CN110646462A - Crude oil wax precipitation point testing method - Google Patents

Abstract

The invention discloses a method for testing the wax precipitation point of crude oil. The first fitting relationship of temperature and its corresponding electrical conductivity; the wax precipitation point of the waxy crude oil is obtained according to the first fitting relationship. The method for testing the wax precipitation point of crude oil provided in the present application adopts a new technology of testing the wax precipitation point of waxy crude oil by using electrical conductivity, which can conveniently obtain the wax precipitation point of waxy crude oil, and has high precision, good repeatability, and is not subject to artificial The influence of factors is small, and the energy saving is economical.

Description

Test method for wax precipitation point of crude oil

technical field

The application relates to the technical field of crude oil testing, in particular to a method for testing the wax precipitation point of crude oil.

Background technique

Waxy crude oil accounts for a large proportion of my country's crude oil production. The wax in the crude oil dissolves in the crude oil in a molecular state at high temperature, and the crude oil is a Newtonian fluid at this time. It has a low viscosity, simple flow characteristics, low transport hazards and low energy consumption. With the decrease of temperature, the viscosity of crude oil increases gradually. Waxes in crude oil exist in the form of crystals at low temperatures, and wax crystals negatively affect the flow of crude oil. In the process of pipeline transportation, the viscosity of crude oil increases, and the energy consumption for transportation increases. In addition, the temperature of the pipe wall is the lowest during the transportation process, and wax crystals are deposited on the pipe wall.

In order to reduce the negative effects of wax precipitation, it is first necessary to study the precipitation temperature of wax. Crude oil starts to cool down from high temperature, and the temperature at which paraffin is precipitated is its wax precipitation point. At present, there are three main methods to test the wax precipitation point: differential scanning calorimetry (also known as DSC thermal analysis method), rotational viscometer test method, and microscopic observation method.

Among them, the DSC thermal analysis method has high precision and low data processing difficulty, and is currently widely used in the petroleum industry. The rotational viscometer test method has high accuracy, but the equipment required is expensive, it needs to be equipped with a rheometer, and the amount of oil sample required for the test is large. Microscopic observation method is not widely used because it needs human eyes for identification, is greatly affected by human factors, and has low precision.

To sum up, the existing methods for testing the wax precipitation point of crude oil are either complicated in equipment and expensive, or have low precision and are not accurate enough.

SUMMARY OF THE INVENTION

In view of the deficiencies in the prior art, one of the purposes of the present application is to provide a method for testing the wax precipitation point of crude oil, which adopts a new technology for testing the wax precipitation point of waxy crude oil by utilizing electrical conductivity, and can conveniently obtain the wax precipitation point of waxy crude oil. Point, and high precision, good repeatability, less affected by human factors, energy saving and economical.

To achieve the above object, the application adopts the following technical solutions:

A method for testing the wax precipitation point of crude oil, comprising the following steps:

cooling the waxy crude oil from the first preset temperature to the second preset temperature, and obtaining the electrical conductivity at a plurality of different crude oil temperatures;

obtaining a first fitting relationship of part of the crude oil temperature and its corresponding electrical conductivity;

The wax precipitation point of the waxy crude oil is obtained according to the first fitting relationship.

As a preferred embodiment, the step of obtaining a first fitting relationship of the temperature of the crude oil and its corresponding electrical conductivity includes:

A coordinate system is established with the abscissa and ordinate coordinates of the crude oil temperature and conductivity, and a plurality of coordinate points corresponding to the crude oil temperature and its corresponding conductivity are marked in the coordinate system;

Starting from the first preset temperature, linear fitting is performed on the principle of passing through the most coordinate points to obtain a first fitting straight line.

As a preferred embodiment, the step of obtaining a first fitting relationship of the temperature of the crude oil and its corresponding electrical conductivity includes:

A coordinate system is established with the abscissa and ordinate coordinates of the crude oil temperature and conductivity, and a plurality of coordinate points corresponding to the crude oil temperature and its corresponding conductivity are marked in the coordinate system;

Linearly fitting the coordinate points between the first preset temperature and the third preset temperature to obtain a second fitting straight line; wherein the third preset temperature is less than the first preset temperature and greater than the third preset temperature 2. Preset temperature.

As a preferred embodiment, the step of obtaining the wax precipitation point of the waxy crude oil according to the first fitting relationship includes:

determining the minimum crude oil temperature corresponding to the coordinate points that conform to the first fitting straight line;

In the remaining coordinate points less than the minimum crude oil temperature, the crude oil temperature corresponding to the coordinate point closest to the minimum crude oil temperature is used as the reference temperature;

The reference temperature is determined as the wax precipitation point of the waxy crude oil according to a predetermined rule.

As a preferred embodiment, the step of obtaining the wax precipitation point of the waxy crude oil according to the first fitting relationship includes:

Determine the coordinate points not participating in the fitting, and take the maximum crude oil temperature of the coordinate points not participating in the fitting as the reference temperature;

The reference temperature is determined as the wax precipitation point of the waxy crude oil according to a predetermined rule.

As a preferred embodiment, the step of obtaining the wax precipitation point of the waxy crude oil according to the first fitting relationship includes:

In the direction of temperature decrease, if a certain coordinate point and all the coordinate points after it are not on the first fitting straight line and are on the same side of the first fitting straight line, the crude oil temperature corresponding to this coordinate point is as a reference temperature;

The reference temperature is determined as the wax precipitation point of the waxy crude oil according to a predetermined rule.

As a preferred embodiment, the step of obtaining a first fitting relationship between the temperature of the crude oil and its corresponding electrical conductivity further includes:

Starting from the second predetermined temperature, linear fitting is performed on the principle of passing through the most coordinate points to obtain a third fitting straight line;

The described step of obtaining the wax precipitation point of the waxy crude oil according to the first fitting relationship includes:

obtaining a point where the first fitting straight line and the third fitting straight line intersect, and using the crude oil temperature corresponding to the intersection point as a reference temperature;

The reference temperature is determined as the wax precipitation point of the waxy crude oil according to a predetermined rule.

As a preferred embodiment, the predetermined rule includes: taking the reference temperature as the wax precipitation point of the waxy crude oil.

As a preferred embodiment, the predetermined rule includes: taking the temperature obtained by subtracting the fourth predetermined value from the reference temperature as the lower limit temperature, and taking the temperature obtained by adding the fifth predetermined value to the reference temperature as the upper limit temperature, The wax precipitation point of the waxy crude oil is determined to be between the lower limit temperature and the upper limit temperature.

As a preferred embodiment, the wax content of the waxy crude oil is not lower than 2.5%; the water content of the waxy crude oil is lower than 0.5%; the first preset temperature is 80°C, and the first preset temperature is 80°C. 2. The preset temperature is -20°C; the range of the cooling rate is 0.1°C/min～10°C/min; the frequency of obtaining the conductivity is to obtain the conductivity every 0.1min～10min.

Beneficial effects:

The method for testing the wax precipitation point of crude oil provided by the embodiments of the present application adopts a new technology for testing the wax precipitation point of waxy crude oil by using electrical conductivity. Since the electrical conductivity is easy to measure, the wax precipitation point of waxy crude oil can be conveniently obtained. The method has the characteristics of high precision, good repeatability, little influence by human factors, energy saving and economy.

With reference to the following description and drawings, specific embodiments of the invention are disclosed in detail, indicating the manner in which the principles of the invention may be employed. It should be understood that embodiments of the present invention are not thereby limited in scope. Embodiments of the invention include many changes, modifications and equivalents within the spirit and scope of the appended claims.

Features described and/or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, in combination with, or instead of features in other embodiments .

It should be emphasized that the term "comprising/comprising" when used herein refers to the presence of a feature, integer, step or component, but does not exclude the presence or addition of one or more other features, integers, steps or components.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention, and for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

Fig. 1 is the step flow diagram of a kind of crude oil wax precipitation point test method provided by the embodiment of the application;

Fig. 2 is the first specific step flow chart of step S20 in Fig. 1;

Fig. 3 is the second specific step flow chart of step S20 in Fig. 1;

Fig. 4 is the flow chart of the third specific step of step S20 in Fig. 1;

Fig. 5 is the first specific step flow chart of step S30 in Fig. 1;

Fig. 6 is the second specific step flow chart of step S30 in Fig. 1;

Fig. 7 is the third specific step flow chart of step S30 in Fig. 1;

FIG. 8 is a flowchart of the fourth specific step of step S30 in FIG. 1;

FIG. 9 is a graph showing the relationship between conductivity and temperature in an embodiment of the present application.

Detailed ways

In order to make those skilled in the art better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described The embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

Unless otherwise defined, 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 terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The embodiments of the present application provide a method for testing the wax precipitation point of crude oil, which adopts a new technology for testing the wax precipitation point of waxy crude oil by using electrical conductivity, which can conveniently obtain the wax precipitation point of waxy crude oil, and has high accuracy and repeatability. Good, less affected by human factors, energy saving and economical.

See Figure 1. 1 is a flow chart of steps of a method for testing the wax precipitation point of crude oil provided by an embodiment of the application. Although the present application provides the operation steps of the method as described in the following examples or flow charts, more or less operation steps may be included in the method based on routine or without creative effort. In addition, in the steps of the method that do not have a necessary causal relationship logically, the execution order of these steps is not limited to the execution order provided in the embodiments of the present application.

As shown in Figure 1, a method for testing the wax precipitation point of crude oil is provided in the embodiment of the present application, which can include the following steps:

Step S10: Cool the waxy crude oil from the first preset temperature to the second preset temperature, and obtain the electrical conductivity at a plurality of different crude oil temperatures.

When classifying crude oil according to wax content, crude oil with a mass fraction of wax lower than 2.5% is called low-wax crude oil, and crude oil with a mass fraction of wax between 2.5% and 10.0% is called waxy crude oil. Crude oils with a fraction above 10.0% are called high wax crudes. In most professional literature on storage and transportation, waxy crude oil and high waxy crude oil are often collectively referred to as waxy crude oil. Wherein, the wax content is calculated based on the total weight of the waxy crude oil as 100%. In the embodiment of the present application, the wax content of the crude oil is not less than 2.5%, that is, the method is applicable to waxy crude oil and high waxy crude oil.

In the embodiment of the present application, the water content of the crude oil is lower than 0.5%. Excessive water content will change the conductivity of the oil sample, resulting in large measurement errors. Specifically, the influence of the increase in water content on the electrical conductivity is divided into the following two cases. In the first case, a water-in-oil emulsion will be formed. At this time, the polar substances in the oil are transferred to the water, and the polar substances are enriched by the water or transferred to the interface of the water. Conductive substances have no effect, and the wax precipitation point cannot be tested. The second case is that the water in the crude oil is in a free state. At this time, the water in the tested system is not uniform, the conductivity increases, and the precipitation of wax does not hinder the water, and the wax precipitation point cannot be tested. The method for measuring wax point by electrical conductivity is based on the formation of a suspension system of wax crystals in crude oil. In the presence of water, it will interfere with the test. Therefore, the water content of crude oil is selected to be lower than 0.5% in the embodiment of the present application.

It should be noted that the cooling interval for testing needs to include the wax precipitation point of the waxy crude oil. If the wax precipitation point of the waxy crude oil is not included in the cooling interval, the wax precipitation point of the waxy crude oil must not be detected. Crude oils with different wax content and water content have different wax precipitation points. The embodiments of the present application do not specifically limit the values of the first preset temperature and the second preset temperature, 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 selecting a waxy crude oil with a wax content of 10%, the first preset temperature may be selected as 80°C, and the second preset temperature may be selected as -20°C. That is, the temperature variation range of the crude oil is 80°C to -20°C.

In the embodiments of the present application, when cooling the waxy crude oil, considering that the cooling rate is too fast, the oil sample is prone to the problem of uneven temperature, and the cooling rate is too slow, which takes a long time. Therefore, in order to further improve the efficiency and accuracy, in the embodiment of the present application, the range of the cooling rate is selected to be 0.1° C./min˜10° C./min. The frequency of obtaining the electrical conductivity is to obtain the electrical conductivity once every 0.1 min to 10 min. Among them, the frequency of obtaining the conductivity can be matched with the cooling rate. For example, after each cooling is completed, the conductivity is measured once, which is convenient for operation and recording.

The embodiments of the present application do not limit the method for obtaining the conductivity, for example, methods such as an alternating current method, a direct current method, and a conductivity tester can be used to measure the conductivity of the crude oil. For example, a complex impedance diagram can also be obtained by testing with a PSM frequency response analyzer and an electrode cup, and after analyzing and converting the complex impedance diagram, the conductivity of the crude oil can be obtained.

Step S20: Obtain a first fitting relationship of part of the crude oil temperature and its corresponding electrical conductivity.

In step S20, it is necessary to obtain a first fitting relationship between the temperature of some crude oil and its corresponding electrical conductivity. Wherein, the temperature of the part of the crude oil may include a first preset temperature. The first fitting relationship may be obtained by linear fitting.

Specifically, as shown in FIG. 2 , step S20 may include the following sub-steps:

Step S201: establishing a coordinate system with the abscissa and ordinate coordinates of the crude oil temperature and conductivity, and marking a plurality of coordinate points corresponding to the crude oil temperature and its corresponding conductivity in the coordinate system;

Step S202: Starting from the first preset temperature, perform linear fitting on the principle of passing through the most coordinate points to obtain a first fitting straight line.

After completing step S201, it can be seen from the obtained coordinate point diagram of crude oil temperature and electrical conductivity that as the temperature decreases, the electrical conductivity as a whole tends to decrease, but it decreases rapidly at the beginning, and then decreases more rapidly. slow. For the temperature section where the conductivity decreases rapidly, it can be defined as the high temperature section. The remaining temperature segments in the corresponding relationship graph where the conductivity decreases more slowly can be defined as the low temperature segment.

In step S202, when performing linear fitting, starting from the first preset temperature (ie, the highest temperature), a first fitting straight line is fitted in the high temperature section, and the first fitting straight line passes through the coordinate points at most.

After step S202, as shown in FIG. 4, the following steps may also be included:

Step S203: Starting from the second predetermined temperature, perform linear fitting on the principle of passing through the most coordinate points to obtain a third fitting straight line.

In step S203, when performing linear fitting, starting from the second preset temperature (ie, the lowest temperature), a third fitting straight line is fitted in the low temperature section, and the third fitting straight line passes through the coordinate points at most.

In addition, as shown in FIG. 3, step S202 can also be replaced by the following steps:

Step S212: Perform linear fitting on the coordinate points located 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 smaller than the first preset temperature and greater than the second preset temperature. That is, when performing the linear fitting, the third preset temperature is selected first, and between the first preset temperature and the third preset temperature, the variation law of the electrical conductivity is roughly linear. Preferably, the electrical conductivity changes linearly between the first preset temperature and the third preset temperature. A second fitting straight line is drawn according to the coordinate points between the first preset temperature and the third preset temperature.

Step S30: Obtain the wax precipitation point of the waxy crude oil according to the first fitting relationship.

After the first fitting relationship is obtained, that is, after the first fitting straight line or the second fitting straight line is obtained, the wax precipitation point of the crude oil can be obtained. Specifically, as shown in FIG. 5 , step S30 includes the following steps:

Step S301: Determine the minimum crude oil temperature corresponding to the coordinate points that conform to the first fitting straight line;

Step S302: in the remaining coordinate points less than the minimum crude oil temperature, the crude oil temperature corresponding to the coordinate point closest to the minimum crude oil temperature is used as the reference temperature;

Step S303: Determine the reference temperature as the wax precipitation point of the waxy crude oil according to a predetermined rule.

In step S301, the minimum crude oil temperature is selected from a coordinate point that conforms to the first fitting straight line or the second fitting straight line, where "conforms" means that the coordinate point is taken into account when performing linear fitting, and the coordinate point is not It is required that the coordinate point must be on the first fitting straight line or the second fitting straight line. When performing linear fitting, it is necessary to consider letting as many coordinate points in the high temperature section pass through the first fitting straight line, or let as many coordinate points as possible between the first preset temperature and the third preset temperature pass through the second fitting line. Line up. Therefore, there must be some coordinate points. Although they are not on the first fitting straight line or the second fitting straight line, these coordinate points are considered in the fitting process of the first fitting straight line or the second fitting straight line. Then these coordinate points also "fit" the first fitting straight line or the second fitting straight line.

In step S303, the predetermined rule has different implementations. In one embodiment, the predetermined rule includes: taking the reference temperature as the wax precipitation point of the waxy crude oil. This method is convenient and quick.

In another embodiment, the predetermined rule includes: taking a temperature obtained by subtracting a fourth predetermined value from the reference temperature as a lower limit temperature, and taking a temperature obtained by adding a fifth predetermined value to the reference temperature as an upper limit temperature, The wax precipitation point of the waxy crude oil is determined to be between the lower limit temperature and the upper limit temperature.

Considering that there will be some errors in this method, after the reference temperature is obtained, within the allowable range of the error, a value can be taken within an appropriate range near the reference temperature, and this value can be used as the wax precipitation point. What is determined by this step is a value interval, and any value within the interval can be selected for the wax precipitation point. In addition, if the temperature corresponding to a coordinate point near the reference temperature (for example, a coordinate point whose temperature is adjacent to the reference temperature) is used as the wax precipitation point, it also falls within the scope to be protected by the embodiments of the present application.

Specifically, according to the results of multiple tests, the appropriate fourth predetermined value and fifth predetermined value can be selected to confirm the value range of the wax precipitation point. In the case of different test conditions such as wax content, moisture content, cooling interval, cooling speed, frequency of obtaining electrical conductivity, etc., the selected fourth predetermined value and fifth predetermined value may be different. In a specific embodiment, both the fourth predetermined value and the fifth predetermined value may be selected to be 1.5°C.

In another embodiment, as shown in FIG. 6 , step S30 may include the following steps:

Step S311: Determine the coordinate points not participating in the fitting, and use the maximum crude oil temperature of the coordinate points not participating in the fitting as the reference temperature;

Step S312: Determine the reference temperature as the wax precipitation point of the waxy crude oil according to a predetermined rule.

In step S311, the coordinate points that do not participate in the fitting are opposite to the "coordinate points that conform to the first fitting straight line or the second fitting straight line" in step S301. In step S312, the predetermined rule is consistent with that in step S303, the explanation of which is detailed above, and will not be repeated here.

In yet another embodiment, as shown in FIG. 7 , step S30 may include the following steps:

Step S321: In the direction of temperature decrease, if a certain coordinate point and all the coordinate points after it are not on the first fitting straight line and are located on the same side of the first fitting straight line, the coordinate point corresponding to the The crude oil temperature is used as the reference temperature;

Step S322: Determine the reference temperature as the wax precipitation point of the waxy crude oil according to a predetermined rule.

In the above step S321, the key to finding the reference temperature coordinate point is to check whether the point deviates significantly from the first fitting straight line or the second fitting straight line. The first fitted straight line obtained after linear fitting in step S202 does not pass through all the points in the high temperature segment, and some points in the high temperature segment slightly deviate from the first fitted straight line, which is allowed during linear fitting. The point in the high temperature segment that deviates slightly from the first fitting straight line is not the coordinate point to be found in step S321. When a certain point and all the points after it are not on the first fitting straight line and are all located on the same side of the first fitting straight line, it can be determined that the point is the coordinate point to be found. Similarly, when a point and all the points after it are not on the second fitting straight line, and are all located on the same side of the second fitting straight line, it can also be determined that the point is the coordinate point to be found.

In step S322, the predetermined rule is consistent with that in step S303, the explanation of which is detailed above, and will not be repeated here.

After step S203 is performed, as shown in FIG. 8 , the step S30 specifically includes:

Step S331: Obtain a point where the first fitting straight line and the third fitting straight line intersect, and use the crude oil temperature corresponding to the intersection point as a reference temperature;

Step S332: Determine the reference temperature as the wax precipitation point of the waxy crude oil according to a predetermined rule.

The intersection point in step S331 may be a point where the first fitting straight line and the third fitting straight line intersect, or may be a point where the second fitting straight line and the third fitting straight line intersect. Since the first fitting straight line and the second fitting straight line are the corresponding relationship between the temperature and the conductivity in the high temperature section, their slopes are relatively large; the third fitting line is the corresponding relationship between the temperature and the conductivity in the low temperature section, and the slope is relatively small. The third fitted straight line and the first fitted straight line, or, the slopes of the third fitted straight line and the second fitted straight line are necessarily different, and the slopes of the first fitted straight line and the second fitted straight line are greater than the third fitted straight line The slope of. In the above step S331, the point where the first fitting straight line and the third fitting straight line intersect, or the point where the second fitting straight line and the third fitting straight line intersect, can be found, so that the crude oil corresponding to the intersection point can be found. temperature as the reference temperature.

In step S332, the predetermined rule is consistent with that in step S303, the explanation of which is detailed above, and will not be repeated here.

The method for testing the wax precipitation point of crude oil provided by the embodiments of the present application adopts a new technology for testing the wax precipitation point of waxy crude oil by using electrical conductivity. Since the electrical conductivity is easy to measure, the wax precipitation point of waxy crude oil can be conveniently obtained. The method has the characteristics of high precision, good repeatability, little influence by human factors, energy saving and economy.

In a specific embodiment, crude oil with a wax content of 10% is selected as the test oil sample, and it is cooled from 80°C to -20°C at a cooling rate of 1°C/min, and the conductivity is tested every minute. Among them, the acquisition frequency of electrical conductivity corresponds to the cooling rate, and the wax precipitation point can be accurate to the single digit to achieve the accuracy required by the project. The electrical conductivity of crude oil was tested by direct current method. The electric field voltage was 10V. For the crude oil used in this example, the applied electric field voltage is too high, posing a danger to the personal safety of the tester. If the voltage is too low, the data stability will be affected.

Finally, the corresponding relationship diagram of different temperature and conductivity as shown in Fig. 9 is obtained. In FIG. 9 , the abscissa is temperature, and the unit is degrees Celsius (° C.); the ordinate is the conductivity, and the unit is microsiemens/meter (μs/m). Combining the above steps S202 and S301 to S303, and taking the reference temperature as the wax precipitation point, it can be obtained that the wax precipitation point of the crude oil is 29°C.

The same test oil sample was tested by DSC thermal analysis method, and the obtained wax precipitation point was 30°C. Since it is generally believed in the industry that the DSC thermal analysis method has a high degree of accuracy, the wax precipitation point (29°C) measured in this example is compared with the wax precipitation point (30°C) measured by the DSC thermal analysis method, and it is found that the error is: 1°C, about 3.33%. It can be seen that the accuracy of the method for testing the wax precipitation point of crude oil provided by the embodiments of the present application is relatively high.

In another embodiment, crude oil with a wax content of 4.3% is selected as the test oil sample, and other conditions and steps are the same as in the previous embodiment, and the wax precipitation point of the crude oil is 11°C. The wax precipitation point of the crude oil measured by DSC thermal analysis was 12.4°C.

In yet another embodiment, crude oil with a wax content of 15.8% is selected as the test oil sample, and other conditions and steps are the same as in the first embodiment, and the wax precipitation point of the crude oil is 41°C. The wax precipitation point of the crude oil measured by DSC thermal analysis was 42.3°C.

The following table is drawn after comparing the above three embodiments with the results of the wax precipitation point measured by the DSC thermal analysis method.

It can be seen from the above table that the test results of the method provided by the embodiment of the present application to test the wax precipitation point of waxy crude oil are compared with the test results of the DSC thermal analysis method, and the error is within 1.5°C, which is within the acceptable error range of the industry.

It should be noted that, in the description of this application, the terms "first", "second", etc. are only used for the purpose of description and to distinguish similar objects, and there is no sequence between the two, nor can they be understood as indicating or imply relative importance. Also, in the description of this application, unless otherwise specified, "plurality" means two or more.

Any numerical value recited herein includes all values of the lower value and the upper value in one unit increments from the lower value to the upper value, there being a separation of at least two units between any lower value and any higher value That's it. For example, if the number of components or process variables (eg, temperature, pressure, time, etc.) are stated to have values from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, the intent is to illustrate that the The specification also explicitly lists values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32, and the like. For values less than 1, one unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1. These are merely examples of what is intended to be express, and all possible combinations of numerical values recited between the lowest value and the highest value are considered to be expressly set forth in this specification in a similar fashion.

Unless otherwise stated, all ranges include the endpoints and all numbers between the endpoints. "About" or "approximately" used with a range applies to both endpoints of the range. Thus, "about 20 to 30" is intended to cover "about 20 to about 30," including at least the indicated endpoints.

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, components, components or steps that do not materially affect the essential novel characteristics of the combination. Use of the terms "comprising" or "comprising" to describe combinations of elements, ingredients, components or steps herein also contemplates embodiments consisting essentially of those elements, ingredients, components or steps. By use of the term "may" herein, it is intended to indicate that "may" include any described attributes that are optional.

A plurality of elements, components, components or steps can be provided by a single integrated element, component, component or step. Alternatively, a single integrated element, component, component or step may be divided into separate multiple elements, components, components or steps. The disclosure of "a" or "an" used to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

It should be understood that the above description is for purposes of illustration and not limitation. From reading the above description, many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art. 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 incorporated herein by reference for the purpose of being comprehensive. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended to disclaim such subject matter, nor should it be construed that the inventor did not consider such subject matter to be 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.

Images