (pressure) given to it by the outside world will determine how much stress it will produce inside it, until this stress reaches the maximum stress it can produce (this maximum stress is related to the material, density, and diameter of the elastomer). Once the elastomer produces the maximum stress, it means that deformation has occurred. Therefore, when designing the parameters of the marbles and cladding, it is necessary to know the maximum (internal) stress values ​​that can be produced by each under the action of external forces. The design goal is that the smaller one can resist the external force without producing plastic deformation. At this time, the design parameters of the one with the larger maximum stress value will not be adjusted.

[0023] The above idea is based on the assumption that the device can rotate under the action of external force. Then, when the combined external force just reaches a balance, so that the device cannot rotate, the solution is to make the smaller of the above maximum stresses smaller than the external force, and rely on the local plastic deformation of the device to achieve the purpose of releasing the external force.

[0024] A method for designing a device for preventing shale gas well casing deformation comprises the following steps:

[0025] S1: Select the same grade of steel as the casing as the material of the metal marbles and the outer cladding; that is, determine the density of the metal marbles and the outer cladding.

[0026] S2: According to the maximum stress value from the formation outside the casing, in formula (a), the maximum stress value acting on the casing is taken to determine the diameter of the metal marble;

[0027] S3: According to the maximum stress value existing in the formation outside the casing, in formula (b), the maximum stress value acting on the casing is taken to determine the thickness of the outer cladding;

[0028] S4: Determine the inner diameter of the outer cladding, which is equal to the sum of the diameter of the metal marble determined in step S2 and the outer diameter of the casing;

[0029] S5: According to the inner diameter of the outer layer and the diameter parameters of the metal marbles, holes are designed and excavated on the inner lining layer. If there are gaps between adjacent metal marbles, the sizes of these gaps are evenly distributed.

[0030] Furthermore, the diameter of the metal marbles is designed with two levels of values, the first level value is equal to the calculated value of step S2, and the second level value is 1-5 mm smaller than the first level value. The metal marbles of the two levels of values ​​are arranged at intervals inside the outer layer (i.e., a small-sized marble is arranged on each side of a large-sized marble), and a cap-shaped rubber pad is filled in the gap between the metal marbles of the second level value (small-sized marbles) and the outer layer. The cap-shaped rubber pad is stuck between the outer layer and the inner lining layer at the same time.

[0031] Beneficial effects of the present invention:

[0032] The present invention provides a pair of semi-annular slips composed of an outer layer, a metal marble and an inner lining layer, and arranges them outside the casing coupling. When an external force acts on the casing coupling and causes it to deform, the slips rotate to release abnormal pressure, thereby protecting the coupling. In the case where the combined external force just reaches a balance and the device fails to rotate, the purpose of releasing the external force can also be achieved by relying on the local plastic deformation of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is an appearance diagram of the semi-annular slip of the present invention;

[0034] Figure 2 It is a top view of the upper and lower cone ring parts of the semi-annular slip;

[0035] Figure 3 is a longitudinal sectional view of a semi-annular slip portion;

[0036] Figure 4 This is the plan view of the outer cladding after it is unfolded;

[0037] Figure 5 1 is a diagram of the composition of the slips, casing and couplings of the present invention; (a) shows the state of the slips in place outside the casing coupling, (b) shows the appearance of the slips (side view), and (c) shows the casing and couplings;

[0038] Figure 6 It is an overall picture of two semi-annular slips connected by pins;

[0039] Figure 7 It is a schematic diagram of the force on the casing in a vertical well and a horizontal well;

[0040] In the figure, 1, outer layer, 2, metal marbles, 3, inner lining layer, 4, cap-shaped rubber pad. DETAILED DESCRIPTION

[0041] like Figure 1 to Figure 6As shown, a device for preventing casing deformation of a shale gas well is composed of a pair of semi-annular slips, the main structure of which includes an outer cladding 1, a metal marble 2 and an inner lining 3; the outer cladding 1 is integrally formed and is a semi-circular ring as a whole, and the semi-circular ring is divided into an upper cone ring, a lower cone ring, and a semi-cylindrical ring located between the upper cone ring and the lower cone ring, the upper cone ring and the lower cone ring are the same in shape and size, and the center of the upper end face of the upper cone ring is not on the same vertical axis as the center of the lower end face;

[0042] A half circle of craters is arranged along the inner arc surface of the upper cone ring and the lower cone ring, and metal marbles 2 are embedded in the craters; the inner lining layer 3 is arranged in the inner arc surface, and the inner lining layer 3 is provided with holes having the same number as the craters, and the diameter of the holes is smaller than the diameter of the metal marbles 2;

[0043] The inner lining layer 3 is in the shape of a hollow semicircular ring as a whole, and is used to clamp the metal marbles 2. All the metal marbles 2 are tightly wrapped and clamped by the annular space formed by the outer layer 1 and the inner lining layer 3 to prevent the metal marbles 2 from falling.

[0044] Two grooves are provided on the upper and lower edges of the outer covering 1, one of which is used to embed the edge of the inner lining 3, and the other is used to set an annular sealing ring, which is located on the outside of the inner lining 3; the outside of the inner lining 3 refers to the side away from the main body of the outer covering 1 and close to the casing coupling.

[0045] The outer cladding 1 is also provided with pin holes for embedding pins connecting the two semi-annular slips.

[0046] The length of the semi-annular slip is: along the axis direction of the casing coupling, from the center of the casing coupling, extending 50 cm upward and downward respectively. The outer surface of the outer cladding 1 is plated with an anti-stick coating, and the material of the anti-stick coating is Teflon or nano anti-stick coating.

[0047] The density and diameter parameters of the metal marbles are determined according to the maximum stress value that can be generated, and the relationship is:

[0048]

[0049] Where, T d is the maximum stress value that the metal marble can produce in each direction, a1, b1, k1, k2 are constants, ρ1 is the density of the metal marble, and d1 is the diameter of the metal marble.

[0050] The design parameters of the metal marbles in this embodiment are shown in Table 1.

[0051] Table 1 Relationship between the maximum stress of metal marbles and the density and diameter of the marbles (ρ = density g / cm 3 ; d = diameter in mm; T d = Maximum stress MPa)

[0052]

[0053] According to the results in Table 1, the parameters in relation (a) are obtained, and then the relationship between density and diameter under maximum stress is obtained. When the density is constant, the required diameter can be obtained.

[0054] The density and thickness parameters of the outer cladding are determined according to the maximum stress value that can be generated, and the relationship is:

[0055]

[0056] Where, T b is the maximum stress value that the outer cladding can produce in each direction, a2, b2, k3, k4 are constants, ρ2 is the outer cladding density, and d2 is the outer cladding thickness.

[0057] The design parameters of the outer cladding layer of this embodiment are shown in Table 2.

[0058] Table 2 Relationship between the maximum stress of the outer cladding and the density and thickness of the outer cladding (ρ = density g / cm 3 ; d = thickness mm; T b = Maximum stress MPa)

[0059]

[0060] Similarly, the required outer cladding thickness value is obtained.

[0061] The stress value that the entire device is subjected to is the minimum value between the maximum stress value that the metal marble can produce and the maximum stress value that the outer cladding can produce.

[0062] Before an elastomer undergoes plastic deformation, the amount of stress (pressure) given to it by the outside world will determine how much stress it will produce inside it, until this stress reaches the maximum stress it can produce (this maximum stress is related to the material, density, and diameter of the elastomer). Once the elastomer produces the maximum stress, it means that deformation has occurred. Therefore, when designing the parameters of the marbles and cladding, it is necessary to know the maximum (internal) stress values ​​that can be produced by each under the action of external forces. The design goal is that the smaller one can resist the external force without producing plastic deformation. At this time, the design parameters of the one with the larger maximum stress value will not be adjusted.

[0063] The above idea is based on the assumption that the device can rotate under the action of external force. Then, when the combined external force just reaches a balance, so that the device cannot rotate, the solution is to make the smaller of the above maximum stresses smaller than the external force, and rely on the local plastic deformation of the device to achieve the purpose of releasing the external force.

[0064] A method for designing a device for preventing shale gas well casing deformation comprises the following steps:

[0065] S1: Select steel of the same grade as the casing as the material of the metal marbles 2 and the outer cladding 1; that is, determine the density of the metal marbles and the outer cladding. The density of the steel selected in this embodiment is 7.81g / cm 3 ;

[0066] S2: According to the maximum stress value existing in the formation outside the casing, in formula (a), the maximum stress value acting on the casing is taken to determine the diameter of the metal marble 2;

[0067] S3: According to the maximum stress value existing in the formation outside the casing, in formula (b), the maximum stress value acting on the casing is taken to determine the thickness of the outer cladding 1;

[0068] S4: Determine the inner diameter of the outer cladding 1, which is equal to the sum of the diameter of the metal marble 2 determined in step S2 and the outer diameter of the sleeve;

[0069] S5: According to the inner diameter value of the outer cladding layer 1 and the diameter parameters of the metal marbles 2, holes are designed and excavated on the inner lining layer 3. If there are gaps between adjacent metal marbles 2, the sizes of these gaps are evenly distributed.

[0070] The diameter of the metal marbles 2 is designed with two-level values, the first-level value is equal to the calculated value of step S2, and the second-level value is 2 mm smaller than the first-level value. The metal marbles 2 of the two-level values ​​are arranged at intervals inside the outer layer 1 (i.e., a small-sized marble is arranged on each side of a large-sized marble), and a cap-shaped rubber pad 4 is filled in the gap between the metal marbles 2 of the second-level value (small-sized marbles) and the outer layer 1. The cap-shaped rubber pad 4 is stuck between the outer layer 1 and the inner lining layer 3 at the same time.

[0071] Mechanism of casing deformation: After the casing is lowered into the well, it will be subjected to pressure from the surrounding strata. At the same time, the fluid in the well also exerts pressure on the casing. When the yield strength of the casing is sufficient to withstand the combined effect of internal and external pressures, the casing remains in its original state and does not deform. However, the ground stress of the formation itself will change with factors such as the movement of the earth's crust, changes in the formation structure, and artificial fracturing operations. This change will cause the pressure acting on the casing to change. The dynamic pressure changes that the casing is subjected to are more likely to cause the casing to deform than the static pressure that the casing is subjected to as mentioned above.

[0072] like Figure 7As shown in the figure, the ground stress from the formation acts on the casing through the cement sheath. The better the cementing quality, the better the consolidation effect of the cement sheath, casing and formation, and the easier it is to transmit the change of ground stress to the casing. The casing is continuously affected by the ground stress of the oil and gas field in the formation. When this effect is in a relatively static state, the casing change will be the result of a long-term, slow change; when this effect is in a state of relative motion, the casing change will be the result of an instantaneous, rapid change ( Figure 7 The bamboo tube in the middle is a casing with a collar. The left picture shows a vertical well, and the right picture shows a horizontal well.) The main factors causing sudden changes in ground stress include changes in formation structure and the implementation of downhole operations such as fracturing.

[0073] The mechanism of action of the device of the present invention is: when a force acts on an object, if the object can slide or rotate, the force will be released, thereby reducing the plastic deformation of the object caused by the force. A rotating body that can rotate with the external force is set between the casing and the cement ring, especially at the casing coupling. When the local stress changes and causes a greater pressure on the casing, the force acts on the rotating body through the cement ring, and the stimulated rotating body rotates, thereby reducing or avoiding the further stress burden on the casing caused by the force.

[0074] Instructions for use: (1) Assembly of a single semi-annular slip: Apply silicone grease to the inner surface of the outer cladding, and place the marbles one by one into the crater of the outer cladding; apply silicone grease to the inner surface of the inner lining (the side close to the crater) and the gap between the marbles, and insert the inner lining and the annular sealing ring into the two grooves of the outer cladding in sequence; (2) Installation of the semi-annular slip at the casing coupling: With the help of a special working cylinder, apply silicone grease to the space between the inner lining and the top of the marbles, that is, the outer surface of the inner lining; buckle a pair of semi-annular slips on the outer surface of the casing coupling, and connect the pair of semi-annular slips with pins; when connecting, pay attention to the consistency of the upper and lower gaps between the joint surfaces of the pairs of semi-annular slips.

[0075] Among them, during the production process, the slips must complete the magnetization process together with the casing coupling to prevent the slips from having a negative impact on the logging curve of the casing coupling.

[0076] The paired semi-annular slips are installed on the outside of the casing coupling when the casing is lowered. After installation, the device and the casing coupling are tightly combined along the casing axis and vertically along the casing axis. When the cementing operation is completed, due to the bonding effect of the cement ring, the slips are in a fixed state in both the longitudinal and transverse directions (i.e., the casing axis and vertically along the casing axis).

[0077] After that, three situations will occur: First, when the anti-sticking effect of the device's outer coating remains good and the cement bonding does not cause a decisive obstacle to the free rotation of the device, in the direction perpendicular to the casing axis, when an external force acts on the slip, the slip will rotate around the casing coupling. Second, when the anti-sticking effect of the device's outer coating fails and the resistance of the cement bonding to the rotation of the device is greater than other combined external forces, the device will not rotate. Third, when the anti-sticking effect of the device's outer coating remains good and the cement bonding does not cause a decisive obstacle to the free rotation of the device, but at this time the combined external force on the slip just reaches a balance in all directions on the same horizontal plane, the device will also remain motionless.

[0078] When situation 2 or situation 3 occurs, the slip will not rotate for a long time or a short time. At this time, the release of the device to the external force is mainly completed by the rubber pad between some marbles and the outer layer. At the same time, the external force is a constantly changing process. Especially during hydraulic fracturing operations, the forces from all directions will quickly break the balance described in situation 3 above. The cement ring around the slip will also be damaged to a certain extent, resulting in a random direction of force on the slip, causing the slip to rotate. In addition, the maximum stress of the marbles with a smaller diameter is less than the maximum stress of the marbles with a larger diameter and the outer layer. This situation will cause the small diameter marbles to be deformed first when the device does not rotate for a long time, resulting in the release of external force. At the same time, the static state of the slip will be broken and rotate synchronously.

[0079] It can be seen that in any of the above three situations, the slips can rotate under changing conditions, thereby releasing the changes in ground stress from the stratum and protecting the coupling from damage.

[0080] After the casing is lowered, the coupling position is determined by the magnetic coupling positioning logging method, and then the coupling signal with the device of the present invention is compared and analyzed with the coupling signal without the device of the present invention on the logging curve to obtain the state of the slips after the casing coupling is in place underground. If necessary, the dynamics of the excited rotation of the device of the present invention can be mastered by measuring the magnetic positioning curve of the casing coupling (measured once at intervals during the production process).

Claims

1. A device for preventing shale gas well casing deformation, characterized in that: The invention is composed of a pair of semi-annular slips, wherein the main structure of the semi-annular slips comprises an outer layer (1), a metal marble (2) and an inner lining layer (3); the outer layer (1) is integrally formed and is in the form of a semi-circular ring as a whole, and the semi-circular ring is divided into an upper cone ring, a lower cone ring, and a semi-cylindrical ring located between the upper cone ring and the lower cone ring, wherein the upper cone ring and the lower cone ring have the same shape and size, and the center of the upper end face of the upper cone ring is not on the same vertical axis as the center of the lower end face; A half circle of craters is arranged along the inner arc surface of the upper cone ring and the lower cone ring, and metal marbles (2) are embedded in the craters; the inner lining layer (3) is arranged in the inner arc surface, and the inner lining layer (3) is provided with holes having the same number as the craters, and the diameter of the holes is smaller than the diameter of the metal marbles (2); Two grooves are respectively provided at the upper and lower edges of the outer covering layer (1), one of which is used to embed the edge of the inner lining layer (3), and the other is used to set an annular sealing ring, and the annular sealing ring is located outside the inner lining layer (3); The outer cladding (1) is also provided with pin holes for embedding pins for connecting the two semi-annular slips.

2. A device for preventing casing deformation in a shale gas well according to claim 1, characterized in that: The length of the semi-annular slip is: along the axial direction of the casing coupling, from the center of the casing coupling, extending 25cm to 100cm upward and downward respectively.

3. The device for preventing casing deformation in shale gas wells according to claim 1, characterized in that: An anti-stick coating is plated on the outer surface of the outer covering layer (1), and the material of the anti-stick coating is Teflon or nano anti-stick coating.

4. The device for preventing casing deformation in shale gas wells according to claim 1, characterized in that: The density and diameter parameters of the metal marble (2) are determined according to the maximum stress value that can be generated, and the relationship is: Where, T d is the maximum stress value that the metal marble can produce in each direction, a1, b1, k1, k2 are constants, ρ1 is the density of the metal marble, and d1 is the diameter of the metal marble.

5. The device for preventing casing deformation in shale gas wells according to claim 1, characterized in that: The density and thickness parameters of the outer cladding (1) are determined according to the maximum stress value that can be generated, and the relationship is: Where, T b is the maximum stress value that the outer cladding can produce in each direction, a2, b2, k3, k4 are constants, ρ2 is the outer cladding density, and d2 is the outer cladding thickness.

6. A design method for preventing shale gas well casing deformation, characterized in that: The following steps are involved: S1: Select steel of the same grade as the casing as the material of the metal marble (2) and the outer cladding (1); S2: According to the maximum stress value existing in the formation outside the casing, in formula (a), the maximum stress value acting on the casing is taken to determine the diameter of the metal marble (2); S3: According to the maximum stress value existing in the formation outside the casing, in formula (b), the maximum stress value acting on the casing is taken to determine the thickness of the outer cladding (1); S4: Determine the inner diameter of the outer cladding (1), which is equal to the sum of the diameter of the metal marble (2) determined in step S2 and the outer diameter of the casing; S5: Design and dig holes on the inner lining layer (3) according to the inner diameter value of the outer cladding layer (1) and the diameter parameter of the metal marbles (2).

7. A method for designing a device for preventing casing deformation in a shale gas well according to claim 6, characterized in that: The diameter of the metal marbles (2) is designed with two levels of values, the first level value is equal to the calculated value of step S2, and the second level value is 1-5 mm smaller than the first level value. The metal marbles (2) with two levels of values ​​are arranged at intervals inside the outer layer (1), and a cap-shaped rubber pad (4) is filled in the gap between the metal marbles (2) with the second level value and the outer layer (1).

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