Casing displacement prediction method based on one-way sealing hanger

Abstract

The invention discloses a casing displacement prediction method based on a one-way sealing hanger, and the method comprises the following steps: obtaining the distribution of each part of fluid in a casing based on the fluid injection time and injection amount, and further obtaining the position of cement slurry when the cement slurry weightlessness occurs; based on the distribution of the fluid of each part in the casing pipe, in combination with the density of the fluid of each part, obtaining the pressure distribution in the casing pipe and the annulus pressure distribution during pressure building and cement waiting; hydration weightlessness during cement paste pressure building and cement solidification waiting is considered, and annulus pressure distribution after cement paste weightlessness is obtained; on the basis of a sleeve deformation theory, differential pressure displacement of the sleeve is obtained, and on the basis of hydration heat release of the cement paste and thermal expansion of the cement paste, thermal displacement of the sleeve is calculated; the sum of the differential pressure displacement and the thermal displacement is the predicted value of the total displacement of the casing pipe. According to the method disclosed by the invention, the influence of the transient analysis in the whole period of well cementation cement injection and the hydration reaction during the cement paste setting waiting period is considered, and the casing displacement during well cementation operation can be effectively predicted.

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] In the cementing operation of oil and gas wells, the integrity of the wellbore seal is crucial to ensure the long-term stability of the oil and gas wells. In the actual construction process, due to the influence of factors such as the hydration reaction and temperature change of cement slurry during the waiting period, the cement slurry is prone to volume shrinkage after evolving into cement stone, resulting in the failure of the bond between the cement slurry and the casing wall, forming micro gaps. These micro gaps form potential flow channels outside the casing, allowing oil and gas to pass through the cement ring sealing area and directly flow upward from the annulus, resulting in interlayer gas channeling and annulus pressure problems, causing the sealing failure of the oil and gas well. In addition, the residual fluid in the micro gap will accelerate the corrosion of the casing material under high temperature and high pressure environment, shortening the service life of the oil and gas well. The existence of micro gaps not only affects the normal production of oil and gas wells, but may also cause environmental pollution and safety accidents, bringing great challenges to the long-term stable production of oil fields. Therefore, reducing or even eliminating the micro gaps generated in cementing operations is of great engineering significance.

[0003] At present, when cementing the tail pipe, clean water or low-density fluid is mostly used for slurry replacement, so that the pressure in the pipe is lower than the annular pressure at the end of cementing, which causes the casing to deform elastically toward the center of the wellbore and generate prestress, that is, the prestressed cementing method. Under this cementing method, as the cement slurry undergoes hydration reaction during the waiting period, the annular pressure decreases, the casing gradually recovers its deformation, expands toward the well wall, and produces radial displacement to effectively compact the cement ring, thereby compensating for the micro-gap caused by the shrinkage of the cement slurry after it solidifies into cement stone. However, the prestressed cementing method is not only implemented on conventional cementing equipment. During the construction of this method, a cement truck with high pump pressure is required. Since clean water replaces the cement slurry and the isolation fluid, the pressure in the pipe is much lower than the annular pressure, and the pressure difference is too high, which places high requirements on the cement truck pump; at the same time, the back pressure valve in the floating collar is required to be high. The back pressure valve can prevent the cement slurry in the annular space from entering the pipe during the cementing displacement process or at the end of the displacement. If the back pressure valve fails, it will lead to cementing failure. The greater the pressure difference between the inside and outside of the pipe, the more superior the performance requirements of the back pressure valve. When prestressed cementing is used, the pressure difference between the annulus and the inside of the pipe is several tens of MPa, which requires a floating collar with high pressure bearing capacity, increasing the cost of cementing accessories; in addition, when prestressed cementing is performed, the effective external extrusion pressure on the casing is large, and a casing with high external extrusion resistance is required. Therefore, when prestressed cementing is used, a cement truck with high pump pressure, a floating collar with high pressure bearing capacity, and a casing with high external extrusion resistance strength are required, which in turn increases the cost of well commissioning.

[0004] For prestressed cementing, one of the current methods is to install a one-way blind plate on the tail pipe hanger. At the end of cementing, the blind plate seals the hanger mouth when the drill string is lifted up by inverting. During the waiting period of pressure buildup, since the hanger is sealed, not only the wellhead pressure cannot be transmitted to the fluid in the casing through the blind plate, but also the fluid above the blind plate only acts on the blind plate and cannot be transmitted to the pipe. At this time, the pressure in the tail pipe is only the static liquid column pressure of the tail pipe section fluid, and the annular pressure is the sum of the annular fluid pressure and the wellhead pressure value, which causes the annular pressure to be much greater than the pressure in the pipe, causing the casing to shrink into the wellbore. When the cement slurry gradually evolves into liquid plastic or plastic products, the annular pressure decreases, and the casing rebounds toward the well wall, thereby alleviating the annular micro-gap caused by volume shrinkage during the process of cement slurry evolving into cement stone. This method can also achieve the prestressed effect, while eliminating the high pump pressure cement stone, high pressure bearing capacity floating collar and high anti-external squeeze casing required for prestressed cementing. However, if you want to achieve better cementing effects, the selection of cementing parameters is the key. The existing technology can only roughly estimate the casing displacement under different cementing parameters through experience, which has relatively low accuracy and limited guidance effect on the site. Summary of the invention

[0005] In order 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 amount, the distribution of each part of the fluid in 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 period of holding pressure and waiting for setting, when the static gel strength of cement slurry reaches 240Pa during the period of holding pressure and waiting for setting, 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 inner pipe 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 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 the hydration reaction of the cement slurry during the waiting period of setting, and can effectively predict the casing displacement during cementing operations, providing theoretical guidance for the subsequent evaluation of cement ring 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 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 result of the pressure distribution in the tail pipe section during the pressure holding and solidification waiting 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 modes of the present invention will be described clearly and completely 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 sealing hanger comprises the following steps:

[0018] S1. Based on the fluid injection time and injection amount, the distribution of each part of the fluid in 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;

[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] According to the volume and displacement of each fluid during on-site construction, calculate the time taken for each fluid to be injected into the wellbore: Where t is the time taken for 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 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 position node j;

[0024] Based on the end time of cement injection, the distribution of various fluids in the pipe during the period of cement slurry pressure holding 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 subsequent stages, such as pressure holding and waiting for solidification and cement slurry weight loss, the fluid distribution no longer changes). Therefore, in this embodiment, only the time of pressure holding and waiting for solidification of the cement slurry needs to be entered.

[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 are obtained;

[0027] The pressure inside the casing during the holding pressure and condensation 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, and h j represents the depth step at the tail pipe 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 '=P 0 +∑ρ ai HkDJ j cosθ, where P a , represents the annular pressure during the period of pressure holding and condensation, p 0 Indicates the wellbore 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 gravitational acceleration, 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 in the wellbore by segmentation. As for the segment length, those skilled in the art can segment according to the actual situation, such as a depth step of 10m, etc.

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

[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 the 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 inner pipe pressure and the annular space 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 the temperature change process is calculated; the sum of the pressure differential displacement and the thermal displacement is the predicted value of the total displacement of the casing.

[0034] 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 temperature of the casing and cement slurry varies uniformly along the radial direction.

[0035] During the cement slurry pressure holding and setting stage, the casing is regarded as an elastic material, and the radial displacement of the casing is considered under the pressure difference between the inner pressure and the annular pressure, and 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] By solving the displacement equation, the radial displacement u generated by the outer wall of the casing is obtained 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 Indicates the annular pressure; r 1 Indicates the inner radius of the casing; r 2 Indicates 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 under the action of temperature changes during the hydration of cement slurry.

[0047] a) Strain under temperature influence:

[0048] ε θT =(1+μ)βΔT

[0049] In the formula, 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] In the formula, u T represents thermal displacement;

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

[0054] u sl2 =-(1+μ)r 2 βΔT

[0055] Where, μ represents the Poisson's ratio of the casing; r 2 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: usl =u sl1 +u sl2 .

[0057] The following is an embodiment of the present invention. A natural gas well was drilled to 5492m and cemented. A 139.7×9.17mm drill pipe was used to hang a 196.85×16.83mm tail pipe for cementing. A one-way sealing blind plate was installed on the hanger. The tail pipe bell mouth position was 2746m, and the overlap section length was 400.38m. The size of the upper casing was 282.58×18.64mm, and the average hole diameter of the open hole section was 260.1mm. The drilling fluid density in the wellbore was 2.27g / 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 heavy flushing fluid; displacement 20L / s injection 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 Plug fluid: displacement 21L / s, injection 50m 3 Density 2.27g / cm 3 Drilling fluid; displacement 22L / s injection 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 injected 4m 3 Density 1.00g / cm 3 Clean water impact pressure.

[0058] Substitute the above construction parameters into step 1 to calculate the slurry distribution in the pipe and annulus during cementing. Figure 1 This is the slurry density distribution curve in the wellbore after cementing. After cementing, the hanger blind plate is sealed and the fluid in the well section above the hanger is completely replaced with a density of 2.27 g / cm 3Drilling 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 for solidification, the slurry density distribution is used, and the pressure distribution in the tail section 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 stabilize. At this time, by analyzing the annular slurry density distribution after displacing the drilling fluid 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, when the blind plate seal of the one-way sealing hanger is holding the pressure and waiting for solidification, the calculation results of the tail section pressure distribution are as follows: Figure 3 As shown in the curve, the results show that a large pressure difference is formed between the inner wall and the outer wall of the tail pipe section casing, and the average pressure difference is 71.83MPa.

[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 shrinkage displacement of the casing of the tail pipe section of the example of the present invention.

[0061] The above description is only 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 the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification 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 still falls within the scope of the technical solution of the present invention.

Claims

1. A method for predicting casing displacement based on a one-way sealing hanger, characterized in that: The following steps are involved: Based on the fluid injection time and injection amount, the distribution of each part of the fluid in 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; 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 period of holding pressure and waiting for setting, when the static gel strength of cement slurry reaches 240Pa during the period of holding pressure and waiting for setting, 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 the temperature change process is calculated; the sum of the pressure difference displacement and the thermal displacement is the predicted value of the total displacement of the casing.

2. The method according to claim 1, characterized in that The method for obtaining the fluid distribution comprises the following steps: 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; According to the volume and displacement of each fluid during on-site construction, calculate the time taken for each fluid to be injected into the wellbore: Where t is the time taken for 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; Calculate the volume of different fluids at different points in time: In the formula 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 position node j; Based on the time when cement injection is completed, the distribution of various fluids in the pipe when the cement slurry is pressurized and solidified can be obtained.

3. The method according to claim 1, characterized in that The pressure inside the casing during the holding pressure and condensation 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, and h j represents the depth step at the tail pipe section j, and θ represents the well inclination angle.

4. The method according to claim 1, characterized in that: 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 holding pressure of the wellbore, 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 gravitational acceleration, and θ represents the well inclination angle.

5. The method according to claim 1, characterized in that The annular pressure distribution after cement slurry weight loss is calculated using the following formula: 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 the casing.

6. The method according to claim 1, characterized in that The differential pressure displacement of the casing under the action of the inner pressure and the annular pressure is calculated by the following formula: In the formula, u sl1 represents differential pressure displacement, E represents elastic modulus of casing, μ represents Poisson's ratio of casing, P p Indicates the pressure inside the pipe, P a represents the annulus pressure, r1 represents the inner diameter of the casing, and r2 represents the outer diameter of the casing.

7. The method according to claim 1, characterized in that 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, β represents thermal expansion coefficient of casing, r2 represents outer diameter of casing, and μ represents Poisson's ratio of casing.

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