RU2787871C2 - Method for assessment of effect from mixing of agent for exclusion and mixing of oil, using co2, and method for selection of agent for exclusion and mixing of oil, using co2 - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention concerns a method for assessment of a mixing-contributing effect of an agent for exclusion and mixing of oil, using CO₂. According to this method, volumetric expansion is measured at an interface of CO₂-oil with a gradual increase in pressure, and a curve of mixing percentage-pressure (“δ-P curve”) is built, and the mixing-contributing effect of the agent for exclusion and mixing of oil, using CO₂, is assessed by comparison of characteristics of δ-P curves. In addition, the invention concerns a method for preliminary selection of an agent for exclusion and mixing of oil, using CO₂.

EFFECT: development of a simple and fast method for experimental assessment of a mixing-contributing effect of an additive for mixing.

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Description

FIELD OF TECHNOLOGY

The present invention relates to a method for rapidly evaluating the mixing effect (hereinafter also referred to as "miscibility-promoting effect") of a CO ₂ oil displacement and blending agent (hereinafter also abbreviated as "mixing aid"), and in particular, to a method for rapidly evaluating the miscibility-promoting effect of a CO ₂ oil displacement and blending agent through a volumetric expansion process, and also relates to the field of oilfield chemistry.

BACKGROUND TO THE INVENTION

CO ₂ oil displacement is a relatively new oil displacement process that has been successfully used in tertiary oil recovery in the United States. CO ₂ oil displacement, in particular CO ₂ miscibility oil displacement, can greatly improve oil displacement efficiency, so interest and research into CO ₂ oil displacement is rapidly increasing in the context of growing attention to the full recovery of oil resources in existing oil field. However, there is still no example of a successful application of CO ₂ oil displacement in China, and one of the reasons for this is the significant differences in the composition and properties of oil fields in China and the USA. In China, due to the heavier composition of the oil phase and its higher viscosity, the miscibility pressure with CO ₂ is higher. This higher miscibility pressure not only increases operating costs, but also creates certain potential safety risks and has a major impact on sweep efficiency and sweep efficiency, making it difficult to achieve the actual recovery expected ideally.

Thus, an important part of the development of CO ₂ oil displacement technology has been to further reduce the miscibility pressure between CO ₂ and crude oil. In related research, reducing the minimum miscibility pressure (MMP) by reducing the interfacial tension between crude oil and CO ₂ with the use of a blending aid is an important area of current research. For a particular field, in order to achieve the best effect of oil displacement using CO ₂ , it is desirable to select the best of the many possible mixing additives. In order to compare the miscibility-promoting effects of different blending aids during screening, it is often necessary to add a particular blending aid and directly measure the corresponding minimum miscibility pressure. At present, the method of measuring the minimum miscibility pressure by laboratory oil displacement test conducted on a thin tube model filled with sand (China Petroleum Industrial Standard SY/T 6573-2003) is the standard method for determining the miscibility pressure, simulating the process of oil displacement with using CO ₂ , in the art and has the widest application, and the obtained minimum miscibility pressure value is also the most accurate. However, this method is characterized by a relatively long working cycle, usually more than one month, and, accordingly, requires a large amount of experimental work. Similarly, to determine the interfacial tension on the surface of CO ₂ -oil, it is also possible to apply experimental methods such as the bubble rise rate measurement method, the interfacial tension measurement method, and the like; however, these methods also have disadvantages such as time duration, large amount of experimental work, and the like. In addition, other methods have also been developed for estimating the minimum miscibility pressure (Non-Patent Document 1), such as improved methods using the equation of state, CC prediction models _MMP , prediction models of multi-contact characteristic lines, etc., however, all these methods are still theoretical prediction methods based on experimental results. Therefore, in order to select blending aids applicable to a particular oilfield operating system, there is a strong need in the art to develop a simple and rapid method for experimentally evaluating the miscibility-enhancing effect of a blending aid.

Non-Patent Document 1: Zhao Haifeng et al., Study of CO ₂ miscible displacement mechanism and minimum miscibility pressure [J], China Petroleum and Chemical Standards and Quality, 2016, 36 (17): 95-98.

BRIEF DESCRIPTION OF THE INVENTION

In order to solve the above problem, through careful study with great focus and through numerous experiments, the inventors of the present invention surprisingly found that by measuring the volumetric expansion ratio of oil at different CO ₂ pressure levels, the miscibility-promoting effect of various blending additives can be quantitatively and easily compared, and at the same time, the miscibility-promoting effect can be experimentally evaluated relatively accurately, so that an appropriate blending aid can be quickly selected for a particular oil field, thus completing the present invention.

In a first aspect, the present invention provides a method for evaluating the miscibility-promoting effect of a CO ₂ oil displacement and mixing agent, characterized by measuring the volumetric expansion at the CO ₂ -oil interface with a gradual increase in pressure, and plotting a percent mixed phase-pressure curve (hereinafter also referred to as "percent miscibility-pressure curve" or "δ-P curve") and the miscibility-promoting effect of the CO ₂ oil displacement and mixing agent was evaluated by comparing the characteristics of the δ-P curves.

In a preferred embodiment, the method comprises the following steps:

(1) adding a given volume of oil to a constant volume autoclave equipped with a viewing window and a gas intake path, closing the autoclave, placing the autoclave in a constant temperature water bath, observing through the viewing window and recording the initial liquid level H ₀ , and connecting a source of gaseous CO ₂ and a pressure gauge to the gas intake path;

(2) introduction of high pressure CO ₂ into the autoclave with a load of the agent under investigation to displace and mix oil using CO ₂ until a predetermined pressure level P is reached, turn off the gas intake path, ensure that gas-liquid equilibrium is reached, register the level pressure P, observation through the viewing window and registration of the liquid level H;

(3) continuously introducing CO ₂ to pressurize the autoclave until another predetermined pressure level is reached, and recording the corresponding pressure level and liquid level in accordance with the method in step (2);

(4) repeating step (3) until the liquid level rises to the upper boundary of the autoclave tank, and recording the corresponding pressure level P _m and height of the upper boundary of the autoclave tank H _m ;

(5) calculating the miscibility percentage δ corresponding to each pressure level according to the following formula (1) and plotting the δ-P curve:

формула (1),

Formula 1),

then ensuring depressurization and cleaning of the autoclave;

(6) repeating steps (1)-(5) using different test CO ₂ oil displacement and blending agents to obtain δ-P curves corresponding to these CO ₂ oil displacement and blending agents tested; and

(7) comparing the characteristics of the δ-P curves corresponding to these test CO ₂ displacement and blending agents to evaluate the miscibility-promoting effect of each test CO ₂ oil displacement and blending agent.

In a preferred embodiment, the oil is selected from one or more of kerosene, light oil and crude oil.

Preferably in step (1) the ratio of the initial liquid level H ₀ and the height of the upper boundary of the autoclave tank H _m is from 1:2 to 1:5, preferably 1:3; the temperature of the constant temperature water bath is a constant temperature selected from the range of 40-80°C.

Preferably, in step (2), the mass fraction of the blending aid in CO ₂ gas is in the range of 0.1% to 5%, preferably 1%; pressure increase is carried out using a single-cylinder plunger pump; the predetermined pressure level is 4-8 MPa, preferably 5 MPa; gas-liquid equilibrium means that after shutting off the gas receiving path for CO ₂ , the pressure gauge readings change by no more than 0.01 MPa, and the liquid level changes by no more than 0.01 cm within 5 minutes.

Preferably, in step (4), P _m is determined as the minimum miscibility pressure.

Preferably, in step (7), the characteristics are selected from one or more of the following factors: the corresponding liquid level H at a certain pressure level, the slope of the curve k at a certain pressure level, the corresponding CO ₂ pressure level P when the liquid level reaches a certain height, and P _m .

In another aspect, the present invention also provides a method for preselecting a blending aid, comprising: using the same amount of different blending aids, evaluating the mixing promoting effect using the evaluation method of the present invention, and selecting a suitable blending aid according to characteristics of the percent miscibility-pressure curve.

Compared with the method of the prior art, with the method of the present invention, the miscibility-promoting effect of the CO ₂ oil displacement and mixing agent can be conveniently and quickly evaluated, and the evaluation result is stable and reliable, the required time and labor the load is greatly reduced and numerous large batch experiments can be carried out at the same time, so that preselection can be ensured during the research and development of the blending aid, and guidance on the quantification of the appropriate blending aid under investigation can be obtained. Thus, the method of the present invention has significant advantages in cutting-edge studies in the field of miscible displacement of oil using CO ₂ and in subsequent industrial applications.

BRIEF DESCRIPTION OF GRAPHICS

FIG. 1 shows δ-P curves in a CO ₂ -kerosene system with glyceryl trioctanoate, glyceryl trilaurate or Tween-80 as blending additives according to the method of Examples 1-3 respectively and Comparative Example 1.

FIG. 2 shows the δ-P curves obtained in the CO ₂ -kerosene system with various concentrations of glyceryl trilaurate as a blending additive according to the method of examples 2, 4 and 5.

FIG. 3 shows δ-P curves obtained in a CO ₂ -kerosene system with glyceryl trilaurate as a blending aid at various temperatures according to the method of Examples 2, 6 and 7.

FIG. 4 shows δ-P curves obtained in a CO ₂ -kerosene system, a CO ₂ -light oil system, or a CO ₂ -crude oil system with glyceryl trilaurate as a blending additive according to the method of Examples 2, 8, and 9, respectively.

DETAILED DESCRIPTION

It is known to those skilled in the art that when oil is displaced using CO ₂ with a gradual increase in pressure, CO ₂ is gradually dissolved in the oil phase, which leads to volumetric expansion of the oil phase. However, the present inventors have discovered for the first time that since the blending aid can increase the affinity of CO ₂ and the oil, it appears macroscopically that the volume expansion of the oil phase will further increase at the same pressure in the CO ₂ -oil system to which the blending aid is added. Following this principle, in the case of a mixing additive with a better miscibility-promoting effect, the percent miscibility-pressure curve (δ-P curve) is further shifted to the left, that is, the same volume expansion effect is achieved at a lower pressure.

In some embodiments of the present invention, percent miscibility δ means the percentage increase in volume of the oil phase in the CO ₂ -oil system compared to the increase in miscible volume when a fully miscible phase forms between the CO ₂ and the oil phase. Accordingly, the percent miscibility-pressure curve (δ-P curve) refers to the operating curve obtained by changing the pressure level in the system and measuring the percent miscibility values at different pressure levels, and plotting the percent miscibility values corresponding to the pressure levels, while other conditions remain unchanged. Sometimes "volume change factor versus pressure curve" can also be used to refer to the δ-P curve, but it should be understood that the percent miscibility is not limited to the volume change factor alone. In some embodiments, the δ-P curve is measured in a constant volume vessel in which the pressure is increased by introducing additional CO ₂ into the vessel. In some embodiments, the δ-P curve may be measured in a variable volume vessel where the amount of CO ₂ in the system remains constant and the pressure is controlled by varying the volume of the vessel. In fact, in the case where different blending additives are to be sampled, any suitable method for obtaining the δ-P curve can be chosen by those skilled in the art, provided that the measurement conditions therein remain unchanged. In a preferred embodiment, for ease of implementation and ease of control, the measurement to obtain the δ-P curve is performed using a constant volume vessel.

The container used should provide information on the volume of the oil phase. In some embodiments, the measurement container used is transparent to determine the volume of the oil phase in the measurement. In some embodiments, the measurement vessel has a viewing window so that the volume of the oil phase can be determined by observing the height of the oil phase interface. In some embodiments, the measurement vessel is equipped with a sensor that can collect and output data on the volume of the oil phase.

Similarly, the container used must be capable of providing pressure information. In some embodiments, pressure information is obtained from a pressure gauge connected to the CO ₂ gas path. In additional embodiments, the measurement container used is equipped with a sensor that can collect and output pressure information. In some embodiments, the measurement vessel used is a constant volume autoclave with a viewing window and a gas inlet path, where the height of the oil phase interface is observed through the viewing window, and the pressure in the autoclave is determined through the gas inlet path.

In addition, in some embodiments of the present invention, in a constant volume autoclave, if the liquid level of the oil phase exactly reaches the upper boundary of the autoclave tank, then only one phase is present in the entire autoclave tank, that is, a miscible phase state is reached, so the corresponding pressure P _m in this time is the minimum mixing pressure.

In the context of the present invention, "mixing aid" refers to any agent that is introduced into the oil displacement system together with the carrier gas, which is CO ₂ , and plays a role in reducing the minimum miscibility pressure by reducing the interfacial tension between the oil phase and CO ₂ . Preferably the mixing aid is a surfactant.

In a preferred embodiment, step (2) can be carried out with agitation, preferably using a magnetic stirrer, in order to achieve gas-liquid equilibrium more quickly.

In the present invention, in order to reduce the viscosity of the oil phase, in order to facilitate mixing and thus accelerate the achievement of gas-liquid equilibrium for CO ₂ -oil phase, while taking into account the need to simulate the actual reservoir temperature of the field, the entire process is preferably carried out at a constant temperature, selected from the range of 40-80°C. In some embodiments, the entire process is performed at a constant temperature that is equal to the temperature of the oil phase source formation. In some embodiments, the entire process is performed at a certain constant temperature that differs from the oil phase source formation temperature by no more than 20°C, preferably no more than 10°C, more preferably no more than 5°C. The reservoir temperature of the source of the oil phase refers to the temperature of the formation of the field in which the oil phase is formed. In some embodiments, the formation temperature of the source of the oil phase may be determined based on an arbitrary measured ten-point average temperature of the formation of the field from which the oil phase is derived.

The method of the present invention also makes use of various variables, which are also contemplated by the present invention. For example, those skilled in the art will appreciate that the methods of the present invention can also be used to optimize a range of amounts of a particular blending aid to obtain an amount of blending aid that achieves the best balance between reagent cost and oil displacement efficiency.

Examples

Hereinafter, the present invention is described in more detail using examples, but the present invention is not limited to these examples.

The reagents used in the following examples are as follows:

kerosene: Macklin, model: K812242;

light oil product: No. 5 light oil product provided by the Research Institute of Petroleum Exploration and Development (RIPED) of China;

crude oil: provided from a certain area of the Changqing oil field;

CO ₂ : 99.9% pure gas in a high pressure bottle supplied by Beijing Haikeyuanchang Practical Gas Co. Ltd.;

glyceryl trioctanoate: chemically pure, Macklin;

glyceryltrilaurate: chemically pure, Macklin;

Tween-80: chemically pure, Sinopharm Chemical Reagent Co. Ltd.;

fixed volume autoclave: own production, with viewing window and gas path using a single-cylinder plunger pump for gas supply.

Example 1

20.00 ml of kerosene was added to the constant volume autoclave, then a magnetic stirring bar was placed and the constant volume autoclave was closed, placed in a constant temperature water bath at a water temperature of 40° C., and the initial liquid level (H ₀ ) was recorded; connected gas inlet path for CO ₂ for introduction into the autoclave CO ₂ high pressure with a load of 1 wt. % glyceryl trioctanoate as a mixing additive until the pressure reached 5 MPa, and then the CO ₂ inlet path was turned off and left for more than half an hour to reach equilibrium until the pressure gauge showed a change of no more than 0.01 MPa , and the liquid level changed by no more than 0.01 cm within 5 minutes. Then, at this time, the corresponding pressure level (P) and liquid level (H) were recorded. Thereafter, additional CO ₂ was introduced to pressurize the system until a certain pressure level was reached, and then the corresponding pressure level and liquid level were recorded. Then this process was repeated until the liquid level rose to the upper boundary of the autoclave tank, while registering the pressure P _m and the height of the upper boundary of the autoclave tank H _m .

The volume change rate corresponding to each pressure level was calculated by the following formula. Then a δ-P curve was built.

Under the same conditions, glycerol trilaurate and Tween-80 were used as mixing aids and evaluated for mixing promoting effect, with the results shown in Example 2 and Example 3, respectively; in addition, the same system was measured without using any mixing aid, and the results are shown in Comparative Example 1.

FIG. 1 shows the δ-P curves of Examples 1-3 and Comparative Example 1. As can be easily seen from FIG. 1, each of Examples 1 to 3 shows lower P _m values compared to Comparative Example 1, and each of all curves shows a leftward bias trend; on the other hand, by comparing the characteristics of the δ-P curve in Examples 1-3, the respective mixing aid effects of these mixing aids can be easily compared and traced.

For the study, the same method was used as in example 2, except for changing the amount of glycerol trilaurate by 0.5 wt. % and 2 wt. %, and the results are shown in Example 4 and Example 5, respectively.

FIG. 2 shows the δ-P curves from Example 2, Example 4 and Example 5. As can be easily seen from FIG. 2, when the concentration of glycerol trilaurate increases, the P _m value decreases and the entire curve shifts to the left.

Using the same research method as in example 1, except for using 1 wt. % glycerol trilaurate as a mixing additive, the temperature of the constant temperature water bath was adjusted to 50°C and 60°C, and the results are shown in Example 6 and Example 7, respectively.

FIG. 3 shows the δ-P curves from Example 2, Example 6 and Example 7. As can be easily seen from FIG. 3, as the temperature rises, the value of P _m also increases, and the entire curve tends to shift to the right.

In addition, the experiment of Example 8 was carried out under the same conditions as in Example 1, except that 1 wt. % glycerol trilaurate and replaced kerosene with a light oil product. In addition, the experiment of Example 9 was carried out under the same conditions as in Example 1, except that 1 wt. % glycerol trilaurate and replaced kerosene with crude oil.

FIG. 4 shows the δ-P curves from Example 2, Example 8 and Example 9. As can be easily seen from FIG. 4, in kerosene, the blending aid of Example 2 quickly provided a very high percentage of miscibility at lower concentrations, thus the kerosene has a significantly better miscibility-enhancing effect compared to the light oil system of Example 8 and the crude oil system of Example nine.

In addition, for Example 9, the minimum miscibility pressure of crude oil obtained according to Non-Patent Document 2 using the method of measuring interfacial tension is 20.04 MPa; accordingly, the minimum miscibility pressure obtained in Example 9 is 21.03 MPa. Both results essentially agree with each other, and thus it can be seen that by means of the method of the present invention, the value of the minimum miscibility pressure of the CO ₂ -oil phase system can be obtained relatively accurately.

Non-Patent Document 2: Yang Siyu et al. The optimization and evaluation of mixing aid molecules for CO ₂ oil-displacing [J], Xinjiang Petroleum Geology, 2015, 36 (5): 555-559.

The pressure and liquid level data of Examples 1 to 9 and Comparative Example 1 described above are shown in Table 1 below.

Table 1. Pressure and liquid level data

Embodiments of the present invention are described in detail above, but the present invention is not limited to the specific details of the above described embodiments. Various simple variations of the technical solution of the present invention can be made within the scope of the technical solution of the present invention, and such simple variations are within the scope of the present invention.

It should be noted that each of the specific technical features described in the above embodiments may be combined in any suitable manner, provided that no conflict arises. To avoid unnecessary repetition, other possible combinations will not be described in the present invention.

In addition, various other embodiments of the present invention may also be carried out in any combination, unless this is contrary to the idea of the present invention, which should also be considered as a disclosure of the present invention.

Claims (19)

1. A method for evaluating the miscibility-promoting effect of a CO ₂ oil displacement and blending agent, characterized in that the volumetric expansion at the CO ₂ -oil interface is measured with a gradual increase in pressure, and a percent miscibility-pressure curve ("δ-curve") is plotted. P"), and evaluate the miscibility-promoting effect of the CO ₂ oil displacement and blending agent by comparing the characteristics of the δ-P curves, wherein the method includes the following steps: (1) adding a given volume of oil to a constant volume autoclave equipped with a viewing window and a gas intake path, closing the autoclave, placing the autoclave in a constant temperature water bath, observing through the viewing window and recording the initial liquid level H ₀ , and connecting a source of gaseous CO ₂ and a pressure gauge to the gas intake path; (2) introduction of high pressure CO ₂ into the autoclave with a load of the agent under investigation to displace and mix oil using CO ₂ until a predetermined pressure level P is reached, shutdown of the gas intake path, ensuring the achievement of gas-liquid equilibrium, recording the pressure level P, observation through the viewing window and registration of the liquid level H; (3) continuously introducing CO ₂ to pressurize the autoclave until another predetermined pressure level is reached, and recording the corresponding pressure level and liquid level in accordance with the method in step (2); (4) repeating step (3) until the liquid level rises to the upper boundary of the autoclave tank, and recording the corresponding pressure level P _m and height of the upper boundary of the autoclave tank H _m ; (5) Calculate the miscibility percentage δ corresponding to each pressure level according to the following formula (1) and plot the δ-P curve:

Formula 1), then ensuring depressurization and cleaning of the autoclave; (6) repeating steps (1)-(5) using different test CO ₂ oil displacement and blending agents to obtain δ-P curves corresponding to these CO ₂ oil displacement and blending agents tested; and (7) comparing the characteristics of the δ-P curves corresponding to these test CO ₂ displacement and blending agents to evaluate the miscibility-promoting effect of each test CO ₂ oil displacement and blending agent. 2. The method of claim 1 wherein the oil is selected from one or more of kerosene, light oil and crude oil. 3. The method according to p. 1, where in stage (1) the ratio of the initial liquid level H ₀ and the height of the upper boundary of the autoclave tank H _m is from 1:2 to 1:5; the temperature of the constant temperature water bath is a constant temperature selected from the range of 40-80°C. 4. The method according to p. 1, where in stage (1) the ratio of the initial liquid level H ₀ and the height of the upper boundary of the autoclave tank H _m is 1:3. 5. The method according to p. 1, where in stage (2) the mass fraction of means for displacement and mixing of oil using CO ₂ in gaseous CO ₂ is in the range from 0.1% to 5%; pressure increase is carried out using a single-cylinder plunger pump; the specified pressure level is 4-8 MPa; gas-liquid equilibrium means that after shutting off the gas receiving path for CO ₂ , the pressure gauge readings change by no more than 0.01 MPa, and the liquid level changes by no more than 0.01 cm within 5 minutes. 6. The method according to p. 1, where in stage (2) the mass fraction of the means for displacement and mixing of oil using CO ₂ in gaseous CO ₂ is 1%; pressure increase is carried out using a single-cylinder plunger pump; the predetermined pressure level is 5 MPa, preferably 5 MPa; gas-liquid equilibrium means that after shutting off the gas receiving path for CO ₂ , the pressure gauge readings change by no more than 0.01 MPa, and the liquid level changes by no more than 0.01 cm within 5 minutes. 7. The method according to claim 1, where in step (4) P _m is determined as the minimum miscibility pressure. 8. The method according to claim 1, where in step (7) the characteristics are selected from one or more of the following factors: the corresponding liquid level H at a certain pressure level, the slope of the curve k at a certain pressure level, the corresponding CO ₂ pressure level P when the level liquid reaches a certain height, and P _m . 9. The method of pre-selection of a means for displacing and mixing oil using CO ₂ , including: using the same amount of different means for displacing and mixing oil using CO ₂ , evaluating the miscibility-promoting effect using the evaluation method according to any one of paragraphs. 1-7 and selecting a suitable CO ₂ oil displacement and blending agent according to the characteristics of the δ-P curve.

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