CN113341111B - Cement paste critical point testing method and device - Google Patents

Cement paste critical point testing method and device Download PDF

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Publication number
CN113341111B
CN113341111B CN202010134493.3A CN202010134493A CN113341111B CN 113341111 B CN113341111 B CN 113341111B CN 202010134493 A CN202010134493 A CN 202010134493A CN 113341111 B CN113341111 B CN 113341111B
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expansion
contraction
testing
cement paste
radial direction
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CN113341111A (en
Inventor
王福云
马辉运
唐诗国
李�杰
郑友志
夏宏伟
李维
焦利宾
辜涛
李斌
谢明华
杨涛
余江
青胜兰
郭枫林
赵晓丽
付嫱
卿阳
宋文豪
马云龙
黄馨
李梦雪
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Petrochina Co Ltd
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Petrochina Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/38—Concrete; ceramics; glass; bricks
    • G01N33/383—Concrete, cement
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N19/00—Investigating materials by mechanical methods
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/16—Investigating or analyzing materials by the use of thermal means by investigating thermal coefficient of expansion

Abstract

The application discloses a cement paste critical point testing method and device, and belongs to the technical field of oil-gas well cementation. According to the cement paste critical point testing method provided by the embodiment of the application, the radial expansion and contraction amounts of cement paste and transmission medium in the radial direction can be obtained through the radial testing device, and then the radial expansion and contraction amount of cement paste is determined according to the obtained radial expansion and contraction amount of the transmission medium, so that the radial critical point of cement paste is obtained according to the radial expansion and contraction amount of cement paste, and therefore, reference can be provided for the design of cement paste systems of different well sections.

Description

Cement paste critical point testing method and device
Technical Field
The application relates to the technical field of oil and gas well cementation. In particular to a method and a device for testing critical points of cement paste.
Background
In the technical field of oil and gas well cementation, if the well cementation quality is poor, high-pressure fluid can enter a low-pressure layer to cause gas channeling, so that oil and gas resources are lost or a reservoir is damaged. And the volume change of cement paste used for well cementation under the conditions of high temperature and high pressure in the well can influence the well cementation quality. In particular, the expansion and contraction of cement paste in radial direction can cause problems of interface cementing quality, and when severe, micro gaps are formed to provide channels for oil, gas and water channeling. Therefore, it is necessary to test the critical point of radial expansion and contraction of cement paste, and reference is provided for different well section cement paste system designs. Wherein the critical point is a point at which the cement paste neither expands nor contracts in the radial direction.
In the related art, only the expansion and contraction amount of the cement paste in the axial direction can be tested through the axial testing device, but the expansion and contraction amount of the cement paste in the radial direction cannot be tested, so that the critical point of the cement paste in the radial direction cannot be determined, and therefore, reference cannot be provided for the cement paste system design of different well sections.
Disclosure of Invention
The embodiment of the application provides a method and a device for testing the critical point of cement paste, which can be used for testing the critical point of cement paste in the radial direction and providing references for cement paste system design of different well sections. The specific technical scheme is as follows:
in one aspect, the embodiment of the application provides a cement paste critical point testing method, which comprises the following steps:
acquiring a test temperature and a test pressure for testing the cement paste, wherein the cement paste is injected into a well to be tested;
firstly adding the cement paste into a reaction kettle of a radial testing device, and then adding a transmission medium, wherein the reaction kettle is controlled to be at the testing temperature and the testing pressure respectively through a heater and a pressurizer of the radial testing device, and the transmission medium is used for transmitting heat to the cement paste;
testing the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction through a radial expansion and contraction ring of the radial testing device and a volume change parameter tester;
Acquiring the expansion and contraction amount of the transmission medium in the radial direction under the test temperature and the test pressure;
taking the difference between the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction and the expansion and contraction amount of the transmission medium in the radial direction as the expansion and contraction amount of the cement paste in the radial direction;
continuously testing the cement paste by changing the test temperature or the test pressure until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts;
based on the plurality of expansion and contraction amounts, a critical point of the cement paste in a radial direction is determined.
In one possible implementation, the testing of the cement slurry is continued by changing the testing temperature or the testing pressure until the cement slurry is expanded and contracted in the radial direction from expanding to contracting or from contracting to expanding, so as to obtain a plurality of expansion and contraction amounts, including:
when the cement paste expands in the radial direction under the test temperature and the test pressure, the test pressure is kept unchanged, the test temperature is reduced, and the cement paste is continuously tested until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction, so that a plurality of expansion and contraction amounts corresponding to a plurality of test temperatures are obtained;
When the cement paste contracts in the radial direction under the test temperature and the test pressure, the test pressure is kept unchanged, the test temperature is raised to continue to test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, and a plurality of expansion and contraction amounts corresponding to a plurality of test temperatures are obtained.
In another possible implementation manner, the testing of the cement slurry is continued by changing the testing temperature or the testing pressure until the cement slurry is expanded and contracted in the radial direction from expanding to contracting or from contracting to expanding, so as to obtain a plurality of expansion and contraction amounts, including:
when the cement paste expands in the radial direction under the test temperature and the test pressure, the test temperature is kept unchanged, the test pressure is reduced, and the cement paste is continuously tested until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction, so that a plurality of expansion and contraction amounts corresponding to a plurality of test pressures are obtained;
when the cement paste contracts in the radial direction under the test temperature and the test pressure, the test temperature is kept unchanged, the test pressure is increased to continue to test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, and a plurality of expansion and contraction amounts corresponding to a plurality of test pressures are obtained.
In another possible implementation, the determining the critical point of the cement slurry in the radial direction based on the plurality of expansion and contraction amounts includes:
based on the expansion and contraction amounts, the test temperatures and the change relation function of the temperature of the well to be tested along with the depth, performing polynomial fitting by taking the expansion and contraction amounts as an ordinate and the test temperature as an abscissa to obtain a first curve of the expansion and contraction amounts along with the change of the test temperature;
and taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction.
In another possible implementation, before the intersection point of the first curve and the abscissa is taken as the critical point of the cement slurry in the radial direction, the method further includes:
determining whether the square value of the fitting coefficient of the first curve is larger than a preset threshold value;
and when the square value of the fitting coefficient is not smaller than a preset threshold value, executing the step of taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction.
In another possible implementation, the method further includes:
and when the square value of the fitting coefficient is smaller than the preset threshold value, executing the step of continuously testing the cement paste by changing the test temperature or the test pressure until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts.
In another possible implementation, the method further includes:
acquiring the change relation between the depth and the temperature of the well to be tested;
and obtaining a change relation function of the temperature of the well to be tested along with the depth change according to the change relation.
In another possible implementation, the determining the critical point of the cement slurry in the radial direction based on the plurality of expansion and contraction amounts includes:
based on the expansion and contraction amounts, the test pressures and the change relation function of the pressure of the well to be tested along with the depth change, performing polynomial fitting by taking the expansion and contraction amounts as an ordinate and the test pressure as an abscissa to obtain a second curve of the expansion and contraction amounts along with the change of the test pressure;
and taking the intersection point of the second curve and the abscissa as a critical point of the cement paste in the radial direction.
In another aspect, there is provided a cement paste critical point testing apparatus, the apparatus comprising:
the first acquisition module is used for acquiring the test temperature and the test pressure for testing the cement paste, wherein the cement paste is injected into a well to be tested;
the control module is used for adding the cement paste into the reaction kettle of the radial testing device firstly, then adding a transmission medium, and respectively controlling the reaction kettle to be at the testing temperature and the testing pressure through a heater and a pressurizer of the radial testing device, wherein the transmission medium is used for transmitting heat to the cement paste;
The first testing module is used for testing the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction through a radial expansion and contraction ring of the radial testing device and a volume change parameter tester;
the second acquisition module is used for acquiring the expansion and contraction amount of the transmission medium in the radial direction at the test temperature and the test pressure;
a first determining module, configured to use a difference between an expansion and contraction amount of the cement paste and the transmission medium in a radial direction and an expansion and contraction amount of the transmission medium in the radial direction as an expansion and contraction amount of the cement paste in the radial direction;
the second testing module is used for continuously testing the cement paste by changing the testing temperature or the testing pressure until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts;
and a second determining module for determining a critical point of the cement slurry in the radial direction based on the expansion and contraction amounts.
In a possible implementation manner, the second testing module is further configured to, when the cement paste expands in a radial direction at the testing temperature and the testing pressure, keep the testing pressure unchanged, reduce the testing temperature, and continue to test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing temperatures;
And the second testing module is further used for keeping the testing pressure unchanged when the cement paste contracts in the radial direction under the testing temperature and the testing pressure, and increasing the testing temperature to continuously test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing temperatures.
In another possible implementation manner, the second testing module is further configured to, when the cement paste expands in a radial direction at the testing temperature and the testing pressure, maintain the testing temperature unchanged, reduce the testing pressure, and continue to test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing pressures;
and the second testing module is further used for keeping the testing temperature unchanged when the cement paste contracts in the radial direction under the testing temperature and the testing pressure, and increasing the testing pressure to continuously test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing pressures.
In another possible implementation manner, the second determining module is further configured to perform polynomial fitting with the expansion and contraction amounts as an ordinate and the test temperature as an abscissa based on a change relation function of the expansion and contraction amounts, the test temperatures, and the temperature of the well to be tested along with the depth change, to obtain a first curve of the expansion and contraction amounts along with the change of the test temperature; and taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction.
In another possible implementation, the apparatus further includes:
a third determining module, configured to determine whether a square value of a fitting coefficient of the first curve is greater than a preset threshold;
and the third determining module is further configured to, when the square value of the fitting coefficient is not less than a preset threshold value, use an intersection point of the first curve and the abscissa as a critical point of the cement slurry in the radial direction.
In another possible implementation manner, the second testing module is further configured to, when the square value of the fitting coefficient is smaller than the preset threshold, continue testing the cement slurry by changing the testing temperature or the testing pressure until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts.
In another possible implementation, the apparatus further includes:
the first measuring module is used for measuring the temperatures corresponding to different depths in the well to be tested and obtaining the change relation between the depths of the well to be tested and the temperatures; and obtaining a change relation function of the temperature of the well to be tested along with the depth change according to the change relation.
In another possible implementation manner, the second determining module is further configured to perform polynomial fitting based on a change relation function of the expansion and contraction amounts, the test pressures and the pressure of the well to be tested along with the depth change, with the expansion and contraction amounts as an ordinate and the test pressure as an abscissa, to obtain a second curve of the expansion and contraction amounts along with the change of the test pressure; and taking the intersection point of the second curve and the abscissa as a critical point of the cement paste in the radial direction.
The technical scheme provided by the embodiment of the application has the beneficial effects that:
according to the cement paste critical point testing method provided by the embodiment of the application, the testing temperature and the testing pressure for testing the cement paste are obtained, the cement paste is firstly added into the reaction kettle, then the transmission medium is added, and the reaction kettle is respectively controlled to be under the testing temperature and the testing pressure by the warmer and the pressurizer; testing the expansion and contraction amounts of cement paste and a transmission medium in the radial direction through a radial expansion and contraction ring and a volume change parameter tester; acquiring the expansion and contraction amounts of the transmission medium in the radial direction under the test temperature and the test pressure, and taking the difference between the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction and the expansion and contraction amounts of the transmission medium in the radial direction as the expansion and contraction amounts of the cement paste in the radial direction; continuously testing the cement slurry by changing the test temperature or the test pressure until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts; based on the plurality of expansion and contraction amounts, a critical point of the cement paste in the radial direction is determined. According to the method, the radial expansion and contraction amounts of the cement paste and the transmission medium can be obtained through the radial testing device, the radial expansion and contraction amounts of the cement paste are determined according to the obtained radial expansion and contraction amounts of the transmission medium, and then the radial critical point of the cement paste is obtained according to the radial expansion and contraction amounts of the cement paste, so that references can be provided for the design of cement paste systems of different well sections.
Drawings
FIG. 1 is a flow chart of a method for testing critical points of cement slurries according to an embodiment of the present application;
FIG. 2 is a schematic diagram of a radial testing device according to an embodiment of the present application;
FIG. 3 is a schematic diagram showing the expansion and contraction amount of cement slurry in radial direction along with the change of temperature or pressure according to the embodiment of the application;
FIG. 4 is a schematic illustration of the radial expansion and contraction of cement slurry with test temperature, as provided in example 1, with test pressure maintained;
FIG. 5 is a graph showing the radial expansion and contraction of cement slurry with test temperature, wherein the test pressure is kept unchanged in the embodiment 2;
fig. 6 is a schematic structural diagram of a cement paste critical point testing device according to an embodiment of the present application.
Detailed Description
In order to make the technical scheme and advantages of the present application more clear, the following further describes the embodiments of the present application in detail.
The cement sheath formed after cement paste solidification is an important safeguard measure for safe and efficient production of oil and gas wells, the volume change of the cement sheath under high temperature and high pressure conditions in the well can influence the service life of the oil and gas wells, the casing is extruded when the volume expansion of the cement sheath is serious, the well cementation is failed, the interface cementation quality can be problematic due to the shrinkage of the cement sheath, and a micro-gap can be formed when the volume expansion of the cement sheath is serious, so that a channel is provided for oil, gas and water channeling. Therefore, it is necessary to test the critical point of radial expansion and contraction of cement paste, thereby providing reference for different well section cement paste system designs.
In the test method of oil well cement (GB/T19139), the application performance of oil well cement is specified, including the test methods of density, compressive strength, nondestructive sonic test, thickening time, static water loss, permeability, rheological property, gel strength, stability, downhole fluid compatibility, arctic cement injection test method and the like, and the pressure drop and flow state calculation method of cement paste in casing and annulus, but the test specification of the critical point of radial expansion and contraction of cement paste under the conditions of high temperature and high pressure is not mentioned.
In the related art, only the expansion and contraction amount of the cement paste in the axial direction can be tested through the axial testing device, but the expansion and contraction amount of the cement paste in the radial direction cannot be tested, so that the critical point of the cement paste in the radial direction cannot be determined, and therefore, reference cannot be provided for the cement paste system design of different well sections.
The testing method provided by the embodiment of the application not only can test the expansion and contraction amount of the cement paste in the radial direction, but also can determine the critical point of the cement paste in the radial direction according to the expansion and contraction amount of the cement paste in the radial direction. According to the testing method provided by the embodiment of the application, the radial critical point of the well cementation cement ring can be accurately tested by measuring the radial expansion and contraction amount of the cement paste and utilizing numerical fitting, so that the testing method has very important significance for the critical point of the well cementation engineering when the volume stability of the cement paste system is in high temperature and high pressure in the well and for the system selection in the design of different well section cement paste systems.
The embodiment of the application provides a cement paste critical point testing method, which is shown in fig. 1, and comprises the following steps:
step 101: and obtaining the test temperature and the test pressure for testing the cement paste.
In this step, the cement slurry is the cement slurry injected into the well to be tested. The test temperature and the test pressure can be the temperature and the pressure corresponding to the target well section in the well to be tested, and can also be the temperature and the pressure corresponding to any well section. In the embodiment of the present application, the test temperature and the test pressure may be set and changed as required, which is not particularly limited.
Step 102: cement slurry is added into a reaction kettle of the radial testing device, then a transmission medium is added, and the reaction kettle is controlled to be under the testing temperature and the testing pressure respectively through a warmer and a pressurizer.
Wherein the transmission medium is used for transmitting heat for cement paste. The cement slurry and the transmission medium may be separated by a rubber septum.
Referring to fig. 2, the radial test apparatus includes: the device comprises a reaction kettle, a warmer, a pressurizer, a radial expansion and contraction ring and a volume change parameter tester. The warmer, the pressurizer and the volume change parameter tester are all connected with the reaction kettle, and the radial expansion and contraction ring is positioned in the reaction kettle. The cement slurry and the transmission medium may expand or contract along the radially expanding and contracting ring. The warmer and the pressurizer are respectively used for controlling the temperature and the pressure of the reaction kettle. The volume change parameter tester can test the deformation of the radial expansion and contraction ring when the cement paste and the transmission medium expand and contract in the radial direction; and obtaining the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction according to the deformation amount.
In the embodiment of the application, when the cement paste expands, the expansion and contraction amount can be set to be a positive value; the shrinkage of the cement slurry is negative, and the specific test conditions can be seen in fig. 3.
Prior to this step, the cement slurry may be formulated according to API standards.
Step 103: the radial expansion and contraction amount of cement paste and transmission medium in the radial direction is tested by a radial expansion and contraction ring and a volume change parameter tester.
When the cement paste and the transmission medium expand and contract in the radial direction, the cement paste and the transmission medium expand or contract along the radial expansion and contraction ring, so that the radial expansion and contraction ring deforms. At this time, the deformation amount of the radial expansion and contraction ring which is deformed can be measured by the volume change parameter tester. The deformation of the radial expansion and contraction ring is used as the expansion and contraction of cement paste and transmission medium in radial direction.
The deformation of the radial expansion and contraction ring is caused by the expansion and contraction of cement paste and a transmission medium, and the deformation of the radial expansion and contraction ring can reflect the expansion and contraction of cement paste and the transmission medium. Therefore, in this step, the deformation amount of the radial expansion and contraction ring can be used as the expansion and contraction amount of the cement paste and the transmission medium in the radial direction.
Step 104: and acquiring the expansion and contraction amount of the transmission medium in the radial direction under the test temperature and the test pressure.
The kind of the transmission medium may be set and changed as needed, and for example, the transmission medium may be water or oil. In the embodiments of the present application, the transmission medium is water. The water may be distilled water, tap water or treated water carried in the oil and gas produced from the well to be tested. When the water is transmitted as water and the water is the treated water carried in the oil gas extracted from the well to be tested, the compatibility of the transmission medium and the stratum is good, and the real environment of cement paste in the well can be more truly simulated.
When the transmission medium is determined, the amount of expansion and contraction of the transmission medium in the radial direction is known at different temperatures and different pressures. Therefore, in this step, the expansion and contraction amounts of the transmission medium in the radial direction at the test temperature and the test pressure can be obtained.
It should be noted that, after step 101 is performed, steps 102 to 103 may be performed, and then step 104 may be performed. Step 101 may be performed, step 104 may be performed, and steps 102-103 may be performed. In the embodiment of the present application, this order is not particularly limited.
Step 105: and taking the difference between the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction and the expansion and contraction amount of the transmission medium in the radial direction as the expansion and contraction amount of the cement paste in the radial direction.
In the embodiment of the application, the transmission medium also expands and contracts in the radial direction, so that the expansion and contraction amount measured by the radial test device is the expansion and contraction amount of the cement paste and the transmission medium together. Considering the influence of expansion and contraction of the transmission medium in the radial direction, in the step, the interference of the transmission medium on the expansion and contraction amount of the cement paste is eliminated, and the expansion and contraction amount of the cement paste in the radial direction can be measured more accurately.
Step 106: and continuously testing the cement slurry by changing the testing temperature or the testing pressure until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts.
In one possible implementation, the cement slurry may be continuously tested by varying the test temperature.
The implementation mode is specifically as follows:
when the cement paste expands in the radial direction under the test temperature and the test pressure, the test pressure is kept unchanged, the test temperature is reduced, and the cement paste is continuously tested until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction, so that a plurality of expansion and contraction amounts corresponding to a plurality of test temperatures are obtained;
When the cement paste contracts in the radial direction at the test temperature and the test pressure, the test pressure is kept unchanged, the test temperature is increased to continuously test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, and a plurality of expansion and contraction amounts corresponding to a plurality of test temperatures are obtained.
In another possible implementation, the cement slurry can also be continuously tested by changing the test pressure, and the implementation is specifically that:
when the cement paste expands in the radial direction under the test temperature and the test pressure, the test temperature is kept unchanged, the test pressure is reduced, and the cement paste is continuously tested until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction, so that a plurality of expansion and contraction amounts corresponding to a plurality of test pressures are obtained;
when the cement paste contracts in the radial direction at the test temperature and the test pressure, the test temperature is kept unchanged, the test pressure is increased to continuously test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, and a plurality of expansion and contraction amounts corresponding to a plurality of test pressures are obtained.
In the embodiment of the application, the temperature or pressure when the expansion and contraction states of the cement are changed can be obtained by changing the test temperature or the test pressure.
Step 107: based on the plurality of expansion and contraction amounts, a critical point of the cement paste in the radial direction is determined.
In one possible implementation, the critical point of the cement slurry in the radial direction can be determined by a plurality of expansion and contraction amounts and a plurality of test temperatures. Specifically, the method can be realized by the following steps (1) to (4), and comprises the following steps:
(1) Based on a plurality of expansion and contraction amounts, a plurality of test temperatures and a change relation function of the temperature of the well to be tested along with the change of the depth, taking the expansion and contraction amounts as an ordinate and the test temperature as an abscissa, and performing polynomial fitting to obtain a first curve of the expansion and contraction amounts along with the change of the test temperature.
In this step, a two-dimensional coordinate system may be established, and a first curve may be obtained by performing polynomial fitting according to a change relation function, with the expansion and contraction amounts as ordinate and the test temperature as abscissa. The functions corresponding to the first curve and the change relation function are the same in type. For example, if the change relation function is a unitary linear function, the first curve obtained by fitting is also a unitary linear function; and if the change relation function is a unitary quadratic function, the first curve obtained by fitting is also a unitary quadratic function.
In one possible implementation manner, the change relation function may be obtained by the following implementation manner, specifically: measuring temperatures corresponding to different depths in the well to be tested, and obtaining a change relation between the depths and the temperatures of the well to be tested; and obtaining a change relation function of the temperature of the well to be tested along with the depth change according to the change relation.
The deeper the depth, the higher the corresponding temperature. In the embodiment of the application, the change relation of the temperature along with the change of the depth is obtained by measuring the corresponding relation between the depth and the temperature, and the change relation function is determined according to the change relation.
In the embodiment of the application, if the change relation function of the temperature along with the depth change is a unitary quadratic function, the first curve obtained by fitting is also a unitary quadratic function, and the expression y=ax can be used for the first curve 2 +bx+c. Wherein y represents the expansion and contraction amount, x represents the test temperature, and a, b and c represent parameters, respectively. And performing unitary quadratic fitting according to the expansion and contraction amounts and the test temperatures to obtain a first curve and a corresponding relation.
(2) It is determined whether the square value of the fitting coefficient of the first curve is greater than a preset threshold.
The square value of the fitting coefficient may reflect the fitting degree between the estimated value of the first curve and the actual data, and the higher the fitting degree is, the higher the reliability of the first curve is. The square value of the fitting coefficient is between 0 and 1, and the closer the square value of the fitting coefficient is to 1, the higher the reliability of the first curve is. When the square value of the fitting coefficient of the first curve is not smaller than a preset threshold value, executing the step (3); and (4) when the square value of the fitting coefficient is smaller than a preset threshold value, executing the step (4).
The preset threshold may be set and changed as required, and in the embodiment of the present application, this is not particularly limited. For example, the preset threshold may be 0.95, 0.96, or 0.98.
(3) And when the square value of the fitting coefficient is not smaller than a preset threshold value, taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction.
When the square value of the fitting coefficient is not smaller than a preset threshold value, the first curve fitting is better, and at the moment, the intersection point of the first curve and the abscissa is the critical point of the cement paste in the radial direction, namely, the cement paste does not expand or contract in the radial direction at the temperature corresponding to the test pressure and the critical point.
(4) When the square value of the fitting coefficient is smaller than the preset threshold, step 107 is executed until the square value of the fitting coefficient is not smaller than the preset threshold, and step (3) is executed.
When the square value of the fitting coefficient is smaller than a preset threshold value, continuing to test the cement slurry by changing the test temperature until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts; based on a plurality of expansion and contraction amounts, a plurality of test temperatures and the change relation function, taking the expansion and contraction amounts as an ordinate and the test temperatures as an abscissa, performing polynomial fitting to obtain a first curve of the expansion and contraction amounts changing along with the test temperatures; determining whether the square value of the fitting coefficient of the first curve is larger than a preset threshold value; when the square value of the fitting coefficient is not smaller than a preset threshold value, taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction; and (3) when the square value of the fitting coefficient is smaller than a preset threshold value, continuing to execute the steps until the square value of the fitting coefficient is not smaller than the preset threshold value, and executing the step (3).
In another possible implementation, the critical point of the cement slurry in the radial direction can also be determined by a plurality of expansion and contraction amounts, a plurality of test pressures and a variation relation function of the pressure with the depth. The method comprises the following steps: based on a change relation function of a plurality of expansion and contraction amounts, a plurality of test pressures and the pressure of the well to be tested along with the change of the depth, taking the expansion and contraction amounts as an ordinate and the test pressure as an abscissa, and performing polynomial fitting to obtain a second curve of the expansion and contraction amounts along with the change of the test pressure; the intersection point of the second curve and the abscissa is taken as a critical point of the cement paste in the radial direction. The implementation process is similar to the process of determining the critical point of cement slurry in the radial direction based on the change relation function of a plurality of expansion and contraction amounts, a plurality of test temperatures and the change of the temperature along with the depth, and is not repeated here.
According to the cement paste critical point testing method provided by the embodiment of the application, the testing temperature and the testing pressure for testing the cement paste are obtained, the cement paste is firstly added into the reaction kettle, then the transmission medium is added, and the reaction kettle is respectively controlled to be under the testing temperature and the testing pressure by the warmer and the pressurizer; testing the expansion and contraction amounts of cement paste and a transmission medium in the radial direction through a radial expansion and contraction ring and a volume change parameter tester; acquiring the expansion and contraction amounts of the transmission medium in the radial direction under the test temperature and the test pressure, and taking the difference between the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction and the expansion and contraction amounts of the transmission medium in the radial direction as the expansion and contraction amounts of the cement paste in the radial direction; continuously testing the cement slurry by changing the test temperature or the test pressure until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts; based on the plurality of expansion and contraction amounts, a critical point of the cement paste in the radial direction is determined. According to the method, the radial expansion and contraction amounts of the cement paste and the transmission medium can be obtained through the radial testing device, the radial expansion and contraction amounts of the cement paste are determined according to the obtained radial expansion and contraction amounts of the transmission medium, and then the radial critical point of the cement paste is obtained according to the radial expansion and contraction amounts of the cement paste, so that references can be provided for the design of cement paste systems of different well sections.
The technical scheme of the application will be described in detail through specific examples.
Example 1
In this embodiment, a plurality of expansion and contraction amounts, a plurality of test temperatures, and a function of a change relation of temperature with a change in depth are taken as examples to determine a critical point of cement paste in a radial direction.
And step 1, acquiring the test temperature and the test pressure for testing the cement paste.
In this example, the test temperature was 95℃and the test pressure was 21MPa;
step 2: cement slurry is added into the reaction kettle, then a transmission medium is added, and the reaction kettle is controlled to be under the test temperature and the test pressure respectively through a warmer and a pressurizer.
The cement paste is 7 inch liner cementing cement paste of Chongqi field X1 well which is adopted on site, is flexible cement paste with large temperature difference, and has the density of 1.90g/cm 3 . The cement slurry may be formulated according to API standards.
Step 3: the radial expansion and contraction amount of cement paste and transmission medium in the radial direction is tested by a radial expansion and contraction ring and a volume change parameter tester.
Step 4: and acquiring the expansion and contraction amount of the transmission medium in the radial direction under the test temperature and the test pressure.
Step 5: and taking the difference between the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction and the expansion and contraction amount of the transmission medium in the radial direction as the expansion and contraction amount of the cement paste in the radial direction.
Through the steps 3-5, the testing pressure is 21MPa, and the radial expansion and shrinkage of the cement paste is-1.94% at the testing temperature of 95 ℃.
Step 6: and continuously testing the cement paste by changing the testing temperature until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts.
In the embodiment of the application, when the cement paste expands, the expansion and contraction amount is set to be a positive value; when the cement paste contracts, the expansion and contraction amount is negative. In step 5, the expansion and contraction amount of the cement paste in the radial direction is negative, and the cement paste is known to contract in the radial direction, so that the cement paste is continuously tested at the elevated temperature until the cement paste expands in the radial direction, and a plurality of expansion and contraction amounts are obtained.
Wherein the test temperatures are 120 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃ and the corresponding expansion and contraction amounts are-0.8%, 1.41%, 0.7%, 0.5% and 2.58%, respectively.
Step 7: based on the plurality of expansion and contraction amounts, a critical point of the cement paste in the radial direction is determined.
The plurality of test temperatures are respectively: 95 ℃, 120 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃ and a plurality of corresponding expansion and contraction amounts are respectively as follows: -1.94%, -0.8%, -1.41%, 0.7%, 0.5%, 2.58%.
According to the change relation function of the temperature along with the depth change, the expansion and contraction amount is taken as an ordinate, the test temperature is taken as an abscissa, and a curve of the expansion and contraction amount along with the test temperature change is obtained through fitting, and the curve is shown in fig. 4. As can be seen from fig. 4: the cement paste has a critical point of 157 ℃ in the radial direction, namely, the cement paste does not expand nor contract in the radial direction under the pressure of 21MPa and 157 ℃.
Example 2
In this embodiment, a plurality of expansion and contraction amounts, a plurality of test temperatures, and a function of a change relation of temperature with a change in depth are taken as examples to determine a critical point of cement paste in a radial direction.
And step 1, acquiring the test temperature and the test pressure for testing the cement paste.
In this example, the test temperature was 95℃and the test pressure was 21MPa;
step 2: cement slurry is added into the reaction kettle, then a transmission medium is added, and the reaction kettle is controlled to be under the test temperature and the test pressure respectively through a warmer and a pressurizer.
The cement paste is 7 inch liner cementing cement paste of Chongqi field X2 well which is adopted on site, is tough channeling-preventing cement paste, and has the density of 1.90g/cm 3 . The cement slurry may be formulated according to API standards.
Step 3: the radial expansion and contraction amount of cement paste and transmission medium in the radial direction is tested by a radial expansion and contraction ring and a volume change parameter tester.
Step 4: and acquiring the expansion and contraction amount of the transmission medium in the radial direction under the test temperature and the test pressure.
Step 5: and taking the difference between the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction and the expansion and contraction amount of the transmission medium in the radial direction as the expansion and contraction amount of the cement paste in the radial direction.
Through the steps 3-5, the expansion and contraction amount of the cement paste in the radial direction is-2.28% when the test pressure is 21MPa and the test temperature is 95 ℃.
Step 6: and continuously testing the cement paste by changing the testing temperature until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts.
In the embodiment of the application, when the cement paste expands, the expansion and contraction amount is set to be a positive value; when the cement paste contracts, the expansion and contraction amount is negative. In step 5, the expansion and contraction amount of the cement paste in the radial direction is negative, and the cement paste is known to contract in the radial direction, so that the cement paste is continuously tested at the elevated temperature until the cement paste expands in the radial direction, and a plurality of expansion and contraction amounts are obtained.
Wherein the test temperatures are 120 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃ and the corresponding expansion and contraction amounts are-2.17%, 1.05%, 0.53%, 1.45% and 1.97% respectively.
Step 7: based on the plurality of expansion and contraction amounts, a critical point of the cement paste in the radial direction is determined.
The plurality of test temperatures are respectively: 95 ℃, 120 ℃, 150 ℃,160 ℃, 170 ℃, 180 ℃ and a plurality of corresponding expansion and contraction amounts are respectively as follows: -2.28%, -2.17%, -1.05%, 0.53%, 1.45%, 1.97%.
According to the change relation function of the temperature along with the depth change, the expansion and contraction amount is taken as an ordinate, the test temperature is taken as an abscissa, and a curve of the expansion and contraction amount along with the test temperature change is obtained through fitting, and the curve is shown in fig. 5. As can be seen from fig. 5: the critical point of the cement paste in the radial direction is 160 ℃, namely, the cement paste is neither expanded nor contracted in the radial direction under the pressure of 21MPa and 160 ℃.
The embodiment of the application provides a cement paste critical point testing device, referring to fig. 6, the device comprises:
the first obtaining module 601 is configured to obtain a test temperature and a test pressure for testing cement slurry, where the cement slurry is injected into a well to be tested;
the control module 602 is configured to add cement slurry to the reaction kettle of the radial testing device, and then add a transmission medium, where the reaction kettle is controlled to be at a test temperature and a test pressure by the heater and the pressurizer of the radial testing device, respectively, and the transmission medium is used to transmit heat for the cement slurry;
A first testing module 603, configured to test the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction through a radial expansion and contraction ring of the radial testing device and a volume change parameter tester;
a second obtaining module 604, configured to obtain an expansion and contraction amount of the transmission medium in a radial direction at a test temperature and a test pressure;
a first determining module 605, configured to use a difference between an expansion and contraction amount of the cement paste and the transmission medium in the radial direction and an expansion and contraction amount of the transmission medium in the radial direction as an expansion and contraction amount of the cement paste in the radial direction;
the second testing module 606 is configured to continuously test the cement slurry by changing the testing temperature or the testing pressure until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts;
a second determining module 607 is configured to determine a critical point of the cement slurry in a radial direction based on the plurality of expansion and contraction amounts.
In a possible implementation manner, the second testing module 606 is further configured to, when the cement slurry expands in the radial direction at the testing temperature and the testing pressure, keep the testing pressure unchanged, and reduce the testing temperature to continue to test the cement slurry until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing temperatures;
The second testing module 606 is further configured to, when the cement slurry contracts in the radial direction at the testing temperature and the testing pressure, maintain the testing pressure unchanged, and raise the testing temperature to continue to test the cement slurry until the expansion and contraction state of the cement slurry in the radial direction is changed from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing temperatures.
In another possible implementation manner, the second testing module 606 is further configured to, when the cement slurry expands in the radial direction at the testing temperature and the testing pressure, keep the testing temperature unchanged, and reduce the testing pressure to continue to test the cement slurry until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing pressures;
the second testing module 606 is further configured to, when the cement slurry contracts in the radial direction at the testing temperature and the testing pressure, maintain the testing temperature unchanged, and raise the testing pressure to continue to test the cement slurry until the expansion and contraction state of the cement slurry in the radial direction is changed from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts corresponding to the plurality of testing pressures.
In another possible implementation manner, the second determining module 607 is further configured to perform polynomial fitting based on a function of a change relation of the expansion and contraction amounts, the test temperatures, and the temperature of the well to be tested with respect to the depth, with the expansion and contraction amounts as an ordinate and the test temperatures as an abscissa, to obtain a first curve of the expansion and contraction amounts with respect to the test temperatures; the intersection point of the first curve and the abscissa is taken as a critical point of the cement paste in the radial direction.
In another possible implementation, the apparatus further includes:
the third determining module is used for determining whether the square value of the fitting coefficient of the first curve is larger than a preset threshold value or not;
and the third determining module is further used for taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction when the square value of the fitting coefficient is not smaller than a preset threshold value.
In another possible implementation manner, the second testing module 606 is further configured to, when the square value of the fitting coefficient is smaller than the preset threshold, continue testing the cement slurry by changing the testing temperature or the testing pressure until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts.
In another possible implementation, the apparatus further includes:
the first measuring module is used for measuring the temperatures corresponding to different depths in the well to be tested and obtaining the change relation between the depths and the temperatures of the well to be tested; and obtaining a change relation function of the temperature of the well to be tested along with the depth change according to the change relation.
In another possible implementation manner, the second determining module 607 is further configured to perform polynomial fitting based on a function of a change relation of the expansion and contraction amounts, the test pressures, and the pressure of the well to be tested with respect to the depth, with the expansion and contraction amounts as an ordinate and the test pressures as an abscissa, to obtain a second curve of the expansion and contraction amounts with respect to the test pressures; the intersection point of the second curve and the abscissa is taken as a critical point of the cement paste in the radial direction.
According to the cement paste critical point testing device provided by the embodiment of the application, the testing temperature and the testing pressure for testing the cement paste are obtained, the cement paste is firstly added into the reaction kettle, then the transmission medium is added, and the reaction kettle is respectively controlled to be under the testing temperature and the testing pressure by the warmer and the pressurizer; testing the expansion and contraction amounts of cement paste and a transmission medium in the radial direction through a radial expansion and contraction ring and a volume change parameter tester; acquiring the expansion and contraction amounts of the transmission medium in the radial direction under the test temperature and the test pressure, and taking the difference between the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction and the expansion and contraction amounts of the transmission medium in the radial direction as the expansion and contraction amounts of the cement paste in the radial direction; continuously testing the cement slurry by changing the test temperature or the test pressure until the expansion and contraction state of the cement slurry in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts; based on the plurality of expansion and contraction amounts, a critical point of the cement paste in the radial direction is determined. The device can obtain the expansion and contraction amounts of cement paste and transmission medium in the radial direction through the radial testing device, then determine the expansion and contraction amounts of cement paste in the radial direction according to the obtained expansion and contraction amounts of the transmission medium in the radial direction, and further obtain the critical point of cement paste in the radial direction according to the expansion and contraction amounts of the cement paste in the radial direction, so that references can be provided for the design of cement paste systems of different well sections.
The foregoing description is only for the convenience of those skilled in the art to understand the technical solution of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims (12)

1. A method for testing critical points of cement paste, the method comprising:
acquiring a test temperature and a test pressure for testing the cement paste, wherein the cement paste is injected into a well to be tested;
firstly adding the cement paste into a reaction kettle of a radial testing device, and then adding a transmission medium, wherein the reaction kettle is controlled to be at the testing temperature and the testing pressure respectively through a heater and a pressurizer of the radial testing device, and the transmission medium is used for transmitting heat to the cement paste;
testing the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction through a radial expansion and contraction ring of the radial testing device and a volume change parameter tester;
acquiring the expansion and contraction amount of the transmission medium in the radial direction under the test temperature and the test pressure;
taking the difference between the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction and the expansion and contraction amount of the transmission medium in the radial direction as the expansion and contraction amount of the cement paste in the radial direction;
Continuously testing the cement paste by changing the test temperature or the test pressure until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts;
if the cement paste is tested by changing the test temperature, after the expansion and contraction amounts are obtained, performing polynomial fitting by taking the expansion and contraction amounts as an ordinate and the test temperature as an abscissa based on a change relation function of the expansion and contraction amounts, the test temperatures and the temperature of the well to be tested along with the depth change, so as to obtain a first curve of the expansion and contraction amounts along with the change of the test temperature;
taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction;
the determining process of the change relation function of the temperature of the well to be tested along with the change of the depth comprises the following steps:
measuring the temperatures corresponding to different depths in the well to be tested to obtain the change relation between the depths of the well to be tested and the temperatures;
and obtaining a change relation function of the temperature of the well to be tested along with the depth change according to the change relation.
2. The method of claim 1, wherein the testing of the cement slurry is continued by changing the test temperature or the test pressure until the cement slurry expands and contracts in the radial direction from expanding to contracting or from contracting to expanding, resulting in a plurality of expansion and contraction amounts, comprising:
When the cement paste expands in the radial direction under the test temperature and the test pressure, the test pressure is kept unchanged, the test temperature is reduced, and the cement paste is continuously tested until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction, so that a plurality of expansion and contraction amounts corresponding to a plurality of test temperatures are obtained;
when the cement paste contracts in the radial direction under the test temperature and the test pressure, the test pressure is kept unchanged, the test temperature is raised to continue to test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, and a plurality of expansion and contraction amounts corresponding to a plurality of test temperatures are obtained.
3. The method of claim 1, wherein the testing of the cement slurry is continued by changing the test temperature or the test pressure until the cement slurry expands and contracts in the radial direction from expanding to contracting or from contracting to expanding, resulting in a plurality of expansion and contraction amounts, comprising:
when the cement paste expands in the radial direction under the test temperature and the test pressure, the test temperature is kept unchanged, the test pressure is reduced, and the cement paste is continuously tested until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction, so that a plurality of expansion and contraction amounts corresponding to a plurality of test pressures are obtained;
When the cement paste contracts in the radial direction under the test temperature and the test pressure, the test temperature is kept unchanged, the test pressure is increased to continue to test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, and a plurality of expansion and contraction amounts corresponding to a plurality of test pressures are obtained.
4. The method of claim 1, wherein the intersection of the first curve and the abscissa is taken as a critical point of the cement slurry in the radial direction, the method further comprising:
determining whether the square value of the fitting coefficient of the first curve is larger than a preset threshold value;
and when the square value of the fitting coefficient is not smaller than a preset threshold value, executing the step of taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction.
5. The method according to claim 4, wherein the method further comprises:
and when the square value of the fitting coefficient is smaller than the preset threshold value, executing the step of continuously testing the cement paste by changing the test temperature or the test pressure until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts.
6. A method according to claim 3, wherein if the cement slurry is tested by varying the test pressure, after obtaining the plurality of expansion and contraction amounts, the method further comprises:
based on the expansion and contraction amounts, the test pressures and the change relation function of the pressure of the well to be tested along with the depth change, performing polynomial fitting by taking the expansion and contraction amounts as an ordinate and the test pressure as an abscissa to obtain a second curve of the expansion and contraction amounts along with the change of the test pressure;
and taking the intersection point of the second curve and the abscissa as a critical point of the cement paste in the radial direction.
7. A cement slurry critical point testing apparatus, the apparatus comprising:
the first acquisition module is used for acquiring the test temperature and the test pressure for testing the cement paste, wherein the cement paste is injected into a well to be tested;
the control module is used for adding the cement paste into the reaction kettle of the radial testing device firstly, then adding a transmission medium, and respectively controlling the reaction kettle to be at the testing temperature and the testing pressure through a heater and a pressurizer of the radial testing device, wherein the transmission medium is used for transmitting heat to the cement paste;
The first testing module is used for testing the expansion and contraction amounts of the cement paste and the transmission medium in the radial direction through a radial expansion and contraction ring of the radial testing device and a volume change parameter tester;
the second acquisition module is used for acquiring the expansion and contraction amount of the transmission medium in the radial direction at the test temperature and the test pressure;
a first determining module, configured to use a difference between an expansion and contraction amount of the cement paste and the transmission medium in a radial direction and an expansion and contraction amount of the transmission medium in the radial direction as an expansion and contraction amount of the cement paste in the radial direction;
the second testing module is used for continuously testing the cement paste by changing the testing temperature or the testing pressure until the expansion and contraction state of the cement paste in the radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts;
the second determining module is configured to, if the cement slurry is tested by changing the test temperature, obtain a plurality of expansion and contraction amounts, and then perform polynomial fitting based on a change relation function of the expansion and contraction amounts, the plurality of test temperatures, and the temperature of the well to be tested along with the depth change, with the expansion and contraction amounts as ordinate and the test temperature as abscissa, to obtain a first curve of the expansion and contraction amounts along with the change of the test temperature; taking the intersection point of the first curve and the abscissa as a critical point of the cement paste in the radial direction;
The first measuring module is used for measuring the temperatures corresponding to different depths in the well to be tested and obtaining the change relation between the depths of the well to be tested and the temperatures; and obtaining a change relation function of the temperature of the well to be tested along with the depth change according to the change relation.
8. The apparatus of claim 7, wherein the second testing module is further configured to, when the cement slurry expands in a radial direction at the testing temperature and the testing pressure, maintain the testing pressure unchanged, and reduce the testing temperature to continue testing the cement slurry until an expansion and contraction state of the cement slurry in the radial direction changes from expansion to contraction, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing temperatures;
and the second testing module is further used for keeping the testing pressure unchanged when the cement paste contracts in the radial direction under the testing temperature and the testing pressure, and increasing the testing temperature to continuously test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing temperatures.
9. The apparatus of claim 7, wherein the second testing module is further configured to maintain the testing temperature while the cement slurry expands in the radial direction at the testing temperature and the testing pressure, and reduce the testing pressure to continue testing the cement slurry until the cement slurry expands and contracts in the radial direction from expanding to contracting, thereby obtaining a plurality of expansion and contraction amounts corresponding to a plurality of testing pressures;
and the second testing module is further used for keeping the testing temperature unchanged when the cement paste contracts in the radial direction under the testing temperature and the testing pressure, and increasing the testing pressure to continuously test the cement paste until the expansion and contraction state of the cement paste in the radial direction is changed from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts corresponding to a plurality of testing pressures.
10. The apparatus of claim 7, wherein the apparatus further comprises:
a third determining module, configured to determine whether a square value of a fitting coefficient of the first curve is greater than a preset threshold;
and the third determining module is further configured to, when the square value of the fitting coefficient is not less than a preset threshold value, use an intersection point of the first curve and the abscissa as a critical point of the cement slurry in the radial direction.
11. The apparatus of claim 10, wherein the second testing module is further configured to, when the square value of the fitting coefficient is smaller than the preset threshold value, continue testing the cement slurry by changing a testing temperature or a testing pressure until an expansion and contraction state of the cement slurry in a radial direction is changed from expansion to contraction or from contraction to expansion, so as to obtain a plurality of expansion and contraction amounts.
12. The apparatus of claim 9, wherein, if the cement slurry is tested by changing the test pressure, the second determining module is further configured to perform polynomial fitting to obtain a second curve of the expansion and contraction amount with the test pressure based on a change relation function of the expansion and contraction amounts, the test pressures, and the pressure of the well to be tested with depth, with the expansion and contraction amount as an ordinate and the test pressure as an abscissa; and taking the intersection point of the second curve and the abscissa as a critical point of the cement paste in the radial direction.
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