CN102797443B - Method for exploiting residual crude oil in low-permeability oilfield by using polymer micro/nanoparticle - Google Patents

Abstract

The invention relates to a method for exploiting remaining crude oil in a low-permeability oilfield by using nano-micron polymer particles, which comprises the following steps: (1) water flooding in the early stage of the low-permeability oilfield; (2) measuring the average throat radius of the low-permeability oilfield Determine the r _{particle size} of the nano-micron polymer particles, wherein the particle size of the nano-micron polymer particles satisfies (3) According to the determined r _{particle size} of the nano-micron polymer particles, the multi-component copolymerization of the nano-micron polymer particles is obtained by the distillation precipitation method; (4) The nano-micron polymer particles in step (3) are injected into the oil layer, and the low-permeability oilfield follow-up water drive. The advantages of the present invention are: the nano-micron polymer particle injection system can selectively enter large, medium and small pores, has a stronger effect of expanding the swept volume and oil washing ability, better exploits remaining oil in low-permeability layers, and improves crude oil recovery. Yield, increase economic benefits.

Description

A method of exploiting remaining crude oil in low-permeability oilfields using nano-micron polymer particles

technical field

The invention belongs to the field of oil recovery in oil fields, and relates to tertiary oil recovery technology in oil fields, in particular to a method for exploiting remaining crude oil in low-permeability oil fields by using nano-micrometer polymer particles.

Background technique

At present, many oil fields in China are in the stage of high water cut and high recovery degree, low comprehensive recovery rate, low production of many wells. In the 1980s, my country developed chemical flooding tertiary oil recovery technology. Tertiary oil recovery is compared with primary oil recovery and secondary oil recovery. In the early stage of oil exploitation, the oil recovery is only using the natural energy of the formation as primary oil recovery, and the recovery rate is only about 10%. Reaching about 25% to 40%; tertiary oil recovery is to use physical, chemical and biological means to continue to exploit the remaining underground oil.

Now the chemical flooding technology is in a stage of vigorous development, and the research work on chemical flooding mainly includes polymer flooding, alkali-polymer flooding, surfactant-alkali flooding, surfactant-polymer flooding and alkali-surfactant- polymer flooding, etc. These chemical composite flooding have not only carried out extensive indoor mechanism research, but also carried out pilot tests on site, and achieved obvious results.

At present, these chemical flooding tertiary oil recovery methods are mainly applicable to medium and high permeability oil fields. For low-permeability oilfields, there are surfactant and microbial methods, but such methods are difficult to be applied due to reasons such as technology, economy, and low production in low-permeability oilfields. In addition, tertiary oil recovery methods are mostly suitable for use in medium-high water cut periods, while low-permeability oilfields The more important problem to be solved is the problem of flow and control of water cut rise. At present, the methods for improving flow (improving the seepage condition at the bottom of the well) include maintaining formation pressure, fracturing, water injection, optimizing well pattern, and horizontal well exploitation. However, these methods are still difficult to produce large-scale mining effects. The development of horizontal wells often fails to achieve the expected results due to insufficient supply capacity due to low permeability, and the effective mining time is short and the recovery rate is low.

Contents of the invention

In order to solve the above problems, the present invention provides a new method for exploiting remaining crude oil in low-permeability oil fields in combination with a novel nano-micron polymer particle.

The present invention provides a method for exploiting remaining crude oil in a low-permeability oilfield by using nano-micron polymer particles, which adopts the method of "water flooding + micro-nano polymer particle flooding", and the specific steps are as follows:

(1) Early water flooding in low permeability oilfields;

(2) Measuring the average throat radius in low-permeability oilfields Determine the r _{particle size} of the nano-micron polymer particles, wherein the particle size of the nano-micron polymer particles satisfies

(3) According to the determined r- _{particle size} of the nano-micron polymer particles, the multi-component copolymerization by distillation and precipitation method is used to obtain nano-micron polymer particles;

(4) The nano-micron polymer particles in step (3) are injected into the oil layer, and the low-permeability oil field is followed by water flooding.

Wherein in step (3), the specific steps for obtaining nano-micron polymer particles by multi-component copolymerization by distillation precipitation method are as follows:

(3-1) Take acrylamide, one or more mixtures of acrylic acid and its derivatives, wherein the molar ratio of acrylamide to one or more of acrylic acid and its derivatives is 1:10-10 : 1, Add to the reaction vessel, add solvent into the reaction vessel, mix thoroughly, and then ultrasonically disperse, add cross-linking agent and initiator to the reaction vessel, and ultrasonically disperse; (3-2) Heat up the heater , heat up to a boiling state within 10-18 minutes, then keep the oil bath temperature at about 90°C, and keep this state for 15 minutes; (3-3) Adjust the heater temperature to 110-120°C, increase the distillation intensity, The solvent in the reaction vessel continuously flows into the receiving vessel. After 90-100 minutes, all the solvent in the reaction vessel is distilled out; (3-4) Stop heating, add ethanol into the reaction vessel, and ultrasonically disperse it, and then centrifuge (3-5) Purification: use ethanol to ultrasonically disperse and centrifuge twice to purify the obtained microspheres; (3-6) then place the purified microspheres in a 40 Dry in an oven at -60°C for 10-14 hours to obtain the required composite polymer microspheres.

Preferably, the acrylic acid derivative is 2-acrylamido-methylpropanesulfonic acid (AMPS) or methyl methacrylate (MMA).

Preferably, the molar ratio of acrylic acid to methyl methacrylate is 1:3.

Preferably, the solvent is one or more of acetonitrile, methanol, ethanol, ethyl acetate and tetrahydrofuran, and the amount used is 17.3-36.5 times the molar mass of acrylamide.

Preferably, it is characterized in that the crosslinking agent is N, N-methylenebisacrylamide or divinylbenzene, and the dosage is 1-10% (mol percentage) of acrylamide; the initiator is azobis The dosage of isobutyronitrile, azobisisoheptanonitrile or dimethyl azobisisobutyrate is 0.5-2% (mol percentage) of acrylamide.

Preferably, in step (3-3), the velocity ratio of the solvent refluxed into the reaction vessel and the solvent distilled out is kept at about 2.

Preferably, the size of the micro-nano polymer particle slug injected in the step (4) is 0.1-0.3 PV.

Preferably, the concentration range of the nano-micron polymer particles injected in the step (4) is 1000-2500 mg/L.

Preferably, the concentration of nanometer polymer particles injected in the step (4) is 1000 mg/L or 1500 mg/L or 2500 mg/L.

In addition, the nano-micron polymer particles used have an initial particle size distribution range of 200nm-1.2 μm, and a particle size distribution range of 400 nm-13 μm after hydration; wherein the nano-micron polymer particles have hydration swelling characteristics.

And, wherein, the size of the nanometer polymer particles used in the step (2) satisfies belongs to nanoscale flow, when It belongs to micron-scale flow.

The invention has the advantages that: the nano-micron polymer particle injection system can selectively enter the large, medium and small pores, has a stronger effect of expanding the swept volume and oil washing ability, better exploits the remaining oil in the low-permeability layer, and improves crude oil recovery rate and increase economic benefits.

Description of drawings

Fig. 1 The relationship between oil water cut and production time in nano-micron polymer particle flooding and water flooding

Fig. 2 The relationship between oil recovery degree of nano-micron polymer particle flooding and water flooding as a function of production time

Figure 3 Nano-micron polymer particles pass quickly or deform through narrow pore channels;

Figure 4 Nano-micron polymer particles stagnate or flow slowly in large pore spaces;

Fig. 5 The relationship curve between recovery factor and injection pore volume multiple;

Fig. 6 is the schematic diagram of this method polymerization reactor device;

Fig. 7 is a scanning electron microscope image of four groups of composite dry microspheres classified with different hydration particle sizes (the scale bars in the figure are all 5 μm).

Among Fig. 6, 1 is a round-bottomed flask, 2 is a reaction solution, 3 is a condensation reflux pipe, 4 is a condensation joint, and 5 is a receiving vessel.

6 is a heating device.

detailed description

Utilize the present invention to carry out test in Daqing Oilfield, Shengli Oilfield and other oilfield test areas, and all receive remarkable development effect. Below taking the oil reservoirs of Daqing Oil Production No. 2 Plant, No. 3 Plant and No. 9 Plant as an example, further illustrate the present invention in conjunction with the accompanying drawings.

Example one:

The South 2nd and 3rd areas of Daqing Oil Production Plant 2 are located at the southern end of the Saertu anticline structure. The dip angle of the strata is 10° on the west side and 3.5° on the east side; It is deposited at the outer front of the delta, and its lithology is mainly composed of fine sandstone, fine siltstone and argillaceous siltstone, containing a small amount of mixed layers of illite and smectite, with low expansibility and high chlorite content. The lithology of the surface and inner layer is mainly fine and siltstone, with an average air permeability of 22.5mD, an average porosity of 27.12%, and an average original oil saturation of 62.37%.

According to the principles and standards of well selection, the water wells in the Gaotaizi oil layer area in the second and third areas of the South were analyzed. -51, High 167-51, High 169-53, and High 170-53 are composed of 8 water wells. There are 21 oil wells in the well area and 6 central production wells. The area of the profile control well area is 1.209km ² , and the geological reserves of Gao I and II groups are 263.9994×10 ⁴ t.

Comparison of flooding effects of injecting nano-micron polymer particles. Three sets of water flooding + nano-micron polymer particle flooding, water flooding + polymer flooding, and water flooding were designed in the laboratory experiment to compare the oil displacement effects. The results show that water flooding + nano-micron polymer particle flooding has the lowest water cut and the largest range of enhanced oil recovery. As shown in Figure 1 and 2. This is because the nano-micron polymer, as a new type of step-by-step control and displacement agent, can undergo physical and chemical changes in the deep part of the reservoir to realize fluid flow redirection. At the same time, the control and flooding of nano-micron polymer particles has the characteristics of "blocking the large but not the small", which makes the flow or retention in the form of network distribution in the large pores achieve the effect of step-by-step profile control. Compared with the obvious change to the direction favorable to displacement, the swept volume has been expanded to a certain extent. Among them, water flooding + polymer flooding, and water flooding are all carried out by methods known in the art.

Wherein the water flooding+nano-micron polymer particle flooding of the present invention adopts the following steps:

(1) Early water flooding in low permeability oilfields;

(2) Measuring the average throat radius in low-permeability oilfields Determine the r _{particle size} of the nano-micron polymer particles, wherein the particle size of the nano-micron polymer particles satisfies

(3) According to the determined r- _{particle size} of the nano-micron polymer particles, the multi-component copolymerization by distillation and precipitation method is used to obtain nano-micron polymer particles;

(4) The nano-micron polymer particles in step (3) are injected into the oil layer, and the low-permeability oil field is followed by water flooding.

Determination of the relationship between injected nano-micron polymer particle size and throat radius. Measured by constant velocity mercury porosimetry Calculation shows that when When , the nano-micron polymer particles can smoothly pass through the channel, which is nano-scale flow; when When the nano-micron polymer particles have a radius of several nanometers to several microns, the seepage flow is characterized by deformation and elastic passage, and there is resistance, which is a micron-scale flow; when When the nano-micron polymer particles pass through the pores, there is great resistance, and it is difficult to pass through, forming a blockage. From the indoor microscopic model test, it can be seen that the nano-micron polymer particles injected into the formation rapidly deform and flow through the narrow oil layer pore channels (Fig. 3), while stagnation or slow flow occurs in large pore spaces (Fig. 4 ), to achieve the effect of increasing the displacement swept volume and improving the tertiary recovery. It can also be measured by other methods known in the art

Determination of Slug Size of Injected Nanomicron Polymer Particles. In the indoor core test, six plans were designed to inject nano-micron polymer particles with slug sizes of 0.05PV, 0.1PV, 0.15PV, 0.2PV, 0.25PV and 0.3PV at a fixed concentration of 1500mg/l. 7.96%, 12.86%, 15.42%, 17.63%, 19.12%, 20.28%. It can be seen that the oil production increased significantly after injecting nano-micron polymer particles, and when 0.1PV nano-micron polymer particles were injected, the recovery factor increased most significantly (Fig. 5). The ratio of output to input is the largest, followed by 0.2PV. From this point of view, it is better to choose option 1 for the injection slug, that is, to inject 0.1PV nano-micron polymer particles for oil displacement.

Determination of Injected Nanoscale Polymer Particle Slug Concentration. The laboratory core test also designed the influence of different nano-micron polymer particle slug concentrations on the cumulative oil recovery under the optimal PV number. See Table 1. The results show that when the injection solubility of polymer particles is 100-300mg/l, the effect of oil recovery is not obvious, and the recovery rate is small; when the injection concentration reaches 500mg/l, the effect can be clearly reflected; the injection concentration is 1000mg/l When the injection concentration is above 1500mg/l, the investment of chemical agent is large, However, the rate of oil increase is small, and the ratio of output to input is unsatisfactory.

Table 1 Effect of slug concentration on cumulative oil recovery

plan Slug concentration (mg/l) Moisture content till 2009 (%) Recovery rate until 2009 (%) 1 100 98.8 23.32 2 300 98.8 27.68 3 500 98.7 31.46

4 1000 98.3 35.95 5 1500 98.6 38.62 6 2000 98.9 39.40 7 water drive 97.0 20.29

According to the optimal parameters determined by the above laboratory tests, it can be obtained from the actual application in the oilfields of the second and third areas of the South. After the nano-micron step-by-step depth profile control is effective, the oil increase effect of a single well is obvious, the water cut of the block decreases and the production increases. From the end of the profile control, the accumulative oil increase was 20,400 tons within 5 years.

Economic benefits after infusion of micron polymer particles. 761.12 tons of nano-micron polymer particle emulsion is required, the unit price of pharmaceutical costs is 21,600 yuan/ton, the total cost of injection equipment is 320,000 yuan, the cost of on-site construction is about 860,000 yuan, and the total investment cost is 17.6209 million yuan. The market oil price is about 35 million yuan/ton, and the economic benefit is 17.164 million yuan, and the output-input ratio reaches 4.05.

The embodiment of obtaining nano-micron polymer particles by multi-component copolymerization by distillation and precipitation method is as follows:

Example 1:

Take 1 mol of acrylamide and 10 mol of acrylic acid, put them into the single-necked round bottom flask 1 (reaction vessel), add 35.6 mol of acetonitrile solvent into the bottle, mix well, and ultrasonically disperse them, then add 0.1 mol of N-N Methylenebisacrylamide (MBAA), adding 0.02mol of azobisisobutyronitrile (AIBN) is also ultrasonically dispersed; (2) The round bottom flask containing the reaction solution 2 is placed in an oil bath (heating device 6) , tilt downward at a certain angle, such as 30°, and install the condensing return pipe 3, the condensing joint 4 and the receiving container 5; (3) The oil bath starts to heat up, and rises from normal temperature to boiling within 15 minutes. Keep it at about 90°C for 15 minutes; (4) Adjust the temperature of the oil bath to 110°C, increase the distillation intensity, and the solvent in the flask will continuously flow into the receiving container. After about 90 minutes, the solvent in the flask Almost all are distilled. Under the situation that guarantees this distillation effect, can adopt any condensing device setting mode, such as the condensing device that the present invention preferably adopts is set to: the velocity ratio of the solvent that keeps backflowing in the reaction flask and the solvent that distills out is at about 2. (5) Stop the reaction, and the white solid in the flask is dispersed by adding ethanol ultrasonically and separated by centrifugation; (6) Purification: use ethanol ultrasonic cleaning and centrifugation twice to purify the obtained microspheres; (7) Then The obtained solid is placed in an oven at 40-60° C. for 14 hours, dried to obtain the required polymer microsphere powder, weighed and packaged after grinding. The microspheres obtained in this example are composite polymer microspheres P(AM-AA) of acrylamide and acrylic acid.

Example 2:

Take 10 mol of acrylamide and 1 mol of 2-acrylamido-methylpropanesulfonic acid (AMPS), add them into a single-necked round bottom flask, add 173 mol of acetonitrile solvent into the bottle, mix well, disperse it by ultrasonic, and put it into the round bottom flask Add 0.1mol of divinylbenzene to the flask, add 0.05mol of azobisisoheptanonitrile and ultrasonically disperse it; Tilt at a certain angle, such as 30°, and install the condensing return pipe, condensing joint and receiving container; (3) The oil bath starts to heat up, and rises from normal temperature to boiling within 18 minutes. The temperature of the oil bath is kept at about 90°C. 15 minutes in this state; (4) Adjust the temperature of the oil bath to 120°C, increase the distillation intensity, and the solvent in the flask will continuously flow into the receiving container. After about 100 minutes, almost all the solvent in the flask will be distilled out. Under the situation that guarantees this distillation effect, can adopt any condensing device setting mode, such as the condensing device that the present invention preferably adopts is set to: the velocity ratio of the solvent that keeps backflowing in the reaction flask and the solvent that distills out is at about 2. (5) Stop the reaction, and the white solid in the flask is dispersed by adding ethanol ultrasonically and separated by centrifugation; (6) Purification: use ethanol ultrasonic cleaning and centrifugation twice to purify the obtained microspheres; (7) Then The obtained solid is placed in an oven at 40-60° C. for 10 hours, dried to obtain the required polymer microsphere powder, weighed and packaged after grinding. The microspheres obtained in this example are composite polymer microspheres P(AM-AMPS) of acrylamide and 2-acrylamido-methylpropanesulfonic acid (AMPS).

Example 3:

Take 1 mol of acrylamide and 5 mol of methyl methacrylate (MMA), put them into a single-necked round-bottomed flask, add 24.4 mol of acetonitrile solvent into the bottle, mix well, and disperse by ultrasonic, then add 0.05 mol into the round-bottomed flask N-N methylene bisacrylamide (MBAA), adding 0.01mol dimethyl azobisisobutyrate is also ultrasonically dispersed; (2) The round bottom flask containing the reaction solution is placed in an oil bath (heating device) In the middle, tilt down at a certain angle, such as 30°, and install the condensing return pipe, condensing joint and receiving container; (3) The oil bath starts to heat up, and rises from normal temperature to boiling within 10 minutes, and the temperature of the oil bath is maintained at 90 ℃, keep this state for 15 minutes; (4) adjust the temperature of the oil bath to 115 ℃, increase the distillation intensity, and the solvent in the flask will continuously flow into the receiving container. After about 100 minutes, almost all the solvent in the flask will be distilled come out. Under the situation that guarantees this distillation effect, can adopt any condensing device setting mode, such as the condensing device that the present invention preferably adopts is set to: the velocity ratio of the solvent that keeps backflowing in the reaction flask and the solvent that distills out is at about 2. (5) Stop the reaction, and the white solid in the flask is dispersed by adding ethanol ultrasonically and separated by centrifugation; (6) Purification: use ethanol ultrasonic cleaning and centrifugation twice to purify the obtained microspheres; (7) Then The obtained solid is placed in an oven at 40-60° C. for 12 hours, dried to obtain the required polymer microsphere powder, weighed and packaged after grinding. The microsphere that this embodiment obtains is the composite polymer microsphere P (AM-MMA) of acrylamide and methyl methacrylate

Example 4:

Take 1 mol of acrylamide, 1 mol of acrylic acid, and 3 mol of methyl methacrylate, and add them to a single-necked round-bottomed flask, add 36.5 mol of acetonitrile solvent into the bottle, mix thoroughly, and disperse them by ultrasonic waves, then add 0.08 mol of acetonitrile to the round-bottomed flask N-N methylenebisacrylamide (MBAA), adding 0.007mol of azobisisobutyronitrile (AIBN) is also ultrasonically dispersed; (2) The round bottom flask containing the reaction solution is placed in an oil bath (heating device) , tilt down at a certain angle, such as 30°, and install the condensing return pipe, condensing joint and receiving container; (3) The oil bath starts to heat up, and rises from normal temperature to boiling within 20 minutes, and the temperature of the oil bath is kept at 90 ℃, keep this state for 15 minutes; (4) Adjust the temperature of the oil bath to 110-120 ℃, increase the distillation intensity, and the solvent in the flask will continuously flow into the receiving container. After about 100 minutes, the solvent in the flask is almost All distilled out. Under the situation that guarantees this distillation effect, can adopt any condensing device setting mode, such as the condensing device that the present invention preferably adopts is set to: the velocity ratio of the solvent that keeps backflowing in the reaction flask and the solvent that distills out is at about 2. (5) Stop the reaction, and the white solid in the flask is dispersed by adding ethanol ultrasonically and separated by centrifugation; (6) Purification: use ethanol ultrasonic cleaning and centrifugation twice to purify the obtained microspheres; (7) Then The obtained solid is placed in an oven at 40-60° C. for 14 hours, dried to obtain the required polymer microsphere powder, weighed and packaged after grinding. The microspheres obtained in this example are composite polymer microspheres P(AM-AA-MMA) of terpolymerization of acrylamide, acrylic acid, and methyl methacrylate.

Although the present invention provides four embodiments, it should not be understood as a limitation of the present invention. Although the reaction solvent has adopted acetonitrile solvent. But any oil-soluble solvent can be applied in the present invention, such as one or more of methanol, ethanol, ethyl acetate, methyl ethyl ketone and tetrahydrofuran. Although the present invention adopts N-N methylenebisacrylamide as the crosslinking agent, any crosslinking agent can also be used, such as divinylbenzene, chemically pure grade, that is, it does not contain free radicals that prevent the polymerization process. Impurities; although the present invention has adopted azobisisobutyronitrile (AIBN) as initiator, any oil-soluble azo initiators can also be used, such as azobisisobutyronitrile, azobisisoheptanonitrile or azobisisoheptanonitrile Dimethyl azidoisobutyrate. Adopt oil bath pot as heater in the polymerization process among the present invention, but any type heater is all possible, can also sand bath, hot air bath, electric stove or other heaters that can provide heat source for example; Although the present invention adopts The round bottom flask is used as the reaction vessel, but those skilled in the art should understand that any container common in the art can be used as the reaction vessel; the condensing reflux device is a certain angle inclined downwards, such as the condensing reflux pipe installed at 30 degrees, the condensing joint and the receiver container, or directly use a Liebig condenser, but any common condensation reflux device in the art can also be used, as long as the distillation effect can be guaranteed. The particle size distribution of the obtained microspheres is uniform, and the microspheres are controllable between 200nm and 12μm, which solves the problem of chaotic particle size and different sizes of the microspheres during the synthesis of nano-micron polymer microspheres; and the prepared microspheres No matter in the oil phase or water phase solvent, it is not easy to agglomerate, and it is in a good monodisperse state; the whole reaction process is simple and easy to operate, and the distillation process is the recovery process of the solvent. The recovered solvent can be reused, and there is no need for secondary The step of purifying or removing the polymerization inhibitor makes up for the disadvantages of low monomer concentration and large solvent consumption, thereby contributing to industrial production, and is an excellent method for preparing composite polymer microspheres. According to the prepared microspheres, the corresponding hydration experiments were carried out, and it was found that the microspheres can swell in water, and different microspheres have different hydration abilities, and microspheres with different particle sizes from 200nm to 12μm were obtained ( Figure 7 only shows four different particle sizes, but different particle sizes can be selected according to needs), which can be selectively injected into the formation, so as to achieve the purpose of water plugging, profile control, and enhanced recovery.

The solvent must first satisfy the properties of dissolving the monomers of the polymerization reaction and being able to precipitate the corresponding polymer obtained. In this way, in the reaction system, as the temperature rises, the initiator decomposes to generate free radicals, which can react with the polymerized monomers to form new free radicals, and then attack the new monomers, so that the free radical chain continues to grow , causing its own polarity to change. According to the principle of similar miscibility, as the molecular weight of the polymer chain increases, the solubility in the reaction medium gradually decreases. After reaching the critical chain length, it precipitates from the medium, and multiple chain segments interact with each other. The entanglement forms a stable nucleus suspended in the medium, and the formed primary growth nucleus absorbs monomers and free radicals in the reaction medium, and continues to undergo polymerization reaction in the nucleus to form polymer microspheres. However, when free radicals encounter some more active molecules in the solution, such as oxygen atoms, they will react with them to terminate the growth of free radical chains, so the presence of oxygen in the solvent will hinder the polymerization reaction. According to Henry's law for gases, the solubility of oxygen in a boiling solvent is almost zero. Thus polymerizations in boiling solvents do not require nitrogen blankets and procedures.

In addition, because the acetonitrile solvent can dissolve the added monomer and initiator very well, the initial stage of the system is a homogeneous solution. As the reaction progresses, the system reaches a boiling state. At this time, both heat transfer and mass transfer reach the maximum, and the system It is not necessary to add a stirring device in the process, once the stirring is added, the sphericity of the obtained polymer microspheres is not good enough or agglomerated. This preparation method has the following advantages:

(1) Uniform particle size: the diameter of dry microspheres is small, and the diameters of various dry microspheres are all in the range of 200nm to 12μm, and the diameter distribution is very narrow, which can be within 4%. Ease of large-scale production: In the boiling state, the system is isotropic, and the heat transfer and mass transfer between materials are at the maximum state, which is very conducive to large-scale polymerization reactions.

(2) Short reaction time: Since the polymerization temperature is around 82°, the decomposition rate of the initiator and the growth rate of the free radical chain are much larger than usual, thus greatly shortening the polymerization time, that is, the time required for the conversion rate to reach 90% . In this method, the whole reaction time only needs about 2 hours.

(3) Polymer microspheres with various functional groups can be obtained by this distillation precipitation method, such as polyacrylamide microspheres (PAM), composite polymer microspheres P(AM-AA) of acrylamide and acrylic acid, Composite polymer microspheres P(AM-MAA) of acrylamide and methacrylic acid, composite polymer microspheres P(AM-MMA) of acrylamide and methyl methacrylate, acrylamide and 2-acrylamido-methacrylate The composite polymer microspheres P(AM-AMPS) of methyl propane sulfonic acid (AMPS), and the composite polymer microspheres P(AM-AA-MMA) of terpolymerization of acrylamide, acrylic acid and methyl methacrylate. Since different monomers have different functional properties, different composite polymer microspheres prepared have different functions. For example, due to the high temperature and salt resistance of AMPS, the obtained P(AM-AMPS) microspheres also have anti- High temperature and high salt performance.

(4) The equipment is simple and easy to operate: in the present invention, only a condensation reflux device is needed, no nitrogen protection device, no stirring device, no precise temperature control device, because the boiling point of the system is only related to the external pressure and system composition Related, the boiling point remains unchanged within a certain range under normal pressure, so the temperature of the system is relatively stable, and no precise temperature control device is required. Combining the three aspects, the aggregation device is greatly simplified.

(5) Environmental protection and economy: Since distillation is required in the polymerization process, and the distillation process is also a solvent purification process, the distilled solvent can be repeated for the next polymerization reaction, which is economical and environmentally friendly, and has no special effects on the participating drugs. Other purification requirements save costs and improve reaction efficiency.

Example two:

The Longhupao Oilfield of Daqing No. 9 Oil Production Factory is located in Duerbert Mongolian Autonomous County, Daqing City, Heilongjiang Province. The structure is located on the west side of the Qijia-Gulong Sag in the central sag area of the Songliao Basin. It is an axis at the northern end of the Longhupao-Honggang Terrace. The short-axis three-level anticline structure is close to the north and south. The producing oil-bearing area is 27.5km ² , and the geological reserves are 1316×10 ⁴ t. The production horizons are mainly Sartu oil layer and Putaohua oil layer. The air permeability of the Sa and Pu oil layers is generally between 1 and 100mD, with an average permeability of 57mD and an average porosity of 20.6%.

According to the depth profile control mechanism of nano-micron polymer particles, the selection principle of test well area mainly considers blocks with strong heterogeneity, high water cut, difference between pump pressure and oil pressure greater than 2MPa, and rich remaining oil. According to this principle, the primary selection of test well areas was carried out in each block of Longhupao Oilfield. Preliminary selection of four well areas: Long 21-18 well area (including Long 21-18, 25-18 two well groups), Long 28-19 well area, Long 79-20 well area (including Long 77-19, 79 -20, 81-19 three well groups), Long 79-22 well area (including Long 77-23, 79-22, 79-24, 81-23 four well groups).

Wherein the water flooding+nano-micron polymer particle flooding of the present invention adopts the following steps:

(1) Early water flooding in low permeability oilfields;

(2) Measuring the average throat radius in low-permeability oilfields Determine the r _{particle size} of the nano-micron polymer particles, wherein the particle size of the nano-micron polymer particles satisfies

(3) According to the determined r- _{particle size} of the nano-micron polymer particles, the multi-component copolymerization by distillation and precipitation method is used to obtain nano-micron polymer particles;

(4) The nano-micron polymer particles in step (3) are injected into the oil layer, and the low-permeability oil field is followed by water flooding.

The embodiment in which nano-micrometer polymer particles are obtained by multi-component copolymerization by distillation and precipitation is prepared by the method listed in Example 1.

Determination of Slug Size of Injected Nanomicron Polymer Particles. Indoor core test simulation designed six sets of schemes for injecting nano-micron polymer particles with slug sizes of 0.05PV, 0.1PV, 0.15V, 0.2PV, 0.25PV and 0.3PV, and the incremental recovery factors were 12.78%, 15.06%, 19.37%, 21.52%, 23.45%, 25.14%. It can be seen that the oil production increased significantly after injecting nano-micron polymer particles, and when 0.2PV nano-micron polymer particles were injected, the recovery factor increased most significantly (Fig. 5). The ratio of output to input is the largest. From this point of view, it is better to choose option 4 for the injection slug, that is, to inject 0.2PV nano-micron polymer particles for oil displacement.

Determination of Injected Nanoscale Polymer Particle Slug Concentration. In the laboratory core test, the influence of the slug concentration of injected different nano-micron polymer particles on the cumulative oil recovery was designed. See Table 2. The results show that when the injection concentration of polymer particles is 1500mg/l, the oil displacement effect is better. By the end of 2009, the oil recovery can be increased by 10.07% compared with water flooding, and the output-input ratio is the largest.

Table 2 Effect of slug concentration on cumulative oil production

plan Slug concentration (mg/l) Moisture content till 2009 (%) Recovery rate until 2009 (%) 1 500 98.7 22.14 2 1000 98.5 25.59 3 1500 98.4 31.94 4 2000 98.6 37.75 5 2500 98.6 38.06 6 3000 98.7 40.37 7 water drive 97.3 21.87

According to the optimal parameters determined by the above laboratory tests, it can be obtained from the actual application in Longhupao Oilfield. After the nano-micron step-by-step depth profile control is effective, the water cut in the block is lower than the normal water injection, and the maximum can be lower by 5 percentage points. Well 79-23 can be lower by 10 percentage points; block production is higher than normal water injection, with a maximum daily production increase of 35%, and the central well Long 79-23 daily production maximum increase of 100%.

Economic benefits after infusion of nano-micron polymer particles. 954.02 tons of nano-micron polymer particle emulsion is required, and the unit price of pharmaceutical costs is 21,600 yuan/ton; the total cost of injection equipment is 350,000 yuan, and the cost of on-site construction is about 900,000 yuan; the cumulative oil increase in 5 years is 23,700 tons, and the oil price is about 3,500 yuan/ton . After the nano-micron polymer particle profile control, the total investment cost is 21.8568 million yuan, and the economic benefit is 82.95 million yuan, and the output-input ratio reaches 3.8.

Example three:

The eastern part of the third north area of Daqing Oil Production Plant 3 is located in the pure oil area in the northern part of Saertu Oilfield, Changyuan, Daqing, with an oil-bearing area of 20.2km ² and geological reserves of 12336×104t. This area is located in the northern part of the anticline structure of Sartu Oilfield. The structure is relatively gentle, the dip angle of the formation is about 2°, the terrain is flat, and the average altitude of the ground is about 150.0m. A total of 10 faults are developed in this area, all of which are normal faults. The faults are all north-northwest in direction. The average dip angle of the faults is about 52°, the average permeability is 101.23mD, and the average porosity is 24.71%.

According to the principles and standards of well selection, the water wells in the oil layer area of the third north area were analyzed, and 8 water wells were selected to carry out water flooding depth profile control, and the profile control well area was 8 injection and 21 production. The profile control well group consists of North 3-4-467, North 3-4-469, North 3-4-496, North 3-5-468, North 3-5-68, North 3-J6-467, North 3- J6-469, 3-J6-66, a total of 8 water wells, 21 oil wells in the well area, 6 central production wells. The area of the profile control well area is 3.169km ² , the geological reserves of the Sa1 and II groups are 294.0897×10 ⁴ t, the area of the central well area is 0.51km ² , and the geological reserves are 97.3×10 ⁴ t. Wherein the water flooding+nano-micron polymer particle flooding of the present invention adopts the following steps:

(1) Early water flooding in low permeability oilfields;

(2) Measuring the average throat radius in low-permeability oilfields Determine the r _{particle size} of the nano-micron polymer particles, wherein the particle size of the nano-micron polymer particles satisfies

(3) According to the determined r- _{particle size} of the nano-micron polymer particles, the multi-component copolymerization by distillation and precipitation method is used to obtain nano-micron polymer particles;

(4) The nano-micron polymer particles in step (3) are injected into the oil layer, and the low-permeability oil field is followed by water flooding.

The embodiment in which nano-micrometer polymer particles are obtained by multi-component copolymerization by distillation and precipitation is prepared by the method listed in Example 1.

Determination of Slug Size of Injected Nanomicron Polymer Particles. The laboratory core test designed six sets of plans for injecting nano-micron polymer particles with slug sizes of 0.1PV, 0.15V, 0.2PV, 0.25V, 0.3PV, and 0.35PV, and the incremental recovery factors were 12.38%, 14.56%, and 16.93% respectively. %, 19.42%, 24.35%, 26.94%. It can be seen that the oil production increased significantly after the injection of nano-micron polymer particles. Combining the cost of chemicals and the income, when 0.3V nano-micron polymer particles were injected, the recovery factor increased most significantly (Fig. 5). The input ratio is the largest, followed by 0.35. From this point of view, it is better to choose option 5 for the injection slug, that is, to inject 0.3V functional nano-micron polymer particles for oil displacement.

Determination of Injected Nanoscale Polymer Particle Slug Concentration. In the laboratory core test, the influence of the slug concentration of injected different nano-micron polymer particles on the cumulative oil recovery was designed. See Table 3. The results show that when the injection concentration of polymer particles is 2500mg/l, the oil displacement effect is better. By the end of 2009, the oil recovery can be increased by 16.79% compared with water flooding, and the output-input ratio is the largest.

Table 3 Effect of slug concentration on cumulative oil production

plan Slug concentration (mg/l) Moisture content till 2009 (%) Recovery rate until 2009 (%) 1 500 98.6 24.42 2 1000 98.6 26.39 3 1500 98.4 29.08 4 2000 98.2 33.17

5 2500 98.3 38.96 6 3000 98.7 42.13 7 water drive 97.2 22.17

Economic benefits after infusion of nano-micron polymer particles. 1,127.43 tons of nano-micron polymer particle flooding emulsions are required, the unit price of chemicals is 21,600 yuan/ton, the total cost of injection equipment is 400,000 yuan, the total cost of on-site construction is 1.02 million yuan, and the total investment cost is 25.7723 million yuan. According to the prediction results, after the injection of nano-micron polymer particles, the water cut in the well area will drop by 1.1 percentage points. After the profile control is completed, when the water cut reaches 87.9%, the cumulative oil increase will be 29,300 tons within 5 years, and the market oil price will be about 3,500 yuan/ton , the economic benefit is 102.55 million yuan, and the output-input ratio reaches 3.98.

Claims (2)

1. A method of utilizing nano-micron polymer particles to exploit the remaining crude oil in low-permeability oilfields, characterized in that, the method of water flooding with nano-micron polymer particle flooding is adopted, and the concrete steps are as follows: (1) Early water flooding in low permeability oilfields; (2) Measuring the average throat radius of low-permeability oilfields Determine the r _{particle size} of the nano-micron polymer particles, wherein the particle size of the nano-micron polymer particles satisfies (3) According to the r _{particle size} of the determined nano-micron polymer particles, multi-component copolymerization by distillation and precipitation method is used to obtain nano-micron polymer particles; (4) Inject the nano-micron polymer particles in step (3) into the oil layer, and follow-up water flooding in low-permeability oil fields; In the step (3), the concrete steps for obtaining nano-micron polymer particles by multi-component copolymerization by distillation and precipitation are: (3-1) Take acrylamide, one or more mixtures of acrylic acid and its derivatives, wherein the molar ratio of acrylamide to one or more of acrylic acid and its derivatives is 1:10-10 : 1, add to the reaction vessel, add solvent to the reaction vessel, mix thoroughly, then ultrasonically disperse, add cross-linking agent and initiator to the reaction vessel, also ultrasonically disperse; (3-2) The heater heats up and heats up to a boiling state within 10-18 minutes, and then keeps the oil bath temperature at about 90°C for 15 minutes; (3-3) Adjust the temperature of the heater to 110-120° C., increase the distillation intensity, and the solvent in the reaction vessel continuously flows into the receiving vessel. After 90-100 minutes, all the solvent in the reaction vessel is distilled out; (3-4) Stop heating, add ethanol to the reaction vessel, and ultrasonically disperse, then centrifuge to separate the microspheres obtained by the reaction; (3-5) Purification: use ethanol to ultrasonically disperse and centrifuge twice to purify the obtained microspheres; (3-6) Then put the purified microspheres in an oven at 40-60° C. for 10-14 hours, and dry to obtain the required composite polymer microspheres; Acrylic acid derivatives are 2-acrylamido-methylpropanesulfonic acid (AMPS) or methyl methacrylate (MMA); The solvent is one or more of acetonitrile, methanol, ethanol, ethyl acetate and tetrahydrofuran, and the amount used is 17.3-36.5 times the molar mass of acrylamide; The crosslinking agent is N, N-methylenebisacrylamide or divinylbenzene, and the dosage is 1-10% (mol percentage) of acrylamide; the initiator is azobisisobutyronitrile, azo Diisoheptanonitrile or dimethyl azobisisobutyrate, the dosage is 0.5-2% (mol percentage) of acrylamide; In step (3-3), the speed ratio of the solvent that keeps backflowing into the reaction vessel and the solvent that distills out is around 2; The size of the nanometer polymer particle slug injected in the step (4) is 0.1-0.3PV; The concentration range of nanometer polymer particles injected in the step (4) is 1000-2500mg/L; The used nano-micron polymer particles have an initial particle size distribution range of 200nm-1.2um, and a particle size distribution range of 400nm-13um after hydration; wherein, the nano-micron polymer particles have hydration expansion characteristics. 2. method as claimed in claim 1, is characterized in that, the mol ratio of the mixing of described acrylic acid and methyl methacrylate is 1:3.