阅读说明：本技术 一种纳米颗粒驱油剂及一种提高采收率的方法 (Nanoparticle oil displacement agent and method for improving recovery ratio ) 是由 王沫然 雷文海 鲁旭康 刘洋 于 2021-11-05 设计创作，主要内容包括：本申请提供了一种纳米颗粒驱油剂及一种提高采收率的方法,通过选择适合纳米颗粒发挥作用的储层环境,制备特定的驱油剂,驱替时采用注入-泄压-再注入的方式实现纳米颗粒注入-促进原油释放-驱替释放的原油,达到提高采收率的目的。并且通过驱油剂中的纳米颗粒吸附在液-液表面以降低界面张力,吸附在粗糙固体表面形成二级粗糙度实现水膜的延伸和生长,利用驱替过程中的表面能差异将原油释放出来。(The application provides a nanoparticle oil displacement agent and a method for improving the recovery ratio, wherein a specific oil displacement agent is prepared by selecting a reservoir environment suitable for nanoparticles to play a role, and the injection, pressure relief and reinjection of nanoparticles are adopted during displacement to realize the injection, crude oil release promotion and crude oil release displacement release of nanoparticles, so that the aim of improving the recovery ratio is fulfilled. And the nano particles in the oil displacement agent are adsorbed on the liquid-liquid surface to reduce the interfacial tension, and are adsorbed on the rough solid surface to form secondary roughness so as to realize the extension and growth of a water film, and crude oil is released by utilizing the surface energy difference in the displacement process.)

1. An oil displacing agent comprising silica nanoparticles and a solvent;

the particle size of the silica nanoparticles is not more than one tenth of the average characteristic pore size of the target reservoir; the silicon dioxide nanoparticles are not agglomerated before the oil displacement agent is injected into the target reservoir;

the concentration of silica nanoparticles in the oil displacing agent is 0.1 wt.% to 10 wt.%; preferably, the concentration of the silica nanoparticles in the oil displacing agent is 3 wt.% to 5 wt.%.

2. The oil-displacing agent of claim 1, wherein the oil-displacing agent further comprises a salt, the type and concentration of the salt being selected to avoid aggregation between silica nanoparticles due to van der waals forces;

alternatively, the concentration of the salt is 0.01g/L to 10 g/L; preferably, the concentration of the salt is 0.9g/L to 2.2 g/L;

optionally, the salt is selected from any one or more of a water soluble sodium salt, a water soluble aluminium salt, a water soluble iron salt and a water soluble magnesium salt.

3. The oil-displacing agent of claim 1, wherein the silica nanoparticles have a D90 of less than 2 times the average particle diameter.

4. The oil-displacing agent according to any one of claims 1 to 3,

the target reservoir is a reservoir which takes one or two of silicon dioxide and carbonate as main components and has wettability determined as water-wet, or the rock of the target reservoir is not water-wet but has rock surface potential positive;

optionally, the target reservoir is one or both of a sandstone reservoir and a carbonate reservoir, and preferably, the content of organic matter in the target reservoir is less than 20 wt.% in the target stratum.

5. An oil-displacing agent according to any one of claims 1 to 3, wherein the pH of the oil-displacing agent is 8.5 to 11.

6. The oil-displacing agent according to any one of claims 1 to 3, wherein the particle size distribution of the silica nanoparticles is measured and then measured again at intervals of 24 hours, and the change in the particle size distribution is within 10%.

7. The oil displacing agent of any one of claims 1 to 3, wherein the target reservoir selection method comprises:

1) judging whether the stratum is wet by water by adopting a wettability judging method;

the wettability judging method comprises an Amott wettability index I_AUSBM wettability index I_UAnd a relative permeability curve;

2) and if the wettability judging method is adopted to judge that the stratum is not wet, selecting the target stratum by adopting a surface potential judging method.

8. The oil-displacing agent according to claim 7, wherein Amott wettability index I is used when judging the method_AWhen, I_A>The reservoir of 0 is the target reservoir; when judged method using USBM wettability index I_UWhen, I_U>The reservoir of 0 is a target reservoir; when the relative permeability curve is used in the judgment method, the reservoir with the saturation degree of the isosmotic point being more than 50% is taken as the target reservoir.

9. The oil displacing agent according to claim 7, wherein when the judging method uses a surface potential judging method, a Zeta potential of rock particles in water is measured using an electrophoresis method, and a reservoir with a positive surface charge when the Zeta potential is greater than 0 is a target reservoir.

10. Use of an oil-displacing agent according to any one of claims 1 to 9, comprising the steps of,

a) injecting the oil displacing agent into the reservoir of interest through an injection well until the oil displacing agent is visible in a production well;

b) stopping injecting the oil displacement agent until the difference between the pressure of the injection well and the pressure of the production well is less than 10% of the average value, and then closing the injection well and the production well simultaneously;

c) injecting the oil displacement agent, and displacing and extracting crude oil;

optionally, the injection time of the oil displacement agent in the step c) is not less than that of the oil displacement agent in the step a);

alternatively, steps a), b) and c) may be cycled through a plurality of times;

alternatively, step a) and step b) may be cycled multiple times, preferably, water may be used as the displacement fluid in step c) after multiple cycles of step a) and step b).

Technical Field

The patent refers to the field of 'investigating or analysing materials by determining their chemical or physical properties'.

Background

At present, the external dependence of crude oil in China is high, the exploration and development of oil and gas resources are related to the development of national economy and the stable operation of society, and the improvement of the recovery ratio through a new method and technology is an important means for improving the oil and gas yield and guaranteeing the national energy safety. Among them, chemical flooding by adding various chemical agents to a displacement fluid is a widely used means for increasing the recovery ratio. However, the conventional chemical flooding method has problems such as environmental pollution, large consumption, serious ineffective loss in the formation, and the like.

The nano particle suspension is a novel material capable of effectively improving the oil recovery ratio, is widely researched in laboratories in recent years, and has a good application prospect due to small size, large specific surface area, good thermal and mechanical properties, low cost, small pollution and the like. However, the mechanism of the existing nanoparticle oil displacement agent for improving the recovery ratio is not clear, and various designed nanoparticle oil displacement agents do not form an effective actual application-oriented scheme for improving the recovery ratio on the basis of certain specific enhanced displacement capabilities, cannot exert the functions of the nanoparticle oil displacement agents in a targeted manner, and are difficult to obtain stable and reliable performances on an oil field site.

Disclosure of Invention

The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the present application.

The application provides a method for improving the recovery ratio of a silica nanoparticle oil displacement agent, which comprises the steps of selecting a reservoir environment suitable for nanoparticles to play a role, preparing the specific silica nanoparticle oil displacement agent, and realizing the injection of nanoparticles, the promotion of crude oil release and the displacement of released crude oil by adopting an injection-pressure relief-reinjection mode during displacement, so as to achieve the purpose of improving the recovery ratio. And the nano particles are adsorbed on the liquid-liquid surface to reduce the interfacial tension, and adsorbed on the rough solid surface to form secondary roughness so as to realize the extension and growth of a water film, and crude oil is released by utilizing the surface energy difference in the displacement process.

The nano oil displacement agent comprising the mechanism can improve the recovery rate by enhancing the spreading and growth of a water film through secondary roughness formed by adsorption on the solid surface.

The application provides an oil displacement agent, which comprises silicon dioxide nanoparticles and a solvent;

the particle size of the silica nanoparticles is not more than one tenth of the average characteristic pore size of the target reservoir; the silicon dioxide nanoparticles are not agglomerated before the oil displacement agent is injected into the target reservoir;

for example, when the average characteristic pore diameter of the rock of the target reservoir is 1 μm, the average particle diameter of the silica nanoparticles is 100nm or less; when the average characteristic pore diameter of the rock of the target reservoir is 500nm, the average particle size of the silica nanoparticles is less than or equal to 50 nm; when the average characteristic pore diameter of the rock of the target reservoir is 100nm, the average particle size of the silica nanoparticles is less than or equal to 10 nm; in order to ensure the adsorption capacity of the nanoparticles, the average particle size of the nanoparticles should be generally less than 200 nm.

The reservoir is one or two of a sandstone reservoir or a carbonate reservoir;

the target reservoir applicable to the present application can be judged by the following method: first, a wettability determination method is used to determine whether a reservoir is water-wet.

The wettability judging method described above, when using Amott wettability index I_AMake a judgment of_A>If the reservoir of 0 is water wet, the reservoir can be selected as a target reservoir; when USBM wettability index I is used_UMake a judgment of_U>If the reservoir of 0 is water wet, the reservoir can be selected as a target reservoir; when the relative permeability curve is used for judgment, and the reservoir with the saturation degree of the isosmotic point being more than 50% is water wet, the reservoir can be selected as a target reservoir;

if the reservoir is a non-water-wet reservoir, the target reservoir can be selected by adopting a surface potential judgment method, and the reservoir with positive rock surface charge is selected as the target reservoir;

the surface potential determination method selects the Zeta potential of rock particles of the reservoir measured by an electrophoresis method in water, if the Zeta potential is greater than 0, the surface charge of the reservoir is positive, and the reservoir can be selected as a target reservoir.

The concentration of silica nanoparticles in the oil displacing agent is 0.1 wt.% to 10 wt.%; preferably, the concentration of the silica nanoparticles in the oil displacing agent is 3 wt.% to 5 wt.%.

In one embodiment, the method for obtaining the average characteristic pore size includes the following steps: the method comprises the steps of driving a exploration well into a target reservoir to obtain a core, or searching the core of the target reservoir in a core database, counting pore size distribution (at least 10 blocks) of different representative rocks, sequencing the average pore size distribution of the counted core from large to small, selecting 60-80% of the pore size distribution of rocks in a sequencing table as characteristic pore size distribution of low-permeability rocks, and taking the average pore size as the average characteristic pore size of the low-permeability rocks.

In one embodiment provided by the application, the oil displacement agent further comprises a salt, the type and concentration of the salt are selected to avoid aggregation between the silica nanoparticles due to van der waals force, and the selected salt can enhance the adsorption effect;

in one embodiment provided herein, the salt is at a concentration of 0.01g/L to 10 g/L; preferably, the concentration of the salt is 0.9g/L to 2.2 g/L;

in one embodiment provided herein, the salt is selected from any one or more of a water soluble sodium salt, a water soluble aluminum salt, a water soluble iron salt, and a water soluble magnesium salt.

In one embodiment provided herein, the silica nanoparticles D90 are less than 2 times the average particle size. The D90 is the particle size with a cumulative particle distribution of 90%, i.e. the volume fraction of particles smaller than this is 90% of the total particles.

In one embodiment provided herein, the target reservoir is either or both of a sandstone reservoir and a carbonate reservoir, and preferably the target reservoir has a content of organic matter of less than 20 wt.% that does not include crude oil.

In one embodiment provided herein, the pH of the oil-displacing agent is from 8.5 to 11.

In another aspect, the present application provides a method for preparing the oil displacement agent, comprising the following steps:

preparing a high-concentration silica nanoparticle oil-displacing agent stock solution, preparing silica sol by adopting an ion exchange method, and then obtaining the stable and reliable silica nanoparticle oil-displacing agent stock solution by adjusting the pH and salinity of the silica sol.

In an embodiment provided by the present application, the preparation method of the oil displacement agent includes the following steps:

(1) obtaining an aqueous silicic acid solution, SiO in the aqueous silicic acid solution₂From 4 wt.% to 9 wt.%; the concentration of anionic impurities in the aqueous silicic acid solution is less than 0.01 wt.%; the pH value of the silicic acid aqueous solution is 8 to 10.5;

(2) heating the silicic acid aqueous solution obtained in the step (1) to 85-95 ℃, preserving heat for 40-55 min, and aging to obtain seed crystal mother liquor;

(3) mixing active silicic acid with the seed crystal mother liquor to obtain a mixture;

the active silicic acid is a silicic acid solution with the mass fraction of 3 wt.% to 8 wt.%, the pH is 2 to 4, and the content of metal impurity ions is less than 500 ppm;

(4) stirring the mixture in the step (3) under a heating condition, obtaining a crude silica sol product through particle size growth, and adjusting the crude silica sol product to 20-60 wt.% to obtain an oil displacement agent stock solution; and adding salt into the oil displacement agent stock solution, and diluting with water to obtain the oil displacement agent.

In one embodiment provided herein, in step (1), the method for preparing the aqueous silicic acid solution comprises the steps of: the preparation method of the dilute polysilicic acid solution comprises the following steps: dilution of liquid sodium silicate to SiO with deionized water₂And 4 wt.% to 9 wt.%, removing sodium ions and other cationic impurities through a strong acid type cation exchange resin, removing chloride ions and other anionic impurities through a weak base type anion exchange resin to obtain a high-purity active silicic acid solution, and adding NaOH to the active silicic acid solution to adjust the pH value to obtain a silicic acid aqueous solution with the pH value of 8 to 10.5.

In one embodiment provided herein, in step (3), the mass ratio of the active silicic acid solution to the seed crystal mother liquor is 6 to 8, and the pH of the mixture is 8 to 10.5.

In one embodiment provided herein, in the step (4), the stirring under heating is performed at 85 to 95 ℃ at a rate of 250 to 300 r/min;

in one embodiment provided herein, the pH of the oil-displacing agent stock in step (4) is from 10.5 to 12.

In another aspect, the application provides the use of the oil displacement agent, which comprises the following steps,

a) injecting the oil displacement agent into the target formation through an injection well until the oil displacement agent is visible in a production well (breakthrough occurs when a large amount of crude oil is trapped in the formation);

b) stopping injecting the oil displacement agent until the difference between the ratio of the pressure of the injection well and the pressure of the production well is less than 10% of the average value to reduce the resistance of the oil phase to entering the high permeability region (i.e., the flow channel of the nanoparticle displacement fluid); simultaneously closing said injection well and said production well;

nanoparticle oil-displacing agents that have been injected into the formation form secondary roughness structures by adsorption on the walls to maintain and stabilize the development of a water film. On one hand, the oil-water interfacial tension in the nanoparticle displacement fluid flow channel is small, and the oil-water interfacial tension at the far end of the water film formed by adsorption is large; on the other hand, the water film attached to the solid surface has large specific surface area, so that the formed surface energy is large, the specific surface area of the nano-particle displacement fluid in contact with the oil phase is small, and the formed surface energy is small. The region of nanoparticle displacement fluid in step (a) tends to be a region of high permeability, which is readily accessible for collection.

c) Injecting the oil displacement agent, and displacing and extracting crude oil;

in one embodiment provided herein, the injection amount of the oil displacement agent in step a) may be 0.1 to 1 PV;

in one embodiment provided herein, the time for closing the injection and production wells in step b) may be 1 month to 2 months;

in one embodiment provided herein, the injection time of the oil displacement agent in step c) may be the same as that in step a;

in one embodiment provided herein, steps a), b), and c) may be cycled through a plurality of times;

in one embodiment provided herein, steps a) and b) may be cycled multiple times, preferably, water may be used as the displacement fluid in step c) after multiple cycles of steps a) and b).

Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the application. Other advantages of the present application may be realized and attained by the invention in its aspects as described in the specification.

Drawings

The accompanying drawings are included to provide an understanding of the present disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the examples serve to explain the principles of the disclosure and not to limit the disclosure.

Fig. 1 is a comparison of the displacement effect of the oil displacement agent prepared in example 1 and deionized water in different material oil reservoir chips.

Fig. 2 is a comparison of the silica nanoparticle flooding and deionized water flooding effects at a local viewing angle in a hydrophilic reservoir chip.

Fig. 3 shows the influence of the oil displacement agent prepared in example 1 with different concentrations on the development of a water film and the collection effect of the oil displacement agent on oil droplets trapped in dead pores at different times.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, embodiments of the present application are described in detail below. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.

Examples

(1) Selecting a reservoir suitable for the oil displacement agent provided by the application to play a role, selecting a certain block of the Changqing oil field to analyze, and obtaining 10 cores through a detection well; the oil field reservoir is a sandstone reservoir. The rock core in the reservoir of the oil well shows that the content of organic matters (not including crude oil) is different from 3 percent to 8 percent, and the content of the organic matters is low. The following Amott wettability index was obtained by the Amott wettability test method.

Table 1: amott wettability index

Core number	1	2	3	4	5
						IA	0.6	0.8	0.3	0.1	0.5
Core number	6	7	8	9	10
						IA	0.0	-0.1	0.1	0.2	0.3

From the Amott wettability index, the vast majority of sandstone reservoirs are water-wet reservoirs (only one of 10 cores is weak oil-wet), and the organic matter content is low, which indicates that the reservoirs are mainly composed of silicon dioxide and can use silicon dioxide nanoparticle oil-displacing agents.

Determining a proper nanoparticle particle size, counting the pore size distribution of the reservoir, scanning by adopting a CT structure and reconstructing a digital structure, and counting the particle size distribution by adopting a maximum sphere method (for example, the selection of the pore size distribution characteristics of a real core in example 1 in Chinese patent CN 110302853B), so as to obtain the following average pore size.

Table 2: core average pore statistics

Core number	4	3	5	7	9
						Average pore (micron)	15.40	11.20	6.10	2.10	0.83
Core number	10	1	6	2	8
						Average pore (micron)	0.75	0.43	0.40	0.38	0.30

The average pore size of the hypotonic region is selected to be 0.75 microns to 0.40 microns, and the average characteristic pore size of the target reservoir is selected to be 0.43 microns.

(2) Preparation of silica nanoparticle oil-displacing agent

Firstly, preparing a high-concentration silica nanoparticle oil-displacing agent stock solution, preparing silica sol by adopting an ion exchange method, and then obtaining the stable and reliable silica nanoparticle oil-displacing agent stock solution by adjusting the pH and salinity of the silica sol. When the oil displacement agent is used, the oil displacement agent can be diluted to a specific concentration by using clear water or deionized water.

The method comprises the following steps:

(2.1) dilution of liquid sodium silicate to SiO with deionized Water₂Removing sodium ions and other cationic impurities through strong acid type cation exchange resin to obtain a diluted polysilicic acid solution, wherein the mass fraction of the diluted polysilicic acid solution is 4-9 wt%;

(2.2) removing chloride ions and other anion impurities from the diluted polysilicic acid solution obtained in the step (2.1) through weak base type anion exchange resin to obtain a high-purity active silicic acid solution;

(2.3) adding NaOH into the active silicic acid obtained in the step (2.2) to adjust the pH value, so as to obtain a silicic acid aqueous solution with the pH value of 8-10.5;

(2.4) heating the silicic acid aqueous solution obtained in the step (2.3) to 85-95 ℃, preserving heat for 40-55 min, and aging to obtain seed crystal mother liquor;

(2.5) continuously adding active silicic acid into the seed crystal mother liquor obtained in the step (2.4), wherein the mass ratio of the added active silicic acid to the seed crystal mother liquor is 6-8, the pH value is kept at 8-10.5 by adding NaOH, stirring is carried out at the temperature of 85-95 ℃ at the speed of 250-300 r/min, and a crude silica sol is obtained by particle size growth; the particle size of the nano-particle oil displacement agent is selected according to the average characteristic pore diameter of the hypotonic rock determined in the step (1) as a reference, and is at least less than 1/10 of the average pore diameter. Since the average characteristic pore size of the hypotonic rock is 0.43 μm, the nanoparticles should be selected to have an average particle size of 43nm or less.

In this example, the target nanoparticles were selected to have an average particle size of 20nm (i.e., particle D90 was less than 2 times the average particle size).

(2.6) passing the crude silica sol obtained in the step (2.5) through an ultrafiltration membrane or a reduced pressure distillation device to obtain a high-concentration silica nanoparticle displacement fluid stock solution with uniform particle size and mass fraction of 40 wt.%;

(2.7) adjusting the pH of the stock solution to 10.56 in order to improve the adsorption activity and action effect of the silica nanoparticles while maintaining stability and dispersibility; the ionic composition in the solution is adjusted by adding salts.

(2.8) diluting with water to obtain an oil displacement agent with the mass fraction of the silicon dioxide nano particles being 4 wt.%; the pH value of the oil displacement agent is 9.98; the total dissolved concentration of the above salts was 1.635 g/L; the kind and content of the salt are shown in Table 3.

Table 3: species and content of salt in examples

Species of	Content (μ g/mL)
		NaCl	1100
AlCl3	390
		FeCl3	56
MgSO4	14
		NaHCO3	75

The oil displacement agent can reduce the oil-water interfacial tension (deionized water and n-decane) from 47.19mN/m to 39.51mN/m (measured by a hanging drop method by using a DSA25 instrument of Kruss company), and the average particle size of the oil displacement agent is 22.5 nm; after standing for 24h, the particles had an average particle size of 23.2 nm.

Example 2

This example is an effect test of enhanced recovery of the oil displacement agent prepared in example 1, and in example 2, oil reservoir chips having the same structure as that of the reservoir in the Changqing oil field prepared in example 1 were used, wherein one chip material was a weak hydrophilic structure as in the real case, and the other chip material of the control group was a neutral environment. The oil displacing agent prepared in example 1 and deionized water were used for comparison in both sets of experimental structures.

The experimental procedure was as follows:

firstly, the oil displacement agent prepared in the embodiment 1 is injected from an injection port of an oil reservoir chip, the flow rate is 1 muL/min, and the injection amount is 1PV until the front edge of the displacement fluid reaches an outlet through microscope observation;

and secondly, stopping injecting the oil displacement agent until the difference value between the pressure at the main inlet and the pressure at the outlet is less than 10% of the average value, and closing the injection port and the outlet at the same time for 45 min.

And finally, injecting the oil displacement agent again, wherein the injection flow rate of the oil displacement agent is still 1 mu L/min, and the injection is continued until no residual oil is produced.

When water was used, the experiments were repeated using water instead of the oil displacing agent in the above step.

Fig. 1 is a graph showing the displacement effect of the oil displacement agent and deionized water prepared in example 1 after the completion of displacement. It can be seen that the nanoparticles can function due to their adsorption in a hydrophilic environment, with a large amount of trapped residual oil displaced out, while in a neutral environment (non-hydrophilic or oleophilic reservoir environment, and not satisfying a positive reservoir surface charge), the nanoparticles cannot function, with a displacement effect similar to that in water. The recovery factor for the four cases in fig. 1 is shown in the following table:

table 4: recovery effect of different kinds of displacement fluids

Displacement fluid	Solid environment	Recovery of oil
			Oil displacement agent	Hydrophilic	64.9％
Deionized water	Hydrophilic	45.3％
			Oil displacement agent	Neutral property	47.5％
Deionized water	Neutral property	40.4％

Fig. 2 is a partial microscopic effect of displacement of an oil displacement agent and deionized water in the hydrophilic reservoir chip.

After the oil displacement agent is injected into the porous medium, trapped residual oil can be collected through the development of a water film, and deionized water has no similar effect.

Fig. 3 shows the effect of the oil displacement agent on the development of a water film and the collection of residual oil trapped in dead pores under different concentrations, and it can be seen that the effect is optimal for the 4 wt.% oil displacement agent, and the whole oil droplets can spontaneously enter the main channel from the dead pores; in the range of 3 to 5 wt.%, the oil displacing agent is capable of avoiding detachment of the entire oil droplets and squeezing out most of the oil droplets; less than 3 wt.% and more than 5 wt.% it can be seen that the oil displacing agent is able to squeeze out a portion of the oil droplets into the main channels. As can be seen from the figure, the oil displacing agent is able to enhance the spreading of the water film and squeeze out the oil droplets trapped in the porous medium, compared to deionized water.