CN114059957B - Method for improving sealing performance of cement sheath at overlapping section of sleeve - Google Patents
Method for improving sealing performance of cement sheath at overlapping section of sleeve Download PDFInfo
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- CN114059957B CN114059957B CN202010776968.9A CN202010776968A CN114059957B CN 114059957 B CN114059957 B CN 114059957B CN 202010776968 A CN202010776968 A CN 202010776968A CN 114059957 B CN114059957 B CN 114059957B
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- 239000004568 cement Substances 0.000 title claims abstract description 296
- 238000000034 method Methods 0.000 title claims abstract description 50
- 238000007789 sealing Methods 0.000 title claims abstract description 26
- 238000009413 insulation Methods 0.000 claims abstract description 84
- 230000001052 transient effect Effects 0.000 claims abstract description 29
- 239000012530 fluid Substances 0.000 claims description 56
- 238000010276 construction Methods 0.000 claims description 20
- 238000012546 transfer Methods 0.000 claims description 19
- 230000009471 action Effects 0.000 claims description 18
- 230000005465 channeling Effects 0.000 claims description 18
- 230000015572 biosynthetic process Effects 0.000 claims description 17
- 239000007788 liquid Substances 0.000 claims description 15
- 239000000463 material Substances 0.000 claims description 15
- 230000008859 change Effects 0.000 claims description 12
- 239000003129 oil well Substances 0.000 claims description 11
- 239000011148 porous material Substances 0.000 claims description 11
- 230000008569 process Effects 0.000 claims description 11
- 230000006378 damage Effects 0.000 claims description 10
- 239000004575 stone Substances 0.000 claims description 10
- 238000005553 drilling Methods 0.000 claims description 9
- 238000005259 measurement Methods 0.000 claims description 9
- 230000003213 activating effect Effects 0.000 claims description 7
- 230000000694 effects Effects 0.000 claims description 7
- 238000002347 injection Methods 0.000 claims description 7
- 239000007924 injection Substances 0.000 claims description 7
- 238000006073 displacement reaction Methods 0.000 claims description 6
- 238000002474 experimental method Methods 0.000 claims description 4
- 239000011435 rock Substances 0.000 claims description 4
- 230000001808 coupling effect Effects 0.000 claims description 3
- 238000003825 pressing Methods 0.000 claims description 3
- 238000004080 punching Methods 0.000 claims description 3
- 239000002131 composite material Substances 0.000 claims 3
- 238000013461 design Methods 0.000 claims 1
- 230000005540 biological transmission Effects 0.000 abstract 1
- 230000000903 blocking effect Effects 0.000 abstract 1
- 239000011248 coating agent Substances 0.000 description 7
- 238000000576 coating method Methods 0.000 description 7
- 239000006260 foam Substances 0.000 description 4
- 239000012774 insulation material Substances 0.000 description 3
- 239000004033 plastic Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 239000010425 asbestos Substances 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 239000011810 insulating material Substances 0.000 description 2
- 229910052895 riebeckite Inorganic materials 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 239000003570 air Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000009699 differential effect Effects 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
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- 230000004048 modification Effects 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
Classifications
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B33/00—Sealing or packing boreholes or wells
- E21B33/10—Sealing or packing boreholes or wells in the borehole
- E21B33/13—Methods or devices for cementing, for plugging holes, crevices, or the like
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- Geochemistry & Mineralogy (AREA)
- Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
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Abstract
The application discloses a method for improving the sealing performance of cement sheath at the overlapping section of a casing, which comprises the steps of arranging a heat insulation layer and a rigid sleeve outside an oil layer casing to form a well cementation structure with the oil layer casing, the heat insulation layer, the rigid sleeve, an inner cement sheath, a technical casing, an outer cement sheath and a stratum sequentially arranged from inside to outside, wherein a cementing surface between the inner cement sheath and the rigid sleeve is a first interface, and the heat insulation layer is used for blocking the transmission of the bottom-hole transient temperature drop from the oil layer casing to the rigid sleeve and reducing the gap between the rigid sleeve and the inner cement sheath caused by thermal deformation. The application considers the thermodynamic influence of the first interface of the transient temperature drop inner cement sheath in the oil layer casing, so that the inner cement sheath is not directly cemented with the oil layer casing, but cemented with the rigid sheath, the severe temperature drop at the bottom of the well is isolated by the heat insulation layer, and the problem that the rigid sheath and the inner cement sheath deform uncoordinated to generate a micro gap due to the severe temperature drop at the bottom of the well is effectively solved. Thereby reducing the influence of the bottom hole temperature drop on the sealing performance of the cement sheath interface.
Description
Technical Field
The invention relates to the technical field of well cementation, in particular to a method for improving the sealing performance of a cement sheath at a sleeve overlapping section.
Background
In the development of oil and gas wells, cementing is an important operation in the drilling process, and cementing refers to a construction operation of running a casing into a well and injecting cement into an annular space between a wellbore and the casing. The straight well section is a steel-to-steel well completion structure, namely, an inner sleeve and an outer sleeve are adopted, the sleeve positioned at the inner layer is an oil layer sleeve, the sleeve positioned at the outer layer is a technical sleeve, an inner cement ring is formed by pouring between the two layers of sleeves, an outer cement ring is formed by pouring between the technical sleeve and a borehole, and the overlapping position of the two layers of sleeves is called a sleeve overlapping section. The cementing surface between the inner cement sheath and the oil layer casing is a first interface, and the cementing surface between the inner cement sheath and the technical casing is a second interface.
The inner cement paste at the overlapping section of the sleeve cannot be supplemented by the pressure of formation fluid in the solidification process, so that the initial stress of the inner cement sheath can be gradually reduced along with the hydration of the interior of the cement sheath in the solidification process, the contact stress of the first interface of the inner cement sheath is reduced, and the capacity of preventing fluid from flowing along the inner interface of the cement sheath is weakened. Or the oil layer casing is expanded and contracted under the action of high internal pressure, so that the first interface of the inner cement sheath is plastically deformed, and the sealing is invalid. Therefore, the existing solution is to adopt a cement slurry system with low elastic modulus, and a technical method for reducing the first interfacial plastic deformation of an inner cement sheath by adding a layer of elastic rubber material outside the oil layer casing is formed.
However, in the actual well cementation process, the problem of tightness of the first interface of the inner cement sheath at the overlapping section of the sleeve in the prior art cannot be well solved.
Disclosure of Invention
Therefore, the invention aims to provide a method for improving the sealing performance of the cement sheath at the overlapping section of the sleeve, so as to reduce the influence of bottom hole temperature drop on the sealing performance of the cement sheath interface and improve the sealing performance of the cement sheath at the overlapping section of the sleeve.
In order to achieve the above purpose, the present invention provides the following technical solutions:
The method for improving the tightness of the cement sheath at the overlapping section of the casing pipe comprises the steps of arranging a heat insulation layer and a rigid sleeve outside the oil layer casing pipe, and forming a well cementation structure of the oil layer casing pipe, the heat insulation layer, the rigid sleeve, an inner cement sheath, a technical casing pipe, an outer cement sheath and a stratum from inside to outside, wherein a cementing surface between the inner cement sheath and the rigid sleeve is a first interface, and the heat insulation layer is used for preventing the bottom hole transient temperature drop from being transmitted to the rigid sleeve by the oil layer casing pipe, so that a gap between the rigid sleeve and the inner cement sheath due to thermal deformation is reduced.
Preferably, in the method, the method for designing a well cementation structure includes:
S100, establishing a first finite element analysis model comprising an oil layer casing pipe, a heat insulation layer, a rigid sleeve, an inner cement sheath, a technical casing pipe, an outer cement sheath and a stratum;
S200, under the action of temperature load, analyzing parameters related to stress characteristics of a cementing unit between the rigid sleeve and the inner cement sheath in the first finite element analysis model;
s300, calculating to obtain parameter ranges of the heat insulation layer, the rigid sleeve and the inner cement sheath, which meet the requirement of maintaining the integrity of the cementing unit between the rigid sleeve and the inner cement sheath under the transient temperature drop effect in the shaft.
Preferably, in the above method, in the step S200, while the temperature load acts, a fluid load is applied between the rigid sleeve and the inner cement sheath, and parameters related to stress characteristics of a cementing unit between the rigid sleeve and the inner cement sheath in the first finite element analysis model are analyzed;
and then, in step S300, calculating to obtain parameter ranges of the thermal insulation layer, the rigid sleeve and the inner cement sheath, which satisfy the transient temperature drop in the well bore and the integrity of the cementing unit between the rigid sleeve and the inner cement sheath under the action of the fluid channeling of the first interface.
Preferably, in the method, in step S200, under a temperature load and a fluid load applied between the rigid sleeve and the inner cement sheath, parameters related to stress characteristics of a cementing unit between the rigid sleeve and the inner cement sheath in the first finite element analysis model are analyzed, and specifically include:
S201, setting a failure criterion of the destruction of the cementing unit between the rigid sleeve and the inner cement sheath;
S202, applying temperature load and pressure load to the inner wall of the oil well casing in the first finite element analysis model, and analyzing a first influence rule of parameters of the rigid sleeve, the heat insulation layer and the inner cement sheath on the integrity of a cementing unit between the rigid sleeve and the inner cement sheath under the coupling action of temperature and pressure in a shaft;
S203, stopping applying pressure load to the inner wall of the oil layer casing in the first finite element analysis model, and analyzing a change rule of a stress state of a cementing unit between the rigid sleeve and the inner cement sheath under the action of temperature load;
s204, applying fluid load between the rigid sleeve and the inner cement sheath in the first finite element analysis model, and analyzing a second influence rule of parameters of the rigid sleeve, the heat insulation layer and the inner cement sheath on the integrity of a cementing surface between the rigid sleeve and the inner cement sheath;
Thereafter, the step 300 specifically includes: and calculating the rigid sleeve, the heat insulation layer and the inner cement ring with different parameters in the first finite element analysis model according to the failure criterion, the first influence rule, the stress state change rule and the second influence rule to obtain parameter ranges of the heat insulation layer, the rigid sleeve and the inner cement ring, which correspond to the failure criterion, the first influence rule, the stress state change rule and the second influence rule at the same time.
Preferably, in the above method, in step S100, a first finite element analysis model including a casing, a thermal insulation layer, a rigid sleeve, an inner cement sheath, a technical casing, an outer cement sheath, and a stratum is built, specifically:
S110, establishing a second finite element analysis model comprising the technical sleeve, the outer cement sheath and the stratum;
S120, applying initial pressure and temperature load of an inner cement sheath at final setting time to the inner wall of the technical casing in the second finite element analysis model to obtain the outer diameter of the inner cement sheath;
S130, adding a first geometric component comprising the oil casing, the thermal insulation layer and the rigid sleeve into the second finite element analysis model, setting parameters of the thermal insulation layer and the rigid sleeve, and meshing the first geometric component to establish a third finite element analysis model comprising the oil casing, the thermal insulation layer, the rigid sleeve, the technical casing, an outer cement sheath and a stratum;
S140, applying displacement fluid load to the inner wall of the oil layer casing in the third finite element analysis model, and applying initial stress of an inner cement sheath at final setting time to the outer wall of the rigid sheath to obtain the outer diameter of the rigid sheath, namely the inner diameter of the inner cement sheath;
S150, adding a second geometric component comprising the inner cement sheath into the third finite element analysis model, dividing grids, and setting the unit type, the material parameters and the initial stress of the second geometric component;
s160, activating the second geometric component, and setting contact behavior between the inner cement sheath and the rigid sleeve to simulate fluid channeling along the first interface;
S170, setting a heat transfer mode at the interface between the inner wall of the oil layer sleeve and the fluid in the well bore to be convection heat transfer, and setting an analysis step type to be steady-state transient analysis to obtain the first finite element analysis model comprising the oil layer sleeve, the heat insulation layer, the rigid sleeve, the inner cement sheath, the technical sleeve, the outer cement sheath and the stratum.
Preferably, in the above method, the establishing in step S110 a second finite element analysis model including the technical casing, the outer cement sheath, and the stratum specifically includes:
S111, obtaining the borehole size at the time of electric measurement and the pressure of a liquid column in the borehole, and calculating the original borehole size under the condition without drilling fluid;
S112, establishing a fourth finite element analysis model comprising the technical casing and the stratum according to the original borehole size under the condition of no drilling fluid and the actual size of the unstressed technical casing;
S113, applying displacement liquid column pressure to the inner wall of the technical casing in the fourth finite element analysis model during primary well cementation construction, and applying formation fluid pressure to the annulus between the technical casing and the well bore to obtain the sizes of the outer wall of the technical casing and the well bore during primary well cementation, namely the size of the outer cement sheath;
s114, adding a third geometric component comprising an outer cement loop into the fourth finite element analysis model, meshing the third geometric component, and setting the unit type, the material parameters and the initial stress of the third geometric component;
S115, activating a third geometric component in the fourth finite element analysis model, setting a heat transfer mode at the interface of the inner wall of the technical sleeve and the fluid to be convection heat transfer, setting an analysis step type to be non-steady state transient analysis, and establishing a second finite element analysis model comprising the technical sleeve, the outer cement sheath and the stratum.
Preferably, in the above method, the failure criterion in step S201 includes:
A maximum tensile stress criterion for the first interface temperature difference effect of the inner cement sheath;
A second nominal stress criterion for a first interfacial fluid channeling of the inner cement sheath.
Preferably, in the above method, before the step S100, the method further includes a step S001:
obtaining geological parameters at the overlapping section of the sleeve;
acquiring construction parameters of the two cementing operations of the technical casing and the oil layer casing at the overlapping section of the casing;
Obtaining thermodynamic parameters of the oil layer casing, the rigid sleeve, the heat insulation layer and the technical casing at the casing punching section;
Acquiring mechanical parameters and thermodynamic parameters of the inner cement sheath and the outer cement sheath, the cementing strength of the inner cement sheath and the rigid sheath and the mechanical parameters and thermodynamic parameters of the stratum at the overlapping section of the sleeve under the action of temperature and pressure;
Then, the parameters in the step S001 are applied to build a first finite element analysis model including a casing, a thermal insulation layer, a rigid sleeve, an inner cement sheath, a technical sleeve, an outer cement sheath, and a stratum in the step S100.
Preferably, in the above method, the geological parameters include the earth stress of the formation, pore pressure and initial formation temperature;
the construction parameters comprise liquid injection temperature, liquid injection time and construction pressure;
Thermodynamic parameters of the oil well casing, the rigid sleeve, the heat insulation layer and the technical casing comprise the convective heat transfer coefficient of fluid, the heat transfer coefficient and expansion coefficient of the casing, and the heat transfer coefficient between the rigid sleeve and the oil well casing;
The mechanical parameters of the oil layer casing and the technical casing comprise elastic modulus and poisson ratio;
the mechanical parameters of the inner cement sheath, the outer cement sheath, and the formation include elastic modulus, poisson's ratio, flexural strength, and yield strength;
thermodynamic parameters of the inner cement sheath, the outer cement sheath, and the formation include thermal conductivity and thermal expansion coefficients.
Preferably, in the above method, the obtaining mechanical parameters and thermodynamic parameters of the inner cement sheath and the outer cement sheath, the cementing strength of the inner cement sheath and the rigid sheath, and the mechanical parameters and thermodynamic parameters of the stratum at the overlapping section of the casing in the step S001 under the action of temperature and pressure specifically include:
maintaining the cement stone according to construction parameters of two times of well cementation and annular pressure and temperature at a sleeve overlapping section in the construction process, and measuring pore pressure at the final setting time of the cement stone by adopting a pore pressure measuring device;
adopting a rock mechanical strength tester to obtain mechanical parameters of cement stones and stratum;
measuring the cementing strength between the inner cement sheath and the rigid sleeve by adopting a cementing interface cementing measuring device;
And (5) obtaining thermodynamic parameters of the cement stone and the stratum by adopting a thermodynamic measurement experiment indoors.
Compared with the prior art, the invention has the beneficial effects that:
According to the method for improving the sealing performance of the cement sheath at the overlapping section of the casing, the heat insulation layer and the rigid sleeve are arranged outside the oil layer casing, so that a well cementation structure is formed, wherein the oil layer casing, the heat insulation layer, the rigid sleeve, the inner cement sheath, the technical casing, the outer cement sheath and the stratum are sequentially arranged from inside to outside, a cementing surface between the inner cement sheath and the rigid sleeve is a first interface, the heat insulation layer is used for preventing the bottom hole transient temperature drop from being transmitted to the rigid sleeve by the oil layer casing, and a gap generated by thermal deformation between the rigid sleeve and the inner cement sheath is reduced.
Compared with the prior art, the invention considers the thermodynamic influence of the first interface of the transient temperature drop inner cement sheath in the oil layer casing which is not considered in the prior art, and on the basis of the original well cementation structure, the heat insulation layer and the rigid sheath are additionally arranged outside the oil layer casing, the inner cement sheath is not directly glued with the oil layer casing, but glued with the rigid sheath, and the severe bottom temperature drop of the well is isolated through the heat insulation layer, so that the transient temperature drop is transmitted to the rigid sheath, the temperature of the rigid sheath is similar to that of the inner cement sheath, and the problem that the rigid sheath and the inner cement sheath deform uncoordinated to generate a micro gap due to the severe bottom temperature drop of the well is effectively solved. Thereby reducing the influence of the bottom hole temperature drop on the sealing performance of the cement sheath interface.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic view of a longitudinal structure of a well cementing structure according to an embodiment of the present invention;
FIG. 2 is a schematic cross-sectional view of a well cementing structure according to an embodiment of the present invention;
FIG. 3 is a schematic flow chart of a method for improving the sealing performance of a cement sheath at a sleeve overlapping section according to an embodiment of the invention;
FIG. 4 is a flow chart of another method for improving the sealing performance of a cement sheath at a sleeve overlapping section according to an embodiment of the invention.
Wherein, 1 is the oil layer sleeve, 2 is the inner cement sheath, 3 is the technical sleeve, 4 is the outer cement sheath, 5 is the stratum, 6 is the rigid sleeve, 7 is the insulating layer.
Detailed Description
The core of the invention is to provide a method for improving the sealing performance of the cement sheath at the overlapping section of the sleeve, so that the influence of the bottom hole temperature drop on the sealing performance of the cement sheath interface is reduced, and the sealing performance of the cement sheath at the overlapping section of the sleeve is improved.
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1 and 2, an embodiment of the present invention provides a method for improving the sealing performance of a cement sheath at a sleeve overlapping section, which comprises the following steps: the heat insulation layer 7 and the rigid sleeve 6 are arranged outside the oil layer sleeve 1, the heat insulation layer 7, the rigid sleeve 6, the inner cement sheath 2, the technical sleeve 3, the outer cement sheath 4 and the well cementation structure of the stratum 5 are sequentially arranged from inside to outside, the cementing surface between the inner cement sheath 2 and the rigid sleeve 6 is a first interface, the rigid sleeve 6 is made of rigid materials with good rigidity, the heat insulation layer 7 is used for preventing the bottom hole transient temperature drop from being transferred to the rigid sleeve 6 from the oil layer sleeve 1, and the gap between the rigid sleeve 6 and the inner cement sheath 2 due to thermal deformation is reduced.
Compared with the prior art, the invention considers the thermodynamic influence of the first interface of the transient temperature drop inner cement sheath 2 in the oil well casing 1 which is not considered in the prior art, and the cementing surface on the inner side of the inner cement sheath 2 is subjected to larger temperature stress due to the larger thermodynamic coefficient difference between the oil well casing 1 and the inner cement sheath 2 due to the transient temperature drop in the well shaft, so that the cementing failure of the first interface of the inner cement sheath 2 is caused. Therefore, from the angle, on the basis of the original well cementation structure, the heat insulation layer 7 and the rigid sleeve 6 are additionally arranged outside the oil layer sleeve 1, the inner layer cement sheath 2 is not directly glued with the oil layer sleeve 1, but is glued with the rigid sleeve 6, the severe bottom hole temperature drop is isolated through the heat insulation layer 7, the transient temperature drop is reduced and transferred to the rigid sleeve 6, so that the rigid sleeve 6 and the inner layer cement sheath 2 keep similar temperature, the problem that the rigid sleeve 6 and the inner layer cement sheath 2 are deformed and are not coordinated to generate a micro gap is avoided, and the problem that the oil layer sleeve 1 and the inner layer cement sheath 2 are deformed and are not coordinated to generate the micro gap due to the severe bottom hole temperature drop is effectively solved. Thereby reducing the influence of the bottom hole temperature drop on the sealing performance of the cement sheath interface.
As shown in fig. 3, in this embodiment, the method for designing the well cementation structure includes the following steps:
Step S100, a first finite element analysis model comprising an oil layer casing 1, a heat insulation layer 7, a rigid sleeve 6, an inner cement sheath 2, a technical casing 3, an outer cement sheath 4 and a stratum 5 is established, and the model is established in finite element analysis software;
Step S200, under the action of temperature load, a first finite element analysis model applies temperature load in the oil layer casing 1, and parameters related to stress characteristics of a cementing unit between the rigid sleeve 6 and the inner cement sheath 2 in the first finite element analysis model are analyzed to obtain the influence of temperature on the tightness of a first interface;
step S300, calculating and obtaining parameter ranges of the heat insulation layer 7, the rigid sleeve 6 and the inner cement sheath 2 which can maintain the integrity of the cementing unit between the rigid sleeve 6 and the inner cement sheath 2 under the transient temperature drop effect in the shaft; wherein the parameters are geometric parameters, mechanical parameters and thermodynamic parameters.
Compared with the prior art, the method and the device analyze the parameters related to the integrity of the first interface cementing unit of the inner cement sheath 2 in the first finite element analysis model by establishing the first finite element analysis model which considers the transient temperature drop in the oil well casing 1 and comprises the oil well casing 1, the heat insulation layer 7, the rigid sleeve 6, the inner cement sheath 2, the technical casing 3, the outer cement sheath 4 and the stratum 5. The influence of parameters of different heat insulation layers 7, rigid sleeves 6 and inner cement rings 2 on the tightness of the inner cement rings 2 is analyzed through a first finite element analysis model, the optimal range of the parameters of the heat insulation layers 7, the rigid sleeves 6 and the inner cement rings 2 is determined, a reference basis is provided for a process for improving the tightness of the inner cement rings 2 at the overlapping section of the sleeve, the mechanical parameters of the inner cement rings 2 can be optimized on the basis, the outer structure of the oil layer sleeve 1 consisting of the heat insulation layers 7 and the rigid sleeves 6 is designed, and therefore, the damage of transient temperature drop in the oil layer sleeve 1 at the overlapping section of the sleeve to a first interface cementing unit of the inner cement rings 2 is improved, and the purpose of improving the tightness of the inner cement rings 2 at the overlapping section of the sleeve is achieved.
Further, in this embodiment, as shown in fig. 4, in step S200, while applying a temperature load to the casing 1 of the first finite element analysis model, a fluid load is applied between the rigid sleeve 6 and the inner cement sheath 2 to simulate fluid channeling of the first interface, and parameters related to stress characteristics of the cementing unit between the rigid sleeve 6 and the inner cement sheath 2 in the first finite element analysis model are analyzed;
Step S300 is then to calculate and obtain parameter ranges of the thermal insulation layer 7, the rigid sleeve 6 and the inner cement sheath 2 satisfying the transient temperature drop in the wellbore and maintaining the integrity of the cementing unit between the rigid sleeve 6 and the inner cement sheath 2 under the action of the fluid channeling of the first interface. In the case of restricting fluid channeling of the first interface of the inner cement sheath 2, the thickness and rigidity of the rigid sleeve 6 and the elastic modulus of the inner cement sheath 2 are mainly improved, so that mechanical environments with higher rigidity are formed on two sides of the first interface of the inner cement sheath 2, thereby restricting fluid channeling of the first interface of the inner cement sheath 2.
The method not only considers the transient temperature drop in the oil casing 1, but also considers the influence of fluid channeling on the integrity of the first interface in the cementing surface between the inner cement sheath 2 and the rigid sleeve 6. According to the invention, parameters related to the integrity of a first interface cementing unit of the inner cement sheath 2 in a first finite element analysis model are analyzed by establishing the first finite element analysis model considering the transient temperature drop in the oil casing 1 and the fluid channeling of the first interface of the inner cement sheath 2. The influence of parameters of different heat insulation layers 7, rigid sleeves 6 and inner cement rings 2 on the tightness of the inner cement rings 2 is analyzed through a first finite element analysis model, the optimal range of the parameters of the heat insulation layers 7, the rigid sleeves 6 and the inner cement rings 2 is determined, a reference basis is provided for a process for improving the tightness of the inner cement rings 2 at the overlapping section of the sleeve, the mechanical parameters of the inner cement rings 2 can be optimized on the basis, the outer structure of the oil layer sleeve 1 consisting of the heat insulation layers 7 and the rigid sleeves 6 is designed, and therefore the damage of the inner temperature drop of the oil layer sleeve 1 at the overlapping section of the sleeve and the damage of the fluid channeling of the interface to a first interface unit of the inner cement rings 2 at the overlapping section of the sleeve are improved, so that the sealing capability of the inner cement rings 2 at the overlapping section of the sleeve is improved.
In this embodiment, the step S200 is optimized, and the parameters related to the stress characteristics of the cementing unit between the rigid sleeve 6 and the inner cement sheath 2 in the first finite element analysis model are analyzed under the action of the temperature load and the application of the fluid load between the rigid sleeve 6 and the inner cement sheath 2 in the step S200, which specifically includes the following steps:
step S201, setting a failure criterion of the cementing unit between the rigid sleeve 6 and the inner cement sheath 2;
step S202, applying temperature load and pressure load to the inner wall of the oil well casing 1 in a first finite element analysis model, and analyzing a first influence rule of parameters of the rigid sleeve 6, the heat insulation layer 7 and the inner cement sheath 2 on the integrity of a cementing unit between the rigid sleeve 6 and the inner cement sheath 2 under the coupling action of temperature and pressure in a shaft;
step S203, stopping applying pressure load to the inner wall of the oil layer casing 1 in the first finite element analysis model, and analyzing the change rule of the stress state of the cementing unit between the rigid sleeve 6 and the inner cement sheath 2 under the action of temperature load;
Step S204, applying fluid load between the rigid sleeve 6 and the inner cement sheath 2 in the first finite element analysis model, and analyzing a second influence rule of parameters of the rigid sleeve 6, the heat insulation layer 7 and the inner cement sheath 2 on the integrity of a cementing surface between the rigid sleeve 6 and the inner cement sheath 2;
Thereafter, step 300 is specifically: according to the failure criterion, the first influence rule, the stress state change rule and the second influence rule obtained in the above, the rigid sleeve 6, the heat insulation layer 7 and the inner cement sheath 2 with different parameters are calculated in the first finite element analysis model, and the parameter ranges of the heat insulation layer 7, the rigid sleeve 6 and the inner cement sheath 2 corresponding to the failure criterion, the first influence rule, the stress state change rule and the second influence rule are obtained.
According to the method, the influence of pressure and transient temperature drop in the oil layer casing 1 and the influence of fluid channeling of the first interface of the inner cement sheath 2 on the first interface integrity of the inner cement sheath 2 are considered, the parameters of different rigid sleeves 6, heat insulation layers 7 and the inner cement sheath 2 are changed, the parameter ranges meeting the three influence factors are obtained, and the well cementation structure capable of effectively improving the sealing performance of the cement sheath at the overlapping section of the casing is obtained.
Further, the present embodiment optimizes step S100, and establishes a first finite element analysis model including the casing 1, the insulating layer 7, the rigid sleeve 6, the inner cement sheath 2, the technical casing 3, the outer cement sheath 4, and the stratum 5 in step S100, and specifically includes the following steps:
Step S110, a second finite element analysis model comprising the technical sleeve 3, the outer cement sheath 4 and the stratum 5 is established in finite element analysis software;
step S120, applying initial pressure and temperature load of an inner cement sheath at final setting time to the inner wall of the technical sleeve 3 in the second finite element analysis model to obtain the outer diameter of the inner cement sheath 2, wherein the outer diameter of the inner cement sheath 2 is the inner diameter of the technical sleeve 3, and the initial pressure of the inner cement sheath 2 is pore pressure at the final setting time of the inner cement sheath 2;
step S130, adding a first geometric component comprising the oil layer sleeve 1, the heat insulating layer 7 and the rigid sleeve 6 into a second finite element analysis model, setting parameters of the heat insulating layer 7 and the rigid sleeve 6, and meshing the first geometric component to establish a third finite element analysis model comprising the oil layer sleeve 1, the heat insulating layer 7, the rigid sleeve 6, the technical sleeve 3, the outer cement sheath 4 and the stratum 5;
Step S140, applying displacement fluid load to the inner wall of the oil layer casing 1 in the third finite element analysis model, applying initial stress of the inner cement sheath 2 at final setting time to the outer wall of the rigid sheath 6, obtaining the outer diameter of the rigid sheath 6, namely the inner diameter of the inner cement sheath 2, and finally obtaining the geometric dimension of the inner cement sheath 2 through the outer diameter of the inner cement sheath 2 obtained in step S120 and the inner diameter of the inner cement sheath 2 obtained in step S140;
Step S150, adding a second geometric component including the inner cement sheath 2 into the third finite element analysis model, meshing the second geometric component, and setting a unit type, a material parameter and an initial stress of the second geometric component, where the unit type may be CPE4T, the material parameter includes an elastic modulus, poisson ratio, density, thermal conductivity, thermal expansion coefficient, and specific heat, and the initial stress is pore pressure of the inner cement sheath 2 at the final setting time.
Step S160, activating a second geometric component, specifically using model CHANGE ADD keywords to excite the second geometric component, reducing the initial stress of the inner cement sheath 2 to 0MPa, and forming the initial stress of the inner cement sheath 2 after well cementation by the interference fit of the inner cement sheath 2 with the technical sleeve 3 and the rigid sleeve 6; setting a contact behavior (English name: cohesive behavior) between the inner cement sheath 2 and the rigid sleeve 6 of the third finite element analysis model based on the damage mechanics theory so as to simulate fluid channeling along the first interface, namely inserting a damage unit between the inner cement sheath 2 and the rigid sleeve based on the damage mechanics theory, and representing the fluid channeling along the first interface by simulating failure of the damage unit;
Step S170, setting a heat transfer mode at the interface between the inner wall of the oil layer sleeve 1 and the fluid in the shaft as convection heat transfer, and setting an analysis step type as steady-state transient analysis to obtain a first finite element analysis model comprising the oil layer sleeve 1, the heat insulation layer 7, the rigid sleeve 6, the inner cement sheath 2, the technical sleeve 3, the outer cement sheath 4 and the stratum 5.
The first finite element analysis model obtained by the above steps considers the transient temperature drop in the casing 1 and the effect of fluid channeling of the first interface of the inner cement sheath 2 on the first interface integrity of the inner cement sheath 2.
In this embodiment, when step S110 is optimized, a second finite element analysis model including the technical casing 3, the outer cement sheath 4, and the formation 5 is built in step S110, and specifically includes the following steps:
step S111, obtaining the borehole size at the time of electric measurement and the pressure of a liquid column in the borehole, and calculating the original borehole size under the condition without drilling fluid;
Specifically, the pressure of the fluid column in the well bore at the moment of electrical measurement:
p1＝9.81×10-3×Hρ (1)
Wherein:
p 1 -electric measurement of the liquid column pressure in the wellbore, MPa;
h, the height of a liquid column in a well bore, m;
ρ—drilling fluid density in the wellbore, g/cm 3;
wellbore dimensions in the absence of fluid in the wellbore:
Wherein:
r f1 -wellbore size, m, when no fluid is in the wellbore;
r f0 -electrical measurement of wellbore size, m;
p i -ground stress, MPa;
p 1 -liquid column pressure in the wellbore, MPa;
Wherein the dimension of the technical sleeve 3 is the actual dimension, the dimension of the borehole is the dimension r f1 without drilling fluid pressure, the dimension of the outer wall of the stratum is set to be 10 times of the dimension of the borehole, and the boundary effect is eliminated.
Step S112, establishing a geometric model comprising the technical casing 3 and the stratum 5 according to the original borehole size under the condition of no drilling fluid and the actual size of the unstressed technical casing 3, meshing the geometric model, setting unit types and material parameters, and establishing a fourth finite element analysis model comprising the technical casing 3 and the stratum 5. Wherein, the geometric model adopts the sweep grid division, and the unit type is CPE4T, and the material parameter includes: modulus of elasticity, poisson's ratio, density, coefficient of thermal conductivity, coefficient of thermal expansion, specific heat.
Step S113, applying displacement liquid column pressure to the inner wall of the technical casing 3 in the fourth finite element analysis model during first well cementation construction, and applying formation fluid pressure to the annulus between the technical casing 3 and the well bore to obtain the outer wall of the technical casing 3 and the size of the well bore during first well cementation, namely obtaining the size of an outer cement sheath 4, wherein the inner diameter of the outer cement sheath 4 is the outer diameter of the technical casing 3, and the outer diameter of the outer cement sheath 4 is the inner diameter of the well bore;
Step S114, adding a third geometric component comprising an outer cement sheath 4 into the fourth finite element analysis model, meshing the third geometric component, and setting a unit type, a material parameter and an initial stress of the third geometric component, wherein the unit type is CPE4T, and the material parameter comprises: modulus of elasticity, poisson's ratio, density, coefficient of thermal conductivity, coefficient of thermal expansion, specific heat;
In step S115, activating a third geometric component in the fourth finite element analysis model, specifically activating the third geometric component by using model CHANGE ADD keywords, setting the initial stress of the activated outer cement sheath 4 as the formation fluid pressure by using initial condition (Chinese interpretation: initial condition) keywords, setting the heat transfer mode at the interface between the inner wall of the technical sleeve 3 and the fluid as convection heat transfer, setting the analysis step type as unsteady transient analysis, and establishing a second finite element analysis model comprising the technical sleeve 3, the outer cement sheath 4 and the formation 5.
In the present embodiment, the failure criterion in step S201 is optimized, and includes:
maximum tensile stress criterion for the first interfacial temperature differential effect of the inner cement sheath 2: sigma 1＝0,σ1 is the first interface cementing stress, the first interface cementing stress is reduced to 0MPa, and the cementing unit is damaged.
Second nominal stress criterion for first interface fluid channeling of inner cement sheath 2: Where t n、ts、tt refers to the normal and tangential stresses of the cementitious unit and t n 0、ts 0、tt 0 refers to the tensile and shear strength of the interface, when the interface stress meets this strength criterion, the interface begins to be damaged.
The method for improving the sealing performance of the cement sheath in the overlapping section of the casing is further optimized in this embodiment, and before the first finite element analysis model is built in step S100 in the above embodiment, relevant parameters for building the model need to be collected, and the process specifically includes step S001:
obtaining geological parameters at the overlapped section of the sleeve, wherein the geological parameters comprise the ground stress, pore pressure and initial stratum temperature of the stratum;
Acquiring construction parameters of two times of well cementation of a technical sleeve 3 and an oil layer sleeve 1 at a sleeve overlapping section, wherein the construction parameters comprise liquid injection temperature, liquid injection time and construction pressure;
obtaining thermodynamic parameters of the oil layer casing 1, the rigid sleeve 6, the heat insulation layer 7 and the technical casing 3 at the casing punching section and mechanical parameters of the oil layer casing 1 and the technical casing 3, wherein the thermodynamic parameters of the oil layer casing 1, the rigid sleeve 6, the heat insulation layer 7 and the technical casing 3 comprise convective heat transfer coefficients of fluid, heat conduction coefficients and expansion coefficients of the casing, heat conduction coefficients between the rigid sleeve 6 and the oil layer casing 1, and the mechanical parameters of the oil layer casing 1 and the technical casing 3 comprise elastic modulus and poisson ratio;
Acquiring mechanical parameters and thermodynamic parameters of the inner cement sheath 2 and the outer cement sheath 4 at the overlapping section of the sleeve under the action of temperature and pressure, the cementing strength of the inner cement sheath 2 and the rigid sleeve 6 and the mechanical parameters and thermodynamic parameters of the stratum at the overlapping section of the sleeve, wherein the mechanical parameters of the inner cement sheath 2, the outer cement sheath 4 and the stratum 5 comprise elastic modulus, poisson ratio, flexural strength and yield strength; thermodynamic parameters of the inner cement sheath 2, the outer cement sheath 4, and the formation 5 include thermal conductivity and thermal expansion coefficients.
Thereafter, the first finite element analysis model including the casing 1, the insulating layer 7, the rigid jacket 6, the inner cement sheath 2, the technical casing 3, the outer cement sheath 4, and the formation 5 in step S100 is established using the parameters in step S001. Specifically, based on the theory of thermoelastic plastic mechanics, a second finite element analysis model is established according to the mechanical parameters and construction parameters of the stratum 5 and the outer cement sheath 4 at the overlapping section of the casing in the first well cementation, and then, based on the second finite element analysis model, a first finite element analysis model is established by adopting an interference fit method and a damage mechanics theory.
Further, in the embodiment, in step S001, the mechanical parameters and thermodynamic parameters of the inner cement sheath 2 and the outer cement sheath 4, the cementing strength of the inner cement sheath 2 and the rigid sheath 6, and the mechanical parameters and thermodynamic parameters of the stratum 5 at the overlapping section of the casing are obtained under the action of temperature and pressure, specifically:
Curing the set cement in a high-temperature high-pressure curing kettle according to construction parameters of the two-time well cementation and annular pressure and temperature at a sleeve overlapping section in the construction process, wherein the curing time is 48 hours, the final setting time of the set cement in the second-time well cementation is measured by using a Vicat, and the pore pressure at the final setting time of the set cement in the second-time well cementation is measured by using a pore pressure measuring device;
before the experiment, the measuring device is heated to the bottom hole temperature in advance, and the prepared cement slurry is cured for 20min under the bottom hole temperature condition;
Adopting a rock mechanical strength tester, in particular a high-temperature triaxial rock mechanical tester, to obtain mechanical parameters of the cement stone and the stratum 5;
Measuring the cementing strength between the inner cement sheath 2 and the rigid sleeve 6 by adopting a cementing interface cementing measuring device;
thermodynamic measurement experiments are adopted indoors to obtain thermodynamic parameters of the cement stone and the stratum 5.
Through the above work before modeling, the relevant parameters necessary for modeling are obtained.
In this embodiment, the thermal insulation layer 7 may be air, i.e. an annulus with a certain thickness is formed between the casing 1 and the rigid sleeve 6, forming the geometry of the casing 1-annulus-rigid sleeve 6. Or the heat insulation layer 7 is a heat insulation material sleeved on the outer wall of the oil layer sleeve 1 and/or a heat insulation coating sprayed on the inner wall of the rigid sleeve 6 and/or gas or foam filled in the annular space. Specifically, the heat insulating layer 7 may be a heat insulating material alone, which has low thermal conductivity, and is sleeved on the oil sleeve 1, so as to block the temperature drop transferred from the oil sleeve 1, and the heat insulating material may be an asbestos net or the like. Or the heat insulating layer 7 can be a heat insulating coating independently, the heat insulating coating is sprayed on the inner wall of the rigid sleeve 6, and the heat insulating coating can be a ceramic heat insulating coating and the like. Or the insulating layer 7 may be solely a gas or foam filled in the annulus. Or any combination of the three forms of the insulating layer 7. As long as the insulation between the casing 1 and the rigid jacket 6 is achieved.
In this embodiment, to the condition that the thermal insulation layer 7 is provided with the annular space, namely, the annular space with a certain thickness is formed between the oil layer casing 1 and the rigid sleeve 6, and because the annular space is reserved between the oil layer casing 1 and the rigid sleeve 6, the oil layer casing 1 is not contacted with the rigid sleeve 6, the annular space reserves space for the expansion deformation of the oil layer casing 1, thereby effectively eliminating the influence of the expansion of the oil layer casing 1 under the action of high internal pressure on the rigid sleeve 6, further solving the problem that the plastic deformation of the inner wall of the inner cement sheath 2 generates the micro-gap, and the annular space is used as the thermal insulation layer 7, under the condition that the thickness of the rigid sleeve 6 is not influenced, the severe temperature drop at the bottom of the well is isolated through the thermal insulation layer 7, thereby reducing the influence on the temperature of the rigid sleeve 6, and effectively solving the problem that the rigid sleeve 6 and the inner cement sheath 2 deform uncooled to generate the micro-gap. Thereby reducing the influence of higher wellbore internal pressure and bottom hole temperature drop on the sealing performance of the cement sheath interface in the fracturing or gas injection process.
The main purpose of the first finite element analysis model is to analyze the influence of different structures and different material performance parameters on the first interface cementing unit of the inner cement sheath 2 under the bottom hole temperature drop working condition, so as to determine the structural scheme and the material properties of the heat insulation layer 7 and the rigid sleeve 6. In particular, the insulating layer 7 comprises a single coating of air, foam, asbestos mesh or ceramic.
Specifically, the present embodiment provides a specific structural dimension of the thermal insulation layer 7 and the rigid sleeve 6, and the geometric thickness of the thermal insulation layer 7 and the rigid sleeve 6 in the model is calculated according to the parameter range of the material itself.
The minimum distance between the outer wall of the casing 1 and the inner wall of the rigid jacket 6 is the sum of the thickness of the insulating layer 7 and the amount of expansion deformation of the casing 1. In order to reduce the micro-gap generated by deformation between the outer wall of the rigid sleeve 6 and the inner wall of the inner cement sheath 2, it is necessary to ensure that the inner and outer dimensions of the rigid sleeve 6 do not change, and the oil layer casing 1 expands and deforms due to high pressure in the pipe and occupies the space of the annulus, so that, in the case of arranging the thermal insulation layer 7 in the annulus, the annulus satisfies both the placement space of the thermal insulation layer 7 and the expansion space of the oil layer casing 1, and therefore, the minimum distance between the outer wall of the oil layer casing 1 and the inner wall of the rigid sleeve 6, i.e., the minimum distance of the annulus should be the sum of the thickness of the thermal insulation layer 7 and the expansion deformation amount of the oil layer casing 1. Because the size of the coupling connected with the outer wall of the rigid sleeve 6 is fixed, the outer diameter size of the oil casing 1 is usually the standard value, therefore, the thickness of the rigid sleeve 6 can be determined according to the space between the oil casing 1 and the rigid sleeve 6, and when the space adopts the minimum space, the thickness of the rigid sleeve 6 is the maximum value, and the structural strength of the rigid sleeve 6 is improved. Taking 139.7mm oil casing 1 as an example, the inner diameter of the collar size is 6.9mm larger than the outer diameter of the oil casing 1, namely, the outer diameter of the rigid sleeve 6 is 6.9mm larger than the outer diameter of the oil casing 1, when the heat insulation layer 7 is a heat insulation material sleeved on the outer wall of the oil casing 1 and having a thickness of 0.5mm, the expansion deformation amount of the oil casing 1 is less than 0.1mm under 70MPa, so that the distance between the rigid sleeve 6 and the oil casing 1 is the sum of the thickness of the heat insulation material and the expansion deformation amount of the oil casing 1, namely, 0.6mm, and the thickness of the rigid sleeve 6 is 6.9mm minus 0.6mm, and the result is 6.3mm. In addition, when the heat insulation layer 7 is foam or air filled in the annular space or is a heat insulation coating sprayed on the inner wall of the rigid sleeve 6, the distance between the rigid sleeve 6 and the oil layer sleeve 1 can be reduced to 0.1mm, and the thickness of the rigid sleeve 6 can be increased to 6.8mm, so that the purpose of increasing the size selection range of the rigid sleeve 6 is realized.
In this embodiment, the rigid sleeve 6 is a steel tube, which improves the structural strength and rigidity.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. The method for improving the tightness of the cement sheath at the overlapping section of the casing is characterized in that a heat insulation layer and a rigid sleeve are arranged outside the oil layer casing to form a well cementation structure in which the oil layer casing, the heat insulation layer, the rigid sleeve, an inner cement sheath, a technical casing, an outer cement sheath and a stratum are sequentially arranged from inside to outside, a cementing surface between the inner cement sheath and the rigid sleeve is a first interface, and the heat insulation layer is used for preventing the bottom hole transient temperature drop from being transmitted to the rigid sleeve by the oil layer casing and reducing a gap between the rigid sleeve and the inner cement sheath due to thermal deformation;
The design method of the well cementation structure comprises the following steps:
S100, establishing a first finite element analysis model comprising an oil layer casing pipe, a heat insulation layer, a rigid sleeve, an inner cement sheath, a technical casing pipe, an outer cement sheath and a stratum;
S200, under the action of temperature load, analyzing parameters related to stress characteristics of a cementing unit between the rigid sleeve and the inner cement sheath in the first finite element analysis model;
s300, calculating to obtain parameter ranges of the heat insulation layer, the rigid sleeve and the inner cement sheath, which meet the requirement of maintaining the integrity of the cementing unit between the rigid sleeve and the inner cement sheath under the transient temperature drop effect in the shaft.
2. The method of improving the tightness of a cement sheath in a section of overlapping casing according to claim 1, characterized in that in said step S200, while the temperature load is acting, it further comprises applying a fluid load between said rigid sheath and said inner cement sheath, analyzing parameters of said first finite element analysis model related to the stress characteristics of the cementing unit between said rigid sheath and said inner cement sheath;
and then, in step S300, calculating to obtain parameter ranges of the thermal insulation layer, the rigid sleeve and the inner cement sheath, which satisfy the transient temperature drop in the well bore and the integrity of the cementing unit between the rigid sleeve and the inner cement sheath under the action of the fluid channeling of the first interface.
3. The method for improving the sealing performance of the cement sheath of the overlapped section of the casing according to claim 2, wherein the analyzing the parameters related to the stress characteristics of the cementing unit between the rigid sheath and the inner cement sheath in the first finite element analysis model under the action of the temperature load and the application of the fluid load between the rigid sheath and the inner cement sheath in the step S200 specifically comprises:
S201, setting a failure criterion of the destruction of the cementing unit between the rigid sleeve and the inner cement sheath;
S202, applying temperature load and pressure load to the inner wall of the oil well casing in the first finite element analysis model, and analyzing a first influence rule of parameters of the rigid sleeve, the heat insulation layer and the inner cement sheath on the integrity of a cementing unit between the rigid sleeve and the inner cement sheath under the coupling action of temperature and pressure in a shaft;
S203, stopping applying pressure load to the inner wall of the oil layer casing in the first finite element analysis model, and analyzing a change rule of a stress state of a cementing unit between the rigid sleeve and the inner cement sheath under the action of temperature load;
s204, applying fluid load between the rigid sleeve and the inner cement sheath in the first finite element analysis model, and analyzing a second influence rule of parameters of the rigid sleeve, the heat insulation layer and the inner cement sheath on the integrity of a cementing surface between the rigid sleeve and the inner cement sheath;
Thereafter, the step 300 specifically includes: and calculating the rigid sleeve, the heat insulation layer and the inner cement ring with different parameters in the first finite element analysis model according to the failure criterion, the first influence rule, the stress state change rule and the second influence rule to obtain parameter ranges of the heat insulation layer, the rigid sleeve and the inner cement ring, which correspond to the failure criterion, the first influence rule, the stress state change rule and the second influence rule at the same time.
4. The method for improving the sealing performance of the cement sheath of the overlapping section of the casing according to claim 1, wherein the step S100 is to build a first finite element analysis model comprising a casing, a thermal insulation layer, a rigid sheath, an inner cement sheath, a technical casing, an outer cement sheath and a stratum, specifically:
S110, establishing a second finite element analysis model comprising the technical sleeve, the outer cement sheath and the stratum;
S120, applying initial pressure and temperature load of an inner cement sheath at final setting time to the inner wall of the technical casing in the second finite element analysis model to obtain the outer diameter of the inner cement sheath;
S130, adding a first geometric component comprising the oil casing, the thermal insulation layer and the rigid sleeve into the second finite element analysis model, setting parameters of the thermal insulation layer and the rigid sleeve, and meshing the first geometric component to establish a third finite element analysis model comprising the oil casing, the thermal insulation layer, the rigid sleeve, the technical casing, an outer cement sheath and a stratum;
S140, applying displacement fluid load to the inner wall of the oil layer casing in the third finite element analysis model, and applying initial stress of an inner cement sheath at final setting time to the outer wall of the rigid sheath to obtain the outer diameter of the rigid sheath, namely the inner diameter of the inner cement sheath;
S150, adding a second geometric component comprising the inner cement sheath into the third finite element analysis model, dividing grids, and setting the unit type, the material parameters and the initial stress of the second geometric component;
s160, activating the second geometric component, and setting contact behavior between the inner cement sheath and the rigid sleeve to simulate fluid channeling along the first interface;
S170, setting a heat transfer mode at the interface between the inner wall of the oil layer sleeve and the fluid in the well bore to be convection heat transfer, and setting an analysis step type to be steady-state transient analysis to obtain the first finite element analysis model comprising the oil layer sleeve, the heat insulation layer, the rigid sleeve, the inner cement sheath, the technical sleeve, the outer cement sheath and the stratum.
5. The method for improving the sealing performance of the cement sheath of the overlapped section of the casing according to claim 4, wherein the establishing in the step S110 comprises the second finite element analysis model of the technical casing, the outer cement sheath and the stratum, specifically:
S111, obtaining the borehole size at the time of electric measurement and the pressure of a liquid column in the borehole, and calculating the original borehole size under the condition without drilling fluid;
S112, establishing a fourth finite element analysis model comprising the technical casing and the stratum according to the original borehole size under the condition of no drilling fluid and the actual size of the unstressed technical casing;
S113, applying displacement liquid column pressure to the inner wall of the technical casing in the fourth finite element analysis model during primary well cementation construction, and applying formation fluid pressure to the annulus between the technical casing and the well bore to obtain the sizes of the outer wall of the technical casing and the well bore during primary well cementation, namely the size of the outer cement sheath;
s114, adding a third geometric component comprising an outer cement loop into the fourth finite element analysis model, meshing the third geometric component, and setting the unit type, the material parameters and the initial stress of the third geometric component;
S115, activating a third geometric component in the fourth finite element analysis model, setting a heat transfer mode at the interface of the inner wall of the technical sleeve and the fluid to be convection heat transfer, setting an analysis step type to be non-steady state transient analysis, and establishing a second finite element analysis model comprising the technical sleeve, the outer cement sheath and the stratum.
6. A method of improving the seal of a cement sheath in a casing composite section according to claim 3, wherein the failure criteria in step S201 comprises:
A maximum tensile stress criterion for the first interface temperature difference effect of the inner cement sheath;
A second nominal stress criterion for a first interfacial fluid channeling of the inner cement sheath.
7. The method of improving the sealing of a cement sheath at a composite section of a casing according to any one of claims 1 to 6, further comprising, prior to step S100, step S001:
obtaining geological parameters at the overlapping section of the sleeve;
acquiring construction parameters of the two cementing operations of the technical casing and the oil layer casing at the overlapping section of the casing;
Obtaining thermodynamic parameters of the oil layer casing, the rigid sleeve, the heat insulation layer and the technical casing at the casing punching section;
Acquiring mechanical parameters and thermodynamic parameters of the inner cement sheath and the outer cement sheath, the cementing strength of the inner cement sheath and the rigid sheath and the mechanical parameters and thermodynamic parameters of the stratum at the overlapping section of the sleeve under the action of temperature and pressure;
Then, the parameters in the step S001 are applied to build a first finite element analysis model including a casing, a thermal insulation layer, a rigid sleeve, an inner cement sheath, a technical sleeve, an outer cement sheath, and a stratum in the step S100.
8. The method of improving the leak tightness of a cement sheath in a casing composite section of claim 7, wherein the geological parameters include the earth stress, pore pressure and initial formation temperature of the formation;
the construction parameters comprise liquid injection temperature, liquid injection time and construction pressure;
Thermodynamic parameters of the oil well casing, the rigid sleeve, the heat insulation layer and the technical casing comprise the convective heat transfer coefficient of fluid, the heat transfer coefficient and expansion coefficient of the casing, and the heat transfer coefficient between the rigid sleeve and the oil well casing;
The mechanical parameters of the oil layer casing and the technical casing comprise elastic modulus and poisson ratio;
the mechanical parameters of the inner cement sheath, the outer cement sheath, and the formation include elastic modulus, poisson's ratio, flexural strength, and yield strength;
thermodynamic parameters of the inner cement sheath, the outer cement sheath, and the formation include thermal conductivity and thermal expansion coefficients.
9. The method for improving the tightness of the cement sheath of the overlapping section of the casing according to claim 7, wherein the obtaining the mechanical parameters and the thermodynamic parameters of the inner cement sheath and the outer cement sheath, the cementing strength of the inner cement sheath and the rigid sheath, and the mechanical parameters and the thermodynamic parameters of the stratum at the overlapping section of the casing in the step S001 specifically comprises:
maintaining the cement stone according to construction parameters of two times of well cementation and annular pressure and temperature at a sleeve overlapping section in the construction process, and measuring pore pressure at the final setting time of the cement stone by adopting a pore pressure measuring device;
adopting a rock mechanical strength tester to obtain mechanical parameters of cement stones and stratum;
measuring the cementing strength between the inner cement sheath and the rigid sleeve by adopting a cementing interface cementing measuring device;
And (5) obtaining thermodynamic parameters of the cement stone and the stratum by adopting a thermodynamic measurement experiment indoors.
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