CN110646462A - Crude oil wax precipitation point testing method - Google Patents
Crude oil wax precipitation point testing method Download PDFInfo
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- CN110646462A CN110646462A CN201910869091.5A CN201910869091A CN110646462A CN 110646462 A CN110646462 A CN 110646462A CN 201910869091 A CN201910869091 A CN 201910869091A CN 110646462 A CN110646462 A CN 110646462A
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Abstract
The invention discloses a crude oil wax precipitation point testing method, which comprises the following steps: cooling the wax-containing crude oil from a first preset temperature to a second preset temperature to obtain the electrical conductivity of the wax-containing crude oil at different temperatures; acquiring a first fitting relation of the temperature of part of the crude oil and the corresponding conductivity of the part of the crude oil; and obtaining wax precipitation points of the wax-containing crude oil according to the first fitting relation. The crude oil wax precipitation point testing method provided by the application adopts a new technology for testing wax precipitation points of wax-containing crude oil by using electric conductivity, can conveniently obtain the wax precipitation points of the wax-containing crude oil, and has the advantages of higher precision, good repeatability, small influence of human factors, energy conservation and economy.
Description
Technical Field
The application relates to the technical field of crude oil testing, in particular to a crude oil wax precipitation point testing method.
Background
The wax-containing crude oil accounts for a large proportion of crude oil output in China. The wax in the crude oil dissolves in the crude oil in a molecular state at high temperature, and the crude oil is Newtonian fluid. The viscosity is low, the flow characteristics are simple, the conveying danger is low and the energy consumption is low. The viscosity of the crude oil gradually increases with decreasing temperature. Wax in crude oil exists in crystalline form at low temperatures, and wax crystals negatively affect the flow of crude oil. In the pipeline transportation process, the viscosity of crude oil is increased, and the energy consumption for transportation is increased. In addition, the temperature at the pipe wall is the lowest in the transportation process, wax crystals are deposited at the pipe wall, and the inner diameter of the pipeline is reduced after a deposition layer is formed, so that the transportation capacity of the pipeline is damaged.
In order to reduce the negative effects caused by wax precipitation, it is necessary to first study the precipitation temperature of the wax. The temperature of the crude oil is reduced from high temperature, and the temperature when the paraffin is separated out is the wax precipitation point of the crude oil. At present, three methods are mainly used for testing wax precipitation points: differential scanning calorimetry (also known as DSC thermal analysis), rotational viscometer test, microscopic observation.
The DSC thermal analysis method is high in precision and small in data processing difficulty, is commonly adopted by the petroleum industry at present, but is complex in required equipment, expensive in cost and required to be provided with a microbalance and nitrogen purging equipment. The rotational viscometer has high testing precision, but the needed equipment is expensive, a rheometer is needed, and the oil sample amount needed in the testing is large. The microscopic observation method is not widely used because human eyes are needed for identification, the influence of human factors is large, and the precision is low.
In conclusion, the existing method for testing the wax precipitation point of the crude oil has complex equipment and high manufacturing cost; or the accuracy is low and not accurate enough.
Disclosure of Invention
In view of the defects of the prior art, one of the purposes of the present application is to provide a method for testing wax precipitation points of crude oil, which adopts a new technology for testing wax precipitation points of wax-containing crude oil by using conductivity, can conveniently obtain the wax precipitation points of the wax-containing crude oil, and has the advantages of high precision, good repeatability, small influence of human factors, energy saving and economy.
In order to achieve the purpose, the technical scheme is as follows:
a crude oil wax precipitation point test method comprises the following steps:
cooling the wax-containing crude oil from a first preset temperature to a second preset temperature to obtain the electrical conductivity of the wax-containing crude oil at different temperatures;
acquiring a first fitting relation of the temperature of part of the crude oil and the corresponding conductivity of the part of the crude oil;
and obtaining wax precipitation points of the wax-containing crude oil according to the first fitting relation.
As a preferred embodiment, the step of obtaining a first fitted relationship of the temperatures of the portions of the crude oil and their corresponding conductivities comprises:
establishing a coordinate system by taking the temperature and the conductivity of the crude oil as horizontal and vertical coordinates, and marking a plurality of coordinate points corresponding to the temperature and the corresponding conductivity of the crude oil in the coordinate system;
and carrying out linear fitting from a first preset temperature by using a principle of passing through the coordinate points at most to obtain a first fitting straight line.
As a preferred embodiment, the step of obtaining a first fitted relationship of the temperatures of the portions of the crude oil and their corresponding conductivities comprises:
establishing a coordinate system by taking the temperature and the conductivity of the crude oil as horizontal and vertical coordinates, and marking a plurality of coordinate points corresponding to the temperature and the corresponding conductivity of the crude oil in the coordinate system;
performing linear fitting on the coordinate point between the first preset temperature and the third preset temperature to obtain a second fitting straight line; the third preset temperature is less than the first preset temperature and greater than the second preset temperature.
As a preferred embodiment, the step of obtaining the wax precipitation points of the waxy crude oil according to the first fitting relation comprises:
determining a minimum crude oil temperature corresponding to the coordinate point of the first fitted straight line;
taking the crude oil temperature corresponding to the coordinate point closest to the minimum crude oil temperature as a reference temperature in the remaining coordinate points lower than the minimum crude oil temperature;
and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
As a preferred embodiment, the step of obtaining the wax precipitation points of the waxy crude oil according to the first fitting relation comprises:
determining coordinate points which do not participate in fitting, and taking the maximum crude oil temperature of the coordinate points which do not participate in fitting as a reference temperature;
and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
As a preferred embodiment, the step of obtaining the wax precipitation points of the waxy crude oil according to the first fitting relation comprises:
in the temperature reduction direction, if a certain coordinate point and all the coordinate points after the certain coordinate point are not on the first fitting straight line and are positioned on the same side of the first fitting straight line, the crude oil temperature corresponding to the coordinate point is taken as a reference temperature;
and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
As a preferred embodiment, the step of obtaining a first fitted relationship of the temperatures of the portions of the crude oil and their corresponding conductivities further comprises:
performing linear fitting from a second preset temperature by using the principle of passing through the coordinate points at most to obtain a third fitted straight line;
the step of obtaining wax precipitation points of the waxy crude oil according to the first fitting relationship comprises:
obtaining the intersection point of the first fitted straight line and the third fitted straight line, and taking the crude oil temperature corresponding to the intersection point as a reference temperature;
and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
As a preferred embodiment, the predetermined rule includes: and taking the reference temperature as the wax precipitation point of the wax-containing crude oil.
As a preferred embodiment, the predetermined rule includes: and taking the temperature obtained by subtracting a fourth preset value from the reference temperature as a lower limit temperature, taking the temperature obtained by adding a fifth preset value to the reference temperature as an upper limit temperature, and determining that the wax precipitation point of the waxy crude oil is between the lower limit temperature and the upper limit temperature.
As a preferred embodiment, the wax content of the waxy crude oil is not less than 2.5%; the water content of the wax-containing crude oil is lower than 0.5%; the first preset temperature is 80 ℃, and the second preset temperature is-20 ℃; the temperature reduction speed ranges from 0.1 ℃/min to 10 ℃/min; the frequency of acquiring the conductivity is to acquire the conductivity once every 0.1min to 10 min.
Has the advantages that:
the crude oil wax precipitation point testing method provided by the embodiment of the application adopts a new technology for testing wax precipitation points of wax-containing crude oil by using electric conductivity, and the wax precipitation points of the wax-containing crude oil can be conveniently obtained because the electric conductivity is easy to measure. The method has the characteristics of high precision, good repeatability, small influence of human factors, energy conservation, economy and the like.
Specific embodiments of the present invention are disclosed in detail with reference to the following description and drawings, indicating the manner in which the principles of the invention may be employed. It should be understood that the embodiments of the invention are not so limited in scope. The embodiments of the invention include many variations, modifications and equivalents within the spirit and scope of the appended claims.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments, in combination with or instead of the features of the other embodiments.
It should be emphasized that the term "comprises/comprising" when used herein, is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps or components.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.
FIG. 1 is a flow chart illustrating the steps of a method for testing wax appearance points of crude oil according to an embodiment of the present disclosure;
FIG. 2 is a flowchart illustrating a first specific step of step S20 in FIG. 1;
FIG. 3 is a flowchart illustrating a second specific step of step S20 in FIG. 1;
FIG. 4 is a flowchart illustrating a third specific step of step S20 in FIG. 1;
FIG. 5 is a flowchart illustrating a first specific step of step S30 in FIG. 1;
FIG. 6 is a flowchart illustrating a second specific step of step S30 in FIG. 1;
FIG. 7 is a flowchart illustrating a third specific step of step S30 in FIG. 1;
FIG. 8 is a flowchart illustrating a fourth specific step of step S30 in FIG. 1;
FIG. 9 is a graph of conductivity versus temperature in an embodiment of the present application.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The embodiment of the application provides a crude oil wax precipitation point testing method, which adopts a new technology for testing wax precipitation points of wax-containing crude oil by using electric conductivity, can conveniently obtain the wax precipitation points of the wax-containing crude oil, and has the advantages of higher precision, good repeatability, small influence of human factors, energy conservation and economy.
Please refer to fig. 1. Fig. 1 is a flowchart illustrating steps of a method for testing wax precipitation point of crude oil according to an embodiment of the present disclosure. Although the present application provides method steps as described in the following examples or flowcharts, more or fewer steps may be included in the method, with or without the assistance of inventive faculty. In addition, in the steps of the method which do not logically have the necessary cause and effect relationship, the execution sequence of the steps is not limited to the execution sequence provided in the embodiment of the application.
As shown in fig. 1, the present application provides a method for testing wax precipitation point of crude oil, which may include the following steps:
step S10: and cooling the wax-containing crude oil from the first preset temperature to the second preset temperature to obtain the electrical conductivity of the wax-containing crude oil at different temperatures.
When crude oil is classified according to wax content, crude oil with wax mass fraction lower than 2.5% is called low wax crude oil, crude oil with wax mass fraction between 2.5% and 10.0% is called waxy crude oil, and crude oil with wax mass fraction higher than 10.0% is called high wax crude oil. Waxy crudes and highly waxy crudes are often collectively referred to as waxy crudes in most storage and transportation specialty literature. Wherein the wax content is calculated based on the total weight of the wax-containing crude oil being 100%. In the embodiments of the present application, the wax content of the crude oil is not less than 2.5%, i.e., the present process is applicable to both waxy crude oils and highly waxy crude oils.
In an embodiment of the present application, the crude oil has a water content of less than 0.5%. The excessive water content can change the conductivity of the oil sample, thereby causing large measurement errors. Specifically, the influence of the increase in the water content on the electrical conductivity is classified into the following two cases. In the first case, a water-in-oil emulsion is formed, in which the polar substances in the oil are transferred to the water, the polar substances are enriched by the water or transferred to the interface of the water, the conductivity is reduced, and the precipitation of wax does not affect the conductive substance and the wax precipitation point cannot be tested. The second case is when the water in the crude oil is free, where the water is not homogeneous in the system being tested, the conductivity rises, and the wax precipitation has no hindering effect on the water and the wax precipitation point cannot be tested. The method for measuring the wax precipitation point by utilizing the conductivity is established on the basis that a suspension system is formed by wax crystals in crude oil, and the test can be interfered under the condition that water exists, so that the water content of the crude oil is selected to be lower than 0.5 percent in the embodiment of the application.
It should be noted that the temperature drop interval in which the test is performed needs to include the wax precipitation point of the waxy crude oil. If the temperature reduction interval does not include the wax precipitation point of the wax-containing crude oil, the wax precipitation point of the wax-containing crude oil cannot be necessarily measured. Crude oil with different wax content and water content has different wax precipitation points. The values of the first preset temperature and the second preset temperature are not specifically limited in the embodiment of the present application, and the values of the first preset temperature and the second preset temperature need to be selected according to the specific properties of the waxy crude oil selected during the test. For example, when a waxy crude oil having a wax content of 10% is selected, the first predetermined temperature may be 80 ℃ and the second predetermined temperature may be-20 ℃. Namely, the temperature variation range of the crude oil is 80 ℃ to-20 ℃.
In this application embodiment, when the wax-containing crude oil is cooled, the problem of uneven temperature easily appears in the oil sample in consideration of the excessively fast cooling speed, and the cooling speed is excessively slow, and then it is long time consuming. Therefore, in order to further improve the efficiency and the accuracy, the temperature reduction speed is selected to be 0.1-10 ℃/min in the embodiment of the application. The frequency of acquiring the conductivity is to acquire the conductivity once every 0.1min to 10 min. The frequency of acquiring the conductivity can be matched with the cooling speed, for example, the conductivity is measured once after the cooling is completed every time, and the operation and the record are convenient.
The method for obtaining the conductivity is not limited in the embodiments of the present application, and for example, the conductivity of the crude oil may be measured by an alternating current method, a direct current method, a conductivity tester, or the like. For example, a PSM frequency response analyzer and an electrode cup can be used for testing to obtain a complex impedance diagram, and the conductivity of the crude oil can be obtained after the complex impedance diagram is analyzed and converted.
Step S20: a first fit relationship of the temperatures of the portions of the crude oil and their corresponding conductivities is obtained.
In step S20, a first fit relationship between the temperature of the portion of crude oil and its corresponding conductivity is obtained. Wherein the portion of the crude oil temperature may comprise a first predetermined temperature. The first fit relationship may be obtained by a linear fit.
Specifically, as shown in fig. 2, step S20 may include the following sub-steps:
step S201: establishing a coordinate system by taking the temperature and the conductivity of the crude oil as horizontal and vertical coordinates, and marking a plurality of coordinate points corresponding to the temperature and the corresponding conductivity of the crude oil in the coordinate system;
step S202: and carrying out linear fitting from a first preset temperature by using a principle of passing through the coordinate points at most to obtain a first fitting straight line.
After step S201 is completed, from the obtained coordinate point diagram of the crude oil temperature and conductivity, it can be seen that: as the temperature decreases, the conductivity generally tends to decrease, but initially decreases faster and then decreases slower. The temperature zone in which the conductivity decreases more rapidly can be defined as a high temperature zone. The temperature section in which the remaining conductivity decreases more slowly in the map can be defined as a low temperature section.
In step S202, when linear fitting is performed, a first fitted straight line is fitted in the high temperature section from a first preset temperature (i.e., the highest temperature), and the first fitted straight line passes through the maximum coordinate points.
After step S202, as shown in fig. 4, the following steps may be further included:
step S203: and starting from the second preset temperature, carrying out linear fitting according to the principle of passing through the coordinate points at most to obtain a third fitted straight line.
In step S203, when linear fitting is performed, a third fitted straight line is fitted in the low temperature section from the second preset temperature (i.e., the lowest temperature), and the third fitted straight line passes through the maximum coordinate points.
In addition, as shown in fig. 3, step S202 may also be replaced by the following steps:
step S212: and performing linear fitting on the coordinate point between the first preset temperature and the third preset temperature to obtain a second fitting straight line.
In step S212, the third preset temperature is less than the first preset temperature and greater than the second preset temperature. When linear fitting is carried out, a third preset temperature is selected, and the change rule of the conductivity is approximately linearly changed between the first preset temperature and the third preset temperature. Preferably, the electrical conductivity varies linearly between the first predetermined temperature and the third predetermined temperature. And drawing a second fitting straight line according to the coordinate point between the first preset temperature and the third preset temperature.
Step S30: and obtaining wax precipitation points of the wax-containing crude oil according to the first fitting relation.
And obtaining the wax precipitation points of the crude oil after obtaining the first fitting relation or the second fitting straight line. Specifically, as shown in fig. 5, step S30 includes the following steps:
step S301: determining a minimum crude oil temperature corresponding to the coordinate point of the first fitted straight line;
step S302: taking the crude oil temperature corresponding to the coordinate point closest to the minimum crude oil temperature as a reference temperature in the remaining coordinate points lower than the minimum crude oil temperature;
step S303: and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
In step S301, the minimum crude oil temperature is selected from coordinate points corresponding to the first fitted straight line or the second fitted straight line, where "corresponding" means that the coordinate points are taken into consideration when performing linear fitting, and the coordinate points are not required to be necessarily on the first fitted straight line or the second fitted straight line. When linear fitting is performed, it is necessary to consider that as many coordinate points as possible in the high-temperature range pass through the first fitting straight line, or that as many coordinate points as possible between the first preset temperature and the third preset temperature pass through the second fitting straight line. There must therefore be some coordinate points which, although not on the first or second fitted straight line, are taken into account in the fitting of the first or second fitted straight line, and which then "fit" into said first or second fitted straight line.
In step S303, the predetermined rule has different embodiments. In one embodiment, the predetermined rule includes: and taking the reference temperature as the wax precipitation point of the wax-containing crude oil. The method is convenient and fast.
In another embodiment, the predetermined rule includes: and taking the temperature obtained by subtracting a fourth preset value from the reference temperature as a lower limit temperature, taking the temperature obtained by adding a fifth preset value to the reference temperature as an upper limit temperature, and determining that the wax precipitation point of the waxy crude oil is between the lower limit temperature and the upper limit temperature.
Because the method has some errors, after the reference temperature is obtained, the value can be taken in a proper range near the reference temperature within the range allowed by the error, and the value is taken as the wax precipitation point. The step is utilized to determine a value interval, and any value in the interval can be selected for wax precipitation points. In addition, if a temperature corresponding to a coordinate point near the reference temperature (for example, a coordinate point at which the temperature is adjacent to the reference temperature) is used as the wax precipitation point, the temperature is also within the scope of the embodiments of the present application.
Specifically, according to the results of multiple tests, a suitable fourth predetermined value and a suitable fifth predetermined value can be selected to confirm the value range of the wax precipitation point. Under the condition that the test conditions such as wax content, water content, cooling interval, cooling speed and frequency for obtaining conductivity are different, the selected fourth preset value and the selected fifth preset value can be different. In a specific embodiment, the fourth predetermined value and the fifth predetermined value may be both selected to be 1.5 ℃.
In another embodiment, as shown in fig. 6, step S30 may include the following steps:
step S311: determining coordinate points which do not participate in fitting, and taking the maximum crude oil temperature of the coordinate points which do not participate in fitting as a reference temperature;
step S312: and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
In step S311, the coordinate points not involved in the fitting are opposite to the "coordinate points corresponding to the first fitted straight line or the second fitted straight line" in step S301. In step S312, the predetermined rule is the same as that in step S303, and the explanation is detailed above and will not be repeated here.
In still another embodiment, as shown in fig. 7, the step S30 may include the steps of:
step S321: in the temperature reduction direction, if a certain coordinate point and all the coordinate points after the certain coordinate point are not on the first fitting straight line and are positioned on the same side of the first fitting straight line, the crude oil temperature corresponding to the coordinate point is taken as a reference temperature;
step S322: and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
In the above step S321, the key to find the reference temperature coordinate point is to see whether the point is significantly deviated from the first fitted straight line or the second fitted straight line. The first fitting straight line obtained after the linear fitting in step S202 does not pass through all the points in the high temperature section, and some points in the high temperature section slightly deviate from the first fitting straight line, which is allowed when the linear fitting is performed. The point slightly deviating from the first fitted straight line in the high temperature section is not the coordinate point to be searched for in step S321. When a certain point and all the points after the certain point are not on the first fitted straight line and are located on the same side of the first fitted straight line, the certain point can be determined as the coordinate point to be searched. Similarly, when a certain point and all the points after the certain point are not on the second fitted straight line and are located on the same side of the second fitted straight line, the certain point can also be determined as the coordinate point to be searched.
In step S322, the predetermined rule is the same as that in step S303, and the explanation is detailed above and will not be repeated here.
After step S203, as shown in fig. 8, step S30 specifically includes:
step S331: obtaining the intersection point of the first fitted straight line and the third fitted straight line, and taking the crude oil temperature corresponding to the intersection point as a reference temperature;
step S332: and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
In step S331, the intersection point may be a point where the first fitted straight line and the third fitted straight line intersect, or a point where the second fitted straight line and the third fitted straight line intersect. The first fitting straight line and the second fitting straight line are the corresponding relation between the temperature and the conductivity of the high-temperature section, and the slope is larger; the third fitting straight line is the corresponding relation between the temperature of the low-temperature section and the conductivity, and the slope of the third fitting straight line is smaller. The slope of the third fitting straight line is different from that of the first fitting straight line, or the slope of the third fitting straight line is different from that of the second fitting straight line, and the slope of the first fitting straight line and the slope of the second fitting straight line are greater than that of the third fitting straight line. Then, in step S331, the point where the first fitted straight line and the third fitted straight line intersect or the point where the second fitted straight line and the third fitted straight line intersect can be found, so that the crude oil temperature corresponding to the intersection point can be used as the reference temperature.
In step S332, the predetermined rule is the same as that in step S303, and the explanation is detailed above and will not be repeated here.
The crude oil wax precipitation point testing method provided by the embodiment of the application adopts a new technology for testing wax precipitation points of wax-containing crude oil by using electric conductivity, and the wax precipitation points of the wax-containing crude oil can be conveniently obtained because the electric conductivity is easy to measure. The method has the characteristics of high precision, good repeatability, small influence of human factors, energy conservation, economy and the like.
In a specific embodiment, crude oil with 10% wax content is selected as a test oil sample, and the temperature of the test oil sample is reduced from 80 ℃ to-20 ℃, the temperature reduction speed is 1 ℃/min, and the conductivity is tested once per minute. The conductivity acquisition frequency corresponds to the cooling speed, and the wax precipitation point can be accurate to one position to achieve the precision required by engineering. And testing the conductivity of the crude oil by a direct current method. The electric field voltage was 10V. For the crude oil used in this example, the applied electric field voltage was too high, posing a personal safety hazard to the tester. The voltage is too low and data stability is affected.
Finally, a corresponding relationship diagram of different temperatures and conductivities is obtained as shown in fig. 9. In FIG. 9, the abscissa is temperature in degrees Celsius (. degree. C.); the ordinate is the conductivity in microsiemens per meter (. mu.s/m). By combining the above steps S202 and S301 to S303, the wax precipitation point of the crude oil can be obtained as 29 ℃ by using the reference temperature as the wax precipitation point.
The same test oil sample was tested by DSC thermogram analysis to obtain a wax appearance of 30 ℃. Since DSC thermogram is widely recognized in the art to have high accuracy, comparing the wax appearance point (29 ℃) measured in this example with the wax appearance point (30 ℃) measured by DSC thermogram, the error was found to be 1 ℃ and about 3.33%. It can be seen that the crude oil wax precipitation point testing method provided by the embodiment of the application has high precision.
In another example, crude oil with wax content of 4.3% is selected as the test oil sample, and the rest conditions and steps are the same as the previous example, so that the wax precipitation point of the crude oil is 11 ℃. The wax appearance point of this crude oil was 12.4 ℃ as measured by DSC thermogram.
In yet another example, a crude oil with a wax content of 15.8% was selected as the test oil sample, and the remaining conditions and steps were the same as in the first example, resulting in a wax appearance of 41 ℃. The wax appearance point of this crude oil was 42.3 ℃ as measured by DSC thermogram.
The following table is prepared by comparing the three examples with the results of wax appearance by DSC thermogravimetry.
From the above table, it can be seen that the test result of the method provided by the embodiment of the present application for testing the wax precipitation point of the waxy crude oil has an error within 1.5 ℃ compared with the test result of the DSC thermal analysis method, and is within an industrially acceptable error range.
It should be noted that, in the description of the present application, the terms "first", "second", and the like are used for descriptive purposes only and for distinguishing similar objects, and no precedence between the two is intended or should be construed to indicate or imply relative importance. In addition, in the description of the present application, "a plurality" means two or more unless otherwise specified.
Any numerical value recited herein includes all values from the lower value to the upper value that are incremented by one unit, provided that there is a separation of at least two units between any lower value and any higher value. For example, if it is stated that the number of a component or a value of a process variable (e.g., temperature, pressure, time, etc.) is from 1 to 90, preferably from 20 to 80, and more preferably from 30 to 70, it is intended that equivalents such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also expressly enumerated in this specification. For values less than 1, one unit is suitably considered to be 0.0001, 0.001, 0.01, 0.1. These are only examples of what is intended to be explicitly recited, and all possible combinations of numerical values between the lowest value and the highest value that are explicitly recited in the specification in a similar manner are to be considered.
Unless otherwise indicated, all ranges include the endpoints and all numbers between the endpoints. The use of "about" or "approximately" with a range applies to both endpoints of the range. Thus, "about 20 to about 30" is intended to cover "about 20 to about 30", including at least the endpoints specified.
All articles and references disclosed, including patent applications and publications, are hereby incorporated by reference for all purposes. The term "consisting essentially of …" describing a combination shall include the identified element, ingredient, component or step as well as other elements, ingredients, components or steps that do not materially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe combinations of elements, components, or steps herein also contemplates embodiments that consist essentially of such elements, components, or steps. By using the term "may" herein, it is intended to indicate that any of the described attributes that "may" include are optional.
A plurality of elements, components, parts or steps can be provided by a single integrated element, component, part or step. Alternatively, a single integrated element, component, part or step may be divided into separate plural elements, components, parts or steps. The disclosure of "a" or "an" to describe an element, ingredient, component or step is not intended to foreclose other elements, ingredients, components or steps.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Many embodiments and many applications other than the examples provided will be apparent to those of skill in the art upon reading the above description. The scope of the present teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are hereby incorporated by reference for all purposes. The omission in the foregoing claims of any aspect of subject matter that is disclosed herein is not intended to forego such subject matter, nor should the inventors be construed as having contemplated such subject matter as being part of the disclosed subject matter.
Claims (10)
1. A crude oil wax precipitation point test method is characterized by comprising the following steps:
cooling the wax-containing crude oil from a first preset temperature to a second preset temperature to obtain the electrical conductivity of the wax-containing crude oil at different temperatures;
acquiring a first fitting relation of the temperature of part of the crude oil and the corresponding conductivity of the part of the crude oil;
and obtaining wax precipitation points of the wax-containing crude oil according to the first fitting relation.
2. The crude oil wax precipitation point test method of claim 1, wherein said step of obtaining a first fit relationship of the temperature of a portion of the crude oil and its corresponding conductivity comprises:
establishing a coordinate system by taking the temperature and the conductivity of the crude oil as horizontal and vertical coordinates, and marking a plurality of coordinate points corresponding to the temperature and the corresponding conductivity of the crude oil in the coordinate system;
and carrying out linear fitting from a first preset temperature by using a principle of passing through the coordinate points at most to obtain a first fitting straight line.
3. The crude oil wax precipitation point test method of claim 1, wherein said step of obtaining a first fit relationship of the temperature of a portion of the crude oil and its corresponding conductivity comprises:
establishing a coordinate system by taking the temperature and the conductivity of the crude oil as horizontal and vertical coordinates, and marking a plurality of coordinate points corresponding to the temperature and the corresponding conductivity of the crude oil in the coordinate system;
performing linear fitting on the coordinate point between the first preset temperature and the third preset temperature to obtain a second fitting straight line; the third preset temperature is less than the first preset temperature and greater than the second preset temperature.
4. The method for testing wax appearance points of crude oil according to claim 2, wherein the step of obtaining wax appearance points of the waxy crude oil according to the first fitted relationship comprises:
determining a minimum crude oil temperature corresponding to the coordinate point of the first fitted straight line;
taking the crude oil temperature corresponding to the coordinate point closest to the minimum crude oil temperature as a reference temperature in the remaining coordinate points lower than the minimum crude oil temperature;
and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
5. The method for testing wax appearance points of crude oil according to claim 2, wherein the step of obtaining wax appearance points of the waxy crude oil according to the first fitted relationship comprises:
determining coordinate points which do not participate in fitting, and taking the maximum crude oil temperature of the coordinate points which do not participate in fitting as a reference temperature;
and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
6. The method for testing wax appearance points of crude oil according to claim 2, wherein the step of obtaining wax appearance points of the waxy crude oil according to the first fitted relationship comprises:
in the temperature reduction direction, if a certain coordinate point and all the coordinate points after the certain coordinate point are not on the first fitting straight line and are positioned on the same side of the first fitting straight line, the crude oil temperature corresponding to the coordinate point is taken as a reference temperature;
and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
7. The crude oil wax appearance point test method of claim 2 wherein the step of obtaining a first fit relationship of the temperature of a portion of the crude oil and its corresponding conductivity further comprises:
performing linear fitting from a second preset temperature by using the principle of passing through the coordinate points at most to obtain a third fitted straight line;
the step of obtaining wax precipitation points of the waxy crude oil according to the first fitting relationship comprises:
obtaining the intersection point of the first fitted straight line and the third fitted straight line, and taking the crude oil temperature corresponding to the intersection point as a reference temperature;
and determining the reference temperature as the wax precipitation point of the wax-containing crude oil according to a preset rule.
8. The crude oil wax appearance point test method according to any one of claims 4 to 7, wherein the predetermined rule comprises: and taking the reference temperature as the wax precipitation point of the wax-containing crude oil.
9. The crude oil wax appearance point test method according to any one of claims 4 to 7, wherein the predetermined rule comprises: and taking the temperature obtained by subtracting a fourth preset value from the reference temperature as a lower limit temperature, taking the temperature obtained by adding a fifth preset value to the reference temperature as an upper limit temperature, and determining that the wax precipitation point of the waxy crude oil is between the lower limit temperature and the upper limit temperature.
10. The crude oil wax precipitation point test method of claim 1, wherein the wax fraction of the waxy crude oil is not less than 2.5%; the water content of the wax-containing crude oil is lower than 0.5%; the first preset temperature is 80 ℃, and the second preset temperature is-20 ℃; the temperature reduction speed ranges from 0.1 ℃/min to 10 ℃/min; the frequency of acquiring the conductivity is to acquire the conductivity once every 0.1min to 10 min.
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