Prediction method of casing displacement based on one-way seal hanger

Abstract

The present invention discloses a method for predicting casing displacement based on a one-way sealing hanger, comprising the following steps: based on the fluid injection time and injection volume, obtaining the distribution of each part of the fluid in the casing, and then obtaining the position of the cement slurry when the cement slurry loses weight; based on the distribution of each part of the fluid in the casing, combined with the density of each part of the fluid, obtaining the pressure distribution in the casing and the annular pressure distribution during the pressure holding and setting period; considering the hydration weight loss of the cement slurry during the pressure holding and setting period, obtaining the annular pressure distribution after the cement slurry loses weight; based on the casing deformation theory, obtaining the pressure differential displacement of the casing, and calculating the thermal displacement of the casing based on the heat release of cement slurry hydration and the thermal expansion of the cement slurry; the sum of the pressure differential displacement and the thermal displacement is the predicted value of the total casing displacement. The method of the present invention takes into account the transient analysis of the entire cementing and cementing cycle and the influence of the hydration reaction of the cement slurry during the setting period, and can effectively predict the casing displacement during cementing operations.

Description

Technical Field

[0001] The invention relates to the technical field of well cementing, and in particular to a method for predicting casing displacement based on a one-way sealing hanger. Background Art

[0002] During oil and gas well cementing operations, maintaining a complete wellbore seal is crucial for ensuring the long-term stability of the well. During actual cementing operations, the cement slurry, due to factors such as hydration reactions and temperature fluctuations during the curing period, undergoes volumetric shrinkage after transforming into cement paste. This can lead to bond failure between the cement slurry and the casing wall, resulting in the formation of microgaps. These microgaps create potential flow channels outside the casing, allowing oil and gas to penetrate the cement sheath seal and migrate directly upward through the annulus, causing interlayer gas channeling, annular pressure, and seal failure. Furthermore, residual fluid in these microgaps, under high temperature and high pressure, can accelerate corrosion of the casing material, shortening the service life of the well. The presence of microgaps not only impacts the normal production of the well but can also cause environmental pollution and safety incidents, posing a significant challenge to the long-term stability of oilfield production. Therefore, reducing or even eliminating microgaps generated during cementing operations is of great engineering significance.

[0003] Currently, liner cementing often uses clean water or low-density fluids for slurry displacement. This results in a lower pressure inside the casing than in the annulus at the end of cementing, causing the casing to elastically deform toward the wellbore center, creating prestress. This is known as prestressed cementing. During the waiting period, as the cement slurry hydrates, the annulus pressure decreases, causing the casing to gradually recover its deformation and expand toward the wellbore wall. This radial displacement effectively compacts the cement sheath, thereby compensating for the micro-gaps caused by shrinkage after the cement slurry solidifies into cement paste. However, prestressed cementing is not limited to conventional cementing equipment. During this process, high-pressure cementing trucks are required. Because clean water displaces the slurry and spacer fluid, the pressure inside the casing is significantly lower than the annulus pressure, resulting in a high pressure differential and placing high demands on the truck's pump. Furthermore, high requirements are placed on the back-pressure valve in the float collar. This valve prevents cement slurry from the annulus from entering the casing during or at the end of cementing. Failure of the valve can lead to cementing failure. The greater the pressure differential between the inside and outside of the casing, the higher the performance requirements for the back-pressure valve. When using prestressed cementing, the pressure differential between the annulus and the casing can reach tens of MPa, requiring high-pressure float collars, which increases the cost of cementing accessories. Furthermore, during prestressed cementing, the effective external extrusion pressure on the casing is high, requiring casing with high external extrusion resistance. Therefore, prestressed cementing requires high-pressure cement trucks, high-pressure float collars, and casing with high external extrusion resistance, further increasing the cost of commissioning the well.

[0004] A current method for prestressed cementing involves installing a one-way blind plate on the liner hanger. At the end of cementing, the blind plate seals the hanger opening when the drill string is reversed and lifted. During the period of pressure buildup, the seal prevents wellhead pressure from being transmitted through the blind plate to the casing fluid. Furthermore, the fluid above the blind plate acts only on the blind plate and cannot be transmitted into the casing. At this point, the pressure within the liner is solely the hydrostatic pressure of the liner fluid, while the annular pressure is the sum of the annular fluid pressure and the wellhead pressure. This results in annular pressure significantly greater than the casing pressure, causing the casing to contract into the wellbore. As the cement slurry gradually transforms into a liquid or plastic product, the annular pressure decreases, and the casing rebounds toward the wellbore wall, alleviating the annular microgaps caused by volumetric contraction during the transformation of the cement slurry into cement paste. This method also achieves the same prestressing effect while eliminating the high-pressure cement paste, high-pressure-bearing float collars, and high-extrusion-resistance casing required for prestressed cementing. However, if you want to achieve the best cementing effect, the selection of cementing parameters is the key. The existing technology can only roughly estimate the casing displacement under different cementing parameter conditions through experience, which is relatively inaccurate and has limited guidance effect on the site. Summary of the Invention

[0005] To solve at least one of the above problems, the present invention proposes a method for predicting casing displacement based on a one-way sealing hanger. The method has relatively low cost and high prediction accuracy.

[0006] The technical solution of the present invention is: a method for predicting casing displacement based on a one-way sealing hanger, comprising the following steps:

[0007] Based on the fluid injection time and injection volume, the distribution of the fluid in each part of the casing when the cement slurry is pressurized and solidified is obtained, and based on the fluid distribution, the position of the cement slurry when the cement slurry loses weight is obtained;

[0008] Based on the distribution of fluids in each part of the casing and the density of each part of the fluid, the pressure distribution in the casing and the annular space during the pressure holding and solidification period are obtained;

[0009] Considering the hydration weight loss of cement slurry during the pressure holding and setting period, when the static gel strength of cement slurry reaches 240Pa during the pressure holding and setting period, the annular pressure distribution after the cement slurry loses weight is obtained;

[0010] Based on the casing deformation theory, the pressure differential displacement of the casing under the action of the internal pressure and the annular pressure is calculated. The thermal displacement of the casing during temperature changes is calculated based on the heat release of cement slurry hydration and the thermal expansion of the cement slurry. The sum of the pressure differential displacement and the thermal displacement is the predicted value of the total casing displacement.

[0011] Beneficial effects: The method of the present invention takes into account the transient analysis of the entire cementing cycle and the influence of hydration reaction of cement slurry during the setting period, and can effectively predict the casing displacement during cementing operations, providing theoretical guidance for the subsequent evaluation of cement sheath sealing. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a slurry density distribution curve in the wellbore after cementing is completed according to an embodiment of the present invention;

[0013] Figure 2 This is the density distribution curve in the annulus after the displacement is completed in the embodiment of the present invention;

[0014] Figure 3 This is a diagram showing the calculation results of the pressure distribution in the tail pipe section during the pressure holding and solidification period according to an embodiment of the present invention;

[0015] Figure 4 This is a prediction diagram of the shrinkage displacement of the casing of the tail pipe section according to an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The specific implementation methods of the present invention will be clearly and completely described below with reference to examples and drawings. Obviously, the described examples are only some embodiments of the present invention, rather than all embodiments.

[0017] A method for predicting casing displacement based on a one-way seal hanger comprises the following steps:

[0018] S1. Based on the fluid injection time and injection volume, the distribution of the fluid in each part of the casing during the cement slurry pressure holding and setting is obtained, and based on the fluid distribution, the position of the cement slurry when the cement slurry loses weight is obtained;

[0019] Get the casing volume and annulus volume: Where V p is the volume of the flow channel at each node j; D o is the outer diameter of the casing; e is the wall thickness of the casing; dl is the depth step; Where D is the wellbore diameter;

[0020] Based on the volume and displacement of each fluid during on-site construction, calculate the time it takes for each fluid to be injected into the wellbore: Where, t is the time it takes for the fluid to be injected into the wellbore; V i is the volume of each fluid; Q i is the displacement of each fluid when injected; i is the type of fluid; n is the number of fluids;

[0021] Calculate the volume of different fluids at different points in time:

[0022]

[0023] In the formula is the total volume of fluid injected from the start of injection to time t for the i-th group of fluid; is the total volume of the flow channel from the casing inlet to the node j;

[0024] Based on the cementing completion time, the distribution of various fluids in the pipe during the period of cement slurry pressure buildup and solidification can be obtained.

[0025] In fact, the above formula can be used to calculate the fluid distribution at different time points during the cementing process. However, in this embodiment, only the fluid distribution at the end of cementing is required (at the end of this stage, no further fluid is injected, so the fluid distribution in subsequent stages, such as pressure holding and waiting for setting and cement slurry weight loss, does not change). Therefore, in this embodiment, only the time of cement slurry pressure holding and waiting for setting needs to be included.

[0026] S2. Based on the distribution of the fluid in each part of the casing and the density of the fluid in each part, the pressure distribution in the casing and the annular pressure distribution during the pressure holding and solidification period are obtained;

[0027] The pressure inside the casing during the holding pressure and solidification period is calculated using the following formula: P p =∑ρ pi gh j cosθ, where P p represents the pressure distribution inside the casing, ρ pi represents the density of the i-th fluid in the tube, g represents the acceleration due to gravity, h j represents the depth step at the liner section j, and θ represents the well inclination angle;

[0028] The annular pressure during the holding pressure period is calculated using the following formula: P a '=P0+∑ρ ai HkDJ j cosθ, where P a , represents the annular pressure during the holding pressure period, p0 represents the wellbore holding pressure, ρ ai represents the density of the i-th fluid in the annulus, H j represents the depth step at wellbore j, g represents the acceleration of gravity, and θ represents the well inclination angle.

[0029] For the above h j and H j Mainly considering the length of the wellbore, we divide the wellbore into multiple depth steps and calculate the pressure distribution within the wellbore by segmenting. As for the segment length, those skilled in the art can segment according to actual conditions, such as a depth step of 10m.

[0030] S3. Considering the hydration weight loss of cement slurry during the holding pressure and setting period, when the static gel strength of cement slurry reaches 240 Pa during the holding pressure and setting period, obtain the annular pressure distribution after the cement slurry loses weight;

[0031] It is calculated as follows: Where, P a represents the annular pressure distribution, P top represents the top pressure of cement slurry, ρ c represents the cement paste density, ρ w Indicates water density, L cem Indicates the length of cement slurry section, SGS c It represents the static gel strength of cement slurry, D represents the wellbore diameter, and Do represents the outer diameter of casing.

[0032] In this embodiment, SGS c The value is 240Pa.

[0033] S4. Based on the casing deformation theory, the pressure differential displacement of the casing under the action of the internal pressure and the annular pressure is calculated; based on the heat release of cement slurry hydration and the thermal expansion of cement slurry, the thermal displacement of the casing during temperature changes is calculated; the sum of the pressure differential displacement and the thermal displacement is the predicted value of the total casing displacement.

[0034] Among them, after the cement slurry is injected, the casing and cement slurry will solidify into a whole, so the bending deformation can be ignored, the axial load can be ignored, and the three-dimensional wellbore model can be simplified to a plane strain model. The wellbore model is regarded as a two-dimensional plane stress problem of a thick-walled cylinder, and the following is established: Figure 2 The wellbore plane physical model shown is assumed to be a homogeneous isotropic material. The casing and cement slurry are completely bonded during the solidification process, the casing is not damaged, and the temperatures of the casing and cement slurry vary uniformly along the radial direction.

[0035] During the cement slurry pressure holding and setting stage, the casing is regarded as an elastic material. Considering the radial displacement of the casing under the pressure difference between the inner pressure and the annular pressure, the displacement equation of the casing outer wall under the pressure difference is obtained.

[0036] a) Geometric equations:

[0037]

[0038] Where: ε r represents radial strain; ω θ represents the circumferential strain; γ rθ represents shear strain; u r represents radial displacement; v θ represents the circumferential displacement;

[0039] b) Constitutive equation:

[0040]

[0041] c) Based on the geometric equation and constitutive equation, the displacement equation can be derived:

[0042]

[0043] The radial displacement u generated by the outer wall of the casing is obtained by solving the displacement equation sl1 , the calculation equation is as follows.

[0044]

[0045] E represents the elastic modulus of the casing; μ represents the Poisson's ratio of the casing; P p Indicates the pressure inside the pipe; P a represents the annular pressure; r1 represents the inner radius of the casing; r2 represents the outer radius of the casing.

[0046] Since the heat released during the hydration of cement slurry causes the wellbore temperature to rise, the cement slurry will expand, causing thermal displacement of the casing. Therefore, it is necessary to consider the radial thermal displacement of the outer wall of the casing due to the temperature change during the hydration of cement slurry.

[0047] a) Strain under temperature influence:

[0048] ε θT =(1+μ)βΔT

[0049] Where, ε T represents thermal strain; μ represents Poisson's ratio; β represents the thermal expansion coefficient of the casing; ΔT represents the temperature change;

[0050] b) Wall displacement under temperature influence:

[0051] u T =(1+μ)rβΔT

[0052] Where u T represents thermal displacement;

[0053] Therefore, the temperature change during the heat release of cement slurry produces radial thermal displacement u on the outer wall of the casing. sl2 for:

[0054] u sl2 =-(1+μ)r2βΔT

[0055] Where, μ represents the Poisson's ratio of the casing; r2 represents the outer radius of the casing; β represents the thermal expansion coefficient of the casing; ΔT represents the temperature change;

[0056] The final total displacement of the casing is: u sl =u sl1 +u sl2 .

[0057] The following is an example of the present invention. A natural gas well was drilled to 5492 m and cemented. A 139.7 × 9.17 mm drill pipe was used to suspend a 196.85 × 16.83 mm tail pipe for cementing. A one-way sealing blind plate was installed on the hanger. The tail pipe bell mouth was located at 2746 m, and the overlap section was 400.38 m long. The dimensions of the upper casing were 282.58 × 18.64 mm, and the average diameter of the open hole section was 260.1 mm. The drilling fluid density in the wellbore was 2.27 g / cm 3 The cementing process uses the following slurry column structure to inject in sequence: 20L / s injection 3m 3 Density 1.03g / cm 3 Flushing fluid: Displacement 20L / s, injection 12m 3 Density 2.30g / cm 3 Isolation fluid; displacement 15L / s injection 13m 3 Density 2.30g / cm 3 Add weight to the flushing fluid; discharge volume 20L / s and inject into 1m 3 Density 1.03g / cm 3 Flushing fluid: Displacement 20L / s, injection 19m 3 Density 2.32g / cm 3 Slow-setting cement slurry; displacement 20L / s injection 54.5m 3 Density 2.32g / cm 3 Quick-drying cement slurry; displacement 22L / s injection 2m 3 Density 1.03g / cm 3 Tamponade liquid: displacement 21L / s, injection 50m 3 Density 2.27g / cm 3 Drilling fluid: 22L / s injection per 10m 3 Density 2.30g / cm 3 Isolation fluid; displacement 20L / s injection 23m 3 Density 2.27g / cm 3 Drilling fluid: displacement 13L / s, injection 4m 3 Density 1.00g / cm 3 Clean water pressure.

[0058] Substitute the above construction parameters into step 1 to calculate the slurry distribution in the pipe and annulus during cementing. Figure 1 The density distribution curve of the slurry in the wellbore after cementing is completed. After the cementing construction is completed, the hanger blind plate is sealed and the fluid in the well section above the hanger is completely replaced with a density of 2.27g / cm 3 Drilling fluid, the density distribution in the annulus is as follows Figure 2 shown.

[0059] After the displacement is completed, the wellhead is pressurized to hold the pressure and wait for solidification. The wellhead pressure is set to 10MPa. During the holding pressure and waiting process, the slurry density distribution is obtained and the pressure distribution in the tail pipe is obtained based on the calculation. As the cement slurry hydration reaction proceeds, the cement slurry loses weight during the holding pressure process, and the annular pressure decreases and tends to be stable. At this time, by analyzing the annular slurry density distribution after the drilling fluid is displaced in the well section above the hanger in step 2, the annular pressure distribution after weight loss can be calculated in combination with the S3 calculation formula. Finally, the pressure distribution calculation results of the tail pipe section when the blind plate seal of the one-way sealing hanger is holding the pressure and waiting for solidification are as follows: Figure 3 As shown in the curve, the results show that a large pressure difference is formed between the inner and outer walls of the tail pipe section casing, with an average pressure difference of 71.83 MPa.

[0060] During the pressure holding and setting stage, the casing shrinkage displacement can be predicted according to S4 through the pressure difference between the inner and outer walls of the casing. The casing shrinkage displacement includes the displacement caused by the pressure difference and the thermal displacement caused by the hydration expansion of the cement slurry. Figure 4 This is a prediction diagram of the casing shrinkage displacement of the tail pipe section of the example of the present invention.

[0061] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for predicting casing displacement based on a one-way seal hanger, characterized in that: The following steps are involved: Based on the fluid injection time and injection volume, the distribution of the fluid in each part of the casing during the cement slurry pressure holding and solidification is obtained, and the position of the cement slurry when the cement slurry loses weight is obtained based on the fluid distribution; Based on the distribution of fluids in each part of the casing and the density of each part of the fluid, the pressure distribution in the casing and the annular space during the pressure holding and solidification period are obtained; Considering the hydration weight loss of cement slurry during the pressure holding and setting period, when the static gel strength of cement slurry reaches 240Pa during the pressure holding and setting period, the annular pressure distribution after the cement slurry loses weight is obtained; Based on the casing deformation theory, the differential pressure displacement of the casing under the action of the inner pressure and the annular pressure is calculated; Based on the heat release of cement slurry hydration and the thermal expansion of cement slurry, the thermal displacement of the casing during temperature change is calculated; the sum of the pressure difference displacement and the thermal displacement is the predicted value of the total displacement of the casing; The differential pressure displacement of the casing under the action of the internal pressure and the annular pressure is calculated using the following formula: Where u sl1 represents the differential pressure displacement, E represents the elastic modulus of the casing, μ represents the Poisson's ratio of the casing, P p Indicates the pressure inside the pipe, P a represents the annular pressure, r1 represents the inner diameter of the casing, and r2 represents the outer diameter of the casing; The thermal displacement of the casing during temperature changes is calculated using the following formula: sl2 =-(1+μ)r2βΔT, where u sl2 represents thermal displacement, ΔT represents temperature change, and β represents the thermal expansion coefficient of the casing.

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